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In this study, we investigated the pollination ecology and floral lip morphology of Gongora bufonia Lindl., an epiphytic orchid from tropical forest, to better understand the peculiarities of its unusual pollination mechanism. Field observations on pollination were performed and floral lip samples were prepared for anatomical, histochemical, and ultrastructural analyses. Male Eufriesea violacea (Blanchard) bees use the second and third pairs of legs to hold on the epichile and collect the fragrance in the hypochile region. During this process, the bee slips and falls on the column and receives the pollinarium, which is attached to the rear edge of the bee's scutellum. A subsequent visit (usually to another flower) and fall through the flower may result in insertion of a pollinium into the stigmatic slit at the apex of the column. The fragrance production occurs in the hypochile region, specifically in the papillose epidermal cells and in the subepidermal parenchyma layers. The wax production occurs in the epichile region, exclusively in the epidermal cells. The cells of both regions, hypochile and epichile, have ultrastructural features of lipophilic secretion. The slippery quality of the epichile epidermis is due to wax deposits; this is probably essential to the pollination mechanism of G. bufonia. Keywords: fragrance, Gongora, Orchidaceae, pollination, ultrastructure, wax. Dans cette etude, les auteurs ont examine l'ecologie de la pollinisation et la morphologie du labelle de Gongora bufonia Lindl., une orchidee epiphyte de la foret tropicale, afin de mieux comprendre les particularites de son mecanisme inhabituel de pollinisation. Les observations de la pollinisation ont ete realisees sur le terrain et des echantillons de labelle ont ete prepares aux fins d'analyses anatomiques, histochimiques et ultra-structurales. Les abeilles males Eufriesea violacea (Blanchard) utilisent les deuxieme et troisieme paires de pattes pour se retenir a l'epichile et recueillir la fragrance de la region de l'hypochile. Au cours de ce processus, l'abeille glisse et tombe sur la colonne pour recevoir la pollinie, qui est attachee a l'extremite posterieure du scutellum de l'abeille. Une visite subsequente (habituellement sur une autre fleur) et la chute dans la fleur peut resulter en l'insertion d'une pollinie dans la fente stigmatique a l'apex de la colonne. La production de fragrance se deroule dans la region de l'hypochile, specifiquement dans les cellules epidermiques papilleuses et dans les couches parenchymateuses sous-epidermiques. La production de cire se deroule dans la region de l'epichile, exclusivement dans les cellules epidermiques. Les cellules des deux regions, l'hypochile et l'epichile, possedent des caracteristiques ultra-structurales d'une secretion lipophile. Le caractere glissant de l'epiderme de l'epichile est du au depot de cire, ce qui est probablement essentiel au mecanisme de pollinisation de G. bufonia. [Traduit par la Redaction] Mots-cles: fragrance, Gongora, Orchidaceae, pollinisation, ultrastructure, cire., Introduction Orchidaceae is an important Neotropical family, and 10% of all species offer fragrance as the only floral resource (van der Pijl and Dodson 1966; Willmer 2011). Interaction with males [...]

We investigated altitudinal variation (550-1650 m) in relative growth rates (RGR) and carbon-based secondary compounds (CBSC) in the cephalolichen Lobaria pulmonaria (L.) Hoffm. and the chlorolichen Hypogymnia occidentalis L. H. Pike transplanted for 14 months in a U-shaped valley in inland southern British Columbia. Prior to transplantation, half of the thalli were treated with phosphorus (P) to examine effects of P on carbon allocation. Growth in L. pulmonaria was substantially higher in the toe-slope position, corresponding to much higher bark pH. Sixty-four percent of the variation in RGR was accounted for by positive pH effects and adverse effects of direct light exposure in the best subset multiple regression model. For H. occidentalis, 57% of the variation in RGR was accounted for by positive and negative effects of indirect and direct light, respectively. Neither altitude nor P had a noticeable effect on RGR, the former possibly reflecting a trade-off between orographic precipitation and inversion-boosted nocturnal dew in valley bottom localities. Neither was there any correlation between altitude and CBSCs, although treatment with P did significantly trigger secondary metabolism inL. pulmonaria, but not in H. occidentalis. No significant intraspecific relationship between growth and CBSC investments was noted. Key words: relative growth rate, lichen compounds, phosphorus, bark pH, elevation. Les auteurs ont examine la variation altitudinale (550-1650 m) sur les taux relatifs de croissance (TRC) et les composes secondaires bases sur le carbone (CSBC) chez le cephalolichen Lobaria pulmonaria (L.) Hoffm. et le chlorolichen Hypogymnia occidentalis L. H. Pike, transplantes pendant 14 mois dans une vallee en U, dans le sud de l'interieur de la Colombie canadienne. Avant la transplantation, on a traite la moitie des thalles avec du phosphore (P) pour examiner ses effets sur l'allocation du carbone. On a observe une croissance substantiellement plus grande chez le L. pulmonaria au pied de la pente, correspondant a un pH beaucoup plus eleve de l'ecorce. Soixante-quatre pour cent de la variation du TRC s'explique par les effets positifs du pH et les effets adverses de l'exposition directe a la lumiere dans le sous ensemble du modele de regression. Chez le H. occidentalis, 57% de la variation du TRC s'explique par les effets positifs ou negatifs de la lumiere indirecte ou directe, respectivement. Ni l'altitude ni le P n'exercent un effet sur le TRC, le premier refletant possiblement un compromis entre la precipitation orographique et la rosee accentuee par l'inversion dans les localites du fond de la vallee. On ne retrouve pas non plus de correlation entre l'altitude et les CSBC, bien que le traitement avec le P ait significativement accelere le metabolisme secondaire chez le L. pulmonaria, mais non chez le H. occidentalis. On n'a observe aucune relation intraspecifique entre la croissance et les allocations aux CSBC. [Traduit par la Redaction] Mots-cles: taux relatif de croissance, composes licheniques, phosphore, pH de l'ecorce, elevation., Introduction Epiphytic lichen richness and species composition vary considerably with altitude (e.g., Goward and Ahti 1992; Wolf 1993; Pirintsos et al. 1995; Cornelissen et al. 2001; Austrheim 2002; Werth et [...]

Relationships between genetic (allozyme) variation and landscape age and structure were investigated in 17 calcareous grassland demes of the moss Homalothecium lutescens (Hedw.) H. Rob. on the Baltic island of Oland. Mean within-deme gene diversity ([H.sub.S] = 0.152) was moderate compared with other bryophyte studies, and the between-deme proportion of the total diversity ([G.sub.ST] = 0.100, Jost's D = 0.011) was low but significantly different from zero. Clonal mixing, measured as the proportion of two adjacent shoots having different haplotypes, was relatively high (mean 0.32 over all demes). [H.sub.S] was higher in old grassland fragments, but negatively related to vascular plant species richness. Allelic richness (A) was positively associated with the area of old (≥ 280 years) grassland in the surroundings: although demes in old grasslands are genetically more variable than those in younger grasslands, proximity to large areas of old grassland may promote genetic variability even in younger grassland demes. The importance of management continuity for species diversity has been stressed in many earlier grassland studies. Here, we conclude that grassland fragments with a long history of grazing continuity are also positively associated with variability at within-species level, as exemplified by the bryophyte H. lutescens. Key words: allozymes, bryophytes, calcareous grassland, genetic variation, landscape history. Dans dix-sept prairies calcaires de Ule d'Oland sur la Baltique, l'auteure a etudie les relations entre la variation genetique (allozyme) et l'age, avec la structure des demes de la mousse Homalothecium lutescens (Hedw.) H. Rob. La variation genetique moyenne pour un deme donne ([H.sub.S] = 0,152) est moderee comparativement a d'autres etudes de bryophytes et la proportion de la variation totale entre demes ([G.sub.ST] = 0,100, Jost's D = 0,011) est faible, mais significativement differente de zero. Le melange clonal mesure comme la proportion de deux tiges adjacentes ayant des haplotypes differents, est relativement elevee (moyenne de 0,32 pour l'ensemble des demes). La diversite genetique pour [H.sub.S] s'avere plus elevee dans les fragments de vieilles prairies, mais negativement reliee a la richesse en especes de plantes vasculaires. La richesse allelique (A) montre une association positive reliee avec l'aire de la vieille prairie ([greater than or equal to] 280 ans) environnante: bien que les demes de la vieille prairie soient genetiquement plus variables que celles des prairies plus jeunes, la proximite de grandes surfaces de vieilles prairies peut promouvoir la variabilite genetique, meme dans les demes des prairies plus jeunes. On a deja souligne l'importance de la continuite de l'amenagement pour la diversite des especes dans des etudes antecedentes sur les prairies. L'auteure conclut que les fragments de prairies ayant connu une longue continuite de paturage sont egalement associes avec de la variabilite a l'echelle intra specifique, comme le montre la bryophyte H. lutescens. [Traduit par la Redaction] Mots-cles: allozymes, bryophytes, prairie calcaire, variation genetique, histoire du paysage., Introduction The potential for species or populations to adapt to a changing environment is expected to be influenced by the levels of genetic variation that are available for natural selection [...]

A small number of species, including Mimosa pudica, use rapid leaf movement as a presumptive defensive strategy. How movement-based defenses change in response to mechanical damage and whether changes are localized or systemic is unknown. This is in contrast to a substantial literature describing how mechanical leaf damage can cause morphological and chemical responses within a diversity of plant species. Depending on the species and the stimuli, these chemical and morphological responses can be localized to the tissues damaged or systemic throughout the plant body. Here we report the results of a small experiment designed to test the following: (i) whether mechanical leaf damage influences subsequent leaf closure behavior, and (ii) whether changes were systemic or localized. To do this, we scored leaves using a behavioral assay (time-to-reopen leaves following a subsequent touch stimuli) for several days before and following mechanical damage. Leaves above and below the damaged leaf were observed, on damaged and undamaged plants, allowing us to assess whether any change was systemic. We found leaf damage caused strong localized effects, greatly increasing the time-to-reopen of the damaged, but not adjacent, leaves. Neither the physiological cause nor fitness consequences of this behavioral shift are known. Interestingly, this altered behavior resulted in damaged leaves remaining 'hidden' longer than undamaged leaves. If leaf closure reduces risk of herbivory, there could be adaptive value, analogous to inducible chemical and morphological defenses. Key words: plant defense, plant behavioral ecology, rapid leaf movement, localized response, induced response, plant- animal interactions, sensitive plant, mechanical damage. Un petit nombre d'especes, incluant le Mimosa pudica, utilisent un mouvement foliaire rapide comme strategie presumee de defense. On ne sait pas comment les defenses basees sur le mouvement se modifient en reaction au dommage mecanique et si les changements sont localises ou systemiques. Ceci est en contraste avec une litterature substantielle decrivant comment un dommage foliaire mecanique peut causer des reactions morphologiques et chimiques chez une diversite d'especes vegetales. Selon l'espece et le stimulus, ces reactions chimiques et morphologiques peuvent se restreindre au tissus endommage, ou encore etre systemiques dans l'ensemble du corps de la plante. Les auteurs font etat des resultats d'une petite experience concue pour verifier : (i) si un dommage mecanique foliaire influence le comportement subsequent de la fermeture foliaire, et (ii) si ces modifications sont systemiques ou localisees. Ils ont note les feuilles en utilisant un test de comportement (temps requis pour la reouverture des feuilles apres un stimulus par touche) pendant plusieurs jours avant et apres un dommage mecanique. Ils ont observe les feuilles au dessus et au dessous de la feuille endommagee, sur des plantes endommagees ou non, ce qui a permis d'evaluer s'il y avait des changements systemiques. Ils ont constate que le dommage foliaire cause de forts effets localises, augmentant grandement le temps requis pour la reouverture des feuilles, mais non de celles adjacentes. On ne connait ni la cause physiologique ni les consequences d'adaptation de cette modification comportementale. Il est interessant de noter que ce comportement modifie a conduit les feuilles endommagees a demeurer 'cachees' plus longtemps que les feuilles intactes. Si la fermeture des feuilles reduit le risque d'herbivorie, elle pourrait avoir une valeur adaptative analogue aux defenses chimiques et morphologiques inductibles. [Traduit par la Redaction] Mots-cles : defense des plantes, ecologie du comportement, mouvement foliaire rapide, reaction localisee, reaction induite, interactions plante-animal, sensitive, dommage mecanique., Introduction A suite of morphological and chemical defenses are commonly employed by plants to defend against herbivores. A relatively small number of plant species also exhibit rapid leaf movement (closure) [...]

White spruce (Picea glauca (Moench) Voss) cone crops were measured from 1986 to 2011 in the Kluane region of southwestern Yukon to test the hypothesis that the size of cone crops could be predicted from spring and summer temperature and rainfall of years t, t - 1, and t - 2. We counted cones in the top 3 m of an average of 700 white spruce trees each year spread over 3-14 sites along 210 km of the Alaska Highway and the Haines Highway. We tested the conventional explanation for white spruce cone crops that implicates summer temperatures and rainfall in years t and t - 1 and rejected it, since it explained very little of the variation in our 26 years of data. We used exploratory data analysis with robust multiple regressions coupled with Akaike's information criterion corrected (AICc) analysis to determine the best statistical model to predict the size of cone crops. We could statistically explain 54% of the variation in cone crops from July and August temperatures of years t - 1 and t - 2 and May precipitation of year t - 2. There was no indication of a periodicity in cone crops, and years of large cone crops were synchronous over the Kluane region with few exceptions. This is the first quantitative model developed for the prediction of white spruce cone crops in the Canadian boreal forest and has the surprising result that weather conditions 2 years prior to the cone crop are the most significant predictors. Key words: white spruce cone production, Yukon, climate, Kluane, Picea glauca. Les auteurs ont emis l'hypothese a savoir si l'on peut predire l'importance de la production des cones chez l'epinette blanche (Picea glauca (Moench) Voss) a partir des temperatures du printemps et de l'automne et des precipitations des annees t, t - 1, et t - 2. Pour verifier l'hypothese, ils ont mesure la production des cones de 1986 a 2011 dans la region de Kluane dans le sud-ouest du Yukon. Chaque annee, ils ont compte les cones dans les 3 m superieurs d'une moyenne de 700 tiges d'epinettes blanches dispersees dans 3-14 sites sur une longueur de 210 km le long des autoroutes de l'Alaska et Haines. Ils ont verifie l' explication conventionnelle pour la production des cones chez l' epinette blanche impliquant les temperatures estivales et les precipitations des annees t et t - 1, et l'ont rejetee puisqu'elle explique tres peu de la variation dans leurs donnees de 26 annees. Ils ont utilise l' analyse exploratoire des donnees avec des regressions multiples robustes couplees avec l' analyse du critere d' information d'Akaike corrige (AICc) pour determiner le meilleur modele statistique permettant de predire la production de cones. Ils ont pu ainsi expliquer 54 % de la variation de la production des cones a partir des temperatures de juillet et aout des annees t - 1et t - 2 et la precipitation de mai de l'annee t - 2. Il n'y a aucune indication de periodicite dans la production des cones, et les annees de forte production sont synchrones sur l'ensemble de la region de Kluane avec quelques exceptions. Il s'agit du premier modele quantitatif developpe pour la prediction des productions de cones chez l'epinette blanche dans la foret boreale canadienne avec le resultat surprenant que les conditions climatiques 2 ans avant l' annee de production constituent les meilleurs predicteurs. Mots-cles : production de cones de l'epinette blanche, Yukon, climat, Kluane, Picea glauca. [Traduit par la Redaction], Introduction Cone crops of white spruce (Picea glauca (Moench) Voss) in the boreal forest region vary dramatically from year to year. A combination of climatic events are usually put forward [...]

Under sink-limited conditions, source activity is modulated to remain in balance with the use of carbohydrates by the sink, but this feedback control has been studied in only a few systems so far. Sink and source activities were investigated throughout the season. Plants were subjected to two photoperiod regimes combined with two irradiance levels to produce three different daily amounts of photons. Net photosynthetic rate and the photochemical efficiency of photosynthesis were initially higher under a long photoperiod, but decreased early in the growth season, whereas they remained fairly constant until a few days before leaf senescence under a short photoperiod. The rates of starch and biomass accumulation in the bulb were also faster under a long photoperiod at the beginning of the season but reached similar levels under both short and long photoperiods later on. Response to photoperiod cannot be explained by changes in daily amounts of photons, as none of the variables reported were affected by instantaneous or daily irradiance. It appears that the total amount of carbohydrate synthesized under a long photoperiod was in excess compared to the ability of the sink to store or use them, inducing a feedback inhibition of net photosynthetic rate to restore the source-sink balance. Key words: Erythronium americanum, photoperiod, source-sink relationships, carbohydrates, sink limitation. Lorsque la croissance est limitee par les puits, l'activite de la source est modulee afin de demeurer en equilibre avec l'utilisation des hydrates de carbone par le puits. Ce retrocontrole n'a ete etudie que dans tres peu de systeme a ce jour. Les activites de la source et du puits ont ete etudiees au cours de la saison de croissance. Les plants ont ete soumis a deux regimes de photoperiode combines a deux niveaux d'irradiance, afin d'obtenir trois quantites differentes de photons au cours de la journee. Le taux de photosynthese nette et l'efficacite photochimique de la photosynthese ont d'abord ete plus eleves sous longue photoperiode. Cependant, ils ont diminue tot dans la saison de croissance, alors qu'ils sont restes relativement constants sous courte photoperiode jusqu'a quelques jours avant la senescence foliaire. Les taux d'accumulation d'amidon et de biomasse dans le bulbe ont aussi ete plus rapides au debut de la saison sous longue photoperiode mais, ont atteint par la suite, un niveau similaire entre les deux photoperiodes. La reponse de la photoperiode ne peut pas etre expliquee par des changements de la quantite journaliere de photons etant donne qu'aucune des variables analysees n'a ete affectee par l'irradiance instantanee ni par l'irradiance journaliere. Il semble que la quantite totale d'hydrates de carbone synthetises par la source sous longue photoperiode etait en exces par rapport a la capacite du puits a les stocker ou a les utiliser, induisant alors un retrocontrole negatif du taux de photosynthese nette afin de restaurer l'equilibre entre la source et le puits. Mots-cles: Erythronium americanum, photoperiode, relations source-puits, reserves carbonees, limitation par les puits., Introduction Spring ephemerals are characterized by a short epigeous growth period that starts quickly after snowmelt and ends during canopy closure (Muller 1978). During this period, the perennial organ (i.e., [...]

In species such as aspen (Populus tremuloides Michx.), trees are interconnected through their root system owing to their regeneration mode by root suckering. These root connections challenge classic notions of forest dynamics that consider trees as individuals competing for resources, because root connections allow trees to share water, minerals, and carbohydrates. The purpose of this study was to demonstrate that trees can directly influence the physiology of other nearby trees through root connections. In the summers of 2007 and 2008, pairs of aspen suckers (i.e., two suckers connected by a parental root) were selected and divided into three height classes and compared with each other (dominant, codominant, suppressed). Suckers distally positioned on the parental root were manually defoliated, and the effects of defoliation on photosynthesis, stomatal conductance, and specific leaf area (SLA) were measured on connected but nondefoliated suckers. Results showed that defoliation caused physiological responses in the interconnected trees in summer 2007, which was drier than summer 2008. Defoliation of a connected sucker had a greater effect on suppressed suckers, for which mean photosynthesis rate increased by 17% compared with that of controls. The effect was less important for codominant (14% increase) and dominant (12%) trees. SLA of suppressed suckers also increased, while the increase in SLA values was smaller for codominant and dominant suckers. In summer 2008, no defoliation effect was observed, probably owing to high moisture conditions that resulted in much higher stomatal conductance values compared with those in 2007 (+55%). Under high humidity conditions, leaf specific hydraulic conductance does not constrain stomatal conductance, so the rate of C[O.sub.2] assimilation was probably at its maximum capacity. This study demonstrated that trees could physiologically interact through root connections, and these interactions should thus be considered in studies of stand dynamics. Key words: gas exchange, root link, specific leaf area, clonal integration. Chez des especes comme le tremble (Populus tremuloides Michx.), les arbres sont interconnectes par l'intermediaire de leurs systemes racinaires, du a leur mode de regeneration par drageonnage. Ces connexions racinaires remettent en question les notions de la dynamique des forets considerant les arbres comme des individus competitionnant pour les ressources, puisque les connexions racinaires permettent aux arbres de partager l'eau, les mineraux et les glucides. L'etude visait a demontrer que l'arbre peut influencer directement la physiologie des autres par ses connections racinaires. Pendant les etes de 2007 et 2008, les auteurs ont selectionne des paires de drageons de peupliers (c.-a-d. deux drageons relies par une racine mere) et les ont divises en trois classes pour les comparer les uns aux autres (dominant, codominant, domine). Ils ont defolie manuellement les drageons en position distale sur la racine mere et ils ont mesure les effets de la defoliation sur la photosynthese, la conductance stomatale et la surface foliaire specifique (SFS) sur les drageons connectes, mais non defolies. Les resultats montrent que la defoliation entraine des reactions physiologiques chez les arbres interconnectes, a l'ete 2007 un ete plus sec que celui de 2008. La defoliation d'un drageon connecte a exerce un effet plus marque sur les drageons domines, ou le taux moyen de photosynthese a augmente de 17 % par rapport aux temoins. L'effet fut moins important chez les arbres codominants (14 %) et dominants (12 %). La SFS des drageons des drageons domines a egalement augmente, alors que l'augmentation de la SFS fut plus faible chez les drageons codominants et dominants. A l'ete 2008, on a observe aucun effet de la defoliation, probablement parce que les conditions de forte humidite ont engendre des valeurs de conductance stomatale beaucoup plus fortes, comparativement a 2007 (+55 %). Sous des conditions de forte humidite, la conductance hydraulique specifique ne limite pas la conductance stomatale, de sorte que l'assimilation du C[O.sub.2] etait probablement a sa capacite maximale. Cette etude demontre que les arbres peuvent interagir physiologiquement par leurs connexions racinaires, ce que l'on devrait alors considerer dans les etudes de la dynamique des peuplements. Mots-cles : echanges gazeux, lien racinaire, surface foliaire specifique, integration clonale. [Traduit par la Redaction], Introduction Trees are traditionally considered discrete entities competing with each other for resources. However, this concept of individuality is challenged by species for which trees are interconnected through their root [...]

A defence mechanism against nematodes produced by Sphaerobolus stellatus Tode and Sphaerobolus iowensis L.B. Walker is described for the first time. Within 24 h of introduction, some individuals of a mycophagous nematode (Aphelenchoides sp.) exhibited lethargic behaviour marked by the cessation of feeding and a reduction in movement. The anterior portion of the affected nematodes appeared swollen and was encapsulated with an amorphous material of unknown composition. The nematode stylet could not penetrate this encapsulating matrix, preventing further hyphal grazing and subsequently leading to death of the nematodes, possibly due to starvation. Immobilized nematodes were not consumed by the fungi. It is hypothesized that when the feeding nematodes pierce a specialized structure found in Sphaerobolus cultures, referred to as a gloeocystidium, the contents are released and solidify on the nematode heads. It is proposed that the gloeocystidia function to protect the hyphal system and act as a general antifeedant mechanism against mycophagous nematodes and possibly other fungus-feeding microfauna. Key words: antifeedant, Aphelenchoides, Coprinopsis macrocephala, fungivory, gloeocystidium, mycophagy. Les auteurs decrivent pour la premiere fois un mecanisme de defense contre les nematodes, developpe par les Sphaerobolus stellatus Tode et Sphaerobolus iowensis L.B. Walker. Moins de 24 heures apres leur introduction, certains individus d'un nematode mycophage (Aphelenchoides sp.) montrent un comportement lethargique caracterise par un arret d'alimentation et une reduction des mouvements. La portion anterieure du nematode affecte apparait enflee et encapsulee avec un materiel amorphe de composition inconnue. Le stylet du nematode ne peut penetrer la matrice d'encapsulation, prevenant ainsi d'autres penetrations des hyphes et conduisant subsequemment a la mort du nematode possiblement par inanition. Les champignons ne consomment pas les nematodes immobilises. On propose l'hypothese qu'au cours de son alimentation, le nematode perce une structure specialisee, observee dans les cultures des Sphaerobolus, appelee gloeocystidium, dont les contenus se relachent et se solidifient sur la tete des nematodes. On propose que les gloeocystidia arrivent a proteger le mycelium, agissant comme un mecanisme general contre le broutage des nematodes mycophages et possiblement d'autres elements mycophage de la microfaune. Mots-cles : antibroutage, Aphelenchoides, Coprinopsis macrocephala, fungivorie, gloeocystidium, mycophagie. [Traduit par la Redaction], Introduction The extensive hyphal systems produced by lignicolous and mycorrhizal fungi may be subjected to intensive grazing by mycophagous invertebrates during vegetative growth, including amoebae (Chakraborty et al. 1985), nematodes [...]

A broad compilation of modern carbon isotope compositions in all C3 plant types shows a monotonic increase in [delta][sup.13]C with decreasing mean annual precipitation (MAP) that differs from previous models. Corrections for temperature, altitude, or latitude are smaller than previously estimated. As corrected for altitude, latitude, and the [delta][sup.13]C of atmospheric C[O.sub.2], these data permit refined interpretation of MAP, paleodiet, and paleoecology of ecosystems dominated by C3 plants, either prior to 7-8 million years ago (Ma), or more recently at mid- to high latitudes. Twenty-nine published paleontological studies suggest preservational or scientific bias toward dry ecosystems, although wet ecosystems are also represented. Unambiguous isotopic evidence for C4 plants is lacking prior to 7-8 Ma, and hominid ecosystems at 4.4 Ma show no isotopic evidence for dense forests. Consideration of global plant biomass indicates that average [delta][sup.13]C of C3 plants is commonly overestimated by approximately 2[per thousand] aridity | carbon cycle | closed canopy | paleoprecipitation doi/ 10.1073/pnas.1004933107

Traits have been widely used in plant ecology to understand the rules governing community assembly, and to characterize primary strategies that define community structure and ecosystem properties. Relatively little is known as to whether the traits that are ecologically important at macroecological scales are either variable, or of consequence at fine scales within species. We measured trait variation within populations of the grassland plants Festuca ovina L. and Koeieria macrantha (Ledeb.) Schult., to test the hypothesis that fine-scale intraspecific trait variation drives local community structure. Both species showed large genotypic variation for all traits. Size-related traits of genotypes of K. macrantha observed under monoculture predicted their performance in model grassland communities that possessed both genetic and species diversity. The same correspondence was much weaker for the experimental population of F. ovina. A trade-off in allocation between shoot mass and relative allocation to reproduction was evident in the experimental population of F. ovina. Furthermore, both species showed evidence of a positive relationship between specific leaf area (SLA) and allocation to culm mass. This trait covariation indicates the existence of intraspecific trade-offs in life-history and growth strategies similar to those used to define primary plant strategies, which potentially buffers both species abundance and species coexistence against environmental challenges. Key words: community ecology, genotypic diversity, perennial grasses, primary plant strategies, species coexistence, trait trade-offs. En ecologie vegetale, on a largement utilise les caracteres genetiques pour comprendre les regles regissant l'assemblage des communaules, el pour caracteriser les strategies primaires definissant la structure des communautes el les proprietes des ecosystemes. On ne sait pas vraiment si les caracteres ecologiquement importants aux echelles macroecologiques sont variables ou encore une consequence aux fines echelles dans l'espece. Les auteurs ont mesure la variation de caracteres a l'interieur de populations de plantes des prairies, les Festuca ovina L. et Koeleria macrantha (Ledeb.) Schult., pour verifier l'hypothese a savoir que la variation intraspecifique des caracteres aux fines echelles guide la structure de la communaute locale. Les deux especes montrent une importante variation genotypique pour tous les caracteres. Les caracteres lies a la grandeur chez les genotypes du K. macrantha observes en monoculture permettent de predire leur performance dans des communautes herbacees modeles possedant a la fois une diversite genetique et specifique. La meme correspondance s'avere beaucoup plus faible chez la population experimentale du F. ovina. De plus, les deux especes montrent l'existence d'une relation positive entre la surface foliaire specifique (SLA) et l'allocation a la masse des chaumes. La co-variatiou de ces caracteres indique l'existence de compromis intraspecifiques dans le cycle vital et des strategies de croissance, semblables a celles utilisees pour definir les strategies primaires des plantes, lesquelles tamponnent potentiellement l'abondance des deux especes et leur coexistence devant des defis environnemeniaux. Mots-cles : ecologie des communautes, diversite genotypique, herbes perennes, strategie primaire des plantes, coexistence des especes, compromis entre caracteres. [Traduit par la Redaction], Introduction Life-history theory predicts that species growing in specific environments will share similarity in certain key traits or combinations of traits (MacLeod 1894; MacArthur and Wilson 1963; Caswell et al. [...]

Stratigraphic records from peatlands suggest that the shift from a rich fen (calcareous fen) to an ombrotrophic bog can occur rapidly. This shift constitutes a switch from a species-rich ecosystem to a species-poor one with greater carbon storage. In this process, the invasion and expansion of acidifying bog species of Sphagnum (peat mosses) play a key role. To test under what conditions an acidifying bog species could invade a rich fen, we conducted three experiments, contrasting the bog species S. fucsum with the rich-fen species S. warnstorfii and S. teres. We first tested the effect of calcareous water by growing the three species at different constant height above the water table (HWT; 2, 7, and 14 cm) in a rich-fen pool and measured maximum photosynthetic rate and production and difference in length growth as an indicator of competition. In none of the species was the photosynthetic capacity negatively affected when placed at low HWT, but S. fuscum was a weaker competitor at low HWT. In our second experiment we transplanted the three species into microhabitats with different and naturally varying HWT in a rich fen. Here, S. fuscum nearly ceased to photosynthesize when transplanted to low HWT (brown moss carpet), while it performed similarly to the two rich-fen species at the intermediate level (S. warnstorfii hummock level). In contrast to S. fuscum, the rich-fen sphagna performed equally well in both habitats. The brown moss carpet was seasonally flooded, and in our third experiment we found that S. fuscum, but not S. teres, was severely damaged when submerged in rich-fen water. Our results suggest two thresholds in HWT affecting the ecosystem switch: one level that reduces the risk of submergence and a higher one that makes bog sphagna competitive against the rich-fen species. Key words: allogenic succession; bog; calcareous; catastrophic shift; competition; drought; flooding; Hallefjard, Sweden; mire; ombrotrophication; photosynthesis; Sphagnum spp.

We explored interactions among plant growth forms in the understory of mature boreal mixedwood forests in western Canada by investigating the competitive influence of erect shrubs on herbs (forbs and grasses). We established 10 pairs of plots; all erect shrubs were removed in one plot of each pair (removals) and left intact in the other plot (controls). Two years later, we harvested all aboveground biomass of the herbaceous layer (herb biomass: this included graminoids, forbs, trailing shrubs, and species with a woody base but not woody stems) from the 20 plots. We tested for significant differences in understory species biomass and composition between control and removal plots and examined the influence of 25 environmental factors on species composition of the herbaceous layer. Competition intensity was measured by the natural logarithm of response ratio (In RR) index based on herb biomass. After erect shrub removal, there was a significant increase in herb biomass, mostly due to an increase of the most common species (e.g.. Cornus canadensis Linnaeus, Linnaea borealis Linnaeus). The values of competition intensity (In RR) varied among herb species but were, overall, positive, indicating a release from competition following shrub removal. Composition of the herbaceous layer was significantly different between removal and control plots and was also significantly related to seven environmental factors, which explained 40% of the variation in composition. Our study suggests that there is asymmetric competition for light between erect shrub and herb species in boreal ecosystems. Key words: removal experiment, functional diversity, understory community, species interactions, dominant species, boreal forest. Les auteurs ont etudie les interactions entre les formes de croissance des plantes en sous etage de forets boreales mixtes matures dans l'ouest du Canada, en examinant l'influence competitive des arbustes dresses et des herbacees. Ils ont etabli 10 paires de parcelles, supprimant tons les arbustes dresses dans une parcelle de chaque paire (supprimes) et en laissant intacte l'autre parcelle (temoins). Deux ans plus tard, ils ont recolte toute la biomasse epigee de la strate herbacee (biomasse herbacee; incluant les plantes gramineennes et non-gramineennes, les arbustes rampants et les especes munies d'une base ligneuse mais sans tige ligneuse) des 20 parcelles. Ils ont effectue des lests de differences significatives pour la biomasse des especes de sous etage et la composition entre les parcelles temoins et de suppression, pour examiner l'influence de 25 facteurs environnementaux sur la composition en especes de la strate herbacee. Ils ont mesure l'intensite de la competition par le log du Rapport de Reaction (In RR), un index base sur la biomasse herbacee. Suite a la suppression des arbustes dresses, on observe une augmentation significative de la biomasse herbacee, due en grande partie a une augmentation des especes les plus communes (e.g. Cornus canadensis Linnaeus, Linnaea borealis Linnaeus). La valeur de l'intensite de la competition (In RR) varie entre les especes herbacees, mais demeure dans l'ensemble positive, ce qui indique une liberation de la competition suite a l'enlevement des arbustes. La composition de la strate herbacee s'avere significativement differente, entre les parcelles avec suppression et temoins, et montre egalement une relation significative avec sept facteurs environnementaux, lesquels expliquent 40 % de la variation de la composition. Les resultats suggerent l'existence d'une competition asymetrique pour la lumiere entre les especes arbustives dressees et herbacees, dans les ecosystemes boreaux. Mois-cles : experience d'elimination, diversite fonctionnelle, communaute de sous etage, interactions interspecifiques, especes dominantes, foret boreale. [Traduit par la Redaction], Introduction Interactions among plant species play an important role in regulating composition of local communities and ecosystems (Brooker 2006) and in mediating ecosystem functioning when a given species or functional [...]

Quantification of seed arrival as an ecological flux may improve understanding of patch dynamics and variations in community structure across the landscape. Microsites favorable for germination are continually being created and destroyed in coastal ecosystems, so seed dispersal to multiple patches is essential for survival and growth. In order to elucidate the role that patches play in seed dispersal on barrier islands, our study was conducted on three Virginia, USA barrier islands: Metompkin, Hog, and Smith, which represent a range of size, topographic complexity and species richness. Artificial perches with an attached fecal seed trap were installed along transects on the islands. Each island had at least one transect positioned at both a woody and a graminoid site. Seed dispersal varied seasonally with most dispersal events (one dispersal event equals one seed collected) occurring during the spring (n = 248) versus the summer (n = 4). Seed dispersal events were greatest on Hog Island (n = 421) and least on Metompkin Island (n = 5). Morella spp. (Morella cerifera and Morella pensylvanica) accounted for 62% of the total seeds collected. Three species that appeared during spring seed counts, Callicarpa americana, Rubus sp. and Sassafras albidum, were not observed within a 10 m proximity of any of the transects. Spatial variation in island position, vegetation structure and island topography were important for seed dispersal. The greatest abundance and diversity of seeds were collected on Hog Island, centrally located relative to the other islands. These results indicate that while the role patches play in influencing seed dispersal is related to island position and location on a given island, we may need to define patches in greater detail to accurately predict which locations will receive the most bird-dispersed seeds., INTRODUCTION Barrier islands systems exemplify highly dynamic interconnected landscapes (Young et al., 2007). Due to the interrelatedness of the system as a whole, spatial scale patterns play an important role [...]

Declines of whitebark pine (Pinus albicaulis Engelm.) have occurred across much of the species' range over the last 40 years due to mountain pine beetle outbreaks and white pine blister rust infection. Management efforts to stem these declines are increasing, yet the long-term success of whitebark pine depends on the species itself adapting to the modern environment. Natural regeneration will be a critical part of this process. We examined patterns in natural whitebark pine regeneration as related to the biophysical environment in sixty 0.1 ha plots in Montana, Idaho, and Oregon. Whitebark pine regeneration was present in 97% of our plots and varied widely in density from 0 to 17 000 seedlings/ha and 0 to 2680 saplings/ha. Using nonparametric correlation analysis and ordination techniques, we found whitebark pine regeneration abundance was unrelated to stand age but significantly related to several biophysical site characteristics, including positive relationships with elevation and canopy tree mortality caused by mountain pine beetle and negative relationships with moisture availability, temperature, and subalpine fir importance. Our findings indicate that whitebark pine is regenerating in many areas and that the widespread mortality from recent mountain pine beetle outbreaks may provide suitable settings for whitebark pine regeneration given sufficient seed sources. Resume: Des declins du pin a ecorce blanche (Pinus albicaulis Engelm.) sont survenus dans presque toute son aire de repartition au cours des 40 dernieres annees a cause des infestations du dendroctone du pin ponderosa et des infections de la rouille vesiculeuse du pin blanc. Les efforts d'amenagement pour enrayer ces declins augmentent, mais a long terme, le succes du pin a ecorce blanche depend de son adaptation a l'environnement moderne. La regeneration naturelle sera un element crucial de ce processus. Nous avons etudie les patrons de la regeneration naturelle du pin a ecorce blanche en fonction de l'environnement biophysique dans 60 placettes de 0,1 ha dans les etats du Montana, de l'Idaho et de l'Oregon, aux E tats-Unis. La regeneration du pin a ecorce blanche etait presente dans 97% des placettes et sa densite variait enorme ment, soit de 0 a 17 000 semis/ha et de 0 a 2680 gaules/ha. En utilisant des techniques d'analyse de correlation non parame trique et d'ordination, nous avons etabli que l'abondance de la regeneration de pin a ecorce blanche n'etait pas reliee a l'age du peuplement, mais qu'elle etait reliee a plusieurs caracteristiques biophysiques de la station, incluant des relations positives avec l'altitude et avec la mortalite des arbres dominants causee par le dendroctone du pin ponderosa et des relations negatives avec la disponibilite en eau, la temperature et l'abondance du sapin subalpin. Nos resultats indiquent que le pin a ecorce blanche se regenere a plusieurs endroits et que la forte mortalite causee par les recentes infestations du dendroctone du pin ponderosa peut creer des conditions adequates pour l'etablissement de sa regeneration si les sources de semences sont suffisantes. [Traduit par la Redaction], Introduction The continued persistence of whitebark pine (Pinus albicaulis Engelm.) as an important species in high-elevation forests of western North America is a topic of major concern among land managers [...]

We investigated the structure and dynamics of the multi-stemmed understory shrub Lindera triloba (Sieb. et Zucc.) Blume over 3 years in an old-growth coniferous forest, and quantitatively evaluated the factors affecting the ramet production, growth, and survival. Most genets sprouted continuously and exhibited multiple-stemmed structures with a few large and many small ramets. The skewed ramet-size distribution within genets resulted from the local crowding of neighboring trees, but not from the number of ramets within genets. This indicated that inter-plant competition is asymmetric (i.e., larger individuals outcompete one-sidedly smaller ones), but intra-plant competition (i.e., competition among ramets within genets) is symmetric (i.e., smaller ones also competitively affect larger ones). The local crowding of neighboring understory trees consistently negatively affected the ramet production, growth, and survival of L. triloba. Intra-genet crowding (i.e., crowding of ramets within genets) also negatively affected the ramet dynamics. On the other hand, the largest-ramet size within genets had positive relationships with the ramet dynamics, indicating that physiological integration within genets plays a role as supporting younger ramets. Based on our results, to fully understand genet persistence strategies in clonal shrub species, it is important to consider the effects of intra-genet crowding and modular integration, as well as plant-to-plant interaction. Key words: clonal growth, physiological integration, competition, size structure. Les auteurs ont examine la structure et la dynamique de l'espece arbustive de sous-bois a tiges multiples, le Lindera triloba (Sieb. et Zucc.) Blume, au cours de 3 annees dans une vieille foret de coniferes; ils ont evalue quantitativement les facteurs qui influencent la production des ramettes, leur croissance et leur survie. La plupart des genets bourgeonnent continuellement et montrent des structures a plusieurs tiges avec quelques grosses et plusieurs petites ramettes. La curtose observee dans la distribution de la dimension des ramettes, entre les genets, provient de l'entassement localise; des arbres voisins, mais non du nombre de ramettes au sein des genets. Ceci indique que la competition entre plants est asymetrique (i.e., les individus plus gros eliminent d'un cote les plus petits), mais que la competition a l'interieur du plant (i.e., competition entre les ramettes au sein des genets) est symetrique (i.e., les plus petits affectent egalement les plus gros par competition). L'attroupement local des arbres voisins du sous-bois affecte negativement de facon congrue la production de ramettes, la croissance et la survie du L. triloba. L'attroupement au sein du genet (i.e., attroupement des ramettes au sein des genets), affecte aussi negativement la dynamique des ramettes. D'un autre cote, la ramette la plus grosse dans les genets montre une relation positive avec la dynamique des ramettes, ce qui indique que l'integration physiologique au sein des genets joue un role comme support pour les jeunes ramettes. A partir de ces resultats, pour comprendre completement les strategies de persistance chez les especes arbustives clonales, il faut considerer les effets de l'attroupement au sein des genets et l'integration modulaire aussi bien que l'interaction plante-plante. Mots-cles: croissance clonale, integration physiologique, competition, structure dimensionnelle. [Traduit par la Redaction], Introduction Basal sprouting is one of the common growth forms of many shrub species that grow clonally on forest floors (Jenik 1994). Sprouting results from responses to recover the aboveground [...]

ABSTRACT. In order to ensure the sustainable development of the North, increased anthropogenic pressure on subarctic environments must be accompanied by appropriate restoration techniques. Locally adapted restoration guidelines need to [...]

Time lag analysis (TLA) is a distance-based approach used to study temporal dynamics of ecological communities by measuring community dissimilarity over increasing time lags. Despite its increased use in recent years, its performance in comparison with other more direct methods (i.e., canonical ordination) has not been evaluated. This study fills this gap using extensive simulations and real data sets from experimental temporary ponds (true zooplankton communities) and landscape studies (landscape categories as pseudo-communities) that differ in community structure and anthropogenic stress history. Modeling time with a principal coordinate of neighborhood matrices (PCNM) approach, the canonical ordination technique (redundancy analysis; RDA) consistently outperformed the other statistical tests (i.e., TLAs, Mantel test, and RDA based on linear time trends) using all real data. In addition, the RDA-PCNM revealed different patterns of temporal change, and the strength of each individual time pattern, in terms of adjusted variance explained, could be evaluated. It also identified species contributions to these patterns of temporal change. This additional information is not provided by distance-based methods. The simulation study revealed better Type I error properties of the canonical ordination techniques compared with the distance-based approaches when no deterministic component of change was imposed on the communities. The simulation also revealed that strong emphasis on uniform deterministic change and low variability at other temporal scales is needed to result in decreased statistical power of the RDA-PCNM approach relative to the other methods. Based on the statistical performance of and information content provided by RDA-PCNM models, this technique serves ecologists as a powerful tool for modeling temporal change of ecological (pseudo-) communities. Key words: canonical ordination; community ecology; distance-based methods; principal coordinate o[ neighborhood matrices ( PCNM ) ; statistical power; temporal dynamics.

A species is expected to occur where the prevailing biotic and abiotic conditions fall within its fundamental niche. Geographic range limits should, therefore, occur when the survival and fitness of individuals along ecological gradients is reduced to the point at which populations are no longer self-sustaining. Abrupt limits to a species' distribution are expected to reflect abrupt changes in the ecological conditions that cause sharp declines in fitness across the limit. We investigated the correlation between geographic variation in environment and fitness across the abrupt northern range limit of a coastal dune plant, Camissoniopsis cheiranthifolia (Onagraceae). In each of 64 plots distributed across five sites along a 200-km transect spanning the species' northern range limit (four within the range plus one beyond the limit), we measured plant community composition as a proxy for variation in biotic and abiotic environmental factors and lifetime fitness of genetically standardized experimental populations of C. cheiranthifolia. There was substantial variation in plant community composition among plots and sites across the range limit, and fitness of experimental plants covaried strongly with the first principal component of plant community composition. However, we did not detect an abrupt shift in plant community or the expected decline in fitness across the range limit. In fact, fitness and recruitment increased toward the limit and were relatively high beyond the limit. This suggests that habitat beyond the range did not occur outside of the species' fundamental niche. These results challenge niche-based explanations for range limits and suggest that hypotheses involving the finer-scale distribution of habitat patches or constraints on dispersal warrant more serious consideration. Key words: Camissoniopsis cheiranthifolia; coastal dunes; demography; fitness; geographic ranges; Pacific coast; plant community structure; range limits; seedling recruitment; transplant experiment.

Fundamental gaps remain in our knowledge of how positive species interactions, such as facilitation and mutualism, structure and maintain populations and communities. Foundation species create extensive biogenic habitats, but we know little of how their traits, such as density, age, and patch size, modify their ability to facilitate other species. We tested the role of facilitator traits in cobble beach plant communities in New England, USA. In this system, intertidal beds of the cordgrass Spartina alterniflora facilitate populations of halophytic forbs at higher shore elevations by buffering wave action, stabilizing cobbles, and limiting physical disturbance. Using descriptive and experimental techniques, we tested the hypotheses that (1) the density and height of cordgrass shoots modify the strength of the cordgrass-forb facilitation, and (2) cordgrass peat alone contributes to the facilitation of forbs. Increased shoot density, as well as the combination of cordgrass peat and shoots, positively affected two life history stages (seedling and adult) of the abundant forb Suaeda linearis, demonstrating that cordgrass traits modify the strength of facilitation in this system. Since the expression of traits varies within and among patches of any given foundation species, traits can and should be used to predict the strength of facilitation, to guide the development of conservation strategies, and to develop more accurate models of species interactions. Key words: cobble beach; facilitation; foundation species; habitat; Spartina alterniflora; species interaction; Suaeda linearis.

Digital image analysis could be a rapid and precise technique for estimating legume proportions in grass swards. In 2004, we conducted a pot study to evaluate a digital image analysis (DIA) system for estimation of legume dry matter (DM) contribution in legume-grass mixtures. Examination of pure swards and binary legume-grass mixtures of red clover (Trifolium pratense L.), white clover (T. repens L.), alfalfa (Medicago sativa L.), and perennial ryegrass (Lolium perenne L.) took place after 35, 49, and 63 d of growth. To estimate the cover percentage of legumes in the swards, a total of 64 digital pictures were taken. The DM contribution of legumes (% of total biomass) showed a significant relationship with the proportion of image area covered by legumes (% of total area), which was classified visually. A DIA system for grayscale images was developed with the software Optimas. We found that DIA could be used to accurately predict legume contribution in mature swards. Legume contribution, as estimated by DIA, was significantly correlated with DM contribution of red clover ([R.sup.2] = 0.87), white clover ([R.sup.2] = 0.85), and alfalfa ([R.sup.2] = 0.79). Bare ground reduced the predictive ability of DIA in young or open swards. Use of DIA may be limited until we refine the method to deal with bare ground and different leaf shapes associated with various weed species.

Knowledge of target environments in breeding programs is important to better direct the development of germplasm. The objectives of this study were to identify associations among barley (Hordeum vulgare L.) growing environments to identify mega-environments to select the best locations to breed barley. Twenty-seven years of grain yield data from the International Barley Yield Trial (IBYT) conducted by the ICARDA-CIMMYT Barley Breeding Program, consisting of 750 grain yield trials of two replications representing 235 locations in 75 countries, were analyzed using pattern analysis to group sites across years that represent similar selection environments. The shifted multiplicative model (SHMM) was employed to group sites within each year. Environments clustered into three main groups and squared Euclidean distances were used to identify a representative location within each cluster. Group 1 locations were characterized as being cool with intermediate precipitation; Group 2 locations were warmer and drier; and Group 3 sites were generally cool and had the highest average precipitation. The respective representative key locations for each of the three groups were Leida, Spain; Boulifa, Tunisia; and Setif, Algeria. All three key locations are located in the Northern Hemisphere between 36[degrees] and 41[degrees] latitude. The results of this study show that the global adaptation of barley is possible and can be improved by breeding and selection for adaptation within the three main mega-environments identified.

A study was conducted to determine if consideration of ecological site classification in combination with stand age would describe total ecosystem carbon (C) better than consideration of just stand age alone. The research was conducted in the 9250 ha University of Northern British Columbia/The University of British Columbia Aleza Lake Research Forest in central British Columbia. Over three field seasons (2003-2005), 38, 72, and 27 plots were established in mesic, subhygric, and hygric stands, respectively, with stand ages ranging from 5 to 350+ years. Mineral soil C stocks were significantly influenced by moisture regime, where hygric > subhygric > mesic (93, 77, and 65 t C * [ha.sup.-1], respectively). Mineral soil and forest floor C stocks were not related to stand age, indicating their resilience to partial-cut and clear-cut forest harvesting systems historically implemented throughout the study area. Subhygric stands had the highest total ecosystem C stocks in the Aleza Lake Research Forest, having approximately 18% more C than mesic and hygric stands, principally due to higher mineral soil C stocks (than mesic stands) and improved C sequestration in large trees (over hygric stands). Consideration of ecological site classification in addition to stand age information improved total ecosystem C stock estimates over the use of stand age alone. Cette etude a ete realisee dans le but de determiner si la classification ecologique d'une station combinee a l'age du peuplement permet d'obtenir une meilleure estimation de la quantite totale de carbone (C) dans l'ecosysteme que celle qu'on obtient en tenant compte seulement de l'age du peuplement. L'etude a ete realisee dans la foret experimentale du lac Aleza (UNBC et UBC) qui couvre 9250 ha dans le centre de la Colombie-Britannique. Pendant trois saisons de terrain (2003-2005), respectivement 38, 72 et 27 placettes ont ete etablies dans des stations mesiques, subhygriques et hygriques ou l'age du peuplement variait de 5 a 350 ans et plus. Les stocks de C dans le sol mineral etaient significativement influences par le regime hydrique et atteignaient respectivement 93, 77 et 65 t * [ha.sup.-1] dans les stations hygriques, subhygriques et mesiques. Les stocks de C dans le sol mineral et la couverture morte n'etaient pas relies a l'age du peuplement, ce qui est un indice de leur resilience aux regimes de coupe partielle et de coupe a blanc implantes depuis longtemps partout dans l'aire d'etude. Dans les stations subhygriques, on a observe les stocks de C total dans l'ecosysteme les plus eleves dans la foret experimentale, soit approximativement 18 % plus de C que dans les stations mesiques et hygriques, principalement a cause des stocks de C plus eleves dans le sol mineral, comparativement aux stations mesiques, et d'une meilleure sequestration du C chez les gros arbres, comparativement aux stations hygriques. Le fait de tenir compte de la classification ecologique de la station, en plus de l'age du peuplement, ameliore les estimations du stock de C total dans l'ecosysteme comparativement a l'utilisation de seulement l'age du peuplement. [Traduit par la Redaction], Introduction Carbon (C) stocks and sequestration in terrestrial ecosystems have garnered increased interest since the fourth Intergovernmental Panel on Climate Change Assessment (IPCC 2007) which has heightened climate change concerns, [...]

Here, we present the second part of a quantitative theory for the structure and dynamics of forests under demographic and resource steady state. The theory is based on individual-level allometric scaling relations for how trees use resources, fill space, and grow. These scale up to determine emergent properties of diverse forests, including size--frequency distributions, spacing relations, canopy configurations, mortality rates, population dynamics, successional dynamics, and resource flux rates. The theory uniquely makes quantitative predictions for both stand-level scaling exponents and normalizations. We evaluate these predictions by compiling and analyzing macroecological datasets from several tropical forests. The close match between theoretical predictions and data suggests that forests are organized by a set of very general scaling rules. Our mechanistic theory is based on allometric scaling relations, is complementary to 'demographic theory,' but is fundamentally different in approach. It provides a quantitative baseline for understanding deviations from predictions due to other factors, including disturbance, variation in branching architecture, asymmetric competition, resource limitation, and other sources of mortality, which are not included in the deliberately simplified theory. The theory should apply to a wide range of forests despite large differences in abiotic environment, species diversity, and taxonomic and functional composition. allometry | mortality rate | plant ecology | size distribution | competitive thinning

Keywords: mycorrhizas, symbiosis, mycorrhizosphere, associated bacteria, endobacteria, genome projects Abstract This review focuses on interactions among plants, mycorrhizal fungi, and bacteria, testing the hypothesis whether mycorrhizas can be defined as tripartite associations. After summarizing the main biological features of mycorrhizas, we illustrate the different types of interaction occurring between mycorrhizal fungi and bacteria, from loosely associated microbes to endobacteria. We then discuss, in the context of nutritional strategies, the mechanisms that operate among members of the consortium and that often promote plant growth. Release of active molecules, including volatiles, and physical contact among the partners seem important for the establishment of the bacteria/mycorrhizal fungus/plant network. The potential involvement of quorum sensing and Type III secretion systems is discussed, even if the exact nature of the complex interspecies/interphylum interactions remains unclear.

Decomposition is a critical source of plant nutrients, and drives the largest flux of terrestrial C to the atmosphere. Decomposing soil organic matter typically contains litter from multiple plant species, yet we lack a mechanistic understanding of how species diversity influences decomposition processes. Here, we show that soil C and N cycling during decomposition are controlled by the composition and diversity of chemical compounds within plant litter mixtures, rather than by simple metrics of plant species diversity. We amended native soils with litter mixtures containing up to 4 alpine plant species, and we used 9 litter chemical traits to evaluate the chemical composition (i.e., the identity and quantity of compounds) and chemical diversity of the litter mixtures. The chemical composition of the litter mixtures was the strongest predictor of soil respiration, net N mineralization, and microbial biomass N. Soil respiration and net N mineralization rates were also significantly correlated with the chemical diversity of the litter mixtures. In contrast, soil C and N cycling rates were poorly correlated with plant species richness, and there was no relationship between species richness and the chemical diversity of the litter mixtures. These results indicate that the composition and diversity of chemical compounds in litter are potentially important functional traits affecting decomposition, and simple metrics like plant species richness may fail to capture variation in these traits. Litter chemical traits therefore provide a mechanistic link between organisms, species diversity, and key components of belowground ecosystem function. decomposition | species richness | chemical diversity | litter mixtures

Traits associated with seed dispersal vary tremendously among sympatric wind-dispersed plants. We used two contrasting tropical tree species, seed traps, micrometeorology, and a mechanistic model to evaluate how variation in four key traits affects seed dispersal by wind. The conceptual framework of movement ecology, wherein external factors (wind) interact with internal factors (plant traits) that enable movement and determine when and where movement occurs, fully captures the variable inputs and outputs of wind dispersal models and informs their interpretation. We used model calculations to evaluate the spatial pattern of dispersed seeds for the 16 factorial combinations of four traits. The study species differed dramatically in traits related to the timing of seed release, and a strong species by season interaction affected most aspects of the spatial pattern of dispersed seeds. A rich interplay among plant traits and seasonal differences in atmospheric conditions caused this interaction. Several of the same plant traits are crucial for both seed dispersal and other aspects of life history variation. Observed traits that limit dispersal are likely to be constrained by their life history consequences. atmospheric turbulence | conditional seed release | Coupled Eulerian-Lagrangian closure (CELC) model | long distance dispersal | tropical forest

Fungi and protists make up an ecological group, trichomycetes, that inhabit the guts of invertebrates, mostly aquatic insects. Trichomycetes are reported herein from arthropods collected in lotic habitats (fast flowing streams) and lentic environments (ponds, ditches, seeps, and lakes) from 11 sites in Algonquin Park and 6 other sites in Ontario, Canada. Thirty-two trichomycete species were recovered, including 7 new species: Legeriomyces algonquinensis, Legeriosimilis leptocerci, Legeriosimilis whitneyi, and Paramoebidium umbonatum are described from mayfly nymphs (Ephemeroptera); Pennella digitata and Glotzia incilis from black fly and midge larvae (Diptera), respectively; and Arundinula opeongoensis from a crayfish (Crustacea). Legeriomyces rarus Lichtw. & M.C. Williams and Stachylina penetralis Lichtw. are new North American records, and seven species are documented for the first time in Canada. More common and widely distributed trichomycete species such as Harpella melusinae Leger & Duboscq and Smittium culicis Manier, were also recovered. Most previous studies on trichomycetes have been done primarily in lotic environments but clearly lentic systems (e.g., ponds and lakes) harbour diverse arthropod communities and further exploration of these habitats will continue to increase our knowledge of trichomycete diversity. Key words: Amoebidiales, Eccrinales, Harpellales, insect fungal endobionts, symbiotic protista. Les champignons et les protistes comportent un groupe ecologique, les trichomycetes, qui habitent les intestins de la plupart des insectes aquatiques. Les auteurs rapportent des ttrichomycetes provenant d'arthropodes vivants dans des habitats lotiques (cours d'eau rapides) et des environnements lentiques (etangs, fosses, suintement et lacs) recoltes sur 11 sites dans le parc Algonquin et six autres sites en Ontario, au Canada. On a trouve 33 especes de trichomycetes, incluant sept nouvelles especes pour l'Amerique du Nord: Lageriomyces algonquinensis, Lageriosimilis leptocerci, Lageriosimilis whitneyi et Paramoebidium umbonatum, decrits a partir de nymphes d'ephemeres (Ephemeroptera); Pennella digitata et Glotzia incilis a partir de mouches noires et de brulots (Diptera) respectivement; et Arundinula opeongoensis a partir d'un ecrevisse (Crustacea). Le Lageriomyces rarus Lichtw. & M. C. Williams et le Stachylina penetralis Lichtw. Sept especes sont repertoriees pour la premiere fois au Canada. On a egalement retrouve des especes de trichomycetes communes et largement distribuees, comme l'Harpella melusinae Leger & Duboscq et le Smittum culicis Manier. La plupart des etudes antecedentes sur les trichomycetes ont ete conduites surtout en environnements lotiques, mais il est clair que les systemes lentiques (etangs et lacs) comportent diverses communautes d'arthropodes et que d'autres explorations de ces habitats vont permettre d'augmenter notre connaissance de la diversite des trichomycetes. Mots-cles : Amaoebidiales, Eccrinales, Harpellales, champignons endosymbiontes des insectes, protistes symbiotiques. [Traduit par la Redaction], Introduction Canada has a wide variety of freshwater aquatic habitats such as lakes, ponds, swamps, rivers, and streams, making up extensive watersheds. Information on Canada's immense hydrologic diversity is available [...]

The coexistence between genetically modified (GM) and non-GM maize (Zea mays L.) fields is subjected to regulation in several countries. A strategy to reduce cross-pollination from GM to non-GM fields was evaluated, on the basis of reducing the flowering coincidence by sowing at separate times. The trial included narrow plots in which transgenic maize was sown before, simultaneously, and after adjacent non-GM maize. A three-week delay between GM and non-GM sowing dates resulted in flowering delays below 5 d for early sowings, but up to 10 to 15 d for late sowings. Cross-pollination was monitored by xenia effect and validated by real-time PCR. The combined effect of flowering delay and distance from the pollen source was evaluated. Cross-pollination dramatically decreased with distance between pollen source and receptor. Flowering delay interacted with distance to the pollen donor source and further reduced GM pollen flow in all cases. Thus, it acted as a regulatory factor. A flowering delay of 92.9 growing degree units (GDU) (7 d in our experimental conditions) was enough to reduce the adventitious presence of GM kernels in non-GM maize plots down to residual values. This study illustrates the possibility of improving coexistence through temporal separation of flowering dates on the basis of appropriate delays in sowing dates.

Spaciinodum collinsonii, a Triassic sphenophyte from the central Transantarctic Mountains, Antarctica, is reinterpreted based on new material in order to clarify discrepancies from previous work and to detail the development and ecology of the Spaciinodum plant. Vegetative stems have alternating nodes and internodes, nodes distinguished by a solid diaphragm of tissue, internodes by the presence of vallecular (cortical) and carinal canals, and a hollow pith. Whorls of branches arise immediately above the nodes, alternating with the leaves of the subjacent nodes. Branches develop in the cortex and are anatomically similar to the stems. While Spaciinodum is similar to extant Equisetum, it is distinctive in that its large vallecular canals form a complete ring within the cortex and are separated only by thin fimbrils of tissue. The majority of specimens of Spaciinodum are now believed to be dormant buds with condensed nodes and internodes, with progressively longer internodal regions more basally. More apical portions of buds have cellular internodes because the areas where the canals will form have not yet ruptured from elongation. The abundance of buds and the absence of elongated stems in the permineralized peat deposit suggest that Spaciinodum underwent dormancy during the dark Antarctic winters. Key words: Antarctica; dormancy; Equisetophyte; Triassic; Spaciinodum; stem bud.

In the Rocky Mountain Forest District of British Columbia, a dramatic series of fires occurred during 2003, setting the stage for an abundant morel crop in the following year. During 2004, the abundance of post-fire morels (Morchella spp.) was measured and the plant community associated with morel production was characterized. Morel production averaged 6473 [+ or -] 2721 morels* [ha.sup.-1] in five burnt forests that were surveyed. Production ranged from 1702* [ha.sup.-1] at Plumbob Mountain to a significantly higher 16827* [ha.sup.-1] in the Kootenay National Park, where the highest level of duff consumption (71%) was also observed. Several plant species had high importance in morel habitat, and were also associated with above-average morel abundance: Chamerion angustifolium (L.) Holub, Arnica cordifolia Hook., Erythronium grandiflorum Pursh, Spiraea betulifolia Pallas subsp. lucida (Dougl. ex Greene) Taylor and MacBryde, Menziesia ferruginea Sm., Rosa acicularis Lindl. subsp. sayi (Schwein.) W.H. Lewis, Pinus contorta Dougl. ex Loud. var. latifolia Engelm., Abies lasiocarpa (Hook.) Nutt., and Picea glauca (Moench) Voss x engelmannii (Torr. & Gray ex Hook.) Brayshaw. Compositae and Vaccinium spp. were important species when considered as groups. Grass species, including Calamagrostis rubescens Buckl., were more proximate to morel-free plots. The characteristics of morel habitats observed in this study may be useful in future management of the resource, through conservation of habitat, management of prescribed burning, and postponement of salvage logging in potentially highly productive areas. Key words: Morchella, indicators, fire, mushroom. Le District forestier des montagnes Rocheuses, en Colombie canadienne, a connu en 2003 de spectaculaires incendies de foret, preparant les sites pour une abondante recolte de morilles l'annee suivante. En 2004, les auteurs ont mesure l'abondance de morilles (Morchella spp.) post incendie et ont caracterise la communaute vegetale associee. La production moyenne de morilles a atteint 6473 [+ or -] 2721 morilles* [ha.sup.-1] dans les cinq forets brulees observees. La production allait de 1702* [ha.sup.-1] in Plumbob Mountain a une quantite significativement plus elevee de 16827* [ha.sup.-1] dans le Parc national de Kootnay, ou la litiere a le plus fortement brule (71 %). On a observe plusieurs especes de plantes d'importance dans l'habitat des morilles egalement associees avec une abondance au-dessus de la moyenne des sporophores: Chamerion angustifolium (L.) Holub, Arnica cordifolia Hook., Erythronium grandiflorum Pursh, Spirea betulifolia Pallas subsp. lucida (Dougl. ex Greene) Taylor and MacBryde, Menziesia ferruginea Sm., Rosa acicularis Lindl. subsp. sayi (Schwein.) W.H. Lewis, Pinus contorta Dougl. ex Loud. var. latifolia Engelm., Abies lasiocarpa (Hook.) Nutt., and Picea glauca (Moench) Voss xengelmannii (Torr. & Gray ex Hook.) Brayshaw. Les composees et les Vaccinium spp. occupent une place importante comme groupes. Les graminees, incluant le Calamagrostis rubescens, se retrouvent plutot a proximite des parcelles sans morille. Les caracteristiques des habitats de la morille, observees dans cette etude, pourraient etre utiles pour l'amenagement de la ressource, en assurant la conservation de l'habitat, l'utilisation du brulage controle, et la remise a plus tard de la recolte sur les surfaces a fort potentiel de production. Mots-cles : Morchella, indicateurs, feu, champignon. [Traduit par la Redaction], Introduction After a large forest fire, the emergence of phoenicoid mushrooms signals the renewal of forest life, as well as the almost certain arrival of morel pickers. Cooked morels (Morchella [...]

Temporal heterogeneity of watering affects plant growth. When the same total amount of water is supplied, frequent watering leads to greater plant size than infrequent watering. However, the effects of a given watering regime can differ when nutrient levels vary. An experiment was designed to test the hypothesis that the effects of temporal heterogeneity of watering on plant growth also vary as a function of nutrient levels. Perilla frutescens (L.) Britton was grown using different combinations of nutrient levels and watering frequencies, with total water held constant across the treatments. The effects on plant size were analysed after 36 d. Under nutrient-rich conditions, frequent watering resulted in significantly larger plants than infrequent watering. However, under nutrient-poor conditions, no significant difference was detected between the different watering frequencies. The temporal heterogeneity of watering thus appears to have different effects on plant growth at different nutrient levels. Therefore, the watering heterogeneity should be examined with nutrients as unity, because the watering heterogeneity and nutrients affect plant growth in an interactive manner. Key words: biomass allocation to roots, plant size, resource heterogeneity, watering frequency. Une heterogeneite temporale de l'irrigation influence la croissance des plantes. L'utilisation d'une meme quantite totale d'eau avec des arrosages frequents donne des plantes plus grosses que les arrosages moins frequents. Cependant, les effets d'un regime donne d'arrosage peuvent differer lorsque les apports en nutriments varient. Les auteurs ont conduit une experience pour verifier l'hypothese que les effets d'une heterogeneite temporale de l'irrigation sur la croissance des plantes varient egalement selon les apports en nutriments. Ils ont cultive le Perilla frutescens (L.) Britton en utilisant diverses combinaisons d'apports en nutriments et differentes frequences d'arrosage, en maintenant l'apport total en eau constant pour tous les traitements. Ils ont analyse les effets sur les plantes apres 36 jours. Sous des conditions riches en nutriments, l'arrosage frequent conduit a des plantes significativement plus grosses qu'avec les arrosages moins frequents. Cependant, sous des conditions pauvres en nutriments, on n'observe aucune difference entre les differentes frequences de traitement. L'heterogeneite temporale de l'irrigation semble avoir differents effets sur la croissance des plantes avec differents apports en nutriments. Par consequent, on devrait examiner l'heterogeneite de l'irrigation en utilisant les nutriments comme unite, parce que l'heterogeneite de l'irrigation et les nutriments affectent la croissance de la plante de facon interactive. Mots-cles : allocation de biomasse aux racines, dimension des plantes, heterogeneite des ressources, frequence d'irrigation. [Traduit par la Redaction], Introduction Resources utilized by plants exhibit temporal and spatial heterogeneity in terms of their distribution and abundance in natural environments (Jackson and Caldwell 1993a, 1993b; Farley and Fitter 1999; James [...]

Fall-planted safflower (Carthamus tinctorius L.) offers potentially higher yield than springsown types. Yet winter survival in relation to fall growth and physiological aspects of acclimation has not been determined. Our objectives were (i) to determine the relationship between fall growth and winter survival in safflower, (ii) to assess if selection improved winter survival, and (iii) to determine if water relations and membrane leakage distinguished safflower varying in winter survival. Fall growth, leaf water relations, and leaf membrane leakage were measured in fall 2004 and 2005 at Pullman and Central Ferry, WA, and winter survival was determined. Average minimum winter temperatures were 1.0[degrees]C at Central Ferry and -3.9[degrees]C at Pullman, with extremes of -7.2[degrees]C at Central Ferry and -19.5[degrees]C at Pullman. For the 21 accessions evaluated, low fall plant habit was required for survival, but survival also varied substantially among low-habit types. Two cycles of recurrent mass selection on five low-habit types improved winter survival from 21 to 59% at Central Ferry and from 8 to 18% at Pullman. The highest survival was for BJ-27 after two selection cycles, averaging 90% at Central Ferry and 38% at Pullman. Accession BJ-27 maintained higher leaf pressure potential during fall acclimation in 2004-2005 and in 2005-2006 had higher pressure potential and membrane stability on the 8 January sampling than less-hardy types. The results show that both low habit and physiological acclimation capacity are needed for high winter survival in safflower.

Wheat (Triticum aestivum L.) cultivars with high canopy temperature depression (CTD) tend to have higher grain yield under dry, hot conditions. Therefore, CTD has been used as a selection criterion to improve adaptation to drought and heat. The CTD is a result of the leaf's energy balance, which includes terms determined by environment and physiological traits. We hypothesized that one or more of several physiological traits contributed to consistent CTD differences among three closely-related winter wheat lines grown under dryland conditions. For three years we measured several leaf traits, including CTD, leaf dimension, gas exchange rates, and carbon-13 isotope discrimination ([DELTA]). Soil water content was also monitored. Data showed that daytime CTD was related to the leaf size in these wheat lines. The most drought-tolerant line, TX86A8072, had consistently smaller and narrower leaves than TX86A5606, the least drought tolerant. For TX86A8072, dryland and irrigated average noon CTD was -0.8[degrees]C, and average flag leaf area (LA) 11 [cm.sup.2], for TX86A5606, values were -1.7[degrees]C and 12.5 [cm.sup.2], respectively. However, TX86A8072 also had higher CTD (i.e., lower temperatures) than TX86A5606 at night, despite a theoretically greater sensible heat transfer coefficient, suggesting greater nighttime transpiration (T). Implications of these traits on nighttime leaf energy balance and possible adaptive roles of nighttime T are discussed.

A well-known, but largely untested, prediction in plant reproductive ecology is that dioecious taxa should produce larger, more, higher-quality, or better-defended seeds than cosexual taxa. Using a data set composed of 972 species in 104 families, representing the flora of the Tambopata Wildlife Reserve (Madre de Dios, Peru), we evaluated the first component of this prediction, examining ecological and evolutionary relationships between breeding system and mean seed size with two kinds of tests. First, we conducted cross-species analyses to determine whether species with different breeding systems differed significantly with respect to mean individual seed size. Second, we used a hypothesized phylogeny to identify pairs of the most closely related taxa or clades within the Tambopata community that differed with respect to breeding system. Comparing pair members allowed us to determine whether evolutionary divergence in breeding system (between taxa with unisexual vs. cosexual individuals) was consistently associated with evolutionary change in seed size. In both analyses, we controlled for potentially confounding effects of growth form by examining these relationships within woody and nonwoody taxa. Cross-species analyses revealed that dioecious species produced larger seeds than cosexual species among woody species, shrubs, lianas (each growth form analyzed separately), and all species pooled, but not among trees. Phylogenetically independent contrasts upheld the significant association between breeding system and seed size among woody taxa, lianas, and all taxa pooled, but not among shrubs. We discuss the implications of our findings for evolutionary hypotheses regarding associations between dioecy and seed size. Key words: angiosperms, breeding system, dioecy; monoecy; plant growth forms; rain forest; seed size.

If controls over primary productivity and plant community composition are mainly environmental, as opposed to biological, then global change may result in large-scale alterations in ecosystem structure and function. This view appears to be favored among investigations of plant biomass and community responses to experimental and observed warming. In far northern and arctic ecosystems, such studies predict increasing dominance of woody shrubs with future warming and emphasize the carbon (C)-sequestration potential and consequent atmospheric feedback potential of such responses. In contrast to previous studies, we incorporated natural herbivory by muskoxen and caribou into a 5-year experimental investigation of arctic plant community response to warming. In accordance with other studies, warming increased total community biomass by promoting growth of deciduous shrubs (dwarf birch and gray willow). However, muskoxen and caribou reduced total community biomass response, and responses of birch and willow, to warming by 19%, 46%, and 11%, respectively. Furthermore, under warming alone, the plant community shifted after 5 years away from graminoid-dominated toward dwarf birch-dominated. In contrast, where herbivores grazed, plant community composition on warmed plots did not differ from that on ambient plots after 5 years. These results highlight the potentially important and overlooked influences of vertebrate herbivores on plant community response to warming and emphasize that conservation and management of large herbivores may be an important component of mitigating ecosystem response to climate change. arctic | climate change | global warming | herbivory | species interactions

A change in climate would be expected to shift plant distribution as species expand in newly favorable areas and decline in increasingly hostile locations. We compared surveys of plant cover that were made in 1977 and 2006-2007 along a 2,314-m elevation gradient in Southern California's Santa Rosa Mountains. Southern California's climate warmed at the surface, the precipitation variability increased, and the amount of snow decreased during the 30-year period preceding the second survey. We found that the average elevation of the dominant plant species rose by [approximately equal to] 65 m between the surveys. This shift cannot be attributed to changes in air pollution or fire frequency and appears to be a consequence of changes in regional climate. plant migration | range shift

Demography is central to both ecology and evolution, and characterizing the feedback between ecology and evolution is critical for understanding organisms' life histories and how these might evolve through time. Here, we show how, by combining a range of theoretical approaches with the statistical analysis of individually structured databases, accurate prediction of life history decisions is possible in natural density-regulated populations undergoing large fluctuations in demographic rates from year to year. Our predictions are remarkably accurate and statistically well defined. In addition, we show that the predicted trait values are evolutionarily and convergence stable and that protected polymorphisms are possible. adaptive dynamics | Carlina vulgaris | Carduus nutans | coexistence | relative nonlinearity of competition

A central goal of comparative plant ecology is to understand how functional traits vary among species and to what extent this variation has adaptive value. Here we evaluate relationships between four functional traits (seed volume, specific leaf area, wood density, and adult stature) and two demographic attributes (diameter growth and tree mortality) for large trees of 240 tree species from five Neotropical forests. We evaluate how these key functional traits are related to survival and growth and whether similar relationships between traits and demography hold across different tropical forests. There was a tendency for a trade-off between growth and survival across rain forest tree species. Wood density, seed volume, and adult stature were significant predictors of growth and/or mortality. Both growth and mortality rates declined with an increase in wood density. This is consistent with greater construction costs and greater resistance to stem damage for denser wood. Growth and mortality rates also declined as seed volume increased. This is consistent with an adaptive syndrome in which species tolerant of low resource availability (in this case shade-tolerant species) have large seeds to establish successfully and low inherent growth and mortality rates. Growth increased and mortality decreased with an increase in adult stature, because taller species have a greater access to light and longer life spans. Specific leaf area was, surprisingly, only modestly informative for the performance of large trees and had ambiguous relationships with growth and survival. Single traits accounted for 9-55% of the interspecific variation in growth and mortality rates at individual sites. Significant correlations with demographic rates tended to be similar across forests and for phylogenetically independent contrasts as well as for cross-species analyses that treated each species as an independent observation. In combination, the morphological traits explained 41% of the variation in growth rate and 54% of the variation in mortality rate, with wood density being the best predictor of growth and mortality. Relationships between functional traits and demographic rates were statistically similar across a wide range of Neotropical forests. The consistency of these results strongly suggests that tropical rain forest species face similar trade-offs in different sites and converge on similar sets of solutions. Key words: demography; functional ecology; height; life-history theory; seed mass; shade tolerance; species coexistence; specific leaf area; trees; tropical rain forest; wood density.

Trade-offs in allocation to resprouting vs. seedling regeneration in plants are predicted to occur along fire disturbance gradients. Increased resprouting ability should be generally favored in plant communities with a high probability of crown fire return. Hence, communities dominated by resprouters are predicted to have smaller seed banks than those dominated by species killed by fire. We tested whether there were trait shifts in resprouting ability among growth forms (short-lived herbaceous vs. ground-dwelling perennials vs. shrubs) and among communities (rocky outcrop vs. sclerophyll forest) with contrasting probabilities of crown fire return. Resprouting was more common in ground-dwelling perennials and in the sclerophyll forest community with a high probability of crown fire. Soil seed banks were sampled in rocky outcrop and sclerophyll forest communities in recently burned (18 months) and long-since-burned (12 years) locations at interspersed replicated sites. Collected seed banks were treated with orthogonal treatments of fire stimuli or no stimuli, and seedling emergence was measured in controlled conditions. Seed bank composition reflected the pattern of extant vegetation, with resprouting species being more common in the community with a higher probability of crown fire. Overall, however, resprouting species were poorly represented in the seed bank compared to those species killed by fire. Predicted shifts in allocation to seed production were strongly manifested in community seed banks across the disturbance gradient. Fewer species, seedlings, and seedlings per adult emerged from seed banks in the sclerophyll forest. This suggests that the dominance of resprouting species influences recruitment at the community scale. Community patterns in the seed bank also reflected predicted trade-offs with plant size and growth rate. Short-lived species that are killed by fire dominated the seed bank on rocky outcrops, while longer-lived resprouting species were found in low abundance. Life history trade-offs in persistence and regeneration strongly contribute to coexistence patterns between and within communities with contrasting probabilities of fire return. Key words: coexistence; community ecology; ecological strategies; fire ecology; fire regime; persistence traits, plant functional types; resprouting; rocky outcrops; sclerophyll forest; spatial scales; sprouting.

Identifying optimal fire regimes for a given species requires monitoring its responses to different fire regimes. This study examined the effects of fire during the lightning season and clipping in different seasons on the induction of flowering in a fire-adapted species, Pityopsis graminifolia, in two different fire-dependent ecosystems (oak forest edges in north Mississippi and longleaf pine savannas in south Mississippi). The two ecosystems differed in the frequency of lightning (higher in south Mississippi) and the timing of peak drought conditions during the lightning season (earlier in south Mississippi). Flowering was induced by prescribed fires during the lightning season in both regions. Flowering was greater in unburned controls in north Mississippi than in south Mississippi. These differences persisted in a common grass-dominated environment in the greenhouse, suggesting a genetically-based bet-hedging strategy with respect to fire-induced flowering in north Mississippi. Flowering of both varieties responded better to clipping during peak drought periods during the lightning season than to clipping treatments at other times of the year, but the causes of such seasonal differences (be they genetic or environmental) remain unresolved at this time and require further investigation., INTRODUCTION Despite widespread recognition of the occurrence of fire-dependent ecosystems throughout North America, ecologically optimal fire regimes (i.e., those to which fire-dependent species are best adapted) are poorly understood at [...]

Abstract: In forests characterized by a dense woody and herbaceous understory layer, seedling recruitment is often directly suppressed via interspecific competition. Alternatively, these dense layers may indirectly lower tree recruitment [...]

Abstract: The understory layer encompasses the majority of plant species diversity in forested ecosystems and may be sensitive to timber harvest disturbance. We hypothesize that (i) uneven-aged, low-intensity silvicultural systems [...]

Relative growth rate (RGR) is currently the most commonly used method for measuring and comparing species' intrinsic growth potential. Comparative studies have, for example, revealed that small-seeded species have higher RGR, leading to the common belief that small-seeded species possess physiological adaptations for rapid growth that would allow them to outgrow large-seeded species, given sufficient time. We show that, because RGR declines as individual plants grow, it is heavily biased by initial size and does not measure the size-corrected growth potential that determines the outcome of competition in the long term. We develop a daily growth model that includes a simple mechanistic representation of aboveground and belowground growth and its dependency on plant size and environmental factors. Intrinsic growth potential is encapsulated by the size-independent growth coefficient, G. We parameterized the model using repeated-harvest data from 1724 plants of nine species growing in contrasting nutrient and temperature regimes. Using information-theoretic criteria, we found evidence for interspecific differences in only three of nine model parameters: G, aboveground allocation, and frost damage. With other parameters shared between species, the model accurately reproduced above- and belowground biomass trajectories for all nine species in each set of environmental conditions. In contrast to conventional wisdom, the relationship between G and seed size was positive, despite a strong negative correlation between seed size and average RGR, meaning that large-seeded rather than small-seeded species have higher size-corrected growth potential. Further, we found a significant positive correlation between G and frost damage that, according to simulations, causes rank reversals in final biomass under daily temperature changes of [+ or -] 5[degrees]C. We recommend the wider use of this new kind of plant growth analysis as a better way of understanding underlying differences in species' physiology: but we recognize that RGR is still a useful metric if considering the potential rate of population increase in empty habitats. Key words: coexistence; community ecology; ecophysiology; European sand-dune annual species; exponential vs. linear growth; likelihood; neutral theory; relative growth rate (RGR); storage effect; trade

Little is known about how exotics influence the ecophysiology of co-occurring native plants or how invader impact on plant physiology may be mediated by community diversity or resource levels. We measured the effect of the widespread invasive forb spotted knapweed (Centaurea maculosa) on leaf traits (leaf dry matter content, specific leaf area, leaf nitrogen percentage, leaf C:N ratios, and [[delta].sup.3]C as a proxy for water use efficiency) of two co-occurring native perennial grassland species, Monarda fistulosa (bee balm) and Koeleria macrantha (Junegrass). The impact of spotted knapweed was assessed across plots that varied in functional diversity and that either experienced ambient rainfall or received supplemental water. Impact was determined by comparing leaf traits between identical knapweed-invaded and noninvaded assemblages. Virtually all M. fistulosa leaf traits were affected by spotted knapweed. Knapweed impact, however, did not scale with its abundance; the impact of knapweed on M. fistulosa was similar across heavily invaded low-diversity assemblages and lightly invaded high-diversity assemblages. In uninvaded assemblages, M. fistulosa [[delta].sup.13]C, leaf nitrogen, and C:N ratios were unaffected by native functional group richness, whereas leaf dry matter content significantly increased and specific leaf area significantly decreased across the diversity gradient. The effects of spotted knapweed on K. macrantha were weak; instead native functional group richness strongly affected K. macrantha leaf C:N ratio, [[delta].sup.13]C, and specific leaf area, but not leaf dry matter content. Leaf traits for both species changed in response to spotted knapweed or functional richness, and in a manner that may promote slower biomass accumulation and efficient conservation of resources. Taken together, our results show that an invader can alter native plant physiology, but that these effects are not a simple function of how many invaders exist in the community. Key words: Centaurea maculosa; functional richness; invader impact; Koeleria macrantha; leaf traits; Monarda fistulosa; plant physiology; spotted knapweed; water use efficiency.

Current and expected changes in biodiversity have motivated major experiments, which reported a positive relationship between plant species diversity and primary production. As a first step in addressing this relationship, these manipulative experiments controlled as many potential confounding covariables as possible and assembled artificial ecosystems for the purpose of the experiments. As a new step in this endeavor, we asked how plant species richness relates to productivity in a natural ecosystem. Here, we report on an experiment conducted in a natural ecosystem in the Patagonian steppe, in which we assessed the biodiversity effect on primary production. Using a plant species diversity gradient generated by removing species while maintaining constant biomass, we found that aboveground net primary production increased with the number of plant species. We also found that the biodiversity effect was larger in natural than in artificial ecosystems. This result supports previous findings and also suggests that the effect of biodiversity in natural ecosystems may be much larger than currently thought. biodiversity | carbon cycle | ecosystem functioning | Patagonian steppe resource partitioning

The effectiveness of early generation selection for grain yield in a cowpea [Vigna unguiculata (L.) Walp.] population was examined in the Guinea and Sudan savanna agroecologies of Ghana where genotype x location interaction is known to be large. A set of 131 [F.sub.3:4] lines were developed from a cross between a local cultivar and an unadapted source of large grain size. Mild selection was practiced during line development at one location in the Guinea savanna zone to eliminate poorly adapted lines. Unreplicated F3 plant data were collected on all the lines at the one location during the development of the lines. Multilocation trials were conducted with lines formed by bulk harvest of [F.sub.4] families to assess how effectively the early generation selection protocol was able to generate superior lines for the target agroecology. Genotypic correlation for grain yield between locations was high only between the two locations in the Guinea savanna zone. Narrow-sense heritability estimates were low and not different from zero for grain yield, but heritability estimates for days to flowering and seed size were large. [F.sub.4] lines derived from the highest 10% performing [F.sub.3] individuals were no higher yielding than [F.sub.4] lines derived from the remaining [F.sub.3] individuals, indicating that early generation selection for yield was ineffective. Single-seed descent (SSD) or bulk breeding methods will be more efficient than pedigree breeding for developing cowpea varieties with high yield potential for this agroecology.

Abstract: This paper discusses local understanding of plants and habitats, based on the linguistic evidence [terms for plants and (or) habitats] gathered from ethnobotanical and ethnoecological field work conducted with [...]