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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 [...]

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 [...]

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, [...]

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 [...]

Disturbance often promotes plant invasion. Small disturbances to the forest floor expose bare soil to light which may promote seed germination and establishment. We tested the hypothesis that small disturbances to the litter layer allow invasive species to become established in forest interiors. We found that seedlings of the invasive shrub Lonicera maackii were found in sites with significantly lower leaf litter mass than regularly spaced points along a transect. We then investigated establishment and survival of L. maackii and the invasive biennial Alliaria petiolata in plots randomly assigned to three treatments: litter removed, litter added and control. Significantly more L. maackii seedlings established in the litter removed and control plots than the litter added treatments, but there was no effect on survival. Significantly more A. petiolata seedlings established in the litter removed plots than in the control or litter added treatments. Survival of established A. petiolata seedlings was significantly greater in control than in litter removed plots, but the final number of A. petiolata seedlings was greatest in the litter removed treatment. Our results confirm that bare patches of soil in the forest interior are colonization sites for invasive plant species., INTRODUCTION Habitat disturbance is often invoked as a causal reason for the invasion of an exotic plant species (Hobbs and Huenneke, 1992). Generally the focus is on large disturbances that [...]

Until recently, one-way relationships between flow dynamics, geomorphology and plant ecology were considered dominantly when studying the functioning of fiver systems, whereby fluvial landforms and hydrogeomorphic processes drive the evolution of riparian plant communities. However, biological communities may significantly control geomorphic processes and have strong impacts on landform dynamics. In order to fully identify the processes linked to river dynamics (changes in time and space of fluvial landforms and associated plant communities), conceptual multidisciplinary progress is clearly needed. To understand the mutual interactions and feedbacks between fluvial landforms and vegetation community dynamics, this paper presents a detailed literature review of fluvial geomorphology, riparian plant ecology and hydraulic engineering knowledge. The historical and recent development of ecological plant succession theory toward the integration of hydrogeomorphic disturbances is discussed as well as the integration of vegetation within geomorphology as a significant landform control factor, incorporating both hydrogeomorphic controls on riparian vegetation dynamics and mechanical impacts of vegetation structures on flow properties and sediment dynamics. Recent progress in ecology, hydraulic engineering and fluvial geomorphology emphasises interdependence between biological and physical forms and processes. Based on this literature review, a 'fluvial biogeomorphic succession' concept is proposed to link fluvial landform and riparian vegetation community evolution within a bi-directional model. The succession of fluvial landforms and associated vegetation communities is composed of four main critical phases that represent a shift in the relative dominance of hydrogeomorphic and ecological processes as a response to biostabilisation and passive bioconstruction processes. The positive feedbacks associated with this shift lead to the development of characteristic biogeomorphic structures such as vegetated banks, islands or floodplains, which are moderated by the biogeomorphic functional roles of 'ecosystem engineers' that induce or reinforce the positive feedbacks. This fluvial biogeomorphic succession concept relates the natural Darwinian selection and ecological succession theories to fluvial geomorphology. Keywords: vegetation dynamics; fluvial landforms; biogeomorphic succession; ecosystem engineers; niche construction; abiotic-biotic feedbacks; critical thresholds

The regional expression of millennial-scale climate variability during the last glacial is examined with particular reference to the vegetation response in Greece. Inspection of three pollen records from contrasting bioclimatic areas suggests that differences in the magnitude of cold events as recognized in the North Atlantic and western Mediterranean are expressed in terms of tree population changes only in areas with a range of favorable habitats. By contrast, records from sites where populations approach their tolerance threshold do not appear to resolve differences in the amplitude of the climate oscillations. Understanding the importance of local factors in modulating the biological response to climate change is critical when attempting to establish the spatial pattern of millennial variability. Keywords: paleoclimatology, paleoecology, last glacial, North Atlantic, Greece.

ABSTRACT. On the North Slope of Alaska, attempts have been made to revegetate areas damaged by development. Some revegetation projects strive to achieve specific performance standards based on percent vegetation [...]

I studied several factors that affected rates of seedling establishment for northern blazing star (Liatris scariosa var. novae-angliae) at Kennebunk, Maine. Fire stimulated blazing star fecundity in four ways: (1) There was a four-fold increase in the number of flowering plants in recently burned units (10.6%) compared to plants in units that had not been burned for 4 y (2.4%). (2) The number of seeds per flower head was greater in recently burned units. (3) Among flower heads that had been infested with predacious moth larvae, the percentage of depredated seeds (40-50%) was lower in recently burned units than in units that had not been burned for two or more years (78-93%). (4) Under natural conditions, seedling establishment was much greater in management units that had been burned 20 mo previously than in management units that had been burned either within the past 8 mo, or units that had not been burned for more than 4 y. These results suggest that northern blazing star benefits from fire and that these four factors are temporally linked. Fire reduced levels of seed predation and increased seed production, providing a large supply of viable seeds. Fire also reduced litter, thus providing a suitable substrate for seedling establishment and development.

The invasive shrub Lonicera maackii (Rupr.) Herder (Amur honeysuckle) dominates the understory of many deciduous forests in southwestern Ohio and other areas. Extensive sampling of an isolated population of L. maackii was used to elucidate its colonization of a forest woodlot and subsequent growth anti development. The current population age structure indicated that colonization likely occurred by a series of small dispersal events. The population remained small for about ten years and then increased dramatically, presumably due to the seed reproduction of the early colonizers Young prereproductive shrubs are characterized by rapid height growth and high stem recruitment. After shrubs become reproductive at age 5-8, height growth continues but basal stem recruitment ix reduced and radial growth increases shrub basal area. Allocation of primary production apparently shifts from stem recruitment and height growth in young shrubs to a balance of height growth, radial expansion and reproduction in older shrubs., INTRODUCTION Invasive species have been studied in forests because of their potential to displace native flora and modify community structure and function (Huenneke and Vitousek, 1990; Nuzzo, 1993; Woods, 1993, [...]

The biosphere's great carbonate deposits, from caliche soils to deep-sea carbonate oozes, precipitate largely as by-products of autotrophic nutrient acquisition physiologies. Protons constitute the critical link: Calcification generates protons, which plants and photosynthetic symbioses use to assimilate bicarbonate and nutrients. A calcium ATPase-based 'trans' mechanism underlies most biological calcification. This permits high calcium carbonate supersaturations and rapid carbonate precipitation. The competitive advantages of calcification become especially apparent in light and nutrient-deficient alkaline environments. Calcareous plants often dominate the lower euphotic zone in both the benthos and the plankton. Geographically and seasonally, massive calcification concentrates in nutrient-deficient environments including alkaline soils, coral reefs, cyanobacterial mats and coccolithophorid blooms. Structural and defensive uses for calcareous skeletons are sometimes overrated. Keywords: calcium; carbonate; bicarbonate; proton; acid; calcareous; nutrient; reef

The purpose of this study was to determine the most important nonanthropogenic factors affecting understory (herbs, shrubs and low-growing vines) diversity in forested landscapes of southern Indiana. Fourteen environmental variables were measured for 46 sites. Multiple regression analysis showed significant positive correlation between understory diversity and tree seedling diversity and soil subgroup. Slope aspect, soil rooting depth and number of standing dead trees were significantly negatively correlated with understory diversity. Mesic sites were more diverse in common understory species than xeric sites but had lower total cover and different species., INTRODUCTION The understory is typically the most diverse stratum within North American Eastern Deciduous Forests. High understory diversity has been attributed to intrastand heterogeneity due to differences in nutrient, light [...]

Observations of Juncus and Iva, two salt-marsh plants, to assess the relation between their distribution patterns and the structure and organization of surrounding plants reveal that positive plant interactions help the plants to adjust to harsh physical conditions. Juncus and Iva share a symbiotic relationship, with Juncus decreasing the salinity of the soil and helping Iva survive. Plant interaction on marsh edges changes from positive to negative as elevation increases and physical conditions become conducive to growth.

Spatial distribution is an important factor determining the intensity and outcome of plant competition. The commonly used measure of angular distributions of plants around a target plant (1 - r) is shown to be limited to unimodal distributions. We present a new index which is based on the variance of the differences between the azimuth of neighboring plants. The new index is an improvement as it characterizes the angular dispersion in both unimodal and multimodal distributions.

Plant field experiments published between 1979 and 1988 in seven journals were studied to address questions about the patterns of interspecific competition over time and space, their effects on community structure, and competitive ability among species. Competition seemed to have strong effects on community structure as shown in its significant effects on distribution patterns, relative abundances and diversity. It was also seen that interspecific competition was usually stronger than intraspecific competition with respect to competitive effect and response.

The steady state solution of the Daisyworld model of Watson and Lovelock (1983) is examined in detail. Focus is on the two-daisy state, which exhibits homeostasis over a large range of solar luminosities. The analytical approach used makes clear the dependence of the steady state and the size of the domain over which it exists on the various parameters of the system as well as the mechanism for its attractivity. It is shown that the self-regulatory effect of the biota is based on a priori specifying a relation between the equilibrium effective temperature [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and the equilibrium effective albedo [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. This relation originates first, from the assumption that the local temperature contrast between the black and white daisies is given by the local albedo contrast, and second, from the requirement that the equilibrium expansion rates of the black and white daisies are equal. The regulation is found to work best when the local albedo contrast is large and when the system is capable of redistributing heat in an efficient manner. It is shown that the attractivity of the steady state is due to the temperature-dependence of the expansion rate of the daisies, i.e., the close-coupling between climate and the biota. Some aspects of the Daisymodel seem fairly realistic, such as the conditions for optimal temperature regulation. On the other hand, the basic assumptions of the model give rise to local temperatures (of the regions of black daisies, white daisies and uncovered ground) which are independent of the incoming radiation. This property of fixed local temperatures and the associated heat transport mechanism itself do not seem to have parallels in the real Earth system.

Canopy gaps in a second growth forest in East Tennessee were studied to document succession, sapling species partitioning in individual gaps and possible sapling adaptations for gap colonization. Ten gaps (64 to 309 [m.sup.2], mean = 186 [m.sup.2]) and four closed canopy plots (200 [m.sup.2] each) were surveyed. All trees were identified and located, extension growth of the leader stem of saplings (n = 933) was measured and diameter at breast height (dbh) of trees > 3 m tall (n = 504) was measured. Sapling composition in gaps was dominated by Fagus grandifolia Ehrh., Acer rubrum L. and A. saccharum Marsh., indicating that several species in the current canopy, dominated by Quercus spp, Pinus spp, Liriodendron tulipifera L. and F. grandifolia Ehrh., will eventually be replaced. There was little evidence of within gap partitioning either between the north and south portions of gaps or between their centers and edges, perhaps due to a history of instability in disturbance regimes. All three dominant sapling species showed significantly greater extension growth in gaps than in closed forest. Acer rubrum grew significantly less in gaps than A. saccharum. Under closed canopy this result was reversed, suggesting that while A. saccharum may be better adapted to using gaps, A. rubrum may grow better beneath the canopy., INTRODUCTION Ecological studies of tree by tree replacement in light gaps within primary old growth forests of Eastern North America are now fairly common (Barden, 1981; Romme and Martin, 1982; [...]

How vegetation develops from a source of potential species remains poorly understood. I explored whether colonizing species assemble randomly, or if local deterministic factors alter species establishment to create consistent vegetation patterns. Early primary successional vegetation in 111 small self-contained depressions (potholes) on Mount St. Helens was sampled. Mean richness was 8.8 species and mean cover was 2.6%. Mean percent similarity (PS) between potholes was 46%. A nearby grid of 100 contiguous 100 [m.sup.2] quadrats on a level barren plain was sampled for comparison. Barren quadrats had mean richness of 12.2 species, mean cover of 1.4% and mean PS of 63%. Pothole vegetation was much more variable than that of the barrens. Canonical correspondence analysis revealed a slight relationship between environmental factors and pothole vegetation. Species composition, cover and species rank orders were predicted extremely well by a stochastic model based on observed frequencies and random accumulation of species. These findings suggest that early colonization of isolated sites is stochastic, and that dispersal affects species composition more strongly than environmental factors or competitive interactions. Which species succeed at any particular site is poorly predictable, but once established, a local population can persist. As a result, there is often a poor correlation between species composition and environmental factors in mature vegetation., INTRODUCTION Community structure in mature vegetation is often assumed to result from deterministic links between plants and their environment. Many ecologists have recognized the importance of both historical and stochastic [...]