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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 review of historical information and scientific literature concerning vegetation of the Black Belt region, in Mississippi and Alabama, is used to generate a hypothetical framework of ecological gradients. Remnants of native grassland are well known, but the original pattern of grassland versus woodland appears to have had a complex relationship with soil and disturbance regime. This paper approaches the problem by first displaying variation among soil series along two generalized catenas: (1) from alluvial lowlands, to chalky slopes, to more acid uplands; (2) from relatively mesic well-drained soils, usually more sloping and often relatively shallow (above parent material), to more poorly drained soils, including xerohydric vertisols that often erode down to seasonally xeric subsoils. Fifteen types of native vegetation are outlined, with brief descriptions based on diverse sources. These types are overlaid on the diagram of soil catenas, showing the most characteristic vegetation that appears to have existed in different sections. The result provides a useful initial model for the gradient from lowland to upland vegetation (1). However, variation of disturbance regime in space and time has probably limited the consistency of associations between vegetation and the drainage-related gradient (2). Deeper woods are concentrated on more mesic sites, and became increasingly restricted when human influence spread over the landscape. Grasslands may have originally occurred on a wide range of chalky, clayey or sandy soils, from hydric to xeric, but became greatly modified after European settlement., INTRODUCTION The Black Belt in Mississippi and Alabama is readily defined in terms of its calcareous geology and chalky soils, together with its largely agricultural modern land uses (USFS 2007). [...]

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. [...]

Southeastern Illinois is dominated by cropland, and the remaining pastures or grasslands are marginally suitable for breeding Loggerhead Shrikes (Lanius ludovicianus), owing, in part, to limited nest sites. From 1998 through 2000, we recorded poor nest success (26%) among shrikes, although results of earlier studies (1967-1972) in this region indicated that nest success was 72 to 80%. Clutch size (5.7 eggs) and fledglings/ successful nest (4.4 young/successful nest) were similar to those reported in previous studies. During our study, generalist mammalian predators were abundant, and most nest failures (88%) were caused by predation. We suggest that the loss of grassland habitat and agricultural intensification has resulted in reduced nest success, and this may be true in other areas of the species' range as well., The Loggerhead Shrike (Lanius ludovicianus) is of conservation interest throughout its range, and has been designated a 'Bird of Conservation Concern' (U.S. Fish and Wildlife Service 2002). The range of [...]

Phosphorus (P) loss from soils can impair surface water quality. A study was conducted to test the efficacy of fly-ash to decrease phosphorus loss in 11 grassland soils. A preliminary toxicity and leaching experiment indicated that heavy metal concentrations (As, Cd, Pb, Se) in leachate and pasture from a soil treated with ash up to 50 mg/kg were not different from the control (unamended soil). Heavy metal concentrations in the ash were generally below limits for maximum concentrations in soil. Following incubation of fly ash at a rate of 20 mg/kg for 3 months with 11 grassland soils packed into boxes, overland flow was generated by simulated rainfall on each boxed soil. Analysis of overland flow indicated that in 2 semi-arid soils, P loss decreased due to decreased particulate P (PP) loss and low organic C concentration (70 g/kg), P loss increased due to increased soil pH from 6 to 7 where P is most soluble. In all soils, despite an increase in P in recalcitrant soil P fractions, increased soil pH stimulated soil C and P mineralisation (decreased organic C by, on average, 4.1 g/kg), decreased soil organic P, and increased inorganic P in labile fractions. It is concluded that the application of fly-ash from this source should not be used as an amendment to decrease P loss in pastures where soil pH is commonly Additional keywords: sediment, overland flow, particulate P, grazing, pasture, cropland., Introduction Phosphorus (P) loss from soils to surface waters is recognised as a key factor in accelerated eutrophication, causing poor water quality. Mitigation of P loss has centered on management [...]

Grassland agriculture is an important industry for livestock production and land management throughout the world. We review the principles of nutrient cycling in grassland agriculture, discuss examples of grassland farming systems research, and demonstrate the usefulness of whole-farm simulation for integrating economic and environmental components. Comprehensive studies conducted at the Karkendamm experimental farm in northern Germany and the De Marke experimental farm in the Netherlands have quantified nutrient flows and developed innovative strategies to reduce nutrient losses in grassland farming systems. This research has focused on improving the utilization of manure nutrients on the farm by including grain crops in cropping systems with grassland and by incorporating manure handling techniques that reduce nitrogen losses. Although the information generated in experimental farms is not always directly applicable to other climates and soils, it is being transferred to other regions through computer simulation. A whole-farm model calibrated and verified with the experimental farm data is being used to evaluate and refine these strategies for commercial farms in other areas. Simulation of farms in northern Europe illustrate that on the sandy soils of this region, maize (Zea mays L.) silage can be used along with grasslands to increase farm profitability while maintaining or reducing nutrient loss to the environment. Use of cover crops, low emission barns, covered manure storages, and direct injection of manure into soil greatly reduces N losses from these farms, but their use creates a net cost to the producer. By integrating experimental farm data with whole-farm simulation, more sustainable grassland production systems can be cost-effectively evaluated, refined, and transferred to commercial production., GRASSLAND AGRICULTURE is defined as 'a farming system that emphasizes the importance of grasses and legumes in livestock and land management. Farmers who plan row crops and livestock around their [...]

Carbon dioxide. C[O.sub.2]. Some think of the gas in positive terms, such as making plants grow or trading carbon credits. Others think that its rising levels in the atmosphere may [...]

Grassland passerines were surveyed during summer 1995 on the Buffalo Ridge Wind Resource Area in southwestern Minnesota to determine the relative influence of wind turbines on overall densities of upland nesting birds in Conservation Reserve Program (CRP) grasslands. Birds were surveyed along 40 m fixed width transects that were placed along wind turbine strings within three CRP fields and in three CRP fields without turbines. Conservation Reserve Program grasslands without turbines and areas located 180 m from turbines supported higher densities (261.0-312.5 males/100 ha) of grassland birds than areas within 80 m of turbines (58.2-128.0 males/100 ha). Human disturbance, turbine noise, and physical movements of turbines during operation may have distrurbed nesting birds. We recommend that wind turbines be placed within cropland habitats that support lower densities of grassland passerines than those found in CRP grasslands., Technological advances that have reduced the cost of electricity generated from windplants have enabled the wind-power industry to expand from California into the eastern United States and Canada (Nelson and [...]

ABSTRACT. Livestock induced sediment loss is one of the potential detrimental impacts from grazing grasslands. Near Coshocton, Ohio, a 26-ha unimproved pasture watershed was grazed year-around, and no fertilizer was [...]

We used the eddy covariance technique to measure exchanges of water vapor, energy, and [CO.sub.2] between California serpentine grassland and the atmosphere. Even though the system was built around an inexpensive, one-dimensional sonic anemometer and a closed-path [CO.sub.2] analyzer, energy balance closure was accurate to ± 20% at a net radiation of 500 W/[m.sup.2], and the spectra and cospectra indicated only modest information loss from incompletely resolved high-frequency turbulence. In the early and middle parts of the growing season, net radiation, latent heat, and sensible heat all had similar diurnal dynamics, with latent heat accounting for [approximately equal] 60% of the net radiation. Late in the growing season, energy dissipation by latent heat dropped dramatically, even though the vapor pressure gradient remained high. The Ω factor, an index of the role of canopy conductance in regulating transpiration (Jarvis and McNaughton 1986), decreased from 0.8 early in the growing season (indicating predominant control of transpiration by net radiation) to 0.1 late in the growing season (indicating a shift to control of transpiration by canopy conductance and vapor pressure deficit). Canopy conductance was a linear function of the product of net photosynthesis and relative humidity, divided by the [CO.sub.2] concentration, as predicted by Ball (1988). The slope of the relationship, however, was greater early in the growing season than at other times. Whole-ecosystem carbon exchange rates were modest, with midday net photosynthesis reaching maximum values of 6-8 µmol [multiplied by] [m.sup.-2] [multiplied by] [s.sup.-1] in early April. Diurnal variation in photosynthesis roughly paralleled variation in photosynthetically active photon flux density (PFD), but with the daily maximum increasing with canopy development early in the growing season and decreasing with drought at the end of the growing season. Photosynthesis did not clearly saturate at high levels of PFD. Ecosystem dark respiration increased strongly ([Q.sub.10] = 4.6) with increasing soil surface temperature. The efficiency with which absorbed radiation was used in ecosystem photosynthesis, integrated over entire days, was 0.0115 ± 0.0015 mol [CO.sub.2]/mol PFD ( [approximately equal] 20% of the values measured for healthy, single leaves under low light conditions) until late in the growing season, when the efficiency fell sharply. Using simple assumptions to extrapolate measurements from 11 d to the entire growing season, we estimate ecosystem annual gross primary production to be 11.1 mol [CO.sub.2]/[m.sup.2], yielding an annual net primary production of [approximately equal] 133 g biomass/[m.sup.2]. This is near the center of the range of published values from above-ground harvest studies., Key words: California serpentine grassland; canopy [CO.sub.2] exchange; canopy energy exchange; eddy covariance; light-use efficiency; omega factor; scaling. INTRODUCTION Relative to the state of the art at the leaf level, [...]

In an experimental test of plant community invasibility, we introduced seeds of a native ruderal, California poppy (Eschscholzia californica), at fixed density into experimental plots in a California winter annual grassland. Each of the 42 plots, which ranged in size from 2 [m.sup.2] to 32 [m.sup.2], had been studied for 4 yr previous to the introduction, with the common observation that a subset of plots of each size consistently held more species than others. It was primarily in these more species-rich plots that establishment and reproduction by the experimental invader occurred. Success of the invader per plot, measured as the total number of plants germinating, producing seeds, or perennating, varied with plot size, but the statistical contribution of plot size was secondary to that of local species number. Contributing variables were the extent of small mammal disturbance (positive) and the degree to which a single resident plant species (in particular, Bromus diandrus) dominated a plot (negative). In contrast to theories of competitive exclusion via niche partitioning, species-rich plots were more invasible. Key words: Bromus diandrus: California annual grassland; disturbance; dominance: Eschscholzia californica; invasibility; plot size; species richness., INTRODUCTION Certain ecological communities seem especially prone to invasion by a new species, and determining why they are more vulnerable has been a long-standing problem in ecology (Robinson and Valentine [...]

The hypothesis that biodiversity influences the productivity (that is, the rate of biomass production) and stability of ecosystems has recently resurfaced (1-3), but it remains contentious (4-6). It is unclear [...]

Before elaborate programs of fire suppression were instituted in North America in the 20th century, wildfires occurred frequently and were critical contributors to the health and maintenance of many different [...]

The beautiful Cienega Valley in southern Arizona is a perfect example of a viable international wildlife corridor. Located within 20 miles (32 kilometers) of the U.S./Mexico border, it boasts a [...]

They used to call it the inland sea--the vast expanse of tallgrass prairie that once covered most of the Midwest. As the constant prairie wind blew across the grass that [...]