bluuebunny/crossref_metadata_2025_split huggingface dataset:
Similarity between seed bank and vegetation in a semi‐arid annual plant community: The role of productivity and grazing
Authors: Osem Yagil , Perevolotsky Avi , Kigel Jaime 
Published: February 2009

AbstractQuestion:Large variation in the similarity between seed bank and standing vegetation generally occurs along environmental gradients. We asked: 1. How is seed bank‐vegetation similarity in Mediterranean semi‐arid annual plant communities related to variation in primary productivity; 2. How is this productivity‐similarity relationship affected by exclusion from grazing.Location:Mediterranean, semi‐arid rangeland in the Northern Negev desert, Israel.Methods:Density of seeds and plants, and species composition of the seed bank and vegetation were compared in grazed and ungrazed subplots, in four neighbouring topographic sites differing in productivity. Seed bank samples were collected in autumn, just before the rainy season, and vegetation samples in the following spring, at peak above‐ground biomass, when net primary productivity was assessed.Results:Quantitative and qualitative similarities between seed bank and the vegetation (Sørensen index values) varied between 0.14–0.61 and 0.40–0.68. Quantitative similarity and productivity were positively and linearly related within the low productivity range (up to 160 g.m‐2), in both grazed and ungrazed subplots. In contrast, at higher productivity levels (up to 500 g.m‐2), similarity decreased slightly with productivity in the ungrazed subplots, but no trend occurred in the grazed subplots. At low productivity, grazing did not affect similarity, while at higher productivity grazing prevented the reduction in similarity with increasing productivity.Conclusion:seed bank—vegetation similarity, with and without grazing, is positively related to productivity up to a threshold range, above which soil resource availability is no longer the factor limiting plant density. Above this range grazing prevents a reduction in similarity with increasing productivity, by diminishing vegetation cover and litter accumulation that constrain germination, seedling emergence and plant survival.
Successional replacement mediated by frequency and severity of wind and snow disturbances in a Picea‐Abies forest
Authors: Nishimura Takashi B. 
Published: February 2009

AbstractQuestion:How do wind and snow disturbances affect the successional replacement of Picea glehnii by Abies sachalinensis in a sub‐alpine coniferous forest?Location:Cool temperate, northern Japan.Methods:Tree demography (growth, mortality and recruitment rates) was determined by repeated measurements of stem diameter and height, and multiple censuses in four Picea‐Abies stands undergoing succession. Above‐ground stand bio‐mass, residence time and tree growth trajectories of the component species were estimated to examine successional changes in structure and dynamics. Individual based simulations were used to examine the effects of disturbances that slowed down succession. Multiple regression analyses were used to determine the relative importance of disturbance frequency and intensity on species composition during succession.Results:Above‐ground biomass was larger in P. glehnii than in A. sachalinensis stands, whereas residence time, a proxy of productivity, was much shorter for A. sachalinensis than for P. glehnii populations. During successional replacement, both species increased in initial growth rate and decreased in size‐dependency of growth in canopy gaps. These plastic growth responses were more prominent in P. glehnii than in A. sachalinensis. Disturbance frequency was the most important predictor of species composition in the simulations, and windstorms were more important than snowfall in terms of disturbance intensity.Conclusions:The frequency of natural disturbances does not have the potential to initiate stand dynamics but it does, however, slow down succession. When disturbance is locally frequent because of the direction and pitch of the topography, early‐successional P. glehnii stands may persist for thousands of years.
Determinants and spatial modeling of tree β‐diversity in a tropical forest landscape in Panama
Authors: Chust Guillem , Chave Jérôme , Condit Richard , Aguilar Salomon , Lao Suzanne , Pérez Rolando 
Published: February 2009

AbstractQuestions:The objectives of this study were to clarify the extent to which environmental factors and geographical distance account for tropical floristic composition, and propose a methodology for delimiting the boundaries of floristic types based on species similarity.Location:The Panama Canal watershed.Methods:To assess which factors (climate, topography, geology and geographical distance) account for floristic composition, we performed Mantel tests on distance matrices and partitioned variation in species composition using canonical analysis. We used a permutation‐based regression model computed on distance matrices and a hierarchical clustering of the tree composition to construct a predictive map of forest types of the Panama Canal Watershed.Results:We found that spatial variation alone explained 22–27% of species variation, while the fraction of species variation explained by environmental variables was smaller (10–12%); 13–19% of the variation was accounted for by the joint effect of environmental variation and geographic distance. The similarity‐based map emphasizes the principal division in tree flora between the drier Pacific side and the wetter Caribbean slopes.Conclusions:The distribution of Panamanian tree species appears to be primarily determined by dispersal limitation, then by environmental heterogeneity. ‘Environmental segregation’processes do play an important role. Maps of broad‐scale vegetation patterns based on thorough tree inventories can be used in conservation planning in the tropics.
Species responses to experimentally induced habitat changes in a Corynephorus grassland
Authors: Hasse Thilo , Daniëls Fred J.A. 
Published: February 2009

AbstractQuestion:To which extent do external ecological factors effect Corynephorus grassland vegetation?Location:Central Netherlands.Methods:We implemented different treatments (sand deposition, litter deposition, nitrogen input, mechanical disturbance, control) in permanent plots representing different successional phases in Corynephorus grassland. Plots were recorded just before the treatments and during the subsequent two years. Vegetation changes were analysed by Redundancy Analysis for repeated measurements and Correspondence Analysis, changes in single species abundances by ANOVA.Results:Species composition hardly changed during the observation period. Several single species abundances showed significant responses to different treatments, most often decrements as direct effects of cover, removal, or dieback. However, Corynephorus canescens and Polytrichum piliferum benefited from sand deposition, the exotic moss Campylopus introflexus from litter deposition. In the colonization phase Polytrichum, Campylopus and Cladonia diversa increased irrespective treatment. Therophytes such as Spergula morisonii showed the strongest negative response to drought, grasses (e.g. Corynephorus canescens) and bryophytes (e.g. Polytrichumpiliferum) were less susceptible. Most lichens did not respond at all.Conclusions:The experiment confirms the high stability of Corynephorus grassland vegetation. Most vegetation changes are in accordance with the hypothetical series of successional phases. In contrast, changes in abundance of single species express considerable dynamics within the vegetation. Species responses also depend on extreme weather conditions as well as on the successional phase of the grassland vegetation and therefore on the competition situation.
Estimating epiphytic macrolichen biomass from topography, stand structure and lichen community data
Authors: Berryman Shanti , McCune Bruce 
Published: February 2009

AbstractQuestion/Location:We modelled lichen epiphyte biomass in relation to topography, stand structure, and lichen community composition in the central Cascades of western Oregon.Methods:Sampling was stratified by stand structure. Epiphyte biomass was estimated based on lichen litter for three functional groups: cyanolichens, forage lichens, and matrix lichens. Regression models for estimating lichen biomass (log10kg.ha‐1) were developed based on three pools of predictors, each pool demanding different levels of effort to obtain the data. First, we created models from topographic predictors that are easily extracted from GIS data. We then developed models based on both topographic and stand‐structure variables. Finally, we developed models using topography, stand structure, and lichen community data.Results/Conclusions:Lichen biomass changed with elevation, cyanolichen biomass highest at low elevations (470–950 m) and forage lichen biomass highest at higher elevations (950–1470 m). Lichen biomass was lowest in even‐aged young stands and highest in mature stands with remnant trees and in old‐growth. Stands with remnant trees had more lichen biomass than even‐aged stands.Models with the greatest explanatory power were: cyanolichen biomass predicted as a function of elevation, stand age index, the sum of Lobaria oregana and L. pulmonaria abundance, and cyanolichen species richness (R2= 0.85); forage lichen biomass predicted as a function of stand age index and, Alectoria sarmentosa abundance (R2= 0.55); and matrix lichen biomass predicted as a function of stand age index and matrix lichen abundance (R2= 0.58). These models are useful tools for understanding and predicting the distribution of epiphytic macrolichen biomass at a landscape scale.
Forest lichen communities and environment—How consistent are relationships across scales?
Authors: Will‐Wolf Susan , Geiser Linda H. , Neitlich Peter , Reis Anne H. 
Published: February 2009

AbstractQuestion:How consistent are relationships of forest lichen community composition with environmental variables across geographic scales within region and across regions?Location:Northwestern continental USA and east central continental USA.Method:Four macrolichen data sets were compiled using identical plot sample protocol: species abundance estimated in 0.4‐ha permanent plots on a systematic grid, as part of government (USDA‐FS) forest inventory programs. One data set in each region represented a large area; the other represented part of the large area. We used global NMS ordination of plots based on species abundance to extract major axes of variation in community composition. Correlations of species, guilds, and environmental variables with ordination axes were compared between geographic scales for the two regions.Results:Primary axes of community variation at larger scales were correlated with climate variables and related geographic variables such as latitude and elevation, and with pollution. Forest vegetation variables such as stand age and tree species composition became more important at small scales. Community variation unexplained by macro‐environment variables also became more important at small scales. Of several hundred species tested, ten lichen species showed consistent behaviour between scales within region (one also across regions) and are thus potential general indicators of ecological conditions in forests. Of six lichen guilds tested, several show strong patterns not consistently related to environmental conditionsConclusions:Interpretation of lichen species and community composition as indicating particular environmental conditions is context‐dependent in most cases. Observed relationships should not be generalized beyond the geographic and ecological scale of observation.
Plant characteristics are poor predictors of microsite colonization during the first two years of primary succession
Authors: Walker Lawrence R. , Bellingham Peter J. , Peltzer Duane A. 
Published: February 2009

Abstract:Questions:Do plant characteristics predict microsite colonization in severe habitats dominated by abiotic factors? Specifically, does colonization of microsites differ among shrubs, forbs and grasses or between wind‐ and water‐dispersed plants, non‐native and native plants, or N‐fixing and non‐N‐fixing plants?Location:Kowhai River floodplain, Kaikoura, South Island, New Zealand.Methods:Five microsite characteristics were measured for > 1000 individuals representing 27 colonizing plant species on a two‐year old surface of a primary succession on a New Zealand floodplain. The microsite characteristics included surface contour (convex, concave, or flat), the position of the plant (e.g., upstream, downstream) relative to the closest rock with > 20 cm maximum dimension, the distance to that same rock, the depth of the base of the stem below the surface of a plane resting on the adjacent microrelief, and soil particle size (gravel, pebbles or sand).Results:All plants preferred concave microsites near large rocks relative to systematically placed null points. We found no clear preferences for microhabitats by dispersal mode, native vs. non‐native status, or plants with or without nitrogen‐fixing symbionts, but grasses preferentially colonized fine soil particles. Highly variable responses among species contributed to these results. Better predictability of microsite preference was obtained for individual species than forplants grouped by characteristics.ConclusionsOur results suggest that in severe habitats with strong abiotic filters and low microsite availability, such as found in early primary succession, coarse categories of species characteristics are poor predictors of colonization success.
Wildfire effects on ß‐diversity and species turnover in a forested landscape
Authors: Reilly Matthew J. , Wimberly Michael C. , Newell Claire L. 
Published: February 2009

AbstractQuestions: What are the effects of fire on the relationships between community composition and environment? Does fire affect ß‐diversity and rates of species turnover along spatial and environmental gradients? Do these effects differ among functional groups?Location: Linville Gorge, in the southern Appalachians of western North Carolina, USA.Methods: We sampled all vascular plants in 20 plots (200 to 400 m2) before and after a wildfire. We used Non‐metric Multidimensional Scaling to compare pre‐ and post‐fire relationships between community composition and elevation, fire history, and topographic moisture. We compared Whittaker's ßw and quantified rates of species turnover along geographic and environmental gradients for all plants, trees, shrubs, and herbs. Randomization tests were used to determine whether rates of species turnover changed after the fire.Results: Correlations between community composition and environmental variables generally increased after fire. The largest increase was for elevation, reflecting its potential to influence fire severity. ßw decreased only slightly and the only statistically significant change in species turnover rates occurred for herbs over geographic distance.Conclusions: Large changes in community composition occurred after fire due to immigration of herbaceous species. Community‐environment correlations increased but ß‐diversity did not change because fire effects and immigration were influenced by the same environmental gradients that structured vegetation pre‐fire. Results differed for herbaceous species that responded to environmental but not spatial gradients post‐fire. Dispersal limitation and community resilience through resprouting or regeneration from serotinous cones in dominant woody vegetation maintain ß‐diversity and species turnover after fire.
Importance and intensity of competition along a fertility gradient and across species
Authors: Gaucherand Stéphanie , Liancourt Pierre , Lavorel Sandra 
Published: February 2009

AbstractQuestions: 1. Can the importance and the intensity of competition vary independently along a nutrient gradient? 2. Are these variations species dependent?Location: Sub‐alpine pastures of the northern French Alps.Methods: Competition intensity measures how much competition decreases the performances of an organism. Competition importance measures how much competition contributes to affect performance, among other processes (such as environmental stress or disturbance). Competition intensity and importance were measured on three co‐occurring species: Festuca rubra, a perennial grass, and two forbs of contrasting basal area, Chaerophyllum hirsutum and Alchemilla xantho‐chlora. A neighbour removal experiment was performed on Festuca rubra in three sub‐alpine grassland communities differing in fertility and on Chaerophyllum hirsutum and Alchemilla xanthochlora in the two more fertile of these communities. The importance of competition was quantified using an index proposed by Brooker et al. (2005).Results: Competition intensity and importance showed different patterns of variation along the fertility gradient for Festuca rubra: competition importance decreased with decreasing fertility whereas competition intensity did not change. The largest forb was the least affected by competition. Our results suggest that the importance of competition for all three species depended on their individual tolerance to low nutrient availability.Conclusions: 1. The distinction between the importance and the intensity of competition is helpful to explain conflicting results obtained on the variations of competition indices along productivity gradients. 2. The choice of a phytometer can affect the conclusions drawn from empirical studies.
Structural segregation and scales of spatial dependency in Abies amabilis forests
Authors: Larson J. Andrew , Franklin F. Jerry 
Published: February 2009

AbstractQuestion: Is a mosaic structure apparent in the spatial distribution of trees in old‐growth Abies amabilis forests?Location: Montane forests of the western Cascade Range, Washington, USA.Methods: Maps of tree locations were created for study areas located in two, 300‐year old stands and a single 600‐year old stand. Stand structure parameters were calculated using several subsample quadrats sizes (56.25 ‐ 306.25 m2), which were drawn randomly with replacement at a density of 250 quadrats per ha from the stem maps in the computing environment. Spatial cross‐covariance functions between different canopy strata were estimated using the spline cross‐correlogram.Results: Negative spatial correlation (segregation) between subcanopy tree density and areas of high overstorey occupancy was detected. Understorey and midstorey tree densities were positively spatially correlated. These general trends were apparent across the range of observational scales investigated. Significant spatial correlation between canopy strata was observed at spatial scales of 12 ‐ 44 m and extended to the largest scales in the 600‐year old stand.Conclusion: The observed spatial segregation between canopy strata supports the hypothesis that old A. amabilis forests form fine‐scale structural mosaics. Structural segregation at small scales may be due to competitive interactions as well as exogenous forcing of tree locations (e.g. by mortality due to pathogens or disturbance), however segregation at large scales in the 600‐year old stand is likely due to exogenous factors alone. This study reinforces the idea that horizontal heterogeneity is an emergent property of old‐growth forests.
The distribution and habitat associations of non‐native plant species in urban riparian habitats
Authors: Maskell L.C. , Bullock J.M. , Smart S.M. , Thompson K. , Hulme P.E. 
Published: February 2009

AbstractQuestions: 1. What are the distribution and habitat associations of non‐native (neophyte) species in riparian zones? 2. Are there significant differences, in terms of plant species diversity, composition, habitat condition and species attributes, between plant communities where non‐natives are present or abundant and those where non‐natives are absent or infrequent? 3. Are the observed differences generic to non‐natives or do individual non‐native species differ in their vegetation associations?Location: West Midlands Conurbation (WMC), UK.Methods: 56 sites were located randomly on four rivers across the WMC. Ten 2 m × 2 m quadrats were placed within 15 m of the river to sample vegetation within the floodplain at each site. All vascular plants were recorded along with site information such as surrounding land use and habitat types.Results: Non‐native species were found in many vegetation types and on all rivers in the WMC. There were higher numbers of non‐natives on more degraded, human‐modified rivers. More non‐native species were found in woodland, scrub and tall herb habitats than in grasslands. We distinguish two types of communities with non‐natives. In communities colonized following disturbance, in comparison to quadrats containing no non‐native species, those with non‐natives had higher species diversity and more forbs, annuals and shortlived monocarpic perennials. Native species in quadrats containing non‐natives were characteristic of conditions of higher fertility and pH, had a larger specific leaf area and were less stress tolerant or competitive. In later successional communities dominated by particular non‐natives, native diversity declined with increasing cover of non‐natives. Associated native species were characteristic of low light conditions.Conclusions: Communities containing non‐natives can be associated with particular types of native species. Extrinsic factors (disturbance, eutrophication) affected both native and non‐native species. In disturbed riparian habitats the key determinant of diversity is dominance by competitive invasive species regardless of their native or non‐native origin.
Vegetation, environment, and time: The origination and termination of ecosystems
Authors: Jackson Stephen T. 
Published: February 2009

AbstractTerrestrial ecosystems originate when particular plant species attain dominance at specific locations under specific environmental regimes. Ecosystems terminate, gradually or abruptly, when the dominant species or functional types are replaced by others, usually owing to environmental change or severe and irreversible disturbance. Assessing whether current ecosystems are sustainable in the face of future environmental change can be aided by examining the range of environmental variation those ecosystems have experienced in the past, and by determining the environmental conditions under which those ecosystems arose. The range of environmental variation depends on the time scale at which it is assessed. A narrow time span (e.g. 200–300 years) may underestimate the range of variation within which an ecosystem is sustainable, and it may also underestimate the risk of major transformation or disruption of that ecosystem by environmental change. Longer time spans (e.g. 1000–2000 years) increase the range of variation, by encompassing a larger sample of natural variability as well as non‐stationary variability in the earth system. Most modern ecosystems disappear when the time span is expanded to 10000–15 000 years owing to secular changes in earth's climate system. Paleo‐ecological records can pinpoint the time of origination of specific ecosystems, and paleo‐environmental records can reveal the specific environmental changes that led to development of those ecosystems and the range of environmental variation under which those ecosystems have maintained themselves in the past. This information can help identify critical environmental thresholds beyond which specific modern ecosystems can no longer be sustained.