bluuebunny/crossref_metadata_2025_split huggingface dataset:
A test of three juvenile plant competitive response strategies
Authors: Carlyle Cameron N. , Fraser Lauchlan H. 
Published: February 2009

AbstractQuestions:1. Are there competitive response strategies for light in juvenile plants? 2. If so, do plant traits (e.g. seed weight, relative growth rate, height and biomass) correlate with the strategies?Location:Controlled greenhouse study using perennial vegetation typical of wet meadows in Northeast Ohio, USA.Methods:We used two light manipulations in a greenhouse to screen ten replicates of 19 plant species for three proposed competitive response strategies (‘escape’, ‘forage’, ‘persist’). We measured the time it took a seedling to die and the maximum height achieved when grown in the dark to assess two strategies, persist and escape. The biomass of seedlings when grown under a controlled, low‐intensity, shifting light source was measured to test a third strategy, forage.Results:We found significant variation across species in the measurements used to assess each strategy. The species ranking for each strategy was not concordant across strategies. Traits were found that correlated with the escape strategy (seed weight, height and biomass) and persist strategy (time to reach maximum height). No traits were found that correlate with the forage strategy.Conclusions:There appear to be trade‐offs by plants in the three strategies tested in this study. Species which had the best performance on one strategy typically scored poorly on the other strategies. However, many species fall in the middle range, ranking similarly across the ‘persist’, ‘escape’, and ‘forage’ strategies.
Tree regeneration responses to Chusquea montana bamboo die‐off in a subalpine Nothofagus forest in the southern Andes
Authors: Holz C. Andrés , Veblen Thomas T. 
Published: February 2009

AbstractQuestion:The aim of the present study is to examine how a rare flowering and massive die‐off event of a dominant understorey bamboo affected tree regeneration processes in a subalpine Nothofagus forest. In particular, we assess the effects of the die‐off event on tree seedling demography (establishment and survival) and on the height growth of previously established juveniles, and we determine how these effects vary in relation to stand age and canopy conditions.Location:Carirriñe Pass and Choshuenco Volcano at 1200 m a.s.l. in a mixed subalpine temperate forest in northern Patagonia (40°S, 71°W), spanning the Chilean and Argentinian border.Methods:Regeneration processes in Nothofagus pumilio and N. dombeyi were examined under different canopy conditions (closed or gap), in both young and old stands, and in patches of flowered and non‐flowered Chusquea bamboo during the first three growing seasons following the simultaneous flowering and die‐off of Chusquea montana f. montana in November‐December 2001. We installed permanent plots under all forest conditions and measured seedling and sapling height growth and new seedling establishment following the bamboo die‐off. To assess potential variation in tree seed sources, seed fall was collected and seed viability was measured. To assess for potential variation in the understorey light conditions and infer its influence on tree regeneration, hemispherical photographs of the canopy were taken at each plot.Results:Bamboo die‐off triggered accelerated growth in height of Nothofagus seedlings and saplings in gaps in old stands. Bamboo die‐off did not result in new tree seedling establishment; however, die‐off did increase the survival of newly established seedlings.Conclusion:The predominant response of Nothofagus spp. to the bamboo die‐off event was the accelerated height growth of previously established juveniles (i.e. a re‐organization response). Successful recruitment into the canopy of these relatively shade‐intolerant tree species appears to be dependent on previously existing canopy gaps. It is likely that the release in height of previously established juveniles of Nothofagus after the bamboo die‐off will eventually result in development of even‐sized and relatively even‐aged, patches of canopy trees.
Patterns of plant invasion along an environmental stress gradient
Authors: MacDougall A.S. , Boucher J. , Turkington R. , Bradfield G.E. 
Published: February 2009

Abstract.Question:Do stressful environments facilitate plant invasion by providing refuges from intense above‐ground competition associated with productive areas, or prevent it by favouring locally adapted native species?Location:An invaded and fragmented oak savanna ecosystem structured along a landscape‐level stress gradient associated with soil depth, elevation, and canopy openness.Methods:Vegetation and environmental data were collected from 184 plots in seven savanna remnants along the gradient. Using multivariate (CCA) and post‐hoc regression analyses, we determined the relationship between environment and the richness and abundance of invasives.Results:46 of 119 species were naturalized exotics. CCA indicated the importance of environmental variation (mostly soil depth) for community structure but not for invasion; invasive species richness was similar in all areas. However, the abundance of invasives and their impacts on native diversity appear to increase significantly in less stressful habitats. Deeper soils had lower evenness and significantly fewer native species. This result was associated with dominance by exotic perennial grasses and large increases in vegetation height, suggesting strong above‐ground competition.Conclusions:Low‐stress environments were not more invasible per se but appear to be more susceptible to invasion by species with strong competitive impacts. The causes of decreasing exotic impact with decreasing soil depth may reflect shifts in competitive intensity or an increased importance of stress tolerance, both of which may favour natives. Alternatively, this ecosystem may simply lack high‐impact invaders capable of dominating shallow soils. Conservation challenges are twofold for this endangered plant community: controlling invasives that currently dominate deeper‐soils and accounting for a diverse pool of invaders that proliferate when the current dominants are removed.
Facilitative succession in a boreal bryophyte community driven by changes in available moisture and light
Authors: Fenton Nicole J. , Bergeron Yves 
Published: February 2009

AbstractQuestion:What are the drivers of bryophyte succession in paludifying boreal Picea mariana forests?Location:The Clay‐Belt of Quebec and Ontario, Canada.Methods:The bryophyte community and habitat variables (forest floor thickness, water table, stand density, canopy openness micro‐climate and presence of ericaceous species) were analysed in a chronosequence of 13 stands from 50 to more than 350 years since fire.Results:Across the chronosequence, feathermosses were replaced by shade and desiccation tolerant slower growing hummock Sphagna and then by faster growing hollow Sphagna. These changes were linked with both increasing light availability and the movement of the water table into the forest floor.Conclusions:As water table rise is dependent on forest floor thickness, which is in turn influenced by the presence of Sphagna, this successional sequence represents an example of facilitation. Furthermore, it emphasizes the importance of water table rise in determining stand level, and landscape level variables such as carbon balance.
Seasonal shifts in competition and facilitation in subalpine plant communities of the central Caucasus
Authors: Kikvidze Zaal , Khetsuriani Liana , Kikodze David , Callaway Ragan M. 
Published: February 2009

AbstractQuestion:Temporal and spatial shifts in competitive and facilitative interactions among plants have important implications for species coexistence and community diversity. Many studies have focused on inter‐seasonal variation in these interactions, but very few have examined short‐term intra‐seasonal shifts between competition and facilitation. In the central Caucasus Mountains the subalpine climate changes considerably over the season, with a relatively benign (humid and cooler) first part followed by a much more stressful (drier and warmer) second part. We ask: do plant interactions shift from competitive to facilitative during the growing season as environmental conditions change from mesic to dry?Location:The central Caucasus Mountains, Georgia.Methods:We experimentally investigated shifts in the balance of positive and negative interactions in plant communities over the course of a single growing season by conducting sequential removal experiments on two co‐dominant species.Results:We found that during the wet and cool first half of the growing season, target plants without neighbours accumulated significantly more biomass than individuals with neighbours, indicating competition. However, in the drier second half of the growing season competitive interactions were shifted to facilitation as individuals without neighbours accumulated significantly less biomass.Conclusions:In general, these results support the view that competitive and facilitative effects exist in dynamic tension in plant communities with facilitation intensifying as abiotic stress increases, also within a growing season.
Biogeographical determinants of lichen species diversity on islets in the West‐Estonian Archipelago
Authors: Jüriado Inga , Suija Ave , Liira Jaan 
Published: February 2009

AbstractQuestions:Do islet area, number of biotopes and distance from the mainland shape lichen species richness on islets? Are there any species‐ or substrate group‐specific trends associated with these factors?Location:Islets of the west Estonian Archipelago, Estonia.Methods:A species list was compiled for each of the 32 islets and the relative abundance of each species was estimated. The lichens were divided into seven groups according to their substrate preferences. Generalized linear model (GLIM) analysis was applied to test the effect of the islet traits on the number of lichen species on the islets and in the substrate groups. The probability of presence/absence and abundance of the most frequent species according to the islet traits were tested with GLIM and general linear mixed model.Results:The lichen flora of the islets consisted of 326 taxa, the number of lichen species per islet varied from 2 to 197. Total number of species per islet and within the substrate groups was positively correlated with islet area and with number of biotopes, and negatively correlated with distance from the mainland; however, these relationships varied among the substrate groups. Although individual lichen species showed variation in responses, general trends in island biogeography were evident.Conclusions:The distribution pattern of lichens on the studied islets follows the theory of island biogeography: the number of species per islet depends on isolation, area and biotope diversity. Species specific traits, such as dispersal strategy and growth form, as well as availability of a particular substrate are important for formation of the lichen flora on islets.
Edge influence on the old‐growth forest indicator lichen Alectoria sarmentosa in natural ecotones
Authors: Esseen Per‐Anders 
Published: February 2009

AbstractQuestion:Is the pendulous epiphytic indicator lichen Alectoria sarmentosa influenced by proximity to forest edge in natural old‐growth forests?Location:Large (28 400 ha), naturally heterogeneous boreal landscape in northern Sweden dominated by old‐growth Picea abies forest in a matrix of open wetland.Methods:The abundance of A. sarmentosa and forest structure were quantified in ten edge‐interior transects (0–100 m) at southern to western forest edges. Four 10 m × 50 m plots were sampled along each transect. Mass of A. sarmentosa in the lower canopy (0–5 m) of P. abies was estimated from maximum thallus length.Results:The maximum length of A. sarmentosa was four times lower, and the lichen mass 16 times lower, at the forest edge compared to the forest interior. Lichen mass showed a monotonic decrease from the interior to the edge. Mean distance of edge influence was 58 m for lichen mass, and extended longer into the forest than changes in stand structural variables. The response of A. sarmentosa to edges is a result of a combination of changes in microclimate and substrate availability.Conclusions:The indicator species A. sarmentosa is strongly affected by proximity to forest edge in natural old‐growth forests. Edge influence is thus important in controlling the abundance of this group of pendulous lichens in natural forest ecosystems. Distance of edge influence was longer in natural wetland‐forest ecotones than previously reported for fragmented forests; this was probably due to higher lichen abundance and lower site productivity in the study area. Understanding lichen response to natural landscape structure may help us to improve conditions for epiphytes in managed forests.
Interaction between a lichen and a fungal parasite in a successional community: Implications for conservation
Authors: Hedenås H. , Lundin K. , Ericson L. 
Published: February 2009

AbstractQuestion:Populus tremula(Aspen) is a post‐fire successional tree with a large number of host‐specific lichens. One,Ramalina sinensis, will colonize very young aspen stands. The apothecia of this species are attacked by a parasitic fungus,Abrothallus suecicus.The incidence and severity of disease caused by this parasite was studied in nine stands between 22 and 180 years old.Location:Central Sweden.Method:Thalli ofR. sinensiswere randomly sampled from nine stands. Each thallus was weighed and the number of diseased and non‐diseased apothecia were scored for each thallus.Results:The data show (1) an increase in both disease incidence and disease severity with increasing stand age; (2) that smaller thalli show an increasing probability of being diseased in older stands; (3) that high disease levels prevail in older aspen stands; and (4) a broad variation in disease severity for thalli of similar size in the four older stands.Conclusions:The studied chronosequence is too short to elucidate whether theAbrothallus‐Ramalinasystem is driven by disease escape in space and time, or co‐existence. However, the high disease levels in older stands suggest that conservation programs aiming to sustain this system cannot only focus on preservation of isolated old‐growth stands, but also need to incorporate continuous creation of young stands. If succession is ignored, conservation of organisms originally adapted to, now vanishing, large‐scale disturbance regimes is likely to fail. We point out the need to assess the role of disease in conservation.
Environment, disturbance history and rain forest composition across the islands of Tonga, Western Polynesia
Authors: Franklin Janet , Wiser Susan K. , Drake Donald R. , Burrows Larry E. , Sykes William R. 
Published: February 2009

AbstractQuestions:How do forest types differ in their distinctiveness among islands in relation to environmental and anthropogenic disturbance gradients? Are biogeographic factors also involved?Location:Tonga, ca. 170 oceanic islands totalling 700 km2spread across 8° of latitude in Western Polynesia.MethodRelative basal area was analysed for 134 species of woody plants in 187 plots. We used clustering, indirect gradient analysis, and indicator species analysis to identify continuous and discontinuous variation in species composition across geographical, environmental and disturbance gradients. Partial DCA related environmental to compositional gradients for each major forest type after accounting for locality. CCA and partial CCA partitioned observed compositional variation into components explained by environment/disturbance, locality and covariation between them.Results:Differences among forest types are related to environment and degree of anthropogenic disturbance. After accounting for inter‐island differences, compositional variation (1) in coastal forest types is related to substrate, steepness and proximity to coast; (2) in early‐successional, lowland rain forest to proximity to the coast, steepness and cultivation disturbance; (3) in late‐successional, lowland forest types to elevation. For coastal/littoral forests, most of the compositional variation (71%) is explained by disturbance and environmental variables that do not covary with island while for both early and late‐successional forests there is a higher degree of compositional variation reflecting covariation between disturbance/environment and island.Conclusions:There are regional similarities, across islands, among littoral/coastal forest types dominated by widespread seawater‐dispersed species. The early‐successional species that dominate secondary forests are distributed broadly across islands and environmental gradients, consistent with the gradient‐in‐time model of succession. Among‐island differences in early‐successional forest may reflect differences in land‐use practices rather than environmental differences or biogeographical history. In late‐successional forests, variation in composition among islands can be partly explained by differences among islands and hypothesized tight links between species and environment. Disentangling the effects of anthropogenic disturbance history versus biogeographic history on late‐successional forest in this region awaits further study.
Trait convergence and trait divergence in herbaceous plant communities: Mechanisms and consequences
Authors: Grime J. Philip 
Published: February 2009

In landscapes subject to intensive agriculture, both soil fertility and vegetation disturbance are capable of impacting strongly, evenly and simultaneously on the herbaceous plant cover and each tends to impose uniformity on the traits of constituent species. In more natural and ancient grasslands greater spatial and temporal variation in both productivity and disturbance occurs and both factors have been implicated in the maintenance of species‐richness in herbaceous communities. However, empirical data suggest that disturbance is the more potent driver of trait differentiation and species co‐existence at a local scale. This may arise from the great diversity in opportunities for establishment, growth or reproduction that arise when the intensity of competition is reduced by damage to the vegetation.In contrast to the diversifying effects of local disturbances, productivity‐related plant traits (growth rate, leaf longevity, leaf chemistry, leaf toughness, decomposition rate) appear to be less variable on a local scale. This difference in the effects of the productivity and disturbance filters arises from the relative constancy of productivity within the community and the diversity in agency and in spatial and temporal scales exhibited by disturbance events. Also, evolutionary responses to disturbances involve minor adaptive shifts in phenological and regenerative traits and are more likely to occur as micro‐evolutionary steps than the shifts in linked traits in the core physiology associated with the capacity to exploit productive and unproductive habitats.During the assembly of a community and over its subsequent lifespan filters with diversifying and convergent effects may operate simultaneously on recruitment from the local species pool and impose contrasted effects on the similarity of the trait values exhibited by co‐existing species. Moreover, as a consequence of the frequent association of productivity with the convergence filter, an additional difference is predicted in terms of the effects of the two filters on ecosystem functioning. Convergence in traits selected by the productivity filter will exert effects on both the plant community and the ecosystem while divergent effects of the disturbance filter will be restricted to the plant community.
Soil heterogeneity and community composition jointly influence grassland biomass
Authors: Maestre Fernando T. , Bradford Mark A. , Reynolds James F. 
Published: February 2009

Abstract:Question:Does the spatial pattern of nutrient supply modify community biomass responses to changes in both species composition and richness?Location:Duke University Phytotron (Durham, North Carolina, USA).Methods:We conducted a microcosm experiment to evaluate individual plant and whole community responses to species richness, species composition and soil nutrient heterogeneity. The experiment consisted of seven levels of species composition (all possible combinations ofLolium perenne, Poa pratensisandPlantago lanceolata) crossed with three levels of soil nutrient distribution (homogeneous, heterogeneous‐up, and heterogeneous‐down, where up and down indicates the location of a nutrient patch in either the upper or the lower half of the soil column, respectively).Results:Communities containingPlantagoandLoliumresponded to nutrient heterogeneity by increasing above‐ and below‐ground biomass. Nutrient heterogeneity also increased size inequalities among individuals of these species. Significant species composition X nutrient heterogeneity interactions on community biomass and individual size inequality were observed when nutrient patches were located in the upper 10 cm of the soil columns. However, root proliferation in nutrient patches was equivalent regardless of the vertical placement of the patch.Conclusions:Our results suggest that nutrient heterogeneity may interact with plant species composition to determine community biomass, and that small‐scale vertical differences in the location of nutrient patches affect individual and community responses to this heterogeneity.
Tornado damage ofQuercus stellataandQuercus marilandicain the Cross Timbers, Oklahoma, USA
Authors: Shirakura Fumiko , Sasaki Kiyoshi , Arévalo José Ramón , Palmer Michael W. 
Published: February 2009

Abstract:Questions:The Cross Timbers are a mosaic of savannas, grasslands and upland forests, occupying a significant portion of south‐central North America. Our questions here were (1) how does a severe tornado affect the two most dominant tree species of the areaQuercus marilandicaandQ. stellatawith respect to damage and mortality; (2) how do such patterns vary as a function of tree size? What are the implications of disturbance for codominance in species‐poor systems?Location:The Cross Timbers in Oklahoma, USA.Methods:We established a 14.48‐ha permanent plot following a severe tornado in 2003. We identified, numbered and tagged each tree and recorded its diameter at breast height (DBH), spatial coordinates, status (dead or alive), and damage type. We examined (1) relative abundance before and after the tornado; (2) differences in damage and mortality, and (3) the influence of tree diameter on the probability of damage and mortality for each species.Results:Differences in species identity and tree characteristics were significantly related to tree mortality following the tornado, after accounting for spatial locations. The odds of mortality were 12.0 times greater forQ. marilandicathan forQ. stellata.Such greater vulnerability ofQ. marilandicaversusQ. stellatawas also reflected in changes in density and basal area. Tree diameter clearly influenced the damage and mortality pattern inQ. stellata; larger trees sustained more damage and mortality. However,Q. marilandicadid not exhibit size‐dependent mortality.Conclusion:The tornado affected the two dominant species differently. The intra‐ and inter‐specific differences in windstorm susceptibility may allow coexistence of the two species and are potentially important in the dynamics of the Cross Timbers. Species more damaged might finally benefit from the wind disturbance due to their resprouting ability.