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Aims: Plant species' distribution ranges are expected to shift towards previously uncolonized locations in response to climate warming. Mountain trails, which often access to areas of special ecological value as well as remote and climatically extreme locations, could influence such shifts through changes in dispersal and disturbance. Trails may facilitate the dispersal of propagules to new locations, influence the seed bank by changing propagule input and persistence and change establishment success through the creation of gaps and disruption of biotic interactions. However, knowledge regarding the influence of mountain trails on seed rain, seed bank abundance and seedling emergence in alpine ecosystems is lacking. In this study, we examine the influence of hiking trails on dispersal patterns in mountain ecosystems. Location: Dovrefjell, Scandes mountains, Norway. Methods: We surveyed seed rain, seed bank abundance and seedling emergence along four hiking trails spanning climate gradients with a mean 2.5°C difference between warmest and coldest location at four elevations per trail and at 0.5, 7 and 17 m from the trail (48 plots, in 16 transects). Results: Seed rain was 3.4 times higher in trailside plots than in those 17 m away and declined with colder climate at all distances from trails. Seed bank abundance on trailsides at the warmest location was eight times higher than in plots at 17 m distance, while there was no significant difference at colder locations. Seedling establishment was disturbance‐driven along the whole climate gradient, with 3.5 times more seedlings on trailsides than at 17 m distance. Conclusion: Mountain trails have the potential to facilitate vegetation shifts by capturing more seed rain and creating opportunities for seedling establishment. Our findings highlight the importance of including trail effects in studies of vegetation shifts. [ABSTRACT FROM AUTHOR]

Aims: Spruce beetles (Dendroctonus rufipennis) are causing widespread spruce (Picea spp.) mortality in subalpine forests in western North America. Spruce beetles are changing forest structure and composition by killing a dominant overstory species, but we know little about how the understory community responds to the increase in resource availability brought about by spruce mortality, what mechanisms drive its response, or how its response affects other forest properties and processes. Location: Glacier Lakes Ecosystem Experiments Site, Medicine Bow Mountains, Wyoming, USA. Methods: We measured understory community cover and richness in 75 permanent plots during and 10 years after an epidemic spruce beetle outbreak, and measured trait values for 46 common understory species. We used linear regression to determine how the understory community has changed over time and along a gradient of spruce mortality, and to evaluate the relative support for two mechanisms contributing to species responses. Results: Understory cover nearly doubled between sampling periods and increased the most where spruce mortality was most severe. Understory richness doubled and showed a weak positive trend with spruce mortality. Understory species with the largest increases in cover were the most frequent across the landscape before the disturbance, were the tallest at maturity and had the lowest leaf turgor loss points. Fir seedling density decreased over time, with decreases lessening with increases in understory cover. Changes in spruce seedling density were not predicted by changes in understory cover. Conclusions: Our findings highlight some of the diverse ways in which understory communities can be altered by spruce beetle outbreaks, and how the direction and magnitude of change can depend on the amount of spruce mortality as well as on priority effects and traits of pre-disturbance species. Our findings also highlight how understory community changes can have implications for other forest properties and processes, such as tree regeneration and forest recovery. [ABSTRACT FROM AUTHOR]

Questions: The effects of agriculture on forest biodiversity and ecosystem properties can persist decades or centuries after abandonment. Many Pacific island nations are experiencing declines in traditional agriculture. Seed dispersal and seedling recruitment are critical to forest regeneration, and this is particularly relevant for Polynesia where native seed disperser diversity is low and species have been extirpated to crisis levels. In this study we asked: are secondary lowland tropical forests converging to mature forest, and are there seedling recruitment and survival differences between forest types? Location: The Polynesian island of Tutuila, American Samoa, where traditional agriculture has been on the decline since the 1940s and secondary forests comprise 70% of all forest area. Methods: We surveyed 34 vegetation plots (containing 2,232 adult trees and 6,579 tree seedlings) across mature forest and >50 years old secondary lowland rain forest. We quantitatively compared forest diversity, structure and the 3-year seedling regeneration dynamics of the tree community. Results: Although species richness and stem densities were similar between mature and secondary forest, most diversity and structure parameters remained distinguishable between the two forest types. Basal area remained significantly higher in mature forest; the diagnostic tree species of mature and secondary forest differed; and community composition (as indicated by NMDS) remained significantly different. However, seedling survivorship did not differ between forest types and seedling recruitment patterns indicated that there remained a suite of effective seed dispersers on Tutuila. Conclusions: We conclude that (a) community differences between mature and secondary lowland rainforest were driven by the abundance of diagnostic species rather than exclusion of species from a forest type, and (b) there was no evidence of biophysical or ecological barriers to forest recovery of lowland secondary rain forest, or its convergence towards mature lowland rain forest. Nevertheless, more than 50 years after agricultural abandonment, secondary forest remains distinct from mature forest, highlighting that land use legacies are long-term drivers of forest composition and successional trajectory in post-agricultural landscapes of Polynesia. [ABSTRACT FROM AUTHOR]

Questions: Cold temperatures and freezing may hinder the process of forest expansion in moist climate regions, as predicted by the frost hypothesis. We examined the role of frost on the survival and regrowth of tree saplings under field conditions of open grasslands. Location: Cambará do Sul, Rio Grande do Sul. Methods: We established a field experiment protecting one of two groups of saplings of forest species from frost in grassland areas during the winter. We monitored 672 saplings from a total of seven species for 56 days. Saplings were brought back to the laboratory to evaluate regrowth rate and height. Survival curves of the two groups were compared using a Kaplan–Meier estimator. Correlation analysis was undertaken to estimate the relationship between survival and regrowth rate and a variance analysis was used to compare plant height between both groups. Results: Species respond distinctly to frost incidence, with some not being affected by frost (two gymnosperms and Myrcianthes pungens). Most protected saplings had a higher above-ground survival rate than unprotected ones (96.4% and 73.2%, respectively). Moreover, saplings that were damaged by frost showed differences in regrowth and height according to species identity, notwithstanding the fact that those from protected plots showed higher regrowth and height (88% and 25.65 cm compared to 68% and 17.15 cm). Conclusions: Our results showed clear negative effects of frost on the survival rate of aerial parts of saplings during the winter and the regeneration of damaged plants. Species-specific traits can offer frost resistance; however, together with other disturbances, frost may hinder the establishment of forest trees over grassland areas where frost events are common during the winter. [ABSTRACT FROM AUTHOR]

Questions: Which environmental factors influence fine‐grain beta diversity of vegetation and do they vary among taxonomic groups? Location: Palaearctic biogeographic realm. Methods: We extracted 4,654 nested‐plot series with at least four different grain sizes between 0.0001 m² and 1,024 m² from the GrassPlot database, covering a wide range of different grassland and other open habitat types. We derived extensive environmental and structural information for these series. For each series and four taxonomic groups (vascular plants, bryophytes, lichens, all), we calculated the slope parameter (z‐value) of the power law species–area relationship (SAR), as a beta diversity measure. We tested whether z‐values differed among taxonomic groups and with respect to biogeographic gradients (latitude, elevation, macroclimate), ecological (site) characteristics (several stress–productivity, disturbance and heterogeneity measures, including land use) and alpha diversity (c‐value of the power law SAR). Results: Mean z‐values were highest for lichens, intermediate for vascular plants and lowest for bryophytes. Bivariate regressions of z‐values against environmental variables had rather low predictive power (mean R² = 0.07 for vascular plants, less for other taxa). For vascular plants, the strongest predictors of z‐values were herb layer cover (negative), elevation (positive), rock and stone cover (positive) and the c‐value (U‐shaped). All tested metrics related to land use (fertilization, livestock grazing, mowing, burning, decrease in naturalness) led to a decrease in z‐values. Other predictors had little or no impact on z‐values. The patterns for bryophytes, lichens and all taxa combined were similar but weaker than those for vascular plants. Conclusions: We conclude that productivity has negative and heterogeneity positive effects on z‐values, while the effect of disturbance varies depending on type and intensity. These patterns and the differences among taxonomic groups can be explained via the effects of these drivers on the mean occupancy of species, which is mathematically linked to beta diversity.We analysed fine‐grain beta diversity of grasslands and other open habitats in the Palaearctic using 4,654 nested‐plot series and the z‐values of power‐law species–area relationships. Mean z‐values were highest for lichens, intermediate for vascular plants and lowest for bryophytes. The strongest environmental predictors of z‐values were herb layer cover (negative), elevation (positive), rock and stone cover (positive) and the c‐value (U‐shaped). In a conceptual figure, we summarize the resulting hypotheses how different predictors could influence z‐values via mean occupancy. [ABSTRACT FROM AUTHOR]

Questions: Do burn severity and soil chemistry drive species and trait composition on recently burned clear‐cuttings? Does the spatial distribution of common, easily dispersed colonizers vary with distance to fire perimeter? Location: A 13,000 ha production forest landscape in boreal southern Sweden burned in a wildfire in 2014. Methods: Vascular plants and bryophytes were recorded in permanent plots on clear‐cuts two and five years following fire, covering a burn severity gradient. Soil carbon content (reflecting burn severity), pH and nutrients were measured at plot level. Trait data were retrieved from the BIEN and LEDA databases and analyzed using community‐weighted mean (CWM) trait values. Statistical analyses included generalized linear mixed models (GLMMs), non‐metric multidimensional scaling (NMDS) and multivariate ANOVA. Results: Low burn severity resulted in higher frequency of legacy species (e.g. Vaccinium myrtillus), while high burn severity facilitated colonizing species (e.g. Senecio sylvaticus). Vegetation varied with soil chemistry, expressed through pH. Species composition changed between years and deviated from unburned clear‐cuts. After five years the most common taxa on burned plots were the vascular plants Chamaenerion angustifolium, Betula spp. and Populus tremula and the bryophytes Ceratodon purpureus and Polytrichum juniperinum. CWM specific leaf area (SLA) decreased markedly with time and root buds increased with total carbon content in the soil (i.e., toward less severely burned plots), while soil pH was not associated with any studied trait. Chamaenerion angustifolium decreased with distance to the fire perimeter, while Ceratodon purpureus increased. Conclusions: Burn severity and soil pH weakly drive vegetation dynamics in the early phase following fire on clear‐cuts, indicating a large influence of stochastic processes. Deciduous trees are common already after five years and their further expansion will affect light and nutrient availability. To understand future vegetation trajectories on burned clear‐cuts, studies need to incorporate the light factor and links between tree species' identity and soil nutrient availability. [ABSTRACT FROM AUTHOR]

Questions: Disturbances can cause fluctuations in resource availability that influence plant performance. In systems with such dynamics, inter‐specific differences in resource capture may promote co‐existence by partitioning competition between periods of high or low resource availability. Such differences in resource use strategy have been described with the Plant Economics Spectrum, which hypothesizes that functions related to resource use and processing should co‐vary and can be predicted from plant traits. In pyrogenic systems, fires are associated with short‐term increases in soil nitrogen availability ("pulses"), and thus contribute to a fluctuating resource supply. In this study, we sought to understand whether plants differed in their capacity to capture a nitrogen pulse, and to what extent that ability influenced biomass recovery. Methods: In two consecutive greenhouse experiments, we tested whether two functions — nitrogen assimilation (Experiment 1) and biomass regrowth after disturbance (Experiment 2) — co‐varied, and how each function corresponded to leaf and root functional traits. Results: In Experiment 1, four co‐occurring shrubs differed in their temporal patterns of nitrogen uptake, and nitrogen uptake was positively correlated with resource‐acquisitive leaf traits (leaf percent nitrogen). In Experiment 2, the biomass regrowth of a resource acquisitive and a resource conservative species was the same regardless of competitive environment (i.e., when grown in pots of mixed‐species or same‐species pairs). Rather than being associated with the capture of new nitrogen, biomass resprouting of both species was associated with the size of below‐ground resource stores and specific root length. Conclusions: Our work suggests that resource acquisition and processing may be decoupled from each other after disturbance, and also highlights the need for explicit tests of the relationships between root traits and above‐ground plant function. We compared two metrics of plant performance — nitrogen assimilation and biomass resprouting — of shrubs native to frequently disturbed longleaf pine forest. Biomass resprouting after disturbance was independent of nitrogen assimilation. Increased nitrogen capture was associated with resource‐acquisitive plant traits (leaf nitrogen content); increased resprouting after disturbance was associated with resource‐conservative plant traits (below‐ground biomass and specific root length). [ABSTRACT FROM AUTHOR]

This paper describes the species composition of remnant grasslands in the aspen parkland region of Alberta and its relation to soil characteristics and small-scale disturbance. Our findings are consistent with the centrifugal model of communities with Festuca hallii dominating undisturbed `core' habitat and the composition of more `peripheral' habitats varying in soil properties and in the magnitude of disturbance. Invasive non-native species are not present in the core habitatand are present only in the disturbed sites, most abundantly in those with the highest soil nitrogen. The centrifugal model, as it applies to these remnant grasslands, differs from its previous application to wetlands and forests in that the core communities are not on the most fertile sites, but on the least disturbed. These findings have implications for the management of prairie remnants to exclude invasiveexotic species. [ABSTRACT FROM AUTHOR]

Questions: How has the composition and diversity of canopy tree species in a riparian woodland changed over time? How are the compositional changes related to impact of elephants? Does the composition of juvenile plants indicate that the woodland retains the potential to recover its former composition? Location: Northern Botswana adjoining the Linyanti River. Methods: We assessed the species composition of the riparian woodland in 2007/2008 along belt transects, recording living and dead individuals in different size classes plus signs of elephant damage and the presence of juvenile plants. We related this current composition to the composition recorded in a previous survey in 1991/1992 and reconstructed the earlier composition by combining living and dead trees recorded in 1991/1992. We established the association between mortality and impact agent, severity, year and size class using model selection statistics. Changes in species diversity were assessed using the Shannon diversity index. Results: The composition of canopy trees changed from the initial dominance of two Acacia spp. towards the current situation with these two species forming <5% of the woodland canopy. Dead trees were strongly associated with severe damage inflicted by elephants, including bark stripping and felling. As the acacia trees declined, elephant impacts shifted onto other canopy tree species. The woodland canopy became progressively more open because recruitment from juvenile and sapling stages to replace trees that had died was also suppressed. Nevertheless, the tree species that had decreased in abundance in the canopy remained abundant as juvenile plants. Conclusion: Substantial changes in woodland composition can occur in the presence of high elephant concentrations because of the selective damage that elephants impose on particular tree species and size classes. The loss of functionally important species may not be reflected by changes in compositional diversity measures. [ABSTRACT FROM AUTHOR]

Abstract: Question: In temperate grasslands and savannas that were historically maintained by frequent, low‐intensity fires, disturbance by fire may promote community resistance to winter climate change by favouring slow‐growing, resource‐conservative species that may also be more cold‐tolerant. The lack of functional trait data for measuring cold tolerance, however, has prevented testing this idea. We ask, are slower growing, resource‐conservative species more cold‐tolerant than fast‐growing species, and are plant responses to fire frequency and cold tolerance related? Location: Prairies and savannas of south‐central Wisconsin, USA. Methods: We measured leaf cold tolerance for 120 plant species from prairies and savannas and compared cold tolerance to fire affinity as well as other functional traits describing plant strategies. Results: As predicted, resource‐conservative species are more cold‐tolerant than fast‐growing species in temperate grasslands and savannas. Cold tolerance is also associated with disturbance regime such that species found in frequently burned sites are more cold‐tolerant. Conclusions: The ability to predict the degree of susceptibility of species and communities to winter climate change and extreme climate events, such as freezing, will provide insight into the conservation and management practices to promote species persistence into the future. Under climate change, communities composed of more stress‐tolerant species may be more likely to persist. Our results demonstrate that cold‐tolerant species are more common in temperate grasslands and savannas managed with frequent, low‐intensity fire that simulate historic disturbance regimes. Identifying and maintaining ecosystems composed of stress‐tolerant species may play a key role in preserving natural communities under environmental uncertainty. [ABSTRACT FROM AUTHOR]

Abstract: Question: The European forest‐steppe ecotone extends over 6,000 km from the Carpathian to the Ural Mountains. It is extensively used for agriculture with very few patches of semi‐natural vegetation. Little is known about the history of the forest‐steppe ecotone in Eastern Europe and here we examine its Holocene dynamics and stability and investigate when it was transformed to the modern agro‐pastoral landscapes. Location: Mid‐Russian Upland. Methods: We summarize the information from five pollen diagrams for the last 7,000 years and estimate forest cover using the best modern analogue technique. We use the PCA and principal curve analysis to evaluate compositional changes. Results: The pollen data suggest that the East European forest‐steppe boundary was located 50–70 km further northwest from the presumed present position during the period 7,000–4,500 cal yr BP. After 4,500 cal year BP, it moved approximately 100–130 km to the southeast. Since 2,000 cal year BP land use affected the boundary, while a total forest clearance and transformation to agricultural landscapes took place in the last 400 years. Pollen data indicate a NW–SE direction of the forest‐steppe vegetation gradient. Prior to clearance, open lime–pedunculate oak forests existed in the NW, while the south was characterized by pine woodlands with an admixture of oak and lime with 20%–40% forest cover. Conclusions: The East European forest‐steppe ecotone is sensitive to climate change. The Late Holocene expansion of forest cover is in agreement with evidence suggesting an increase in moisture availability during this time. The rapid recovery to a similar composition after human disturbance indicates a high resilience of woodland in the ecotone, which may be connected to a naturally high disturbance regime, possibly through fire. The information revealed on the position of the gradient and natural composition of the forest is currently not depicted in maps of the potential natural vegetation. [ABSTRACT FROM AUTHOR]

Abstract: Question: Flood disturbance in peatlands can create temporary or permanently submerged areas where tolerant species may persist and replace intolerant species over time. Fen moss species and communities occur along a hummock–hollow gradient in natural ecosystems, but their resistance and resilience to different durations of submergence has yet to be tested. We asked what are the short‐ and long‐term effects of submergence duration on four common boreal fen moss species and the implications for ecosystem resilience? Location: Rich fen near Fort McMurray, Alberta, Canada. Methods: To examine the effect of submergence duration on fen moss species and communities, we harvested and submerged monoculture plugs dominated by Hamatocaulis vernicosus, Sphagnum warnstorfii, Tomentypnum nitens and Aulacomnium palustre in the field under rich fen water for 1–8 weeks. After submergence, we planted the plugs in bare peat at the same site to evaluate the short‐ and long‐term responses of each species and changes in moss community composition over time. Results: We found that moss species response to duration of submergence is not strictly related to their occurrence along a hummock–hollow gradient and that tolerant species maintain or restore moss cover. H. vernicosus was most tolerant to submergence of all durations, whereas S. warnstorfii was nearly eliminated by submergence. Over the long term, more tolerant species replaced less tolerant species, increasing diversity and moss community resilience. Overall, moss communities without S. warnstorfii were resilient to 4 weeks of submergence because T. nitens and H. vernicosus maintained dominance or established where the cover of less resilient species was limited. Conclusions: We show that moss species varied in their responses to submergence duration, resulting in shifts in community composition and long‐term effects on community resilience with longer durations of submergence. This provides insight into how moss communities provide stability to peatlands in response to disturbance through shifts in community composition that support tolerant dominant species. [ABSTRACT FROM AUTHOR]

Abstract: Questions: We evaluate the role of past land use on long‐term forest succession and ask fundamental questions: (i) are successional patterns along a chronosequence consistent through time; (ii) is past land use or physiography a greater driver of forest composition; and (iii) does forest composition converge with age? Location: Thomas Jefferson's Monticello plantation, Virginia Piedmont, USA. Methods: Combining dendroecology, historical documents and a repeated vegetation survey from 1934, we reconstruct forest histories along a chronosequence that retains a temporal dimension. Tree‐ring data indicate initial canopy status and canopy release events using time series analysis with intervention detection. Results: Forest extent was lowest during Jefferson's tenure; however, tree ring and documentary evidence revealed the location of Jefferson's timber zone. Jefferson‐era trees in this zone are largely on the west slope with scattered Pinus recruitment starting in the late 18th century, followed by Quercus species. Pinus cohorts also recruited into former agricultural fields on south and east slopes in two chronosequence stages from the 20th century. Synchronized release events were observed during the early 1800s, 1850s–1860s and 1960s, indicating periods of intense forest use. Ordination of repeated vegetation surveys showed a progression in forest age that explained more variation in forest composition than elevation and slope. The forest age gradient is also evident independently from tree‐ring data, but the ordination does not show convergence in composition with forest age. Conclusion: Past land use is a greater driver of forest composition than an inferred soil moisture gradient. The composition of the most recent chronosequence stage suggests that future forest dynamics may be novel compared to the prior two centuries because of differences in land use and species availability. These land‐use legacies demonstrate how colonial‐era agricultural decisions at Monticello continue to impact forest growth and composition more than two centuries later. [ABSTRACT FROM AUTHOR]

Questions Do composition and richness of woody plants differ between gaps and closed canopy in subtropical forests, and does this difference vary across life stages of tree species? Is tree species richness in gaps a function of regeneration density? Location Subtropical Shorea robusta Gaertn (Sal) forest, central Nepal. Methods We collected vegetation data from two old-growth S. robusta forest stands. We sampled 128 plots of 100 m2 equally spread between the two habitats: gap and closed canopy. In each plot, we recorded the total number of woody species, number of individuals of seedlings and saplings of tree species and measured the DBH of all saplings. We compared species richness and composition of total woody species, seedlings and saplings between the two habitats. We used ordination to analyse species composition, and an individual-based species accumulation curves to illustrate the effect of density on species richness. Results The species composition of total woody species and seedlings was similar in both habitats, but species composition of saplings differed between habitats. Total woody and seedling richness were similar between habitats at one site, but were richer under closed canopy at the other site. Sapling richness was higher in gaps at both sites and was a function of stem density at one site, but not at the other site. Conclusions Gaps are not always areas of higher woody species richness and therefore may be less important than expected for the overall species richness of woody plants. Instead, they are potentially important for enhancing local tree richness by increasing sapling richness. Gap disturbance is the primary driver of structural heterogeneity in forests where topographic and edaphic gradients are negligible. [ABSTRACT FROM AUTHOR]

Questions Popular methods to analyse community-trait-environment relationships constrain community patterns by trait and environment relationships. What if some traits are strongly associated with community composition but unrelated to environmental variables and vice versa? We take a different approach, unconstrained by this assumption using non-parametric methods. We applied this technique to lichen (fungal/algal and/or cyanobacterial symbioses) communities across environmental and fire age gradients by measuring richness and cover of four important functional traits: energy generation (type of photosynthetic symbiont), water relations (inferred from growth form), dispersal capability (from vegetative propagules) and microsite specificity (measured by substrate affinity). Location Denali National Park and Preserve, Alaska, USA. Methods We ordinated plots in species space and regressed trait and environmental variables against ordination axes, resulting in one- or two-dimensional trait and environment surfaces. We then superimposed these surfaces on the ordination to create a new visual display, the 'hilltop plot', which enabled simultaneous measurement and display of one- and two-dimensional, non-linear community-trait-environment associations. Results Most traits examined show non-linear relationships with community structure. Fire favoured simple cladoniiform lichens, species with higher vegetative dispersal capacity and specificity to grow on wood, but excluded the 'reindeer' lichens, which had lower cover even more than 20 yrs after fire. Forests had more sorediate lichens than non-forested habitats, whereas high elevation, rocky areas had more green algal and fruticose lichens. Cyanobacterial lichen richness was positively related to shrub cover, while tripartite (cyanobacteria and green algae in a single lichen) and foliose lichen richness was highest in areas with higher moss cover. Conclusions Different combinations of lichen functional traits peaked along environmental and disturbance gradients, which we interpreted as balancing energy generation, water relations, vegetative dispersal and habitat specificity. Our method of trait-environment-community analysis revealed numerous one- and two-dimensional, non-linear relationships between community composition and functional traits, environmental variables and fire age gradients, which informed mechanisms behind community assembly. Our results indicate non-parametric and non-linear methods of trait-environment-community analysis have the potential to detect patterns that would have been missed using current popular techniques. [ABSTRACT FROM AUTHOR]

Questions How does heathland vegetation composition change during ca. 100 yr of succession in the absence of management? Is succession divergent or mono-directional? Do soil conditions and land-use history explain the variation in vegetation dynamics? Is there evidence for alternative stable states? Location Nørholm hede, a 350-ha heathland in southwest Denmark that was abandoned in 1895 and left to develop naturally via succession. Methods Permanent vegetation inventory plots were established and have been revisited 11 times between 1921 and 2012. Soil conditions were recorded in 2012. We used clustering, linear mixed models, linear models, ANOVA and multivariate techniques (redundancy analysis and principal response curves) to investigate changes in the plant community and how differences in plant community composition related to soil conditions and disturbance history. Results Ericaceous dwarf shrubs dominated most of the heathland initially. A dominance shift from dwarf shrubs to grasses occurred on about half of the plots. The other half of the plots remained dominated by dwarf shrubs, although Empetrum nigrum expanded at the expense of Calluna vulgaris. Lichen cover decreased dramatically across all plots. The divergent successional pattern was not explained by nutrient concentrations. Grasses mainly expanded in areas where they already had a substantial presence, and this initial presence was largely correlated with historical soil disturbance. Plots where dwarf shrubs remained dominant had a relatively thick O-horizon. Conclusions Vegetation dynamics during heathland succession were not deterministically determined by soil conditions. Grass and tree expansion occurred slowly and dwarf shrub dominance was stable for more than 100 yr on large parts of the heath, even in the absence of management. Management actions that disturb stable dwarf shrub vegetation may enhance grass and tree colonization. [ABSTRACT FROM AUTHOR]

Question Recent research in boreal forest suggests that an 'open matrix' model may be more appropriate than the traditional model of spatially discrete gap dynamics for describing forest disturbance and regeneration, but what is the evidence from temperate broad-leaved deciduous forests concerning the prevalence of these alternative models? Location Semi-natural temperate broad-leaved deciduous forest in southern England. Methods Multi-temporal Li DAR data were used to monitor the changes in tree canopy height and canopy gaps over a 10-yr period for a 130-ha area of forest. Gap dynamics were characterized by quantifying gap creation, expansion, contraction and closure. By identifying the types and rates of canopy height transitions, areas of gap contraction and closure were attributed to the processes of lateral crown growth or vertical regeneration. Results Across the study site there was a zonation in canopy and gap properties and their dynamics. Many areas of the forest had the characteristics of open wood-pasture dominated by large, complex gaps being maintained under a regime of chronic disturbance. In these areas, several characteristics of the gap dynamics indicated that regeneration was restricted and this may be attributable to spatially-focused overgrazing by large herbivores. In contrast, other areas were characterized by high, closed canopy forest with small, discrete gaps where gap creation and infill were balanced. Conclusions At the landscape-scale broad-leaved deciduous forests contain a spatial mosaic of zones, which conform to different models of disturbance and regeneration dynamics; discrete gap dynamics and open matrix regimes are juxtaposed. It is now important to elucidate the abiotic factors and biotic interactions that determine the spatio-temporal distribution of the different regimes and to examine whether such a 'regime mosaic' model is applicable in other forest types. [ABSTRACT FROM AUTHOR]

Question: For over a century, ecologists have grappled with the question "what drives species diversity?" Urgent global issues such as loss of biodiversity and the relative importance of species richness for ecosystem function and services has heightened the relative importance of understanding processes that control species diversity. Here we present the plans for a global coordinated distributed experiment for herbaceous communities, the HerbDivNet, to test the humpbacked model, a unimodal relationship between species richness and aboveground plant biomass plus dead plant litter HBM, to determine whether scale may influence the HBM, and to explore drivers of plant diversity. Location: Globally distributed experiment. Methods: We propose a nested, standardized sampling design 8 × 8 m, with 1 m² plots, taken from multiple site locations along a range of sites varying in primary productivity. Results and Conclusions:We welcome others with an interest in using global, standardized, coordinated distributed experiments to explore patterns and processes in herbaceous plant communities to join HerbDivNet in the search of new insights to drivers of plant species diversity. [ABSTRACT FROM AUTHOR]

Questions Do mortality rates of boreal bryophytes associated with leaf litter burial vary with degree of shelter on forest floor microsites in spruce-dominated forests? Do erect and prostrate species respond similarly? What is the relative importance of deciduous leaves (from aspen and birch) vs conifer needles as bryophyte mortality agents? Location Boreal spruce forests of central Sweden. Methods A transplant study examining mortality was set up with four different bryophyte species: two creeping, prostrate liverworts ( Calypogeia integristipula and Lepidozia reptans) and two more erect mosses ( Rhytidiadelphus triquetrus and Hylocomiastrum umbratum). We tested for differences in mortality rates associated with leaf litter burial in three microhabitats differing in degree of shelter on the forest floor, i.e. sheltered (large boulders, tree bases of spruce) and unsheltered (open forest floor). Results After two growing seasons, 12.7% of the bryophyte transplants (40 out of 316, of which 37 transplants were prostrate liverworts) were dead, presumably due to litter burial. These two prostrate liverworts displayed significantly higher mortality rates close to boulders and at tree bases compared to unsheltered forest floors. Furthermore, although only comprising a small portion of the canopy (<10%), deciduous litter accounted for 53% of all transplants that were buried by litter, compared to 47% for conifer needle litter. Conclusion We find fine-scale spatial patchiness in the responses of bryophytes to litter fall. Mortality of prostrate liverworts associated with litter burial varies among microhabitats on the forest floor, with significantly higher mortality at sheltered microsites (here exemplified by boulders and tree bases) compared to erect moss species. Bryophytes close to microtopographic structures (e.g. boulders and trees) are more strongly exposed to litter burial, but such structures can also function as refuges under disturbance events such as clear-cuts and windthrows. In addition, they may contain convex surfaces that accumulate less litter than flat or convex forest floor surfaces. The observed large effect of litter burial associated with bryophyte mortality, and the variation among microhabitats and species growth forms, suggest that incorporation of litter fall is of vital importance for our understanding of the dynamics of forest bryophyte communities. [ABSTRACT FROM AUTHOR]

Questions Functional redundancy in assemblages may insure ecosystem processes after perturbation, potentially causing temporary or permanent local species extinctions. Yet, functional redundancy has only been inferred by indirect evidence or measured by methods that may not be the most appropriate. Here, we apply an existing method to measure functional redundancy, which is the fraction of species diversity not expressed by functional diversity, to assess whether functional redundancy affects community resilience after disturbance. Location Subtropical grassland, south Brazil (30°05′46″S, 51°40′37″W). Method Species traits and community composition were assessed in quadrats before grazing and after community recovery. Grazing intensity ( G) was measured in each quadrat. We used traits linked to grazing intensity to define functional redundancy ( FR) as the difference of Gini- Simpson index of species diversity ( D) and Rao's quadratic entropy ( Q). Also, with the same traits, we defined community functional stability ( S) as the similarity between trait-based community composition before grazing and 47 and 180 d after grazing ending. Using path analysis we assessed different postulated causal models linking functional diversity ( Q), functional redundancy ( FR), grazing intensity ( G) and community-weighted mean traits to community stability ( S) under grazing. Results Path analysis revealed the most valid causal model FR → S ← G, with a significant positive path coefficient for FR → S and a marginally significant negative one for S ← G. Since FR and G were independent in their covariation and in their effects on S, the model discriminated community resistance to grazing (the effect of G on S) from community resilience after grazing caused by functional redundancy (indicated by the effect of FR on S). Conclusion We show that expressing functional redundancy mathematically is a useful tool for testing causal models linking diversity to community stability. The results support the conclusion that functional redundancy enhanced community resilience, therefore corroborating the insurance hypothesis. [ABSTRACT FROM AUTHOR]

Question Does the seed bank have a different functional trait signature to the vegetation and is this difference affected by productivity and disturbance? Do functional diversity differences exist between the vegetation and seed bank and are the differences modulated by productivity and disturbance. Location An area of diverse land use on the west coast of Scotland. Methods Parallel vegetation and seed bank surveys were carried out across 30 sites contrasting in land use, and hence productivity and disturbance regime. Data were analysed to assess overall differences between the seed bank and vegetation in community-weighted mean for selected functional traits and to test if the difference was affected by productivity or disturbance. Three functional diversity indices were calculated for each seed bank and vegetation sample - functional richness, functional divergence and functional evenness - and each index was assessed for overall differences between the seed bank, the vegetation and differences modulated by disturbance and productivity. Results There were clear differences in many community-weighted mean traits between the seed bank and the vegetation. Plants in the vegetation were characterized by increased stature, more conservative leaf traits, wind pollination and by being perennial, whereas plants in the seed bank had higher seed longevity, higher seed masses and were more frequently insect- or self-pollinated. There was no difference in functional richness between the seed bank and the vegetation, and while both the seed bank and the vegetation functional richness were significantly lower than expected, the vegetation showed a bigger deviation from expectations compared to the seed bank. The functional diversity indices revealed different relationships between seed bank and vegetation against productivity and disturbance. Functional divergence (and its standardized effect size) indicated stronger habitat filtering for the vegetation at high levels of productivity or disturbance, while the effect size of functional richness and functional evenness suggested stronger filtering on the seed bank at high levels of productivity and disturbance. Conclusions The significant difference in traits between the seed bank and vegetation mean that following disturbance this is likely to have a considerable impact (at least in the short term) on ecosystem function. Functional diversity patterns were less clear, with conflicting evidence on habitat filtering, depending on the metric chosen. [ABSTRACT FROM AUTHOR]

Questions How do fire and grazing by bison affect the composition and structure of tallgrass prairie plant communities and their temporal stability? Are these responses modulated by topographic location? Location Konza Prairie Biological Station, Kansas, USA. Methods Plant community composition was monitored in permanent plots in native grassland sites receiving different long-term prescribed burning and bison grazing regimes across a topographic gradient (lowlands, slopes, uplands) following 20 yr of variable burning treatments and 13 yr of grazing by bison. A combination of multivariate analyses was used to determine how community structure, life forms and individual species responded to the accumulated effects of long-term fire and grazing by native bison in upland, slope and lowland soils. Results Species diversity was maximized in sites that were infrequently burned and grazed by bison with the strongest response on infrequently burned slope sites, while diversity was lowest on frequently burned ungrazed sites and on frequently burned slope sites. In general, grass cover was highest in infrequently burned ungrazed sites and lowest on frequently burned grazed sites, while forb richness was highest in infrequently burned and grazed sites. Community response to fire and grazing differed across the topographic gradient. In general, frequent burning favoured C4 grasses, which reduced the abundance of C3 forbs, especially in lowland sites. Responses of dominant grasses and forbs to fire and grazing varied depending on topographic position. Community stability was positively correlated with species richness. Conclusions Overall, we found that fire and grazing are the main determinants of plant community composition and structure in this grassland system, but that topography mediates these effects. A combination of bison grazing and periodic fire is necessary to maximize diversity and community stability across this native grassland landscape. [ABSTRACT FROM AUTHOR]

Question: What was the role of fire during the establishment of the current overstory (ca. 1870-1940) in mixed-oak forests of eastern North America?Location: Nine sites representing a 240-km latitudinal gradient on the Allegheny and Cumberland Plateaus of eastern North America. Methods: Basal cross-sections were collected from 225 trees. Samples were surfaced, and fire scars were dated. Fire history diagrams were constructed and fire return intervals were calculated for each site. Geographic patterns of fire occurrence, and fire-climate relationships were assessed. Results: Fire was a frequent and widespread occurrence during the formation of mixed-oak forests, which initiated after large-scale land clearing in the region ca. 1870. Fire return ranged from 1.7 to 11.1 years during a period of frequent burning from 1875 to 1936. Fires were widespread during this period, sometimes occurring across the study region in the same year. Fires occurred in a variety of climate conditions, including both drought and non-drought years. Fires were rare from 1936 to the present. Conclusions: A variety of fire regime characteristics were discerned. First, a period of frequent fire lasted approximately 60 years during the establishment of the current oak overstory. Second, fire occurred during a variety of climate conditions, including wet climates and extreme drought. Finally, there was within-site temporal variability in fire occurrence. These reference conditions could be mimicked in ongoing oak restoration activities, improving the likelihood of restoration success. [ABSTRACT FROM AUTHOR]

Questions: In a system of five annual plant species restricted to nest-mounds of the ant Lasius flavus in a perennial grassland: 1. Are the population dynamics influenced by ant disturbance? 2. Is the survival of the annuals at the scale of the whole grassland possible under the observed conditions of disturbance dynamics? 3. Which phases in the annuals' life cycle and patch types contribute most to population growth? Location: Borec hill, northern Czechia, 50°31′ N, 13°59′ E, 446 m a.s.l. Methods: Local population dynamics of the annuals were analysed separately for five patch types that differed in the proportion of bare soil. Vitality rates were assessed directly in the field, but also in a garden experiment, during 2000-2001 and 2001-2002. Population dynamics at the scale of the whole grassland was analysed with a megamatrix approach, combining patch dynamics of the nest-mounds with patch-specific population dynamics. Contributions of different phases and patch types to growth rate were estimated by elasticity analysis. Results: Nest-mounds differed in the percentage of bare soil. Increasing moss cover significantly reduced germination and seed production of all studied annuals and decreased their population growth rates (λ). Although successional processes dominated over ant disturbance, populations of all species could survive well (λ »1) in the grassland according to the 2000-2001 megamatrix dynamics. Based on the dynamics from the following period, two species would not survive in a long-term perspective due to random environmental variation. Whereas the A-A transition (adult plants originating from adults of the previous year) had the highest elasticity under open conditions and ?good period' demography, the importance of persistent seeds increased under reverse conditions. This, however, differed among species. Conclusions: Ant-disturbance was shown to be critical for the population survival of five annual species in the studied grassland. The fate of the annual populations in the grassland system also depends on random environmental variation, which may override the effect of ant activity. [ABSTRACT FROM AUTHOR]

Question: Predicting the future abundance and distribution of invasive plants requires knowing how they respond to environmental conditions. In arid and semi-arid ecosystems where water is a limiting resource, environmental conditions and disturbance patterns influence invasions by altering acquisition and utilization of water over space and time. We ask: 1. How do variations in climatic and soil properties influence temporal soil water dynamics? 2. How does this variation affect the establishment of Bromus tectorum (cheatgrass), a cool-season annual grass that has successfully colonized much of the U.S. Great Basin? Location: Short-grass Steppe in northeastern Colorado, USA; Arid Lands Ecology reserve in southeastern Washington, USA; and the Patagonian steppe of the Chubut province in Argentina. Methods: We utilized a soil water model to simulate seasonal soil water dynamics in multiple combinations of climatic and soil properties. In addition, we utilized a gap dynamics model to simulate the impact of disturbance regime and seed availability on competition between B. tectorum and native plants. Results: Our results suggest that climate is very important, but that soil properties do not significantly influence the probability of observing conditions suitable for B. tectorum establishment. Results of the plant competition model indicate that frequent disturbance causes more Bromus tectorum in invaded areas and higher seed availability causes faster invasion. Conclusions: These results imply a general framework for understanding Bromus tectorum invasion in which climatic conditions dictate which areas are susceptible to invasion, disturbance regime dictates the severity of invasion and seed availability dictates the speed of invasion. [ABSTRACT FROM AUTHOR]

Questions: To what extent can spatial structure and its causes be determined in a highly disturbed environment? What are the main determinants of pattern and are these species-specific? How much do spatial patterns change over generations? Location: Wimmera region of southern Australia. Methods: Broad-leaved weeds were counted in 225,000 contiguous 20-cm square quadrats. A substantial number of these quadrats were recorded again after two and four years. An hierarchical ‘adaptive analysis’ approach was used to select spatial analytical methods to examine specific aspects of pattern and variation in pattern from year to year. Results: Patterns varied among species and included both dense and sparse patches surrounded by areas of zero density, diffuse gradations of density and clear anisotropy. Patterns in Erodium botrys and Oxalis pes-caprae persisted over years, whereas patterns in Arctotheca calendula were less pronounced and varied over time. Edaphic factors appeared to have only a minor influence over the spatial distribution of the weed community as a whole. In Oxalis pes-caprae, whose patches were hypothesized to have been shaped by cultivation, there was no spread in four years, despite further tillage. Outlying plants of O. pes-caprae failed to establish new patches, even in the year of greatest population increase. Little evidence of localised recruitment events was found. Conclusions: Despite repeated annual disturbances by natural and anthropogenic mechanisms, clear and interpretable spatial structure develops in annual weeds over a range of spatial resolutions. Adaptive analysis is a useful approach to the characterization of such patterns. [ABSTRACT FROM AUTHOR]

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 area Quercus marilandica and Q. stellata with 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 for Q. marilandica than for Q. stellata. Such greater vulnerability of Q. marilandica versus Q. stellata was also reflected in changes in density and basal area. Tree diameter clearly influenced the damage and mortality pattern in Q. stellata; larger trees sustained more damage and mortality. However, Q. marilandica did 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. [ABSTRACT FROM AUTHOR]

Question: How do reduced levels of summer grazing by reindeer affect the abundance, composition and species richness of mountain plant communities? Location: Arctic-alpine mountain vegetation 700-850 m a.s.l., Saana Conservation Area, northwestern Finnish Lapland. Methods: Permanent plots were established in 1990 and resampled in 1999 or 2001. The number of reindeer had considerably declined from the 1980s to the 1990s and we followed the recovery of vegetation. The comparisons between 1990 and 1999/2001 were made at seven sites differing in their original grazing pressure. Results: At the initially heavily grazed sites, lichen abundances increased, but at the lightly grazed sites the abundances of lichens decreased. Graminoids declined at all sites, but the change seemed to be greatest at the most heavily grazed sites. Forbs increased slightly across all sites. At the species level, lichens and graminoids responded most notably to the reduction of grazing pressure. Individual species responses in shrubs were variable and among forbs, typical species of species-rich Dryas heaths increased. Total species richness increased at all sites and the change was greater at heavily grazed sites. This increase resulted mainly from increased bryophyte and lichen species richness but also from a slight increase in vascular plant species richness. Conclusions: These results suggest that lichens are the group most responsive to the reduction of heavy summer grazing by reindeer and that lichens and forbs typical in arctic-alpine Dryas heaths are favoured over graminoids under reduced grazing. Heavy grazing decreases overall species richness with the most pronounced effects on bryophyte and lichen species richness. The results support the hypothesis that heavy summer grazing may shift the composition of mountain plant communities towards that of grasslands and show how this shift may be reversed under reduced grazing. [ABSTRACT FROM AUTHOR]

Questions: What are the most relevant environmental variables influencing the distribution and the species richness of epiphytic lichens in heterogeneous areas of the Mediterranean region? What is the relative importance of substrate- vs. environmental-related variables? How do climatic and disturbance factors interact? Location: The study was carried out in the Liguria region (northwestern Italy). This is a complex region where steep environmental gradients occur over a few kilometres of longitude and latitude. Methods: Data on lichen species frequencies, collected on the basis of stratified random sampling, were analyzed using nonmetric multidimensional scaling (NMS) and DCA. Indicator Value Analysis (IVA) analysis was used to find indicator species for the environmental predictors. Results: In the survey area, epiphytic lichen distribution depends on both substrate- and environment-related factors. Climatic variables (in particular average yearly temperature and rainfall), anthropogenic pressures (particularly harvesting and atmospheric pollution), bark pH and texture were associated with the main axes of variability in the dataset. Mean annual rainfall is the best predictor for epiphytic lichen richness in the survey area. The particular effects of the Mediterranean region (e.g. the influence of forest fires) and of heterogeneous areas (the variability of diversity in relation to habitat) were pointed out. Several indicator species, closely linked to particular ecological conditions, were found for both substrate- and environment-related variables. Conclusions: The main variables involved seemed to be the same reported for other areas, but their relative importance and their spatial scale of action were in some cases different, probably due to the geomorphological and climatic heterogeneity of the survey area. The significant influence of climatic predictors and disturbance factors on epiphytic lichens was confirmed, suggesting that these organisms may be used successfully to describe ecological trends in natural environments, also providing practical information at ecosystem level. [ABSTRACT FROM AUTHOR]

Question: What are the shape, abundance, size, and structural characteristics of sapling patches in an old-growth Pinus jeffreyi-mixed conifer forest with a relatively intact disturbance regime? Location: Sierra San Pedro Martir, Baja California, Mexico. Methods: Regeneration was quantified by sampling sapling patches on seven 1200 m permanently marked line transects. For all patches intersected, tree size, species, age, and patch canopy cover were recorded. Patch structural characteristics were statistically compared to data from unbiased forest inventory plots. The minimum regeneration patch was defined as three saplings in a 49-m² area. Results: We sampled 54 sapling regeneration patches. Patch size varied from 6.6 to 674.8 m². A small portion of the forest was in patches (patch fraction = 3.8%, patch abundance = 8.5 per ha). The majority of the patches were small; 64.8% were less than the mean patch area of 100.1 m². Patches were shaped as a rhombus. For all forest characteristics, mean values inside patches were significantly different than those from the unbiased forest inventory plots. Conclusions: These forests have a fine-grained pattern of regeneration patches. Our largest patch size of 674.8 m² is the smallest reported in Pinus jeffreyi, P. ponderosa, and mixed conifer forests; other studies have probably had more difficulty delineating regeneration patches because of forest ingrowth from fire exclusion. Frequent fire, irregular seed crops, and seed dispersal by small mammals and birds could create this regeneration patch regime. High variation in nutrient availability after fire could also contribute to increased stand patchiness. [ABSTRACT FROM AUTHOR]

Composition and density of the soil seed banks, together with seedling emergence in the field, were examined on Svalbard. 1213 soil samples were collected from six drymesic habitats in three regions representing various stages of colonization from bare moraines to full vegetation cover and spanning a range of typical nutrient and thermal regimes. Of the 165 vascular plant species native to Svalbard, 72 were present as mature plants at the study sites and of these 70% germinated seed. Proglacial soil had 12 seedlings per m 2, disturbed Dryas heath 131, intact Dryas heath 91, polar heath 715, thermophilic heath 3113, and a bird cliff 10437 seedlings. Highest seed bank species richness was at the thermophilic heath (26 species). Seedlings of 27 species emerged in the field, with fewer seedlings in disturbed habitats (60 seedlings per m 2 ) than in intact Dryas heath (142), suggesting that an absence of 'safe sites' limited seedling establishment in disturbed habitats. Measurement of seedling emergence in the field increased awareness of which species are able to germinate naturally. This may be underestimated by up to 31% if greenhouse trials alone are used, owing partly to unsuitability of greenhouse conditions for germination of some species and also to practical limitations of amount of soil sampled. Most thermophilic species failed to germinate and some species present at several sites only germinated from the thermophilic heath seed bank, suggesting that climate constrains recruitment from seeds in the High Arctic. [ABSTRACT FROM AUTHOR]

We evaluate the potential influence of disturbance on the predictability of alpine plant species distribution from equilibrium-based habitat distribution models. Firstly, abundance data of 71 plant species were correlated with a comprehensive set of environmental variables using ordinal regression models. Subsequently,the residual spatial autocorrelation (at distances of 40 to 320 m) in these models was explored. The additional amount of variance explained by spatial structuring was compared with a set of functional traits assumed to confer advantages in disturbed or undisturbed habitats. We found significant residual spatial autocorrelation in the habitat models of most of the species that were analysed. The amount of this autocorrelation was positively correlated with the dispersal capacity of the species, levelling off with increasing spatial scale. Both trends indicate that dispersal and colonization processes, whose frequency is enhanced by disturbance, influence the distribution of many alpine plant species. Since habitat distribution models commonly ignore such spatial processes they miss an important driver of local-to landscape-scale plant distribution. [ABSTRACT FROM AUTHOR]

We propose a hierarchical approach for plant functional classification in disturbed ecosystems to be used for vegetation modelling and global plant trait comparisons. Our framework is based on the persistence of plants at different levels of organization. We assume that the main parameters to determine persistence in chronically disturbed ecosystems are those related to: Individual-persistence capacity, Propagule-persistence capacity (persistence at the population level), Competitive capacity (persistence at the community level) and Dispersal capacity (persistence at the landscape level). The IPCD approach is illustrated for fire-prone and grazed ecosystems from the Mediterranean region and Australia and by assuming a binary classification of the four traits determining persistence which give a total 16 possible functional types. The IPCD framework provides a simple structured and synthetic view from which more elaborated schemes can be developed. [ABSTRACT FROM AUTHOR]

In 1991, the catastrophic Typhoon 9119 created many treefall gaps inan old-growth beech (Fagus crenata) forest on Mt. Garyu, southwestern Japan. In a 3.3-ha plot, the density and basal area of fatally damaged trunks (DBH >= 20 cm) were 29.1 trunks/ha (16.9% of all pre-typhoon trunks) and 9.1 m2/ha (24.4% of total pre-typhoon basalarea), respectively. Many of the dominant beech were lost and largertrunks were damaged. The pre- and post-typhoon DBH distribution bothhad an inverse J-shape. Spatial distribution of living trunks was not random but clustered irrespective of typhoon damage or DBH size, suggesting that the stand structure of the study plot would be an unusual one as compared with the previous study stands in Japanese beech forests. The death of pre-typhoon trunks, seemed to die standing or tobe killed by snap-off, occurred singly; however, the typhoon fatallydamaged many clustered trunks at the same time. Uprooting was the most frequent cause of gaps created by the typhoon. The intermediate DBH size class (40 - 70 cm) would be more likely to be uprooted than snapped-off. The DBH distribution of snap-off may reflect the total pre-typhoon trunk distribution. Branch-fall had a flat DBH distribution.Uprooting might have a clustered distribution, while snap-off and branch-fall both had random distributions. The smaller trunks of snap-off and branch-fall seemed to result from injuries caused by the fall of larger trunks. [ABSTRACT FROM AUTHOR]

We studied the effects of windthrow on the understory plant species composition of a pine forest (dominated by Pinus strobus) and an oak forest (dominated by Quercus ellipsoidalis). We recorded the presenceof vascular plant species in randomly located quadrats in the two forests, and in three microsite types associated with tipup mounds (pit, old soil and new soil) in the pine forest at irregular intervals over the course of 14 years. The understories of the two forests remained distinct throughout the study. The frequency of occurrence of a number of forest floor species considerably increased; few species decreased. The disturbance specialists Rubus idaeus and Polygonum cilinode increased in frequency throughout the study in the pine forest, butare beginning to decline in the less disturbed oak forest. Annuals and biennials preferentially colonized the disturbed soil of microsites on tipups, and declined in frequency after about 7 yr. Both forestshave increased in understory species richness, but have not changed substantially in the distribution of growth forms. Despite early differences in species composition, microsite types associated with tipupmounds became more similar through time. Although small in magnitude, there was a directional change in understory composition at both forests, with no apparent sign of a return to pre-disturbance conditions. [ABSTRACT FROM AUTHOR]

Patterns of mortality, recruitment, and forest turnover were investigated using permanent plot data from temperate forests in 14 localities throughout New Zealand. Tree mortality and recruitment rates were calculated from tagged trees =/> 10 cm diameter at 1.4 m on individual 400 m2 plots, and turnover rates were calculated as the mean of mortality and recruitment rates. Turnover rates (1.4% per year) were very similar to those recorded for tropical forests (i.e. 1.5% per year). As was shown in tropical forests, we also found significant relationships between forest turnover and species richness. In New Zealand forests there was also a decrease in species richness and turnover rates with increasing latitude. Although species richness is well known to decline with latitude, our study provides support for apossible link between seasonality and disturbance with tree turnoverand species diversity. While tree mortality and recruitment rates were approximately in balance at some localities, in others there were imbalances between mortality and recruitment rate. [ABSTRACT FROM AUTHOR]

It is not simple to predict how environmental changes may impact tropical forest species diversity. Published hypotheses are almost invariably too incomplete, too poorly specified and too dependent upon unrealistic assumptions to be useful. Ecologists have sought theoreticalsimplicity, and while this has provided many elegant abstract concepts, it has hindered the attainment of more practical goals. The problem is not how to judge the individual hypotheses and arguments, but rather how to build upon and combine the many hard-won facts and principles into an integrated science. Controversy is inevitable when the assumptions, definitions and applications of a given hypothesis are unclear. Elegance, as an end in itself, has too often been used to justify abstract simplification and a lack of operational definition. Clarifying and combining hypotheses while avoiding assumptions providesa potentially more useful, if less elegant, standpoint. An appraisalof Connell's intermediate disturbance hypothesis, and its application to long-term observations from a Ugandan forest illustrates these concerns, Current emphases encourage ecologists to exclude consideration of environmental instability and non-pristine ecosystems. In reality, many environmental changes and ecological processes contribute toboth the accumulation and erosion of diversity, at all spatial and temporal scales. Site histories, contexts, long-term processes, species-pool dynamics, and the role of people require greater emphasis. These considerations reveal that many environmental changes, even those associated with degradation, can lead to a transient rise in species densities. Drawing on related studies, such as forest yield prediction, suggests that the formulation and calibration of simulation modelsprovides the most tractable means to address the complexity of real vegetation. Simulation-based approaches will become increasingly useful both in unifying the study of vegetation dynamics and in providingimpro [ABSTRACT FROM AUTHOR]

Structural dynamics of a natural tropical seasonal - mixed deciduous- forest were studied over a 4-yr period at Mae Klong Watershed Research Station, Kanchanaburi Province, western Thailand, with particular reference to the role of forest fires and undergrowth bamboos. All trees > 5 cm DBH in a permanent plot of 200 m x 200 m were censused every two years from 1992 to 1996. The forest was characterized by a low stem density and basal area and relatively high species diversity.Both the bamboo undergrowth and frequent forest fires could be dominant factors that prevent continuous regeneration. Recruitment, mortality, gain (growth of survival tree plus ingrowth) and loss in basal area (by tree death) during the four years were 6.70%/yr, 2.91%/yr, 1.22%/yr and 1.34%/yr, respectively. Mortality was size dependent; middle size trees (30 - 50 cm) had the lowest mortality, while the smallest (5 - 10 cm) had the highest mortality. Tree recruitment was observed particularly in the first two years, mostly in the area where dieback of undergrowth bamboo occurred. The bias of the spatial distribution of recruitment to the area of bamboo die-back was significant andstronger than that to the forest canopy gaps. Successful regeneration of trees which survive competition with other herbs and trees afterdieback of bamboo could occur when repeated forest fires did not occur in subsequent years. It is suggested that both the fire disturbance regime and bamboo life-cycle greatly influence the structure and dynamics of this seasonal tropical forest. [ABSTRACT FROM AUTHOR]

Structure, diversity and dynamics of five Japanese temperate old-growth forests were compared, differing from each other in. i.a., climate, dominant tree type, topography, disturbance regime. The forests were Aya, Ogawa, Kanumazawa Riparian, Kanumazawa upland and Senju. A permanent plot (1 - 6 ha) was established in each forest and trees werecensused several times at intervals of two years. Mean annual recruitment rates and mortality rates in these forests were both in the range of 0.5 to 4.6%/yr at the community level. Analyses of the structure and dynamics of populations showed that the underlying process was different among the forests. Some forests experienced compositional shifts in their canopies, others had a constant canopy composition butappeared to lack effective regeneration in recent years. The recruitment rate appeared to be strongly affected by competitive undergrowthvegetation such as dwarf bamboo which has been controlled by naturaldisturbance or human impact. It is likely that the forests with mostly low recruitment rates had a low species diversity. The current variation in structure, diversity and dynamics of the studied forests might have been determined not only by physical conditions (e.g. climate) but also by chance factors (e.g. disturbance, outbreak of deer population). [ABSTRACT FROM AUTHOR]

In 1964 a census of all trees > 9.7 cm diameter at breast height (DBH) was conducted on 22 plots totalling 13.2 ha in lowland tropical evergreen rain forest on Kolombangara, Solomon Islands. Over the following 30 yr (1964-1994), populations of all individuals > 4.85 cm DBH of the 12 most common tree species and amounts of disturbance have been monitored on a declining number of these plots (in 1994, nine plotstotalling 5.4 ha were still being recorded). Between November 1967 and April 1970, Kolombangara was struck by four cyclones, although only two of these caused substantial amounts of damage to the canopy structure. Multivariate analysis hits identified six forest types on Kolombangara (Greig-Smith et al. 1967). The species richness and diversity of trees in the 1961 census, turnover rates of the populations monitored over 1964-1975, and the amount of disturbance sustained duringa cyclone in 1970, were all positively correlated across five of theforest types. The sixth forest type was a consistent outlier in these analyses and is believed to have been seriously disturbed by humansabout a century ago. The floristics, turnover and disturbance data support Connell's intermediate disturbance hypothesis. The most species-rich forest types contained a higher proportion of fast-growing individuals are species that are early-successional and which have low density timber. Properties of these species rendered them more susceptible to damage when struck by the 1970 cyclone. They showed higher turnover rates because disturbance-dependent species are also characterised by higher mortality and recruitment rates. Thus, periodic cyclones appear to favour the maintenance of differences in species diversity and composition between forest types. [ABSTRACT FROM AUTHOR]

Can the interaction of episodic and chronic disturbances explain themaintenance of savanna-like patterns? We explored the morphological and spatial patterns of the leguminous shrub Retama sphaerocarpa in aMediterranean environment in relation to disturbance. Various morphological variables of R. sphaerocarpa shrubland were found to be determined by a combination of two types of disturbance: (1) mechanical cutting: an episodic, heavy, short-term disturbance of anthropogenic origin for management purposes, and (2) herbivore activity primarily byrabbits: generally a chronic, more lenient, long-term disturbance. The intensities of these two types of disturbance were not correlated.Mechanical cutting effects on R. sphaerocarpa shrubland morphology predominated quantitatively over herbivore effects. Herbivores generally produced open shrubland with fewer, more scattered, thicker branched, larger R. sphaerocarpa shrubs. In contrast, intense sprouting after cutting produced a higher density of smaller R. sphaerocarpa shrubs with denser aerial biomass. However, heavy herbivory in abnormally dry periods produced some effects similar to those of mechanical cutting. The size of R. sphaerocarpa shrubs was positively related to seed production. Thus, the means of propagation depended upon the type of disturbance: episodic disturbances resulted in intense sprouting, whereas chronic herbivore activity resulted in the formation of thick branches that produced a large number of seeds. The combination of these two disturbances determine, in part, space occupancy patterns of dominant woody species in this Mediterranean landscape and similar savanna-type ecosystems. Investigations of environmental constraints onvegetation distribution and abundance should take into account the historical role of herbivores in shaping present systems. [ABSTRACT FROM AUTHOR]

Long-term regeneration dynamics of Mediterranean maquis was investigated by analysing historical aerial photographs of Mt. Carmel, one ofthe largest protected areas in the Mediterranesaan region of Israel.Two sets of aerial photographs were processed, one from 1960 (beforethe area was protected), and the second from 1992 (21 yr after the area was declared a nature reserve). The photographs of each year wereclassified into three vegetation states based on the percentage cover of trees: open maquis with tree cover <33.3%, moderately developed maquis (tree cover 33.3-66.6%), and closed maquis (tree cover >66.6%). Grid maps constructed from the classified images were used to determine probabilities of transition between vegetation states. Closed maquis showed zero probability of transition to either open or moderately developed maquis. Probabilities of 'forward' transitions (transitions from low-cover to high-cover classes) were higher on north-facingthan on south-facing slopes. On north facing slopes, the area of open maquis decreased from 87% to 46% during the period studied, while that of closed maquis increased from 3% to 29%. On south-facing slopesopen maquis decreased from 87% to 69% while closed maquis increased from 1% to 8%. Within a particular aspect, tree cover in 1960 was a reliable predictor of tree cover in 1992. This indicates that micro-scale patterns of tree distribution in 1960 were important in determining the stucture of the maquis 32 yr later. Simulations based on the empirically derived transition probabilities suggest that, under current climatic conditions, the process of maquis regeneration on Mt. Carmel may take 500-1000 yr. [ABSTRACT FROM AUTHOR]

Mechanical damage by floodwaters is frequently invoked to explain the distribution of riparian plant species, but data have been lacking to relate vegetation to specific estimates of flood damage potential.This research uses detailed estimates of unit stream power (an appropriate measure of the potential for mechanical damage) in conjunctionwith vegetation cover data to test this relationship at 37 valley-bottom sites in the Transverse Ranges of Southern California. A computer program, HEC-2, was used to model the slope and the variation in flow depth and velocity of the 20-yr flood across the sites. Regressionmodels tested the influence of stream power (and of height above thewater table) on the woody species composition of 393 4-m cross-section segments of the valley-bottom sites. Results indicate that unit stream power does have a significant effect on the riparian vegetation,but that the amount of that influence and its importance relative tothe influence of height above the water table varies between watersheds. Some species are found primarily in locations of high stream power, while others are limited to portions of the valley bottom that experience only low stream power. [ABSTRACT FROM AUTHOR]