Showing papers in "Journal of Vegetation Science in 2006"

Trait convergence and trait divergence in herbaceous plant communities: Mechanisms and consequences

Abstract: 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 v...

Statistical determination of diagnostic species for site groups of unequal size

Abstract: Aim: Concentration of species occurrences in groups of classified sites can be quantified with statistical measures of fidelity, which can be used for the determination of diagnostic species. However, for most available measures fidelity depends on the number of sites within individual groups. As the classified data sets typically contain site groups of unequal size, such measures do not enable a comparison of numerical fidelity values of species between different site groups. We therefore propose a new method of measuring fidelity with presence/absence data after equalization of the size of the site groups. We compare the properties of this new method with other measures of statistical fidelity, in particular with the Dufrene-Legendre Indicator Value (IndVal) index. Methods: The size of site groups in the data set is equalized, while relative frequencies of species occurrence within and outside of these groups are kept constant. Then fidelity is calculated using the phi coefficient of associatio...

Effects of altitude and topography on species richness of vascular plants, bryophytes and lichens in alpine communities

Abstract: Question: What is the relationship between species richness of vascular plants, bryophytes and macrolichens, and two important gradients in the alpine environment, altitude and local topography? Location: Northernmost Fennoscandia, 250-1525 m a.s.l. corresponding to the range between timberline and mountain top. Methods: The vegetation was sampled in six mountain areas. For each 25 vertical metres, the local topographic gradient from wind-blown ridge to snowbed was sampled in quadrats of 0.8 m · 0.8 m. Patterns in species richness were explored using Poisson regression (Generalized Linear Models). Functional groups of species, i.e. evergreen and deciduous dwarfshrubs, forbs, graminoids, mosses, hepatics and lichens were investigated separately. Results: Functional groups showed markedly different patterns with respect to both altitude and topography. Species richness of all vascular plants showed a unimodal relationship with altitude. The same was true for graminoids, forbs and lichens analysed separately, but forb richness peaked at much higher altitudes than total richness. The richness of dwarfshrubs decreased monotonically with altitude, whereas richness of mosses and liverworts showed an increasing trend. Significant interactions between altitude and local topography were present for several groups. The unimodal pattern for total plant species richness was interpreted in terms of local productivity, physical disturbance, trophic interactions, and in terms of species pool effects. Conclusions: Patterns in local species richness result from the action of two opposing forces: declining species pool and decreasing intensity of competition with altitude.

Non-parametric habitat models with automatic interactions

Abstract: Questions: Can a statistical model be designed to represent more directly the nature of organismal response to multiple interacting factors? Can multiplicative kernel smoothers be used for this purpose? What advantages does this approach have over more traditional habitat modelling methods? Methods: Non-parametric multiplicative regression (NPMR) was developed from the premises that: the response variable has a minimum of zero and a physiologically-determined maximum, species respond simultaneously to multiple ecological factors, the response to any one factor is conditioned by the values of other factors, and that if any of the factors is intolerable then the response is zero. Key features of NPMR are interactive effects of predictors, no need to specify an overall model form in advance, and built-in controls on overfitting. The effectiveness of the method is demonstrated with simulated and real data sets. Results: Empirical and theoretical relationships of species response to multiple interacting predictors can be represented effectively by multiplicative kernel smoothers. NPMR allows us to abandon simplistic assumptions about overall model form, while embracing the ecological truism that habitat factors interact.

Controls over invasion of Bromus tectorum: The importance of climate, soil, disturbance and seed availability

Abstract: 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.

Ecosystem changes associated with grazing in subhumid South American grasslands

Abstract: Question: What are the changes in vegetation structure, soil attributes and mesofauna associated with grazing in mesic grasslands? Location: Southern Campos of the Rio de la Plata grasslands, in south-central Uruguay. Methods: We surveyed seven continuously grazed and ungrazed paired plots. Plant and litter cover were recorded on three 5-m interception lines placed parallel to the fence in each plot. We extracted soil fauna from a 10 cm deep composite sample and analysed the oribatids. Soil attributes included bulk density, water content, organic carbon (in particulate and mineral associated organic matter) and nitrogen content and root biomass at different depths. Changes in floristic, Plant Functional Types and mesofauna composition were analysed by Non-metric Multidimensional Scaling. Results: Species number was lower in ungrazed than in grazed plots. Of 105 species in grazed plots only three were exotics. Shrub and litter cover were significantly higher inside the exclosures, while the cover of Cyperaceae-Juncaceae was lower. Grazing treatments differed significantly in plant and oribatid species composition.. Grazing exclusion significantly reduced soil bulk density and increased soil water content. Carbon content in particulate organic matter was lower in the upper soil of ungrazed sites, but deeper in the profile, grazing exclosures had 8% more carbon in the mineral associated organic matter. Conclusions: Our results generally agree with previous studies but deviate from the results of previous analyses in (1) the increase of shrub cover in ungrazed sites; (2) the redistribution of the soil organic carbon in the profile and (3) the low invasibility of the prairies regardless of grazing regime.

Dispersal, diversity and distribution patterns in pioneer vegetation: The role of river-floodplain connectivity

Abstract: Question: Are there changes in dispersal patterns in floodplain pioneer vegetation with effects on seedling number, species richness and species composition along a gradient of declining river-floodplain connectivity? Location: Middle Elbe river floodplain, Germany. Methods: An experiment with five treatments was set up along a gradient of declining river-floodplain connectivity, partitioning seedlings into three groups: (1) emerging solely from water dispersed seeds, (2) from wind/animal dispersed seeds and (3) from the soil diaspore bank. Two controls were established: without any manipulation and exclusion of all seeds. The results were compared with those of vegetation and soil sampling to evaluate the representativeness of the experimental sites in terms of species composition, diversity, seedling number and soil parameters. Results: Water dispersal and the soil diaspore bank were the major dispersal strategies shaping floodplain pioneer vegetation at the Middle Elbe river. The number of see...

Effects of plot size on the ordination of vegetation samples

Abstract: Questions: Do ordination patterns differ when based on vegetation samples recorded in plots of different size? If so, how large is the effect of plot size relative to the effects of data set heterogeneity and of using presence/absence or cover-abundance data? Can we combine plots of different size in a single ordination? Methods: Two homogeneous and two heterogeneous data sets were sampled in Czech forests and grasslands. Coverabundances of plant species were recorded in series of five or six nested quadrats of increasing size (forest 49-961 m2; grassland 1-49 m2). Separate ordinations were computed for plots of each size for each data set, using either species presences/absences or cover-abundances recorded on an ordinal scale. Ordination patterns were compared with Procrustean analysis. Also, ordinations of data sets jointly containing plots of different size were calculated; effects of plot size were evaluated using a Monte Carlo test in constrained ordination. Results: The results were consistent between forest and grassland data sets. In homogeneous data sets, the effect of presence/absence vs. cover-abundance was similar to, or larger than, the effect of plot size; for presence/absence data the differences between ordinations of differently sized plots were smaller than for cover-abundance data. In heterogeneous data sets, the effect of plot size was larger than the effect of presenceabsence vs. cover-abundance. The plots of smaller size (≤ 100 m 2 in forests, ≤ 4 m 2 in grasslands) yielded the most deviating ordination patterns. Joint ordinations of differently sized plots mostly did not yield patterns that would be artifacts of different plot size, except for plots from the homogeneous data sets that differed in size by a factor of four or higher. Conclusions: Variation in plot size does influence ordination patterns. Smaller plots tend to produce less stable ordination patterns, especially in data sets with low β-diversity and species cover-abundances. Data sets containing samples from plots of different sizes can be used for ordination if they represent vegetation with large β-diversity. However, if data sets are homogeneous, i.e. with low β-diversity, the differences in plot sizes should not be very large, in order to avoid the danger of plot size differences distorting the real vegetation differentiation in ordination patterns.

When does dead wood turn into a substrate for spruce replacement

Abstract: Question: How many years must elapse for freshly fallen Picea abies stems to be transformed into a substrate for P. abies recruitment? Location: Natural sub-alpine spruce forest, 1200-1300 m a.s.l., western Carpathians, Poland. Methods: Coarse woody debris (CWD) was measured on nine plots with a total area of 4.3 ha. All individuals of P. abies regeneration growing on dead wood were counted and their age was estimated. Decay rate of logs was determined using dendrochronological cross-dating of samples from logs in different decay stages. Results: Although CWD covered only 4% of the forest floor, 43% of the saplings were growing on decaying logs and stumps. The highest abundance of P. abies recruitment occurs on logs 30-60 years after tree death, when wood is in decay stages no. 4-7 (on an 8 degree decay scale). However, much earlier colonization is possible. The first seedlings may germinate on a log during the second decade after tree death and survive for decades. Their slow growth is possibly due to the gradual progressive decomposition of wood. Conclusions: This study confirms the importance of decaying wood for P. abies recruitment. The decaying logs exhibit continuous and favourable conditions for the germination of P. abies seeds throughout their decay process. Logs, irrespective of their decay stage and age, are colonized by young seedlings. This recruitment bank is constantly renewed.

Facilitative succession in a boreal bryophyte community driven by changes in available moisture and light

Abstract: Question: 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 landsc...

Spontaneous vegetation succession in disused gravel-sand pits: Role of local site and landscape factors

Abstract: Questions: What is the variability of succession over a large geographical area? What is the relative importance of (1) local site factors and (2) landscape factors in determining spontaneous vegetation succession? Location: Various regions of the Czech Republic, Central Europe. The regions represent two categories characterized by agrarian lowlands, with a relatively warm and dry climate, and predominant woodland uplands with a relatively cold and wet climate. Methods: Gravel-sand pits ranged in age from 1–75 years since abandonment. Three types of sites were distinguished: dry, wet and hydric in shallow flooded sites. Vegetation releves were recorded with species cover (%) visually estimated using the space-for-time substitution approach. Local site factors, such as water table and soil characteristics, and landscape characteristics, namely climatic parameters, presence of nearby (semi-) natural plant communities and main land cover categories in the wider surroundings, were evaluated. Results:...

Braun-Blanquet's legacy and data analysis in vegetation science

Abstract: This article investigates whether the Braun-Blanquet abundance/dominance (AD) scores that commonly appear in phytosociological tables can properly be analysed by conventional multivariate analysis methods such as Principal Components Analysis and Correspondence Analysis. The answer is a definite NO. The source of problems is that the AD values express species performance on a scale, namely the ordinal scale, on which differences are not interpretable. There are several arguments suggesting that no matter which methods have been preferred in contemporary numerical syntaxonomy and why, ordinal data should be treated in an ordinal way. In addition to the inadmissibility of arithmetic operations with the AD scores, these arguments include interpretability of dissimilarities derived from ordinal data, consistency of all steps throughout the analysis and universality of the method which enables simultaneous treatment of various measurement scales. All the ordination methods that are commonly used, for ...

Effects of sampling time, species richness and observer on the exhaustiveness of plant censuses

Abstract: Question: How may sampling time affect exhaustiveness of vegetation censuses in interaction with observer effect and quadrat species richness? Location: French lowland forests. Methods: Two data sets comprised of 75 timed, one-hour censuses of vascular plants carried out by five observers on 24 400-m2 forest quadrats were analysed using mixed-effect models. Results: The level of exhaustiveness increased in a semi-logarithmic way with sampling time and decreased with quadrat species richness. After one hour, 20 to 30% of the species remained undetected by single observers. This proportion varied among observers and the discrepancy increased with increasing sampling time. Fixing the sampling time may make richness estimates vary less between observers but the time limit should be at least 30 min to reduce the bias in exhaustiveness between rich and poor quadrats. Conclusions: We advocate the use of sampling methods based on spatially or temporally-replicated censuses and statistical analyses that c...

Determinants and spatial modeling of tree β-diversity in a tropical forest landscape in Panama

Abstract: Questions: The objectives of this study were to clarify the extent to which environmental factors and geographical distance account for tropical floristic composition, and propose a methodology for delimiting the boundaries of floristic types based on species similarity. Location: The Panama Canal watershed. Methods: To assess which factors (climate, topography, geology and geographical distance) account for floristic composition, we performed Mantel tests on distance matrices and partitioned variation in species composition using canonical analysis. We used a permutation-based regression model computed on distance matrices and a hierarchical clustering of the tree composition to construct a predictive map of forest types of the Panama Canal Watershed. Results: We found that spatial variation alone explained 2227% of species variation, while the fraction of species variation explained by environmental variables was smaller (1012%); 13-19% of the variation was accounted for by the joint effect of environmental variation and geographic distance. The similarity-based map emphasizes the principal division in tree flora between the drier Pacific side and the wetter Caribbean slopes. Conclusions: The distribution of Panamanian tree species appears to be primarily determined by dispersal limitation, then by environmental heterogeneity. ‘Environmental segregation’ processes do play an important role. Maps of broadscale vegetation patterns based on thorough tree inventories can be used in conservation planning in the tropics.

Seasonal shifts in competition and facilitation in subalpine plant communities of the central Caucasus

Abstract: Question: 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...

Seed bank, seed dispersal and vegetation cover: Colonization along a newly‐created river channel

Abstract: Question: What is the relative importance of the initial seed bank and subsequent seed dispersal for floristic composition of bank vegetation two years after creation of a newly-cut reach of a river channel? Location: River Cole, West Midlands, United Kingdom. Methods: We took bank and bed sediment samples from a 0.5-km reach of a new river channel cut into intact flood-plain. After river diversion, seed samples deposited on artificial turf mats placed on the river banks and flood-plain edge were taken in summer and winter 2002 and 2003. Seed rain samples from funnel traps were taken during summer 2002 and 2003. We undertook greenhouse germination trials to assess viable seed species within these samples. In summer 2004, we surveyed river bank vegetation. Agglomerative cluster analysis was used to investigate floristic similarity between seed bank, seed rain, seed deposition samples and final bank vegetation cover. DCA was used to explore contrasts between the samples and to assess whether these ...

Indirect facilitation and competition in tree species colonization of sub-Mediterranean grasslands

Abstract: Questions: In the absence of herbivores, what is the importance of shrub facilitation for the colonization of grasslands by Fagus sylvatica and Quercus pubescens? Is there an indirect facilitative effect of shrubs on tree seedlings by limiting herb competition? Location: Causse du Larzac, southern Massif Central, France. Methods: We conducted field experiments on the facilitative role of shrubs in seedling emergence and survival, in relation to potential negative effects of shading and the presence of herbs. The effects of shade and herbs on allocation and root morphology were analysed in a pot experiment. Results: According to these experiments, the establishment of both tree species was facilitated by shrubs, but the two species differed in the processes underlying this facilitation. Shade directly facilitates the emergence rate of both species. Shade also indirectly facilitates Fagus survival by limiting herb competition. No indirect facilitation of Quercus survival was detected. These differences reflect variation in the tolerance of herb competition by seedlings of the two species. The tolerance of herb competition by Quercus seedlings allows regeneration over a wide area under each shrub and some regeneration events in grasslands at low grazing intensity. In contrast, for Fagus, only a narrow area under each shrub is suitable; regeneration is zero in grassland. The high tolerance of herb competition by Quercus seedlings may result from the avoidance of root competition. Conclusions: In grasslands with severe drought stress, and almost obligatory shrub facilitation for tree seedling regeneration, the tolerance of herb competition may alter the precise role of facilitation in the colonization process.

Ecological effects of changes in fire regimes in Pinus ponderosa ecosystems in the Colorado Front Range

Abstract: Question: What is the relative importance of low- and high-severity fires in shaping forest structure across the range of Pinus ponderosa in northern Colorado? Location: Colorado Front Range, USA. Methods: To assess severities of historic fires, 24 sites were sampled across an elevation range of 1800 to 2800 m for fire scars, tree establishment dates, tree mortality, and changes in tree-ring growth. Results: Below 1950 m, the high number of fire scars, scarcity of large post-fire cohorts, and lack of synchronous tree mortality or growth releases, indicate that historic fires were of low severity. In contrast, above 2200 m, fire severity was greater but frequency of widespread fires was substantially less. At 18 sites above 1950 m, 34 to 80% of the live trees date from establishment associated with the last moderate- to high-severity fire. In these 18 sites, only 2 to 52% of the living trees pre-date these fires suggesting that fire severities prior to any effects of fire suppression were sufficie...

The distribution and habitat associations of non‐native plant species in urban riparian habitats

Abstract: Questions: 1. What are the distribution and habitat associations of non-native (neophyte) species in riparian zones? 2. Are there significant differences, in terms of plant species diversity, composition, habitat condition and species attributes, between plant communities where non-natives are present or abundant and those where non-natives are absent or infrequent? 3. Are the observed differences generic to non-natives or do individual non-native species differ in their vegetation associations? Location: West Midlands Conurbation (WMC), UK. Methods: 56 sites were located randomly on four rivers across the WMC. Ten 2 m × 2 m quadrats were placed within 15 m of the river to sample vegetation within the floodplain at each site. All vascular plants were recorded along with site information such as surrounding land use and habitat types. Results: Non-native species were found in many vegetation types and on all rivers in the WMC. There were higher numbers of non-natives on more degraded, human-modifi...

Structure and composition of vegetation along an elevational gradient in Puerto Rico.

Abstract: Question: What are the composition, conservation status, and structural and environmental characteristics of eight mature tropical forest plant communities that occur along an elevational gradient. Location: Northeastern Puerto Rico. Methods: We quantified the species composition, diversity, conservation status, and ecological attributes of eight mature tropical forest plant communities in replicated plots located to sample representative components of important forest types occurring along an elevational gradient. A suite of environmental and vegetation characteristics were sampled at each plot and summarized to characterize communities and analyse trends along the elevational gradient. Results: The set of communities included 374 species; 92% were native, 14% endemic, and 4% critical elements (locally endangered) to the island. All communities, occurring within a wide range of patch sizes and degree of conservation protection, showed a high percentage of native species (> 89% per plot). The lowland moist forest communities, occurring within a matrix of urbanization, agriculture, and disturbance, had the highest degree of invasion by exotics. Community descriptions were nested within a variety of hierarchies to facilitate extrapolation of community characteristics to larger ecosystem units. Basal area, above-ground biomass, canopy heights, and mean species richness peaked at mid elevations. Conclusions: It is significant that all of these forest communities continue to be dominated by native species while existing in a matrix of human and natural disturbance, species invasion, and forest regeneration from widespread agriculture. The lowland moist and dry forest types represent a minority of the protected forested areas in Puerto Rico, serve as unique genetic reservoirs, and should be protected.

Forest lichen communities and environment–How consistent are relationships across scales?

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

Patterns of plant invasion along an environmental stress gradient

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 ha...

Vegetation, environment, and time: The origination and termination of ecosystems

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

Changes in the abundance, composition and species richness of mountain vegetation in relation to summer grazing by reindeer

Abstract: 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 i...

Importance and intensity of competition along a fertility gradient and across species

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

Tree regeneration responses to Chusquea montana bamboo die-off in a subalpine Nothofagus forest in the southern Andes

Abstract: Question: 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: Carirrine 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–Dec...

Variables influencing the distribution of epiphytic lichens in heterogeneous areas: A case study for Liguria, NW Italy

Abstract: 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 non-metric 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 press...

What saplings can tell us about forest expansion over natural grasslands

Abstract: Questions: 1. Do the species composition, richness and diversity of sapling communities vary significantly in differently sized patches? 2. Do forest patches of different sizes differ in woody plant colonization patterns? Location: Sao Francisco de Paula, Rio Grande do Sul, Brazil, 29°28' S, 50°13' W. Methods: Three woody vegetation types, differing in structural development (patch size) and recovering for 10 years from cattle and burning disturbances, were sampled on grassland. We analysed the composition and complexity of the woody sapling communities, through relative abundance, richness and diversity patterns. We also evaluated recruitment status (residents vs. colonizers) of species in communities occurring in different forest patch size classes. Results: 1. There is a compositional gradient in sapling communities strongly associated with forest patch area. 2. Richness and diversity are positively correlated to patch area, but only in poorly structured patches; large patches present richness and diversity values similar to small patches. 3. Resident to colonizer abundance ratio increases from nurse plants to large patches. The species number proportion between residents and colonizers is similar in small and large patches and did not differ between these patch types. 4. Large patches presented a high number of exclusive species, while nurse plants and small patches did not. Conclusions: Woody plant communities in Araucaria forest patches are associated with patch structure development. Richness and diversity patterns are linked to patch colonization patterns. Generalist species colonize the understorey of nurse plants and small patches; resident species cannot recruit many new individuals. In large patches, sapling recruitment by resident adults precludes the immigration of new species into the patches, limiting richness and diversity.

Broad‐scale vegetation‐environment relationships in Eurasian high‐latitude areas

Abstract: Question: How is tundra vegetation related to climatic, soil chemical, geological variables and grazing across a very large section of the Eurasian arctic area? We were particularly interested in broad-scale vegetation-environment relationships and how well do the patterns conform to climate-vegetation schemes. Material and Methods: We sampled vegetation in 1132 plots from 16 sites from different parts of the Eurasian tundra. Clustering and ordination techniques were used for analysing compositional patterns. Vegetation-environment relationships were analysed by fitting of environmental vectors and smooth surfaces onto non-metric multidimensional scaling scattergrams. Results: Dominant vegetation differentiation was associated with a complex set of environmental variables. A general trend differentiated cold and continental areas from relatively warm and weakly continental areas, and several soil chemical and physical variables were associated with this broad-scaled differentiation. Especially so...

Specific leaf area as a superior predictor of changes in field layer abundance during forest succession

Abstract: Question: How accurately can a suite of suggested functional traits predict plant species response to succession from semiopen woodland to closed deciduous canopy forest? Location: Southeastern Sweden. Methods: Abundance of 46 field-layer plant species in a temperate deciduous forest, measured as frequency of occupied plots, was estimated in 1961, 1970 and 2003. Abundance change over time across species was tested for correlations with functional traits and literature information on habitat preference. Results: Increase in abundance was positively correlated with specific leaf area (SLA), weakly negatively correlated with seed mass and not significantly correlated with plant height or start, peak and length of the flowering period. Change in abundance was correlated with the Ellenberg light indicator value, whereas no correlations were found with Ellenberg values for nitrogen, calcium and moisture, or forest preference according to the literature. Conclusions: SLA was a better predictor of how field layer plants responded to succession from semi-open woodland to closed canopy forest than empirically-derived measures of habitat preference. The same holds for SLA in relation to seed size, indicating that interactions in the established life-cycle phase are more important than the recruitment phase for species response to succession.