Trade‐offs between savanna woody plant diversity and carbon storage in the Brazilian Cerrado

Incentivizing carbon storage can be a win‐win pathway to conserving biodiversity and mitigating climate change. In savannas, however, the situation is more complex. Promoting carbon storage through woody encroachment may reduce plant diversity of savanna endemics, even as the diversity of encroaching forest species increases. This trade‐off has important implications for the management of biodiversity and carbon in savanna habitats, but has rarely been evaluated empirically. We quantified the nature of carbon‐diversity relationships in the Brazilian Cerrado by analyzing how woody plant species richness changed with carbon storage in 206 sites across the 2.2 million km² region at two spatial scales. We show that total woody plant species diversity increases with carbon storage, as expected, but that the richness of endemic savanna woody plant species declines with carbon storage both at the local scale, as woody biomass accumulates within plots, and at the landscape scale, as forest replaces savanna. The sharpest trade‐offs between carbon storage and savanna diversity occurred at the early stages of carbon accumulation at the local scale but the final stages of forest encroachment at the landscape scale. Furthermore, the loss of savanna species quickens in the final stages of forest encroachment, and beyond a point, savanna species losses outpace forest species gains with increasing carbon accumulation. Our results suggest that although woody encroachment in savanna ecosystems may provide substantial carbon benefits, it comes at the rapidly accruing cost of woody plant species adapted to the open savanna environment. Moreover, the dependence of carbon‐diversity trade‐offs on the amount of savanna area remaining requires land managers to carefully consider local conditions. Widespread woody encroachment in both Australian and African savannas and grasslands may present similar threats to biodiversity.     

Stochastic losses of fire‐dependent endemic herbs revealed by a 65‐year chronosequence of dispersal‐limited woody plant encroachment

The factors responsible for maintaining diverse groundcover plant communities of high conservation value in frequently burned wet pine savannas are poorly understood. While most management involves manipulating extrinsic factors important in maintaining species diversity (e.g., fire regimes), most ecological theory (e.g., niche theory and neutral theory) examines how traits exhibited by the species promote species coexistence. Furthermore, although many ecologists focus on processes that maintain local species diversity, conservation biologists have argued that other indices (e.g., phylogenetic diversity) are better for evaluating assemblages in terms of their conservation value. I used a null model that employed beta‐diversity calculations based on Raup–Crick distances to test for deterministic herbaceous species losses associated with a 65‐year chronosequence of woody species encroachment within each of three localities. I quantified conservation value of assemblages by measuring taxonomic distinctness, endemism, and floristic quality of plots with and without woody encroachment. Reductions in herb species richness per plot attributable to woody encroachment were largely stochastic, as indicated by a lack of change in the mean or variance in beta‐diversity caused by woody encroachment in the savannas studied here. Taxonomic distinctness, endemism, and floristic quality (when summed across all species) were all greater in areas that had not experienced woody encroachment. However, when corrected for local species richness, only average endemism and floristic quality of assemblages inclusive of herbs and woody plants were greater in areas that had not experienced woody encroachment, due to the more restricted ranges and habitat requirements of herbs. Results suggest that frequent fires maintain diverse assemblages of fire‐dependent herb species endemic to the region. The stochastic loss of plant species, irrespective of their taxonomic distinctness, to woody encroachment suggests that the relevance of niche partitioning or phylogenetic diversity to the management of biodiversity in wet pine savannas is minimal.     

Extinction debt in naturally contracting mountain meadows in the Pacific Northwest,USA: varying responses of plants and feeding guilds of nocturnal moths

Fire suppression and climate change are leading to habitat fragmentation in temperate montane meadows across the globe, raising concerns about biodiversity loss. Restoration strategies may depend on the rate and nature of species response to habitat loss. We examined the effects of habitat loss and fragmentation on plants and nocturnal moths in natural montane meadows in the western Cascades, Oregon, USA, using generalized additive mixed models, non-metric multidimensional scaling, and multiple response permutation procedure. Historic (1949) rather than current (2005) meadow size explained species richness of herbaceous plants and herb-feeding moths and meadow plant community structure, indicating that loss of meadow species may be delayed by many decades following loss of meadow habitat, resulting in an extinction debt. In contrast, abundance of herb-feeding moths and species richness and abundance of woody plant-feeding moths were related to recent meadow configuration: as meadows are invaded by woody plants, abundance of meadow species declines, and woody plants and associated moths increase. Despite decades of fire suppression and climate change, montane meadows in many temperate mountain landscapes may still be amenable to restoration.     

Potential extinction debt due to habitat loss and fragmentation in subalpine moorland ecosystems

Habitat loss and fragmentation would often induce delayed extinction, referred to as extinction debt. Understanding potential extinction debts would allow us to reduce future extinction risk by restoring habitats or implementing conservation actions. Although growing empirical evidence has predicted extinction debts in various ecosystems exposed to direct human disturbances, potential extinction debts in natural ecosystems with minimal direct human disturbance are little studied. Ongoing climate change may cause habitat loss and fragmentation, particularly in natural ecosystems vulnerable to environmental change, potentially leading to future local extinctions. Recent climate change would lead to extended growing season caused by earlier snowmelt in spring, resulting in expansion of shrubby species and thereby habitat loss and fragmentation of mountainous moorlands. We examined the potential extinction debts of species diversity and functional diversity (FD; trait variation or multivariate trait differences within a community) in subalpine moorland ecosystems subjected to few direct human disturbances. Plant species richness for all species and for moorland specialists were primarily explained by the past kernel density of focal moorlands (a proxy for spatial clustering of moorlands around them) but not the past area of the focal moorlands, suggesting potential extinction debt in subalpine moorland ecosystems. The higher kernel density of the focal moorland in the past indicates that it was originally surrounded by more neighborhood moorlands and/or had been locally highly fragmented. Patterns in current plant species richness have been shaped by the historical spatial configuration of moorlands, which have disappeared over time. In contrast, we found no significant relationships between the FD and historical and current landscape variables depicting each moorland. The prevalence of trait convergence might result in a less sensitive response of FD to habitat loss and fragmentation compared to that of species richness. Our finding has an important implication that climate change induced by human activities may threaten biodiversity in natural ecosystems through habitat loss and fragmentation.

     

Diversity of gall wasps (Hymenoptera: Cynipidae) associated with oak trees (Fagaceae: <Emphasis Type="Italic">Quercus</Emphasis>) in a fragmented landscape in Mexico

Habitat fragmentation reduces the available habitat area and increases both the distance between fragments and the amount of fragment edges. Therefore, there are more probabilities of plant population size reduction and species extinction. In the same way, biotic and abiotic changes associated with forest fragmentation can dramatically alter plant growth and phenological patterns. We conducted a 3-year study to analyze effects of habitat fragmentation and seasonal variation on host plant quality (quantity of leaves, diameter at breast height, tree height), gall abundance and species richness in a temperate oak forest. Our results show that host plant quality was significantly higher in isolated oaks and small fragments, increasing the abundance and species richness of oak gall wasp species in most fragmented habitats. Oak canopy cover is altered by forest fragmentation, there being higher production of leaves on trees that are more exposed to fragmentation, and can provide important resources for maintaining gall wasp species diversity in a fragmented landscape. We found higher gall wasp richness and abundance in autumn than in the spring, which matches with the higher quantity of leaves in this season.     

Ecosystem responses to woody plant encroachment in a semiarid savanna rangeland

Woody plant encroachment alters the structure and function of rangeland ecosystems. The objective of this study was to explore the association between woody plant encroachment and various ecosystem properties (i.e. vascular plant species diversity, richness, evenness, soil organic matter, herbaceous biomass, leaf litter and bare ground cover) in a semiarid savanna rangeland, and also to test whether the relationships were influenced by woody species composition, elevation and site. We carried out a vegetation survey in four rangeland sites in the lower Omo region of southwestern Ethiopia, and regressed each one of the ecosystem properties, separately, against woody plant density, elevation and site using multiple linear regressions. We found that vascular plant species diversity, richness and evenness increased with woody plant density, most likely due to increased spatial heterogeneity and soil microclimate improvement. Bare ground cover increased significantly, whereas herbaceous biomass and soil organic matter did not respond to woody encroachment. In a subsequent investigation, we used a redundancy analysis to assess whether ecosystem properties were influenced by the identity of encroaching woody plant species. Species diversity and richness responded positively to Lannea triphylla, whereas leaf litter responded positively to Grewia tenax and G. villosa. Our findings suggest that woody plant encroachment in a semiarid rangeland does alter ecosystem properties. However, its impact is highly variable, influenced by a set of factors including the level of encroachment and identity of encroaching woody species.     

Characterising extinction debt following habitat fragmentation using neutral theory

Habitat loss leads to species extinctions, both immediately and over the long term as ‘extinction debt’ is repaid. The same quantity of habitat can be lost in different spatial patterns with varying habitat fragmentation. How this translates to species loss remains an open problem requiring an understanding of the interplay between community dynamics and habitat structure across temporal and spatial scales. Here we develop formulas that characterise extinction debt in a spatial neutral model after habitat loss and fragmentation. Central to our formulas are two new metrics, which depend on properties of the taxa and landscape: ‘effective area’, measuring the remaining number of individuals and ‘effective connectivity’, measuring individuals’ ability to disperse through fragmented habitat. This formalises the conventional wisdom that habitat area and habitat connectivity are the two critical requirements for long‐term preservation of biodiversity. Our approach suggests that mechanistic fragmentation metrics help resolve debates about fragmentation and species loss.     

Effects of contemporary environment and Quaternary climate change on drylands plant diversity differ between growth forms

Previous studies on large‐scale patterns in plant richness and underlying mechanisms have mostly focused on forests and mountains, while drylands covering most of the world's grasslands and deserts are more poorly investigated for lack of data. Here, we aim to 1) evaluate the plant richness patterns in Inner Asian drylands; 2) compare the relative importance of contemporary environment, historical climate, vegetation changes, and mid‐domain effect (MDE); and 3) explore whether the dominant drivers of species richness differ across growth forms (woody vs herbaceous) and range sizes (common vs rare). Distribution data and growth forms of 13 248 seed plants were compiled from literature and species range sizes were estimated. Generalized linear models and hierarchical partitioning were used to evaluate the relative contribution of different factors. We found that habitat heterogeneity strongly affected both woody and herbaceous species. Precipitation, climate change since the mid‐Holocene and climate seasonality dominated herbaceous richness patterns, while climate change since the Last Glacial Maximum dominated woody richness patterns. Rare species richness was strongly correlated with precipitation, habitat heterogeneity and historical climatic changes, while common species richness was strongly correlated with MDE (woody) or climate seasonality (herbaceous). Temperature had little effects on the species richness patterns of all groups. This study represents the first evaluation of the large‐scale patterns of plant species richness in the Inner Asian drylands. Our results suggest that increasing water deficit due to anthropogenic activities combined with future global warming may increase the extinction risk of many grassland species. Rare species (both herbaceous and woody) may face severe challenges in the future due to increased habitat destruction caused by urbanization and resource exploitation. Overall, our findings indicate that the hypotheses on species richness patterns based on woody plants alone can be insufficient to explain the richness patterns of herbaceous species.     

Relationship of butterfly diversity with nectar plant species richness in and around the Aokigahara primary woodland of Mount Fuji,central Japan

We examined the relationships between the diversities of vegetation, adult nectar plants, and butterflies in and around the Aokigahara primary woodland on the northwestern footslopes of Mount Fuji, central Japan. The results showed that the nectar resource utilization by adult butterflies was significantly biased to herbaceous plants, especially to perennials, compared to woody species, although most of the study area was in and near a primary woodland. There were greater nectar plant species in sites with greater plant species richness. Among the butterfly community indices analyzed, the strongest correlation was detected between butterfly species richness and nectar plant species richness at each site. Another close correlation was detected between the species richness of nectar plants and herbaceous plants at each site. These results suggest that herbaceous plant species richness in a habitat plays a central role in its nectar plant species richness, and the nectar plant richness is a highly important factor supporting its adult butterfly species richness. Consequently, we propose that the maintenance and management of herbaceous plant species richness in a butterfly habitat, which lead to those of its nectar plant species richness, are very important for conservation of butterfly diversity even in and around woodland landscapes of temperate regions.     

Do asynchronies in extinction debt affect the structure of trophic networks? A case study of antagonistic butterfly larvae–plant networks

Habitat loss and fragmentation affect species richness in fragmented habitats and can lead to immediate or time‐delayed species extinctions. Asynchronies in extinction and extinction debt between interacting species may have severe effects on ecological networks. However, these effects remain largely unknown. We evaluated the effects of habitat patch and landscape changes on antagonistic butterfly larvae–plant trophic networks in Mediterranean grasslands in which previous studies had shown the existence of extinction debt in plants but not in butterflies. We sampled current species richness of habitat‐specialist and generalist butterflies and vascular plants in 26 grasslands. We assessed the direct effects of historical and current patch and landscape characteristics on species richness and on butterfly larvae–plant trophic network metrics and robustness. Although positive species‐ and interactions–area relationships were found in all networks, structure and robustness was only affected by patch and landscape changes in networks involving the subset of butterfly specialists. Larger patches had more species (butterflies and host plants) and interactions but also more compartments, which decreased network connectance but increased network stability. Moreover, most likely due to the rescue effect, patch connectivity increased host‐plant species (but not butterfly) richness and total links, and network robustness in specialist networks. On the other hand, patch area loss decreased robustness in specialist butterfly larvae–plant networks and made them more prone to collapse against host plant extinctions. Finally, in all butterfly larvae–plant networks we also detected a past patch and landscape effect on network asymmetry, which indicates that there were different extinction rates and extinction debts for butterflies and host plants. We conclude that asynchronies in extinction and extinction debt in butterfly–plant networks provoked by patch and landscape changes caused changes in species richness and network links in all networks, as well as changes in network structure and robustness in specialist networks.     

Spatial scaling of ecosystem C and N in a subtropical savanna landscape

Widely occurred woody encroachment in grass‐dominated ecosystems has the potential to influence soil organic carbon (SOC) and total nitrogen (TN) pools at local, regional, and global scales. Evaluation of this potential requires assessment of both pool sizes and their spatial patterns. We quantified SOC and TN, their relationships with soil and vegetation attributes, and their spatial scaling along a catena (hill‐slope) gradient in the southern Great Plains, USA where woody cover has increased substantially over the past 100 years. Quadrat variance analysis revealed spatial variation in SOC and TN at two scales. The larger scale variation (40–45 m) was approximately the distance between centers of woody plant communities and their adjoining herbaceous patches. The smaller scale variation (10 m) appeared to reflect the local influence of shrubs on SOC and TN. Litter, root biomass, shrub, and tree basal area (a proxy for plant age) exhibited not only similar spatial scales, but also strong correlations with SOC and TN, suggesting invasive woody plants alter both the storage and spatial scaling of SOC and TN through ecological processes related primarily to root turnover and, to a lesser extent litter production, as mediated by time of occupancy. Forb and grass biomass were not significantly correlated with SOC and TN suggesting that changes in herbaceous vegetation have not been the driving force for the observed changes in SOC and TN. Because SOC and TN varied at two scales, it would be inappropriate to estimate SOC and TN pools at broad scales by extrapolating from point sampling at fine scales. Sampling designs that capture variation at multiple scales are required to estimate SOC and TN pools at broader scales. Knowledge of spatial scaling and correlations will be necessary to design field sampling protocols to quantify the biogeochemical consequences of woody plant encroachment at broad scales.     

Habitat fragmentation and species diversity in competitive communities

Habitat loss is one of the key drivers of the ongoing decline of biodiversity. However, ecologists still argue about how fragmentation of habitat (independent of habitat loss) affects species richness. The recently proposed habitat amount hypothesis posits that species richness only depends on the total amount of habitat in a local landscape. In contrast, empirical studies report contrasting patterns: some find positive and others negative effects of fragmentation per se on species richness. To explain this apparent disparity, we devise a stochastic, spatially explicit model of competitive species communities in heterogeneous habitats. The model shows that habitat loss and fragmentation have complex effects on species diversity in competitive communities. When the total amount of habitat is large, fragmentation per se tends to increase species diversity, but if the total amount of habitat is small, the situation is reversed: fragmentation per se decreases species diversity.     

Savanna woody encroachment is widespread across three continents

Tropical savannas are a globally extensive biome prone to rapid vegetation change in response to changing environmental conditions. Via a meta‐analysis, we quantified savanna woody vegetation change spanning the last century. We found a global trend of woody encroachment that was established prior the 1980s. However, there is critical regional variation in the magnitude of encroachment. Woody cover is increasing most rapidly in the remaining uncleared savannas of South America, most likely due to fire suppression and land fragmentation. In contrast, Australia has experienced low rates of encroachment. When accounting for land use, African savannas have a mean rate annual woody cover increase two and a half times that of Australian savannas. In Africa, encroachment occurs across multiple land uses and is accelerating over time. In Africa and Australia, rising atmospheric CO₂, changing land management and rainfall are likely causes. We argue that the functional traits of each woody flora, specifically the N‐fixing ability and architecture of woody plants, are critical to predicting encroachment over the next century and that African savannas are at high risk of widespread vegetation change.     

A patch-dynamics approach to savanna dynamics and woody plant encroachment – Insights from an arid savanna

The coexistence of woody and grassy plants in savannas has often been attributed to a rooting-niche separation (two-layer hypothesis). Water was assumed to be the limiting resource for both growth forms and grasses were assumed to extract water from the upper soil layer and trees and bushes from the lower layers. Woody plant encroachment (i.e. an increase in density of woody plants often unpalatable to domestic livestock) is a serious problem in many savannas and is believed to be the result of overgrazing in ‘two-layer systems’. Recent research has questioned the universality of both the two-layer hypothesis and the hypothesis that overgrazing is the cause of woody plant encroachment.

We present an alternative hypothesis explaining both tree–grass coexistence and woody plant encroachment in arid savannas. We propose that woody plant encroachment is part of a cyclical succession between open savanna and woody dominance and is driven by two factors: rainfall that is highly variable in space and time, and inter-tree competition. In this case, savanna landscapes are composed of many patches (a few hectares in size) in different states of transition between grassy and woody dominance, i.e. we hypothesize that arid savannas are patch-dynamic systems. We summarize patterns of tree distribution observed in an arid savanna in Namibia and show that these patterns are in agreement with the patch-dynamic savanna hypothesis. We discuss the applicability of this hypothesis to fire-dominated savannas, in which rainfall variability is low and fire drives spatial heterogeneity.

We conclude that field studies are more likely to contribute to a general understanding of tree–grass coexistence and woody plant encroachment if they consider both primary (rain and nutrients) and secondary (fire and grazing) determinants of patch properties across different savannas.     

Plant species coexistence at local scale in temperate swamp forest: test of habitat heterogeneity hypothesis

It has been suggested that a heterogeneous environment enhances species richness and allows for the coexistence of species. However, there is increasing evidence that environmental heterogeneity can have no effect or even a negative effect on plant species richness and plant coexistence at a local scale. We examined whether plant species richness increases with local heterogeneity in the water table depth, microtopography, pH and light availability in a swamp forest community at three local spatial scales (grain: 0.6, 1.2 and 11.4 m). We also used the variance partitioning approach to assess the relative contributions of niche-based and other spatial processes to species occurrence. We found that heterogeneity in microtopography and light availability positively correlated with species richness, in accordance with the habitat heterogeneity hypothesis. However, we recorded different heterogeneity-diversity relationships for particular functional species groups. An increase in the richness of bryophytes and woody plant species was generally related to habitat heterogeneity at all measured spatial scales, whereas a low impact on herbaceous species richness was recorded only at the 11.4 m scale. The distribution of herbaceous plants was primarily explained by other spatial processes, such as dispersal, in contrast to the occurrence of bryophytes, which was better explained by environmental factors. Our results suggest that both niche-based and other spatial processes are important determinants of the plant composition and species turnover at local spatial scales in swamp forests.     

Contrasting effects of habitat quantity and quality on moth communities in fragmented landscapes

Habitat loss is commonly identified as a major threat to the loss of global biodiversity. In this study, we expand on our previous work by addressing the question of how lepidopteran species richness and composition vary among remnants of North American eastern deciduous forest located within agricultural or pastoral landscapes. Specifically, we tested the relative roles of habitat quantity (measured as stand area and percent forest in the greater landscape) and habitat quality (measured as tree species diversity) as determinants of moth species richness. We sampled >19 000 individuals comprising 493 moth species from 21 forest sites in two forested ecoregions. In the unglaciated Western Allegheny Plateau, the species richness of moths with woody host plants diminished as forest stand size and percent forest in the landscape decreased, but the total species richness and abundance of moths were unaffected by stand size, percent forest in the landscape, or tree species diversity. In contrast, the overall species richness and abundance of moths in the glaciated North Central Tillplain were affected primarily by tree species diversity and secondarily by forest size. Higher tree species diversity may reduce species loss from smaller forest stands, suggesting that small, diverse forests can support comparable numbers of species to those in less diverse, large stands. Smaller forests, however, contained a disproportionate number of moth species that possess larvae known to feed on herbaceous vegetation. Thus, although woody plant feeding moths are lost from forests with changes in stand area, new species appear capable of recolonizing smaller fragments from the surrounding habitat matrix. Our study further suggests that when species replacement occurs, local patch size and habitat quality may be more important than landscape context in determining the community structure of forest Lepidoptera.     

Traits related to species persistence and dispersal explain changes in plant communities subjected to habitat loss

Aim Habitat fragmentation is a major driver of biodiversity loss but it is insufficiently known how much its effects vary among species with different life‐history traits; especially in plant communities, the understanding of the role of traits related to species persistence and dispersal in determining dynamics of species communities in fragmented landscapes is still limited. The primary aim of this study was to test how plant traits related to persistence and dispersal and their interactions modify plant species vulnerability to decreasing habitat area and increasing isolation. Location Five regions distributed over four countries in Central and Northern Europe. Methods Our dataset was composed of primary data from studies on the distribution of plant communities in 300 grassland fragments in five regions. The regional datasets were consolidated by standardizing nomenclature and species life‐history traits and by recalculating standardized landscape measures from the original geographical data. We assessed the responses of plant species richness to habitat area, connectivity, plant life‐history traits and their interactions using linear mixed models. Results We found that the negative effect of habitat loss on plant species richness was pervasive across different regions, whereas the effect of habitat isolation on species richness was not evident. This area effect was, however, not equal for all the species, and life‐history traits related to both species persistence and dispersal modified plant sensitivity to habitat loss, indicating that both landscape and local processes determined large‐scale dynamics of plant communities. High competitive ability for light, annual life cycle and animal dispersal emerged as traits enabling species to cope with habitat loss. Main conclusions In highly fragmented rural landscapes in NW Europe, mitigating the spatial isolation of remaining grasslands should be accompanied by restoration measures aimed at improving habitat quality for low competitors, abiotically dispersed and perennial, clonal species.     

Spatial heterogeneity and habitat configuration overcome habitat composition influences on alpha and beta mammal diversity

The effects of habitat fragmentation on different taxa and ecosystems are subject to intense debate, and disentangling them is of utmost importance to support conservation and management strategies. We evaluated the importance of landscape composition and configuration, and spatial heterogeneity to explain α- and β-diversity of mammals across a gradient of percent woody cover and land use diversity. We expected species richness to be positively related to all predictive variables, with the strongest relationship with landscape composition and configuration, and spatial heterogeneity respectively. We also expected landscape to influence β-diversity in the same order of importance expected for species richness, with a stronger influence on nestedness due to deterministic loss of species more sensitive to habitat disturbance. We analyzed landscape structure using: (a) landscape metrics based on thematic maps and (b) image texture of a vegetation index. We compared a set of univariate explanatory models of species richness using AIC, and evaluated how dissimilarities in landscape composition and configuration and spatial heterogeneity affect β-diversity components using a Multiple Regression on distance Matrix. Contrary with our expectations, landscape configuration was the main driver of species richness, followed by spatial heterogeneity and last by landscape composition. Nestedness was explained, in order of importance, by spatial heterogeneity, landscape configuration, and landscape composition. Although conservation policies tend to focus mainly on habitat amount, we advocate that landscape management must include strategies to preserve and improve habitat quality and complexity in natural patches and the surrounding matrix, enabling landscapes to harbor high species diversity.     

Regional variation in abundance and response to fire by Henslow's Sparrows in Louisiana

ABSTRACT Wintering Henslow's Sparrows (Ammodramus henslowii) are generally associated with open grasslands. Results of small‐scale, regionally specific studies have not revealed larger‐scale abundance patterns, but they have shown regional differences in habitat selection. Our objective was to quantify Henslow's Sparrow abundance and vegetation associations across Louisiana, an area that includes multiple types of grassland habitats. Bird densities in longleaf pine savannas of eastern and western Louisiana were over 1.5 times higher than in northern prairies and over 13 times higher than at a site in southwestern Louisiana. The responses of Henslow's Sparrows to fire differed between eastern and western savannas, with abundance increasing three fold over the first 3 yrs after fire in the west, and decreasing three fold over that interval in the east. In both areas, habitat became unsuitable by about 5 yrs after fire, probably due to woody encroachment and loss of herbaceous plants. For sites that contained Henslow's Sparrows at least once during our study, habitat modeling revealed that neither vegetation structure nor plant species composition was important in predicting the occurrence of Henslow's Sparrows within sites or abundance among sites throughout the state, perhaps due to the variety of habitats sampled. Our results suggest that longleaf pine savannas are the most important grasslands for wintering Henslow's Sparrows in Louisiana and that overwintering habitat is probably selected based on regionally specific vegetation features. Optimal fire intervals may vary regionally, particularly between mesic flatwoods savannas and drier upland savannas, perhaps due to different rates of biomass accumulation. Management for Henslow's Sparrows should be based on region‐specific studies, recognizing that appropriate fire regimes may vary among regions.     

Floristic patterns and plant traits of Mediterranean communities in fragmented habitats

Aim To contrast floristic spatial patterns and the importance of habitat fragmentation in two plant communities (grassland and scrubland) in the context of ecological succession. We ask whether plant assemblages are affected by habitat fragmentation and, if so, at what spatial scale? Does the relative importance of the niche differentiation and dispersal‐limitation mechanisms change throughout secondary succession? Is the dispersal‐limitation mechanism related to plant functional traits? Location A Mediterranean region, the massif of Albera (Spain). Methods Using a SPOT satellite image to describe the landscape, we tested the effect of habitat fragmentation on species composition, determining the spatial scale of the assemblage response. We then assessed the relative importance of dispersal‐related factors (habitat fragmentation and geographical distance) and environmental constraints (climate‐related variables) influencing species similarity. We tested the association between dispersal‐related factors and plant traits (dispersal mode and life form). Results In both community types, plant composition was partially affected by the surrounding vegetation. In scrublands, animal‐dispersed and woody plants were abundant in landscapes dominated by closed forests, whereas wind‐dispersed annual herbs were poorly represented in those landscapes. Scrubby assemblages were more dependent on geographical distance, habitat fragmentation and climate conditions (temperature, rainfall and solar radiation); grasslands were described only by habitat fragmentation and rainfall. Plant traits did not explain variation in spatial structuring of assemblages. Main conclusions Plant establishment in early Mediterranean communities may be driven primarily by migration from neighbouring established communities, whereas the importance of habitat specialization and community drift increases over time. Plant life forms and dispersal modes did not explain the spatial variation of species distribution, but species richness within the community with differing plant traits was affected by habitat patchiness.