Past Landscape Structure Research Articles

Linking watershed formation with the phylogenetic distribution of a soil microscopic fungus in Yunnan Province, China

BackgroundPhylogeographic studies have gained prominence in linking past geological events to the distribution patterns of biodiversity, primarily in mountainous regions. However, such studies often focus on plant taxa, neglecting the intricate biogeographical patterns of microbes, particularly soil microbial communities. This article explores the spatial distribution of the nematode-trapping fungus Arthrobotrys oligospora, a widespread microorganism, in a tectonically active region at the southeastern edge of the Qinghai-Tibetan Plateau. By analysing the genetic variation of this fungus alongside the historical structure of major river watersheds, we sought to uncover potential connections between the two. Our study involved sampling 149 strains from 116 sites across six major watersheds in the region.ResultsThe resulting haplotype network revealed five distinct clusters, each corresponding closely to a specific watershed. These clusters exhibited high haplotype diversity and low nucleotide diversity, supporting the notion of watershed-based segregation. Further analysis of haplotypes shared across watersheds provided evidence for three proposed past river connections. In particular, we found numerous shared haplotypes between the Yangtze and Mekong basins, as well as between the Yangtze and the Red basins. Evidence for a Irrawaddy-Salween-Red and a Yangtze-Pearl-Red river connections were also portrayed in our mapping exercise.ConclusionsThese findings emphasize the crucial role of historical geomorphological events in shaping the biogeography of microbial biodiversity, alongside contemporary biotic and abiotic factors. Watershed perimeters emerged as effective predictors of such patterns, suggesting their suitability as analytical units for regional-scale studies. Our study also demonstrates the potential of microorganisms and phylogeographic approaches to complement traditional geological analyses, providing a more comprehensive understanding of past landscape structure and its evolution.

Past landscape structure drives the functional assemblages of plants and birds

Landscape structure is a major driver of biodiversity in agricultural landscapes. However, the response of biodiversity can be delayed after landscape changes. This study aimed to determine the effect of current and past landscape structure on plant and bird assemblages. We used a trait-based approach to understand their responses to landscape simplification and habitat fragmentation. We quantified landscape structure at three different years (1963, 1985, 2000) and sampled current plant and bird assemblages in twenty 1 km2 landscape windows located along the Seine Valley (France). For each window, we calculated plant and bird species richness, Community Weighted Variance (CWV), and Community Weighted Mean (CWM) of five functional traits related to dispersal capacity, reproduction, and life-cycle. We detected non-random patterns of traits for both taxa. Plant and bird species richness was lower in simple landscapes. The functional variance of plant traits was higher in landscapes simple in configuration. Both plant and bird assemblages strongly responded to past landscapes, especially their traits related to reproduction and life-cycle. It suggests that landscapes of the Seine valley will face a functional extinction debt. Further research is needed to better predict the delayed response of biodiversity expected to occur after landscape structure changes.

Genetic variation of litter meadow species reflects gene flow by hay transfer and mowing with agricultural machines

Litter meadows, historically established for litter production, are species-rich and diverse ecosystems. These meadows drastically declined during the last decades along with decreasing litter use in modern livestock housing. The aim of our study was to identify the drivers of genetic variation in litter meadow species. Therefore, we tested whether genetic diversity and differentiation depend on habitat age, landscape structure, habitat quality, and/or population size. We analysed 892 individuals of Angelica sylvestris, Filipendula ulmaria, and Succisa pratensis from 20 litter meadows across the Allgäu in Baden-Württemberg (Germany) using AFLP analyses. All study species showed moderate levels of genetic diversity, while genetic differentiation among populations was low. Neither genetic diversity nor differentiation were clearly driven by habitat age. However, landscape structure, habitat quality as well as population size revealed different impacts on the genetic diversity of our study species. Past and present landscape structures shaped the genetic diversity patterns of A. sylvestris and F. ulmaria. The genetic diversity of F. ulmaria populations was, moreover, influenced by the local habitat quality. S. pratensis populations seemed to be affected only by population size. All explanatory variables represent past as well as present gene flow patterns by anthropogenic land use. Therefore, we assume that genetic diversity and differentiation were shaped by both historical creation of litter meadows via hay transfer and present mowing with agricultural machines. These land use practices caused and still cause gene flow among populations in the declining habitats.

Effects of Past and Present-Day Landscape Structure on Forest Soil Microorganisms

Theory surrounding landscape ecology have been built on the species distribution of birds and plants, but increasing evidence now exists for below-ground organisms, whose dispersal may also be affected by above-ground landscape structures. Uncertainties remain for how communities of microorganisms respond to landscape structure over time, and whether some groups of microorganisms react more than others. Here, we investigated if fungal or bacterial diversity is driven by the amount of forest cover in the current or the past landscape. We tested the Habitat Amount Hypothesis (HAH) on ancient forests of the Cevennes national park, that experienced increased fragmentation 150 years ago, and are today surrounded by recent forests. As ancient forests are often more diverse in plant species, we hypothesized that the higher quantity of ancient forests in the landscape, the richer local fungal and bacterial communities would be. More precisely, we expected that ectomycorrhizal fungi, and pathotrophic fungi, often indicators of mature forests, would be also more sensitive to forest history and therefore to the quantity of ancient forests than bacteria and saprotrophic fungi. We sampled 40 soil cores per 0.5 ha, pooled in 8 composite samples per plot in 27 landscapes and sequenced ITS and 16S markers by Illumina-Mi seq. To identify functional groups of fungi, we relied on their taxonomy and the use of public databases. Our results partly follow the HAH, as fungal richness was positively related with the quantity of ancient forests in the landscape and not by the focal patch size. Ectomycorrhizal and pathotrophic fungi were positively affected by the ancient forest cover, and so were saprotrophic ones, but not bacteria. Local factors also shaped the communities such as soil composition and elevation, confirming classical patterns in soil microbial ecology. Interestingly, past landscape structure was better at explaining fungal community richness than contemporary landscape, suggesting a time lag in the response of communities to landscape modification and a potential extinction debt. Our results reveal the importance of below-ground communities in studies of landscape and historical ecology, with their structure and functions likely to be intimately linked with soil and landscape history.

Fire and hydrologically mediated diversity change in subalpine forests through the Holocene

AbstractQuestionsWe consider whether: (a) fire frequency and hydrologic trends drive changes in subalpine forest community diversity and; (b) if there are cumulative effects on diversity when frequent fire and hydrologic drying occur synchronically?LocationWe use three high elevation sites from Wyoming, USA to investigate the response and resiliency of subalpine forests in the Rocky Mountains to centennial‐to‐millennial drought and fire disturbances in regards to shifts in pollen richness, evenness and diversity.Methods‘We examine ecological changes measured by pollen richness, evenness and diversity between subalpine communities under drying and wetting conditions to determine if there is an amplified effect when differing fire frequencies are considered. Using the inverse Simpson index of pollen diversity on pollen percentages as an estimate of biodiversity.ResultsPeriods of frequent fire display significantly higher diversity (p < 0.05) than periods of infrequent or intermediate fire return intervals regardless of hydrologic trends at Little Windy Hill Pond. Further, sites in the northern and southern Rocky Mountains appear to operate under differing fire regimes with sites in the northern Rocky Mountains not recording periods of frequent fire (>225 year mean fire return interval) through the Holocene.ConclusionsChanges in past pollen abundance and diversity have the ability to capture past landscape structure and ecosystem turnover prior to European settlement of the Americas. If fire regimes in subalpine forests of the Rocky Mountains continue trending towards higher frequencies there is the potential for these areas to experience an increase in vegetation diversity.

Effect of present and past landscape structures on the species richness and composition of ground beetles (Coleoptera: Carabidae) and spiders (Araneae) in a dynamic landscape

Species diversity may have time-lagged responses to landscape changes, but whether species are more strongly related to present or past landscape could vary with the taxa or functional traits. In this study, the effects of present and past landscape structures on carabid and spider communities were investigated. We hypothesized that present landscape structure was more highly correlated to small, omnivorous or macropterous carabids and small or ground-hunting spiders, while past landscape structure was more highly correlated to large or predatory carabids and large spiders. We analyzed landscape data from 1955, 1977, 1984, 1993 and 2013 and species data from 1995 and 2013 within the suburb of Qianjiang, a city in China. We found that both past and present landscape metrics affected present species richness in 1995 and species composition in 2013 due to the correlation between past and present landscape metrics. The time delay or immediate response of species was species-specific and not dependent on different groups in relation to body size, wing morphology, dietary preference or foraging method. The stable landscape structure from 1984 to 1993 had the greatest impact on species richness in 1995. In addition, the semi-natural land without dramatic changes since 1977 significantly affected the carabid species diversity. In addition, the excessive increase in building lands from 1993 to 2013 also significantly affected species composition in 2013. Our studies suggested that both historical and present landscape structures, the magnitude of land use change and each species’ traits should be the focus of biodiversity conservation activities.

A stronger influence of past rather than present landscape structure on present plant species richness of road-field boundaries

Road verges provide a refuge for numerous plant species, especially in agroecosystems characterized for decades by a general decline in semi-natural habitats and edge density. Beyond the influence of present landscape structure on the local structure and composition of plant communities, past landscape structure could also have a substantial effect. Indeed, a temporal delay could especially be hypothesized between periods of landscape changes and biological responses of plant communities. We surveyed plant communities of three adjacent elements of 190 road-field boundaries in Central-Western France: the berm, the embankment and the field margin. We compared the effects of past (1980) and present (2011) surrounding agricultural landscape structure on the plant species richness of each element and on the Sørensen taxonomic compositional dissimilarity index between pairs of elements using linear models and a model averaging procedure. We characterized the landscape structure at both time periods within three circular buffers of 250, 500 and 1000 m radius around the centre of each sampled road-field boundary. In each buffer, we calculated the proportion of grasslands, the proportion of woodlands and the edge density. Despite a weak explanatory power of the landscape structure, species richness of each road-field element was better explained by past than present landscape structure. Species richness of berms, the element of the road-field boundary having the highest proportion of perennial species, was also the most influenced by past landscape structure. As an example, species richness of berms increased with the proportion of woodlands and the edge density when considering a buffer of 500 m radius. In contrast, compositional dissimilarity between pair of elements was neither affected by past nor present landscape structure. Our results suggest that the taxonomic diversity of plant communities of road-field boundaries have a time-lagged response to landscape changes, emphasising that currently implemented management programs represent high stakes for biodiversity conservation in future decades.

Landform transformation and long-term sediment budget for a Chernozem-dominated lowland agricultural catchment

Abstract The loess hilly lands of the South-West Foreland of the West Carpathians are characterized by favorable climatic conditions, smooth topography, fertile soils and a long settlement history. For the first time, we document changes to human-induced landforms in a small zero-order dry valley (0.28 km2) with Calcic Chernozem soils and develop a long-term sediment budget. The original surface was reconstructed based on interpreting records of erosion and deposition from 185 soil cores and six valley cross-sections. The topography inherited from the Pleistocene was transformed through lowering of hillslope ridges and convexities, along with infilling of shallow depressions within the original valley bottom. On convex-convex landforms had an average net erosion of − 0.32 ± 0.01 m, while average net accumulation in the valley bottom was estimated at 0.20 ± 0.01 m. The correlation between change in soil profile depth with profile curvature (− 0.51, p < 0.01) was stronger than with slope (− 0.42, p < 0.01). The sediment budget was calculated using the Average Per Unit (APU) approach. When slope classes were used in calculating net soil loss from catchments was 143·103 Mg·km− 2, whereas 154·103 Mg·km− 2 was estimated when morphometric forms of hillslopes were used instead. Both values are < 60% of estimates for similar loess catchments in Central and Western Europe. Prior to 1949, the landscape structure was characterized by small and narrow fields and vegetative field barriers that limited water and aeolian sediment fluxes in the direction of the thalweg and main wind directions. The landscape structure favoured the low-intensity tillage, erosion and accumulation within fields, and short-distance sheet and rill erosion on hillslopes. The land-use changes in the 1950′s caused removal of barriers for water and aeolian sediment transport, and changed the direction of sediment fluxes of tillage erosion. Past landscape structures should thus be considered when establishing and interpreting sediment budgets for lowland agricultural catchments.

The effect of current and historical landscape structure and species life-history traits on species distribution in dry grassland-like forest openings

Questions In a fragmented landscape, the distribution of plant species is determined not only by local habitat conditions but also by the landscape structure, including its changing nature, and by the life-history traits of species present. Whereas the importance of all these factors has been investigated in a range of previous studies, our understanding of the effects of individual traits on species dependence on landscape structure is still rather limited. The aim of this study was to identify factors responsible for plant species composition in dry grassland-like forest openings and to identify the relationship between life-history traits and species distribution. Location Křivoklatsko Biosphere Reserve, the Czech Republic. Methods We examined the effect of current and past landscape structures, habitat continuity and habitat conditions on species composition. We tested the importance of species traits for species response to the landscape structure. Results In addition to habitat conditions, species composition was determined by landscape structures in the past and at present, and the past landscape structure in each time period separately was equally important to the present landscape structure. Perennial species that are insect- or wind-pollinated, flower over limited periods of time, are relatively tall, are dispersed by animals, are not ruderal, have low nutrient requirements and maintain competitive or partly stress-tolerant strategies were found to be restricted to continuous localities existing at least since 1973 or 1988 and to localities that are currently well interconnected. In contrast, short, self-pollinated, ruderal species prevail in currently less-connected localities. Conclusions The results indicate that knowledge of the past landscape structure is important for understanding the current species distribution, and that species traits can be used as useful predictors of species responses to the past landscape structure.

The effects of plant traits on species' responses to present and historical patch configurations and patch age

Patch configuration is viewed as an important factor affecting the distributions of plant species. Although a number of studies have explored the relationship between plant life‐history traits and species’ distributions in fragmented landscapes, the effect of individual traits on the dependence of species on historical versus current landscape configurations remains unclear.We identified the extent to which present (2000s) and historical (1843, 1954, 1980s) patch configurations (area and connectivity) and patch age affected the distributions of 99 species inhabiting dry calcareous grasslands. We used traits related to dispersal, survival, growth and habitat preferences to explain the dependence of 60 of these species on present and historical configurations, and the age of grassland patches.We found that most of the species had an affinity to currently or historically large, older and more isolated patches. This suggests that many dry grassland species are not in equilibrium with the current landscape, as their distributions still reflect past landscape structures. Rapidly growing species with higher seed bank longevity and nutrient requirements primarily occur in young, large grassland patches whereas species with the opposite traits occur in older, historically large and currently more isolated smaller patches. We hypothesise that patch quality is the reason why different species occupy patches of different age. Species occupying young, large patches commonly disperse by endozoochory. By contrast, no dispersal trait is associated with species occupying old, usually isolated patches. Our results suggest that species occupying old patches are exposed to higher potential risk of extinction, as their distributions are probably limited by the low number and connectivity of available suitable patches and poor dispersal ability. We thus suggest that the dynamics of these species can effectively be supported by improving the quality of young grassland patches.

Relative importance of current and past landscape structure and local habitat conditions for plant species richness in dry grassland-like forest openings.

In fragmented landscapes, plant species richness may depend not only on local habitat conditions but also on landscape structure. In addition, both present and past landscape structure may be important for species richness. There are, however, only a few studies that have investigated the relative importance of all of these factors. The aim of this study was to examine the effect of current and past landscape structures and habitat conditions on species richness at dry grassland-like forest openings in a forested landscape and to assess their relative importance for species richness. We analyzed information on past and present landscape structures using aerial photographs from 1938, 1973, 1988, 2000 and 2007. We calculated the area of each locality and its isolation in the present and in the past and the continuity of localities in GIS. At each locality, we recorded all vascular plant species (296 species in 110 forest openings) and information on abiotic conditions of the localities. We found that the current species richness of the forest openings was significantly determined by local habitat conditions as well as by landscape structure in the present and in the past. The highest species richness was observed on larger and more heterogeneous localities with rocks and shallow soils, which were already large and well connected to other localities in 1938. The changes in the landscape structure in the past can thus have strong effects on current species richness. Future studies attempting to understand determinants of species diversity in fragmented landscapes should also include data on past landscape structure, as it may in fact be more important than the present structure.

Historical habitat connectivity affects current genetic structure in a grassland species

Many recent studies have explored the effects of present and past landscape structure on species distribution and diversity. However, we know little about the effects of past landscape structure on distribution of genetic diversity within and between populations of a single species. Here we describe the relationship between present and past landscape structure (landscape connectivity and habitat size estimated from historical maps) and current genetic structure in a perennial herb, Succisa pratensis. We used allozymes as co-dominant markers to estimate genetic diversity and deviation from Hardy-Weinberg equilibrium in 31 populations distributed within a 5 km(2) agricultural landscape. The results showed that current genetic diversity of populations was related to habitat suitability, habitat age, habitat size and habitat connectivity in the past. The effects of habitat age and past connectivity on genetic diversity were in most cases also significant after taking the current landscape structure into account. Moreover, current genetic similarity between populations was affected by past connectivity after accounting for current landscape structure. In both cases, the oldest time layer (1850) was the most informative. Most populations showed heterozygote excess, indicating disequilibrium due to recent gene flow or selection against homozygotes. These results suggest that habitat age and past connectivity are important determinants of distribution of genetic diversity between populations at a scale of a few kilometres. Landscape history may significantly contribute to our understanding of distribution of current genetic structure within species and the genetic structure may be used to better understand landscape history, even at a small scale.

Species traits weakly involved in plant responses to landscape properties in Mediterranean grasslands

AbstractQuestionsWhat is the role of landscape structure and dynamics, compared with climatic and geographic factors, in determining species frequencies of grassland plant specialists under habitat loss? Do species traits mediate the relationship between plant community composition and environmental variables?LocationTheMediterranean mountain grasslands of southernCatalonia (NE IberianPeninsula), over an area of 100 × 20 km.MethodsUsing redundancy analysis (RDA), we explored the association between frequency of broad plant specialists and both present and past habitat patterns in the landscape (i.e. habitat amount and reduction over the period 1956–2003), after accounting for the effect of geographical location and climate in 29 grassland patches. Then, we constructed a database of biological and ecological plant traits potentially related to population persistence, in order to assess the role of these traits in explaining the found association between species composition and environmental variables. We used a single, three‐table ordination analysis (RLQ) of the species frequencies, environmental variables and species traits to relate species traits to environmental variables, after allowing for phylogenetic dependence of traits.ResultsThe main environmental gradient explaining species frequencies was climatic and geographic. Habitat amount in the current landscape significantly affected species frequencies, while habitat amount in the past landscape did not. A weak but significant association of species traits with environmental variables was detected. Taking into account the phylogenetic signal in plant traits did not change the results.ConclusionsPlant species inMediterranean grasslands seem to respond quickly to landscape change, since no effect of past landscape structure was observed on current species frequencies. Moreover, plant traits did not play a major role in mediating species response to environmental variation in these grasslands. Our findings differ from those obtained in northern and centralEuropean grasslands, probably due to differences in methodology but also to the smaller contrast in environmental conditions between grasslands and the adjacent forests and scrub inMediterranean landscapes.

Historical landscape structure affects plant species richness in wet heathlands with complex landscape dynamics

The spatio-temporal dynamics of wet heathlands from two landscapes in high Ardenne (Belgium), as well as the consequences of such dynamics on plant communities were investigated. Past and present destruction and origin of habitat patches have resulted in a complex network of different aged habitat patches. Current specialist and generalist species richness were assessed in 59 patches and analyzed with respect to present and past patch spatial metrics (controlled for habitat quality). Current patch area affected specialist species richness and current patch connectivity influenced both specialist and generalist species richness. Thirteen of the 59 patches were historical patches, i.e. patches that have remained since the 1770s. In these historical patches, including past landscape structure in the analysis explained more of the variability in current species richness than the current landscape structure alone, suggesting the existence of an extinction debt.

Genetic Variation in Past and Current Landscapes: Conservation Implications Based on Six Endemic Florida Scrub Plants

If genetic variation is often positively correlated with population sizes and the presence of nearby populations and suitable habitats, landscape proxies could inform conservation decisions without genetic analyses. For six Florida scrub endemic plants (Dicerandra frutescens, Eryngium cuneifolium, Hypericum cumulicola, Liatris ohlingerae, Nolina brittoniana, and Warea carteri), we relate two measures of genetic variation, expected heterozygosity and alleles per polymorphic locus (APL), to population size and landscape variables. Presettlement areas were estimated based on soil preferences and GIS soils maps. Four species showed no genetic patterns related to population or landscape factors. The other two species showed significant but inconsistent patterns. ForLiatris ohlingerae, APL was negatively related to population density and weakly, positively related to remaining presettlement habitat within 32 km. ForNolina brittoniana, APL increased with population size. The rather weak effects of population area/size and both past and current landscape structures suggest that genetic variation needs to be directly measured and not inferred for conservation planning.

Time-lag in biological responses to landscape changes in a highly dynamic Atlantic forest region

Time-lagged responses of biological variables to landscape modifications are widely recognized, but rarely considered in ecological studies. In order to test for the existence of time-lags in the response of trees, small mammals, birds and frogs to changes in fragment area and connectivity, we studied a fragmented and highly dynamic landscape in the Atlantic forest region. We also investigated the biological correlates associated with differential responses among taxonomic groups. Species richness and abundance for four taxonomic groups were measured in 21 secondary forest fragments during the same period (2000–2002), following a standardized protocol. Data analyses were based on power regressions and model selection procedures. The model inputs included present (2000) and past (1962, 1981) fragment areas and connectivity, as well as observed changes in these parameters. Although past landscape structure was particularly relevant for trees, all taxonomic groups (except small mammals) were affected by landscape dynamics, exhibiting a time-lagged response. Furthermore, fragment area was more important for species groups with lower dispersal capacity, while species with higher dispersal ability had stronger responses to connectivity measures. Although these secondary forest fragments still maintain a large fraction of their original biodiversity, the delay in biological response combined with high rates of deforestation and fast forest regeneration imply in a reduction in the average age of the forest. This also indicates that future species losses are likely, especially those that are more strictly-forest dwellers. Conservation actions should be implemented to reduce species extinction, to maintain old-growth forests and to favour the regeneration process. Our results demonstrate that landscape history can strongly affect the present distribution pattern of species in fragmented landscapes, and should be considered in conservation planning.

Modeling landscape structure constraints on species dispersal with a cellular automaton: Are there convergences with empirical data?

Landscapes are typically complex systems which do not necessarily allow performing large scale field experiments. A lot of studies hence analyzed correlations between landscape structure and species distribution. However, empirical data integrate a non-reducible part of contingency, which implies a major issue: the generalization of results. In such complex contexts, modeling can be useful since it allows isolating factors and it can play the role of reference for comparisons. In this perspective, we modeled plant species dispersal within a hedgerow network with a simple cellular automaton. In parallel we studied empirically plant species distribution in hedgerows to see whether both, results from the model and results from empirical data were convergent. Results showed that the cellular automaton was characterized by non-linear responses, corresponding to different levels of landscape constraints. Furthermore, convergences were found between the theoretical model and empirical data, in terms of differential responses of plant species to landscape structure, according to dispersal type and habitat specialization. Finally examining past landscape structure, the theoretical model and empirical data converged, demonstrating that past landscape patterns are particularly relevant in terms of statistical explanation of plant species distribution. We conclude that cellular automata were relevant formalizations of dispersal processes at the landscape level.

Distribution pattern of the epiphyteNeckera pennataon three spatial scales – importance of past landscape structure, connectivity and local conditions

We tested which factors explain the distribution pattern of the epiphytic mossNeckera pennataon three spatial scales using the framework of generalized linear models. First, we tested which factors explained its occurrence in forest stands in a 2500 ha landscape. At this scale, we also tested the effect of the historic landscape structure. We recorded its occurrence in all suitable stands. The occurrence probability increased with increasing present quantity ofAcer platanoides, and with increasing present and past quantity ofFraxinus excelsior. The probability also increased with increasing connectivity to occupied stands. However, the connectivity to stands present in 1977 (recorded from infra‐red aerial photographs) explained more of the variation. This suggests that the regional metapopulation size ofN. pennatahas decreased during the past decades, and that its present distribution pattern reflects the age of the remaining stands, and the distribution of past dispersal sources in the landscape. Second, we tested which factors explained the occurrence and abundance on individual trees in three forest stands.Neckera pennatamainly occurred onAcerandFraxinusstems. The most important variable in explaining occurrence probability was connectivity to surrounding occupied trees, which probably reflects the restricted dispersal range in this species. The abundance on occupied trees was also explained by this variable. The occurrence probability and abundance also increased with increasing tree diameter, probably reflecting the time that a tree has been available for colonization and the time since colonization, respectively. The occurrence probability and abundance furthermore decreased on strongly leaning (and deteriorating) trees. The occurrence probability increased with increasing bark roughness, probably reflecting increasing suitability regarding bark chemistry and moisture. Third, we tested its vertical distribution on occupied trees. The main distribution was below 1.6 m.

Changements de la structure du paysage et richesse spécifique des fragments forestiers dans le sud-est du Brésil

We used the Hallé and Oldeman's groups of the present and of the future, as obtained by an architectural analysis of trees, in order to test the hypothesis that the group of young (or potential) trees is more sensitive to parameters of present landscape structure than the group of old trees. The landscape structure and the tree species richness of 11 remnant forest fragments, located in the riparian corridor of the Jacaré-Pepira river (S.E. Brazil), were studied. The results showed that the tree species richness may not be linked to the landscape structure changes that have been occurring since 1962 (date of the oldest aerial photographs from the region). The studied communities are probably still responding to the main landscape structure changes that occurred during the second half of the 19th and the beginning of the 20th century as a consequence of the expansion of coffee plantations. Furthermore, the group of the future presented significant correlations with a greater number of landscape indices, confirming the initial hypothesis of greater sensitivity of the younger trees to the present landscape structure. It appears also that the richness of the group of the future is mainly affected by the present landscape structure while the richness of the group of the present results from interactions with present and past landscape structures.