Tree Assemblages Research Articles

Urban green areas retain just a small fraction of tree reproductive diversity of the Atlantic forest

Urban green spaces have gained notoriety in recent years, as they have been argued to play an important role in supporting native biodiversity, ecosystem services and human well-being. However, such a promising perspective is poorly investigated in the tropical context. Here we examine the role played by urban green areas in a major city (Recife-Brazil) as a repository for Atlantic forest biodiversity relative to pollination systems. Plant assemblages were examined across 17 urban green areas and compared to those from ten old-growth forest stands in the largest Atlantic forest remnant in northeastern Brazil (natural areas). Just a small portion of tree species inhabiting urban green areas is native to the northeastern Brazilian Atlantic forest (29.8 %). At plant community-level, squares and parks were impoverished in terms of number of species and individuals with specialized pollination systems (e.g. bats, Sphingids), as compared to forest remnants. Moreover, urban green areas were dominated by generalist-pollinated trees with reproductive traits associated with easily accessible floral resources and an increase of hermaphrodites. Finally, squares and parks had similarly low functional diversity of reproductive traits. Our results suggest that urban green areas support largely distorted and impoverished tree assemblages in terms of floral rewards and pollination, while services are restricted to those offered by generalist small insects. This pattern emerges mainly from the contribution of exotic plants. This largely limits the tropical urban green areas as biodiversity repositories and potential source for specialized pollination services, what calls for a better use of tropical urban areas as conservation tool.

Beyond taxonomic diversity: Revealing spatial mismatches in phylogenetic and functional diversity facets in Mediterranean tree communities in southern France

Adopting a multifaceted approach of biodiversity is believed to capture different aspects of the ecosystem functioning and it is thus advised for conservation prioritisation, especially for anthropogenic ecosystems but this key topic has never been conducted for the Mediterranean tree assemblages, despite their ecological importance. We explored how the multi-faceted diversity of woody plant assemblages, as measured by taxonomic (TD), functional (FD) and phylogenetic (PD) diversities, are distributed over space in the French part of the Mediterranean biome, and to which extend they are spatially correlated to each other, in order to understand whether one facet can be used as a proxy for another, especially for conservation management purposes.We analysed data from 5885 plots over the study area. We estimated several FD types by considering separately (i) regeneration, (ii) morphology traits (iii) modalities on species ecological properties, and finally (iv) considering all traits together. We used the Rao quadratic entropy to estimate the TD, FD and PD diversity facets. We tested for the links and spatial correlation (congruence) levels among these facets, using simultaneous autoregressive (SAR) models and partial Mantel tests.Spatial structure varied among diversity facets and spatial autocorrelation patterns were identified for all diversity indices from 30 to 50 km distances. We observed a functional convergence and a phylogenetic divergence within tree assemblages comparing to the ones expected given the regional species pool, indicating that even in tree communities with functional similarities, phylogenetic diversity may be high. PD was zero to slightly congruent to FD, regardless the type of functional traits considered. The highest SAR slope (=0.3) and partial Mantel test (=0.2) were revealed between the PD and the FD based on species morphological traits, but still remained considerably low.Each one of the diversity indicators reflected a different tree community spatial pattern. Functional diversity patterns varied according to the type of traits considered. Using only taxonomic indices may be misleading for responding to Mediterranean tree assemblages conservation needs and additional information about the species phylogeny and functional responses to disturbance pressures should be considered in large scale analyses.

DOES THE SIZE OF THE TREES DETERMINE THE RICHNESS AND DISTRIBUTION OF VASCULAR EPIPHYTES IN AMAZONIAN FLOODPLAIN FORESTS?

Vascular epiphytes (VE) are among the most threatened group of plants due to the extraction of trees (phorophytes). Yet, surveys and ecological information on vascular epiphytes are rather scarce particularly in wetlands. To understand the effect of tree assemblage on the occurrence of VE and in order to elucidate ecological patterns of distribution and composition, 16 (25 x 25 m) permanent plots were sampled in an oligotrophic floodplain forest ( igapo - PELD MAUA) and compared to the same amount and size of plots in a nutrient-rich floodplain ( varzea - RDS Mamiraua), both in Central Amazon. All trees and associated VE were counted and identified. The diversity in varzea is driven by the turnover of epiphytes in trees with different diameters, while in igapo there is a pronounced concentration of VE in trees with smaller diameters. Conservation actions in varzea forests should prioritize the maintenance of forest structure, sustaining taxonomic diversity in all diameter classes of trees. In igapo forests efforts to conserve epiphytes must first consider the taxonomic identity and, after, size of trees in the community. The comparison of our results with those of other PELDs in wetlands and other ecosystems will enhance our knowledge on the biogeographic patters and constrains on the distribution of this important botanical component.

Environment and evolutionary history depict phylogenetic alpha and beta diversity in the Atlantic coastal white‐sand woodlands

AbstractQuestionsHow do ecological and evolutionary processes affect the phylogenetic alpha and beta diversity of angiosperm tree assemblages in an evolutionarily young coastal environment?LocationCoastal vegetation of the Brazilian Atlantic Forest Domain (restingas), spanning 20° of latitude.MethodsWe calculated phylogenetic alpha and beta diversity at deep and shallow levels for angiosperm tree species in 136 circular sites of 10 km diameter (hereafter assemblages). The metrics we used for alpha diversity were the mean pairwise distance (MPD) and mean nearest taxon distance (MNTD), and mean pairwise distance separating species in two assemblages (Dpw) and mean nearest taxon distance separating species in two assemblages (Dnn) for beta diversity. We then investigated the relationship between phylogenetic diversity, historical (Quaternary) and current climatic variables, and edaphic conditions along the latitudinal gradient.ResultsWe found that MPD increased with precipitation and latitude. MNTD increased with modern‐day temperature, historical temperature instability and precipitation, and it was higher in more fertile and less saline soils. Dpw did not correlate either with geographic or environmental distances between assemblages. However, Dnn was strongly correlated with both geographic and environmental distances between assemblages.ConclusionsThe increase in MPD with precipitation and latitude suggests the presence of old Gondwanan lineages colonising restingas from refugia at higher latitudes. The increase in MNTD with modern‐day temperature, historical temperature instability, precipitation, and it being higher in more fertile and less saline soils indicates that the distance between phylogenetic closest relatives tends to increase in assemblages less affected by environmental filtering. Low Dpw suggests the presence of widespread lineages across restingas, whereas high Dnn may indicate niche conservatism and dispersal limitation of more derived lineages. Our results offer insights into how ecological and evolutionary processes act to shape current patterns of biodiversity in geologically young environments.

Co-existence between humans and nature: Heritage trees in China’s yangtze River region

The negative consequences of increased urbanization on native biological and cultural diversity have received considerable research attention. Biological and cultural diversity can be sustained by counteracting various processes of floristic homogenization and by reestablishing connections between humans and nature. However, effective instruments to help people reconnect with nature can be lacking, especially in cities. Green spaces provide cultural, aesthetic, and ecological services and can represent a critical component of native plant diversity in urban environments. We examined the species composition of heritage trees and the tangible and cultural values of these trees in 11 major cities in the Yangtze River basin of China. Our analysis explored the similarities of three arboreal types, namely heritage trees, urban greening components, and natural plant communities. Heritage tree species are diverse, containing 310 recorded species representing 159 genera and 64 families. Their tangible and cultural values are mainly medicinal (221 species), followed by timber (186), culture (134), traditional courtyard planting (131) and food (124). Notable geographical differences in heritage tree species composition identified in our analysis could be explained by cities adopting mostly species native to the locality or province. Heritage tree assemblages were similar in composition to undisturbed natural plant communities, and the two populations experienced comparable progressive decline with geographical distance. Urban greening components indicated negligible decline in similarity beyond the 1000 km threshold, indicating common sharing of exotic species across disparate locations. Heritage tree species associated with notable tangible and cultural values, superior genetic constitution, and adaptation to local growth conditions present suitable candidates for urban planting to improve tree performance and urban biodiversity. Their long history of association with local culture and rich cultural values can be enlisted to strengthen the connections of urban communities to nature and history, and to promote nature conservation within cities. Given increasing biological and biocultural homogenization, especially in urban areas, protecting heritage trees and using them in urban greening can slow this trend and enrich stocks of urban biodiversity.

Museomics for reconstructing historical floristic exchanges: Divergence of stone oaks across Wallacea.

Natural history collections and tropical tree diversity are both treasure troves of biological and evolutionary information, but their accessibility for scientific study is impeded by a number of properties. DNA in historical specimens is generally highly fragmented, complicating the recovery of high-grade genetic material. Furthermore, our understanding of hyperdiverse, wide-spread tree assemblages is obstructed by extensive species ranges, fragmented knowledge of tropical tree diversity and phenology, and a widespread lack of species-level diagnostic characters, prohibiting the collecting of readily identifiable specimens which can be used to build, revise or strengthen taxonomic frameworks. This, in turn, delays the application of downstream conservation action. A sizable component of botanical collections are sterile—thus eluding identification and are slowing down progress in systematic treatments of tropical biodiversity. With rapid advances in genomics and bioinformatic approaches to biodiversity research, museomics is emerging as a new field breathing life into natural collections that have been built up over centuries. Using MIGseq (multiplexed ISSR genotyping by sequencing), we generated 10,000s of short loci, for both freshly collected materials and museum specimens (aged >100 years) of Lithocarpus—a widespread tropical tree genus endemic to the Asian tropics. Loci recovery from historical and recently collected samples was not affected by sample age and preservation history of the study material, underscoring the reliability and flexibility of the MIGseq approach. Phylogenomic inference and biogeographic reconstruction across insular Asia, highlights repeated migration and diversification patterns between continental regions and islands. Results indicate that co-occurring insular species at the extremity of the distribution range are not monophyletic, raising the possibility of multiple independent dispersals along the outer edge of Wallacea. This suggests that dispersal of large seeded tree genera throughout Malesia and across Wallacea may have been less affected by large geographic distances and the presence of marine barriers than generally assumed. We demonstrate the utility of MIGseq in museomic studies using non-model taxa, presenting the first range-wide genomic assessment of Lithocarpus and tropical Fagaceae as a proof-of-concept. Our study shows the potential for developing innovative genomic approaches to improve the capture of novel evolutionary signals using valuable natural history collections of hyperdiverse taxa.

Ethnobotany-informed trait ecology: measuring vulnerability of timber provisioning services across forest biomes in Japan

Trait-based functional ecology plays a key role for valuing biodiversity, based on the mechanistic link between species assembly and ecosystem-services. To evaluate the vulnerability of valuable biodiversity to human impacts, this study focused on assemblages of tree species with timber provisioning services and investigated the functional response of their utilitarian traits to forest exploitation. We first merged traditional knowledge of timber use, successional niche, and functional traits of tree species across forest biomes in Japan. Using leaf and wood traits of 514 tree species, we quantified macro-scale patterns of functional identity, richness, and divergence for the timber species and entire tree assemblages in Japan. At the 10-km grid cell level, we conducted a species loss simulation that assumed forest exploitation, in which later successional species were step-wisely removed from the potential tree assemblages. The simulation showed that species loss led to shifting functional identity and changes in functional richness and divergence. Such responses of functional structure were geographically associated with region-specific redundancy or complementarity in tree species assemblages. Specifically, the shift of functional identities was prominent in high latitudes with low species loss and low latitude with higher species loss. The utilitarian value of tree species in higher latitude forests was more closely associated with their ecological niche and functional uniqueness, which indicates vulnerability of trait space to species loss. The changes in trait space, which were associated with non-random species loss, were context-dependently influenced by climate conditions and species pool size. Our findings indicate that the insurance effect of biodiversity was a region-specific feature of forest biomes. We conclude that ethnobotany-informed trait ecology can elucidate the valuable biodiversity for human culture and its vulnerability to species loss; this information is essential for sustainable use of biodiversity resources in human society.

Biogeographic and anthropogenic factors shaping the distribution and species assemblage of heritage trees in China

Heritage trees are recognized as elements of cultural landscapes and as keystone ecological entities in human-dominated landscapes, often bestowing high socio-cultural and ecological values. Current understanding of species distribution patterns and broad-scale species assemblages of heritage trees is limited. This study analyzed the diversity, distribution patterns, and origins of heritage trees and assessed the underlying factors contributing to their occurrence at the national scale in China. Data were drawn from published and online sources representing 561 regions across China. There were 1140 species including 105 endangered ones preserved as heritage trees. Heritage trees originated from four sources of species provenance: natural forest species 73.51 % of total species), native ruderal species (10.53 %), domesticated species (6.75 %) and exotic species (9.21 %). The origin of heritage trees differed across climatic zones. At the national and climatic zone scale, species similarity (Jaccard Index) among regions was low, constrained by geographic distance, climate (e.g., mean annual precipitation) and anthropogenic factors (e.g., population density). Mean annual precipitation, mean annual temperature, population density and GDP per capita were the main determinants of species provenance. Most heritage tree species serve tangible uses, especially domesticated and exotic species. Species assemblages of heritage trees were mainly associated with the local plant species pool, climate, socio-economic development status and human preference. As living heritage, the trees need dedicated protection measures based on their main tangible and cultural values for human, primary threats, and statutory protection degree at the species level. Regional culture, belief, and customary laws should be considered in formulating policies for protection and conservation of these trees.

Spatial and temporal structure of diversity and demographic dynamics along a successional gradient of tropical forests in southern Brazil.

Analysis of the structure, diversity, and demographic dynamics of tree assemblages in tropical forests is especially important in order to evaluate local and regional successional trajectories.We conducted a long‐term study to investigate how the structure, species richness, and diversity of secondary tropical forests change over time. Trees (DBH ≥ 5 cm) in the Atlantic Forest of southern Brazil were sampled twice during a 10‐year period (2007 and 2017) in six stands (1 ha each) that varied in age from their last disturbance (25, 60, 75, 90, and more than 100 years). We compared forest structure (abundance and basal area), species richness, alpha diversity, demographic rates (mortality, recruitment, and loss or gain in basal area), species composition, spatial beta diversity, and temporal beta diversity (based on turnover and nestedness indices) among stand ages and study years.Demographic rates recorded in a 10‐year interval indicate a rapid and dynamic process of species substitution and structural changes. Structural recovery occurred faster than beta diversity and species composition recovery. The successional gradient showed a pattern of species trade‐off over time, with less spatial dissimilarity and faster demographic rates in younger stands. As stands grow older, they show larger spatial turnover of species than younger stands, making them more stochastic in relation to species composition. Stands appear to split chronologically to some extent, but not across a straightforward linear axis, reflecting stochastic changes, providing evidence for the formation of a nonequilibrium community. Policy implications. These results reiterate the complexity and variability in forest succession and serve as a reference for the evaluation and monitoring of local management and conservation actions and for defining regional strategies that consider the diversity of local successional trajectories to evaluate the effectiveness of restoration measures in secondary forests of the Atlantic Forest biome.

Living in small spaces: Forest fragment characterization and its use by Philippine tarsiers (Tarsius syrichta Linnaeus, 1758) in Mindanao Island, Philippines.

The Philippine tarsier (Tarsius syrichta) is a charismatic species that is threatened by illegal hunting and deforestation. Although they occur in forest and disturbed habitats, ecological information about them is still considerably lacking, which consequently hampers our ability to effectively protect tarsiers from further endangerment. Here, we characterized a 36-ha forest fragment in Mindanao Island where a population of tarsiers persist, and assessed the factors that could have influenced their distribution within the area. We sampled trees (> 1cm DBH) within 10×10-m sampling plots (N = 54), which were established within 1-ha grids (N = 32) and locations where tarsiers were captured (N = 22). The habitat was characterized as a regenerating forest over limestone, with a generally homogeneous structure in terms of tree species richness, abundance, mean DBH, and height. In both sampling plots, we found an abundance of trees below 5cm in DBH (> 50%) and between 2.6 and 5 m in height (> 40%), which, accordingly, the tarsiers appeared to prefer to use when foraging or sleeping. Lianas were among the most important features of the forest, possibly being a keystone structure in such habitats. Community assemblage, species richness, and mean height of trees, as well as distance to the forest edge, were found to be significant factors that influenced tarsier distribution in the fragment. Our study provides basic yet critical information on the habitat and ecology of Philippine tarsiers in Mindanao, and highlights the importance of forest fragments with rich flora diversity to the survival of the species.

Leaf litter inputs reinforce islands of nitrogen fertility in a lowland tropical forest

The role of lowland tropical forest tree communities in shaping soil nutrient cycling has been challenging to elucidate in the face of high species diversity. Previously, we showed that differences in tree species composition and canopy foliar nitrogen (N) concentrations correlated with differences in soil N availability in a mature Costa Rican rainforest. Here, we investigate potential mechanisms explaining this correlation. We used imaging spectroscopy to identify study plots containing 10–20 canopy trees with either high or low mean canopy N relative to the landscape mean. Plots were restricted to an uplifted terrace with relatively uniform parent material and climate. In order to assess whether canopy and soil N could be linked by litterfall inputs, we tracked litter production in the plots and measured rates of litter decay and the carbon and N content of leaf litter and leaf litter leachate. We also compared the abundance of putative N fixing trees and rates of free-living N fixation as well as soil pH, texture, cation exchange capacity, and topographic curvature to assess whether biological N fixation and/or soil properties could account for differences in soil N that were, in turn, imprinted on the canopy. We found no evidence of differences in legume communities, free-living N fixation, or abiotic properties. However, soils beneath high canopy N assemblages received ~ 60% more N via leaf litterfall due to variability in litter N content between plot types. The correlation of N in canopy leaves, leaf litter, and soil suggests that, under similar abiotic conditions, litterfall-mediated feedbacks can help maintain soil N differences among tropical tree assemblages in this diverse tropical forest.

Ecological drivers of tree assemblage in tropical, subtropical and subalpine forests

AbstractAimsIt is widely accepted that deterministic and neutral dispersal processes are two of the principal mechanisms driving community assembly. However, the relative importance of these ecological drivers between distinct life stages both at community and individual species levels remains poorly understood in different vegetation types. Here, we address the following questions: (a) is there a ubiquitous process shaping tree assemblage; (b) how does the relative importance of environmental and dispersal processes vary through ontogeny in different vegetation types; and (c) will the spatial patterns of trees at community and individual species levels reflect similar contribution between ecological processes?LocationYunnan province, southwest China.MethodsWe used the Homogeneous Poisson, Homogeneous Thomas, Inhomogeneous Poisson, and Inhomogeneous Thomas point process models to predict the effect of stochastic, dispersal and/or environmental processes, respectively, on the distribution of trees across ontogeny in tropical, subtropical and subalpine forests. To evaluate the relative importance of models, we compared the observed and simulated patterns of the species–area relationship and the pair correlation function g(r) at community and species level, respectively.ResultsThe Homogeneous Thomas model was the model with the lowest Akaike information criterion (AIC) scores across ontogeny and forest types at community level. At the species level, however, Homogeneous Thomas, and Inhomogeneous Thomas predicted the distribution of large and small trees, respectively, with lower AIC values in two of our three plots. In the third plot, the Homogeneous Thomas model is dominant across ontogeny at the species level.ConclusionsTree communities are assembled mainly by the dispersal process at community level. The relative importance of ecological processes for species distribution varies across life stages at the species level, suggesting that there is an ontogenetic shift of ecological processes in shaping tree distribution. Using different summary statistics at both community and species levels helps to discern the different spatial structures of species and increases our appreciation of the processes underpinning community assembly.

Reorganization of tree assemblages over the last century in the northern hardwoods of eastern Canada

AbstractQuestionHow has European settlement of Eastern North America modified tree species assemblages?LocationThe northern temperate forests of the Lower St. Lawrence region (Quebec, Canada).MethodsChanges in relative prevalence of tree taxa were reconstructed with early land survey records (1821–1900) and modern forest inventories (1980–2010). Forest composition reconstructions were then used to analyse changes in tree taxa assemblages at the landscape scale and test for potential landscape homogenization.ResultsOur results show important maple (Acer saccharumandA. rubrum) and poplar (Populus tremuloidesandP. balsamifera) encroachment, shifting from the 6th to the 2nd position of relative prevalence and from the 7th to the 5th position, respectively, resulting in a significant shift in tree assemblage. Maple has spread throughout the whole landscape and tended to become the most abundant taxon in communities where they were already present in pre‐settlement times. Poplar also widely spread throughout the landscape but rarely became the most abundant taxon. Accordingly, deciduous encroachment clearly engendered a spatial homogenization of composition at the landscape scale.ConclusionConsidering that both red maple and trembling aspen are opportunist early‐successional species, the increased relative prevalence of both species, as well as the consequent reorganization of tree taxon assemblages and landscape homogenization, probably resulted from the regional convergence toward an early‐successional state. Along with the restoration of long‐lived shade‐tolerant conifer populations, land and forest managers should aim to increase the heterogeneity of forest stand composition to improve forests resilience to future global changes.

Effects of experimental fires on the phylogenetic and functional diversity of woody species in a neotropical forest

Although tropical forest fires are naturally rare, they have become more frequent and intense in response to recent changes in land use and climate. This shift in fire regime may drive widespread forest degradation in Amazonia, with important consequences not only for species richness but also for functional and phylogenetic diversity. Here, we test the overall hypothesis that fire-induced tree mortality causes more losses in phylogenetic and functional diversity than in taxonomic diversity, because fire kills trees non-randomly. To test this hypothesis, we established a large-scale, long-term (nine-year) fire experiment in southeast Amazonia in three 50-ha plots, with unburned Control and two different fire regimes (burned annually and burned every three years), between 2004 and 2010. Overall, tree assemblages exposed to experimental fires lost more phylogenetic and functional diversity compared to unburned areas, especially where the experimental fires were more intense (in areas burned every three years). The rate of loss of phylogenetic and functional diversity per species-unit was higher for larger trees than for small ones, which indicates that fire-induced mortality is more random for small trees. Our results indicate that fire acts as a selective pressure, filtering species with similar phylogenetic and functional traits. Given that forest fires are likely to become more common and frequent in the region, it is essential to understand their impact above and beyond taxonomic diversity.

Species and phylogenetic endemism in angiosperm trees across the Northern Hemisphere are jointly shaped by modern climate and glacial–interglacial climate change

AbstractAimsPhylogenetic endemism describes the extent to which unique phylogenetic lineages are constrained to restricted geographic areas. Previous studies indicate that species endemism is related to both past and modern climate, but studies of phylogenetic endemism are relatively rare and mainly focused on smaller regions. Here, we provide the first assessment of the patterns of species and phylogenetic endemism in angiosperm trees across the Northern Hemisphere as well as the relative importance of modern climate and glacial–interglacial climate change as drivers of these patterns.LocationNorthern Hemisphere.Major taxaAngiosperm trees.MethodsUsing tree assemblages at the scale of 100 km × 100 km grid cells and simultaneous autoregressive (SAR) models, we assessed the relationships between species endemism, phylogenetic endemism and modern climate variables, Last Glacial Maximum (LGM) to present temperature velocity.ResultsSpecies and phylogenetic endemism were associated with both modern climate and glacial–interglacial climate change, with higher values in areas with stable historical climate and warmer and wetter modern conditions. Notably, the multivariate SAR analyses showed that the combinations of variables with highest Akaike’s information criterion (AIC) weight always included both LGM–present climate instability and modern climate, that is, modern precipitation and temperature.Main conclusionsOur results show that high phylogenetic endemism is partially dependent on long‐term climate stability, highlighting the threat posed by future climate changes to the preservation of rare, phylogenetically distinct lineages of trees.

Exploring the Concept of Lineage Diversity across North American Forests

Lineage diversity can refer to the number of genetic lineages within species or to the number of deeper evolutionary lineages, such as genera or families, within a community or assemblage of species. Here, we study the latter, which we refer to as assemblage lineage diversity (ALD), focusing in particular on its richness dimension. ALD is of interest to ecologists, evolutionary biologists, biogeographers, and those setting conservation priorities, but despite its relevance, it is not clear how to best quantify it. With North American tree assemblages as an example, we explore and compare different metrics that can quantify ALD. We show that both taxonomic measures (e.g., family richness) and Faith’s phylogenetic diversity (PD) are strongly correlated with the number of lineages in recent evolutionary time, but have weaker correlations with the number of lineages deeper in the evolutionary history of an assemblage. We develop a new metric, time integrated lineage diversity (TILD), which serves as a useful complement to PD, by giving equal weight to old and recent lineage diversity. In mapping different ALD metrics across the contiguous United States, both PD and TILD reveal high ALD across large areas of the eastern United States, but TILD gives greater value to the southeast Coastal Plain, southern Rocky Mountains and Pacific Northwest, while PD gives relatively greater value to the southern Appalachians and Midwest. Our results demonstrate the value of using multiple metrics to quantify ALD, in order to highlight areas of both recent and older evolutionary diversity.

Inferring multispecies distributional aggregation level from limited line transect‐derived biodiversity data

Abstract Ecologists have generally concluded that species distributions are not random (e.g. aggregate), based on single‐species studies that applied single‐species–based statistical methods, like the negative binomial model. Although it is common knowledge that some specific species in an ecological community present aggregate distributions, this does not necessarily imply that the entire community presents an aggregate distribution. Studying community‐level distributional aggregation patterns requires different statistical methods. Herein, by utilizing a novel conspecific‐encounter index derived from a multiple species Markov transition model that accounts for the non‐independent sampling of consecutive individuals along line transects, we were able to show that tree assemblages in tropical forest ecosystems can present a strong signal of extensive distributional interspersion. This interesting result is not unexpected, given the fact that neighbouring tree individuals in highly diverse tropical forests are usually of different species, resulting in strong niche packing or interspersed patterns. In contrast, for the amphibian assemblages surveyed from southwestern China and central‐south Vietnam, the conspecific‐encounter index was found to be consistently high, implying that amphibian communities tend to be highly aggregate in space. Conclusively, using the conspecific‐encounter index derived from the Markov non‐independent sampling model, we provide a legible definition of community‐level distributional aggregation as an interspersed or cluster‐like distribution of different species. This definition is not idiosyncratic, as it is coincident with the definition of the contagion index used in landscape ecology. To this end, the model used in this paper establishes a framework explicitly linking community ecology and landscape ecology from a multi‐object perspective.

Tree diversity is not always a strong driver of soil microbial diversity: a 7‐yr‐old diversity experiment with trees

AbstractTrees provide organic substrates in the form of root exudates, litterfall, and fine root turnover. They modify soil physical properties and support soil biological activities. Therefore, trees are hypothesized to control soil biodiversity in forested areas. We predicted that (1) experimental forest plantations with higher tree alpha‐diversity have greater soil microbial alpha‐diversity and (2) that plantations with more divergent tree community composition would have more divergent soil microbial assemblages (Whitaker's beta‐diversity). We tested these predictions by measuring soil bacteria and fungi in a 7‐yr‐old tree biodiversity experiment. The experimental plantation contained 37 different tree assemblages, which were composed of one to four native species from temperate mixed deciduous forests. Further, there was a gradient of functional diversity nested within each level of species diversity. Soil samples were assessed for bacteria and fungi by amplicon sequencing. Tree alpha‐diversity weakly, but significantly, affected bacterial alpha‐diversity, without affecting fungal alpha‐diversity. Tree community composition was weakly, but significantly, linked to soil bacterial and fungal assemblages. In these 7‐yr‐old experimental plantations, tree diversity was not the most influential driver of soil microbial diversity.

Replacement of pine by eucalypt plantations: Effects on the diversity and structure of tree assemblages under land abandonment and implications for landscape management

The conversion of natural and semi-natural forests into plantations is an increasing trend across European landscapes under abandonment. In Northwest Iberian Peninsula, current land use changes, namely neglected management (or even abandonment) of maritime pine (Pinus pinaster) and blue gum eucalypt (Eucalyptus globulus) stands by individual landowners, represents a major challenge for landscape planning and management. The consequences of these changes for within-stand tree diversity and structure are still under-investigated. Here, we evaluate how fine-scale diversity and spatial structure of tree assemblages in the core area of stands change with land conversion. Fifty stands were selected in a farming landscape of Northwest Portugal. At the center of each stand, a 100 m2 plot was surveyed for tree species richness and structural diversity, diameter at breast height (DBH) and spatial location of individual trees. Spatial distribution patterns of trees were evaluated using autocorrelation tests and point pattern analyses. Overall, the interior of pine stands showed higher tree diversity, with more heterogeneous DBH structure and complex patterns of tree distribution, compared to eucalypt and even abandoned mixed stands. Such differences seem to result both from the inherent characteristics of the dominant tree species, and from the differential management applied within each type of forest mosaics. Therefore, active landscape management in the study area should be promoted, particularly focusing on pine co-existence with eucalypt stands in the same landscape as a sustainable strategy to achieve both conservation and production goals.

An integrated assessment of the potential impacts of climate change on Indiana forests

Forests provide myriad ecosystem services, many of which are vital to local and regional economies. Consequently, there is a need to better understand how predicted changes in climate will impact forest dynamics and the implications of such changes for society as a whole. Here we focus on the impacts of climate change on Indiana forests, which are representative of many secondary growth broadleaved forests in the greater Midwest region in terms of their land use history and current composition. We found that predicted changes in climate for the state—warmer and wetter winters/springs and hotter and potentially drier summers—will dramatically shape forest communities, resulting in new assemblages of trees and wildlife that differ from forest communities of the past or present. Overall, suitable habitat is expected to decline for 17–29% of tree species and increase for 43–52% of tree species in the state, depending on the region and climate scenario. Such changes have important consequences for wildlife that depend on certain tree species or have ranges with strong sensitivities to climate. Additionally, these changes will have potential economic impacts on Indiana industries that depend on forest resources and products (both timber and non-timber). Finally, we offer some practical suggestions on how management may minimize the extent of climate-induced ecological impacts and highlight a case study from a tree planting initiative currently underway in the Patoka River National Wildlife Refuge and Management Area.