Simulating functional diversity of European natural forests along climatic gradients

Abstract

Aim We analyse how functional diversity (FD) varies across European natural forests to understand the effects of environmental and competitive filtering on plant trait distribution. Location Forest ecosystems in Europe from 11°W to 36°E and 29.5°N to 62°N. Taxon Pinaceae, Fagaceae and Betulaceae, Oleaceae, Tiliaceae, Aceraceae, Leguminosae (unspecific). Methods We adopted the existing Dynamic Global Vegetation Model Lund‐Potsdam‐Jena managed Land of flexible individual traits (LPJmL‐FIT) for Europe by eliminating both bioclimatic limits of plant functional types (PFTs) and replacing prescribed values of functional traits for PFTs with emergent values under influence of environmental filtering and competition. We quantified functional richness (FR), functional divergence (FDv) and functional evenness (FE) in representative selected sites and at Pan‐European scale resulting from simulated functional and structural trait combinations of individual trees. While FR quantifies the amount of occupied trait space, FDv and FE describe the distribution and abundance of trait combinations, respectively, in a multidimensional trait space. Results Lund‐Potsdam‐Jena managed Land of flexible individual traits reproduces spatial PFTs and local trait distributions and agrees well with observed productivity, biomass and tree height of European natural forests. The observed site‐specific trait distributions and spatial gradients of traits of the leaf‐ and stem‐resource economics spectra coincide with environmental filtering and the competition for light and water in environments with strong abiotic stress. Where deciduous and needle‐leaved trees co‐occur, for example, in boreal and mountainous forests, the potential niche space is wide (high FR), and extreme ends in the niche space are occupied (high FDv). We find high FDv in Mediterranean forests where drought increasingly limits tree growth, thus niche differentiation becomes more important. FDv decreases in temperate forests where a cold climate increasingly limits growth efficiency of broad‐leaved summer green trees, thus reducing the importance of competitive exclusion. Highest FE was simulated in wet Atlantic and southern Europe which indicated relatively even niche occupation and thus high resource‐use efficiency. Main Conclusions We find FD resulting from both environmental and competitive filtering. Pan‐European FR, FDv and FE demonstrate the influence of climate gradients and intra‐ and inter‐PFT competition. The indices underline a generally high FD of natural forests in Europe. Co‐existence of functionally diverse trees across PFTs emerges from alternative (life‐history) strategies, disturbance and tree demography.

Towards a functional phytosociology: the functional ecology of woody diagnostic species and their vegetation classes in Northern Italy

“…Indeed, classes of both evergreen heaths and forests showed a marked tendency toward the stress-tolerant (S) strategy (Fig. 2), confirming also for woody vegetation that in harsh habitats the environmental filter (i.e., abiotic stress) is a key determinant of the community functional composition (Thonicke et al 2020), leading species to share similar traits as a common adaptation to physical constraints (Grime 2006, De Bello et al 2009. Our results support evidence of a convergence toward similar functional response of structural diagnostic species of syntaxa that phytosociology considers to be completely different, as they do not exhibit species in common.…”

Global patterns and climatic controls of forest structural complexity

“…However, a more detailed understanding of relationships between functional diversity, specific functional traits in particular, and forest structural complexity is scarce. Recent advances in mapping functional diversity may allow for an improved understanding of linkages between functional diversity and forest structural complexity across spatial scales [40][41][42] . Identifying the functional drivers of forest structural complexity could help to further unravel the mechanistic underpinnings of relationships between climate and forest structural complexity in more detail.…”

Remotely sensed between‐individual functional trait variation in a temperate forest

“…This partitioning of trait variation can help us to better understand factors shaping the spatial structure of tree communities (Cavender‐Bares et al., 2006 ) and thus can be used as a basis for further studies of relationships between functional diversity and community assembly or ecosystem functioning (Durán et al., 2019 ; Schweiger et al., 2018 ). For example, trait variation can be related to coexistence mechanisms (such as competitive exclusion leading to niche differentiation and increased phylogenetic dispersion among species; see e.g., Allan et al., 2013 ; Valladares et al., 2015 ) or environmental filtering reducing taxonomic variation and phylogenetic dispersion (Thonicke et al., 2020 ). Incorporating individual‐based trait information into biodiversity dynamics models could also improve predicting responses of vegetation to environmental change at various spatial scales.…”

“…For example, trait variation can be related to coexistence mechanisms (such as competitive exclusion leading to niche differentiation and increased phylogenetic dispersion among species; see e.g., Allan et al, 2013;Valladares et al, 2015) or environmental filtering reducing taxonomic variation and phylogenetic dispersion (Thonicke et al, 2020). Incorporating individual-based trait information into biodiversity dynamics models could also improve predicting responses of vegetation to environmental change at various spatial scales.…”