Abstract
AbstractAimWe analyse how functional diversity (FD) varies across European natural forests to understand the effects of environmental and competitive filtering on plant trait distribution.LocationForest ecosystems in Europe from 11°W to 36°E and 29.5°N to 62°N.TaxonPinaceae, Fagaceae and Betulaceae, Oleaceae, Tiliaceae, Aceraceae, Leguminosae (unspecific).MethodsWe 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.ResultsLund‐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 ConclusionsWe 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.
Highlights
Functional diversity (FD) is a key control of the stability and adaptability of ecosystems under climate change (Yachi & Loreau, 1999)
We found simulated vegetation height and biomass to compare well against remotely sensed observations and local in situ data, the comparison of natural forest and actual vegetation is limited as remote-sensing products detect properties of actual vegetation cover which are influenced by current land use and forest management
Simulated specific leaf area (SLA) and wood density (WD) are in close agreement with observed TRY data. These results show that the new version of LPJmL-FIT reproduces the spatial plant functional type (PFT) and local trait distributions as well as the productivity and biomass of European natural forests
Summary
Functional diversity (FD) is a key control of the stability and adaptability of ecosystems under climate change (Yachi & Loreau, 1999). Recent studies investigated a mix of globally important physiological traits (e.g. SLA, WD, seed mass and leaf nitrogen content) and morphological traits (including maximum plant height and basal area) (Ratcliffe et al, 2016; Ruiz-Benito et al, 2017), or separate the effects between those trait types (e.g. Madrigal-Gonzalez et al, 2016; Schneider et al, 2017). They advance our understanding of spatial pattern of plant traits at the landscape and continental scale
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