Functional diversity underlies demographic responses to environmental variation in European forests

Biodiversity loss and climate-driven ecosystem modification is leading to substantial changes in forest structure and function. However, diversity effects on demographic responses to the environment are poorly understood. We tested the diversity hypothesis (measured through functional diversity) and the mass-ratio hypothesis (measured through functional identity) on tree growth, tree mortality and sapling abundance. We sought to determine whether functional diversity underlies demographic responses to environmental variation in European forests.

We covered Europe (Spain, Germany, Wallonia, Finland and Sweden) and we used data from five European National Forest Inventories from boreal to the Mediterranean biomes (c. 700,000 trees in 54,000 plots and 143 tree species) and the main forest types across Europe (i.e. from needle-leaved evergreen forests to broad-leaved deciduous forests). For each forest type, we applied maximum likelihood techniques to quantify the relative importance of stand structure, climate and diversity (i.e. functional diversity and functional identity) as determinants of growth, mortality and sapling abundance. We also tested whether demographic responses to environmental conditions (including stand density, evapotranspiration and temperature anomalies) varied with functional diversity.

Our results suggest that functional diversity had a positive effect on sapling abundance and growth rates in forests across Europe, while no effect was observed for tree mortality. Functional identity had a strong effect on mortality and sapling abundance, with greater mortality rates in forests dominated by needle-leaved individuals and greater abundance of saplings in forests dominated by broad-leaved individuals. Furthermore, we observed that functional diversity modified stand density effects on demographic responses in Mediterranean forests and the influence of evapotranspiration and temperature anomalies in forests widely distributed across Europe. Therefore, functional diversity may play a key role in forest dynamics through complementarity, as well as by modulating growth and recruitment responses to environmental variation.

Figure. Diverse forests with a mix of species including Betula sp., Corylus avellanaQuercus pyrenaicaPopulus sp. and Salix sp. In Sierra de Candelario (Salamanca, Spain) by Jaime Madrigal-Gonzalez in 2016.


Ruiz-Benito, P., Ratcliffe, S., Jump, A., Gómez-Aparicio, L., Madrigal-González, J., Wirth, C., Kändler, G., Lehtonen, A., Dahlgren, J., Kattge, J. & Zavala, M. (2016) Functional diversity underlies demographic responses to environmental variation in European forests. Global Ecology and Biogeography.

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