Species Mixture Effects on Tree Growth

The interest for mixed-species forests has been rising during the past years. There is a broad consensus that forests with higher species diversity are likely to be more adaptable to climate change, resilient to disturbances and provider of a higher level of ecosystem services. Although several studies showed that under certain conditions mixed-species forests can be more productive than single-species stands, the representation of species interactions in empirical forest scenario models has not received much attention so far.

The main objective of this project is to investigate methodologies for quantifying the effects of species mixtures on tree growth along Switzerland’s environmental gradients, and to prepare this knowledge for the use in forest scenario calculations. The project comprises of three major parts: (1) a systematic, descriptive analysis of data from the Swiss National Forest Inventory (NFI) to provide an overview of the frequency and the distribution of pure and mixed forests in Switzerland; (2) quantification of mixing effects with nonlinear mixed-effect models fitted to NFI data and their variability with climatic, edaphic, stand and site conditions, as well as with species composition, across Switzerland’s environmental gradient; (3) identification of the different modes of intra- and inter-specific interactions using competition indices in Swiss mixed-species forests and their integration in growth functions.

The project  advances the understanding of the effects of species mixtures on tree growth under a broad range of environmental conditions in Switzerland. Additionally, it prepares this knowledge for further development of state-of-the-art forest scenario models, which are crucial tools for estimating potential wood supply and for supporting management decisions.

Published results: Mina, M.; Huber, M.O.; Forrester, D.I.; Thürig, E.; Rohner, B., (2017). Multiple factors modulate tree growth complementarity in Central European mixed forests. Journal of Ecology, xx. doi: 10.1111/1365-2745.12846