Forests fulfil many important functions for humanity, and do so particularly well if they contain many different tree species. At the same time, European forests could potentially provide more services than they do at the moment. These are the results of two new studies in which researchers from the Institute of Plant Sciences of the University of Bern were involved.
Forests are very important for society: the wood grown is used for furniture, roof timbers and flooring in our houses; the trees take up carbon from the air and thus reduce ongoing climate change and they help to prevent soil erosion and regulate the water cycle. We also use forests for recreation, such as when we go for a walk or collect mushrooms. The basis for providing these benefits are a series of processes, known as functions: the trees photosynthesise, grow, produce seeds, defend themselves against insects and deer, fight off pathogens and protect themselves against drought. Nutrients are taken up by the trees and are then released when the trees die and are decomposed.
Diversity instead of monocultures
A new study, led by researchers from Leipzig University and the German Centre for Integrative Biodiversity Research (iDiv) and conducted in cooperation with the University of Bern, shows that these processes work better in biodiverse woodlands. These contain several different tree species rather than the single species forests traditionally favoured by managers. As part of the European-wide research project "FunDivEUROPE", researchers investigated the importance of biodiversity for forest functioning in six countries: Germany, Finland, Poland, Romania, Italy and Spain. The scientists selected forest plots that contained one to five tree species. In Germany, for example, mixtures consisted of beech, oak, Norway spruce, birch and hornbeam. The researchers then measured 26 functions in these plots. The functions describe how nutrient and carbon cycles operate and how the trees grow, regenerate and deal with stress. Their findings show that trees in diverse forests grow faster, store more carbon and are more resistant to pests and diseases than trees in species-poor forests. "Therefore, converting monocultures to forests with many tree species in them should generally result in a higher delivery of ecosystem goods and services to humans", says Sophia Ratcliffe from Leipzig University, who led the study.
The research also shows that tree diversity is especially important for forest functioning in regions where water is scarce and the growing seasons are longer, i.e. in southern and central Europe. Christian Wirth, Head of the Department for Systematic Botany and Functional Biodiversity at Leipzig University, Managing Director of the German Centre for Integrative Biodiversity Research (iDiv) and Fellow at the Max Planck Institute for Biogeochemistry, explains why this is important: "Our summers will be drier and longer as a result of climate change. We therefore presume that, in the future, it will be even more important to manage forests so that they have a high diversity of tree species."
Forests are multifunctional
The second study, also published in the journal Ecology Letters, shows that forests could potentially provide a range of services for humanity but that currently most do not provide more than a few. This study was carried out in the same six woodland areas but the scientists combined the data from these sites with large scale surveys of forests that had been carried out in several European countries. The scientists examined 28 ecosystem functions and were able to map the expected levels of these across Europe. They then asked whether forests could provide many services at the same time or whether some functions did not go together and could thus not be found in the same forest. The study found only a few services which "traded-off" with each other meaning, that forest management can in principle be tweaked to allow many services to be provided together.
This has practical implications as first author Fons van der Plas, who was working at the University of Bern while the study was carried out, says: "In recent years, scientists have become increasingly interested in how one could promote so-called ecosystem multifunctionality, the simultaneous provision of multiple ecosystem services. Our study has shown that ecosystem multifunctionality is not just a theoretical concept, but could be common in European forests." Eric Allan who co-led the study adds: "However, currently we don't see many multifunctional forests and this suggests a huge potential for management because there is no reason why forests could not provide many more services than they do at the moment."
Source: German Centre for Integrative Biodiversity Research (iDiv)
S. Ratcliffe et al.: Biodiversity and ecosystem functioning relations in European forests depend on environmental context. Ecology Letters (2017). doi:10.1111/ele.12849
F. van der Plas et al.: Continental mapping of forest ecosystem functions reveals a high but unrealized potential for forest multifunctionality. Ecology Letters (2017). Doi: 10.1111/ele.12868