Disentangling drivers of litter decomposition in a multi-continent network of tree diversity experiments.

Litter decomposition is a key ecosystem function in forests and varies in response to a range of climatic, edaphic, and local stand characteristics. Disentangling the relative contribution of these factors is challenging, especially along large environmental gradients. In particular, knowledge of the effect of management options, such as tree planting density and species composition, on litter decomposition would be highly valuable in forestry. In this study, we made use of 15 tree diversity experiments spread over eight countries and three continents within the global TreeDivNet network. We evaluated the effects of overstory composition (tree identity, species/mixture composition and species richness), plantation conditions (density and age), and climate (temperature and precipitation) on mass loss (after 3 months and 1 year) of two standardized litters: high-quality green tea and low-quality rooibos tea. Across continents, we found that early-stage decomposition of the low-quality rooibos tea was influenced locally by overstory tree identity. Mass loss of rooibos litter was higher under young gymnosperm overstories compared to angiosperm overstories, but this trend reversed with age of the experiment. Tree species richness did not influence decomposition and explained almost no variation in our multi-continent dataset. Hence, in the young plantations of our study, overstory composition effects on decomposition were mainly driven by tree species identity on decomposer communities and forest microclimates. After 12 months of incubation, mass loss of the high-quality green tea litter was mainly influenced by temperature whereas the low-quality rooibos tea litter decomposition showed stronger relationships with overstory composition and stand age. Our findings highlight that decomposition dynamics are not only affected by climate but also by management options, via litter quality of the identity of planted trees but also by overstory composition and structure.

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Déclaration de conflit d'intérêts

Declaration of competing interest All authors reports equipment, drugs, or supplies was provided by UNILEVER Lipton Tea Bags. Juan Zuo reports financial support was provided by Belspo. Nico Eisenhauer and Olga Ferlian reports financial support was provided by German Research Foundation FZT 118, 202548816. Helge Bruelheide, Bo Yang, Stefan Trogisch, Heike Feldhaar, Steffen Seitz reports financial support was provided by German Research Foundation FZT 118, 202548816. Martin Weih reports financial support was provided by Swedisch Energy Agency (36654-1, 36654-2, 36654-3 project DiPTiCC 16-CE32-0003. Michael Scherer-Lorenzen reports administrative support was provided by Federal Forestry Office Thüringer Wald.