2021, Sakschewski, Boris, Bloh, Werner von, Drüke, Markus, Sörensson, Anna Amelia, Ruscica, Romina, Langerwisch, Fanny, Billing, Maik, Bereswill, Sarah, Hirota, Marina, Oliveira, Rafael Silva, Heinke, Jens, Thonicke, Kirsten

A variety of modelling studies have suggested tree rooting depth as a key variable to explain evapotranspiration rates, productivity and the geographical distribution of evergreen forests in tropical South America. However, none of those studies have acknowledged resource investment, timing and physical constraints of tree rooting depth within a competitive environment, undermining the ecological realism of their results. Here, we present an approach of implementing variable rooting strategies and dynamic root growth into the LPJmL4.0 (Lund-Potsdam-Jena managed Land) dynamic global vegetation model (DGVM) and apply it to tropical and sub-tropical South America under contemporary climate conditions. We show how competing rooting strategies which underlie the trade-off between above- and below-ground carbon investment lead to more realistic simulation of intra-annual productivity and evapotranspiration and consequently of forest cover and spatial biomass distribution. We find that climate and soil depth determine a spatially heterogeneous pattern of mean rooting depth and below-ground biomass across the study region. Our findings support the hypothesis that the ability of evergreen trees to adjust their rooting systems to seasonally dry climates is crucial to explaining the current dominance, productivity and evapotranspiration of evergreen forests in tropical South America.

2021, Maréchaux, Isabelle, Langerwisch, Fanny, Huth, Andreas, Bugmann, Harald, Morin, Xavier, Reyer, Christopher P.O., Seidl, Rupert, Collalti, Alessio, Dantas de Paula, Mateus, Fischer, Rico, Gutsch, Martin, Lexer, Manfred J., Lischke, Heike, Rammig, Anja, Rödig, Edna, Sakschewski, Boris, Taubert, Franziska, Thonicke, Kirsten, Vacchiano, Giorgio, Bohn, Friedrich J.

Understanding the processes that shape forest functioning, structure, and diversity remains challenging, although data on forest systems are being collected at a rapid pace and across scales. Forest models have a long history in bridging data with ecological knowledge and can simulate forest dynamics over spatio-temporal scales unreachable by most empirical investigations.We describe the development that different forest modelling communities have followed to underpin the leverage that simulation models offer for advancing our understanding of forest ecosystems.Using three widely applied but contrasting approaches - species distribution models, individual-based forest models, and dynamic global vegetation models - as examples, we show how scientific and technical advances have led models to transgress their initial objectives and limitations. We provide an overview of recent model applications on current important ecological topics and pinpoint ten key questions that could, and should, be tackled with forest models in the next decade.Synthesis. This overview shows that forest models, due to their complementarity and mutual enrichment, represent an invaluable toolkit to address a wide range of fundamental and applied ecological questions, hence fostering a deeper understanding of forest dynamics in the context of global change.