Lessons learned from applying a forest gap model to understandecosystem and carbon dynamics of complex tropical forests

Abstract

tForests worldwide are threatened by various environmental and anthropogenic hazards, especially trop-ical forests. Knowledge on the impacts of these hazards on forest structure and dynamics has beencompiled in empirical studies. However, the results of these studies are often not sufficient for long-term projections and extrapolations to large spatial scales especially for unprecedented environmentalconditions, which require both the identification and understanding of key underlying processes. For-est models bridge this gap by incorporating multiple ecological processes in a dynamic framework (i.e.including a realistic model structure) and addressing the complexity of forest ecosystems. Here, wedescribe the evolution of the individual-based and process-based forest gap model FORMIND and itsapplication to tropical forests. At its core, the model includes physiological processes on tree level (pho-tosynthesis, respiration, tree growth, mortality, regeneration, competition). During the past two decades,FORMIND has been used to address various scientific questions arising from different forest types by con-tinuously extending the model structure. The model applications thus provided understanding in threemain aspects: (1) the grouping of single tree species into plant functional types is a successful approachto reduce complexity in vegetation models, (2) structural realism was necessary to analyze impacts ofnatural and anthropogenic disturbances such as logging, fragmentation, or drought, and (3) complexecological processes such as carbon fluxes in tropical forests – starting from the individual tree level upto the entire forest ecosystem – can be explored as a function of forest structure, species compositionand disturbance regime. Overall, this review shows how the evolution of long-term modelling projectsnot only provides scientific understanding of forest ecosystems, but also provides benefits for ecologicaltheory and empirical study design.