An individual‐based forest model to jointly simulate carbon and tree diversity in Amazonia: description and applications

Abstract

Forest dynamic models predict the current and future states of ecosystems and are a nexus between physiological processes and empirical data, forest plot inventories and remote‐sensing information. The problem of biodiversity representation in these models has long been an impediment to a detailed understanding of ecosystem processes. This challenge is amplified in species‐rich and high‐carbon tropical forests. Here we describe an individual‐based and spatially explicit forest growth simulator, TROLL, that integrates recent advances in plant physiology. Processes (carbon assimilation, allocation, reproduction, and mortality) are linked to species‐specific functional traits, and the model was parameterized for an Amazonian tropical rainforest. We simulated a forest regeneration experiment from bare soil, and we validated it against observations at our sites. Simulated forest regeneration compared well with observations for stem densities, gross primary productivity, aboveground biomass, and floristic composition. After 500 years of regrowth, the simulated forest displayed structural characteristics similar to observations (e.g., leaf area index and trunk diameter distribution). We then assessed the model's sensitivity to a number of key model parameters: light extinction coefficient and carbon quantum yield, and to a lesser extent mortality rate, and carbon allocation, all influenced ecosystem features. To illustrate the potential of the approach, we tested whether variation in species richness and composition influenced ecosystem properties. Overall, species richness had a positive effect on ecosystem processes, but this effect was controlled by the identity of species rather by richness per se. Also, functional trait community means had a stronger effect than functional diversity on ecosystem processes. TROLL should be applicable to many tropical forests sites, and data requirement is tailored to ongoing trait collection efforts. Such a model should foster the dialogue between ecology and the vegetation modeling community, help improve the predictive power of models, and eventually better inform policy choices.

Biodiversity and climate determine the functioning of Neotropical forests

“…We used SEMs to control, as much as possible, for potentially confounding factors, but correlation does not necessarily mean causation. Controlled experiments and modelling studies (e.g., Maréchaux & Chave, ; Sakschewski et al, ) are needed to provide further support for a causal relationship between biodiversity and biomass dynamics in the tropics (van der Sande, Poorter et al, ). Biodiversity is more than merely species richness, because it encompasses forest attributes in general.…”

Functional perspectives on tropical tree demography and forest dynamics

“…Dynamic global vegetation models (DGVMs) are often central to these predictions. Current DGVMs vary in their detail regarding the functional diversity in tropical forests with some including only one to a few functional types rather than a continuous distribution of functions (Díaz and Cabido 1997;Baraloto et al 2010;Xu et al 2016;Butler et al 2017;Maréchaux and Chave 2017). While some inclusion of functional types is better than excluding plant function all together, such models fail to capture trait variation and should break apart these functional types into specific functional trait measurements for each species to incorporate more axes of plant function and continuous variation in traits (Wright et al 2005;Baraloto et al 2010;Funk et al 2017).…”

Assessing the role of megafauna in tropical forest ecosystems and biogeochemical cycles – the potential of vegetation models

“…To overcome some of these problems, we propose an approach that relies on vegetation models (VMs) to complement current studies and integrate knowledge from different fields. VMs developed for tropical biomes (Moorcroft et al 2001, Fischer et al 2016, Maréchaux and Chave 2017 have been designed to simulate, among other processes, forest succession, seed dispersal, and disturbance. Many of the ecological processes associated with plant-animal interactions are simulated in VMs, but the effects of animals are not modelled explicitly.…”

“…Within this framework, VMs offer the potential to synthesize complementary knowledge across fields to address current shortcomings. Some VMs were developed specifically for tropical forests (TROLL (Maréchaux and Chave 2017), ED (Moorcroft et al 2001), and FORMIND (Fischer et al 2016)), while others were developed for more global applications, but have been used in tropical studies at different scales ( LPJ-GUESS (Sitch et al 2003) and ORCHIDEE (Krinner et al 2005, Verbeeck et al 2011). VMs are biogeophysical process-based models reproducing vegetation dynamics by simulating establishment, growth, dispersal, and competition for resources, over many tree generations.…”