A joint individual‐based model coupling growth and mortality reveals that tree vigor is a key component of tropical forest dynamics

Abstract

Tree vigor is often used as a covariate when tree mortality is predicted from tree growth in tropical forest dynamic models, but it is rarely explicitly accounted for in a coherent modeling framework. We quantify tree vigor at the individual tree level, based on the difference between expected and observed growth. The available methods to join nonlinear tree growth and mortality processes are not commonly used by forest ecologists so that we develop an inference methodology based on an MCMC approach, allowing us to sample the parameters of the growth and mortality model according to their posterior distribution using the joint model likelihood. We apply our framework to a set of data on the 20-year dynamics of a forest in Paracou, French Guiana, taking advantage of functional trait-based growth and mortality models already developed independently. Our results showed that growth and mortality are intimately linked and that the vigor estimator is an essential predictor of mortality, highlighting that trees growing more than expected have a far lower probability of dying. Our joint model methodology is sufficiently generic to be used to join two longitudinal and punctual linked processes and thus may be applied to a wide range of growth and mortality models. In the context of global changes, such joint models are urgently needed in tropical forests to analyze, and then predict, the effects of the ongoing changes on the tree dynamics in hyperdiverse tropical forests.

Nutrient-cycling mechanisms other than the direct absorption from soil may control forest structure and dynamics in poor Amazonian soils

“…In both cases, this positive relationship was interpreted as an indirect effect: the high nutrient content would accelerate seedling growth40 or coarse-wood productivity across Amazonia7 and therefore increase the competition for resources (light or water) amongst trees. Other factors may have direct effects on mortality, such as exceptionally heavy rains and waterlogging that increase soil instability42. This higher mortality leads to a lower basal area and to a higher proportion of light-demanding species and to a faster increase in tree diameter but to a lower productivity43.…”

Disentangling competitive vs. climatic drivers of tropical forest mortality

“…Allen et al, 2010;Brando et al, 2014;Condit et al, 1995;Lewis et al, 2011;Nepstad et al, 2007;Phillips et al, 2009Phillips et al, , 2010, past patterns of growth (e.g. Aubry-Kientz, Rossi, Boreux, & Hérault, 2015;Bigler & Bugmann, 2003;Chao et al, 2008;Wyckoff & Clark, 2000) and species-specific traits (e.g. Aubry-Kientz et al, 2013;Chao et al, 2008;Kraft, Metz, Condit, & Chave, 2010;Phillips et al, 2009;Uriarte, Lasky, Boukili, & Chazdon, 2016).…”

Vulnerability of Commercial Tree Species to Water Stress in Logged Forests of the Guiana Shield

“…Forest dynamics is influenced by several non-investigated environmental variables (topography, light availability, etc.) and also by the unique individual tree vigor [50].…”

“…To address the delicate issue of coupling both processes, we used the methodology developed in [50] to link growth and mortality through the individual tree vigor. Tree vigor is estimated with log AGR i,t + 1…”