Metabolic growth mechanisms and theoretical growth potential of global woody plant communities

Predicting the growth and maximum biomass (Mmax) of woody plant
communities (WPCs) is challenging due to the complexity and variability of
tree growth. While Metabolic Scaling Theory (MST) offers a promising
concept, its current theoretical framework is still insufficient. Here, we
applied MST principles and our previous findings to propose an iterative
growth model for the growth and NPP of WPCs (IGMF). This model and its
extension show that WPC growth, net primary productivity, and other carbon
budgets - such as total primary productivity, autotrophic respiration,
organ turnover biomass, and non-structural carbohydrates - can be
expressed as functions of current biomass, maintenance respiration rate
per unit biomass, and stand age or Mmax. These globally convergent
functions allow estimation of the current (2018–2020) global
Mmax of woody plant communities at 1,440  ±  26 Pg, based solely
on their current state, with an additional 510 Pg of remaining biomass
potential. However, machine learning projections suggest that this
potential may decline by 246 Pg by 2100, primarily in evergreen broadleaf
forests. Species richness, by promoting functional convergence, amplifies
the negative effects of temperature and precipitation seasonality on Mmax.
In contrast, warming in the Northern Hemisphere may enhance Mmax in open
shrublands. Our findings reveal WPC growth kinetics and show a shift in
the main contributor to terrestrial carbon sequestration from forests to
shrublands.