Demographic disequilibrium and growth-mortality asymmetry of forests across climate gradients

Abstract

Forests are commonly believed to adapt themselves to environment and ultimately converge to demographic equilibrium characterized by a fixed size-structure. The expectation, however, has been lacking in mathematical rigor and been debating for evidential solidity. Here, by giving a general time-dynamic solution to the forest demographic model and verifying the prediction with worldwide forest inventory data, we show the inherent disequilibrium of forest demography with oscillations of forest-size-structure. Forests adapt to environment in a way of asymmetric growth-mortality tradeoff along climate gradients, which generates divergence to convergence oscillations of size-structure with rising temperature and precipitation. The demographic disequilibrium framework can provide a general basis for elucidating the variability of forest-size-structure with implications on intrinsic ecosystem instability, and for improving the Earth system modeling.