Lotka–Volterra in forestry: Quantifying species interactions and mixed-species dynamics

Most of the world’s forests are mixed-species, yet forestry research and growth and yield modeling have traditionally focused on single-species stands, which are simpler to model and have long been monitored for timber production. Mixed-species forests are increasingly recognized for their resilience to climate change and the ecosystem services they provide, but modeling their dynamics remains challenging. Existing models tend to be complex and individual-based, linking tree-level demography to stand-level behavior in ways that are difficult to generalize or interpret without extensive simulation and field validation. Here we show that the classic Lotka–Volterra competition model from population ecology reproduces many aspects of mixed stands: it quantifies intra- and interspecific competition, simulates species trajectories, estimates carrying capacity, and gives analytical conditions for coexistence. We applied the Lotka–Volterra model to mixed-species forests in southeastern Australia dominated by Eucalyptus regnans (mountain ash) and Acacia dealbata (silver wattle). Using 10 years of data from permanent sample plots, we calibrated the competition coefficients and estimated carrying capacities of 89 m 2 ha −1 for Eucalyptus and 34 m 2 ha −1 for Acacia . The coefficients point to an amensalistic interaction: Eucalyptus suppresses Acacia without being significantly affected in return. The model predicts that Acacia basal area declines once Eucalyptus basal area exceeds 29 m 2 ha −1 , leading to its gradual exclusion from the stand. Although largely overlooked in forestry, the Lotka–Volterra model provides a simple and extensible framework for quantifying species interactions, studying ecosystem change, and informing mixed-species forest management.