The devil in the details: How redefining competition affects long-term simulated forest dynamics

Scaling up processes from individual to community and landscape levels has long been a critical issue in ecology, and seems a particularly relevant question when considering recent dynamics induced by climate or land-use changes. For scaling investigations, individual-based modeling is an exciting tool that allows a wide range of applied and theoretical approaches. Recent models have produced evidence that dispersal mechanisms, or environmental heterogeneity play a significant role in community dynamics. However, the description of competition in these models is often extremely simplistic. We built an individual-, rule-based model (BoreFor) that describes in a more realistic way how dispersal and competition modes affect tree population spatial and temporal dynamics. Through autocorrelation analysis of the time series produced by the model, we show how the way competition is modeled affects the long-term behavior of a tree population. When taller trees only affect individual performance (i.e., typical light decay induced competition), populations oscillate, exhibiting a strong temporal autocorrelation. On the other hand, when conspecifics can affect a taller individual (i.e., soil nutrient limitation), populations quickly reach a steady state characterized by stochastic fluctuations. We link this result with different types of resource limitation observed in northern temperate and sub-boreal forests, emphasizing the implications of such differences for long term biome dynamics.