A simple Markovian individual-based model as a means of understanding forest dynamics

The forests are ecological systems of great complexity which present interaction phenomena associated with the competition between individuals of the same and of different species. This competition is about access to resources (light, water, nutrients, etc.). The scales of forest ecosystems are very long. For this reason we use in this framework Markovian modelling for space and time evolution of population distribution, thanks to an individual-based model in the form of a stochastic branching process. Understanding the behaviour of individual-based models of forest dynamics becomes difficult as their complexity increases. A useful strategy consists in simplifying parts of the original model in order to simulate a simplified version of forest dynamics. This strategy is adopted to understand the spatial pattern structured population in a simple individual-based model. The model is made of two components: birth or recruitment and death (natural mortality and mortality due to competition). The interplay between the spatial pattern of trees and the competition/dispersion level is thus understood and the excessive impact of the low dispersion that favours the establishment of clusters is diagnosed.