Putting forest biodiversity into equations

A mathematical model to come to the rescue of biodiversity in a context of global warming.

Ecosystems involve complex interactions between species and their balance sometimes crucially depends on tiny variations in their environmental parameters. To quantify this idea using a concrete example, Laurent Di Menza from the LMR1Laboratoire de Mathématiques de Reims (CNRS/Université de Reims Champagne-Ardenne) and Virginie Joanne-Fabre from the Habiter Laboratory2Université de Reims Champagne-Ardenne have developed a mathematical model capable of monitoring the evolution in time of a tree population in the Ardennes region’s forest, in northeastern France.

To do so, they opted for a simplified way of putting into equations the complexity of the real system. They divided the forest into plots of land of a few square kilometres and reduced the biodiversity to two types of trees—decidious and coniferous—and three age classes for each type. A set of parameters (growth and mortality rates, factors of occupation, etc.) taken from data provided by the French National Forestry Office (ONF) helped recreate real-life conditions.

In many cases, altering these variables happened to give the tree populations a new form of balance. In some situations however, a very slight increase in the mortality rate of just one type of tree in one age class was found to result in the extinction of all such specimens. “These are very early results and a lot of work needs to be carried out to make our model operational,” stresses Laurent Di Menza. Yet this model could eventually contribute to forest management, particularly in today’s context of climate change.