Extension phenomena: analysing, understanding and foreseeing

Abstract

Spontaneus extensions play an important role in the progression of forests in France and they often concern species, which are technologically interesting. They thus contribute to the diversity of the forests and consequently to that of the forest production. However, they often shut off the landscape. To manage them more efficiently, it must be possible to foresee their extension and their type. This implies having information concerning on the modification of the socio-economic context which determines changes in the use of the soil and/or modification of the agricultural practices, besides the basic underlying process, of the dynamics of vegetation. Apparently, there are two approaches. The first is based on the notion of succession after a complete stop in the use of agricultural or grazing ground. The second approach is based rather on the dynamics of the plant population and its variability as a function of human influences. After an analysis of these two approaches, we explain why the second is preferable. Although this approach, based on the dynamics of the plant population, is relatively difficult to apply, it has the major advantage of going beyond the simple description of types of vegetation, valid only in the area in which it was studied. The interrelations and the processes detected in one spot can be generalised and applied in other places where they will be expressed in a similar or different manner depending on the ecological context. They give a key to understanding the transformations of the landscape, taking into account the features of each element of the mosaic and the operation of the landscape as a whole.