Temps de lecture :2 minutes
Forests are always on the move. With climate variations, they advance and retreat. At the end of the last glaciation, 20,000 years ago, forests that developed in more clement zones recolonised Europe. Moving northward from the south of Spain or Italy, the oak, to name but one species, covered the European continent at the amazing rate of 380 metres per year, on average.
Whether tropical or temperate, forests all evolve according to the cycles in which species follow on from one another without us generally being aware of it. After a forest fire, an avalanche, a storm or even a fallen tree, ‘pioneering’ species take over the new ground and create (or recreate) a forest environment.
Moss and lichen, which are capable of developing in environments that are unstable or deficient in water or organic matter, prepare the way. The first trees and shrubs then appear. Species vary from one type of forest to another, but all have the same characteristics. Thanks to plentiful light and the absence of rivals, they grow very fast and produce a great number of seeds that are spread by wind or animals. Although their lifespan is limited to a few dozen years, these ‘sprinters’ modify in turn the conditions of life in their environment and enable other species to grow.
In the shade of these shrubs, the slow-growing trees can develop. These have a more solid structure able to withstand time. After several hundred years, they will become the pillars of the forest to which creepers and epiphytes attach themselves.
But these changes are imperceptible to the walker. At most, he or she might notice that a tree has fallen here and that others are growing there. But on the timescale of the forest, it is a permanent ballet of movement.
Extrait du livre « Des forêts et des hommes » rédigé par la rédaction de GoodPlanet à l’occasion de l’année internationale des forêts et disponible aux éditions de la Martinière.