Temporal dynamics, i.e. progressive natural changes of ecosystems, are poorly known in conservation biology. They are therefore rarely taken into account in the decisions of either nature managers, scientists or politicians in charge of the designation of protected areas, or reserve managers that apply management guidelines, or foresters that must combine wood production and biodiversity conservation. Yet, they imply questions of prime importance. Why is a given species still rare while all its ecological requirements are met ? Should the forest be left to naturally recolonize protected areas or should we manage these reserves to maintain an optimal biodiversity ? Our research explores this theme by studying bird populations in forested areas with, besides the basic objective of reaching a better understanding of ecological dynamics, an applied objective: to provide field foresters with practical and usable elements for biodiversity conservation.