Fonctionnement primaire et productivité de la forêt landaise: Implications pour une gestion durable

Abstract

This paper begins by describing the present status of the forest biotope of the "Landes de Gascogne" and identifying the main limiting factors. It goes on to give the available information about medium and long term changes in the physical environment, particularly those driven by global climate change, and analyses trends for the main factors that limit the primary production of the forest and possible indicators for monitoring these changes. Forest production in the "Landes de Gascogne" area has been continuously increasing since 1960 and reached a level of 9 m3/ha/year in 1988. Production is curbed by the availability of trophic resources such as the incoming radiation, atmospheric concentration in CO2, soil water and nutrients. Additionally, the access to those various resources is limited by competition with understorey vegetation. Those limitations vary over time, along the annual cycle and over the rotation. Site fertility is also constraining. The available climatic scenarios suggest that the increase in atmospheric CO2 and other greenhouse gases will lead to an increase in average temperature and reinforce the seasonal character of rainfall. This in turn could lead to increased forest production in the most humid and fertile sites. However, the productivity of the driest or nutrient-deficient sites could be lessened. Against this background, present management practices of maritime pine stands can be considered to be consistent with overall indicators of sustainable management. But to preserve the productivity of the Landes de Gascogne forests, additional management criteria for the maritime pine forests should be considered, such as the balance of nutrient cycling in forest ecosystem, especially for nutrients that cannot be or are difficult to renew, e.g., nitrogen. The improvement of soil drainage and subsequent lowering of the soil water table should also be kept compatible with optimal supply of soil water to trees during summer.