Apports des traits fonctionnels végétaux pour l’évaluation écologique des trajectoires de gestion en milieux prairiaux

Contribution of the functional characteristics of plants to the ecological assessment of the evolutive patterns of management in grassland environments

The response of plant communities to extensification can be spotted in such traits as plant height, specific leaf area and dry matter content, whose abundance is changing. They constitute important indicators of the strategies followed by plants to make the best use of the mineral resources, and they give valuable clues for the setting-up of indicators of management.
An experimental approach was used, tested in two sub-alpine pastures, contrasting by their climatic, historical and agronomical characteristics, to examine : 1) whether an extensified utilization led to a lower diversity and 2) whether the changes were linked to a shift between, on the one hand functional structures reflecting a rapid uptake and recycling
of reserves, and, on the other hand functional structures dominated by strategies of nutrient conservation. Extensification and the corresponding decline in fertility led, as suspected, to a lower diversity of species in Le Lautaret, whereas on the other site (Les Saisies), and in accordance with observations made on a number of other pasture sites in the northern Alps, the diversity remained constant, whatever the level of management.
On the other hand, with regard to the functional responses of the
pastures, the analyses showed concordant responses on the two sites. A lower mineral fertility brought about a shift from species with a rapid uptake and re-cycling of resources, with features such as leaves with a low dry matter content, a high specific area and a high protein content, towards species with a conservative management of resources, having the opposite features and a lower height. It is thus possible to identify
functional plant traits for the diagnosis of the advancement of the effects of pasture extensification.