Grasslands in silvopastoral mountain ecosystems
The structure and biodiversity of silvopastoral ecosystems, also called "woodedpastures", is the result of a long tradition of multipurpose extensive land-use. The patterned vegetation consists of semi-natural grasslands found with isolated trees or intermingled with patches of forest or clumped trees. The main interactions among herbaceous vegetation, trees and shrubs, soil and cattle activities in mountain woodedpastures of the Jura Mountains are synthesized, and their sensitivity to land-use and climate change is addressed in this chapter.
Cattle grazing plays a major role in vegetation dynamics of wooded pastures through inducing three types of disturbances: herbage removal, dung deposition, and trampling. At large scales, the selection of grazing areas by cattle depends on various factors such as herbage quality and quantity, water availability, relief, slope, natural and artificial barriers, herd social interactions and learned behaviour. At small scales there is a high complexity in species response to disturbances by cattle, which varies according to the vegetation type, induced by the various light conditions in relation to tree density. Sensitivity of species to gaps induced by trampling is critical, and a complex dynamic of recolonisation is key to understanding plant species coexistence in pastures. This involves, for example, the persistence of subordinate plant species, which are recognized as having a functional importance in ecosystems, especially in the context of perturbation and climate change.
Global warming and associated environmental changes are predicted to have a strong impact on mountain ecosystems over the course of this century. Plant communities transplanted in mesocosms to warmer and drier climate experienced a marked loss in species richness.
Another major finding from this transplantation experiment, was that across land use types, intensively-used unwooded pastures were consistently more responsive to climate change than their counterparts from extensively-used wooded-pastures of either sparsely or densely wooded type. Simulations show that in extensive grazing systems, it is not only the generally lower stocking density, but also the resulting grassland-forest mosaic that contributes to the robust provision of forage. The apparent advantage in terms of productivity of unwooded pastures diminishes with drought, and wooded pastures can become a forage source of similar importance. Such formerly unproductive patches show a clear potential to compensate for the breakdown of productivity within open grasslands. Thus, across the landscape, spatial variation itself stimulates ecosystem resilience and resistance to drought.
Wooded-pastures are a good example of a landscape where high biodiversity can coexist together with an extensive land-use. So, the presence of many transitional zones (ecotones) in a highly heterogeneous and fluctuating environment, creates optimal conditions for biodiversity.
Conservation of these ecosystems, including adaptive management in the face of land-use and climate change, will require a broad approach and integrated management tools with a transdisciplinary and consensual perspective.