Dynamics of Mixed Pine–Oak Forests

Abstract

A long history of human influence, including large-scale afforestation with pines and changes in land-management and conservation priorities, have strongly affected the formation of Mediterranean landscapes with contiguous patches of pine stands and oak woodlands. Consequently, this pine-oak mosaic creates opportunities for cross-colonization of both species and the formation of mixed pine-oak forests. These processes are homologous to classical secondary succession in which abandoned agricultural land is colonized by early-successional pines, which allow the establishment of late-successional oaks. We used the frameworks of forest succession and gap dynamics to explore the evidence for pine and oak regeneration within mixed pine-oak forests, and evaluate the fate of these Mediterranean mixed forests. Our analysis highlights selection towards enhanced oak regeneration and recruitment and lowered survival and recruitment for pines within mixed pine-oak forests, which is expected to drive succession from the intermediate mixed stage towards late-successional oak-dominated forest. However, studies have proposed persistence mechanisms for the maintenance of mixed pine-oak forests as a long-term stable stage, in which gaps form in the mixed forest of pines and oaks, allowing the recruitment of both species. Alternatively, scenarios of novel climates or fire regimes have projected a deterioration of developed forests to vegetation formations dominated by non-tree forms.