A review of the development of Mediterranean pine-oak ecosystems after land abandonment and afforestation: Are they novel ecosystems?

Context: Mediterranean landscapes are composed of different interacting vegetation patches. Pine and oak ecosystems form contiguous patches within these landscapes, in pure stands, or as mixed pine-oak ecosystems. During the nineteenth century, pine forest distribution in the Mediterranean Basin increased dramatically as a result of large-scale re-forestation and spontaneous forest regeneration. At the same time, secondary succession of abandoned agricultural land allowed development of pine and oak ecosystems. Consequently, a pine-oak mosaic has developed, which created opportunities for cross-colonization, i.e. species colonization from one ecosystem in the reciprocal system. Pines shed their wind-dispersed seeds and colonize Mediterranean oak vegetation. Oaks regenerate in different ecosystems, including pine forest understories. Research question: This paper reviews fire-free landscapescale dynamics of pine-oak Mediterranean mosaics and analyze how landscape-scale interactions are leading to pine-oak ecosystems by different processes. Results: Published information from the Mediterranean Basin illustrates pathways of pine-oak ecosystems formation. Using Mediterranean literature, I try to elucidate the factors that (1) control colonization potential and (2) modulate the resistance to colonization, in different habitats, land uses, and landscape settings. Conclusion: Management implications for these mixed pine-oak ecosystems are suggested. The question of whether they are novel ecosystems is discussed.