Long-term recovery of multifunctionality in Mediterranean forests depends on restoration strategy and forest type

Forest area is increasing in temperate biomes through active and passive restoration of old fields. Despite the large extension of restored forests, the success of contrasting restoration strategies (active - planted forests - vs. passive - secondary forests -) over time has never been evaluated in Mediterranean forests. We studied how restoration strategy determined forest restoration success. We evaluated which restoration strategy resulted in forests more like references (i.e. forests with continuous canopy cover since at least the 1940s) in terms of structure, diversity, functional composition, and dynamics. We then assessed whether active restoration accelerated forest recovery compared to passive restoration. We studied a chronosequence of recovery in four forest types (mountain and Mediterranean pine forests and mesic and Mediterranean oak forests) using the data of the Spanish Forest Inventory in central Spain. Each plot was classified as planted, secondary or reference forest. We modelled the response ratios of 11 forest attributes and a multifunctionality index as a function of restoration strategy, forest age, and abiotic and biotic constraints. Secondary forests showed a greater likeness to references than planted forests in oak forests while minor differences between secondary and planted forests were found in pine forests. The recovery speed of most forest attributes in secondary and planted forests was similar. Multifunctionality was higher, and increased more rapidly, in planted than in secondary forests in Mediterranean oak forests. However, multifunctionality was similar for both restoration strategies in the other forest types. Synthesis and applications. The long-term assessment of forest recovery in Mediterranean abandoned fields indicated that both planted forests and natural forest succession are successful restoration strategies, depending on the aim and the forest type. In our research, restoration strategy did not influence the magnitude and speed of forest recovery in pine forests. However, in oak forests, natural forest succession led to forests more alike to references, but planted forests can maximize and accelerate recovery of forest multifunctionality.