Disentangling the importance of intrinsic and extrinsic seed dispersal factors in forest restoration success: a global review

Abstract

Animal‐mediated seed dispersal is envisaged as a key process to promote forest restoration success. Yet, we lack a comprehensive knowledge of the contribution of intrinsic and extrinsic factors which directly and indirectly influence this process and, ultimately, restoration outcomes. Here, we reviewed 157 articles to identify the most relevant intrinsic (e.g., plant and animal species traits) and extrinsic (e.g., connectivity) factors which mediate the seed dispersal process. We analyzed the contribution of such factors to restoration success, as identified in the reviewed articles, globally and for tropical and temperate biomes. Generally, our analysis revealed that the main factors affecting restoration success were the extrinsic ones (i.e., connectivity, type of restoration conducted, forest protection, and disturbance degree), while the ability of animals to achieve long‐distance dispersal was the main intrinsic factor. Differences among biomes were observed for extrinsic factors, specifically for restoration approach, as more intense efforts seem to be needed for successful restoration in tropical systems (i.e., reconstructive restoration), whereas assisted restoration (e.g., perch placements) was mostly enough for temperate ones. Within intrinsic factors, rodent frugivory and “large‐sized” seeds were related to unsuccessful restoration in tropical forests, while frugivory by carnivores and “small‐sized” seeds favored restoration in temperate ones, and the main constraint to success in this biome was ungulate frugivory. Our results highlight the importance of distinguishing between intrinsic and extrinsic factors mediating animal seed dispersal in forest restoration in different biomes. Furthermore, this paper will help to promote adequate measures when planning restoration actions.