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.

Recent tree diversity increase in NE Iberian forests following intense management release: A task for animal‐dispersed and drought‐tolerant species

“…Thus, the key role of animal‐dispersed species with higher drought tolerance for tree diversity increase appears replicated in all bioclimatic regions, although involving different taxonomic identities: for example, A. unedo in mesomediterranean pine forests while C. monogyna in montane ones (Figure S10A). In all cases, higher forest cover appears to be a relevant factor driving the likelihood of recruitment of these species from the regional pool (Table S10), in line with the general benefits of connectivity among forest patches for seed dispersal by animals emphasized in previous studies (Selwyn et al., 2023).…”

“…Seed dispersal type has been identified as a primary trait influencing the filtering effects of dispersal, therefore which species, and in what abundance, can be found in an area (Selwyn et al, 2023).…”

“…In addition to assessing the factors triggering changes in tree species diversity, it will be essential to identify the functional traits of the species involved, as such traits will modulate their ability to surmount the ecological filters shaping recruitment success and, ultimately, the potential complementarity effects in mixed forests. Seed dispersal type has been identified as a primary trait influencing the filtering effects of dispersal, therefore which species, and in what abundance, can be found in an area (Selwyn et al., 2023). Yet, to understand the potential success in tree species recruitment after dispersal, other functional traits influencing environmental filtering such as shade and drought tolerance need to be considered (Thomson et al., 2010).…”

Frugivores enhance potential carbon recovery in fragmented tropical landscapes

“…Studies in temperate regions suggest that natural regeneration is often more e cient than active intervention. At the same time, there is no such consensus in tropical regions, and natural regeneration can be highly variable [20][21][22]. The effectiveness of natural regeneration of tropical forest ecosystems is limited by the dispersal of seeds into degraded areas [28], and in tropical ecosystems seed dispersal mediated by animals plays a fundamental role [7,8].…”

“…Given that the movement of larger frugivores is disproportionately affected by fragmentation [15], the limitation of their movements may strongly limit the recovery of large, late-succession trees, ultimately reducing the carbon storage potential of recovering ecosystems [18,19]. However, empirical evidence for these trends is limited to local scale studies which provide mixed trends [20][21][22], and we lack quantitative information about the importance of animal movement in facilitating forest carbon recovery in fragmented landscapes.…”