Facilitation by pioneer trees and herbivore exclusion allow regeneration of woody species in the semiarid ecosystem of central Chile

Questions: Facilitation by pioneer plants and herbivore exclusion may contribute to plant regeneration and restoration of degraded semiarid ecosystems. In this study we evaluated the main and interactive effects of the exclusion of large and medium-sized mammal herbivores and the presence of the pioneer tree Vachellia caven on natural regeneration of woody species in degraded savannas. Location: Two localities of the native sclerophyllous forest of central Chile Methods: Twelve 30 x 40 m exclosures and twelve non-exclosure areas located near native forests were established in savannas of V. caven in each locality. Regeneration coming from seeds and resprouts was sampled both under the canopy of V. caven and without canopy in each exclosure and non-excluded area. Results: After seven years, species richness and density of older regeneration (0.5-2 m high) were positively affected by herbivore exclusion and the presence of V. caven. No significant interaction between herbivore exclusion and V. caven was observed. Younger regeneration (<0.5 m high) was positively affected by herbivore exclusion and the presence of V. caven only in some years with almost no interactive effect. Conclusions: The exclusion of large and medium-sized exotic herbivores and facilitation by pioneer trees are complementary for regeneration. The variable but permanent presence of younger and older regeneration within exclosures and under V. caven during the experiment may lead to an increase of density and diversity of adult plants and recovery of the native forest. However, this process may be slow due to other limiting factors, for instance, reduced precipitation associated with climate change.

Automated summary

Facilitation by pioneer trees and herbivore exclusion have positive effects on the natural regeneration of woody plants in degraded savannas. Older regeneration is positively affected by both herbivore exclusion and the presence of the pioneer tree Vachellia caven, while younger regeneration is mainly influenced by herbivore exclusion. The combination of both factors can lead to an increase in density and diversity of adult plants and contribute to the recovery of the native forest.