Nurse species facilitate persistence of dry forests in agricultural landscapes in Uruguay

Questions: Park forests are shaped by extensive cattle ranching in the transition between natural riverine forests and open grasslands. The underlying mechanisms driving tree regeneration have not been studied, however, they determine biodiversity, sustainability and multifunctionality of these ecosystems. We explored patterns of tree regeneration by analyzing nurse–beneficiary interactions and tree community composition.
Location: Park forests within the departments of Rio Negro, Paysandú, Artigas and Tacuarembó, República Oriental del Uruguay, South America.
Methods: We established 205 (1 × 1 m2) paired plots in open microhabitat and under the tree canopy to evaluate the patterns of tree regeneration. To assess tree community composition and diversity we carried out forest inventories within one-hectare plots of ten park forests.
Results: Scattered trees in park forests had a positive effect on tree regeneration density, whereas, dense grass coverage had a negative effect. Regeneration density increased and grass cover reduced under the canopy of nurse trees. Regeneration beneficiaries were mainly bird dispersed species with different life strategies. Tree communities varied between forest types and spatially closer forests were more similar.
Conclusions: Our study outlines the importance of park forest trees to the promotion of forest regeneration and recovery in grazed forests. Our results found a positive interaction effect between nurse trees and saplings, based on our results we suggested possible facilitation mechanisms including the provision of shade, reduction of grass competition and the attraction of seed dispersers.