Biotic interactions between trees and colonizing shrubs: Implications for active restoration in southern Patagonian forests

Plant–plant interactions are key to understanding ecosystem services and shaping restoration strategies, as they can produce either negative or positive effects, determining species establishment and growth. Recognizing these interactions during early-life stages provides valuable insights for restoration in human-disturbed areas. One promising approach is nucleation planting, which establishes small clusters of native species in strategically selected sites, being particularly useful in sites with large herbivores. In southern Patagonia, livestock production has historically been the main economic activity, severely impacting extensive areas of Nothofagus antarctica forest through grazing and intentional burning to increase forage. In this context, nucleation planting with Berberis microphylla, a non-palatable shrub, could foster forest recovery in degraded sites. To evaluate this, we conducted an experiment testing the response of trees to varying shrub number, while also assessing intraspecific effects in both species. We measured survival, biomass, and functional traits. Results showed that the combination of four shrubs surrounding a single tree maintained tree survival at levels comparable to trees growing alone, while seedlings exhibited conspecific negative plant number dependence. Additionally, B. microphylla increased its below- to above-ground biomass ratio under higher plant number, indicating resource reallocation and niche differentiation through spatial separation of root systems.