How Does Tree Regeneration Respond to Livestock Exclusion in the Dry Chaco Forest? Contrasting Responses in Two Key Species

Abstract

Aims: Livestock grazing influences forest canopy structures by promoting or inhibiting tree regeneration, making exclusion a commonly used—though not universally effective—strategy to enhance regeneration. We evaluated whether 9 years of livestock exclusion altered tree regeneration relative to adjacent areas with continuous grazing in the Dry Chaco Forest.Location: Dry Chaco Forest at Copo National Park, Santiago del Estero, Argentina.Methods: Using a randomized complete block design with five replicates, we compared sapling community richness, density, and diversity, and measured height and base diameter for two canopy dominants (Aspidosperma quebracho-blanco and Schinopsis lorentzii). Richness, density, and diversity were assessed after 8 years of exclusion, while height and basal diameter were measured after 9 years of exclusion. Rarefaction and rank abundance curves evaluated sapling richness and diversity, while linear mixed models analyzed the total density per species, diameter, and height of saplings from the two dominant species.Results: In the excluded areas, the mean sapling density of A. quebracho-blanco was 0.4 times that observed in the grazed areas, whereas the mean height of S. lorentzii saplings was three times greater than in the grazed areas. Species richness, diversity, and sapling density did not change significantly between treatments. Additionally, no differences were detected either in the mean diameter of dominant species or in the mean height of A. quebracho-blanco.Conclusions: Overall, no significant differences in sapling richness, diversity, or total density were detected between excluded and grazed areas, while A. quebracho-blanco showed lower sapling density, and S. lorentzii saplings were taller in excluded plots. Because excluded stands may still be in recovery and the design lacks a long-term ungrazed reference, these patterns are consistent with two alternative interpretations: (i) limited effects of current grazing on early regeneration and (ii) delayed or context-dependent responses to exclusion. Such contrasting, species-specific outcomes highlight the need for management strategies that combine heterogeneous grazing regimes with long-term monitoring to capture lagged or episodic dynamics.