Meta-analysis of livestock effects on tree regeneration in oak agroforestry systems

Livestock grazing occupies over a quarter of terrestrial land and is prevalent to agroforestry ecosystems, potentially influencing the survival, growth, and density of trees’ early developmental stages. To address the nuanced effects of livestock types and their size-related foraging behaviors on tree recruitment in the face of ongoing debates about their impacts, we conducted a 33-year meta-analysis in Quercus -dominated systems. Our analysis revealed a consistently negative effect of livestock on oak regeneration across early developmental stages—acorns, seedlings, and saplings. Significantly, livestock size influenced oak regeneration, with small-sized livestock, notably sheep and goats, having a more pronounced negative impact compared to mixed-size livestock systems. The effects of small-sized livestock were markedly detrimental on acorn survival and seedling/sapling density. Mixed-size livestock systems, often involving cows and sheep, lessen the negative effects better than single-size, especially small, livestock systems. Such findings challenge the perception of some authors that simply replacing cattle with sheep would be less harmful to oak regeneration, revealing a more complex scenario. Our results advocate for the integration of diverse livestock sizes and the consideration of protective measures, especially for acorns and saplings, to enhance oak regeneration. Future research should expand to underrepresented regions and livestock types to refine global agroforestry management practices.