Effects of tree presence on forage yield and nutritive value in agroforestry livestock systems: a global systematic review

Agroforestry can support carbon neutrality in agricultural and livestock systems while enhancing farm resilience to climate change through diversification. The impacts of climate change on grasslands vary globally, necessitating both mitigation and adaptation strategies. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 statement was applied to conduct a global systematic review evaluating the effect of tree presence on forage yield and quality. This study considered five reviews, four meta-analyses, and 131 research articles. Existing meta-analyses and reviews provide valuable insights, while pot-, field-, and landscape-level studies highlight the complexity of agroforestry across different environments. Findings indicate that herbage biomass is primarily reduced by limited light availability and, to a lesser extent, nutrient competition. In arid regions, water scarcity exacerbates tree-crop competition. The effects on nutritive value vary: under shade, crude protein levels increase in grasses but decline in legumes, while fiber content remains stable or decreases. Grass-legume mixtures enhance both yield and quality, benefiting from species interactions. The adoption of optimal grazing management, considering shade presence alongside forage yield and nutritive value, is crucial for improving animal productivity. Most studies highlight key factors for the long-term success of agroforestry, including low tree density, strategic orientation, thinning, pruning, and appropriate stocking rates. Addressing genetic, nutritional, and management knowledge gaps can further enhance plant and animal resilience to climate change.