Sustainability of Island Pastures Under Global Warming: Impacts on Forage Productivity, Soil Fertility and Forage Quality

The Azorean livestock system depends strongly on pasture-based feeding, making regional agriculture sensitive to global warming. This study assessed the effects of experimental warming on forage productivity, forage quality, and soil fertility in three pastures along an altitudinal gradient over two years (2020–2021). Open-top chambers were used to create warmer conditions, and soil and forage samples were analysed for chemical and mineral composition. Warming increased net forage productivity by 30% and 70% in the lower-altitude pasture in 2020 and 2021, respectively, and by 56% in the intermediate-altitude pasture in 2021. Responses at the highest altitude were weak or not significant. Effects on forage quality were seasonal. In winter and early spring, warming increased crude protein by 14–45% and ash by 4–13% in the lower- and intermediate-altitude pastures. Later in the season, warming was associated with higher fibre fractions, especially in the intermediate-altitude pasture, indicating faster plant maturation. Soil factors significantly structured forage quality, with phosphorus as the main driver. This study contributes to understanding how climate change may affect the sustainability of pasture-based livestock systems in island environments, supporting the development of adaptive management strategies to safeguard productivity, soil fertility, and ecosystem resilience.