How the interplay between management and interannual climatic variability influences the NDVI variation in a sub-Mediterranean pastoral system: Insight into sustainable grassland use under climate change

The modification of precipitation regimes and the increase in summer aridity under the predicted climate change scenarios are hypothesized to have repercussions on the semi-extensive pastoral systems of Mediterranean grasslands, leading to change in forage quantity/quality, increased interannual variability in phytomass production, reduction of the carrying capacity of rangelands, and worsening of animal welfare. The research aims were to find what climatic features affect changes in the annual peak of Aboveground Net Primary Production (ANPP), and how topographic variables and management conditions influence these variations in a pastoral system of central Apennines (Italy). We monitored Normalized Difference Vegetation Index (NDVI) variations at the peak of phytomass production using Landsat satellite images, used as a proxy for ANPP changes in the most productive phase of the growing season, when herds are carried to pastures and hay-meadows are mown, on a dataset of 10,000 randomly sampled pixels (30 × 30 m), in the years 2003, 2007, 2009, 2010, and 2013−2015. We investigated the relation between NDVI and climatic variables, topographic parameters, vegetation physiognomy, and management type, using generalized linear mixed-effects modeling, variation partitioning, and correlation analysis. We observed an increase in average yearly temperatures and high variability in the rainfall seasonal distribution pattern, particularly of spring precipitation. Climatic fluctuations influenced the overall amount of forage production more than management and topographic conditions. The spring variation of climatic variables (precipitation in March, drought stress in April and May), the drought and cold stress intensities in the previous year and the cold stress in the preceding winter were the main drivers of NDVI change. The landform factors interacted with climate variability in determining the amplitude of NDVI changes, which were the widest in semi-flat mountain tops and flat valley bottoms and the smallest in south-facing slopes. The effect of the climatic variables on NDVI was different depending on the management condition, suggesting that grassland management partially filters the climatic drivers of changes in forage production. Based on our results, the most productive grassland communities and the areas used for grazing by domestic herbivores could be the most impacted by the predicted climate changes for the Mediterranean basin, potentially reducing the economic sustainability of semi-extensive farming in the Apennine mountains.