Main ecological and environmental factors affecting forage yield and quality in alpine summer pastures (NW-Italy, Gran Paradiso National Park)

Abstract

Summer pastures in the European Alps play a crucial role in providing high quality forage for grazing livestock and encompass a wide variety of vegetation communities. The main issue of their management is the optimal exploitation of the available forage in relation to environmental constraints, aiming at obtaining the highest forage yield and quality from each vegetation community. In this work, we monitored six different vegetation communities characterized by contrasting topographic features and species compositions throughout the grazing season for two years. We performed botanical and phenological surveys, climate-related measurements, and herbage samplings to assess forage quantity and quality (i.e., digestibility and proximate composition, estimated by near-infrared reflectance spectroscopy). We analysed the influence of climatic, topographic, and vegetation variables on pasture herbage through univariate and multivariate analyses. The cover of wide-leaf grasses primarily promoted biomass production, which was in turn lowered by increasing elevation and slope. On the other hand, a minor effect on forage yield was observed for an increasing cover of sedges and rushes and mean temperatures. Climatic variables (especially water deficit) and advanced phenological stages were the main degrading factors of forage quality in terms of crude protein and digestibility, while enhancing fibre contents. At increasing cover of legumes, fibre content declined and digestibility increased consequently, while the abundance of other non-legume forbs played a significant role in lowering fibre content. Multivariate analysis highlighted the differing influence of single plant species on forage features even within the same functional species pool. However, attention should be paid to the toxicity and low palatability of some plants, especially forbs. Eutrophic vegetation communities, rich in wide-leaf grasses and legumes, could be maintained and enhanced through pastoral management to increase alpine pasture production and quality.