Divergent responses of forage quality indicators to environmental drivers in Eastern Mongolia

Forage quality is crucial for determining livestock productivity as well as ecosystem health, and consequently is a critical parameter for sustainable rangeland management. However, most studies concentrate on forage amount alone, and it remains largely unknown to what extent climate, soil, and disturbance impact seasonal forage quality. Across spring, summer and autumn, we conducted a large-scale field study at 63 sites in the eastern Mongolian steppe, arguably the largest intact steppe region under traditional mobile land use. We performed exploratory multivariate analyses to check the correlation structure among forage indicators and environmental factors separately, and then used linear mixed models to assess the impact of season, and major environmental factors, i.e., precipitation, temperature, soil carbon-nitrogen (C-N) ratio, local disturbance, as well as the interaction between precipitation and disturbance on current standing biomass, and selected indicators of forage quality, i.e., community-weighted nitrogen content, crude protein (CP) yield, digestibility and water content of fresh biomass. Results showed a clear seasonal difference in all indicators except digestibility. Plant N contents at the community level declined significantly from 2.4% in spring to 2.1% in summer, then to 1.5% in autumn, while mean CP yield was 104 kg·ha^-¹in summer and more than halved towards spring. Water content in fresh biomass was highest in summer (54%) and lowest in autumn (30%). Linear modeling revealed that higher precipitation was associated with greater CP yield, while higher disturbance lead to lower CP yield. Temperature was a significant positive predictor of total water content. Digestibility was not sensitive to any predictor tested. We highlight the importance of integrating forage quality and its seasonal dynamics into estimates of grassland carrying capacity.