Response of forage nutritional quality to climate change and human activities in alpine grasslands

The impacts of climate change and human activities on forage nutritional quality will affect nutrient capacity, livestock development and wildlife conservation in alpine regions. However, the response of forage nutritional quality to climate change and human activities remains indistinguishable across the whole Tibet. Here, six forage variables (i.e., crude protein, CP; ether extract, EE; crude ash, Ash; acid detergent fiber, ADF; neutral detergent fiber, NDF; water-soluble carbohydrates, WSC) together represented forage nutritional quality. We estimated potential forage CP, EE, Ash, ADF, NDF and WSC contents using growing mean air temperature, total precipitation and total radiation based on random forest models. We also estimated actual forage CP, EE, Ash, ADF, NDF and WSC contents using growing mean air temperature, total precipitation and total radiation, and maximum normalized difference vegetation index based on random forest models. Climate change had nonlinear effects on potential forage CP, EE, Ash, ADF, NDF and WSC contents. Radiation change predominated the variations of potential forage nutritional quality. Human activities altered the sensitivities of forage nutritional quality to climate change. The effects of human activities on forage nutritional quality increased with increasing longitude and precipitation, and decreasing elevation and radiation. Consequently, we should pay attention to the radiation change besides climate warming and precipitation change, at least for forage nutritional quality in alpine grasslands. The effects of human activities on forage nutritional quality can vary with longitude, elevation, precipitation and radiation in alpine grasslands.