Seasonal Herbage-Livestock Balance and Grassland Pressure Index Analysis in the Yellow River Source Park, Tibet Plateau, China.

Grassland carrying capacity is an indicator for measuring the stability of grassland ecosystems and can provide a basis for formulating regional sustainable grazing strategies. However, most previous studies on this have only considered annual fluctuations, but seasonal changes were ignored. In this study, the herbage yield and nutrient value of two grassland types in Yellow River Source Park (YRSP) were measured by sampling point survey method in four seasons, and the seasonal and annual grassland carrying capacity, carrying numbers of standard sheep unit (SU) were estimated based on the dry matter (DM) content, crude protein, and metabolic energy of herbage. Due to the carrying capacity being low during the yellow and wintering periods, we combined them and calculated the carrying capacity for only three periods, including the flourishing period, greening period, and withering period. The grassland pressure index (GPI) was measured by the ratio of the actual standard sheep number and the calculated number. The results showed that the herbage yield and nutrient output were higher in spring and summer, lower in autumn and winter, and showed a tendency for alpine meadows to be higher than alpine grasslands during the flourishing period ( < 0.05). The unit area carrying capacity varied significantly with the season and showed the seasonal changing characteristics of the flourishing period > greening period > withering period. The seasonal carrying number was much higher than the actual carrying number during the flourishing period and much lower than the actual carrying number during the withering period. In terms of annual carrying capacity, the GPI was balanced when considering livestock alone, while critical overloaded when considering livestock and wildlife. This study suggested the influence of seasonal change on the grassland carrying capacity should be fully considered in the grassland utilization. Meanwhile, the feeding needs of livestock and wildlife should be taken into account, and timely supplemented when forage is in short supply.