Hoof pressure and trampling intensity of yaks are higher than those of Tibetan sheep in a Tianzhu alpine meadow

Trampling by grazing animals exerts a comprehensive and serious effect on grassland vegetation and soil. In order to compare the trampling of yaks and Tibetan sheep under different grazing intensities, we examined the hoof pressure and trampling intensity (based on trampling area and hoof-print count) of white yaks (Poephagus grunniens) and Tibetan sheep (Ovis ammon) in an alpine meadow of Tianzhu County, Gansu Province, China, under conditions where either grazing area or livestock number were controlled. The average areas trampled by yaks and Tibetan sheep were 39.2 and 21.6 cm2 respectively. The average hoof pressure of yaks and Tibetan sheep were 6.89 and 3.13 kg cm–2 respectively. The yak-to-sheep ratio of the average area trampled was 1.81:1, whereas the yak-to-sheep ratio of average hoof pressure was 2.20:1. Average ingestion and walking trampling intensities of yaks were 384.8 × 103 and 247.1 × 103 kg cm–2, respectively, in controlled grazing areas, and 439.1 × 103 and 756.3 × 103 kg cm–2, respectively, in areas of controlled livestock numbers. These values for Tibetan sheep were 15.3 × 103 and 120.3 × 103 kg cm–2 in controlled grazing areas, and 42.6 × 103 and 128.2 × 103 kg cm–2 in areas of controlled livestock numbers. In controlled grazing areas, the ingestion and walking trampling intensities of yaks were 25.2 and 5.4 times higher, respectively, than those of sheep. Under areas of controlled livestock numbers, these values were 10.3 and 5.9 times higher, respectively, than those of sheep. The average trampling intensity of yaks was 7.3 times higher than that of the sheep. Therefore, under conditions of similar grazing intensity, yaks cause more damage than Tibetan sheep in alpine meadows.