Survival of perennial grass seedlings under intensive grazing in semi-arid rangelands.
The hypothesis that intensive grazing practices, such as short-duration grazing, benefit seedling survival through hoof action of the trampling animals was tested in a 1-year study. Estimation of survival rates and hypothesis testing followed the numerical optimization approach to max. likelihood analysis. A total of 1598 Agropyron desertorum seedlings, of which 52.5% were protected from cattle grazing, were used. Seedling survival did not differ between grazed and ungrazed populations prior to the first grazing treatment. Grazing reduced seedling survival in the 1st as well as in a 2nd 3-day grazing period. The treatment effect was most pronounced in the 2nd grazing period. 10 months after cattle were removed from the pastures the two 3-day grazing treatments continued to influence survival of seedlings. Of the 759 seedlings recorded in grazed plots only 3 survived 1 year after their emergence. In contrast, 97 seedlings survived 1 year in the protected plots where 839 seedlings germinated. A. desertorum seedling survival in relation to the proximity of their well-established parent plants was also investigated. The majority of seedlings (56%) emerged in bare soil >10 cm away from established grasses. Survival was more related to grazing treatment than to seedling location.