English abstract
The impacts of grazing animals on the vegetation of arid lands is frequently severe and a major contributor to land degradation. In Oman, this problem has received considerable attention in the southern province of Dhofar, but relatively little research or concern has focused on the northern Batinah region. This project is the first to quantify the vegetation of the Batinah and the degree to which its plant resources have been affected by livestock. The aims of this research are to: 1) identify the perennial plants and quantify their coverage and frequency; 2) evaluate the degree of utilization of the perennial vegetation by livestock; 3) assess the impact of grazing by comparing characteristics of the vegetation in a site protected from grazing with those of adjacent non-protected sites; 4) attempt to use Landsat images to quantify changes that have occurred in the plant coverage from 1985 to 2000.
The research area (250 km) was divided into 10 blocks of 5 x5 km. Two sites were randomly selected in each block for the vegetation analysis. Line transects (800 m long) were used to estimate coverage and frequency at each site. Grazing intensity was approximated by an ordinal scale. The same procedures were used at 4 sites inside a 1 X 4 km site protected from grazing for the past 10 years.
Three vegetation types are common in the eastern Batinah. A shrubland community occurs on wide shallow wadis with finer alluvial soils; Acacia tortilis woodlands characterize higher plains with small surface gravels; and, a wadi community of mixed trees and shrubs occurs along deeper channels that dissect the gravel plains and have various sized rocks and gravels. Vegetation coverage by perennials ranged from 0.9 to 8% on the 21 non-protected sites. Eighteen of these sites were classified as lightly grazed and 3 were moderately grazed. Many plants (64 %) on the lightly grazed sites are species with defensive spines, thorns or noxious chemicals and are considered undesirable fodder. Coverage in the protected sites ranged from 2 to 5.6%. Species that are frequently foraged (e.g., Farsetia aegyptiaca Panicum turgidum, Crotalaria aegyptiaca, Heliotropium europaeum) were significantly larger in the protected site. One grass (Dichanthium cf. faveolatum) was found only in the protected site, and plant litter was much more abundant.
The results confirm several trends previously reported from arid rangelands. Overstocking has reduced coverage by palatable species while increasing coverage and frequency of perennial plants with defensive mechanisms against herbivores. Although the total vegetative cover did not increase after 10 years of protection, the dominant forage species were significantly larger and their frequency has become more compared to plants on grazed rangeland.
