Individual study: Recovery of degraded coastal lowland vegetation through exclusion of livestock, Al-Hassa Oasis, Al-Hassa region, eastern Saudi Arabia
Shaltout K.H., El-Halawany E.F. & El-Kady H.F. (1996) Consequences of protection from grazing on diversity and abundance of the coastal lowland vegetation in eastern Saudi Arabia. Biodiversity and Conservation, 5, 27-36
Degradation of the rangeland is evident in many parts of Saudi Arabia as a result of a long history of overgrazing (mostly by camels and sheep), over-cutting, and many other anthropogenic factors. Protection against overexploitation may provide a chance for regeneration of vegetation in degraded areas, but regeneration attempts have been few in the Arabian Desert region. The present study was aimed at evaluating the possible recovery of vegetation as a result of protection from grazing and other exploitation at a coastal lowland site in eastern Saudi Arabia.
Study site: The study was undertaken at an experimental site (2.5 x 2.5 km), fully protected since 1980, near A1-Hassa Oasis, 20 km south-east of A1-Hufuf city in Al-Hassa region, eastern Saudi Arabia.
Vegetation sampling: Thirty-six blocks of 20 x 20 m were sampled to represent the prevailing (generally sandy) habitat and community variations inside (15 blocks) and outside (21 blocks) the protected area. In each, the following were recorded in spring 1993: species, species cover (using the fine-intercept method); and average height and diameter (based on measurements of 10 randomly selected individuals) of the dominant species, used a s a measure of plant size.
Species richness of the vegetation inside and outside the protected site was calculated as the average number of species per stand, and species turn-over as the ratio between the total number of species and the species richness. Relative evenness and concentration of dominance of species were calculated using Shannon-Weaver and Simpson indices, respectively, on the basis of the relative cover of species.
Soil sampling and soil analysis: In each block, soil samples were collected and soil texture (%sand/silt/clay) and organic matter were estimated. Soil-water extracts were prepared for the determination of electrical conductivity (i.e. as a measure of soil salinity) and pH measured. Determinations of concentrations of important soil nutrients potassium (K), calcium (Ca), sodium (Na), nitrogen (N), phosphorous (P) and magnesium (Mg) were made.
Vegetation: Eight plant communities were prominent in the study area, dominated respectively by Haloxylon salicornicum, Rhanterium epapposum, Seidlitzia rosmarinus, Panicum turgidum, Zygophylleum qatarence, Aleuropus lagopoides, Tamarix aphylla and Saueda aegyptiaca.
Compared to the area open to grazing, the vegetation inside the protected site had a higher numbers of total species (68 vs. 61), species richness/block (18.9 vs. 14.2), relative evenness (0.82 vs. 0.62) and total cover (66.5 vs. 39.7), but lower species turn-over (3.96 vs. 5.10) and relative concentration of dominance (0.28 vs. 0.38). The sizes of some of the dominant species (e.g. T.aphylla, S.rosmarinus, P.turgidum and S.aegyptiaca) were also significantly greater (frequently twice that) inside the protected area compared to individuals outside it.
The difference in total cover and plant size were thus especially marked; it should be noted that a visual estimation indicated that standing dead plant parts contributed, about 40% of the total cover inside the protected area and 20% outside.
Of 50 species of common occurrence, 26 contributed 88% of the total cover inside the protected area and 94% in the area open to grazing; 15 species had significantly higher plant cover, while only two (Frankenia pulverulenta and Kochia indica) had significantly lower cover, inside than outside the protected site.
Soil: Soil salinity and certain soil nutrients (N, K, Mg and Na) were significantly lower inside than outside (where presumably livestock droppings and urine enhanced nutrient availability) the protected area.
In conclusion, 14 years of protection against livestock grazing and human impacts led to recovery of vegetation.
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