A COMPARATIVE ECOLOGICAL STUDY ON THE VEGETATION OF THE PROTECTED ANDGRAZED PARTS OF HEMA-SABIHAH, IN AL-BAHAH REGION, SOUTH WESTERN SAUDI-ARABIA

Using the random quadrat method, a one year ecological study on the ve getation of a traditionally protected and a continuously grazed parts of hema Sabihah was conducted. This was undertaken by recording the: ( a) Flora of the study area (72 species of 32 family were recorded). (b ) Plant height (The height of the important palatable plant Cymbopogon schoenanthus (L.) spreng was decreased by 59% in the area open for gr azing of it's height in the protected part). (c) importance value inde x (IVI) for every species found in the random quadrats, and from that the Total IVI was calculated (e.g. the total IVI in Autumn was 354.5 & 245.7 for the protected and the grazed areas respectively). (d) plant dry biomass gm/m2. (e) chemical and physical properties of the soil. Results of a, b, c, d & e showed that the protected part maintained hi gher species diversity, and palatable plants, e.g., C Schoenanthus (IV I 486. 1). Such high plant diversity played a major role in soil conse rvation. The area open for grazing has a low cover, and consists mainl y of a non-palatable species, e.g. Asphodelus fistulosus L. (IVI 212.4 ) and Psiadia punctulata D.C. (IVI 208.5). The palatable species are s everely destroyed in this part, and represented, if found by their rhi zomes. This resulted in severe soil erosion, and Cross soil texture. T he average soil water soluble nitrogen (N) was higher in this part (2. 17 mug/g dry soil) than that of the protected part (1.03 mug/g dry soi l). However similarities between some of the soil properties were foun d eg. the average soil: water content (2%), pH, (8), organic matter (8 %) and the water soluble P., Ca. and K. and the electrical conductivit y (pm ho/cm). The present study shows both the ecological and economic al importance of such hema system.