Hammada Elegans-rhazya Stricta Competitive Relationships in a Deteriorated Range Site in Raudhat Al-khafs, Saudi Arabia

Rhazya stricta, an evergreen poisonous shrub, is invading many rangeland areas in Saudi Arabia. A field study was conducted in Raudhat AI-Khafs to assess the relationship between R. stricta and Hammada elegans, a valuable and a dominant saltbush range plant in the area. Only eight perennial species were found in the site of which H. elegans and R. stricta were almost exclusively co-dominating the area. Species diversity was low (0.912) indicating a deteriorated condition of the area. Quadrat sampling at three degrees of R. stricta invasion (high, medium and low) showed a decreasing trend in plant crown cover and plant biomass of H. elegans as R. stricta increased. Crown cover of H. elegans decreased from 0.75 to 0.46 m and plant biomass decreased by 23% as R. stricta density increased from 216 to 716 plants/ha. Further, crown cover of R. stricta decreased from 7.4 to 2.46 m and plant biomass decreased by 51% as its density increased. Soil analysis indicated that high plant density of R. stricta was associated with relatively higher concentration of P, K, Mg and Cl. The results suggested that competitive relationship may exist between the two species but further research is needed to understand the effect of R. stricta on H. elegans reproduction and establishment and to determine the proper grazing management that suppresses the invasion of R. stricta