This thesis presents the results of a four year study from 1986 to 1990 on the biology of the leguminous tree Prosopis Cineraria (L.) Druce in the Sharqiya region of the Sultanate of Oman. Descriptive studies were performed on both the woodland habitat and the species. The suitability and methodology of utilising P.cineraria in future forestry programmes in Oman were also examined. Field studies have shown that this drought-tolerant indigenous phreatophyte forms large mono-culture relic woodlands in the sandy deserts of the Sharqiya. It is well adapted to the harsh environment of shifting sand dunes, growing vegetatively through accumulated sand to form tree clumps. Ecological studies have shown that the Prosopis woodland micro-environment supports wildlife not necessarily adapted to arid conditions. P.cineraria is an excellent multi-purpose tree for local people, particularly in providing fodder, fuel wood and shade protection. Over-exploitation and the general absence of natural reproductive regeneration has resulted in the decline in the condition of some Prosopis woodlands in Oman. To ensure their continued survival several methods of conservation were recommended. Studies on the mature trees have shown that the morphological variability of this species in the Sharqiya was high, which contributed to its multi-purpose potential. This variability was both phenotypic and genotype in origin. Glasshouse trials of P.cineraria in Durham have shown that seeds sampled from individual trees produced seedlings that were morphologically variable and were particularly tolerant to high salinities. Variation in morphology and salinity tolerance were related to both their geographical and parental origin. Three P.cineraria field trials in Oman have shown that the climate and soil environment greatly affected seedling growth and morphology. Silvicultural recommendations derived from these trials have been proposed for the propagation of this species in Oman.