The variation in composition, structure, phytomass and net primary productivity was analyzed in a Lasiurus scindicus Henr. dominated community in a semi-moist site of Karachi, Pakistan. Phyto-ecological parameters of vegetation were studied at monthly interval for a year. Fifty nine species in all were encountered from this site. On the basis of phytomass, Lasiurus scindicum was the leading dominant throughout the year except in rainy season when Cenchrus setigerus dominated the community. The maximum density in this site occurred in August when it reached to 588.4 plants m-2. The density of L. scindicus remained more or less unchanged. The changes in the above ground live plant biomass (LB), standing dead (SD), litter (L) and belowground biomass were studied. LB was maximum (694.7 g.m-2) in September and minimum (196.5 g.m-2) in June-averaging to 341.3 ± 42.9 g.m-2. LB proportion of legumes varied from 0.9 to 8.65%. The effects of rainfall remained noticeable for not more than up to 50-60 days. CD was maximum in December (564.6m-2). Litter was maximum in January (249.9g.m-2) and minimum in August (115.8m-2). Above-ground net primary productivity (ANP), as evaluated by various methods, varied from 674.7 to 947.1g.m-2 year-1 (average = 805.3 ± 50.76g.m-2 year-1; CV = 13.8%). Belowground net productivity (BNP was 814.9g.m-2 year-1. Annual efficiency of energy capture by the primary producers was estimated to be0.68% on the basis of half total solar radiation. Annual energy flow diagram through primary producer compartments is presented.