Pak. J. Bot., 42(5): 3431-3440, 2010. SPATIOTEMPORAL ASPECTS OF PLANT COMMUNITY STRUCTURE IN OPEN SCRUB RANGELANDS OF SUB-MOUNTAINOUS HIMALAYAN PLATEAUS IFTIKHAR AHMAD 1 , MUHAMMAD SAJID AQEEL AHMAD 1 *, MUMTAZ HUSSAIN 1 , MUHAMMAD ASHRAF 1,2 , M. YASIN ASHRAF 3 AND MANSOOR HAMEED 1 1 Department of Botany, University of Agriculture, Faisalabad, Pakistan 2 Department of Botany and Microbiology, King-Saud University, Riaydh, Saudi Arabia 3 Nuclear Institute for Agriculture and Biology (NIAB), Faisalabad, Pakistan *Corresponding Author: sajidakeel@yahoo.com Abstract Six ecologically diverse study sites were studied for changes in the structure of open scrub- type plant community over space and time. Ecological data were recorded using Fixed Quadrat Sampling Method and analyzed by using pRDA technique. Results revealed that enough moisture, suitable temperature and availability of macronutrients during summer lead to the maximal complexity of all communities which was follows by autumn and spring. However, the reverse was true during winter. Similarly, the study of different sites also revealed significant variation in plant communities that seemed to be highly associated with the soils physico-chemical properties. For example, most of the species were found to be dominant in soils containing higher macronutrients with high field capacity (Khabeki, Khoora and Knotti Garden sites). Salt and drought tolerant species were dominant in saline soil with steep slopes and at higher elevation (Jallar site). In contrast, moisture loving species were closely associated with the springs and water channels (Knotti Garden and Dape Sharif sites). In conclusion, the spatio-temporal variations in plant communities of this area were found to be a result of the moisture contents, filed capacity, soil macro-nutrients and type and composition of the soil and elevation of selected sites. Introduction Different plant species had different habitat requirements. Therefore species distribution, richness, diversity and cover vary with variation in habitats especially with steepness of slopes (Uniyal et al., 2006). Sometimes alien species causes disturbance in distribution of certain species as Parthenium weed (Parthenium hysterophorus L.) spread on waste lands (Shabbir & Bajwa, 2006). The population of many common medicinal plants growing in the wastelands might be rapidly declining due to fast and aggressive growth of P. hysterophorus as it replaces indigenous natural flora, including herbs utilized by people as a source of medicine. Abiotic components and plants spend their entire life cycles, closely related with each other. Species density for such under story plants was positively related to rainfall, negatively to seasonality where as positively but less consistently related to soil composition and fertility. Understory plant species composition also changes like ferns and many non-fern herbaceous families are absent from the driest sites (Gentry & Emmons, 1987; Wright, 1992). Soone Valley is a source of rich biodiversity, however, presently the species richness have been reported to face a sharp decline in this area (Ahmad et al., 2007). Increasing human interference, clear-cutting for agriculture and fuel wood, over-grazing and over- exploitation of resources for salt and other minerals, over-harvesting of plants species particularly for medicinal purposes, increased disturbances, soil degradation and increasing metal toxicity have been reported as the major threats to the vegetation of this