USDA Forest Service Proceedings RMRS-P-11. 1999 227 In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999. Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc. RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. M. Ajmal Khan is a Professor of Plant Ecology at the Department of Botany, University of Karachi, Karachi-75270, Pakistan. Bilquees Gul is a Plant Ecologist at the Department of Botany, University of Karachi, Paki- stan. Corresponding author and address: P.O. Box 8452, University of Karachi, Karachi-75270, Pakistan, e-mail: ajmal@www.fascom.com Abstract—Pure populations of halophytic shrubs (Suaeda fruticosa, Cressa cretica, Arthrocnemum macrostachyum, Atriplex griffithii, etc.) and perennial grasses (Halopyrum mucronatum, Aeluropus lagopoides, etc.) dominate the vegetation of the Arabian Sea coast at Karachi, Pakistan. The coastal populations maintained a per- sistent seed bank. There is a close relationship between seed bank flora and existing vegetation. The size of the seed bank varies with the species dominating the population. Arthrocnemum macro- stachyum, which dominated the coastal swamps, had the highest seed density, 940,000 seed m –2 , followed by Halopyrum mucronatum, which showed 75,000 seed m –2 . For all other species (Suaeda fruti- cosa, Cressa cretica, Atriplex griffithii, and Aeluropus lagopoides), seed bank varies from 20,000 to 35,000 seed m –2 . Seed bank of all species substantially reduced a few months after dispersal. The desert littoral salt marshes near Karachi, Pakistan, are characterized by a simplicity of structure and composi- tion (Chaudhri 1961). Monospecific patches of vegetation are common with occasional stands dominated by a single species with or without minor associates (Khan, unpub- lished data). The vegetation from seaward to landward is mangrove (Avicennia marina) followed by muddy coastal swamp with A. macrostachyum (Karim and Qadir 1979) and then other communities like Atriplex griffithii Moq. var. stocksii Boiss. (Chenopodiaceae), Suaeda fruticosa (L.) Forssk. (Chenopodiaceae), Halopyrum mucronatum(L.) Stapf. (Poaceae), Aeluropus lagopoides (L.) Trine. Ex Thwarts (Poa- ceae) and Cressa cretica L. (Convolvulaceae) were present on adjacent low dunes. There are few studies on the seed bank of coastal commu- nities and little information is available on the seed bank of subtropical shrub-dominated coastal communities. The coastal shrubs and grasses produce a large number of seeds and most of them disappear a few months after dispersal. Such marshes maintain a persistent seed bank despite a significant loss of seed. The size of coastal salt marsh seed banks varies from a 0 to 140,000 seed m –2 (Jefferies and others 1981; Jerling 1984; Hartman 1988; Ungar and Woodell 1993, 1996), but are usually small. Similar low densities have been encountered in several Arabian Sea coastal communities near Karachi. Seed bank studies from Seed Bank Strategies of Coastal Populations at the Arabian Sea Coast M. Ajmal Khan Bilquees Gul Karachi, Pakistan, have demonstrated that dominant perennial halophytic shrubs and grasses maintain a persis- tent seed bank (Gulzar and Khan 1994; Aziz and Khan 1996). Six different coastal dune communities showed a very small seed bank (30-260 seed m –2 , Gulzar and Khan 1994), while coastal swamp communities had a larger seed bank (11,000 seed m –2 ). The Cressa cretica seed bank at Karachi showed a persistent seed bank (Aziz and Khan 1996), with the number of seeds reaching its maximum (2,500 seed m –2 ) after dispersal and dropping down to 500 seed m –2 a few months later. Gul and Khan (1998) reported that coastal swamps dominated by Arthrocnemum macrostachyum showed a great deal of variation from upper to lower marsh. Upper marsh had the highest number of seeds with higher species diversity. A number of hypotheses have been suggested to explain this relatively small number of seeds. These include: loss of seeds because of coastal abrasion (Hutching and Russell 1989), environmental ex- tremes beyond the range of tolerance (Ungar 1995a,b), and composition of aboveground vegetation and its seed produc- tion (Milton 1939; Hutchings and Russell 1989). Factors that contribute to the distribution and maintenance of seeds in wetland soils include burial, inundation pattern (depth, duration, and timing of water fluctuation), physical and chemical characteristics of the substrate, and distur- bance (Leck 1989). The role of the seed banks in coastal salt marsh communi- ties of arid subtropical regions dominated by perennial halophytic shrubs is poorly understood. Although a large number of seeds is produced (Gul 1993; Khan and Ungar 1996; Noor and Khan 1994; Aziz and Khan 1996) recruit- ment from seeds is rare (Gul 1993). The size of the seed bank varies widely, temporally, and spatially. The role of popu- lation characteristics in maintaining this distribution is largely ignored. We are reporting here the temporal dynam- ics of seed bank of Arabian Sea coast communities, and their size and its relationship with vegetation. Materials and Methods ___________ Study Site The study site is located in Manora creek, near Sands pit at the Karachi coast (24° 48' N, 65° 55' E), Pakistan. Mean ambient summer temperature is 36 °C and mean winter temperature is 25 °C. Rains are received during monsoon season extending from June to September. Avicennia ma- rina dominated the area submersed with seawater, and from the Avicennia marina edge to mean high tide line, the area (110 meters) is dominated by Arthrocnemum macro- stachyum. Toward the landward side there are various