B. Papp szerk.: Studia Botanica Hungarica 29. 1998 (Budapest, 1999)

Iqbal, M. Z., Sherwani, A. K.; Shafiq, M.: Vegetation characteristics and trace metals (Cu, Zn and Pb) in soils along the super highways near Karachi, Pakistan

killed by SO2. From 25 to 7 km, the species diversities of vascular plants decreased progressively as the levels of SO2 to which they were exposed increased. From 7 to 2 km only two plant species remained in most samples. With increased intensity of SO2 exposure, the community height, biomass, production and coverage decreased along with diversity. Roadside plants and crops grown near the roads were found to contain more lead and the lead levels correlated with traffic density and the distance from the motorways (ALBASEL and COTTENIE 1985, BEYER and MOORE 1980, DAVIES and HOUGHTON 1984, HARRISON and JOHNSTON 1985). However, even a large proportion of emissions may be dispersed by the atmosphere from the immediate vicinity of the roads (HARRISON et al. 1985). The toxicity of some metals may be so great that plant growth is retarded before large quantities of the element can be translocated (HAGHIRI 1973). Low concentration of these metals may cause growth retardation, inhibition of photosynthesis, transpiration, foliar injury, chlorosis etc., (BAZZAZ et al. 1974a, b\ ZlMDAHL 1976). The present population of Karachi is estimated to be more than 9.4 millions. According to the Excise and Taxation Department, Karachi had about 600,000 vehicles in the period of 1987 to 1988 and their number is increasing every year. The concentration of pollutants like lead and smoke in the city is increasing day by day (BEG et al. 1987). Rain in Karachi is seasonal, averaging less than 22 cm per year between June and September and rare for the remaining part of the year. Occasionally, there are dry years too, while strong coastal winds and better dew formation are the main features of Karachi. The study area lies in a broad valley which is filled by alluvium, slope wash and wind blown sand. Phytosociological studies around Karachi had been conducted by many workers (CHAUDHRY and QADIR 1958, CHAUDHRY 1961, QADIR et al. 1966, SHAUKAT and QADIR 1970, IQBAL et al. 1983, AHMED et al. 1978, SHAFIQ and IQBAL 1987, 1988, SHAFIQ et al. 1992, IQBAL and HUSSAIN 1994, MEHMOOD and IQBAL 1995). However, no vegetation studies along the main Super Highways were completed so far. In this paper, attempt has been made for discussing the relationship between the vegetation and some trace metals such as lead, copper and zinc. MATERIALS AND METHODS The vegetation is predominantly composed of halophyte and xerophyte species. The disturbance is mainly due to the construction of new structures, cutting, cattle grazing, pollutant disposal etc. Sampling of the vegetation near the main Super Highways joining the two big cities of Pakistan, Karachi and Hyderabad was conducted by quadrat method. Sampling was started from Sohrab