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

Ghoth in the outskirts of Karachi up to a distance of 20 km towards Hyderabad. The sampling of the vegetation was done 7 m away from the road to avoid any road edge effects. The disturbed area was not included in the sampling. At every stand, 20 quadrats of 8.0 m x 1.5 m were taken randomly. Number of individuals of all the species as well as their circumference was recorded. The relative cover, relative density and relative frequency of all the species were calculated. An Importance Value Index (IVI) was obtained by the addition of the above mentioned community attributes. Soil samples from every stands were collected from 30 cm depth, dried at 80 °C for 24 h, ground and sieved to remove particles greater than 1 mm. Then 1 g of soils was weighed into a 250 ml beaker, 10 ml concentrated HNO3 was added and the mixture was evaporated to dryness on a hot plate. After cooling, this procedure was repeated with a second aliquot of HNO3. After this, 10 ml concentrated HCl was added to the residue and warmed to 40-50 °C. The mixture was filtered through a Whatman No. 54 filter paper, the residue washed with In HCl and the filtrate volume was made up to 100 ml. Pb, Cu and Zn were then determined by atomic absorption spectrophotometer (Model Perkin Elmer 23380) upon the solution direct or after tenfold dilution with In HCl. RESULTS AND DISCUSSION Phytosociological results including leading as well as other dominant species and their Importance Value Index have been indicated in Table 1. Metal analysis results for Cu, Zn and Pb for all samples have been also included in this table. In Table 2, mean Importance Value Index, concentration of Cu, Zn and Pb and their ranges have been given only for the 5 most dominant species. This table also shows the number of stands of occurrence of the dominant species. The results indicate that the two species, Senna holosericea and Prosopis juliflora are found in sites where disturbance is the primary factor. S. holosericea and P. juliflora have been found occurring in 10 and 7 stands, out of 20 stands, respectively. In arid regions, the vegetation cover is low and sparse (EMBERGER and LAMEE 1962). Under the arid conditions, the density of vegetation decreases with decreasing precipitation (MOND 1954). Most of the species are characterized by a shallow root system with a considerable horizontal growth (WALTER 1961 ). The highest mean importance values were also been recorded in S. holosericea (55.07) and P. juliflora (53.48). Both species (S. holosericea and P. juliflora) also showed a broad range of importance values, showing their wide ecological amplitude. Though, Abutilon indicum., Fagonia indica, and Blepharis sindica were also found as a leading species in other stands, but their importance value was rather low.