Ecological surveys of certain plant communities around urban areas of Karachi

A phytosociological study was conducted as an initial assessment of the vegetation on different sites to determine the community structure and how the communities were related based on their species composition and edaphic characteristics. The communities were distinct types ranging from halophytes to xerophytes with disturbed in nature. Plant communities based on first leading dominant species (Prosopis, Avicennia, Gynandropis, Salvadora, Ipomea, Halopyrum, Limonium, Abutilon and Calotropis) were explored in the study area. Out of thirtynine plant species, Prosopis juliflora attained the highest total importance value index (I.V.I.) followed by Avicennia marina, Suaeda fruticosa and Gynandropsis gynandra. Nine species attained first leading position. Thirteen species attained second dominant position. However, twelve species attained third dominant position in all stands. P. juliflora was the only species that was found six times as a first dominant, three times as second and one time as a third dominates species. None of the other species was in a position to get first, second and third position as a leading dominant in all stands. The communities were of heterogeneous type, with low species diversity and ranged from 1.36 to 4.54. Most of the plant communities showed less than 50% CMI values. However, Prosopis in association with Pasplidium and Cenchrus community showed highest CMI value (70.00). The soils of the study areas were sandy loam, loamy sand, loamy silt, sandy and silty. The soils are alkaline in nature. An appreciable amount of calcium carbonate (13-26%) with moderate percentage of maximum water holding capacity (19-41%) and high soil EC (593 s/cmμ) were recorded. It was also observed that certain edaphic and human activity, discharge of pollutants with out any pretreatment was found responsible for variation in the nature, structure and composition of vegetation. The plant growth and their continuity was in danger in many disturb areas, especially in some coastal areas where salinity and the incident of Tasman spirit oil spillage was occurred just few months before the survey carried out. Construction of flyover, expansion of the roads and cut down of the natural vegetation producing additional losses to flora of the region. @ JASEM The ecological surveys are necessary for an adequate characterization of a plant community. Disturbed areas considered those, where the integrity of the natural setting and natural system processes has been directly or indirectly affected by human activities. These activities could be for resource extraction, visitor use, development of maintenance, or invasion of nonnative sp. etc. The vegetation in the disturbed areas does not reflect a naturally evolved species composition, but rather a mixture of small remnant patches dominated by native plants patches of largely invasive weedy alien plants, and areas of mixed native and non native plants. All over the world, natural habitats are being degraded. There is evidence of contamination in the most remote parts of the world. The human population is getting larger, spreading and producing more complex and interactive disturbance on plant communities. There are few undisturbed habitats are left in some most part of the world. Nevertheless, there is also a general desire to maintain natural habitat for our enjoyment and for the continue well-being of nature. Plant ecologist have placed increasing emphasis on a gunctional understanding of vegetation (Lehsten and Kleyer, 2007). The response of plant communities to environmental change is often studied by analysing the composition of plant traits across communities. A lot of work has been done in ordinating the tropical, temperate, deciduous, desert and calcareous types of vegetation, whereas littler work has been reported from disturbed vegetation. The ecological survey of such disturbed areas conducted by few researchers, in order to know the damage done to ecology of the area and also to know the diversity and dispersion status of species in the area. In Pakistan some phytosociological studies on plant communities of different areas have been conducted (Akbar and Ahmed, 1991; Dasti and Agnew 1994; Iqbal, 1998). Arshad, et al., (2002) carried out a phytosociological assessment of natural reserve of national park Lalsuhanra and identified three distinct types of plant communities. Ahmed and Khattak, (2001) in quantitative studies on the vegetation of Islamabad concluded that due to large scale artificial addition the original vegetation is vanishing at certain places. Khan et al., (1999) have described structure, composition and above ground standing phytomass for the summer aspect of some grass dominated communities of Karachi. In another studies, Khan and Shaukat (2005) have described above ground standing phytomass of some grass-dominated communities of Karachi for winter aspect. In past, few ecological studies have been made on the plant communities of different areas of Karachi (Shafiq, et al., 1992, Khan, 1993, Iqbal and Hussain, 1994; Iqbal and Shafiq, 1996, Iqbal, et al., 1998; Khan and Shaukat, 2005). Karachi is the biggest city of Pakistan. The city has more than 12 million population and ranked the 10 amongst the biggest cities of the world. Increasing population pressure, expansion in industrial and residential areas, construction of roads, flyovers and invasion of nonnative species activities affected nature, structure and composition of the plant communities. Almost each and every area of the Karachi can be presented as the classical example of disturbance and pollution impact on plant Ecological surveys of certain plant communities around urban areas of Karachi * Corresponding author: Muhammad Zafar Iqbal 52 communities. The city atmosphere is being affected badly by almost every type of environmental pollution. The natural vegetation of the region is either being replace by invasive species or is being removed by man for the construction of roads, flyover, building and industries. Dumping of domestic and industrial trash in Malir, Lyari and Hub rivers is also a common practice in the city, which has also affected the indigenous biodiversities of these wetlands. The aim of present investigation was to provide quantitative description of the vegetation on the disturbed areas of the Karachi city, which is changing from natural to semi-natural form due to anthropogenic disturbances, which are still in progress. MATERIALS AND METHODS A: Description of the area The bioclimate of Karachi in the Holdridg’s system falls in the category of “Tropical Bush Formation”. The rainfall is irregular and average below 200 mm a year mostly in summer. The winter peak of precipitation is very low. Winter is the driest part of the year. Summer, which is very hot, the winter in this part of world is mild. Mean monthly minimum temperature for the month of January remains around 10°C-12.5°C due to the Siberian winds. The insulation is intense with global solar radiation varying from 3580 Kcal.m day for December to 5609 Kcal M day for May. The diffused radiation is 20-30% of the global radiation (Ahmed et al., 1991) Rain in Karachi is seasonal, averaging less than 22 cm per year between June and September and rare for the remainder of the year. Occasionally, there are dry years too while strong coastal winds and better dew formation is the characteristic feature of Karachi. B: Vegetational survey A phytosociological survey of different habitats of Karachi was carried out in the months from July to October 2003 (Fig. 1). The study area is comprised of more than 30 square kilometer. Areas were sampled by Point centered quarter methods (Cottom and Curtis, 1956). Twenty sampling points were established at each venue with regular interval by spacing ten steps. Relative cover, relative frequency, and relative density were obtained. The importance value index (I.V.I.) for each species was obtained by addition of the above community attributes (Curtis and McIntosh, 1951). The community was named according to dominant species, which have highest I.V.I. Homogeneity of community was determined by Raunkiaers Law of frequency (1934). Community maturity index was found by Pichi-Sermoli (1948) and species diversity index was determined by the following formulae of Simpson index. D = N (N-1) / Σ n (n-1) D = Diversity index N = Total number of plants of a species n = number of individuals Σ = Sum of all individuals of a species. 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 SITES D iv er si ty In d ex V al u e Fig. 1. Species diversity index SAMPLING SITE: 1=Near hawksbay; 2= Manora; 3=Karachi University Stop; 4=Saeedabad Baldia Town;5= Peoples’s ground; 6= ManoraGraved;7= Malir river at Korangi crossing; 8= Malir river around Malir river;9= Mikolachi Road;10= Korangi No.5 Shahra -eUloom;11= Mikolachi road;12= Hawksbay;13= Gaboput Kamri; 14= Bahraria complex II;15=March Morr Ecological surveys of certain plant communities around urban areas of Karachi * Corresponding author: Muhammad Zafar Iqbal 53 Fig 1. MAP OF THE SAMPLING SITE: 1=Near hawksbay; 2= Manora; 3=Karachi University Stop; 4=Saeedabad Baldia Town;5= Peoples’s ground; 6= ManoraGraved;7= Malir river at Korangi crossing; 8= Malir river around Malir river;9= Mikolachi Road;10= Korangi No.5 Shahra -eUloom;11= Mikolachi road;12= Hawksbay;13= Gaboput Kamri; 14= Bahraria complex II;15=March Morr C: Soil analysis One composite soil sample from each stand was also taken with the help of soil corer. The samples were brought to the laboratory in polythene bags for physical and chemical analysis. Soil texture was determined by manual as well as mechanical (sieving) methods. Soil structure was observed by hand lens observatory methods. Maximum water holding capacity (M.W.H.C.) of the soil was calculated by the following formulae. M.W.H.C. (%) = Loss in weight/oven dried weight of soil X 100. The soil pH was determined by direct pH reading meter (Model JENWAY PHM 6). Calcium carbonate was determined by acid neutralization method (Qadir et al., 1961). Electrical conductivity (E.C.) of the soil samples was determined by digital conductivity meter (Beckman’s conductivity meter). Sodium contents of the soil were determined by silver titration method (U.S.D.A., 1951).