ECOLOGY AND SPECIES ASSOCIATION OF GRASS SPECIES IN RESPONSE TO ALTITUDINAL GRADIENT IN THE POTOHAR REGION
An investigation was carried out to evaluate impact of altitudinal gradient on species composition and distributional
pattern of individual grass species in the Potohar region. Vegetation was sampled by quadrat method, which were laid along a transect line at different selected sites. All ecological parameters like species composition, pair-wise association and distributional pattern, and community structure significantly changed with altitudinal gradient. Species with broad,distributional range can be related to high degree of tolerance to a variety of environmental stresses.
Material and Methods
Vegetation was studied at 7 different altitudinal ranges in the Potohar region, i.e., from 200 m to 1400 m a.s.l. The other sides were selected, each with a difference of 200 m elevation. Vegetation sampling was done at three distinct regions at each altitudinal range in the Potohar region, each site was separated by at least 50 km. Each region was subdivided on the basis of percent slope, i.e., c. 20, 30 and 45%. Three transect line (100 m long) were selected at each study site and 5 quadrats (1 x 1) were laid along each transect line (Fig. 1). High-pixel photographs of all grasses and their habitats were taken, and plant samples were placed in the Herbarium, Department of Botany, University of Agriculture, Faisalabad. Data for density, frequency and cover were recorded according to Greig-Smith (1983), and then their relative values, importance value and species association
Results and Discussion
Six grasses were selected for detailed morphoanatomical and physiological characteristics, all are widespread in distribution and recorded from all altitudinal ranges . Cynodon dactylon is a stoloniferous species that dominated 600 to 1000 m elevations. Aristida adscensionis is a short-lived perennial that is widespread in distribution, little scattered in distribution but not a dominant component of vegetation at any altitudinal range. Chrysopogon serrulatus and Cymbopogon jwarancusa are tufted perennials, the former dominated 600-1200 m a.s.l., and the later lower elevations (200-400 m a.s.l.). Dichanthium annulatumis a geneculately ascending perennial and Pennisetum orientalis a tussock-forming grass, both with patchy distribution found all over the Potohar region . Lower altitudes (200-400 m a.s.l.) had the dominance of Ochthochloa compressa among other grasses, which is a spreading species.
Chrysopogon serrulatus and Cynodon dactylon jointly dominated 600 m elevation. Cymbopogon jwarancusa and Imperata cylindrica were the other species recorded very frequently at 600 m a.s.l. Other important grasses at this altitudinal range were Dactyloctenium scindicum, Desmostachya bipinnata, Hemarthria compressa and Heteropogon contortus, all were recorded frequently in the region. Distributional pattern of grass species was more or less similar to that recorded for 600 m elevation, the most dominant species were C. serrularus and C. dactylon, which were followed by C. jwarancusa. Other important species were Digitaria adscendens, Ochthochloa compressa and Saccharum spontaneum, all dominated some specific microhabitats.
Three species collectively shared dominance at 1000 m a.s.l., Chrysopogon serrulatus and Desmostachya bipinnata were the most dominant species. Other important species was C. dactylon, which was recorded abundantly at this elevation. Desmostachya bipinnata was recorded frequently but little scattered in distribution. Chrysopogon serrulatus solitarily dominated altitudinal range of 1200 m a.s.l. Three species, C. jwarancusa, D. scindicum and H. contortus were the other dominant.
Discussion
Species distributional pattern, species composition and community structure significantly altered with
altitudinal gradient as reported by a number of researchers all over the world (Luo et al., 2004, Li et al., 2011;
Abbasvand et al., 2014). Similar finding has been recorded in the Potohar region, particularly at higher
altitudes. Variability in climatic and physiographic conditions are exceptionally high in the region, such as
high mountain peaks of Tret, Daleh and Sakesar (c. 1500m a.s.l.), sandy desert in Khushab district, heavily saltaffected foothills near Lillah and Pind Dadan Khan, vast valleys like Vanhar, Soone and Soan, protected areas like
Chinji, Chunbi-Surla, Kala-Chitta hills, Lehri-Jindi and Domeli-Diljabba, drier hills of Kalabagh, cooler Murree
foothills, etc. (Mahmood et al., 2012). These variation is strong enough to impose a drastic change in distributional
pattern.
Acknoledgment
This manuscript is a part of Ph.D. thesis of Sana Fatima, submitted to Department of Botany, University of Agriculture Faisalabad.