Diversity and distribution of the Family Poaceae along an elevation gradient in the sub-Himalayan mountains

Abstract

The mountain ecosystem is a perfect podium to investigate the impact of climate change on overall community structure and species composition. The Potohar region in Pakistan was chosen to study changes in grass-species diversity and the distributional pattern along an altitudinal range of 1000 m (from 400 m to 1400 m). The major objectives of the study were to prepare grass-species listing and species composition, and patterns of their dominance and distribution at various habitats. Three sites separated by a distance of 50 km were selected at each altitude and three transect lines (each of 100 m) were laid at a distance of 500 m. Then five sub-transect lines were laid at distance of 50 m on which five quadrats (1 x 1 m(2)) were laid systematically with a distance of 10 m between the successive quadrats. The diversity of the grass species is high and 114 species were recorded therein. Six grasses, Aristida adscensionis, Cynodon dactylon, Chrysopogon serrulatus, Cymbopogon jwarancusa, Dichanthium annulatum and Panicum orientale, are widely distributed at all altitudinal ranges. Species like A. adscensionis, Cenchrus ciliaris, C. jwarancusa, C. dactylon, Ochthochloa compressa, Panicum antidotale, Paspalum distichum and Phragmites karka dominate because of their high degree of tolerance to multiple stresses. These dominant grasses are highly palatable and support livestock and endemic wildlife species. The distributional range of other grasses is altitudinal-specific and is directly linked to the physiographic parameters and climate variables that influence species richness, dominance, community structure and species distributional pattern along altitudinal gradients. Over-harvesting for essential oil and other medicinal purposes are identified as major threats to species like Cymbopogon martini and Chrysopogon zizanioides. The findings of this study are useful in investigating the composition of grass species of the sub-mountainous rangelands and in developing conservation strategies for rare and endangered species in future studies.