Phytosociology, structure and diversity of the steppe vegetation in the mountains of Northern Pakistan
Peer, Thomas; Gruber, Johann Peter; Millinger, Andreas; Hussain, Farrukh
This study characterizes the grazed vegetation of the eastern Hindu Kush Mountains, located at a transition zone between the winter-rain-influenced Irano-Turanian regions in the West, the arid Central-Asian regions in the North, and the monsooninfluenced Sino-Himalayan regions in the Southeast. We used two-way indicator species analysis (TWINSPAN) for hierarchical classification of community data, and canonical correspondence analysis (CCA) for examining relationships between the vegetation and selected environmental parameters. In relation to locality, altitude, soil conditions and grazing pressure, eleven plant communities, linked to four vegetation types were identified in the study area: (1) the desert steppe, comprising the Artemisia fragrans-Haloxylon thomsonii community, the Stipa orientalis-Kraschenninikovia pungens community, the Eremurus stenophyllus-Scutellaria multicaulis community, and the Koelpinia linearis-Matthiola chorassanica community; (2) the Artemisia brevifolia steppe, comprising the Bromus danthoniae-Artemisia brevifolia community, the Acantholimon kokandense-Artemisia brevifolia community, and the Cerastium cerastioides-Aconitum rotundifolium community; (3) the alpine scree vegetation, composed of the Acantholimon kokandense-Psychrogeton andryaloides community and the Androsace baltistanica-Elymus schugnanicus community, and (4) the alpine mats, with the Oxytropis humifusa-Crepis multicaulis community and the Leontopodium ochroleucum-Festuca alaica community. However, no syntaxonomical classification could be achieved yet due to insufficient samples, lack of particular character species, and taxonomic problems. The above vegetation types and plant communities differ floristically and phytogeographically, with plants showing characteristic patterns of adaptive trait variation. Whereas the steppes in the West exhibit high species diversity, with a notable shift towards Irano-Turanian, Pamirean and Himalayan elements, the northern regions, including the Central Karakorum, are species-poor, with Central-Asian and Tibetan elements being more prominent. As the occurrence of ephemerophytes is tightly linked to sufficient soil humidity in spring, they are a typical feature of plant communities influenced by winter rain. In general, the most important ecological factors influencing the above vegetation types and plant communities are altitude, geographical position (longitude more than latitude), grazing intensity and organic matter content. The results are discussed in relation to the floristic relationships of the phytocoenoses within the geographical and altitudinal range of the study area, and also with respect to those occurring in the adjacent mountains of Karakorum and Ladakh.