Phytosociology, structure and dynamics of Pinus roxburghii associations from Northern Pakistan

Abstract

We investigated the phytosociology, structure and dynamics of Pinus roxburghii in 40 stands in northern areas of Pakistan by using cluster analysis (Ward's agglomerative clustering) and ordination (Non- metric Multidimensional Scaling). Cluster analysis revealed three major groups associated with specific environmental characteristics: (1) P. roxburghii (2) Pinus-Quercus baloot and (3) Pinus-Olea ferruginea community types. NMS-ordination showed the major gradient as an amalgam of elevation (r 2 = 0.441, p <0.01) and slope (r 2 = 0.391, p <0.05) as the two topographic factors correlated with species distribution. The first ordination axis also showed positive correlation with soil variables like pH and electrical conductivity, suggesting that soil chemistry was related to topographic characteristics and probably acted as a secondary gradient. We also examined size class distributions, age structures and growth rates of the three communities in order to describe community development and dynamics. Total tree density was 14700 plants/ha, with P. roxburghii having a relative density of 82% to 100%. Density of juve- nile and total density and basal area of the subordinate tree species were low. The low density of trees in the smallest diameter size-class sug- gested that the recruitment of small P. roxburghii plants into the adult population may be lower than the required replacement rate for the stands. Pooled size-class distributions for the species showed a multimo- dal pattern with some regeneration gaps. Browsing, heavy logging and other anthropogenic activities were the overriding factors responsible for the poor recruitment of P. roxburghii. We concluded from the age struc- ture that the forests were characterized by the dominance of young trees. Growth rate analysis revealed that P. roxburghii was the fastest growing species among the conifers species in Pakistan. In view of its relatively fast growth and longevity, P. roxburghii seems to be a suitable choice for short-term cultural practices in order to enhance wood production in lesser Himalaya and Hindukush ranges of Pakistan.