Contributions to the synecology and syntaxonomy of West Himalayan coniferous forest communities
Phytosociological studies of coniferous forest communities in the montane belt of Kaghan, a major West Himalayan valley in Northern Pakistan, are presented. High mountain relief is predominant in the valley, which is marked by a distinct change of climate soils and vegetation along its longitudinal profile. Under pronounced monsoonal influence in Lower Kaghan the natural vegetation is mainly formed by subtropical and moist-temperate coniferous forests. Towards the inner dry valley moist-temperate forests recede from southern aspects, where scarcely wooded dwarf-shrublands occur. The Braun-Blanquet approach is applied to plant communities of the humid and species-rich southern slope of the West Himalayan range for the first time. Cedrus deodara-, Pinus wallichiana- and Abies pindrow-associations are accordingly described emphasizing their synecological, floristic-sociological, physiognomic, chorological and syndynamic characteristics. The Parrotiopsio-Cedretum deodarae occurs mainly in warm-temperate and moderately humid habitats in the lower montane and in lower zones of the upper montane belt. This association is most competitive and zonal in the interior valley, where the monsoonal influence decreases and the climate gets a Mediterranean character. According to these environmental conditions mesomorphic elements and phanerophytic life forms are prevalent. Moreover, Cedrus-communities are characterized by a comparatively higher proportion of mesic West Himalayan endemites and of thermophilic taxa also occurring in adjoining southern and western floral regions. Due to the great economical value the Cedrus-stands experience an enhanced protection by the Forest Department and the human impact, particularly the grazing pressure, is relatively low. The Androsaco-Pinetum wallichianae has a wide ecological amplitude but is best developed on south-facing slopes of the upper montane belt. It is evident from its distribution pattern that the effect of radiation exposure is the crucial habitat factor resulting in its higher competitiveness. Since southern aspects become free of snow much earlier Pinus-stands are generally more adversely affected by forest grazing. To a greater extent than in Cedrus- and Abies-forests the species combination is influenced by human interferences, even on the level of character species. Due to the occurrence on more xeric southern aspects this association shows the lowest proportion of taxa with distribution in the humid East Himalaya. In contrast, the Ainsliaeo-Abietetum pindrowi, depending on a sufficient supply of humidity is mainly confined to north-facing slopes and topoclimatically moist sites of the upper montane belt. Towards the inner dry valley Abies-stands are restricted to habitats with a thick, long-lasting snow cover maintaining the relative hygric habitat constancy. Cold-humid habitat conditions are reflected by closer floristic affiliations to the East Himalaya as well as by predominating hemikryptophytes. Likewise the species combination points to a considerable grazing intensity. The described associations are well characterized by diagnostic species and have a striking resemblance regarding their floristic-sociological structure. The high presence of a series of taxa occurring in all associations is remarkable. These taxa represent supposed character species of higher syntaxonomic units of moist-temperate coniferous forest communities. Apart from their close syntaxonomic relationship the associations show a mosaic-like distribution pattern in the upper montane belt where they form a zonal vegetation complex. They do not develop further by autogenic succession, i. e. they represent terminal stages of natural succession (climatic terminal communities). Species combinations of their character species groups reveal fine ecological distinctions between these associations in particular regarding chorological-ecological indications. The majority of the character species of the Androsaco-Pinetum is widely distributed in the northern hemisphere. This result correlates with the wide ecological amplitude of this association and at the same time with the intensity of human interferences. The large number of heliophilous, unpalatable and browsing-resistant taxa among the character species of all associations suggests a considerable anthropogenic alteration of community structures.