A tangle in the triangle: vegetation map of the eastern Hindukush (Chitral, northern Pakistan)

Abstract

Chitral is the meeting ground of three major climatic, floristic and ecological regions. The eastern Hindukush Mountains delimit the Irano-Turanian (winter rain), Sino-Himalayan (summer rain), and the Central Asiatic (permanently arid) regions. Flora and vegetation mirror the transitional status of the Chitral triangle. Arranged along prominent altitudinal belts, the vegetation of the eastern Hindukush displays complex regional and local patterns. Variation of total humidity and seasonal distribution of precipitation are key factors in determining ecological conditions. The most prominent climate gradient of Chitral is a sharp decrease of precipitation from south to north. This is overlaid and modified by a general trend towards winter precipitation in the west and summer rain in the east. The vegetation of Chitral includes a fairly diverse array of formations ranging from various forest types to desert, along an altitudinal gradient covering more than 4000 m. Besides these prominent climatic gradients, properties and distribution features of vegetation types have been modified, to a locally different extent, by human impact in the context of mixed mountain agriculture and forest exploitation. Furthermore, historical biogeographical constraints obviously had a significant influence on distribution patterns of many individual taxa. This paper presents an annotated vegetation map, based on a combined approach using remote sensing data (Landsat TM) and floristic data from the authors' own collections and additional herbarium material. Ground checks and analyses of the extensive floristic database rendered it possible to discuss altitudinal zonation and vegetation types in Chitral on a regional scale.