Forest Pattern Analysis Along the Topographical and Climatic Gradient of the Dry West and Humid East Slopes of Dochula, Western Bhutan

Author: Wangda P, Ohsawa M

ABSTRACT

The contrasting vegetation and climatic conditions on east and west sides of Dochula pass is a unique characteristic of the dry valley ecosystem. Temperature declines faster on the west slope than on the east slope. Moisture condition is the determining factor for the contrasting vegetation. Floristically 66 tree species belonging to 29 families were recorded and these included 3 conifers, 37 evergreen broad-leaved and 26 deciduous broad-leaved species. The dry pine forest of Pinus wallichiana and mixed pine-oak forest of Quercus lanata occurred on the west slope of Dochula. Contrastingly humid evergreen broad-leaved forest of Quercus oxyodon, Q. lamellosa, Q. glauca and Castanopsis hystrix occurred on the east slope. Dochula pass at 3000 m asl under cloud zone dominated by Tsuga dumosa, Betula utilis, and Quercus semecarpifolia divide the two slopes. We conclude that west slope vegetation corresponds to dry west Himalayan type and east slope the humid east Himalayan type, however, this gradually transits to dry west Himalayan type of Pinus roxburghii forest towards the dry valley bottom. The diverse forest types found on the west and east slope of Dochula pass can represent as a miniature of whole Himalaya and are the valuable standard pattern of the Himalayan forest types, which needs careful conservation and management.

KEYWORDS:

aspect, evergreen broad-leaved, soil moisture content, lapse rate.

REFERENCES

Grierson AJC & Long DG (1983-2000). Flora of Bhutan Vol. I. Part 1, 2, 3. Vol. II. Part 1, 2, 3 & Vol. III. Part 1, 2. Edinburgh.

Hocking D & Wangdi, J (2000). Review of the literature in Bhutan on Agroforestry. Hunting Technical Services Ltd. Hemel Hempstead, UK

Leith et al. (1990). Climate Diagram World Atlas. Backhuys publishers, Leiden

McCune B & MJ Mefford (1999). PC-ORD. Multivariate Analysis of Ecological Data, Version 4. MjM Software Design, Gleneden Beach, Oregon, USA.

Ohsawa M (1987). Vegetation zones in the Bhutan Himalaya. In: Life Zone Ecology of Bhutan Himalaya I. (ed. M. Ohsawa) pp. 1-73. Chiba University, Chiba.

Ohsawa M (1990). An interpretation of latitudinal patterns of forest limits in South and East Asian mountains. Journal of ecology. 78:326-339.

Ohsawa M (1991). Montane evergreen broad-leaved forests of Bhutan Himalaya In: Life Zone Ecology of Bhutan Himalaya II. (ed. M. Ohsawa) pp. 89-156. Chiba University, Chiba.

Polunin O & Stainton A (1984). Flowers of the Himalaya. Oxford Univ. Press. New Delhi.

Sargent C et al. (1985). The forests of Bhutan: a vital resource for the Himalaya? Journal of Tropical Ecology 1:265-286.

Schweinfurth U (1992). Mapping Mountains: Vegetation in the Himalaya. GeoJournal. 27:1 73-83.

Stainton A (1988). Flowers of the Himalaya, A supplement. Oxford Univ. Press. New Delhi.

Stainton JDA (1972). Forests of Nepal. John Murray.

Statistical year book (2002). Central statistical office, planning commission. Royal Government of Bhutan, Thimphu.