Winter Hardiness of Tree Species at High Altitudes in the East Himalaya, Nepal

Abstract

Maximal winter hardiness of trees in high—altitude forest zones, especially near timberlines in the East Himalaya, was assessed. A timberline coniferous species of the East Himalaya, Abies spectabilis, was marginally hardy to —20° to —23°C. Larix potanini, a high—altitude species which is the least hardy species of the genus Larix, also showed the same range of hardiness. The hardiness of these species is comparable to the least hardy Japanese Abietoideae that are native to the warm—temperature forest zone. Subalpine rhododendrons such as Rododendron campanulatum, R. campylocarpum, etc., were the hardiest of the Himalayan rhododendrons, resisting —20° to —23° in their flower buds. These were less hardy than those occurring in the subalpine forests of Japan and North America. The flower buds of Himalayan rhododendrons ranging as high as 4500 m in the alpine zone, such as R. anthopogon, R. setosum, and R. lepidotum, were slightly hardier. Thus in the Himalayas, rhododendrons and coniferous species, except Pinus and shrubby Juniperus, seem not to have evolved species capable of resisting below —30°, unlike boreal and subalpine forests in central Japan, probably due to high humidity and moderate temperatures in the Himalayan winter, and floristic history.