by Passang Wangchen Norbu
Assistant Director
Forest Inventory Unit
Forest Resources Development Section. Thimphu
The Royal Government of Bhutan
Local name: Yew (English), Keyrang-shing (Sharchop-kha), Dhengrey salla (Lhotsham kha)
Botanical name: Taxus baccata L.
Officers and foresters from other parts of the Himalayas report that the Himalayan yew's foliage contains a chemical known as taxol, discovered only in recent years and now considered to be one of the most important drugs in the fight against cancer. Provided scientific principles are followed, foliage production can be maintained on a sustainable basis. Currently, however, there is little knowledge on the proper management of Bhutan's Himalayan yew. Given this shortage of knowledge, large-scale foliage collection at this juncture would do more harm than good and could even threaten the resource. Thus a conservative approach must be taken.
Morphology
The Himalayan yew is an evergreen tree, generally middle-sized, though sometimes quite large, with a large, spreading crown. Most yew trees tend to be forked, fluted, and with depressions at branch-stem junctions. This is not regarded as a defect (Evans, 1984). Its bark is reddish-gray, thin and smooth, and peels off in longitudinal shreds. Its leaves are 1.5-2.75 by 0.2-0.25 centimetres, usually curved, acuminate margins, slightly inrolled, dark-green and shining above, brownish-yellow and somewhat pale beneath, single nerved and narrowing into a short petiole.
Distribution
According to the Flora of Bhutan, Taxus baccata L. is the only representative of the Taxaceae family in Bhutan. On average, it is a tree of 5 to 12 metres in height. Taller trees grow to 12 metres or more. The tree occurs in scattered localities from Haa District in the west to Mongar District in the east. Reportedly, it also grows in the Kharungla area of Khaling and in the Zukpula-Menthongla belt in Wamrong, under Trashing District (author's personal communication 1992 and 1994).
The Bhutanese yew's habitat is characterised by moist, mixed coniferous forests or cool, broad-leaved forests, from 1,800 to 2,700 metres in altitude. Yew is also listed as one of the characteristic species of the "spruce forest" (2,700 to 3,100 metres) vegetation zone. Yew in Bhutan is best treated as a subspecies of zuccarini pilger (Taxus baccata var. wallichiana).
The extent of the area and forest types where yew occurs are furnished in Table 14.
Approximately 40 to 50 percent of the Himalayan yew's stems fall into the small diametre class of 10 to 20 centimetres. The yew growing stock for northwestern Bhutan is estimated at 1,459.7 cubic metres, equivalent to 1.1 percent of the total forest volume. The mean annual volume increment is estimated at 0.96 percent.
Table 14 Extent and Area of Forest Types Where Yew Occurs
|
Forest type |
Area (ha) |
Vol./ha. (m³) |
Stem/ha (m³) |
Total Vol. (m³) |
Total Stems |
|
Fir and spruce |
128,021 |
0.93 |
3.15 |
119,060 |
403,266 |
|
Mixed conifers |
137,199 |
1.46 |
7.06 |
200,310 |
968,625 |
|
Conifers mixed with broadleaf |
149,679 |
1.03 |
5.56 |
154,169 |
832,215 |
|
Upland hardwood |
207,889 |
0.70 |
3.19 |
145,522 |
663,166 |
|
Total |
622,788 |
|
|
619,061 |
2,867,272 |
Yew growing stock for central and eastern Bhutan is estimated at 1,238 cubic metres. equivalent to 0.6 percent of the total. The annual volume increment is estimated at 0.76 to 1.5 percent. The total area of upland and lowland hardwoods is 1,385,940 hectares. This figure has not yet been separated into upland and lowland areas. Since the occurrence of yew is more likely in the upland areas, only upland hectarage is considered here. Only 15 percent of the total area is considered in estimating yew volume.
Regeneration
Yew has evergreen, needle-like leaves, but produces berry-like fruits instead of cones and is usually dioecious. Monoecious individuals occur very rarely. Like most trees, it does not produce a good seed crop every year. Visits to the yew growing areas of Bhutan reveal that there is a lack of natural regeneration. The reason for this is still unknown. Some believe that yak herders uproot the seedlings, as they are toxic to yaks, while others believe that intense browsing by yaks checks the growth of seedlings.
Himalayan yew has very thin bark and, as is the case with the Pacific yew found in northwestern United States, may be easily killed even by a light ground fire. The fruit is edible and ripens from October to November. Germination of the Himalayan yew is difficult and usually scarification is required to break the dormancy. Himalayan yew sprouts readily from stumps and cut branches. It can be propagated easily with stem and root cuttings.
Uses of Yew Wood
The sap wood is white; the heart wood is orange red, close-grained, hard, smooth, and elastic. It works and polishes extremely well, but is somewhat slow to season. The wood-is eminently suitable for cabinet work and other furniture. In some parts of India's Uttar Pradesh State, local people use the bark as a substitute for tea. In Bhutan, especially in the East, people use the wood for making milk and water containers.
Diagram 3 Yew Occurrence in Bhutan
Since all individual tree species, including yew, are routinely measured during forest management inventories, more information may be available from established forest management units. While processing the data from the Karshong Forest Management Unit of Bumthang District, for example, it was revealed that more yew occurred there than in the western districts.
More work is needed to screen existing databases and inventory reports to pinpoint the most important strata and individual plots where yew is found. Diagram 3 shows the probable areas where yew might be found. These areas are indicated on the map by dots. The density of dots and their number do not reflect the quantity of yew, but are exclusively an indication of the localities where yew occurs.
