東部ネパールヒマラヤの植生 : 日華区系域の植生帯との関連
スポンサーリンク
概要
- 論文の詳細を見る
Though the flora of Himalayas has attracted the attention of a number of researchers, the region is still largely unexplored ecologically. In this paper the author studied the zonatioii of vegetation in different successional stages in east Nepal, and the climax zones were compared with that of East Asia. Altitudinal zonation of climax vegetation in east Nepal Altitudinal zones of vegetation in east Nepal were stated based on the investigation during the field trip in 1971 and 1977 (Fig. 1). The following 5 forest zones were recognized in climax state from lower to higher altitude (Fig. 2). 1) The Shorea zone (below 1000 m) This is the zone of subtropical Shorea forests. Though the forests are most extensive in the southern foothills of Himalayas, they sometimes extend into the mountaineous areas along the big valley system such as Arun and Tamur. Shorea robusta is a leading dominant species in the forests of this zone, but besides this there are several other types of forest dominated by e.g. Adina, Dalbergia, Lagerstroemia, Albizzia, Bombax, etc. 2) The Schima-Castanopsis zone (1000-1900 m) This is the zone of warm temperate forests dominated by Schima wallichii and Castanopsis spp. In the lower altitude of this zone the forests are dominated by Schima and Castanopsis indica with scattered trees of Albizzia, while in the higher altitude the Schima-Castanopsis forests are largely replaced by C. tribuloides and/or C. hystrix forests. On the rocky scree slopes the dominant species is replaced by Quercus lanuginosa. The Pinus roxburghii forest is the most extensive type of forest in west Nepal, while in east Nepal this forest is quite restricted to the south-facing steep slope only. 3) The Quercus zone (1900-2500 m) This is the zone of temperate lauro-fagaceous forests. In the easternmost parts of Nepal these forests are dominated by Quercus lamellosa and Q. lineata and are usually mixed with Litsea spp., Machilus spp., and Acer campbellii. In easternmost parts of Nepal Acer campbellii, which usually dominates the upper forest zone, commonly occurred in this Quercus zone. 4) The Acer zone (2500-3000 m) This is the zone of deciduous broad-leaved trees, such as Acer, Magnolia, and Sorbus. In some parts of this zone there are also coniferous forests dominated by Tsuga dumosa. One of the peculiar features of vegetation in this cool temperate zone of Nepal Himalaya is the presence of the evergreen broad-leaved forests, the Lithocarpus pachyphylla forest and the Quercus semecarpifolia forest. 5) The Abies zone (3000-3800 m) This is the uppermost forest zone bounded on the upper end by the forest limit (ca. 3800 m) and corresponds to the subarctic zone. Betula utilis and Rhododendron spp. are the most commonly accompanying species in this zone. Altitudinal distribution of species in different successional stages The above-mentioned zones of vegetation in climax state might be modified by various factors, among which the most strong and extensive disturbing factor for natural vegetation is the anthropogenic ones in east Nepal, e.g. farming, shifting cultivation, grazing by catties, etc. The extensive areas of secondary vegetation could be observed especially in the region lower than an altitude of 2000 m. As a basic information for the comparison of vegetational zonation in various successional stages the altitudinal distribution of species has been worked out separately for the pioneer and grassland herbs, the pioneer shrubs, the pioneer trees, and the climax trees (Fig. 3). In Fig. 3 certain marked differences in the distributional behaviour of the species can be distinguished in each successional stages. In general species distribution overlaps one another in a greater or lesser degree according to their successional status. In the pioneer and grassland herbs the distribution range of each species was quite large and sometimes reached to 2000 or 3000m of altitudinal range. And moreover the distribution ranges of these species overlap one another to a considerable extent. While in most of climax trees the species distribution ranges are less than 1000 m, and their distribution ranges are less overlapping. Due to these differences of species distribution pattern the zonal differentiation of vegetation is more conspicuous in the climax state than in the pioneer or serai stages. Comparison of climax vegetation zones with those in other parts of East Asia Comparison of the altitudinal zones of vegetation between different mountaineous regions is not so easy because of the lack of an unified principle to identify each zone. In this paper the author tried to compare the zonation between different places by introducing the method of correlation chart (Fig. 4). The chart composed of a coordinates and was used to compare the zonal arrangement of vegetation between two regions. It may be possible to help in examining precisely the pattern of zonation in a certain region by reffering to the well defined zonal pattern in another region. In this connection the zonal pattern of vegetation in Japan and Taiwan as an example was compared to the zones in east Himalaya. The vegetation zonation in Himalaya has a great span along the long mountain slopes from subtropical to arctic climate, therefore the zonal pattern of vegetation could be realized completely. Based on the results of the comparisons, it is recommended that the so-called warm temperate zone in Japan should be separated into two different zones, the temperate (upper half, the Quercus zone) and the actual warm temperate (lower half, the Castanopsis zone). The actual warm temperate zone in central Japan corresponds to only the upper half of the same zone in east Himalaya.
- 1977-12-30