Department of Forest Ecology, XTBG, The Chinese Academy of Sciences, Xuefu Road 50, Kunming 650223, P.R. China
The impacts of human population distribution, agriculture, expansion of tropical crop plantations and tourism on natural forest of Xishuangbanna were discussed in present paper. It is concluded that the local forest has been charged with increasing economic pressures, which raises the alarm of a need of long-term plan of sustainable development for the purpose of effectively protecting local environment and forest ecosystems.
Tropical forest of Xishuangbanna is unique because of its transitional geographic location and climatic features, crossing the tropics and subtropics. Thus both the northern and southern biotas meet in this region (Box et al., 1991; Cao et al., 1996). Although Xishuangbanna covers only 0.2% of the area of China, it maintains nearly 16% of higher plant species of China (Zhang & Cao, 1995). This fact strongly suggests the importance of Xishuangbanna in the biodiversity conservation of China. Four kinds of local primary forest are identified, these are tropical seasonal rain forest, tropical montane rain forest, monsoon forest and evergreen broad-leaved forest, of which tropical seasonal rain forest demonstrates the highest tree species diversity (Cao & Zhang, 1997). A severe decline of local primary forest cover took place in the period from early 1950s through the beginning of 1990s, during which the primary forest cover dropped from about 60% down to about 27%. This led to the loss of habitats for some local animal and plant species and a large number of endangered species (Zhang & Cao, 1995).
Besides the high richness in biodiversity, Xishuangbanna has also more than ten different minority nationalities (including Dai, Hani, Lahu, Bulang, Yi, Jinuo, Yao, Wa, etc.), which account for about 3/4 of the local population. Each of them follows their own traditions and culture. The Dai people, with more than 1/3 of the local population, are the biggest ethnic group in this area, they had begun the cropping practice of upland rice by clearing forests as early as 3700 years ago. Other traditional activities, such as hunting, fishing, fuel-wood collection and food gathering, have been also carried out in the local forest. On the other hand, some useful forest plants are commonly introduced into local home gardens and plantations. An enthnobotanical investigation found that there are 463 species and varieties in the local farmers¡¯ home gardens of Xishuangbanna, which are used as food, medicinal plants and ornamental plants respectively (Long, 1993). About 315 species of cash plants are commonly cultivated by the Dai people (Yu et al., 1985).
Since the middle of 1950s a large number of people from central China, where both the rural and urban areas were heavily populated, immigrated into Xishuangbanna. Because local farms needed manpower to manage the rubber plantations which were mostly established by clearing tropical seasonal rain forest. This led to a drastic growth of the local population and a reduction of the natural forest cover. All the facts mentioned above made pronounced impact on the local natural forest. This paper examines the effects of major economic activities on the forest vegetation through comparing some social and economic parameters with the dynamic trends in forest cover of this area in a broad sense.
Xishuangbanna Dai Autonomous Prefecture consists of Jinghong City, Menghai County and Mengla County (Fig. 1). Menghai is on the southwest of the prefecture, with relatively higher average latitudes (800-1000 m). Whereas Jinghong and Mengla are in the middle and the southeast, with low average latitudes (500-600 m). The heterogeneous topography leads to different patterns of human population and forest. According to the data for 1998, Jinghong covers the biggest land area and has also the biggest population size of the prefecture. Mengla, in contrast, has the smallest population size, although it covers about the same land area as Jinghong (Fig. 2). Moreover, Mengla retains even bigger forest area (including other types of forest vegetation, such as open woodland and brushland, etc.) than Jonghong, which comprises 54.6% of the land area of Mengla, ranking at the first place among the three counties (51.3% for Jinghong and 49.1% for Menghai). This pattern results in the uneven distribution of forest and human population (Fig. 3). Both the land area and forest per caput of Mengla, once again, take rank of the other two counties, nearly as high as two times of them (Fig. 4). This result can be partly explained by the human population densities of the three counties (28.2 persons/ha for Mengla, 52.4 persons/ha for Jinghong and 54.5 persons/ha for Menghai).
A study made on the basis of interpretation of TM images indicated that Mengla maintains large areas of primary forest as compared with Jinghong and Menghai. Secondary forest and plantations principally represent the forest of Jinghong. The forest in Menghai has been seriously disturbed (Zhang et al., 1999). This strongly implies a specious negative relationship between the population density and forest area on a local scale.
Jinghong Mengla Menghai
Figure 2. Distribution of land, forest and population in Xishuangbanna.
Figure 3. Proportional composition of forest area and population of Xishuangbanna.
Figure 4. Land area and forest area of per caput of Menghai, Jinghong and Mengla.
Agriculture in this area was developed at least 3700 years ago. However river basins, valleys, lowlands and hills where tropical seasonal rain forest was distributed were reclaimed in the first place, because there were sufficient water supply and enough temperature conditions in these habitats. And good transportation systems could be easily set up as well. Mountain areas, nevertheless, remained relatively pristine, where only shifting cultivation was practiced by a small number of mountain tribes on a small scale.
The mountainous physical environment lays the basis for the contemporary patterns of human settlement and farmlands. Basins were mostly constructed as urban areas or townships with high population density. In the vicinities of these urban districts a lot of forests were converted into farmlands. For the purpose of adaptive management of rural areas, the local lands are arbitrarily classified into three geomorphologic categories, based on relative altitudinal difference and slope (Table 1). Although the basins constitute only 1/20 of the total land area of this prefecture, more than 1/3 of the farmland in Xishuangbanna was distributed in the basins. Semi-mountains and mountains, in contrast, had less farmland in proportion in 1998 (Fig. 5). Farmland in total made up about 6% of the land area of the prefecture.
Table. 1. Classification of lands in Xishuangbanna
Relative altitudinal difference < 10 m, over 1 km2 in area and < 8¡Æ slope
Relative altitudinal difference 10 - 200 m and > 8¡Æ slope
Relative altitudinal difference > 200 m and > 8¡Æ slope
Figure 5. Topographical distribution of farmland of Xishuangbanna in different.
Dryland rice is one of the main crops grown in shifting cultivation of Xishuangbanna (Cao & Zhang, 1996). In 1998, over 3/4 cultivation area of dryland rice, however, was on mountains, in spite of its lowest yield in comparison with those of basins and semi-mountains (Fig. 6), suggesting a potential impact of shifting cultivation on the montane forest cover. As a whole, the fields in the rotation of shifting cultivation accounted for about 43% of the total farmlands. Menghai made up the smallest proportion of the prefectural land area, but it topped the rank of the total shifting cultivation areas among the three counties (Fig. 7). This could be one of the main reasons why there has been a drastic deforestation in Menghai (Zhang et al., 1999).
Figure 6. Cultivation of dryland rice in Xishuangbanna.
Figure 7. Shifting cultivation fields of Xishuangbanna.
Rubber and tea serve as the major cash crops in local plantations, which made up 88% of the plantations¡¯ areas of the prefecture in 1998. With regard to the yields of rubber plantation and tea plantation, the highest for rubber was achieved in the basins and for tea on semi-mountains respectively (Fig. 8), showing the different habitat preferences of the two crops. However mountains took also large proportions of the cultivation area of the two crops, although mountain habitats produced the lowest yields for both rubber and tea.
Figure 8. Areas and yields of rubber and tea plantations in Xishuangbanna.
Figure 9 shows the changes in the local population since the end of 1940s. It is clear that there was a distinct growth of the total population in the period between late 1950s and middle 1980s when the state-own farms were established, following by a rapid extension of rubber productions (Fig. 10). Looking at the changes in the composition of ethnic groups, however, the proportions of Dai People and other minorities dropped down over this period. On the contrary Han People, the majority of Chinese, increased from 7% to 29% of local population (Fig. 11). This indicates that the in-migration of Han People contributed a lot to the rise of population.
Due to traffic difficulties and the lack of tourism-oriented facilities, Xishuangbanna received few tourists in 1980s and before. However tourism with the purpose of visiting rain forest attractions and experiencing minority ethnic cultures boomed quickly since 1990 (Fig. 12), when the Jinghong Airport was put to use, which created big benefits. In 1998 the total income of tourism accounted for 42% of the gross domestic product of the prefecture. This encouraged local government to develop the tourism as one of the backbone industries for local economy. Thus it can be expected that the tourism industry is to be kept growing in the future.
Figure 9. Changes in the local population of Xishuangbanna.
Figure 10. Growth of rubber production of Xishuangbanna.
Figure 11. Population changes in the main ethnic groups of Xishuangbanna.
Figure 12. Growth of tourists¡¯ visits in Xishuangbanna.
Paralleling to the increase in the local population, crop plantations and tourism industry, the natural forest cover, including primary forest and secondary forest, in this region tended to be going down (Fig. 13). On the other hand, the conversion of primary forest into secondary forest and plantations is getting increasingly serious. Forest patches were increased at a rate of 26.5% every year (Zhang et al., 1999).
Figure 13. Changes in the natural forest cover of Xishuangbanna.
Xishuangbanna plays an important role in China¡¯s biodiversity conservation because of its species-rich forest ecosystems. However the distribution of the forests and human population shows an uneven pattern, following its heterogeneous topography. Natural forest area declined along with the boom of tropical plantations and tourism. And forest fragmentation was aggravated. The growing developments of local economy deserve great concern in terms of sustainable forest management.
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