干旱区生态环境知识资源中心

The treeless desertlike environments of southern Tibet are assumed to be naturally unsuitable for forests. Yet, climatic conditions do allow for the growth of indigenous trees in Lhasa and many parts of southern Tibet, even where there is no high groundwater table or irrigation. This was discovered and proven in a Sino-German research project launched in 1997. The project made an inventory of forest relics, correlated residual tree stands with climatic data, and successfully cultivated nonirrigated indigenous junipers and cypresses. The eroded semi-desert landscape of southern Tibet appears to have a huge potential for reforestation. The area with a potential for tree growth was investigated using the Geographical Information System known as GRASS (Geographical Resource Analysis Support System). Reforestation measures could meet the heavy demand for timber and firewood, help combat erosion on overgrazed slopes, and restore the degraded pastures. Grazing must be excluded on reforestation plots. Simultaneously, rangelands may regenerate after overgrazing. The optimum duration of the ungrazed period varies with altitude, humidity, soil conditions, and the degree of degradation. Successional trends observed on exclosure plots suggest that the drier the climate and the lower the initial degree of herbaceous vegetation cover, the longer the ungrazed period will be beneficial for pasture regeneration. Challenges in research and practice resulting from these preliminary results are highlighted.