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Plate 6.4 - Eastern Tibet, near Ritse, Zitsa Degu (Chin. Jiuzhaigou): while the northern slopes have regenerated a dense forest cover, the southern slopes remain mostly forest free. Daniel Winkler, 4th August 1991

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This paper focuses on two of the most striking phenomena of the forests in eastern Tibet: the existence of forest-free south-facing slopes and modern-day deforestation.

Under the first heading it examines the cumulative historical impact both of fire, and of people and their grazing animals on forest distribution; under the second, it discusses the extent, causes, and possible solutions to the critical problem of modern deforestation.

     Over the last 15 years western research largely has overlooked eastern Tibet both directly, and indirectly as Chinese materials have presented a language barrier. This paper is based on observations of the forests of the south-eastern Tibetan plateau which were made during a six week field study carried out by the author of the forest vegetation of Zitsa Degu (gZi rTsa sDe dGu; Chin. Jiuzhaigou) Nature Reserve (Winkler 1994,1997,1998), north-east of Aba (rNga Ba) in Aba Tibetan Autonomous Prefecture, north-west Sichuan / south-east Amdo ('A mDo) (Maps 2 & 4). It utilises available western language sources and Chinese articles on the forests of the area as secondary source material, and these form the basis for the quantitative account of deforestation.

     An area as vast and inaccessible as the Tibetan Plateau calls for the application of remote sensing technologies. Yet applying remote sensing techniques in high mountain areas with a rugged terrain faces many technical difficulties, especially relief-induced distortions. To try to use digital remote sensing data to evaluate forest cover predominantly spread on north facing slopes, creates even more difficulties due to the lack of data reflection on shady slopes. Since the late 1970's there have been attempts in China to use Landsat MSS (Multi Spectral Scanner) data to perform forest inventories (Fang 1980). The TAR's most recent forest statistics are based on data derived from remote sensing technology (Xinhua 1994). De Wulf et al (1988, 1990) used Landsat MSS-data to map out bamboo forests as possible Giant Panda habitat in west Sichuan. Woodrow (1990) produced a small-scale map based on NOAA-data (National Oceanic and Atmospheric Administration) on the major environmental units of the Tibetan Plateau. So far there is no published comprehensive report on the extent of deforestation based on satellite data. Fix-Kirst (1994) tried to map clear-cut areas around Nyingchi (Nying Khri), yet without achieving the objective. A similar attempt has been made by Andersen and Hansen (1994) south of Derge (sDe dGe). Leber et al (1995) used multisensoral and multitemporal remote sensing data, including Metric Camera, Landsat MSS and TM (Thematic Mapper), Spot PAN (Panchromatic Imagery) and ERS-1 (Earth Resources Satellite One) synthetic aperture radar (SAR) to evaluate environmental changes in the wider Shigatse area, an area presently free of forest.
     The two phenomena introduced above are illustrated in a photograph taken near Longriba, south-east of Aba, on the way to Amchok dGon Pa (Plate 6.1). In the foreground, the left on the north-facing slopes have been totally removed, leaving behind a vast empty area without reforestation. The abundance of standing and fallen dead wood is typical of primary forests. In the
Plate 6.1 - Eastern Tibet, south-east of Aba near Longriba: clear-felled foreground; some of the north-facing slopes [1] are still forest clad, while the south-facing slopes to the left of the ridge are free of forest [2]; there is also fresh clear-felling [3]. Photo courtesy of Bruno Baumann, February 22, 1994
Plate 6.2 - Eastern Tibet, valley at the Konke La pass: in the foreground, the modern clear-felling regrow a scrub covering [3]; in the rearground, forest-clad north-facing slopes [2], and clear-felled south-facing slopes [1]. Daniel Winkler, June 26, 1991

background, to the right the general forest distribution pattern is clearly apparent: the north-facing slopes to the right of the ridge are forest-clad [1], the south-facing slopes [2] are
free of forests. To the left fresh clear-felling [3] has destroyed this pattern. The north-facing slopes are recognisable by their whiter snow cover; the south-facing slopes were only covered the day before by a snow storm.

     An examination of the distribution of vegetation across the overall area gives one a good idea of climatic conditions on the Tibetan plateau. Due to the increasingly continental climatic conditions, there is a steady decrease in average temperature and annual rainfall as one rises from the south-east (rainfall above 1,500mm per annum) to the north-west (rainfall below 100mm per annum); this is matched by a corresponding decrease in biomass and biodiversity. While the south-east has lush dense forests with conifers of over 60 metres in height, especially along the deeply dissected fringes off the Tibetan plateau, in the north-west the less mountainous northern plateau or Changthang (Byang Thang) is characterised by extremely sparse, high-altitude desert vegetation. In between these two extremes exists a whole range of vegetation zones: as one ascends, the spruce-fir forests become sparser and less rich in species, before giving way to open juniper forest; gradually these too are replaced by scrub and grassland, before finally giving way to scanty desert vegetation.
     In addition to the rainfall or precipitation gradient, there is also a land heat-source factor, which raises the altitudinal zones of vegetation along with the rise in the general land-surface of the plateau itself. Hence, while on the fringes of the plateau forests grow up to `only' 3,600 metres, on the plateau itself forests manage to persist at 4,700 metres. The highest true treeline in the world is probably in this area and around the altitude of 4,700 metres, such as the forests around Dzog Chen (rDzogs Chen) Monastery in Der Ge (sDe dGe) (Schäfer 1938: 41) and adjoining western areas up to Nyingchi (Nying Khri).

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