Excerpt from the 1994 published master thesis
Many photos can be found in the photo essay section under Jiuzhaigou
8.2 Summary and Short Outline of this Thesis
8.2.1 Geo-ecological Situation in the Jiuzhai Valley
This thesis - which was conducted in July and August 1991 - describes the spatial distribution of the forest vegetation and its soils. NNW-Sichuan's Jiuzhai valley (in tibetan: Zi Tsha De Gu; 103°46'E-104°05'E / 32°55'N-33°20'N) is located in the Min Shan Mountains on the central eastern slope of the Tibetan Plateau. It is a catchment area shaped by tectonic uplift and water erosion, which is made almost exclusively from intensely folded limestone, extending from 2000m to 4764m a.s.l.. The Jiuzhai tributary is a southern branch of the upper Baishui Jiang. The climate is subtropically influenced. In summer the SE-monsoon dominates, accounting for at least 75% of the precipitation. The winter is influenced by the Westerlies. The precipitation level on the valley floor (Nuorilong, 2400m) is 761mm/a, and on the slopes, around the condensation zone, it is at least 1000mm/a. The annual mean temperature at 2400m is 7,3°C. The mean temperature is 16,8°C in June, and 3,7°C in January. The valley is located in the Holoarctic Floral Kingdom. The flora belongs to the Sino-Japonian Floral Region, which in this area boarders the East-Tibetan Province of the Central Asian Floral Region. The forest area was reduced by timber extraction in the seventies. Figures for the East-Tibetan Plateau suggest that the forest areas were nearly reduced by half in the last 40 years.
8.2.2 Graphic Image
In Abb.5 (see p.92) the emphasis is placed on the forest trees. The N and S-exposures as well as the E and W-exposures are presented. The E and W-exposures are combined and differentiated into a dry, irradiation exposed type and a humid, irradiation protected type. Research shows that E and W-exposure only differs in the formation relative to the level of irradiation and moisture influx.
8.2.3 Three Dimensional Zonation
The warmest and least humid (ca.700 mm/a precipitation) zone lies between 2000m (valley floor) and 2400m to 2600m (shady and sunny-slopes respectively). This area is agriculturally the most intensively used and is preferred for settling by the indigenous Tibetan people. The forests in this zone are dominated by Pine-Oak-Secondary-forests. The highest canopy (B1) is made up of Pinus tabulaeformis. Quercus aliena dominates the sub-canopy layer (B2); in sun exposed locations Fraxinus suaveolens and the evergreen sclerophyllous Quercus baronii are present as well. The shrub layer is dominated by Cotinus coggygria, with Rhododendron micranthum strongly present on shady slopes. The soils are mostly dominated by Rendzinas; in some locations, on loess, Calcaro-Chromic Cambisols have developed. Barely a trace remains of the original Tsuga chinensis-Mixed-Forest.
Between 2400m (2500m on northern slopes) and 2700m the Abies-Picea-Mixed-Forest marks the lower limit of the condensation zone. The Rendzinas are in varying degrees of development. The organic matter of the epipedons are more decomposed than in the lower zone due to higher precipitation and lower irradiation. The canopy of the multi-leveled forest is dense and grows up to 50m in height. Abies ernestii dominates the more humid stands. Less humid stands are taken by Picea wilsonii; Pinus tabulaeformis dominates dry locations. As elevation increases Quercus aliena is handicapped by broken branches. Quercus is commonly associated with Betula albo-sinensis. Small deciduous trees (Acer spp., Tilia spp. and Lauraceae) are interwoven with up to 5m high shrubs (many Caprifoliaceae). Sinarundinaria-bamboo appears but is not competitive. In general the herbaceous understorey is sparse.
Between 2700m and 3200m stands the Bamboo-Forest inhabited by the Giant Panda (Ailuropoda melanoleuca). It is favored with high precipitation (exceeding 1000 mm/a), but still enjoys temperate temperatures.Of these usually humid forests the dryest is the Picea-Larix-Forest, which occurs in irradiation exposed locations on Rendzinas. In the lower elevations Picea wilsonii is competetive. P.asperata und P.purpurea occur around 3000m, where Larix potaninii and Sabina spp. begin to become competitive. In average humid locations, on (Orthic-) Rendzinas, Abies faxoniana dominates along with Picea-species. In humid shady north exposures, on Calcaro-Chromic Cambisols, A.faxoniana alone makes up the canopy layer. A subcanopy consists of Betula utilis and B.albo-sinensis. The shrub layer is clearly dominated by Sinarundinaria (nitida?), so much so that shrubs or small trees are strongly impeded. The herbaceous layer can be abundant when bamboo isn't too dense. Moss benefits from the dampness and the low evaporation rate.
Between 3200m and treeline (approx. 3800m) on all northern exposed slopes Abies faxoniana (canopy coverage ca.60%, height max. 25m) occurs in pure stands on shallow developed Calcaro-Chromic Cambisols. The sub-canopy consists of Betula utilis. Sinarundinaria, like most subtropical species, is absent due to lack of heat. It is fully replaced in its dominance by Rhododendrons. In less moist sites Picea purpurea is competetive. In sun exposed E and W-sites Sabina (Juniperus) species dominate the sub-canopy.
At around 3500m, on the southern exposures, A.faxoniana and P.purpurea give way to Sabina spp. due to extreme diurnal changes of temperature. Sabina species make up open forests without Rhododendrons. Treeline on southern E and W-exposures is around 3800m aswell. On the northern slopes, around and above treeline, Rhododendrons dominate, with some Salix interspersed. The southern slopes above timberline are grasslands with very few shrubs (Berberis, Spiraea).
Directly south exposed slopes from 3000m and upwards are without forests, though there are a few small Picea and Juniper trees. These indicate the potential for forest growth. Forest-free south slopes (respectively, southern slopes, in more continental locations in wider East-Tibet) are the rule. So far this has been attributed solely to climatic conditions (extreme diurnal changes of temperature especially in late winter and desiccation), which are supposed to prevent tree growth (SCHÄFER, WISSMANN, WEIGOLD; HANSON-LOWE; KU / CHEO). The fact that some trees are still growing refutes this hypothesis. In reality there seems to be a combination of causes. On one hand harsh climatic conditions, but on the other interventions by man, especially burning to create grazing grounds for late winter, when southern slopes are rarely snow covered for very long.
8.2.4 Condensed outline
The introduction (1) points out the relevance of this region and this research and deals with the issue of recent deforestation on the Southeastern Plateau. It is followed by a presentation of the results of previous research (2.1-2.2) done in this region (2.3) and by a description of the methods utilized (3).
Next the Jiuzhai-Valley is presented as part of the central eastern slope of the Tibetan Plateau (4). A general overview of location in physical and ethno-geographical regard (4.1) is given. The geological and geomorphological conditions (4.2) are briefly dealt with before the macro-climatic (4.3.1) and the local climatic (4.3.2) situation is presented in more detail. This section closes with the presentation of the geobotanic location.
"Aufnahmen" (5) presents the sample plots in which the vegetation and soil was listed, recorded and briefly annotated. Chapter 6 contains the analysis of these findings. Here the sample plot information is interpreted with support of results of other research. In 6.1 the different forest types found are introduced, their structure and composition characterized, and their locations mapped out. In 6.2 the distribution of species is dealt with. The first part (6.2.1) is concerned with the tree layer, the second (6.2.2) with the shrub layer, the third (6.2.3) with the rest of the understorey and the forth (6.2.4) with the epiphyts. 6.3 deals with the treeline. Special emphasis is placed on the phenomena of forest-free south slopes and its causes (6.3.2). In 6.4 the pedological conditions and their zonation is analysed.
Chapter 7 describes human impact in the valley. It is differentiated into 7.1 traditional Tibetan resource management (forest-management and grazing), and into 7.2, the modern Chinese resource management (forestry and tourism). The summary (8) - also in English - presents a brief essential three dimensional zonation of vegetation, soils, climate and land use. The distribution of the forest vegetation is graphically presented as well.
It is followed by acknowledgements (9) and the bibliography (10). The appendix includes an index of the sample plots (11.1), a vegetation list of WU ZHENGYI (11.2), a list of the recorded species of Jiuzhai Gou (11.3) and annotated photos (11.4)..