Vegetation changes in a river oasis on the southern rim of the Taklamakan Desert in China between 1956 and 2000

The indigenous vegetation surrounding the river oases on the southern rim of the Taklamakan Desert has drastically diminished due to overexploitation as a source of fodder, timber and fuel for the human population. The change in the spatial extent of landscape forms and vegetation types around the Qira oasis was analyzed by comparing SPOT satellite images from 1998 with aerial photographs from 1956. The analysis was supplemented by field surveys in 1999 and 2000. The study is part of a joint Chinese-European project with the aim of assessing the current state of the foreland vegetation, of gathering information on the regeneration potential and of suggesting procedures for a sustainable management. With 33 mm of annual precipitation, plants can only grow if they have access to groundwater, lakes or rivers. Most of the available water comes into the desert via rivers in the form of seasonal flooding events resulting from snow melt in the Kun Lun Mountains. This water is captured in canal systems and used for irrigation of arable fields. Among the eight herbaceous and woody vegetation types and the type of open sand without any plant life that were mapped in 2000 in the oasis foreland, only the latter, the oasis border between cultivated land and open Populus euphratica forests and Tamarix ramosissima-Phragmites australis riverbed vegetation could be clearly identified on the photographs from 1956. The comparison of the images revealed that the oasis increased in area between 1956 and 2000. Shifting sand was successfully combated near to the oasis borders but increased in extent at the outward border of the foreland vegetation. In contrast to expectations, the area covered with Populus trees was smaller in 1956 than today due to some new forests in the north of the oasis that have grown up since 1977. Subfossil wood and leaf remnants of Populus euphratica that were found in many places in the foreland must have originated from forests destroyed before 1956. In the last 50 years, the main Qira River has shifted its bed significantly northward and developed a new furcation with a large new bed in 1986. The natural river dynamics are not only an important factor in forming the oasis' landscape but also in providing the only possible regeneration sites for all occurring plant species. The conclusion of the study is that the oasis landscape has changed considerably in the last 50 years due to natural floodings and to vegetation degradation by human overexploitation. The trend towards decreasing width of the indigenous vegetation belt resulting from the advancing desert and the expansion of arable land is particularly alarming because a decrease in its protective function against shifting sand can be expected in the future

Water use by perennial plants in the transition zone between river oasis and desert in NW China

The study aimed at establishing the role of two possible water sources (inundation, ground water) for the water supply to the perennial plant species Alhagi sparsifolia, Calligonum caput-medusae, Populus euphratica and Tamarix ramosissima growing in the transition zone between a river oasis and the open desert at the southern fringe of the Taklamakan desert (Xinjiang province, NW China). The basic hypothesis was that inundations, which normally occur in summer when rivers from a nearby mountain range carry high water, contribute significantly to the plants' water supply. When, in the first summer, inundations did not occur, four sites, each of which covered by a relatively dense stand of one species, were artificially flooded. Soil and plant water relations as well as meteorological variables were measured during two growing seasons. Water use efficiency of production (WUEp) was calculated by relating biomass production, which was determined using allometric regressions, to water use. The effects of artificial flooding on the plant water relations were negligible. Water use was relatively high, especially in the A. sparsifolia and the P euphratica stands and in a dense stand of T ramosissima (up to approx. 500 kgH(2)O m(-2) year(-1)). Using the total above-ground biomass in the calculation, WUEp was highest in C. caput-medusae and P euphratica, and lowest, in A. sparsifolia. From soil and plant water relations, and against the background of the climate and the productivity of the vegetation, it is concluded that all perennial plants in the transition zone between oases and desert in that region must have sufficient access to ground water to ensure long-term survival. Management of ground water such that it remains continuously accessible to the perennial plants is a prerequisite for the conservation and sustainable use of the vegetation in the transition zone. (c) 2005 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved

Ecological basis for a sustainable management of the indigenous vegetation in a Central-Asian desert: Presentation and first results

To provide an ecological basis for the regeneration and the sustainable use of the vegetation at the transition between eases and sandy desert, a joint European-Chinese research project is being conducted at the southern fringe of the Central-Asian Taklamakan desert (Xinjiang, China). The investigations are being carried out at five study sites located in the foreland of the river oasis of Qira (Cele). Four of these sites are dominated by one species each, which is indigenous on a local (Alhagi sparsifolia, Populus diversifolia, Tarmarix ramosissima) or regional scale (Calligonum spec.). The fifth site is free of vegetation. Subsequent to irrigation performed by artificial flooding, the effects of the consecutive desiccation and of harvest on the water relations of soil and plants (including water-use efficiency and drought tolerance), the demand and turnover of nutrients (especially of nitrogen) and productivity of the respective species are being investigated. The composition of the vegetation and the population biology of the local species are being studied. Concomitantly, socio-economic inquiries are being performed to register the population's demand for plant resources and to provide a basis for the calculation of the management costs. The results of the study should provide a basis for the regeneration of that kind of vegetation which is best suited to meet the population's demand for plant resources and shelter from sand drift. The selection of the vegetation will be made on the basis of its water-use efficiency, productivity and capability of regeneration. The first results and an outlook for the forthcoming research activities are presented