Spatiotemporal Change of Oases and Their Landscape Response in Arid Areas in Northwest China

In this paper,a case study on the spatiotemporal change of the oases and their landscape response in the Beidahe River Basin,a tributary of the Heihe River in an arid area in northwest China,was carried out on the basis of interpretation and analysis of multi-source remote sensing images in 1973,1980,1990,1999 and 2009, landscape indices by Frgastats( version 3. 3) and related statistical methods. The research results were as follows: ① Both expansion and shrinkage of the oases in the Beidahe River Basin occurred periodically in recent 40 years, but oasis expansion was dominant. The oasis area was enlarged from 1 705. 55 km2in 1973 to 1 990. 60 km2in 2009,and the enlargement rate was 16. 71%; ② The oases were changed with an imbalance way at both spatial and temporal scales in the study period. The rapidly-changed area was located mainly in the Jinta Oasis in the lower reaches. Oasis expansion was dominated by the oasis-internal fillingand marginal invasion,and the oasis shrinkage occurred mainly in the fragile oasis-desert ecotone. The oases were gradually shrunk during the period of 1973- 1990 and expanded during the period of 1990- 2009,and their dynamic degrees were reached to the maximum values in recent 10 years; ③ Enlargement of the oases increased the instable development of oasis landscape, which was characterized by the instable change of oasis PD,NP and LPI in the lower reaches and the marginal zone of the oases in the Beidahe River Basin. The increase of oasis fragmentation and ecological fragility was disadvantageous for maintaining the ecosystem stability and sustainable development in arid area,which needs to be paid more attention in the future.