Based on the Landsat MSS/TM/OLI remote
sensing images in 1976, 1989, 1998, 2006 and 2016, the information of oasis
distribution in the Manas River Basin in recent 40 years was extracted, and the
methods of mathematical statistics model and landscape index were used to
analyze the spatiotemporal evolution of the oasis and the change of landscape
patterns in the study area. The results showed that, in recent 40 years, the
oasis in the middle and lower reaches of the Manas River Basin was in a trend
of reduction-expansion-sharp expansion, except the oasis was retreated from
1976 to 1989, the oasis was expanded after 1989, especially during the period
from 2006 to 2016, area of the oasis was expanded by 3 266 km2, and
the net change rate was as high as 4.43%. The change trend of the oasis was
imbalanced and even extremely imbalanced. From 1989 to 2006, the contribution
of grassland to the oasis reduction was the highest. After 2006, the reduction
of waters was the main contributor to the oasis retreat. After 1989, the
contribution of cultivated land to the oasis expansion was the most
significant. The main part of the oasis was holistically shifted northwestward,
and it was shifted northeastward, southwestward, northwestward and
southwestward during different periods. The geometric shapes of the landscapes
in the oasis were trended to simplification, and the fragmentation of the
landscapes in the oasis became more serious, which was related to the
increasing fragmentation of the grassland landscape. The oasis was trended to
centralization, which was closely related to the continuous centralization of
cultivated land.
