Quantitative monitoring of vegetation cover change by using remotely sensed data over Minqin Oasis,Gansu
Received date: 2005-08-21
Revised date: 2006-03-20
Online published: 2006-08-15
The spatial and temporal changes of vegetation cover from 1987 to 2001 over Minqin Oasis,Gansu Province,were studied quantitatively based on the retrieval of vegetation coverage from remotely sensed TM images in the situation of mixed pixels. The result of the study shows that the vegetation cover over Minqin Oasis has greatly changed since 1987,with the increase of the area of the cultivated vegetation（farmlands） by 53.11% and decrease of the area of the medium and high cover vegetation by 25.11%,which indicates that the bush belt around the Oasis is fading away with the constant increase of cultivated vegetation and constant decrease of medium and high cover vegetation,and the long-term ecological security of the Oasis is being threatened severely.The spatial transform processes of vegetation cover in Minqin Oasis are complicated.The spatial transform process for whole Oasis is categorized in a type of reclamation and vegetation degradation,and there are differences for spatial transform processes of vegetation cover among diverse sub-areas of the Oasis,categorized in one type of reclamation and vegetation degradation in the central and southern parts,and another type of vegetation rehabilitation and reclamation in the northern part.The main reasons for the loss of medium and high cover vegetation are reclamation of desertified lands and vegetation degradation.About 42204.81hm2of medium and high cover vegetation lost during the 15 years due to over-reclamation and vegetation degradation in Minqin Oasis,accounting for 81.73% of the original area.The lost vegetation covers are mainly wind protecting and sand binding plants on the edges of the Oasis.The lost vegetation area is larger than the rehabilitated area of vegetation of the corresponding period of time.The lost area of medium and high cover vegetation by reclamation reaches 18776.08hm2,accounting for 44.5% of the total lost area.The decline of groundwater table resulted in by over pumping of groundwater for irrigation is the main cause for vegetation degradation,and the observable rehabilitation of halophytic vegetation in the northern part of the Oasis was probably related to the drastic drop of groundwater table.Controlling reclamation and breeding the steady-going bush vegetation should be the key target for eco-environmental construction in Minqin Oasis.
GAO Zhi-hai,NI Shao-xiang,LI Zeng-yuan,WEI Huai-dong,DING Feng . Quantitative monitoring of vegetation cover change by using remotely sensed data over Minqin Oasis,Gansu[J]. GEOGRAPHICAL RESEARCH, 2006 , 25(4) : 587 -595 . DOI: 10.11821/yj2006040004
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