Evaluating Landscape Stability Considering Fire Disturbance In Zhalong Wetland

Fire is a disturbance factor that have huge influence on wetland ecosystem.The vegetation community and landscape pattern of wetland ecosystem will change greatly after fire,once the wetland ecosystem is disturbed by fire and cannot be eliminated by regulatory function,The ecological equilibrium that disrupted will lead to landscape succession.Therefore,analyzing change of wetland landscape stability and pattern after fire can play a positive role in wetland landscape optimization and management.Based on remote sensing data and historical fire data,the paper selects five contemporaneous remote sensing images,MODIS 17A2 product data and meteorological data during 2004 to 2008 from Zhalong Wetland in Heilongjiang,extracts the burned zone in 2005,with the support of Landscape Ecology and GIS theory,the evaluation indicators of the landscape stability were selected:wetland patch area,shape index,wetland rate,farmland rate,road and ditch factor,residential factor to construct the landscape stability model.The landscape indices such as patch number,average patch size,Shannon diversity index and Shannon evenness index were selected to analyze the dynamic changes of landscape pattern,combined with the analyze of the change of landscape stability by GPP,The conclusions are as follows:(1)Considering the disturbance of nature and man-made,the wetland landscape accounted for 60%?70%and the xerophytic landscape accounted for 30%to 40%of the wetland from 2004 to 2008.The number of xerophytic landscape expressed a slow rising trend while the wetland landscape is opposite.The trend that study area is becoming arid is gradually revealed.In terms of spatial distribution,the landscape pattern that wetland landscape occupied the middle part and xerophytic landscape mostly located at the periphery of the study area did not change obviously.Fires caused the disappearance of a large number of wetland patches,which eventually leading to the homogenization of wetland.(2)The fire severity can be divided into four levels:unburned level,low-burning level,moderate-burning level and high-burning level.The high-burning zone is about81km~2,which is the least of all the burning zone.90%of it is concentrated in the core area of Zhalong Wetland,The moderate-burning zone is about 220.6km~2,which is the largest of all the burning zone of Zhalong Wetland.According to the severity of fire,the burned zone mostly show a buffer-like centralized distribution from the inside to the outside,low burning zone that distributed scattered located in the buffer and experimental area.Fire events is not only caused by a single point of fire,but also by multiple points of fire,thus forming large burning zone and different fire severity levels.(3)The change of wetland landscape stability is mainly due to the fire in 2005.In terms of spatial distribution,the stability of wetland landscape in the southeast(the main burned zone)declined sharply in 2005,the wetland landscape stability was always the core buffer experimental area during the study period.In terms of quantitative change:the weak stability landscape(stability value between 0.5-1)dominated except2005,the stable landscape(stability value between 1-2)played a leading role in other years,In 2008,10%decrease in the proportion of strong landscape(stability values greater than 2).and the whole stability of study area showed a downward trend,and it did not recover to the state before fire.In terms of burning level,the stability of high-burning zone and unburned zone did not increase with time due to the high degree of combustion and intense human disturbance.(4)The fire is the main reason for the change of the Zhalong wetland landscape.The GPP output value of wetland vegetation decreased greatly in 2005 then increased slowly.From the quantitative characteristics:2004 was the year with highest GPP output,the GPP output value increased gradually after fire.The growth rate of burning zone was about 1.3 times of the overall GPP output,the total output growth rate is about 45gC/m2 per year.In terms of spatial distribution:the middle part of the study area with higher GPP values appeared to shrink obviously after fire,then the wetland entered the recovery stage.The earliest areas that showing recovery are Wuyuer River and core area of the research area which is rich in vegetation and water resources.However,The wetland vegetation resources were severely damaged,and did not return to the state of spatial distribution that concentrated of regions with high GPP value before the fire until 2008.