Reed Coverage Change In Zhalong Nature Reserve And Its Response To Climate Factor

Zhalong Nature Reserve is the largest national nature reserve of the rare birds and wetland ecosystem. It is also the largest reed wetland in the world. The reserve is an important habitat for red crowned cranes and other waterfowl birds with thick reed. But in recent years due to the increase of climate change and human activities, Zhalong Nature Reserve Area of reed growth has been seriously affected, resulting in a marked decrease in the number of wetland area and crane.Therefore, it has a great significance for red crowned cranes and other rare bird protection and wetland ecological system of sustainable and healthy development to strengthen the study of wetlandreed.In this paper, NDVI threshold value method was used to the vegetation coverage on the basis of remote sensing and geographic information system technology, with vegetation index NDVI as a starting point, based on the ETM+ remote sensing images from 2000 to 2015 and meteorological data from 2000 to 2014 of Zhalong Nature Reserve. The vegetation coverage were classified("good", "relatively good","commonly", "relatively bad", "bad" and non-green vegetation) and analyzed the changing process of reed coverage of different levels in Zhalong Nature Reserve from 2000 to 2015. Depending on this, made the temporal correlation analysis between different grade coverage of reed and average annual precipitation, annual average temperature, annual average relative humidity and warmest average temperature, so as to discuss the variation characteristics of reed coverage in Zhalong Nature Reserve and its response to climate change.The main results are as follows:(1) The growth of reed in Zhalong wetland was different during 2000 and 2015. The proportion of different levels of coverage was not the same. Overall, the best growth of reed in is 2010. The area of above "relatively good" level was 86.82%. The degradation stage of reed in Zhalong Nature Reserve is between 2000 and 2008. The area of above "relatively good" level were 76.94%,74.42%,69.81%.69.51%,67.36%,50.44%,31.59%,respectively; The improvement stage of reed in Zhalong Nature Reserve is between 2011 and 2015. The area of above "relatively good" level were 60.6%,63.85%,75.06%,68.13%,82.04%, respectively. (2) Most of the reed were in the "good" and " relatively good " stage through the analysis of the area transfer matrix between different grades of 2013～2014,2014～2015 in the past 3 years. In addition, the transfer between the two levels of the reed was the biggest and most significant. From 2013 to 2014, the positive change of vegetation area is 288.11 km2,accounting for 22.61% of the total area; the negative change of vegetation area is 454.23 km2, accounting for 35.65% of the total area. From 2014 to 2015, the positive change of vegetation area is 504.11 km2, accounting for 39.56% of the total area; the negative change of vegetation area is 223.23 km2, accounting for 17.52% of the total area. (3) The average annual precipitation and warmest average temperature showed a trend of increase volatility from 2000 to 2014. The average annual temperature and annual average relative humidity increased steadily. Among them, the average annual temperature and annual relative humidity were correlated with the different grades of reed coverage(P<0.05). The increase of annual average temperature would cause the decline of reed coverage, while the average annual relative humidity was conducive to the increase of reed coverage. In addition, the correlation between average annual precipitation and warmest average temperature and the coverage of reed in Zhalong were not through the significant test (P<0.05). It showed that these climatic conditions had a certain effect on the change of the cover of the reed, but it was not the main factor in Zhalong Nature Reserve.