基于MODIS数据的神农架大九湖泥炭藓沼泽植被指数变化研究

Vegetation index change of Sphagnum palustre bog in Dajiu Lake of Mt. Shennongjia based on MODIS data

泥炭藓是陆地生态系统中最重要的固碳植物之一,固碳量约占全球土壤碳的15%。近几十年来,由全球气候变暖导致的泥炭藓沼泽水热状况变化对泥炭藓的固碳量和速率产生影响。选取我国最重要的亚高山泥炭沼泽--神农架大九湖泥炭藓沼泽为试验区,以分析中纬度地区泥炭藓沼泽植被生长状况受气候变化的影响。研究以2000-2017年MODIS植被指数NDVI和EVI为数据源,通过对比Logistic模型订正后的NDVI和EVI时间序列在泥炭藓沼泽植被生长状况监测中的优劣,选出最佳指标以获得18年来泥炭藓沼泽植被生长状况的变化趋势。研究结果表明:1)Logistic模型能够很好的消除泥炭藓沼泽植被指数时间序列的噪声;2)在季节和年际两个时间尺度上,EVI对泥炭藓沼泽植被生长状况的监测效果均优于NDVI。在季节周期上,虽然EVI和NDVI均得到泥炭藓沼泽植被生长周期规律,但EVI更灵敏。在年际分析中,EVI有更大的值域响应空间,以准确反映泥炭藓沼泽植被的年际变化规律;3)由EVI获得18年来泥炭藓沼泽植被变化趋势指出,泥炭藓沼泽植被呈显著微弱增长,年均EVI增长率为3.8‰(R^2=0.45,P<0.01)。相比于EVI年均值,EVI年内最大值(R^2=0.47,P<0.01)更敏锐的反映泥炭藓沼泽植被生长状况的动态变化。

Sphagnum is one of the most important carbon sequestration plants in terrestrial ecosystem,which accounts for approximately 15%of global soil carbon.In recent decades,the changes in the hydrothermal status of Sphagnum bogs caused by global warming have directly affected the amount and rate of carbon fixed by Sphagnum.In this study,the most important subalpine peat bogs of China,the Mt.Shennongjia Dajiu Lake Sphagnum palustre bog,was selected as the experimental area to analyze the effect of climate change on the vegetation growth of Sphagnum bogs in the mid-latitude area.The Moderate Resolution Imaging Spectroradiometer(MODIS)vegetation indices NDVI(Normalized Difference Vegetation Index)and EVI(Enhanced Vegetation Index)were used as data sources from 2000-2017 to compare the advantages and disadvantages of NDVI and EVI time series,revised by the logistic model in monitoring the vegetation growth status of Sphagnum bogs.The best index was selected to obtain the change trend of Sphagnum bogs vegetation growth in the past 18 years.The results showed that:(1)the logistic model can effectively eliminate the noise on the time series of Sphagnum palustre bog vegetation index.(2)in the seasonal and annual time scales,the EVI monitors the vegetation growth of Sphagnum palustre bog better than NDVI.In the seasonal scale,although both EVI and NDVI reflected the regularity of the growth cycle of Sphagnum palustre bog vegetation,EVI was more sensitive to the time period of the change.In the annual analysis,EVI had a greater range of response space to accurately reflect the annual variation of Sphagnum palustre bog vegetation.(3)the change in the trend of Sphagnum palustre bog vegetation in the past 18 years was obtained by EVI,it was found that the annual average growth rate of Sphagnum palustre bog vegetation showed a remarkably steady growth,with an average annual EVI growth rate of 3.8‰(R^2=0.45,P<0.01).Compared with the annual average of EVI,the annual maximum(R^2=0.47,P<0.01)reflects the dynamic changes of Sphagnum palustre bog vegetation growth more sensitively.