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摘要

引用本文:

DOI:

10.11834/jrs.20209107

收稿日期:

2019-04-09

修改日期:

2019-09-23

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中国东北植被生长幅度与长度对生产力长期趋势与变异影响分析
周玉科
中国科学院地理科学与资源研究所 生态系统网络观测与模拟重点实验室
摘要:

在全球升温背景下,北半球中高纬度植被生产力呈现增强趋势。学界普遍认为植被生长季延长是促进植被生长的重要因素,而夏季植被生长幅度(最大生长能力)对生产力的影响尚不明确。本文基于长时序遥感NDVI数据,探讨生长季长度和幅度对植被生长力的长期趋势与变异的控制作用及差异。首先基于1982-2015年的GIMMS NDVI3g数据,利用曲率求导法确定关键物候参数-生长季开始点、结束点和夏季峰值点,通过曲线下积分方法获得生长季生产力(VIsum),然后在像元和植被覆盖区尺度上探索生长季长度(Length of Growing Season, LOS)、生长幅度(Growing Magnitude, MAG)、VIsum的长期变化趋势与变异,利用相对重要性分析方法,确定LOS和MAG对VIsum的影响。结果表明:研究区总体的LOS呈现微弱缩短趋势,MAG轻微增强,生产力变化趋势不显著。VIsum与LOS的波动性一致,与MAG振幅呈反相位,三个变量的趋势和变异都存在一个10年的周期。在像素尺度的空间分布上,VIsum主要在北部针叶林区、西部草原和南部针叶林区呈增长趋势,LOS和MAG趋势的空间分布基本相反,LOS在中部和东部的农作物区和少部分西部草原呈现缩短趋势(约占植被区81.5%),MAG在农作物区、大兴安岭部分针叶林区、西部草原区为增强趋势(约占植被区16.5%)。表明植被生长周期压缩促进了夏季生长幅度的提升(LOS与MAG负相关)。在各植被覆盖类型中仍然是LOS对VIsum趋势和变异的贡献最大(约为75%)。LOS和MAG对VIsum趋势及变异贡献作用的空间分布完全相反:LOS在北部针叶林和东部阔叶林区占主要控制作用,MAG主要影响西部草原和中-南部农作物区(贡献率27%),但是相对作用仍小于LOS。基于森林站点通量数据的验证表明地面物候和生产力变化趋势与卫星NDVI的发现一致。虽然研究区植被生长季长度仍然是控制生产力长期趋势和变异的主要因素,但是植被生长幅度呈现不断增强的趋势,未来有可能发生控制力的转变。

Impacts of Growth Magnitude and Length on Long-term Trends and Interannual Variation of Vegetation Productivity over Northeastern China
Abstract:

With the global warming, land ecosystem productivity presents a substantial enhanced trend, which is primarily attributed to the prolonged growing season of terrestrial vegetation. However, the impact of summer greatest growing magnitude on vegetation productivity remains unclear. This study aims to explore the different impacts of growing season length (LOS) and magnitude (MAG) on the long-term trends and interannual variability of vegetation productivity, based on long time series of satellite images. Firstly, the GIMMS NDVI3g data was applied to derive the key phenology parameters, including start and end of growing season (SOS, EOS), summer growing peak. Summer vegetation productivity (Summary of Vegetation Index, VIsum) was obtained by integrating the area under growth curve. The long-term trends and interannual variability of SOS, EOS and VIsum was explored at pixel and land cover ecosystem level. Special attention was paid to the impacts of LOS and MAG on VIsum changes. The relative important method was used to quantify contribution of LOS and MAG to VIsum. The results indicate the overall vegetation productivity for Northeastern China do not behave a clear trend, but LOS has a decrease trend and MAG show an increase trend. VIsum presents a consistent fluctuation pattern with LOS, but changes asynchronously with MAG. There is a cycle of 10-years length for the trends and variability of LOS, MAG and VIsum. For the spatial distribution at pixel level, VIsum tends to increase in needle forest of northern and southern part, and the western grassland. The spatial distribution of LOS trend shows an opposite pattern with that of MAG. LOS is becoming shortened in the middle cropland and western grassland (81.5% of vegetated area). While MAG is enhanced in this ecosystem (16.5% of vegetated area). This reflects shortened LOS induces the increase of MAG. Across various land types, LOS contribute mostly to the long-term trends and interannual variability of VIsum (75%). LOS plays a key role in northern needle and eastern broad-leaved forest, MAG accounts for 27% of relative importance. The carbon flux data show a similar change pattern with satellite NDVI in the calculation of phenology parameters and vegetation productivity. Although LOS mainly control the trend and interannual variability, MAG may play a control role in the future as it keeps the increase trend.

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