中国第二、三级阶梯地形过渡带山前植被物候时空变化探析

Spatiotemporal changes of piedmont phenology in the transitional zone between the second and third steps,China

基于1982—2015年GIMMS NDVI 3g V1.0数据、3小时温度、逐日降水和日太阳辐射数据集、数字高程模型、中国植被区划数据及实测物候验证数据,利用季节性植被物候提取法、Theil-Sen median趋势分析法和偏最小二乘回归分析等方法,研究中国第二、三级阶梯地形过渡带植被物候的时空变化规律,探讨植被物候对海拔、经纬度和气候变化的响应。结果表明:(1)34 a间过渡带山前植被物候时空变化显著。时间上,植被物候呈返青期(Start Of Season,SOS)提前(-0.3187 d/a,p<0.01)、枯黄期(End Of Season,EOS)推迟(0.1171 d/a,p>0.1)和生长季长度(Length Of Growing Season,LOS)延长(0.4358 d/a,p<0.01)趋势;空间上,按SOS像元的86.24%提前、EOS像元的69.66%推迟和LOS像元的84.42%延长分布。(2)34 a间过渡带山前植被物候地带性特征明显。垂直地带性方面,在中低纬度地区的物候始末期受以400 m等高线为界的海拔梯度影响,由平原到山地产生SOS平均提前8d,EOS提前25~36 d的分段式变化;水平地带性方面,低纬度和中高纬度地区的植被物候以35°N(秦岭-淮河一线,中国南北方的分界线)、43.5°N(暖温带落叶阔叶林区与温带草原区的分界)为转折点,由南向北SOS以-0.78 d/°、4.89 d/°和-1.56 d/°分段变化,EOS以-3.96 d/°、-1.85 d/°和0.89 d/°分段变化。(3)34 a间过渡带植被物候受气象因素驱动。对于植被返青期,气温对中纬度地区SOS的影响最大,降水的贡献随着纬度的降低而增大,太阳辐射在中纬度地区的贡献力大于低纬度地区;对于植被枯黄期,中纬度地区对EOS的多因素贡献力为太阳辐射>气温>降水(太阳辐射对草原区无贡献力),低纬度地区贡献力排序与之相反;本研究对宏观地理带中不同植被区划的物候变化认知有学术意义,也为地理因素与气候因素共同影响的植被物候变化提供了新的认识。

Based on GIMMS NDVI 3g V1.0 data from 1982 to 2015,meteorological datasets,digital elevation model,China’s vegetation zoning data and measured phenology verification data,we used seasonal vegetation phenology extraction,Theil-Sen median trend analysis and Partial Least Squares(PLS)to investigate the spatiotemporal changes of vegetation phenology in China’s transitional zone between the second and third steps and to explore the response of vegetation phenology to elevation,latitude and climate change.The results shown that:(1)The spatiotemporal changes of vegetation phenology in the study area was significant during the 34 years.Temporally,vegetation phenology showed trends that the start of season(SOS)was significantly advanced,the end of season(EOS)was not significantly delayed and the length of growing season(LOS)was significantly prolonged;spatially,it was distributed by 86.24%advance for SOS pixels,69.66%deferral for EOS pixels and 84.42%extension for LOS pixels.(2)The phenological zonality of the premontane vegetation in the transitional zone was obvious during the study period.In aspect of vertical zonality,vegetation phenology in the midlow latitudes was influenced by the elevation gradient bounded by the 400-m contour,producing a segmented change from plains to mountains;in aspect of horizontal zonality,the vegetation phenology in low and mid-high latitudes was divided by 35°N and 43.5°N as the turning point.(3)The vegetation phenology in the transitional zone was driven by meteorological factors during the 34 years.About SOS,the temperature had the greatest impact on SOS in the middle latitude,the contribution of precipitation increased with the decrease of latitude,and the contribution of solar radiation in the middle latitude was greater than that in the low latitude;about EOS,the contribution ranking of meteorological factors to EOS in middle latitudes was solar radiation>temperature>precipitation(solar radiation made no contribution to the grassland),and the contribution order of meteorological factors in low latitudes was opposite to it.This study has academic significance for the phenological changes of different vegetation divisions in the macro-geographical zones,and also provides new understandings of the joint influence of geographical factors and climatic factors on the phenological changes.