1990—2020年地表物候时空变化对高寒湿地景观演变过程的响应

Response of spatio-temporal variation of land surface phenology to alpine wetland landscape evolution from 1990 to 2020

地表物候是生态系统环境变化的敏感指示器。为探讨物候时空变化和湿地景观生态格局与过程之间的关系,论文以若尔盖高寒湿地为例,基于1990—2020年GIMMS3g NDVI和MODIS NDVI数据集、7期Landsat TM/OLI卫星遥感数据,采用阈值法提取地表物候参数,基于面向对象的分类方法解译出土地利用数据,利用土地覆盖转换指数模型(PNTI)刻画高寒湿地动态变化过程,分析地表物候时空变化与高寒湿地景观格局演变过程的关系。结果表明:(1)1990—2020年研究区呈现前期湿地面积减少后期趋于稳定的特征,根据土地利用类型演变路径和强度分为动态平衡区、退化演变区和恢复演变区,面积占比分别56.84%、 28.14%和15.02%。(2)植被返青期(SOS)、生长盛期(POS)呈南早北晚,枯黄期(EOS)呈中间早周边晚,生长期长度(LOS)呈中间短周边长、西北短东南长的空间分布特征。SOS分布在第96—149天,EOS分布在第249—284天,LOS持续125—173d, POS分布在第179—209天。SOS、POS先推迟后提前、EOS先提前后推迟,LOS呈现先缩短后延长的规律,1990—2005年变化率为-10.8d/10a,而2000—2020年为2.4d/10a。(3) SOS、EOS对高寒湿地恢复/退化演变路径响应敏感,对演变路径方向相同但演变强度等级不同的湿地景观格局演变过程响应则不敏感。SOS、EOS在退化演变区的变化率整体上高于SOS、EOS在恢复演变区及动态平衡区的变化率。SOS提前和EOS推迟可作为高寒湿地退化的指示指标,具有生态预警作用。

Land surface phenology(LSP)is a sensitive indicator of environmental change in ecosystems.The LSP in alpine wetlands can reflect the changing patterns of naturally seasonal phenomena in alpine wetland ecosystems and their response and adaptation to environmental changes,which has become one of the research hotspots in the field of global change.To explore the relationship between spatio-temporal changes of phenology and ecological patterns and processes of wetland landscapes in Zoige alpine wetlands,based on the GIMMS3g NDVI and MODIS NDVI datasets and 7-phase Landsat TM/OLI satellite remote sensing data from 1990 to 2020,the surface phenological parameters were extracted by using the threshold method and the land use data were interpreted by using object-oriented classification method.The Positive and Negative Transformation Index(PNTI)model was used to portray the dynamic change process of alpine wetlands.The results showed that(1)the wetland area in the study area from 1990 to 2020 presented the characteristics of first decreasing and then stabilizing.According to the evolution path and intensity of land use types,it was divided into dynamic equilibrium area,degradation evolution area,and restoration evolution area,accounting for 56.84%,28.14%,and 15.02%,respectively.(2)From the spatial distribution characteristics,the start of the growing season(SOS)and the peak of the growing season(POS)were gradually delayed from south to north,while the end of the growing season(EOS)was gradually delayed from the middle to the periphery.The length of the growing season(LOS)was short in the middle and long in the periphery,short in the northwest and long in the southeast.The SOS ranged mainly from 96 to 149 Julian days,EOS ranged mainly from 249 to 284 Julian days,POS ranged mainly from 179 to 209 Julian days,and LOS was concentrated within 125 to 173 days.In terms of interannual variation,the SOS and POS delayed first and then advanced,while EOS advanced first and then delayed.The LOS shortened first and then extended,with a shortening rate of 10.8 d/10a from 1990 to 2005 and an extension rate of 2.4 d/10a from 2000 to 2020.(3)The SOS and EOS were sensitive to the response of evolutionary processes of landscape patterns in alpine wetlands with different directions of evolutionary paths(i.e.,restoration and degradation),while they were not sensitive to the response of evolutionary paths with the same direction but different intensity levels.The change rates of the SOS and EOS in the degradation evolution area were overall higher than those of SOS and EOS in the restoration evolution area and dynamic equilibrium area.The advance of SOS and delay of EOS can be used as indicators of alpine wetland degradation and has an ecological early warning function.Alpine wetland landscape evolution had no significant effect on LOS and POS at P=0.05 level.