植被物候是反映全球气候变化的重要生态指标,春季返青期物候已经得到广泛研究,但秋季物候及其与春季物候的不对称性仍然不明朗。基于GIMMS NDVI 3 g遥感数据提取中国东北地区植被关键物候参数,利用春季和秋季中返青(衰落)速率、生长期长度、植被活动能力(以NDVI均值表示)3个物候指标的差异来刻画春秋物候的不对称性,定义为物候不对称指数AsyR、AsyL和AsyV(Asymmetry of growing Rate,Length,Vegetation index)。首先利用双逻辑斯蒂曲线拟合和曲率求导方法获取各植被像元的物候期和生长速率参数,其次在像素尺度上探索了3种春秋物候不对称性的时空分布特征。结果表明:3种不对称指数的年际变异显著,研究区整体上3种不对称指数均呈现大约10 a的周期性,AysV和AsyL同相位并与AsyR呈相反相位。3种指数可以从不同角度刻画植被春秋季生长形态不对称性,在时空表现上存在一定的不确定性。AsyR和AsyV在不同植被类型中的空间格局比较相似,并能一定程度上区分农作物和自然植被,AsyL的空间分布规律较差、区分度不高。不对称指数发现,针叶林和阔叶林区域主要为衰落期的植被活动占主要优势,形态上是春季快速成长、秋季缓慢衰落;农作物区表现为缓慢成长和快速衰落;草原区域不对称性不显著。生长形态不对称性可以反映春秋两季的植被活动对整个生长季植被生产力的控制作用,有助于更加细致地探索物候对植被生态系统固碳的影响。在实际应用方面,也可以根据不同植被的物候不对称特征进行植被分类,服务于农业普查和植被生态系统管理。
英文摘要:
Vegetation phenology is an important ecological indicator for global climate change.Plant greenup phenology in the spring time has been well studied,whereas autumn phenology and its asymmetry with spring phenology still remain unclear.Here,the GIMMS NDVI3 g dataset for Northeast China was applied to extract the key phenological parameters during plant growth process,then three phenological asymmetry indices were defined according to the difference between greenup rate and senescence rate(AsyR),growth length in spring and autumn(AsyL),mean vegetation greenness index in spring and autumn(AsyV).First, plant growing curve was fitted with double logistic function and the phenological parameters was calculated. Second,the spatiotemporal pattern of asymmetry indices was explored.The results indicate that the three phenological asymmetry indices show a significant interannual variability and a time cycle of around ten years.The direction of amplitude for AsyV and AsyL was opposite with that of AsyR.Three indices could depict the phenological asymmetries from various perspectives and have a degree of uncertainty.The landscape pattern for AsyV and Asy R is similar.AsyV and AsyR show a capability of distinguishing cropland and natural vegetation cover.AsyL reflects a complex spatial distribution.Phenological asymmetries reveal that coniferous forest and broad-leaved forest present a dominant control of senescence vegetation activities. These natural vegetation commonly show a growth feature of rapid growth in spring and slow decrease in autumn.Cropland exhibits a slowly growing rate in spring and a rapid decrease in autumn.Phenological asymmetry is not significant in grassland area.Phenological asymmetry could enhance our knowledge on ecosystem carbon sink.In a practical way,phenological asymmetry could serve as a useful tools in vegetation type classification,agricultural investigation and plant ecosystem management.