基于通量塔观测资料的北美温带植被物候阈值提取方法

Extraction of temperate vegetation phenology thresholds in North America based on flux tower observation data

通量塔方法可以有效监测植被的季节和物候变化过程·目前,不同物候提取方法间的检验和定量化评估工作还有待加深·本文选取9个北美森林通量塔站的总初级生产力(GPP)和净生态系统生产力(NEP)数据,利用阈值法提取了生长季开始日期(SOS)和结束日期(EOS),关联生态系统的碳源汇功能,分析了不同阈值标准对物候提取结果的影响·结果显示:不同阈值标准对落叶阔叶林(DBF)物候提取结果稳定性的影响较常绿针叶林(ENF)小;GPP绝对阈值和相对阈值提取结果间,DBF站点阈值为GPP=2gC·m-2·d-1的物候提取结果与20%最大GPP值(GPPmax)最接近,阈值为GPP=4gC·m-2·d-1物候提取结果介于20%GPPmax和50%GPPmax之间,生态系统碳汇功能开始日期介于GPP=4gC·m-2·d-1和20%GPPmax提取的SOS之间;ENF站点与阈值为GPP=2gC·m-2·d-1和GPP=4gC·m-2·d-1物候提取结果最接近的分别是20%GPPmax和50%GPPmax,生态系统碳汇功能开始日期介于GPP=2gC·m-2·d-1和10%GPPmax提取的SOS之间·

Flux tower method can effectively monitor the vegetation seasonal and phenological variation processes.At present,the differences in the detection and quantitative evaluation of various phenology extraction methods were not well validated and quantified.Based on the gross primary productivity（GPP） and net ecosystem productivity（NEP） data of temperate forests from 9 forest FLUXNET sites in North America,and by using the start dates（SOS） and end dates（EOS） of the temperate forest growth seasons extracted by different phenology threshold extraction methods,in combining with the forest ecosystem carbon source/sink functions,this paper analyzed the effects of different threshold standards on the extraction results of the vegetations phenology.The results showed that the effects of different threshold standards on the stability of the extracted results of deciduous broadleaved forest（DBF） phenology were smaller than those on the stability of the extracted results of evergreen needleleaved forest（ENF） phenology.Among the extracted absolute and relative thresholds of the forests GPP,the extracted threshold of the DBF daily GPP=2 g C·m-2·d-1 had the best agreement with the DBF daily GPP=20% maximum GPP（GPPmax）,the phenological metrics with a threshold of daily GPP=4 g C·m-2·d-1 was close to that between daily GPP=20%GPPmax and daily GPP=50% GPPmax,and the start date of ecosystem carbon sink function was close to the SOS metrics between daily GPP=4 g C·m-2·d-1 and daily GPP=20% GPPmax.For ENF,the phenological metrics with a threshold of daily GPP=2 g C·m-2·d-1 and daily GPP=4 g C·m-2·d-1 had the best agreement with the daily GPP=20% GPPmax and daily GPP=50% GPPmax,respectively,and the start date of the ecosystem carbon sink function was close to the SOS metrics between daily GPP=2 g C·m-2·d-1 and daily GPP=10% GPPmax.