植物生长季的变化反映了全球气候变化对生态环境的影响。本研究以2000-2006年间MODIS-NDVI影像数据集,使用TIMESAT软件从归一化植被指数(NDVI)时间序列中,分别提取福建省不同森林植被的生长季开始日期(Start of Season,SOS)、生长季结束日期(End of Season,EOS)和生长季长度(Length of season,LOS)等物候参数,并与全省尺度的气温与降水量进行相关分析。结果表明:不同森林类型NDVI与当月月均气温之间具有较显著的相关性(R~2为0.72-0.79,p<0.01),同期温度变化对植被生长的影响相对于降水量更重要;而植被生长对降水量的响应存在大约2个月的时滞效应(R~2为0.54-0.75,p<0.01),说明前期的降水累积对于后续植被生长有较显著影响。福建省森林植被生长季持续时间约213~223 d,开始于每年4月初到4月中旬(第98~103 d),结束于11月中旬前后(第316~321 d)。其中,南亚热带森林生长季长于中亚热带森林,相同气候条件下的阔叶林生长季时间略长于针叶林。另外,春季(2-4月)气温变化是导致福建省内2个气候带森林生长季开始时间、生长季结束时间及生长季长度变化的关键因素,而伴随春季温度升高,植被生长季开始时间提前(R~2为0.83,p<0.01),同时生长季长度延长(R~2为0.80,p<0.01)。7 a间,生长季持续时间呈现微弱延长趋势,总体延长幅度为2.4~3.1 d。
英文摘要:
Vegetation phenology reflects the response of a terrestrial ecosystem to climate change. It is critical to quantitatively explore the relationships between vegetation dynamics and temperature as well as precipitation. We examined the vegetation-climate relationship using the monthly maximum values of normalized difference vegetation index (NDVI) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) between 2000 and 2006 in the subtropical region of Fujian. The dataset was also used to calculate phenoloical metrics including the start of season (SOS), the end of season (EOS) and the length of season (LOS) for each year using TIMESAT. The results indicates that the NDVI of each forest types were significantly positive correlated to the monthly mean temperature under no time-lag condition (R~2=0.72-0.79, p<0.01). This suggests that the current temperature condition dominated over rainfall amount in affecting vegetation growth. There were significant log-linear relationships between NDVI and rainfall with a 2-month time-lag for each forest types (R~2=0.54-0.75, p<0.01), implying that the vegetation growth does not respond immediately to rainfall but to the precedent cumulative rainfall. The phenoloical analysis showed that the SOS began from early to mid April (calendar day 98~103), the EOS appeared in mid-November (calendar day 316~321) and the LOS lasted 213~223 days. The LOS of southern subtropical forests was longer compared to the central subtropical forests; and the LOS of hardwood forests was longer than the conifer forests under similar climate regime. It is possible that the stability of hardwood forests was generally higher and the fluctuations of environmental factors did not limit the growth of hardwood forests compared to the conifer forests. The inter-annual varieties of SOS and LOS were significantly related to spring temperature (February-April), in which the higher spring temperature was related to the earlier SOS (R~2=0.83, p<0.01) and consequently the longer LOS (R~2=0.80, p<0.01). The trend analysis of LOS for four forest types revealed a significant weak increase between 2.4 days to 3.1 days during the study period.