Asymmetric Effects of Daytime and Nighttime Warming on Boreal Forest Spring Phenology

Abstract

Vegetation phenology is the most intuitive and sensitive biological indicator of environmental conditions, and the start of the season (SOS) can reflect the rapid response of terrestrial ecosystems to climate change. At present, the model based on mean temperature neglects the role of the daytime maximum temperature (TMAX) and the nighttime minimum temperature (TMIN) in providing temperature accumulation and cold conditions at leaf onset. This study analyzed the spatiotemporal variations of spring phenology for the boreal forest from 2001 to 2017 based on the moderate-resolution imaging spectro-radiometer (MODIS) enhanced vegetation index (EVI) data (MOD13A2) and investigated the asymmetric effects of daytime and nighttime warming on the boreal forest spring phenology during TMAX and TMIN preseason by partial correlation analysis. The results showed that the spring phenology was delayed with increasing latitude of the boreal forest. Approximately 91.37% of the region showed an advancing trend during the study period, with an average advancement rate of 3.38 ± 0.08 days/decade, and the change rates of different land cover types differed, especially in open shrubland. The length of the TMIN preseason was longer than that of the TMAX preseason and diurnal temperatures showed an asymmetrical increase during different preseasons. The daytime and nighttime warming effects on the boreal forest are asymmetrical. The TMAX has a greater impact on the vegetation spring phenology than TMIN as a whole and the effect also has seasonal differences; the TMAX mainly affects the SOS in spring, while TMIN has a greater impact in winter. The asymmetric effects of daytime and nighttime warming on the SOS in the boreal forest were highlighted in this study, and the results suggest that diurnal temperatures should be added to the forest terrestrial ecosystem model.

Vegetation Phenology in Permafrost Regions of Northeastern China Based on MODIS and Solar-induced Chlorophyll Fluorescence

“…It is usually achieved using vegetation indices (VIs), which are a combination of the reflectance of different spectral bands, aimed at enhancing the sensitivity to green vegetation (Huete et al, 2002). Normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI) are the primary indicators used to estimate the start and end of the growing season (SOS, EOS) at regional and global scales (Myneni et al, 1997;Delbart et al, 2006;Shen et al, 2014;Deng et al, 2019). However, various factors can reduce the accuracy of NDVI or EVI estimation of vegetation phenology, such as the interference of ground shadows, snow and other backgrounds, poor atmospheric conditions, and application in different vegetation types.…”

Remote Sensing of Local Warming Trend in Alberta, Canada during 2001–2020, and Its Relationship with Large-Scale Atmospheric Circulations

“…In addition, global warming is likely responsible for observing the warming trends in the Boreal Forest region in this study. It is impacting the ecosystem variables, such as the early onset of spring due to warming [58,59] leading to the onset of early runoff in March and April [60,61] that changes vegetation phenology of the region by wetting the soils early [62]. Wet soils retain more heat than dry soil, and the mechanism of heating land surface requires some additional time (time lag) [63,64].…”

Response of velocity of vegetation greenup to frost in the Greater Khingan Mountains

“…受寒冷条件的刺激， 即冷激温 [32] 。休眠期所需的低 温是缩短植被变绿时间的必要条件 [33] 。气候变暖 导致冬季气温上升， 植被休眠期间寒冷条件的刺激 不足， 这可能也是导致植被变绿速率呈现负向趋势 的原因之一。 本文研究结果也表明， 大兴安岭地区内的霜冻 整体上加速了森林生态系统的植被变绿， 减缓了草 原生态系统的植被变绿速率。植被在春季变绿需 要一定的温度积累 [34][35] ， 季前期内(通常定义为从春 季开始到 SOS)霜冻天数和强度同时降低导致触发 森林生态系统变绿所需的温度更快累积， 进而加速 了森林生态系统植被变绿。而草原生态系统变绿 所需的温度积累较少， 更容易获得。此外， 草本植 物缺乏抵御霜冻的结构完整性 [36] ， 虽然在春季开始 至 SOP 时段内霜冻天数下降， 但生长季开始之后…”