Phenological Changes in Alpine Grasslands and Their Influencing Factors in Seasonally Frozen Ground Regions Across the Three Parallel Rivers Region, Qinghai-Tibet Plateau

Chun-Ya Wang,Yan-Qiang Wei,Xu-Feng Wang,Priyamvada Bagaria,Xia Cui,Jin-Niu Wang,Dong-Liang Luo,Ning Wu

doi:10.3389/feart.2021.797928

Abstract

Alpine ecosystems are sensitive and vulnerable to climate change. In this study, we extracted three phonological parameters, viz. the start of the growing season (SOS), the end of the growing season (EOS), and the length of the growing season (LOS) from the moderate resolution imaging spectroradiometer (MODIS) normalized difference vegetation index (NDVI) dataset during 2000–2019 for alpine grasslands across the three parallel rivers region (TPRR), and also examined the spatiotemporal heterogeneity of the three phenological parameters in seasonally frozen ground regions (hereafter referred to as SFGR) in response to climate change. The results showed that the multiyear mean SOS gradually delayed from 100 to 160 days along higher elevation, EOS advanced as a whole (from 320 to 280 days), and LOS shortened (from 210 to 130 days). The multiyear mean spatial distribution of all the three parameters showed significant north-to-south differences in the TPRR. In general, the variation trends in all the phenological parameters were not significant (p &gt; 0.05) in the past 20 years, where SOS was advanced by 0.16 days year−l, EOS delayed by 0.08 days year−l, and consequently LOS extended at a rate of 0.07 days year−l, likely due to the warming and drying climate during the study period. In addition, annual mean temperature (AMT) was negatively correlated with SOS (50.26%) and positively correlated with EOS and LOS (72.25 and 60%, respectively). As for the annual mean total precipitation (AMP), it was positively correlated with SOS and EOS (50.77 and 52.97%, respectively) and negatively correlated with LOS (52.07%). Furthermore, a higher freezing index led to a delayed SOS and an advanced EOS and a shortened LOS at the regional scale. Similar to AMT, a higher thawing index advanced the SOS, delayed the EOS, and extended the LOS. Our results confirmed the importance of climate and permafrost status on vegetation phenological processes and also contributed toward understanding the response of cold region ecosystems to global climate change.

Highlights

Plant phenology has attracted strong scientific attention in recent years for its relationship with different driving factors of climate change (Rauste et al, 2007; Shen et al, 2015b; Zhao et al, 2016; Ganjurjav et al, 2020)
The results indicated that vegetation phenology of alpine grasslands in the SFGR during 2000–2019 showed a trend of advancement in spring phenology, postponement of autumn phenology, and longer growing season length
There were differences in the change ranges of phenology, the general trend and spatial distribution pattern were consistent with the findings by Guan et al (2019), which may be related to the selection of data sources, time scale, and different methods of phenology extraction (Che et al, 2014; Ganjurjav et al, 2020)

Summary

Introduction

Plant phenology has attracted strong scientific attention in recent years for its relationship with different driving factors of climate change (Rauste et al, 2007; Shen et al, 2015b; Zhao et al, 2016; Ganjurjav et al, 2020). The emergence of remote sensing technology has greatly broadened the scope of vegetation phenological observations due to its virtues of multi-temporal, long time series, and large-scale regional as well as global datasets (Hmimina et al, 2013; Zhao et al, 2015; Piao et al, 2019). Vegetation indices, such as the NDVI, the enhanced vegetation index (EVI), and the leaf area index (LAI), have been used to infer the timing of vegetation phenology (Delbart et al, 2005; Shen et al, 2014a; Wen et al, 2021)

Methods

Results

Discussion

Conclusion