Divergent changes of the elevational synchronicity in vegetation spring phenology in North China from 2001 to 2017 in connection with variations in chilling

Abstract

Mountain ecosystems are sensitive to climate change, and vegetation phenology provides one of the best signals to exemplify ecosystem responses to climate change. Vegetation phenology of mountain ecosystems is usually characterized with an elevational pattern, with the growing season starts earlier and ends later in lower versus higher elevations. With climate change, this elevational gradient of vegetation phenology is likely to shift as well. However, both the patterns and the underlying driving forces for potential changes in this elevational gradient of vegetation phenology are still unclear. Here, we used 500‐m resolutioned normalized difference vegetation index (NDVI) data from Moderate Resolution Imaging Spectroradiometer (MODIS) for the period of 2001 to 2017 to investigate changes in the start of growing season (SOS) along the elevational gradient for six mountains in northern China dominated by broadleaf deciduous forests. We found that while SOS consistently advanced for most of the pixels, the elevational lapse rate of SOS (SE) showed various trends for different mountains. Specifically, SE showed a significant (p‐value < .05) decreasing trend for the two southernmost mountains, indicating an increasing elevational synchronization in SOS. However, such phenological synchronization was not found in other temperate mountains. As warming has caused relatively consistent increases in heat forcing across different elevations and among different mountains but has led to highly various changes in chilling hours between high and low elevations, we suggested that the distinctive pattern in elevational synchronicity of spring phenology between southern and northern mountains in temperate China was primarily due to their different recent changes in chilling hours. Our work provides a novel key hypothesis for explaining the divergent changes in elevational gradients of vegetation phenology that can be tested in other regions for mountain ecosystems.

Warming-induced phenological mismatch between trees and shrubs explains high-elevation forest expansion

“…Changes in these two factors have been widely used to explain the phenological changes of trees in response to increasing temperature [ 33–36 ]. A warmer spring advances growth reactivation in both primary meristems (buds and leaves) and secondary meristems (cambium) [ 28 , 35 ]. However, warmer conditions reduce chilling accumulation in autumn and winter, and delay spring phenology, mainly by increasing the heat requirement [ 33 , 36 ].…”

Review of vegetation phenology trends in China in a changing climate

“…In the past 40 years, vegetation phenology in China has made great progress. However, despite many investigations on the response of vegetation phenology to climate change (Chen and Xu, 2012; Dai et al, 2021; Wang et al, 2015b), there are still relatively few studies focusing on the ecological and climatic feedbacks of vegetation phenology. In addition to research on the spatiotemporal characteristics and trends of phenology, there are more areas where phenological research could be applied.…”

Diverse variations in middle and high latitudes of the Northern Hemisphere spring phenology sensitivity to diurnal temperature during 1982–2015

“…The changes of heat accumulation and chilling in latitude and altitude gradient will also have different effects on spring phenology (Hänninen, 2016). Dai et al (2021) demonstrated that the chilling change related to altitude is the main reason for the significant reduction of altitude sensitivity of SOS in temperate mountains. Warming, especially at night-time, reduces the preseason chilling in low-latitude and low-altitude areas and delays SOS (Fu et al, 2015), but warming in high-latitude and highaltitude areas will increase the chilling and promote the advance of spring phenology (Güsewell et al, 2017).…”