Abstract
Forest ecosystems in an ecotone and their dynamics to climate change are growing ecological and environmental concerns. Phenology is one of the most critical biological indicators of climate change impacts on forest dynamics. In this study, we estimated and visualized the spatiotemporal patterns of forest phenology from 2001 to 2017 in the Qinling Mountains (QMs) based on the enhanced vegetation index (EVI) from MODerate-resolution Imaging Spectroradiometer (MODIS). We further analyzed this data to reveal the impacts of climate change and topography on the start of the growing season (SOS), end of the growing season (EOS), and the length of growing season (LOS). Our results showed that forest phenology metrics were very sensitive to changes in elevation, with a 2.4 days delayed SOS, 1.4 days advanced EOS, and 3.8 days shortened LOS for every 100 m increase in altitude. During the study period, on average, SOS advanced by 0.13 days year−1, EOS was delayed by 0.22 days year−1, and LOS increased by 0.35 day year−1. The phenological advanced and delayed speed across different elevation is not consistent. The speed of elevation-induced advanced SOS increased slightly with elevation, and the speed of elevation-induced delayed EOS shift reached a maximum value of 1500 m from 2001 to 2017. The sensitivity of SOS and EOS to preseason temperature displays that an increase of 1 °C in the regionally averaged preseason temperature would advance the average SOS by 1.23 days and delay the average EOS by 0.72 days, respectively. This study improved our understanding of the recent variability of forest phenology in mountain ecotones and explored the correlation between forest phenology and climate variables in the context of the ongoing climate warming.
Highlights
Research on phenology focuses on the phases of recurring biological life cycles, how these cycles are influenced by biotic and abiotic drivers and the interrelations among the same or different species [1].Forests 2019, 10, 1007; doi:10.3390/f10111007 www.mdpi.com/journal/forestsForest phenology is one of the most reliable biological indicators for evaluating the impacts of global warming in temperate and boreal zones because of its high sensitivity to climate change [2]
The dates for the end of the growing season (EOS) mainly range from the 260th to
Our study demonstrated that using a MODerate-resolution Imaging Spectroradiometer (MODIS) enhanced vegetation index (EVI) time-series dataset to obtain the phenological metrics offered acceptable reliability, and the results were comparable with the ground observation data and can be used to reveal the forest phenological characteristics
Summary
Research on phenology focuses on the phases of recurring biological life cycles, how these cycles are influenced by biotic and abiotic drivers and the interrelations among the same or different species [1]. Forest phenology is one of the most reliable biological indicators for evaluating the impacts of global warming in temperate and boreal zones because of its high sensitivity to climate change [2]. Variations in forest phenology strongly affect the fitness and distribution of temperate and boreal forests [3] and, the interspecific interactions among plants [4], ecosystem structure and function by varying the length of growing season [5,6], terrestrial ecosystem water and carbon balances [7,8], and climate system energy balances [9]. Extensive research primarily focused on the start of the growing season (SOS) and found an earlier SOS in high latitudes and high altitudes based on the ground observations, satellite remote sensing, and model simulations [11,12,13,14,15,16,17]
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