Abstract
With the increasing temperature and intensified drought, global climate change has profound impacts on tree growth in temperate regions, which consequently regulates terrestrial-atmosphere biogeochemical processes and biophysical feedbacks. Thus, increasing numbers of studies have addressed the long-term annual trends in tree growth and their response to climate change at diverse spatial scales. However, the potential divergence in tree growth trends and growth variability (represented by coefficient of variance) in different seasons across large-scale climate gradients remains poorly understood. Here, we investigated the tree growth trends and growth variability in different seasons across diverse drought conditions in forested regions over northeastern China during the period 1982–2015, using both remote sensing observations and in situ tree-ring measurements. We found clear seasonal divergence in tree growth trends during 1982–2015, and the apparent increase was mainly observed in spring and autumn, attributed mainly to the increase in spring temperature and autumn solar radiation, respectively, but not in summer. The magnitudes of increasing trends in tree growth decrease with the increase of the multi-year average dryness index (MAI) in semi-arid areas (1.5 < MAI < 4.0) in all seasons. We further revealed that the interannual variability in tree growth was much larger in the semi-arid regions than in the humid and semi-humid regions in all seasons, and tree growth variability was significantly and negatively correlated with the variations in temperature and water deficit. Our findings improve our understanding of seasonal divergence in tree growth trends and provide new insights into spatial patterns in forest vulnerability in a warmer and drier climate.
Highlights
Forest ecosystems cover a large percentage of Earth’s land surface [1], and play a crucial role in regulating the global carbon cycle, and biophysical land-atmosphere feedbacks [2,3,4,5]
Our study region is characterized by a continental monsoon climate, with ~60.2% of annual precipitation occurring in summer (June–August) and regular snow in winter
We found water deficit acts as the main limiting factor for annual tree radial growth, which is different from the results of NDVI
Summary
Forest ecosystems cover a large percentage (circa 26%) of Earth’s land surface [1], and play a crucial role in regulating the global carbon cycle, and biophysical land-atmosphere feedbacks [2,3,4,5]. The spatiotemporal variations in climate conditions have changed dramatically, in mid-latitudinal regions [6], which exerts remarkable effects on both the structure and Forests 2019, 10, 39; doi:10.3390/f10010039 www.mdpi.com/journal/forests. On the other hand, forest ecosystems tend to be resilient to and to some extent have already adapted to the changing climate [12]. Trees may adapt to the increasing drought by adjusting their structural and functional attributes, and physiological processes (e.g., changing water use strategies and regulating the distribution of non-structural carbon) [13,14]. The general picture is still lacking regarding the spatial pattern of tree growth variability at the regional level during past decades
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