Disentangling the Key Drivers of Ecosystem Water-Use Efficiency in China’s Subtropical Forests Using an Improved Remote-Sensing-Driven Analytical Model

Abstract

The subtropical forests in China play a pivotal part in the global and regional carbon–water cycle and in regulating the climate. Ecosystem water-use efficiency (WUE) is a crucial index for understanding the trade-off between ecosystem carbon gain and water consumption. However, the underlying mechanisms of the WUE in forest ecosystems, especially the different subtropical forests, have remained unclear. In this paper, we developed a simple framework for estimating forest WUE and revealing the underlying mechanisms of forest WUE changes via a series of numerical experiments. Validated by measured WUE, the simulated WUE from our developed WUE framework showed a good performance. In addition, we found that the subtropical forest WUE experienced a significant increasing trend during 2001–2018, especially in evergreen and deciduous broadleaf forests where the increasing rate was greatest (0.027 gC kg−1 H2O year−1, p < 0.001). Further analysis indicated that the atmospheric CO2 concentration and vapor pressure deficits (VPD), rather than leaf area index (LAI), were the dominant drivers leading to the subtropical forest WUE changes. When summed for the whole subtropical forests, CO2 and VPD had an almost equal spatial impact on annual WUE change trends and accounted for 45.3% and 49.1% of the whole study area, respectively. This suggests that future forest management aiming to increase forest carbon uptake and protect water resources needs to pay more attention to the long-term impacts of climate change on forest WUE.

Divergent Response of Carbon Sink to Climate Change Along Topographical Gradient in China Based on EEMD Detrending

“…At very high elevations (Qinghai‐Tibetan plateau), alpine meadow ecosystem is very sensitive to drought (M. Xu et al., 2021), making PRE and SM dominate NEP changes. Many studies have revealed that VPD affects vegetation more than SM (T. Chen et al., 2023; X. Wang et al., 2019), our study also reveals that VPD is more crucial than SM at lower elevations. However, at higher elevations, SM is more crucial than VPD due to the strong evaporation and shallow soils at high elevations (H. Y. Liu et al., 2018; Shi et al., 2014; You et al., 2020).…”

“…At very high elevations (Qinghai-Tibetan plateau), alpine meadow ecosystem is very sensitive to drought (M. Xu et al, 2021), making PRE and SM dominate NEP changes. Many studies have revealed that VPD affects vegetation more than SM (T. Chen et al, 2023;X. Wang et al, 2019), our study also reveals that VPD is more crucial than SM at lower elevations.…”