Abstract
Abstract. In recent years, China's terrestrial ecosystems have experienced frequent droughts. How these droughts have affected carbon sequestration by the terrestrial ecosystems is still unclear. In this study, the process-based Boreal Ecosystem Productivity Simulator (BEPS) model, driven by remotely sensed vegetation parameters, was employed to assess the effects of droughts on net ecosystem productivity (NEP) of terrestrial ecosystems in China from 2000 to 2011. Droughts of differing severity, as indicated by a standard precipitation index (SPI), hit terrestrial ecosystems in China extensively in 2001, 2006, 2009, and 2011. The national total annual NEP exhibited the slight decline of −11.3 Tg C yr−2 during the aforementioned years of extensive droughts. The NEP reduction ranged from 61.1 Tg C yr−1 to 168.8 Tg C yr−1. National and regional total NEP anomalies were correlated with the annual mean SPI, especially in Northwest China, North China, Central China, and Southwest China. The reductions in annual NEP in 2001 and 2011 might have been caused by a larger decrease in annual gross primary productivity (GPP) than in annual ecosystem respiration (ER). The reductions experienced in 2009 might be due to a decrease in annual GPP and an increase in annual ER, while reductions in 2006 could stem from a larger increase in ER than in GPP. The effects of droughts on NEP lagged up to 3–6 months, due to different responses of GPP and ER. In eastern China, where is humid and warm, droughts have predominant and short-term lagged influences on NEP. In western regions, cold and arid, the drought effects on NEP were relatively weaker but prone to lasting longer.
Highlights
The exchange of carbon dioxide (CO2) between land and the atmosphere is important to the global carbon cycle (Arnone et al, 2008; Schwalm et al, 2010a)
Our simulation indicates that the national total net ecosystem productivity (NEP) of China slightly declined during the period from 2000 to 2011 (−11.3 Tg C yr−1), mainly due to considerable reductions in NEP caused by extensive, severe droughts in 2001, 2006, 2009, and 2011
The decreases in national total NEP ranged from 61.1 Tg C yr−1 to 168.8 Tg C yr−1, approximately 30 to 94 % of the average carbon sink strength of forests during the 1999–2008 period, estimated using forest inventory data (Pan et al, 2011; Guo et al, 2013; Zhang et al, 2013)
Summary
The exchange of carbon dioxide (CO2) between land and the atmosphere is important to the global carbon cycle (Arnone et al, 2008; Schwalm et al, 2010a). Carbon sequestration by terrestrial ecosystems is affected by a number of factors, including climate, atmospheric CO2 concentration, nitrogen deposition, land cover types, and land use change. Extreme climate events, such as drought, could substantially affect ecosystem carbon fluxes and lead to significant inter-annual variability in the regional and even global terrestrial carbon budget (Running, 2008; Xiao et al, 2011). In contrast to gradual climate change, carbon sequestration by terrestrial ecosystems might be strongly impacted by droughts in a relatively short period Both gross primary productivity (GPP) and ecosystem respiration (ER), which releases carbon to the atmosphere, significantly influence carbon sequestration (Baldocchi, 2005; Meir et al, 2008; Schwalm et al, 2010a; van der Molen et al, 2011)
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