Ecosystem water use efficiency was enhanced by the implementation of forest conservation and restoration programs in China

Abstract

The large-scale forest conservation and restoration programs (FCRPs) implemented in China have energetically promoted carbon sequestration and water consumption of terrestrial ecosystems. However, the impact of FCRPs on the coupling between them, that is, ecosystem water use efficiency (EWUE), remains unknown. Using the Mann-Kendall test and the Theil-Sen's slope estimator, we analyzed the EWUE trends of the FCRP-induced forest recovery zones (FFRZs) in the pre- and post-intensification phases of the programs. Then, the random quadrat comparison method was employed to compare the EWUE of FFRZs and that of their adjacent non-recovery zones (NRZs). We also performed partial correlation analysis and contribution analysis to investigate the response of EWUE to FCRP-induced forest recovery. Our study showed that the proportion of FFRZs presenting a significant increasing trend in EWUE expanded from 19.1% for the pre-intensification phase of FCRPs to 35.7% for the post-intensification phase. The EWUE of the FFRZs was significantly higher than that of their neighboring NRZs in arid and semi-arid regions whereas there was no significant difference between them in humid and semi-humid regions. EWUE was positively correlated with FCRP-induced tree cover in 74.6% of the FFRZs during the post-intensification phase of FCRPs. The average contribution of FCRP-induced forest recovery to EWUE change was 4.94 × 10-3 gC⋅mm−1⋅a-1 in the FFRZs, accounting for 39.1% of the total EWUE variation. We concluded that EWUE was significantly enhanced by the implementation of FCRPs in China. However, the EWUE increase could not be sustained by forest restoration in arid and semi-arid regions. Our study highlights that the implementation of FCRPs should pay more attention to the tradeoff between carbon sequestration and water consumption of ecosystems and be tailored to local conditions.