Afforestation promotes the enhancement of forest LAI and NPP in China

Abstract

Recent national wide afforestation in China are playing an increasingly significant role in the global greening trend and CO2 mitigation. However, the long term knowledge of spatiotemporal pattern of plantation forests (PF) is essential to understand the continuability and sustainability of the PF contribution and its spatiotemporal pattern comparing to nature forests (NF). Here we combined an inventory based map of PF, three up-to-date remote sensing leaf area index (LAI) datasets, and a process-based terrestrial biogeochemical model to investigate the interannual variabilities (IAVs) and trends of LAI and net primary productivity (NPP) of natural and plantation forests in China, from 1982 to 2014. We found that PF possessed similar spatiotemporal patterns as those of NF, while they exhibited a greater enhancement of both LAI and NPP since 2000. The total proportions of LAI and NPP in the plantation areas increased from 22% to 23.4%, and 22% to 22.8% from 1982 to 2014, respectively. Although different datasets provided diverse rates, an increasing trend was in agreement. The spatially-explicit analysis also illustrated that the increasing proportions were primarily contributed by the Southern sub-regions, particularly the Southwest and South sub-regions, while the PF in Northern sub-regions (e.g., Inner Mongolia and Northeast) even showed a decreasing contribution trend. The quantitative outputs from this study supported that PF promoted the greening trend in China since the 21st century. However, we also argued that the swift increase in LAI and NPP by PF should mainly result from the growing number of tree plantations and the rapid growth of newly planted forests. The proper management of PF is, therefore, an essential task for the maintenance and long-term improvement of their ecosystem services.