Changes in Gross Primary Production in Response to Afforestation in the Hilly Loess Plateau of Northern Shaanxi, China

Abstract

As a large-scale afforestation initiative, the Grain for Green (GFG) program was implemented for more than decade in the hilly Loess Plateau of Northern Shaanxi starting in 1999 and inevitably affected plant biomass production. This study evaluated the trend and magnitude of gross primary production (GPP) changes with VPM in the study area over 2000–2012 and quantitatively identified GFG’s contribution. The results indicate that the regional mean GPP was 529.6 to 854.7 g C m−2 yr−1, which significantly increased by 1.63% per year during the period. At the pixel level, 80% of the pixels presented an increasing trend in annual GPP, and in nearly half of the region, the increasing trend was statistically significant. Spatial analyses showed that the GPP increased more significantly in the gully areas of the middle north area, while no evident change trend was observed in the southern forestland areas. Statistical data from relevant yearbooks and interpreted data from high-resolution images show that the GFG program promoted vegetation restoration. Taking the increased area of forestland to indicate the achievements of GFG, we estimated, using regression analyses, that the afforestation contributed 40%–60% to the increased GPP in the region during 2000–2012. Overall, the ecosystem had a positive response to the Grain for Green (GFG) program in Northern Shaanxi.