The National Key Forestry Ecology Project has changed the zonal pattern of forest litter production in China

Litterfall transfers organic matter and nutrients from vegetation to soil and serves a major role in the global carbon (C) cycle. To understand the role of China's Key Ecology Project in the global C cycle, the zonality of national-scale forest litter production was investigated using a meta-analysis. The results showed that the mean annual litterfall was 4.947 ± 0.087 Mg ha−1 yr−1 between 1980 and 2016. The mean annual litterfall in primary forests was similar to that in secondary forests; both were significantly greater than that in planted forests. The total and leaf litter production significantly decreased with increasing latitude and altitude and showed a quadratic relationship with longitude. However, a comparison of the regression relationships of litter production of different forest stand origins with latitude, longitude and altitude revealed relatively larger adjusted R2 values (R2adj) for secondary forests (R2adj = 0.488, 0.307, 0.100, all p < 0.01) and primary forests (R2adj = 0.459, 0.223, 0.142, all p < 0.01), followed by planted forests (R2adj = 0.037, 0.017, 0.016, all p < 0.01). The coefficients and intercepts of the models of natural forests were significantly larger than those of planted forests (all p < 0.01, with the exception of two values of 0.081 and one value of 0.392). Based on the regression models, significant differences in the relationship between litter production and geographical factors were found between natural forests and all forests. These findings reveal that The National Key Forestry Ecology Project has changed the zonal pattern of forest litter production in China and imply that estimates of mean annual litter production and quantitative analysis of spatial distribution patterns in different forest stand origins are particularly important for understanding the global C cycle and managing forest resources in China.