Soil Carbon Changes Following Afforestation with Olga Bay Larch (Larix olgensis Henry) in Northeastern China

After converting cropland to forest, carbon is sequestered in the aggrading biomass of the new forests, but the question remains, to what extent will the former arable soil contribute as a sink for CO2? Quantifying changes in soil carbon is an important consideration in the large-scale conversion of cropland to forest. Extensive field studies were undertaken to identify a number of suitable sites for comparison of soil properties under pasture and forest. The present paper describes results from a study of the effects of first rotation larch on soil carbon in seven stands in an afforestation chronosequence compared with adjacent Korean pine, pasture, and cropland. An adjacent 250-year-old natural forest was included to give information on the possible long-term changes in soil carbon in northeast China in 2004. Soil carbon initially decreased during the first 12 yr before a gradual recovery and accumulation of soil carbon occurred. The initial (0–12 yr) decrease in soil carbon was an average 1.2% per year among case studies, whereas the increase in soil carbon (12–33 yr) was 1.90% per year. Together with the carbon sequestration of forest floors, this led to total soil carbon stores of approximately 101.83 Mg/hm2 over the 33-year chronosequence. Within the relatively short time span, carbon sequestration occurred mainly in tree biomass, whereas soil carbon stores were clearly higher in the 250-year-old plantation (184 Mg/hm2). The ongoing redistribution of mineral soil carbon in the young stands and the higher soil carbon contents in the 250-year-old afforested stand suggest that nutrient-rich afforestation soils may become greater sinks for carbon (C) in the long term. (Managing editor: Ya-Qin Han)