Changes Of Carbon Storage In Degraded Shrub Forest After Vegetation Restoration

In order to study the changes of carbon storage and soil labile organic carbon pools in evergreen broad-leaved plantations after transforming from degraded shrub forest(DF) in north subtropical areas of China, this paper taking mixed Schima superba Gardn. et Champ.-Cyclobalanpsis glauca(Thunb.) Oerst. plantation(SP), Elaeocarpus sylvestris(Lour.) Poir pure plantation(EP) and the reserved DF as our test objects, and using the methods of plot investigation and laboratory analysis, we analyzed the vegetation and soil carbon storage in different stands, and we also collected soil samples of 0~50 cm depth to analyze the soil labile organic carbon content. The results of this study is helpful to improve the estimate accuracy of carbon pools, and also provides references for carbon storage changes after forest type conversion(from degraded forest to evergreen broad-leaved plantation) in subtropical areas of China. The main results were as follows:1、Effects of tree species composition on carbon storage of 11 years old evergreen broad-leaved plantationsBoth the vegetation and soil carbon storage significantly increased after the DF was transformed into broad-leaved plantations for 11 years(p<0.05). The increases of vegetation carbon storage appeared mainly in arborous layers. Compared with DF, the soil carbon storage of SP and EP was significantly increased in each interval of 0-50 cm depth, respectively. The vegetation carbon storage was higher in EP than that in SP, with an increase of 99.4%. Compared with SP, the carbon storage in arborous layer of EP was 27.75 t·hm-2 higher, which was as twice as that of SP. The soil carbon storage in EP was 10.17 t·hm-2 higher than that in SP, with a significant difference. In addition, the soil carbon storage in each interval of 0~50 cm depth of EP was higher than that in SP, with significant differences in 0~10 cm and 20~30cm layer. To sum up, the total carbon storage of DF was significantly increased after transformed into evergreen broad-leaved plantation and EP had greater ability of carbon accumulation than SP. Results from the present study suggest that the choice of tree species would be important during the restoration of degraded ecosystems with the aim of enhancing ecosystem carbon storage.2、Effects of tree species composition on soil labile organic carbon of 11 years old evergreen broad-leaved plantationsAs compared with the retained DF, the soil total organic carbon(TOC), easily oxidized carbon(EOC) and light fraction organic matter(LFOM) in both SP and EP stands increased by 52.33%~96.13% and 77.93%~119.85%, 57.89%~100.90% and 21.44%~46.85%, 74.50%~93.75%, and 27.24%~96.09%, respectively. The water-soluble organic carbon(WSOC) had no obvious change after the afforestation. The ratios of WSOC/TOC in the soils followed the order of DF>SP>EP, whereas the EOC/TOC in the soils followed the order of SP>DF>EP. In the three stands, soil WSOC, EOC, and LFOM had extremely significant correlations with soil TOC(p<0.01), and the correlation coefficients of each labile organic carbon with soil TOC were higher in SP than in DF and EP. The soil TOC, EOC, and LFOM in the three stands were extremely significantly correlated with soil nutrients, but the soil WSOC had no significant correlations with soil hydrolysable N and available K in DF, all the same, there was no significant correlation between soil WSOC and available K in EP.3、Effects of stand age on carbon storage in SPWe studied the carbon storage in SP and DF, The results showed that the carbon storage in both vegetations and soils followed the ascending order of DF<7-year-old SP <11-year-old SP. The vegetation carbon storage in 7-year-old SP and 11-year-old SP both had significant increment of 5.49 and 23.64 t·hm-2, as compared with DF. Vegetation carbon storage in 11-year-old SP was 18.15 t·hm-2 larger than that in 7-year-old SP after afforestation. Soil carbon storage in 7-year-old SP and 11-year-old SP was 12.56 and 30.99 t·hm-2 which were much higher than that in DF. Soil carbon storage in 11-year-old SP had an increase of 18.43 t·hm-2 than that in 7-year-old SP, with significant difference in each soil interval of 0~50 cm depth. The total ecosystem carbon storage of DF, 7-year-old SP and 11-year old SP was 54.11, 72.16 and 108.74t·hm-2, respectively. The annual increment of total carbon storage in 7-year-old SP and 11-year-old SP was 2.58 and 4.97 t·hm-2·a-1 compared with DF, respectively. The carbon storage of evergreen broad-leaved young plantations transformed from DF has increased significantly, the long-term effect of stand age on the carbon accumulation need to be further studied.4、Effects of stand age on soil labile organic carbon storage in SPAs compared with DF, the soil TOC, EOC and LFOM in both 7- and 11-year-old SP stands increased by 22.79%~43.34% and 52.33%~96.13%, 11.11%~25.18% and 57.89%~100.90%, 18.18%~85.20% and 74.50%~93.75%, respectively. The WSOC in 7-year-old SP decreased by 4.10%~9.53%(except in 10~20 cm soil layer) and in 11-year-old SP increased by 0.71%~5.37% compared with DF. The ratios of WSOC/TOC in the soils followed the order of DF>7-year-old SP>11-year-old SP, whereas the EOC/TOC in the soils followed the order of 11-year-old SP >DF>7-year-old SP. In the three stands, soil WSOC, EOC, and LFOM had extremely significant correlations with soil TOC, and the correlation coefficients between WSOC and TOC were lower than others. The soil TOC, EOC, and LFOM in the three stands were extremely significantly correlated with soil nutrients, but the soil WSOC in DF had no significant correlations with soil hydrolysable N and available K.