Effects Of Cutting On Carbon Source Or Sink Of Temperate Forested Wetlands In Xiaoxing’an Ling Of China

The soil respiration net carbon emissions (CO2 and CH4), vegetation net primary productivity and annual net carbon sequestration were studied by using static chamber gas chromatography method and Multi N/C 3100, HT 1300 Solids Module (Analytik Jena AG, Germany) and the sample tree analysis method from different cutting processing(natural,45% selective cutting, clear cutting) temperate forest wetlands Alnus sibiricav swamp(M), Betula platyphylla swamp(B),Larix gmelinii Carex schmidtii swamp(LT),Larix gmelinii Moss swamp(LX),Larix gmelinii Sphagnum spp. swamp(LN) in Lesser Xing’an Mountains of China, so as to evaluate effects of forest cutting on Carbon source or sink which based on net ecosystem carbon balance.The results showed that:(1) The cutting changed seasonal distribution pattern of CH4 emission in temperate forested wetlands,M(the selective and clear cutting)changed summer> spring≈autumn≈winter into summer≈spring≈autumn≈winter,LT(clear cutting), LX(the selective and clear cutting), LN (clear cutting) changed summer≈spring≈autumn≈winter into summer≈autumn> winter> spring, summer>spring≈autumn≈winter, summer>spring≈autumn≈winter.(2) The cutting interference affected five forested swamp annual CH4 emission differently.The selective cutting reduced annual CH4 emission of Alnus sibiricav swamp significantly (66.5%,P<0.05),the clear cutting not only reduced annual CH4 emission of Alnus sibiricav swamp significantly(65.5%, P<0.05) but also increased annual CH4 emission of Betula platyphylla swamp, Larix gmelinii Moss swamp, Larix gmelinii Sphagnum spp. swamp(3.1 times to 94.3times,P<0.05).So clear cutting affected more strongly than selective cutting.(3) The clear cutting changed correlation between CH4 emission fluxes and soil temperature from 5cm-40cm soil temperature into 40cm soil temperature in Alnus sibiricav swamp,the main factor in Betula platyphylla swamp changed temperature and 15-40cm soil temperature into 10-40cm,15-40cm soil temperature,the main factor in Larix gmelinii Moss swamp changed into water table(selective cutting)and 5-40cm soil temperature(clear cutting),the main factor in Larix gmelinii Sphagnum spp. swamp changed 0-10 cm soil temperature into water table(selective cutting) and water table,40cm soil temperature(clear cutting).(4)There were two types of seasonal distribution pattern of CO2 emission in five forested swamp, summer>spring>autumn;≈inter showed in Alnus sibiricav swamp,Larix gmelinii Carex schmidtii swamp and Larix gmelinii Sphagnum spp. swamp, summer>spring>autumn> winter showed in Betula platyphylla swamp and Larix gmelinii Moss swamp).Only selective cutting turned Betula platyphylla swamp into summer>spring>autumn≈winter,the others kept original patterns.(5) The cutting interference affected five forested swamp annual CO2 emission differently. The selective cutting increased annual CO2 emission of Alnus sibiricav swamp significantly (24.4%,P<0.05), increased annual CO2 emission of Betula platyphylla swamp and Larix gmelinii Carex schmidtii swamp(12.4%～27.9%,P>0.05),but not significantly,the selective had little influence on Larix gmelinii Moss swamp and Larix gmelinii Sphagnum spp. swamp(-0.8%～-7.2%,P>0.05); The clear cutting increased annual CO2 emission of Alnus sibiricav swamp and Larix gmelinii Moss swamp significantly(34.3%～53.4%,P<0.05),increased annual CO2 emission of Betula platyphylla swamp and Larix gmelinii Moss swamp(14.9%～ 32.0%,P>0.05),but not significantly,but reduced annual CO2 emission of Larix gmelinii Sphagnum spp. swamp(-12.0%,P>0.05). So the clear cutting affected more strongly than selective cutting.(6)The main factor of CO2 emission fluxes did not change obviously in Alnus sibiricav swamp(only increased 40cm soil temperature in clear cutting site),Betula platyphylla swamp and Larix gmelinii Moss swamp reduced the correlation with soil temperature(the former changed0～20cm to 0cm,the latter changed selective cutting 0～30cm to 0～10cm and clear cutting 0～15cm),but increased the correlation with soil temperature in Larix gmelinii Carex schmidtii swamp and Larix gmelinii Moss swamp(the former changed selective cutting 0～ 10cm to 5～20cm and the clear cutting 0～20cm, the latter changed clear cutting 0～20cm to 0～30cm).The correlation with water table of natural sites showed negative correlation in Betula platyphylla swamp, Larix gmelinii Moss swamp and Larix gmelinii Sphagnum spp. swamp,but did not in any other sites.(7)The net primary productivity and annual net carbon sequestration of five natural forested swamp were between0.444～0.882 kg·m-2·a-1 and 0.205～0.402 kgC·m-2·a-1.the clear cutting affected more strongly than selective cutting,the selective cutting reduced net primary productivity of Betula platyphylla swamp about 1/4 significantly,however, clear cutting reduced net primary productivity of five forested swamp 1/3～2/3;The selective cutting reduced net carbon sequestration of Betula platyphylla swamp 1/4 significantly,the clear cutting reduced net carbon sequestration of five forested swamp 2/5～2/3.(8) The selective cutting and the clear cutting interference affected carbon sink/source(-4.22～0.14 tC·hm-2·a-1) of forest swamp wetlands in Lesser Xing’an Mountains differently. The selective cutting increased carbon source intension of Betula platyphylla swamp and Larix gmelinii Carex schmidtii swamp(22.4%～109.8%,P>0.05),and changed Betula platyphylla swamp and Larix gmelinii Sphagnum spp. swamp from carbon absorbed sink to carbon source(only Betula platyphylla swamp significantly);The clear cutting changed five forested swamp to strong carbon source(Alnus sibiricav swamp, Larix gmelinii Carex schmidtii swamp, Larix gmelinii Moss swamp increased 0.8～11.3times,P<0.05; Betula platyphylla swamp and Larix gmelinii Sphagnum spp. swamp changed weak carbon absorbed sink to to strong carbon source(-3.69～-1.57 tC-hm-2·a-1)).The carbon source intension of clear cutting in five forested swamp increased 48.6%-617.0% than the selective cutting(except Larix gmelinii Sphagnum spp. swamp).Therefore, clear cutting affected forested swamp carbon source/sink more strongly. So selective cutting should be taken and clear cutting should be avoided in management of temperate coniferous forest swamp sink.