Effects Of Cutting On Greenhouse Gas Emissions From Forested Swamp In Xiaoxing'an Mountains

Wetlands are important sources and sinks of greenhouse gases, because the human activities are growing intensively, natural wetlands are seriously damaged, especially with the demand of timber increasing continuously, wetlands are seriously disturbed by cutting, which result in the change of greenhouse gases emission. The Alnus sibirica swamp (M), Betula platyphylla swamp (B), Larix gmelinii-Carex schmidtii swamp (LT), Larix gmelinii-moss (LX) and Larix gmelinii-Sphagnum (LN) were studied to reveal the emission variation of CH4, CO2 and N2O under different cutting means (45% selective cutting and clear cutting) in growing season by using a static opaque chamber and gas chromatography method in Xiaoxing'an Mountains. Results indicated that:Cutting couldn't change the seasonal regulation, but selective and clear cutting site of B was 1-2℃lower than control site, comparing to its average temperature, in addition, other types of swamps all had various degrees of increase, and as the cutting strength increasing, the increasing range of temperature also became larger. The average water level in selective cutting and clear cutting sites of M, and in clear cutting sites of LT and LN reduced 3-12cm than control sites, and other types of swamps all raised 1-10cm after cutting.The seasonal variations of CH4 emission in swamps were basically similar, all appeared the regulation as summer>spring>autumn, except that the summer emissions of selective cutting site in M(0.07 mg·m-2·h-1), clear cuting site in LT(-0.07 mg·m-2·h-1) and of control site in LN(-0.06 mg·m-2·h-1) were relatively small. Cutting had little influence on seasonal changing regulation of CO2 emission in forest wetlands, all appeared the regulation as summer>spring>autumn, except that of selective cutting in LT showed as summer (452.77 mg·m-2·h-1)> autumn (298.42 mg·m-2·h-1)> spring (260.10 mg·m-2·h-1). Cutting had quite large influence on seasonal changing regulation of N2O emission without certain regulations, which was considered the result of actions combined temperature and water level.The main impact factors of CH4 emission in forested swamps changed after cutting, the emission in control site of M had significant correlation with soil temperatures at 15cm,30cm and 40cm, that in clear cutting site of B had significant correlation with soil temperatures at 30cm and 40cm, also that in selective cutting site of LT with ground surface temperature and its clear cutting site with soil temperature at 0-15cm. The CH4 emission before and after cutting in forest wetlands had minor correlation with the water level. The CO2 emission before and after cutting had significant correlation with both temperatures and water level, whereas the N20 emission had little correlation with them, but had coherence with the variation of water level. The CH4 emission of M and LT after cutting reduced by 99%, selective cutting site of B reduced by 81% than control site, whereas the other wetlands all increased the CH4 emission after cutting, changing into the source of CH4 from sink. The CO2 emission of M and LT increased by 1/3 to 1/2 after cutting, while other four types of wetlands reduced by 1/4. The N2O emission of M, B and LN increased by 5 to 10 times, that of LT reduced, meanwhile selective cutting site of LX presented to be a N2O sink.The Global Warming Potential (GWP) of forest wetlands changed greatly after cutting, except that of LT showed as clear cutting site>control site>selective cutting site and M showed as control site> clear cutting site>selective cutting site, other types of wetlands all presented as clear cutting site>control site>selective cutting site, which indicated that selective cutting should be adopt to manage forest wetlands from the greenhouse gases controlling point of view.