Abstract:Forest and wetland ecosystems are significant carbon and nitrogen sinks at the global scale, and play an important role sequestering greenhouse gases and regulating climate. The three greenhouse gases fluxes from forest and wetland ecosystems are influenced by many factors,including disturbance. Here, we review the effects of disturbance on greenhouse gases fluxes from forest and wetlands. We separate the effects due to disturbance into two types: disturbance brought about by human activity and through natural means. The former includes forest-harvesting, fertilization, reclamation and tillage, and the latter includes fire, typhoon and hurricane. We discuss the impacts of these different disturbances on the fluxes of CO2, CH4 and N2O from both forest and wetland ecosystems. In many cases the conclusions from the literature were not consistent. Harvesting increased forest soil respiration in most studies; however, there was also one report showing that soil respiration dropped markedly because of a reduction in carbon input after forest removal. The response of three greenhouse gases to harvesting was also not consistent. Reclamation, a major disturbance in wetlands, tended to produce large impacts on the carbon and nitrogen dynamics. Some studies demonstrated an increased CO2 emission when marshlands were transformed to farmland, whereas another reports concluded that marsh reclamation caused the drop in CO2 emission. CH4 flux often decreased, and N2O flux generally increased when the marshes were reclaimed. The effects of fertilizer nitrogen input on greenhouse gases production and emission from marshes soil were complex with differences induced by different nitrogen fertilizers (NH4NO3, (NH4)2SO4, KNO3 and urea). The intensity of fire appeared to have an important influence on CH4 flux; a low-intensity fire increases CH4 flux, whereas a high-intensity fire will decrease CH4 flux. The CO2 flux-responses were also complex; some studies showed that fire inhibited CO2 flux, but others showed promotion effects. Tropical storms (typhoons and hurricanes) are a common disturbance feature in tropical and subtropical coastal forest and wetland ecosystems. CO2 emission generally dropped after the storm and N2O flux often increased.
We concluded our review with an analysis of trends in current research, and pointed out some urgent and key directions in future. A major suggestion was that it is becoming increasingly necessary to understand the mechanism through which the different types of disturbance influence greenhouse gases fluxes from forest and wetland ecosystems, and in particular to assess the effects at different spatial and temporal scales.