| Due to the greenhouse effect caused by the increase of CO2 concentration in the atmosphere,carbon cycle and carbon balance in the ecosystem have become a hot spot in global climate change research,and the effect of forests on the carbon cycle has drawn growing attention.Forest ecosystem carbon pool is one of the most important carbon pools in terrestrial ecosystems and plays an irreplaceable role in regulating CO2 concentrations and mitigating the greenhouse effect.Forest fire disturbance,as a non-continuous disturbance factor of forest ecosystems,leads to the dynamic changes in vegetation carbon pools,litter carbon pools,and soil organic carbon pools,which affects the carbon cycle process of the ecosystem,and hence impacts the atmospheric carbon balance and climate change.In recent years,with the aggravation of climate warming,the frequency and intensity of forest fire disturbance have increased,and its carbon sink effect has caused widespread concern among researchers.However,at present,the quantitative research on the impact of forest fire disturbance on ecosystem carbon pools and its influencing mechanism is not clear.Therefore,this study selects the forest sub-tropical forest area in Guangdong where forest fire disturbance is prone to occur frequently as the research area to study the quantitative impact and mechanism of forest fire disturbance on ecosystem carbon stocks.This study is beneficial to reduce the uncertainty in global carbon balance estimation.Based on the scale of forest ecosystems,four subtropical forest types in Guangdong Province were taken as the research object.By means of adjacent sample plots method,field investigation,and indoor test analysis,standard sample plots were set up for the investigation of vegetation and litter biomass as well as soil sampling.Based on the experimental analysis and statistical analysis,the biomass of vegetation and litter was determined,soil organic carbon content and bulk density were measured,and the density of vegetation,litter along with soil organic carbon was calculated.At the scale of the forest ecosystem,the impact of different forest fire disturbance intensity(i.e.,light,moderate and high forest fire disturbance)on the change and spatial distribution patterns of the various carbon pools(i.e.,vegetation,litter and soil organic carbon pools)and ecosystem carbon pool in the forests.The influence of forest fire disturbance on the carbon pools in different forest ecosystems was quantified,and the influencing factors of fire disturbance intensity,forest type and soil depth on the variation of ecosystem carbon pool were analyzed,in order to reveal the influencing mechanisms of forest fire disturbance on ecosystem carbon pool and its spatial distribution patterns.The research results could clarify the influencing mechanism of forest fire disturbance on the carbon sequestration effect of subtropical forests,construct an evaluation system for the impact of forest fire disturbance on forest carbon pools,deepen the response mechanism of subtropical forests to forest fire disturbance,and provide theoretical support for the mechanism research of the cyclic coupling effect among climate change,forest fire disturbance and ecosystem carbon.It could provide a scientific basis for effective forest fire management strategies,precise estimation of forest carbon sink and forest restoration by forest fire prevention,forest management and emergency management departments.The research results have great theoretical and practical significance for the development of forest fire prevention,disturbance ecology,forest fire ecology,soil ecology,and plant ecology.The main results as follows.1)Significant effects of forest fire disturbance on forest ecosystems carbon densityForest fire disturbance reduced ecosystem carbon density,and the reduction of carbon density increased with the increase of forest fire disturbance intensity.The changes in carbon density of forest ecosystems in the four subtropical forest types of Guangdong Province are control check>light forest fire disturbance>moderate forest fire disturbance>high forest fire disturbance.Compared with the control check,the carbon density of Pinus massoniana forest ecosystem decreased by 6.73%,35.25%,and 44.95%respectively after light,moderate and high fire disturbance,the carbon density of Cunninghamia lanceolata forests ecosystem decreased by 8.29%,26.38%and 42.37%,respectively,and the carbon density of Eucalyptus forest decreased by 13.53%,39.41%and 56.74%,while that of Schima superba forest decreased by 7.99%,23.80%and 41.74%compared with the control.Compared with the control check,the intensity of light forest fire disturbance intensity had no significant effect on ecosystem carbon density(P>0.05),while the moderate and high forest fire disturbance intensity had a significant effect on ecosystem carbon density(P<0.05).The effects of forest fire disturbance on the carbon density of subtropical forest ecosystems in Guangdong province were disturbance>moderate forest fire disturbance>light forest fire disturbance.Two-factor analysis of variance showed that forest fire disturbance intensity and forest type both had significant effects on ecosystem carbon density.The forest fire disturbance intensity explained 71.67%of the ecosystem carbon density variation,and the forest type explained 17.58%of the ecosystem carbon density variation,indicating that forest fire disturbance intensity is the main factor causing the ecosystem carbon density variation.2)Reduction of vegetation carbon density by the forest fire disturbanceVegetation carbon density decreased as the intensity of forest fire disturbance increased,but it differed with components.The change in arbor carbon density under different forest fire disturbance intensity is consistent with the change of vegetation carbon density,while the herbaceous carbon density shows the opposite trend.Under the same forest fire disturbance intensity,the most reduction in the carbon density of each vegetation component occurred in the arbor layer.The effect of light forest fire disturbance on vegetation carbon density was not significant(P>0.05),while moderate and high forest fire disturbance significantly reduced vegetation carbon density(P<0.05).The intensity of forest fire disturbance significantly affected the carbon density of arbor vegetation.However,the order of herb carbon density variation under the disturbance of forest fire was the opposite,which were high forest fire disturbance>moderate forest fire disturbance>light forest fire disturbance>control.The intensity of forest fire disturbance significantly affects the carbon density of arbors and herbs,and it also affects the carbon density of shrubs.The results also showed that although light forest fire disturbance significantly enhanced the carbon density of herbs and it affected the carbon density of shrubs,it did not significantly impact the carbon density of arbors which dominated the vegetation in forest ecosystems.Hence,the light forest fire disturbance did not result in a significant change in vegetation carbon density.However,although the moderate and high forest fire disturbances enhanced the herb carbon density and affected shrub carbon density,they significantly reduced the arbor carbon density.Therefore,the moderate and high forest fire disturbances significantly decreased the carbon density of vegetation.Two-factor analysis of variance showed that both the intensity of forest fire disturbance and forest type had a significant effect on vegetation carbon density,and their interaction also had a significant effect on vegetation carbon density.Forest fire disturbance intensity explained 73.17%of vegetation carbon density variation,forest type explained 12.06%of vegetation carbon density variation,and their interaction explained 9.53%of vegetation density variation,indicating that forest fire disturbance intensity is the main factor causing the vegetation carbon density variation.3)Decrease of litter carbon density by the forest fire disturbanceForest fire disturbance significantly reduced litter carbon density(P<0.05),and the reduction increased with forest fire disturbance intensity.Nevertheless,the impact of different forest fire disturbance intensity on the litter carbon density differed.Although light forest fire disturbance insignificantly reduced the arbor carbon density,it significantly increased the herb and shrub carbon density.Thus,it reduced the source of litter and the litter carbon density.Moderate and high forest fire disturbances significantly increased herb density and affected shrub carbon density,but they significantly reduced arbor carbon density,thereby reducing the source of litter and litter carbon density.Two-factor analysis of variance showed that both forest fire disturbance intensity and forest type had significant effects on litter carbon density.Forest fire disturbance intensity explained 38.73%of litter carbon density variation,and forest type explained 50.97%of litter carbon density variation.4)The reduces of soil organic carbon density and labile organic carbon content by the forest fire disturbanceForest fire disturbance reduced the density of soil organic carbon density,and it decreased with forest fire disturbance intensity,and the decrease rate gradually reduced with soil profile depth.Soil labile organic carbon content showed a downward trend under the different intensity of forest fire disturbance.Light forest fire disturbance only significantly reduced the soil organic carbon density in the surface layer(0-20cm),but it did not cause significant changes in the soil organic carbon density in the layer(0-100cm).Its impact on soil organic carbon density was not significant(P>0.05).Moderate and high forest fire disturbance significantly reduced the soil organic carbon density in the surface layer and shallow layer(20-40cm),which led to significant changes in soil organic carbon density in the layer(0-100cm).Hence they significantly affected soil organic carbon density(P<0.05).The components of labile organic carbon content varied along with the decline of the soil profile with the forest fire disturbance intensity.The decline of soil labile component by high forest fire disturbance was the most drastic.Under the high forest fire disturbance,the decrease of soil liable organic carbon components in surface soil was obvious,and it was less obvious in the shallow soil layer.Nevertheless,it slowly declined in the deeper layer of 40-100 cm.Forest fire disturbance had an effect on fine root biomass of all forest types,but light forest fire disturbance only significantly affected fine root biomass in surface soil(P<0.05),while the moderate and high forest fire disturbance significantly reduced the biomass of fine root in surface and shallow soil(P<0.05).Multivariate analysis of variance showed that the intensity of forest fire disturbance,forest type,and soil depth had significant effects on soil organic carbon density.The interaction between forest fire disturbance intensity and soil depth,along with the interaction between forest type and soil depth played a significant role in soil organic carbon density.Forest fire interference intensity explained 8.78%of soil organic carbon density variation.Forest type explained 5.41%of soil organic carbon density variation.Soil layer depth explained 70.29%of soil organic carbon density variation.The interaction between forest fire disturbance intensity and soil layer depth explained 8.16%of the variation in soil organic carbon density.The interaction between forest type and soil layer depth explained 2.68%of the variation in soil organic carbon density.5)Significant effect of forest fire disturbance on the spatial distribution pattern of ecosystem carbon poolsForest fire disturbance effectively changed the spatial distribution pattern of ecosystem carbon pools.In other words,due to forest fire disturbance,the aboveground(vegetation)and surface(litter)carbon pools of the ecosystem decreased more than the underground(soil organic carbon)carbon pools.The proportion of aboveground and surface carbon pools decreased,while the proportion of underground soil organic carbon pools increased.Soil organic carbon pools in the control plots of Pinus massoniana forest,Cunninghamia lanceolata forest,Eucalyptus robusta forest,and Schima superba forest were 56.51%,61.15%,58.58%,and 61.59%,respectively.Their soil organic carbon pool proportions increased after high forest fire disturbance trends,accounting for 82.97%,78.49%,81.11%,and 70.96%which occupied the dominant position of ecosystem carbon stocks.However,the proportion of vegetation and litter carbon pools declined,and they were in the secondary position of the ecosystem carbon pool.6)The influence mechanism of forest fire disturbance on carbon pool of forest ecosystemForest fire disturbance consumed a large amount of vegetation carbon pool,changed the structure and composition of vegetation and its community,affected the development and growth of vegetation,and regulated the inter-vegetative mechanism,thereby regulating the litter and fine root biomass,and influencing soil organic carbon pool.In addition,forest fire disturbance impacted the net primary productivity of the ecosystem,thereby reducing the sequestration of carbon by the forest ecosystem.Consequently,it led to a reduction in the ecosystem’s carbon pool.Light forest fire disturbance only significantly reduced the litter carbon density and soil surface organic carbon density and fine root biomass,while it did not significantly impact vegetation carbon density.However,because the vegetation carbon density accounted for a large proportion,the effect of light forest fire disturbance on the carbon density of forest ecosystems was not significant.The moderate and high forest fire disturbances not only significantly reduced the organic carbon density and fine root biomass in surface and shallow soil but also significantly reduced the carbon density of vegetation and litter,thus they significantly impacted the forest ecosystem carbon density.In summary,moderate and high forest fire disturbances have a significant impact on the carbon pool of the subtropical forest ecosystem in Guangdong,while light forest fire disturbances have no significant impact on the ecosystem carbon pool.Given moderate and high intensity of forest fire disturbance were likely to cause a large loss of carbon pool of forest ecosystem and environmental pollution,the impact of moderate and high forest fire disturbance on ecosystem carbon pool should be minimized in order to effectively improve the carbon sink effect of forest ecosystems and maintain the carbon balance of the ecosystem.The application of light forest fire disturbance was suggested for forest management and forest fire management.This measure could reduce carbon emission and increase the forest ecosystem carbon pool.At the same time,the research showed that the carbon loss in Schima superba forest ecosystem was the least under the different intensity of forest fire disturbance.Therefore,in order to improve the carbon sink effect of forests,it should be advocated to plant Schima superba forest as an important forest fire prevention arbor species in South China to achieve the sustainable development of forestry. |
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