Decomposition Process Of Larix Gmelinii Coarse Woody Debris(CWD) On Burned Patches In The Greater Khingan Mountains

The decomposition of coarse woody debris(CWD)affects the energy flow and nutrient cycling of forest ecosystems,and maintains the integrity of the structure and function of forest ecosystem,and is an important part of material circulation of land ecosystem.However,due to the slow CWD decomposition process,the cycle of carbon,nitrogen and other substances is often ignored.Previous studies on CWD mainly focused on the input,decomposition,reserve dynamics,and CWD functions,and the results of studies from different regions vary greatly due to the influence of factors such as geographic location,forest type,and succession stage.Wildfires occur frequently in boreal forests and large volumes of coarse woody debris are produced.Quantifying the conversion and decomposition of this material is necessary to clarify the role of boreal forests in carbon cycling.The CWD decomposition process is slow,among which the contribution rate to carbon cycle and the response to environmental changes are still unclear.This paper takes the Greater Khingan Mountains region of China as the study region,and takes zonal vegetation Larix gmelinii in this region as the research object.Combines forest fire combustion with CWD decomposition process after disturbance.Based on quadrat investigation and laboratory experiment,combined with single exponential decay model,the decomposition process of CWD after forest fire was statistically analyzed by using Space-fortime substitution method,and the characteristics of the decomposition process of CWD in Larix gmelinii forest in 33 years after fire disturbance were revealed.Based on quadrat investigation and Fire_CCI 5.1 burned area data,the total amount of CWD caused by fire disturbance in this study area from 2001 to 2019 was estimated.The purpose of this study is to answer what factors affect CWD decomposition process and what is the contribution rate? The following conclusions are drawn.(1)The annual average decomposition rate was 0.019 and the average 50% and 95%mass loss will take approximately 41(19-81)years and 176(81-350)years,respectively.The decomposition rate was higher than that of tree species in high northern latitudes.Because of the short chronosequence,the decomposition rate of coarse woody debris of Larix gmelinii was overestimated.(2)The rate of decomposition increased with decay class.In the lower decay classes,structural components affected decomposition rate,and in the higher decay classes,Water content of the debris had a strong influence on decomposition.Although nitrogen was a small proportion of the debris(0.093%–0.197%),it had a significant influence on rate of decomposition.As a part of the decomposition rate,each index can explain about 42% of the variance.(3)ANOVA results showed that the debris rapidly released nutrients in the early stages of decomposition.Nitrogen gradually accumulated and water contents increased rapidly in the later stages of decomposition with the loss of structural components.C/N and lignin/N ratios were indicators of decomposition rate but they were not sufficient to distinguish decay classes.decomposition.(4)From 2001 to 2019,the forest burning area in the study area decreased year by year,and fluctuated slightly between different years.Spring and autumn are the high incidence periods of forest fires,with the largest fire interference area and wide distribution in spring,and most of the fire interference in autumn is concentrated in the northeast of the study area.Fire_CCI5.1 may overestimate burning area.With Landsat results as a reference,the accuracy of Fire_CCI5.1 is 69.16%(5)According to the data of Fire_CCI5.1,the reserves of CWD and forest carbon reserves were estimated.from 2001 to 2019,the total burned area in the study area was14907.28km2,and the accumulated input CWD mass was 122.97 Tg,of which the carbon mass was 59.95 Tg,and the nitrogen mass was 0.13 Tg.The reserve of CWD in the study area is80.49t/hm2;The carbon storage is 40.21 t/hm2,and nitrogen storage is 84.14kg/hm2.The reserve of CWD in the study area is higher than that in most forest ecosystems(0.2-177.6t/hm2),which is related to frequent fire disturbance.The CWD decomposition process is complex and slow,and it is critical to understand it on a larger space-time scale,more research is needed to calculate decomposition rates accurately and to analyze environmental factors that affect the decomposition process.Combining remote sensing data,quadrat investigation data,forest fire statistics data and other multi-source data to study the carbon release in CWD decomposition process after forest fire disturbance can not only give full play to the advantages of accurate spatial positioning of remote sensing data and reliable model inversion accuracy,but also reflect the quantitative accuracy of carbon storage estimated by quadrat investigation,which is the development direction of CWD research in the future.