Dynamics Of Deadwoods Carbon Storage In Jilin Province

Deadwoods carbon is one of the five major carbon pool of forest ecosystems,which plays an important role in promoting ecosystem energy flow,carbon sequestration,forest succession,maintaining forest species diversity,and balancing the global carbon cycle.Based on the national forest resource inventory(NFI)data at intervals of 5 years from 1994 to 2014,compatible tree biomass equations with each component,which were grouped by species and decay classes,and carbon fractions of above-ground and below-ground part are used to estimate the dynamics of deadwoods carbon storage in Jilin Province and to explore the changes in deadwoods composition and distribution patterns of age groups during the 20-years.Meanwhile,the effect of deadwood species,stand types,and age groups on the deadwoods carbon storage was comprehensively and comparatively analyzed for each inventory,and the relationship between the deadwood carbon storage and the volume of standing trees under different forest types were explored at plot level.Conversion factors from the volume of standing trees to deadwoods carbon strorage were obtained by establishing the volume-derived deadwood carbon storage model and compared by stand type.Besides,dynamic equations of logs was constructed based on the decay rate k and the logs storage given by dynamic equations were compared to that given by biomass equations.The results shows that taking stumps into account,the newly-added deadwoods carbon storage in arbor forests in Jilin province rose slowly at a rate of 0.07 t/hm2,adding a total of 69959.42 Gg.On average,deadwoods accounted for 2.76% of the carbon storage of arbor forests,and its carbon density was 1.83 ± 0.11 t/hm2.The number of broad-leaved deadwoods was higher than that of coniferous deadwoods,but the proportion of broad-leaved deadwoods was decreasing.Many coniferous deadwoods did not appear in previous inventories but appeared in small quantities later.A.fabri,L.gmelinii,Quercus,Betula,Populus and T.tuan were the main tree species of deadwoods.Snags accounted for the largest proportion of deadwoods carbon(47.21%)and were relatively stable at different times.The carbon of stumps(39.38%)decreased with the decline of annual cutting.Logs accounted for the lowest proportion(13.41%),but consecutively rising.There was a significant difference of deadwoods carbon under different forest origin,while their absolute storage are constantly rising.The carbon of natural forests accounted for more than 90% of deadwoods carbon in the province,but over the 20 years,the deadwoods carbon in plantations rose faster than that in natural forests.Under different forest type,broad-leaved mixed forests contributed the largest proportion of deadwoods carbon storage(38%-55%).Among the broad-leaved trees,Quercus contributed the most to deadwood pool,accounting for more than 10% of the total in each inventory,followed by Betula(4%),Populus(3%)and T.tuan(2%).L.gmelinii contributed the most in coniferous species,accounting for more than 3% of the total in each inventory,followed by A.fabri.Other dead pines carbon reserved were less than 1% in most cases.In the distribution pattern of age groups,young stands accounted for the lowest carbon storage proportion while mature forests had the highest on average.Compared to previous inventories,the carbon storage of each age group basically had different degrees of increase.The sharp increase of the near-mature forest in the third inventory(2004)resulted in a change in the distribution pattern of age groups,from the highest proportion of mature forests to the highest proportion of near-mature forests.The conversion factors under six main forest types given by the volume-derived deadwood carbon storage model are: L.gmelinii(0.0126),Quercus(0.0141),Betula(0.0196),T.tuan(0.0187),Populus(0.0293),broad-leaved mixed forest(0.0217)and coniferous and broad-leaved mixed forest(0.0222).The conversion factor of natural mixed forests is greater than that of broad-leaved forests,while that of broad-leaved forests is greater than that of coniferous forests.In different inventories,the conversion factor of coniferous forests represented by L.gmelinii forests were more stable than broad-leaved forests,which remained almost constant during 20 years.The conversion factor of broad-leaved forests showed a curve of decreasing first and then increasing,which could be partially explained by the synthetic action of the the dynamics of the proportion of deadwoods with different cause of death.The balance storage of P.asperata,A.fabri,T.amurensis and P.koraiensis given by the dynamic equations of logs are 0.43 t/hm2,0.38 t/hm2,0.15 t/hm2 and 0.11 t/hm2.The time to reach the balance storage are approximately 300,250,150 and 200 yr,respectively.There are differences between the two estimation methods based on biomass equations and dynamic equations of logs and the former is lower than the latter.Combining the fixed plot inventory data and decay class to estimate deadwood carbon pool at the regional scale is more representative and could reduce estimation error to a large extent.The deadwoods carbon storage in the Jilin province have basically grown during this 20-years,but the absolute storage is very low.Most of the deaths come from forest competition and there exists a heavily deficiency of medium-and large-diameter logs in inventory plots.Excessively low deadwood reserves may adversely affect forest health.