| Global warming has been a common challenge faced by all countries in the world.The increasing the concentration of carbon dioxide is the main cause of global warming.The role of forest as terrestrial sinks of atmospheric carbon dioxide has received increasing attention since the late 1990s.Assessment of forest carbon stock,and studying the spatial pattern and driving factors of forest carbon density in regional forests could improve our knowledge of terrestrial forest ecosystem carbon and should be helpful to the implementation of the forest management activities,in order to mitigate the climate change effectively.It has been one of the hotspots of the forest carbon cycle studies.Mountain forest is an important part of the world's forests,accounting for 24.3%of the total area of all the forests around the world.Shanxi Province is located in the eastern part of the Loess Plateau in China,with mountains and hills accounting for 80.3%of the province's land area.The forest in Shanxi,especially the natural forest,was nearly distributed in the mountainous areas.It provided ideal natural geographical conditions for us to study the biomass carbon stock,and the spatial pattern and the driving factors of the biomass carbon density in mountain forest.Based on the forest inventory data of 2010 and2015 in Shanxi Province,the forest carbon stock and carbon density were estimated by using the variable BEF?biomass expansion factor?,the spatial patterns of biomass carbon density were analyzed using Anselin Local Moran's I,Local Getis-Ord G*and semivariogram analyses,and the driving factors of carbon density.were explored by using multi-group structural equation modeling.The main results were as follows:The total amount of forest biomass carbon stock in Shanxi was 88.00Tg,and the average carbon density was 19.95 Mg·hm-2,substantially lower than the average forest biomass carbon density of China as whole(44.91 Mg·hm-2).The plots which had the biomass carbon density of larger than 30 Mg·hm-2 were mainly distributed in Mian-Huo Mountains in the southwest Taiyue Mountains,and Luya Mountain,Guandi Mountain and Zijing-Wulu Mountains of the Lüliang Mountains.For the arbor forests,the carbon stock for Pinus tabulaefomis forest?15.51 Tg?and Quercus forest?18.15 Tg?was higher than that for other forest types.The carbon density varied greatly among forest types.Picea forest had the highest carbon density(92.35 Mg·hm-2),followed by Larix forest(38.56 Mg·hm-2),Quercus forest(36.37 Mg·hm-2),Betula forest(31.35 Mg·hm-2)and Pinus tabulaefomis forest(25.77Mg·hm-2).?4?The half-mature forest had the largest carbon stock?26.22 Tg?,followed by near-mature and young forests?20.29 and 15.56 Tg,respectively?.The percentage of carbon stock for the young and near-mature forests?22.3%and 29.0%,respectively?in Shanxi was larger than that in China as a whole.The carbon density was the highest for the near-mature forest(41.56 Mg·hm-2),with the half-mature forest(32.94Mg·hm-2)and mature forest(36.67 Mg·hm-2)being higher than young forest(17.16Mg·hm-2)and over-mature forest(15.72 Mg·hm-2).The plots of the young and half-mature forests accounted for 69.01%of the total tree-dominated forest plots,and this indicated that the forest carbon stock in Shanxi province would increase continuously in the future.We collected the data of 878 natural mountainous forest plots of the forest resource inventory data in Shanxi province to explore the spatial patterns and the influencing factors of the biomass carbon density for the natural coniferous forests and the natural deciduous broad-leaved forests.The results showed that the mean biomass carbon density for the natural forests in temperate mountainous areas of Shanxi was 31.53 Mg·hm-2,with no significant difference between the coniferous forests and the deciduous broad-leaved forests.The coefficient of variation of biomass carbon densities was obviously larger in coniferous forest than in deciduous broad-leaved forests.Compared with the deciduous broad-leaved forests,hot spots at the 1%significance level?HS99s?,which have the highest average biomass carbon density of 47.86 Mg·hm-2,for the coniferous forests were distributed in the areas with higher average latitude,higher average elevation,lower mean temperature and lower mean precipitation.These factors,including latitude,elevation,temperature,precipitation,stand age,coverage and forest type,could explain 62.0%of the variation in biomass carbon density for coniferous forests and 51.6%for deciduous broad-leaved forests.The effect of latitude and elevation for the coniferous forests was obviously larger than that for the deciduous broad-leaved forests.Meanwhile,the effect of stand age and coverage showed no differences between the coniferous forests and the deciduous broad-leaved forests.The effect of forest type was greater for the coniferous forests than for the deciduous broad-leaved forests,probably because biomass carbon densities varied more greatly in different forest types of coniferous forests than deciduous broad-leaved forests.Climatic factors including temperature and precipitation had weaker effects on biomass carbon density than other factors in temperate mountainous areas on provincial scale in our study.The areas of the planted forests accounted for 34.86%of that of all the arbor forests in Shanxi Province,and the carbon stock of the planted forests accounted for 33.45%of the total carbon stock of all the forests.The average stand age of the planted forests was 25years,and the annual average stand volume growth was 0.41 m3·hm-2·yr-1.The main forest types included Pinus tabuliformis forests,Larix principis-rupprechtii forests,Robinia pseudoacacia forests,Populus simonii and Platycladus orientalis forests,accounting for74.18%of the total area of the planted forests.The average biomass carbon density of the planted forests was 23.13Mg·hm-2.For the main types of the planted forests,Larix principis-rupprechtii forests had the largest biomass carbon density,followed by Pinus tabuliformis forests,Robinia pseudoacacia forests and Populus simonii,Platycladus orientalis forests.The areas of young and middle-aged forests accounted for 73.55%of the total area of the planted forests,and the carbon stock of them accounted for 70.72%of the total carbon stock of the planted forests.The effects of the driving factors of the biomass carbon density of the planted forests decreased in the order:stand density>precipitation>elevation>stand age.The factors influencing the biomass carbon density showed much great differences among different forest types.The multiple regression model had better explained the variation of biomass carbon density for each forest type except for Populus simonii forests than for all the planted forests.The result of the hot spots analysis?Getis-ord G*?showed that the biomass carbon densities of 80%of the planted forest plots were randomly distributed in space.We collected the data of 508 coniferous forest plots of the forest resource inventory data in 2015 in Shanxi province to analyzed the spatial pattern and driving factors of biomass carbon density for natural coniferous forests and planted coniferous forests.The results of spatial pattern of biomass carbon densities for natural forests showed that the biomass carbon density was generally higher in the north but lower in the south of Shanxi.The spatial pattern for planted forests was substantially different from that for natural forests.The results of multi-group SEM suggested that elevation?or temperature as the alternative factor of elevation?and stand age were important driving factors of biomass carbon density for these two forest types.Compared with other factors,the effects of latitude and elevation on biomass carbon density showed much greater difference between these two forest types.The difference in indirect effect of latitude?mainly through affecting elevation and stand age?between natural and planted forests was to some extent a reflection of the difference between the spatial patterns of biomass carbon densities for natural and planted forests in Shanxi. |
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