| Forest,as the main subject of terrestrial ecosystem,plays an important role on global carbon cycle.How to estimate the carbon storage in forest ecosystems on regional or national scales accurately has been becoming a research emphasis of global climate change.Based on the vegetation inventory data(1983-1987 to 2009)in Hunan province and associated investigation data of 6605 pieces of fixed sites in Huitong ecological station,we estimated carbon storage,dynamics and spatial distribution of forest ecosystems in different investigation periods in Hunan province.Besides,we assessed the current states of carbon storage and influence factors.Furthermore,we assessed the carbon sequestration potential of existing forest vegetation in Hunan.This study would help to accurately evaluate status of forest ecosystem in Hunan province,and provide basic data and scientific foundation for carbon circulation in forest ecosystem.The main results of the research are listed as follows:(1)Carbon concentrations(gC/g)of organs in conifer trees,evergreen broad-leaved trees,deciduous broad-leaved trees,Phyllostachy edulis plantation and shrub were 0.491?0.566,0.421?0.549,0.449?0.550,0.470?0.496 and 0.463?0.505,and averaged 0.519,0.501,0.495,0.486 and 0.484 gC/g,respectively.The mean value of carbon concentration was 0.504gC/g in different organs of main species in Hunan province.Differences of carbon content of organs within one species were not significant.The order of carbon concentrations of different organs was not exactly the same.Generally,Carbon concentration in trunk was higher than that of other organs.And the mean value of aboveground parts was higher than that of belowground parts for most of investigated species.There were significant differences among carbon concentration in the same organs with same species in different provinces.(2)The average carbon storage of vegetation in forest stand was 66.40×10~6 tC during the period of investigation from 1983-1987 to 2009 in Hunan,,account for 4.31%of national stand vegetation.Carbon density increased by 5.65 tC/hm~2 and forests in Hunan served as carbon sink.Among them,the broad-leaved forest was the highest(48.43×10~6tC),and followed by Chinese fir plantations(9.54×10~6tC)and then pine forest(6.68×10~6tC),although the caron density of different stands vegetation fluctuated dramatically.At different stand ages,the young forest,middle-aged forest,near mature forest and' mature forest presented as carbon sink.Among them,carbon sink of middle-aged forest performed best.The carbon density of forest vegetation increased by 4.75,4.09 and 0.83 tC/hm~2 in young,middle-aged and near mature forest,respectively,while the carbon density decreased by 6.87 and 13.88 tC/hm~2 in mature and over-mature forest.Carbon sink of forest vegetation in plantation and natural forest was 41.01×10~6 and 25.39×10~6 tC.In contrast to plantation,the percentage of carbon storage in natural forest vegetation declined in Hunan province.Carbon density of plantation and natural forest vegetation increased by 4.91 and 7.19 tC/hm~2,respectively,the results indicated that forest stands,in recent years,had rapidly recovered in Hunan and carbon storage had increased,and effects of carbon sink had been obvious,which is mainly contributed to Carbon sink function of broad-leaved forest.Quantity of different stands had obvious fluctuation.Mature and over-mature forest had been seriously damaged.Carbon sink function of young and middle-aged forest had gradually played a leading role.Carbon storage of natural forest occupied an important position.Carbon sink function of plantation had gradually increased.Carbon storage of existing forest vegetation(including open forest)in Hunan(2009)was 180.53×10~6tC.And the storage of stand vegetation was the highest,accounting for 63.45%of carbon storage in the whole forest vegetation.Carbon storage of Phyllostachy edulis plantation vegetation was the second,accounting for 21.11%,and was lowest in open forest,accounting for 0.32%.Carbon density of different forests vegetation showed significant differences.The difference was highest in Phyllostachy edulis plantation(48.95 tC/hm~2),followed by forest stands(15.66 tC/hm~2),lowest in open forest(5.56 tC/hm~2).From 1983-1987 to 2009,carbon sink of whole forest vegetation(including open forest)was 84.87×10~6tC,and was highest in forest stands,accounting for 78.24%in the whole forest vegetation.Carbon sink of Phyllostachy edulis plantation and shrub accounted for 28.27×10~6 tC and 2.03×10~6 tC,contributing to 33.31%and 2.39%of whole forest vegetation in Hunan.Carbon sink of economic and open forest declined 8.50×10~6 and 3.33×10~6 tC.Carbon density of forest vegetation rose constantly,with increasing 6.24tC/hm~2.Carbon storage of different forest vegetation changed with forest area.As a whole,Forest stands played a leading role in carbon sink function of forest vegetation in Hunan.(3)From 1983-1987 to 2009,the spatial distribution pattern of carbon storage of stand vegetation presented as:The carbon storage was highest in southwest and south part of Hunan,followed in northwest and east Hunan,and the lowest in middle and north Hunan.Spatial variation of carbon sink of stand vegetation was coincident with that of stands area,referred as rapidly increasing in south,southwest Hunan,Changde and Changsha,slowly increasing in middle Hunan.Spatial variation of carbon density of stand vegetation presented as:the density rapidly increasing in middle Hunan,slowly increasing in northwest,southwest Hunan,Changde and Zhuzhou.Carbon storage of stand vegetation in states had very significant correlations with stand area and carbon density,and closely related with stand area component proportion and differences of carbon density of each stand.Carbon storage of stand vegetation in Chinese fir plantation,pine and broad-leaved forest contributed much to the storage of each state.Spatial variability of carbon storage in three types of stands was obvious.But spatial variation pattern of the storage was relatively stable.Stand vegetation of each state acted as carbon sink.Carbon sink function of different stand vegetation in the same state had obvious differences.Spatial variation pattern of carbon storage of different age classes presented as:the storage in southwest,south,northwest Hunan was higher than that in middle,east and north Hunan.Spatial variability of young and middle-age forest was obvious.Middle-age,near mature and mature forest in each state(except in Changde)acted as carbon sink.Carbon sink of each age class was significantly correlated with area variation,and was not significantly correlated with carbon density of each age class.Carbon density of stand vegetation of same age class had obvious differences in different states,and the difference increased with age class.Spatial variation pattern of carbon density of stand vegetation of each age class was different.Spatial distribution pattern of carbon storage of plantation vegetation did not change.Plantation area,carbon storage of vegetation and carbon density of each state increased.And spatial variation pattern of carbon storage and its area was basically coincident,but the pattern of carbon density was different.The pattern of carbon storage of natural forest vegetation was quite similar with that of plantation.Carbon sink of plantation was higher than natural forest in states(except Southern Hunan Autonomous Prefecture,Zhangjiajie and Changde).Carbon sink of plantation and natural forest had significant positive correlations with area variation in each state,and did not correlated with carbon density.This indicated that carbon sink of plantation and natural forest mainly attributed to increased forest area.In three survey periods,spatial distribution patterns of carbon storage of forest vegetation were basically the same.Forest in each state acted as carbon sink.Among them,carbon sink in Yongzhou was highest.Spatial variation of carbon density of forest vegetation declined,but it was still higher in southwest Hunan,and lower in middle-east Hunan from 2003 to 2004.From 1983-1987 to 2003-2004,carbon density increased on different levels in each state,except Huaihua.(4)The carbon sequestration potential of existing forest vegetation in Hunan was 331.43×10~6 tC.And the order presented as:young forest(157.78×10~6 tC)>middle-aged forest(132.09×10~6 tC)>near mature forest(41.56×10~6 tC).The carbon sequestration potential of immature forest was significantly different among different stand types.And the potential was the highest in broad-leaved forest,followed Chinese fir plantation and pine forest.The potential of immature forest of each state was between 5.86×10~6 to 69.1×10~6tC.and showed significant variations.Existing immature forest in Hunan was growing from 2014 to 2025,and carbon sequestration ability would increase to 54.76×10~6 tC,and carbon sequestration potential of middle-aged forest was highest,the potential of different states had larger differences.When existing immature forest grew up to mature forest,forest could sequestrate carbon 110.47×10~6tC.Carbon sequestration potential was highest when young forest grew up to mature forest.(5)Average content of soil organic carbon of main forests in Hunan was between 9.53 to 22.86 g/kg in 0-80 cm soil layer from 2000 to 2014.Contents of shrub,Phyllostachy edulis plantation and broad-leaved forest were higher than other forest types.Contents of different forest types declined with soil depth,and variation of that occurred in the surface soil(0-40cm).Organic carbon density in 0-80cm was 95.44?181.30tC/hm~2,averaged as 140.75tC/hm~2.The value distributed mainly in soil depth of 0-40 cm,and decreased as soil depth increased.Effects of forest types gradually declined.From 1983-1987 to 2009,organic carbon storage of arbor forest soil(0-80cm)increased by 417.63×10~6t,area weighted average of organic carbon increased by 11.27tC/hm~2.Differences of organic carbon storage of different arbor forest soil(0-80cm)increased over time,and the difference mainly distributed in Chinese fir plantation,pine forest and broad-leaved forest.Soil organic carbon storage of each age class presented different variation trends.The proportion of soil organic carbon storage of young forest to the storage of same period declined,and the proportion of middle-aged and near mature forest increased.Proportion of mature forest had little variation,and proportion of over-matured forest decreased.Organic carbon density of young forest and middle-aged forest increased.Densities of near mature,mature and over-mature forest decreased.Natural forest was the main contributor to soil organic carbon storage in Hunan.The storage of plantation increased gradually.The storage of economic forest,bush forest and Phyllostachy edulis plantation had different contributions and dynamic variations.Variation of forest soil organic carbon storage was closely correlated with area of different forest types.In three survey periods,spatial distribution pattern of forest soil organic carbon storage presented as:the storage was the highest in southwest and south Hunan,lowest in northwest,east,middle and north Hunan.The pattern was basically the same with spatial distribution pattern of stand area.Soil organic carbon storage of each state increased with time process.Stand soil of each state all acted as carbon sank,and had correlations with stand area of each state.Spatial variation pattern of stand soil organic carbon density did not change much,and the variation was caused by differences of area composition proportion of stand types of each state.Soil organic carbon density of each state increased except Hengyang and Xiangtan.With the limitation of stand area,each state can increase soil organic carbon storage and density,by adjusting area composition proportion of stand types,increasing the stand area with higher soil organic carbon density.Spatial distribution pattern of forest soil organic carbon storage in Hunan was basically same with the pattern of stand soil organic carbon.Forest soil organic carbon storage increased with increased forest area.(6)Carbon storage of existing(2009)forest(include open forest)ecosystem in Hunan was 1767.70×10~6tC.Soil organic carbon storage was 8.79 times than the storage of vegetation.Carbon storage was highest(1174.92×10~6tC)in arbor forest ecosystem,and lowest in open forest ecosystem.Average carbon density of existing forest ecosystem was 163.94 tC/hm~2,and highest in Phyllostachy edulis plantation(202.96 tC/hm~2),followed in bush forest(190.86 tC/hm~2),and then in arbor forest(160.64 tC/hm~2),the lowest in economic forest(138.27 tC/hm~2).In arbor forest ecosystem,carbon storage in broad-leaved forest ecosystem was highest(598.12×10~6tC),followed in Chinese fir plantation and pine forest.Carbon density in broad-leaved forest ecosystem was highest(193.96 tC/hm~2),lowest in slash pine forest(98.85 tC/hm~2),lower in Chinese fir plantation,pine forest,poplar forest and eucalyptus forest.Carbon sink in broad-leaved forest ecosystem was highest(440.19×10~6tC),second in Chinese fir plantation(44.66×10~6tC).Carbon sink in pine forest decreased 45.28×10~6 tC.Carbon density in pine forest ecosystem greatly increased,and increased in Chinese fir plantation,but decreased in broad-leaved forest.From 1983-1987 to 2009,carbon sink in forest ecosystem(including open forest)in Hunan was 413.77×10~6 tC,carbon density increased 15.28 tC/hm~2.In arbor forest ecosystem,carbon sink was highest(484.03×10~6 tC),carbon density increased 16.92 tC/hm~2.In Phyllostachy edulis forest ecosystem,carbon sink was 20.87×10~6 tC,carbon density increased 31.69 tC/hm.Carbon sink was 2.03×10~6 tC in bush forest ecosystem,and decreased in economic and open forest ecosystem.Either in arbor forest ecosystem or in economic,Phyllostachy edulis and bush forest ecosystem,spatial distribution pattern of carbon storage changed little,and was coincident with the area pattern of the same period.The pattern of carbon density in arbor,Phyllostachy edulis and open forest ecosystem basically did not change.These results indicated that,the total carbon storage in forest ecosystem,in vegetation and in soil as well were closely correlated with forest area and area composition proportion in Hunan.Forest area and its area composition proportion varied with the guiding of forestry policies and the need of human production activity.For example,deforestation would turn timber protection forest with large area into economic forest.Forest was used for development activities of industry,agriculture and commercial.In past 20 years,large-scale artificial afforestation activities increased forest area dramatically and changed its area composition proportion.Consequently,the carbon storage of regional forest ecosystem and its component was directly or indirectly affected by human activities.Therefore,the carbon sequestration potential of forest ecosystems could be improved substantially in Hunan by afforestation and closed forest,with expanding stand area,increasing broad-leaved forest area and adjusting forest area composition proportion. |
PDF Full Text Request