| Chinese pine(Pinus tabulaeformis Carr.)plantations are the main forest type in Beijing mountain area and even in North China.They played decisive role in reducing carbon in the air and in improving the ecological environment of Beijing.Thinning is an important method to optimize the structure of plantations and to improve the capacity of carbon sequestration.Therefore,exploring the effect of thinning on the carbon sequestration of Pinus tabulaeformis plantations is great vital importance to improve the carbon sequestration ability of Pinus tabulaeformis plantations and to promote its sustainable management.In this paper,Pinus tabulaeformis plantations with 30-35 years old in the northern mountain areas of Beijing were selected to research.In 2002,a thinning trial initiated in these Pinus tabulaeformis plantations and produced 12 momument-sample plots.The trial created four series of thinning intensity as followed:the control(CK),mild thinning(I),moderate thinning(II)and intensity thinning(?).We surveyed the 12 monument-sample plots in 2002 and 2012,and we surveyed 17 cutting trees in 2012 for establishing of biomass equation.Based on situ sample survey,this study quantitative analiedthe law of thinning on the yield of wood and on the carbon sequestration by the effects of thinning on tree growth,carbon storage and carbon sequestration rate of Pinus tabulaeformis plantations from forest carbon sequestration aspect.The principal component analysis(PCA)was employed to better unravel optimized thinning intensity and to quantitatively reveal the tree growth,forest carbon storage and carbon sequestration,and the comprehensive effects of forest carbon sequestration.And the response of Pinus tabulaeformis seedlings to different environmental factors was analyzed by the control experiment to reveal the physiological mechanism of the response effect on forest carbon sequestration to different thinning intensity.The main results and conclusions are as follows:(1)Thinning can significantly promote the growth of DBH,crown width and average single tree volume of Pinus tabulaeformis plantations,and the effect positively correlated with the thinning intensity,so the results of ? thinning was best.After 10a thinning,the average DBH,crown and average single tree volume growth under ? thinning were 2.9 times,1.2 times and 2.0 times of the control plots Compared with the control,the thinning reduced the per unit area volume,and with the increase of thinning intensity,the per unit area volume decreased gradually,so the growth of the per unit area volume under ? intensity was the lowest,which was only 59.65%of the control plot.About forest tree diameter distribution,the ?thinning forest was more typical than the other thinning forest,the average DBH of the trees was significantly higher than that of the control,and it had the 22cm and 23cm diameter trees which were not found in the control.The order of the annual growth of forest tree ring was ?thinning forest>? thinning forest>CK thinning forest>? thinning forest,and the law of the annual growth of forest tree ring changed as time was not obvious,but fluctuating.(2)The effect of thinning on the change of carbon storage in average single tree and tree layer of Pinus tabulaeformis plantations was significant,and the carbon storage of those under ? thinning were the highest,the total carbon storage of average single tree and tree layer increased by 80.32%and 47.15%than the contral plots.The distribution of carbon storage in the tree layer of Pinus tabulaeformis plantations was also affected by thinning,which was mainly reflected in the reduction of the proportion of stem carbon storage and the increase ratio of branches carbon storage.There was no significant effect of thinning on the shrub layer and soil carbon storage of Pinus tabulaeformis plantations,but the carbon storage of litter layer was decreased by thinning.Compared with the control,I thinning intensity increased the total carbon storage of Pinus tabulaeformis forest ecosystem,but there was no significant difference between the ? intensity and ? intensity plots with the control.The annual carbon storage of tree layer in Pinus tabulaeformis plantations showed an increasing trend,and with the increase of thinning intensity,the difference of annual carbon storage with different thinning intensities was increasing,I thinning forest had the highest annual carbon storage,IIIthinning forest had the lowest annual carbon storage.(3)After thinning,the effect of I thinning on the increase of carbon sequestration rate of the average single tree and tree layer of Pinus tabulaeformis plantations was significant,and it's carbon sequestration rate of the average single tree and the forest tree layer of Pinus tabulaeformis plantations were 1.52 and 1.57 times that of the contral.The thinning had no significant effect on the carbon sequestration rate of understory layer,but it could accelerate the decomposition of litter and the input of soil organic carbon.Thinning reduced the proportion of the litter layer carbon storage growthment to the total carbon storage growthment in Pinus tabulaeformis plantation ecosystem from 34.05%(CK)to 21.26%(?),26.06%(?)and 28.11%(?),while thinning increased the proportion of soil layer carbon storage growthment to the total carbon storage growthment from 21.19%(CK)to 32.13%(?),35.12%(?)and 34.09%(?).I thinning was also effective in improving the carbon sequestration rate of Pinus tabulaeformis plantation ecosystem,which increased the carbon sequestration rate of I Pinus tabulaeformis plantation ecosystem by 44.23%compared with the control.The annual increase of carbon storage in the tree layer of Pinus tabulaeformis plantations showed an increasing trend,and the difference between the different thinning intensity forests was increasing.I thinning forest had the highest annual increase of carbon storage.(4)Through the principal component analysis,the evaluation system of thinning intensity effect on forest carbon sequestration of Pinus tabulaeformis plantations was constructed.The comprehensive and quantitative evaluation of thinning effects on forest carbon sequestration showed from the system.The mild thinning intensity(I)was the best of comprehensive evaluation for forest growth of Pinus tabulaeformis plantations.The mild thinning intensity(I)was the best of comprehensive evaluation for forest carbon storage of Pinus tabulaeformis plantations,as the forest ecosystem total carbon atorage was 25.43%higher than that of the control,the total carbon storage of the tree layer was 47.15%higher than that of the control.The thinning had no significant effect on the carbon storage of the shrub and grass layer and the soil layer,but decreased the carbon storage of the litter layer.(5)The mild thinning intensity(I)was the best of comprehensive evaluation for forest carbon sequestration rate of Pinus tabulaeformis plantations,as the carbon sequestration rate of the forest ecosystem was 44.23%higher than that of the control,the carbon sequestration rate of the tree layer was 1.57 times that of the control.There was no significant effect of thinning on the carbon sequestration rate of understory shrub and grass layer,but it could accelerate the decomposition of litter layer and the input of soil organic carbon.Which resulted in the proportion of the litter layer carbon storage increment to the forest ecosystem total carbon saorage increment decreased from 34.05%(CK)to 21.26%(?),26.06%(?)and 28.11%(?),but the proportion of the soil layer carbon storage increment to the forest ecosystem total carbon saorage increment increased from 21.19%(CK)to 32.13%(?),35.12%(?),34.09%(?).(6)The comprehensive evaluation of thinning effect on forest comprehensive carbon sequestration showed that the mild thinning intensity(I)>the moderate thinning intensity(?)>the strong thinning intensity(?)>the control(CK).The mild thinning intensity(?)was the best of comprehensive evaluation for forest comprehensive carbon sequestration effect of Pinus tabulaeformis plantations,as total score of the main components(PCA)of the mild thinning(?)stand was the highest(2.9666),and the score of the control(CK)stand was the lowest(-3.7453).(7)Thinning increased light radiation intensity,temperature,soil water content,soil organic matter content and soil total nitrogen content in Pinus tabulaeformis plantations,especially the mild thinning intensity(?).(8)The control experiment results showed that different light radiation intensity,soil water content,soil nitrogen fertilizer content and the the interactive effect of soil water and nitrogen content had significant effect on photosynthetic carbon sequestration of Pinus tabulaeformis,while thinning changed the light radiation intensity,temperature,soil water content,soil organic matter content and soil total nitrogen content by changing the density of stand,so as to change the photosynthetic carbon sequestration of Pinus tabulaeformis plantation trees and affect the carbon sequestration effect of stand. |
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