Effects Of Crop Tree Release Treatment On Carbon Storage Of Chinese Fir Plantation

To assess the comprehensive effect of crop tree release on Chinese fir plantation, this paper makesa contrast of the change of stand growth, stand structure，understory vegetation diversity and forestcarbon storage among the thinning stands and control stands before thinning and three years afterthinning with field investigation and office analysis of a16-year-old Chinese fir plantation in Lin’anQingshan before and after crop tree release. The results are showing as follows.The effects on forest growth of crop tree release include (1) average DBH growth for three years ofthinning stand and control stand is1.3cm and1.0cm, respectively.3-year average DBH growth ofgeneral and crop tree of thinning stand is1.2cm and1.9cm, respectively, higher than that of controlstand,(2)3-year average volume increment per tree of thinning stand and control stand is0.0241m3and0.0192m3,respectively.3-year average volume increment rate of general and crop trees of thinningstand is16.86%and51.44%higher than that of control stand,(3) because of removed trees, the standvolume of thinning stand merely increases by13.23%, lower than that of control stand whose standvolume increases by22.98%.Whereas the stand volume growth of general and crop trees of thinningstand is higher than that of control stand,(4) positive effects on forest growth of crop tree release isobvious, especially on the growth of the crop trees.The effects on forest structure of crop tree release include (1) DBH structure of thinning standtends to be typical normal distribution after crop tree release, and three years later, the proportion ofDBH of14cm and above diameter class of thinning stand is significantly higher than that of controlstand. The number of trees14cm and above diameter class of thinning stand increases by17.92%compared to that before thinning and26cm diameter class appears in thinning stand which doesn’t existin control stand. Crop tree release is conducive to the production of large-diameter trees,(2) the Hegyicompetition index of crop tree significantly decreases from6.12to4.21after thinning, and the Hegyicompetition index of general tree decreases non-significantly from10.69to9.58. Despite of tree growthfor three years, the Hegyi competition index of crop tree and general tree has no significant changecompared to the year after thinning. The Hegyi competition index of control stand changed little in threeyears. Crop tree release can regulate the competition pressure of crop trees effectively.The effects on understory vegetation diversity of crop tree release include (1) shrubs and herbs abundance index of thinning stand is significantly higher than that of control stand, the same toShannon-Wiener index of herbs of thinning stand is significantly higher than that of control stand, butShannon-Wiener diversity index of shrubs of thinning stand is a non-significantly higher than that ofcontrol stand,(2)there exists heterogeneity in understory environment, species difference of shrubs andherbaceous between thinning area and non-thinning area is large, but forest biodiversity index makes nosignificant difference.The effects on forest ecosystem carbon storage of crop tree release include (1) average carbonstorage growth of single crop tree and single general tree of thinning stand is higher than that of controlstand, and the average carbon storage growth of single crop tree is the highest, to be11.61kg,(2)carbon storage growth of tree layer of thinning stand is similar to that of control stand three years aftercrop tree release but the carbon growth rate of tree layer of thinning stand is higher than that of controlstand, and carbon storage growth of crop trees contributes22.12%to total carbon storage growth of treelayer of thinning stand which is higher than the14.62%contribution made by crop trees to total carbonstorage growth of tree layer of control stand. The positive response of crop trees to crop tree releaseplays an very important role in carbon storage growth of tree layer,(3) carbon storage of understoryvegetation and death matter significantly improve three years after crop tree release, where the largestcarbon storage growth is herbaceous layer, increasing1.42t C ha-1, and the highest carbon storagechange rate is carbon storage of litter and coarse woody debris, they are8.14and19.16times comparedto that of control stand,(4)there is no significant impact on soil carbon pool of crop tree release, butboth0-10cm layer and10-20cm layer soil carbon of thinning zones is non-significantly lower than thatof non-thinning zone,(5) aboveground carbon storage of thinning stand is lower than that of controlstand due to removed trees, but the actual growth of above ground carbon storage of thinning stand issignificantly higher than the growth of control stand three years after crop tree release. Forest carbon ofthinning stand increases4.23t C ha-1three years after crop tree release and thinning stand expresses as acarbon sink stand,(6) the integration carbon storage of inside and outside thinning stand three yearsafter crop tree release is115.60t C ha-1which is similar to integration carbon storage of control standwhich is117.69t C ha-1, and increases10.32t C ha-1compared to that before thinning. Forest standcarbon sequestration has been promoted by crop tree release and forest stand is a carbon sink after3years after crop tree release.