The Effect Of Thinning Intensity On Carbon Storage Distribution Pattern Of Plantation

The forest is the largest carbon sink of terrestrial ecosystem and enhancing the carbon sink function of forest ecosystem could contribute to suppress the increasing of the atmospheric CO2in the current trend. Plantation is the most important forest ecosystem in urban areas. Over a long term, it is always been planted with high density, although improving the unit timber production, but reducing the carbon sink function and sustainable development of those forest, resulting in inadequate functioning of carbon sinks. As a way to improve the ability of the forest carbon sequestration, thinning can not only promote the growth of the individual tree layer, but also can promote the biomass accumulation of understory shrubs and herbaceous andcontribute to promote nutrients returns and increase soil carbon storage. The enhancing effect of thining on plantation’s carbon sink function are determined by thinning intensity, so to explore what kind of thinning intensity can maximize plantations’s carbon sink function is extremely necessary. Artificial water conservation forest in Fengxian District of Shanghai is part of the Huangpu River water conservation forest that was constructed in2003. To study the effects of thinning on the forest structure and function of carbon sinks for this forest, Elaeocarpus Sylvestris and the Cinnamomum camphora-Bischofia polycarpa forest were chosen andthinning treatments were carried out in the end of2009, by setting severe, moderate and weak three thinning intensities., After the treatments, a four-year vegetation investigationwas carried out, and the vertical distribution of underground and aboveground carbon storage、soil nutrients and soil mineralization rate were determined in2013. The main results are as follows:(1)From2009-2013, with the increase of thinning intensity, the recovering rate to pre-thinning of tree layer carbon stocks showed a decreasing trend for Elaeocarpus Sylvestris forestand an increasing trend for Cinnamomum camphora-Bischofia polycarpa forest, which indicating that tree layer of different forests under thinning treatments have different carbon sequestration capacities.(2)With the increase of thinning intensity, the individual aboveground biomass showed an increasing trend for both Elaeocarpus Sylvestris and the Cinnamomum camphora-Bischofia polycarpa forests, indicating that the stronger the thinning intensity, more conducive to the promotion of tree diameter growth. But four years after the thinning treatment, aboveground carbon storage and carbon storage of tree layer has not exceeded the control treatments. Aboveground carbon stocks and carbon storage of tree layer presented the opposite trends with increasing thinning intensity in two forests, which Elaeocarpus Sylvestris forest presented:weak thinning> moderate thinning>severe thinning and the Cinnamomum camphora-Bischofia polycarpa forest presented:severe thinning> moderate thinning> weak thinning. The carbon stocks of seedling layer presented opposite trend with that of tree layer for each forests. The carbon stocks of shrub layer are largest in the moderate thinning for both forests. Except for the control treatments, the carbon stocks of litter layer were largest in moderate thinning for Elaeocarpus Sylvestris forest and largest in severe thinning for Cinnamomum camphora-Bischofia polycarpa forest. Those suggested that the thinning intensity had different effects on carbon stocks of each vertical layer for each forest.(3)Four year after thinning, the root carbon storage of treatments were not over the control treatments, and exhibited same trends along the thinning intensity gradient with the carbon storage of aboveground parts for each forest.. Soil carbon density showed a decreasing trend with increasing soil depth. The soil carbon storage exhibited moderate thinning> weak thinning>control treatment>severe thinning for Elaeocarpus sylvestris forest, and showed control treatment>severe thinning> moderate thinning>weak thinning for Cinnamomum camphora-Bischofia polycarpa forest.(4)Summer soil carbon mineralization rate exhibited different trends with increasing thinning intensity for two forests. The Elaeocarpus Sylvestris forest showed:ck<weak thinning<severe thinning<moderate thinning, and the Cinnamomum camphora-Bischofia polycarpa forest showed:severe thinning <moderate thinning<weak thinning<ck. The summer soil carbon mineralization rate showed negative correlation with soil carbon stocks in Cinnamomum camphora-Bischofia polycarpa forest, which suggested the effect of thinning on soil carbon stocks in evergreen and deciduous broad-leaved mixed forest depends mainly on the soil carbon mineralization rate. The summer carbon mineralization rate showed positively correlation with litter carbon stocks and, not the soil carbon stocks in Elaeocarpus Sylvestris forest.In conclusion, because of only four years after thinning treatment, the carbon stocks of each thinning treatment did not exceed the control treatment for both of Elaeocarpus Sylvestris forest and Cinnamomum camphora-Bischofia polycarpa forest. But thinning treatment had significantly effects on carbon stocks, including:severe thinning treatment most conducive to the carbon accumulation for evergreen and deciduous broad-leaved mixed forest and soil carbon stocks, while weak thinning treatment most conducive to the carbon accumulation for evergreen broadleaved forestand moderate thinning most conducive to the accumulation of its soil carbon stocks.