Comparison On Vegetation Community Characteristics And Carbon Storage Between Afforestation And Abandonment Of Farmland

How to mitigate global climate change and conserve species diversity is one of the hot issues that scientists concerned about.The project of Conversion of Farmland into Forest that implemented in 1998 has aroused people's attention about its benefit of carbon sequestration.With the reduction of the population in the mountain area,abandonment phenomenon emerged in the farmland.In this paper,farmland were restored for 14 years by afforestation and abandonment that respectively become conversion of farmland into forest?FF?and farmland remained bare?FB?in Huitong were taken as the research objects.In order to find their differences in community characteristics and carbon storage.The species composition of the two sites were investigated by field investigation method,and the community characteristics of the vegetation layer,such as species important value,ecological dominance,diversity index,evenness index and similarity coefficient,were analyzed in farmland under two rehabilitation approaches.Based on the methods of field investigation and laboratory bioassay,using biomass equation to estimate the carbon storage of vegetation layers,litter layers in FF and FB.The carbon storage of soil layers were estimated by soil profiles and method of soil auger to obtain basic data.Finally,the net carbon sink produced by afforestation in farmland was estimated under a baseline scenario of the FB.The main conclusions were as follows:?1?Species composition of FB was more abundant than that of FF.There were 89 species at the vegetation layer of FB.There were 9 species at tree layer,which belong to 8 families and 9 genera,and the dominant species was Liquidambar formosana Hance.There were 50 species at shrub layer,which belong to 27 families and 44 genera,and the dominant species was Urena procumbens L.There were 30 species at herb layer,they belong to 22 families and 28 genera respectively,and the dominant species was Dicranopteris pedata?Houttuyn?Nakaike.However,at the vegetation layer of FF only had 39 species.The tree layer just had 1 species.There were 20 species in shrub layer,which belong to 18 families and 20 genera,and the dominant species was Smilax china L.There were 18 species in herb layer,which belong to 14 families and 18 genera,and the dominant species was Woodwardia japonica?L.F.?Sm..In addition,the ecological dominance,diversity index,and evenness index at the shrub layer of FB respectively was 0.886,2.736,0.699.At the herb layer of FB respectively was 0.892,2.561,0.753.The ecological dominance,diversity index,and evenness index at the shrub layer of FF respectively was 0.759,1.928,0.644.At the herb layer of the FF respectively was 0.718,1.736,0.589.The every index of FB were higher than that of FF.The species similarity coefficient that shrub layer and herb layer between two rehabilitation approaches respectively was 0.34 and 0.33,which showed a moderate dissimilar level.In general,the farmland by abandonment approach was more beneficial to the species diversity conservation.?2?The carbon storage of tree layer in FF(71.26 t·hm^-2)was higher than that in FB(25.81 t·hm^-2)and the former was 2.76 times as much as the latter.In the FF,the distribution pattern of carbon storage in each organ showed in the order of stem(35.01 t·hm^-2)> leaf(22.14 t·hm^-2)> bark(5.84 t·hm^-2)> branch(5.06 t·hm^-2)> root(3.21 t·hm^-2);while that in FB showed in the order of stem(11.19 t·hm^-2)> root(6.04 t·hm^-2)> branch(5.19 t·hm^-2)> bark(1.80 t·hm^-2)> leaf(1.59 t·hm^-2).The carbon storage of vegetation layer under canopy in FF(0.430 t·hm^-2)was lower than that in FB(1.044 t·hm^-2).While it showed a opposite trend at the litter layers,FF was 3.363 t·hm^-2 and FB was 0.819 t·hm^-2.The soil carbon storage of 0 80 cm depth in FF(75.46 t·hm^-2)was slightly higher than that in FB(72.55 t·hm^-2),but they had no significant difference.The soil carbon content under two rehabilitation approaches decreased with the increase of soil depth.The soil carbon storage of FB was also decreased with the increase of soil depth.The soil carbon storage of FF was in the order of 20⁴0cm>0¹0 cm>40⁶0 cm>10²0 cm>60⁸0 cm.The allocation that carbon storage of ecosystem under two rehabilitation approaches were soil layers>tree layers>litter layers>herb layers>shrub layers.The study showed that the carbon sequestration capacity by afforestation in the farmland was better than that by abandonment during the period of restored 14 years.In addition,the allocation of carbon storage between species under two rehabilitation approaches was also different.The species that had maximum carbon storage of tree layer in FF and FB was respectively Cunninghamia lanceolata?Lamb.?Hook.,Platycarya strobilacea Sieb.et Zucc..The species that had maximum carbon storage of shrub layer in FF and FB was separately Derris trifoliata Lour.,Eurya nitida Korthals.The species that had maximum carbon storage of herb layer in FF and FB was separately Woodwardia japonica?L.F.?Sm.,Miscanthus sinensis Anderss.?3?The net carbon sinks produced by afforestation of farmland after 14 years were estimated according to the National Forestry Administration's Guidelines on Carbon Accounting and Monitoring for Afforestion Project.The original state of the two plots all were farmland,and using “space replacing time” method to obtain the data about soil of farmland,which was the baseline.The carbon storage of soil in farmland using has published an average carbon storage(40.48 t·hm^-2)for the soil of Xiangxi farmland in Hunan Province.The net carbon sinks produced by afforestation and abandonment of farmland after 14 years respectively was 59.74 t·hm^-2?110.03 t·hm^-2.On this basis,the net carbon sink produced by afforestation of farmland was 184.40 t CO2-e·hm^-2.It showed afforestation of farmland could increase forest carbon sink.So the effect of mitigate climate change should not be ignored.In short,from the perspective of species diversity,if the farmland around have the better stand condition?adequate provenance and species rich?,choose the approach of abandonment will beneficial to the species diversity conservation.From the perspective of carbon sink,conversion of cropland to forest is a superior approach in aspects of carbon sequestration benefit.