Effects Of Abandonment Years On Stand Structure Factors And Carbon Distribution Patterns Of Carbon Pools In A Moso Bamboo Forest Ecosystem

Moso bamboo（Phyllostachys pubescens）has high carbon sequestration capacity,plays an important role in mitigating climate change,and is also regarded as an important basic crop of life and rural building materials,with multiple benefits of economy,ecology and society.With the saturation of the bamboo market and the increase in transportation and labor costs,some Moso bamboo forests have been abandoned by farmers.Many scientists have studied Moso bamboo forests so far,but most of these research objects are natural Moso bamboo forests or that in management,and rarely mention the concept of abandoned bamboo forests that have a history of management but now have not been managed for some time.50 Moso bamboo forest plots with different abandonment times were investigated,and we analyzed the effects of abandonment time on the structural factors and carbon storage allocation pattern.The result showed that:（1）Abandonment affected the forest structural factors,especially after 6 years of abandonment,the indicators are significantly different from those of normal bamboo forests（p<0.05）.The bamboo forest with the longest period of abandonment in this study（15-18 years）has a culm density of 8120±1964ha-1,which is about three times the normal level and about twice the ideal value of several mathematical models.During these periods,the average stand age increased from 2.33±1.14 du to 3.23±1.04 du,the proportion of new bamboos（1du）decreased from 31.2%to 7.1%,and the proportion of bamboo with a age class of 4du increased from 23.0%to 57.8%,and the diameter at breast（DBH）decreased significantly by 15.7%.（2）The carbon storage of the individual culm was reduced by 25.1%due to the smaller DBH.However,the carbon storage of the entire arbor layer（Moso bamboo）still increased significantly（y=2.188x+28.188,r²=0.746,p<0.01）due to the excessive culm density.It was 65.12±6.54 Mg ha^-1,with a maximum increase of 147.3%in abandoned bamboo forests for 15-18 years.Litters and undergrowth vegetation account for only a small part of the entire ecosystem’s carbon storage.Among them,the carbon storage of the undergrowth vegetation increased first and then decreased,and the value in abandoned bamboo forests for 3-6 years was the largest,0.88±0.20 Mg ha^-1.But the value in plots with the longest abandonment period is 0.21±0.08 Mg ha^-1,which is only 36.8%of the normal.The soil organic carbon（SOC）in the topsoil layer（0-20cm）increased significantly（p<0.05）with the abandonment time,while there was no significant difference in the deep（20-40cm）.（3）Abandonment has changed the carbon allocation pattern of the Moso bamboo forest.In the partial correlation matrix controlling the terrain factors,the correlation coefficients of abandoned time and carbon pools were 0.79（bamboo）,0.35（litter）,0.01（SOC）,0.37（total C）.And the order of variable interpretation in the random forest model is from bamboo,understory vegetation,litter,and finally the soil,which is consistent with the path of the material cycle and carbon cycle.Therefore,the growth rate of bamboo-dominated vegetation is faster,and the proportion of vegetation C in the ecosystem has increased from 21.69%to 35.95%with the extension of the abandonment time.Correspondingly,The proportion of SOC in total ecosystem decreased from 76.63%to 62.59%,but it is still the largest carbon pool in Moso bamboo forests.These results enrich our understanding of the structure and carbon allocation pattern of abandoned Moso bamboo forests and provide a significant support for Moso bamboo forest management or future recovery.