Biomass And Its Dynamic Change Of Mongolian Pine Plantation In Mu Us Sandy Land,Inner Mongolia

The Mu Us Sandy Land,located in the north of the Loess Plateau and the south of the Ordos Plateau,belongs to the transition zone from Loess Plateau to Ordos Plateau and is one of the four major sandy lands in China.Mongolian pine（Pinus sylvestris var.mongolica）has been introduced in the Mu Us Sandy land,Inner Mongolia since the 1970s.With the gradual increase of afforestation area,remarkable effects in improving the ecological environment and improving the function of windbreak and sand fixation have been achieved.However,up to now,the biomass of Mongolian pine in this area has not been accurately estimated.In this study,we developed models for height,volume,and different biomass components including stem,branch,leaf,and root of Mongolian pine.The additive system of equations was then obtained.The biomass and productivity allocation patterns at a single tree and stand scale were explored.A conversion equation of biomass to volume at stand scale was established.In addition,the spatial-temporal distribution pattern of Mongolian pine forest biomass was estimated based on remote sensing data,which provided a reliable approach for local ecosystem carbon sink assessment.The main findings are as follows:The optimal tree height model had a good prediction effect with RMSE less than 1.1m and R_adj²over0.78.The one-variable and two-variable volume models showed the best predictive ability based on power functions（R²>0.95）.The additive biomass model of Mongolian pine has good fitting and predicting effects.When D and H were used as compound variables,the estimation effect of total aboveground biomass and trunk components was the best,with a higher R_adj²value and lower RMSE value.On the contrary,when D was the only predictor variable,tree branch and leaf biomass models yield the highest R_adj²and the lowest RMSE.The root biomass model of Mongolian pine based on the power function with D as the predictive variable had a good effect,with a higher R_adj²value and lower RMSE value.With the increase in stand age,the total biomass of Mongolian pine plantations increased from 9.23Mg/hm²in the 10-year-old stands to 95.8 Mg/hm²in the stands over 30 years old.Root biomass accounted for the highest proportion of total biomass with a value of 47.7%,followed by the stem21.6%,foliage 16.8%,and branch biomass 13.9%.The net primary productivity ranged from 1.32 to 18.68 Mg/（hm²·yr）,with an average of 5.19Mg/（hm²·yr）.The share of stem,branch,foliage,and root on total productivity was 22.78%,13.60%,29.52%,and 34.10%,respectively.There were strong correlations between the volume and component biomass of Mongolian pine plantations.The biomass conversion factor given by the biomass-volume conversion model can be used to accurately estimate the biomass of each component and the total biomass of the Mongolian pine forests.From 1990 to 2020,the area of Mongolian pine forests increased from 784 hm²to 10452 hm²,with an increment of 9668 hm².From 2005 to 2010,the area increased the most,from 3356 hm²to 9518 hm².From 1990 to 2020,the biomass increased from 8140 Mg to 132054 Mg,with an increment of 123914Mg.Similarly,from 2005 to 2010,the aboveground biomass increased by 59,609 Mg.The significant increase in biomass was mainly due to the increase of artificial afforestation area.In this study,the tree height model,volume equation,and additive system of biomass equations for Mongolian pine in Mu Us Sandy Land were developed.Furthermore,the stand biomass,productivity,and the dynamic changes of regional biomass were analyzed.Within the results,this study can provide scientific support for ecosystem assessment,carbon sequestration enhancement,and sustainable management of Mongolian pine plantations in this area.