| Forests cover approximately 31 percent of the earth's land area and store about 80% and 40% of above-and below-ground global organic carbon,respectively.Forest ecosystems are then of great importance for global terrestrial carbon storage and carbon cycling.Understanding of the status of forest carbon density and storage in mountain terrain is needed for monitoring of forest carbon in support of ecosystem management for climate change mitigation as well as for parameterization of large-scale models.The Lüliang Mountains are located in the middle reach of the Yellow River.The lower altitude locations of the mountainous range along the Yellow River is one of the areas with the most severe soil erosion in the Loess Plateau.Meanwhile,various types of natural forests are distributed in the middle and high elevations of the mountainous range.Hence,the Lüliang Mountains region is one of the key areas of these national afforestation and forest protection programs.Studying and quantifying the carbon densities and carbon stocks in the region can further explore the influence of different management strategies and environmental factors on forest carbon sequestrations and emissions.However,the forest area dynamics may change substantially between regions due to a wide range of climatic regimes and/or difference in the primary objectives of management measures.This may be especially pronounced in mountain regions,where environmental gradients are compressed and vary at multiple spatial scales.Therefore,how to quantify forest carbon density in mountainous area? What are the differences between estimation methods of forest carbon density? How do environmental factors affect forest carbon density? How to increase the forest carbon density?These studies are not only the basis of forest carbon research,but also an important theoretical reference for regional forest carbon management.In this study,we used the national forest inventory data from Lüliang Mountains to conduct the following studies:(1)Based on the national forest inventory data from 2005 and 2010,the biomass and carbon density of main tree species of the forest communities in the South Lüliang Mountains was estimated by using both the weighted biomass regression model(WBRM)and the continuous function for biomass expansion factor(CFBEF).Meanwhile,we compared and analyzed the difference between the two estimation methods.(2)On the basis of 28 × 112(species × plots)carbon density matrix obtained by WBRM,the classification and ordination were carried out using the methods of TWINSPAN(Two-Way Indicator Species Analysis),and DCA(Detrended Correspondence Analysis)and CCA(Canonical Correspondence Analysis),respectively.Meanwhile,One-way ANOVA and Pearson correlation analysis were used to test the differences of carbon densities among the forest communities,and the relationship of carbon densities with the environmental factors(elevation,slope,aspect and position).(3)Based on the forest inventory data of 3768 sample plots,we estimated the values of carbon densities and carbon stocks of natural and planted forests by using both biomass expansion factor method for tree layer and region type parameter transformation method for other layers(shrub,herb,litter,and dead wood),and analyzed the spatial patterns of carbon densities and the effects of various factors on carbon densities using semivariogram analysis and nested analysis of variance(Nested ANOVA),respectively.(4)The relationship between the total carbon densities(total CD),biomass carbon densities(biomass CD),soil carbon densities(soil CD)and the annual mean temperature,annual precipitation,elevation,soil thickness,stand density,stand age of the dominant tree species in Lüliang Mountains was studied.The main results were as follows:(1)The estimated values from the WBRM were significantly higher than those from the CFBEF(p<0.01).For the same vegetation type from different area,the estimated results from WBRM fluctuate greatly and the CFBEF is relatively stable,and the WBRM was better for the biomass estimation at the medium to small scales because it based on the individual tree compared with the CFBEF based on the sample plot from the different forest types.(2)The forest communities in the south of Lüliang Mountains were classified into 8 forest formations,and a significant difference of carbon density was found among these formations.The carbon density for Form.7(Form.Quercus wutaishanica + Acer mono)and Form.4(Form.Quercus wutaishanica + Pinus tabulaeformis)were significantly higher than others,and the carbon density of Form.1(Form.Pinus bungeana + Platycladus orientalis)was the lowest among the eight formations.The carbon density in2010 is significantly higher than that in 2005.The total carbon density increased with an average value of 1.542 Mg·ha-1·a-1.There was a significant correlation between the carbon density and elevation,and slope.The forest carbon density was higher at shady and half-shady slopes(north and east)than at sunny and half-sunny slopes(south and east-south).The lowest carbon density location was at steep slope.(3)The carbon density was 123.7 Mg ha-1 and 119.7 Mg ha-1 for natural and planted forests respectively.Natural and planted forests accounted for54.8% and 45.2% of the total carbon stock over the whole region,respectively.The biomass carbon density was greater in natural forests than in planted forests(22.5 versus 13.2 Mg ha-1).The higher(lower)spatial carbon density variability of natural(planted)forests was featured with a much smaller(larger)range value of 32.7 km(102.0 km)within which a strong(moderate)spatial autocorrelation could be observed.(4)No significant difference was detected in the carbon densities between natural and planted forests,and the carbon density growth index of planted forests is almost larger than that of natural forests.Planted forests have made a substantial contribution to the total carbon stock of the region due to the implementation of large-scale afforestation and reforestation programs.(5)In order to increase the forest carbon density,the tree species with stronger adaptability to environment conditions should be selected for reforestation.Platycladus orientalis,Pinus tabulaeformis,and Robinia pseudoacacia should be priority considered for planted forest as the dominant tree species,and the Larix principis-rupprechtii,Picea meyeri,and Betula platyphylla for natural forest protection because of the higher carbon density growth index.Quercus wutaishanica has large volume and wide distribution,and the carbon density is higher for mixed forest than pure forest.In summary,stand age,stand density,temperature,and precipitation had significant effects on the carbon density in the region.The carbon density was first increased with the increase of elevation/slope,and then decreased.The spatial variability and the spatial autocorrelation of carbon density was higher,while the range of spatial autocorrelation was smaller for natural forests than for planted. |
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