Carbon storage in soil, tree, shrub, herb, and litter layers of forest ecosystems in Shaanxi during 1989–1993, 1994–1998, 1999–2003, and 2004–2008.

<p>Carbon storage in soil, tree, shrub, herb, and litter layers of forest ecosystems in Shaanxi during 1989–1993, 1994–1998, 1999–2003, and 2004–2008.</p

Forest ecosystem C storage of each city in three regions of Shaanxi Province during 2004–2008.

<p>MAP: mean annual precipitation, MAT: mean annual temperature.</p><p>Forest ecosystem C storage of each city in three regions of Shaanxi Province during 2004–2008.</p

Total C storage of forest ecosystems using three methods during 2004–2008 in Shaanxi Province.

<p>The C density of ecosystems, estimated by field sampling only, was the sum of the mean C density in tree, shrub, herb, litter, and soil layers. The C density of trees was estimated through a forest inventory, and shrub-soil was the sum of the mean C density in the shrub, herb, litter, and soil layers based on field sampling measurements. Method 1: a combination of forest inventory data (tree layer) with field sampling measurements (estimates of storage in the shrub, herb, litter, and soil layers using the relationship between the tree layer and these layers). Method 2: a mean C density method, which calculated the C storage for each forest type by multiplying the mean ecosystem C density by the area obtained only from field sampling. Method 3: an integrated method that estimated C storage in the tree layer based on the forest inventory and estimated C storage in the understory, litter, and soil layers by multiplying the mean C density of these layers by the area based on field sampling.</p><p>Total C storage of forest ecosystems using three methods during 2004–2008 in Shaanxi Province.</p

Biomass-volume conversion formula for each forest type.

<p>B and V are the forest stand biomass (Mg ha^-1) and stand volume (m³ ha^-1). All the regression models are significant (P<0.05); Hardwood: wood density>0.7, which denotes that the hardness of the end of the wood is greater than 700 kg/ cm²; softwood: wood density<0.7.</p><p>Biomass-volume conversion formula for each forest type.</p

C density, storage, and area of forest ecosystems in Shaanxi Province during four periods: 1989–1993, 1994–1998, 1999–2003, and 2004–2008 (mean±95%CI).

<p>* These values represent the area-weighted mean C density of forest ecosystems during different periods.</p><p>C density, storage, and area of forest ecosystems in Shaanxi Province during four periods: 1989–1993, 1994–1998, 1999–2003, and 2004–2008 (mean±95%CI).</p

Temporal-Spatial Pattern of Carbon Stocks in Forest Ecosystems in Shaanxi, Northwest China

<div><p>The precise and accurate quantitative evaluation of the temporal and spatial pattern of carbon (C) storage in forest ecosystems is critical for understanding the role of forests in the global terrestrial C cycle and is essential for formulating forest management policies to combat climate change. In this study, we examined the C dynamics of forest ecosystems in Shaanxi, northwest China, based on four forest inventories (1989–1993, 1994–1998, 1999–2003, and 2004–2008) and field-sampling measurements (2012). The results indicate that the total C storage of forest ecosystems in Shaanxi increased by approximately 29.3%, from 611.72 Tg in 1993 to 790.75 Tg in 2008, partially as a result of ecological restoration projects. The spatial pattern of C storage in forest ecosystems mainly exhibited a latitude-zonal distribution across the province, increasing from north (high latitude) to south (low latitude) generally, which signifies the effect of environmental conditions, chiefly water and heat related factors, on forest growth and C sequestration. In addition, different data sources and estimation methods had a significant effect on the results obtained, with the C stocks in 2008 being considerably overestimated (864.55 Tg) and slightly underestimated (778.07 Tg) when measured using the mean C density method and integrated method, respectively. Overall, our results demonstrated that the forest ecosystem in Shaanxi acted as a C sink over the last few decades. However, further studies should be carried out with a focus on adaption of plants to environmental factors along with forest management for vegetation restoration to maximize the C sequestration potential and to better cope with climate change.</p></div

Methods used for estimation of forest ecosystem C stocks in our study.

<p>Methods used for estimation of forest ecosystem C stocks in our study.</p