Live biomass carbon density is related with species demographics in eastern Qinghai-Tibet Plateau forests

Abstract

Previous assessments of forest carbon sequestration mainly emphasized expanding forests and monitoring their growth over time. However, limited research has tackled enhancing carbon sequestration efficiency in existing forests, particularly by altering tree species demographics. Identifying species with significant contributions to carbon storage through growth and recruitment, as well as pinpointing regions and species with higher mortality rates (MRs), is essential for guiding forest restoration initiatives. This study utilized 1,248 permanent forest plots and 103,773 individual trees to examine the spatiotemporal demographic patterns of 20 dominant tree species from 1979 to 2017 in the Eastern Qinghai-Tibet Plateau and their impacts on forest live biomass carbon density. The findings indicate significant differences in the demographic rates of the 20 dominant tree species. The trees species composition and distribution in the study area were changed with the expansion and reduction of individual numbers of different trees species. For example, the expansion of Alnus cremastogyne, the shrink of Pinus yunnanensis and Pinus armandii populations. The growth rates (GRs) and recruitment rates (RRs) of Abies fabri, Acer miyabei, Betula albosinensis, Picea asperata, Juniperus squamata, Quercus semecarpifolia, and Salix takasagoalpina significantly increased live biomass carbon density. Conversely, increased MRs of Abies fabri, Cupressus funebris, Larix gmelinii, Picea asperata, Pinus armandii, Pinus densata, Pinus yunnanensis, and Salix takasagoalpina reduced forest live biomass carbon density. GRs and RRs offset MRs, resulting in an increase in carbon storage. Competition, which was estimated by the basal area per plot (BAplot), constrained the growth and recruitment and increased mortality of Pinaceae (Pinus armandii, Tsuga chinensis, Pinus yunnanensis, Pinus densata, Larix gmelinii, Picea likiangensis), particularly at low elevations and in the south of the study area. Interspecific variations in GRs, RRs, and MRs suggest selecting optimal species associations with high GRs and RRs, while thinning forests containing species with high MRs in suitable locations. The study enhances insights into the demographic rates of different species, establishes links between population dynamics and forest carbon sequestration, and further demonstrates the importance of adaptive scientific afforestation planning and forest management.

Keywords

• Basal area
• Forest carbon sequestration
• Growth rate
• Mortality rate
• Recruitment rate
• Stand age