Abstract: BackgroundForests play a crucial role in global climate change, and the rich variety of tree species in the northern mountainous region of Beijing provides an essential foundation for studying regional carbon storage and biomass distribution. This paper focuses on five typical tree species: poplar, black locust, Mongolian oak, Pinus tabuliformis Carr, and Pinus tabuliformis Carr.MethodsThrough experimental measurements, we established carbon content and biomass estimation equations for different species, organs, and age groups, accurately estimating biomass and carbon storage on a regional scale. We constructed a locally applicable carbon storage evaluation parameter database, providing scientific support for precise measurement of regional carbon sinks. ResultsThe results showed significant differences in carbon content among species (p < 0.05), with Chinese pine having the highest carbon content (52.23%), significantly higher than poplar (49.18%), black locust (47.60%), Mongolian oak (48.65%), and Chinese arborvitae (50.14%). Significant differences were also observed in the carbon content of various organs, with woody organs (trunk, branches, and roots) having higher carbon content than non-woody organs (leaves), with the trunk having the highest carbon content (51.09%), significantly higher than roots (49.07%) and leaves (48.01%). In biomass distribution, Chinese pine, at 122.01 t/ha, was significantly higher than other species (p < 0.05), followed by Chinese arborvitae (103.92 t/ha). The majority of biomass was concentrated in the trunk, accounting for over 60% and increasing with tree age. Carbon storage assessment also showed significant species effects (p < 0.05), in the order of Chinese pine (64.55 t/ha), Chinese arborvitae (51.42 t/ha), poplar (49.71 t/ha), black locust (47.90 t/ha), and Mongolian oak (46.45 t/ha). The spatial distribution of carbon storage was consistent with biomass trends, with the trunk contributing the most and leaves the least. Additionally, carbon storage showed a nonlinear cumulative trend with tree age, reflecting differences in carbon sequestration efficiency among species during development. ConculsionsOverall, the carbon storage of the arboreal layer in northern mountainous Beijing is 52.01 t/ha. Due to the high proportion of plantations, single tree species, and environmental stress, the overall regional carbon sink potential is limited. This study systematically revealed the main limiting factors of forest carbon sinks in Beijing, providing a strong scientific basis for optimizing tree species structure and improving management practices.