Objectives This study provided data support for the rational allocation, carbon sequestration and sink enhancement measures and precise maintenance of China National Botanical Garden, which contributed to the sustainable development of landscaping and carbon sink.

Methods Taking the main green vegetation of China National Botanical Garden as the research object, it was divided into five categories: forest trees, garden trees, garden shrubs, herbs and bamboo. The 2019 census data of China National Botanical Garden was used as the basis for the study. Stratified typical sampling and supplementary survey were carried out to obtain the measured data, and based on the biomass model and carbon metering parameters of occupation standards. To explore the distribution pattern and influencing factors of carbon storage and carbon density of typical vegetation in National Botanical Garden.

Results The results showed that the estimated total vegetation carbon storage of China National Botanical Garden in 2022 was 8904.71 tons, with garden trees accounting for the greatest proprtion (48.86%) followed by forest trees (28.83%), herbs (11.82%), bamboo (6.89%), and garden shrubs (3.90%). Trees constituted the primary component of the vegetation carbon pool at China National Botanical Garden, accounting for 94.47% of the total vegetation carbon storage (forest trees accounted for 25.55%; garden trees accounted for 68.92%). The carbon storage per tree of gardon trees was 213.2 kg, indicating that the diameter and height of individual trees were relatively large, and the carbon storage per tree of different tree types was significantly different, among which the carbon storage per tree of fast-growing trees was the highest, while that of Malus spectabilis was the lowest, and the carbon storage per tree of fast-growing trees was 41.5 times that of Malus spectabilis. The average carbon density of forest trees was 35.67 t/hm², and the order of the average carbon density of forest trees was as follows: Acer truncatum > Cotinus coggygria Scop. > Platycladus orientalis (Linn.) Franco > Pinus tabulaeformis Carr. > Robinia pseudoacacia Linn.

Conclusions To ensure the consistency of the landscape effect of China National Botanical Garden, the overall carbon storage of garden trees can be improved through reasonable landscape configuration and spatial layout. This could be achieved by gradually adjusting the age structure of garden trees, or locally introducing local trees with high carbon sequestration ability, or building a composite structure of trees, shrubs, and grasses around garden trees. It is suggested to select more trees with higher carbon density and carbon sequestration rates, such as oak and larch, and gradually adjust the tree structure in the mountain forest area, which is conducive to enhancing the carbon sequestration capacity of China National Botanical Garden.