Variations in forest aboveground biomass in Miyun Reservoir of Beijing over the past two decades

Purpose

In recent years, climate change, particularly rising carbon dioxide (CO₂) concentration and global warming, has attracted much attention around the world. Forest ecosystems still play a crucial role in global carbon (C) fixation. Quantifying forest aboveground biomass (AGB) and its temporal variations is essential for understanding external impacts (e.g., urbanization, environmental change) as well as assessing the potential of forest ecosystems assimilating the atmospheric CO₂.

Materials and methods

In this study, we established regression models for AGB estimation in the Miyun Reservoir region, based on relationships between Landsat-derived variables and ground truth AGB values, which were obtained from both plot measurements and estimations using Light Detection and Ranging (LiDAR) dataset. The models were applied to calibrated Landsat images acquired in 1990, 2000, and 2010 to track the forest AGB temporal variations and the corresponding spatial distributions for each period. The AGB estimations using LiDAR showed high consistency with values based on the plot measurements, while the established models presented an acceptable accuracy.

Results and discussion

The AGB density in the Miyun Reservoir experienced an overall increase since 1990 and was averaged at 52.20 and 32.12 t ha^?1, for stand forest and shrub in 2010, respectively. Total AGB in 2010 was estimated to be 4.5 × 10⁷ t, which increased by 8% when compared with the level in 1990. Our results are in the similar range of AGB density reported by other studies carried out in Northern China. Ecological programs including Three-North Shelter Forest Project and Returning Farming to Forest promoted the forest expansion and development during this period, while local farming activities exerted certain negative effects on the surrounding forest systems.

Conclusions

Absolute AGB density values indicated that regions with less external interventions present more consistent biomass accumulation. However, the coarse spatial resolution and 10-year interval of the datasets limited detailed analysis of impacts from urbanization of Beijing City. Future studies incorporating sophisticated ecosystem research methods are expected to uncover the mechanisms and key drivers for the observed variations in the AGB in the Miyun Reservoir region of Beijing, China.