Global warming impacts of carbon dioxide, methane, and albedo in an island forest nature reserve

Forest ecosystems influence climate by sequestering carbon from the atmosphere and by altering the surface energy balance. However, the combined global warming impacts (GWIs), contribution from carbon dioxide (CO _2 ) fluxes, methane (CH _4 ) fluxes, and albedo changes (Δ α ) remain poorly understood. Here, we reported the combined GWIs of CO _2 , CH _4 , and albedo with eddy covariance (EC) measurements during 2020–2022 in a subtropical island forest located in the Nanji Islands National Marine Protected Area in Southern China. We suggested that the island forest acted as a significant carbon sink, with annual CO _2 and CH _4 fluxes of −548.6 ± 11.1 and −5.67 ± 1.1 g C m ^−2 yr ^−1 , respectively, while the daily albedo varied within the range of 0.03–0.15. By converting the radiative forcing induced by CH _4 and albedo change in the forest to CO _2 equivalents, we analyzed the three contributors to the combined GWI. The annual averages GWI of CO _2 uptake, CH _4 uptake, and Δ α were −2 011.6 ± 40.6, −211.3 ± 1.1, and 0.03 ± 4.5 g CO _2 -eq m ^−2 yr ^−1 , respectively, with a mean combined GWI of −2 223 ± 40.8 g CO _2 -eq m ^−2 yr ^−1 . During 2020–2022, the contributions of CO _2 uptake, CH _4 uptake, and Δ α to the combined GWI were 89.7% to 91.4%, 9.4% to 9.6% and −1.0%–0.9%, respectively. Nanji Island forest had a strong positive effect on climate change mitigation, with CO _2 and CH _4 uptake greatly enhancing its cooling benefits. Using Pearson correlation and path analysis, we found photosynthetically active radiation, precipitation, soil water content were the primary factors controlling the GWI dynamics, mainly driving the changes in CO _2 fluxes. This study provided novel insights into the establishment of the overall evaluation framework for ecosystem-scale GWIs of CO _2 and CH _4 fluxes, and albedo based on long-term EC measurements in an island forest.