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.