Anthropogenic increases in greenhouse gas concentrations, primarily through radiative forcing from carbon dioxide, continue to challenge earth’s climate. This study quantified CO2 storage and uptake by dominant forest types and age classes in the middle region of Korea. In addition, the role of forest landscapes in reducing atmospheric CO2 against CO2 emissions based on energy consumption was evaluated. Mean CO2 storage and uptake per unit area by woody plants for three forest types and four age classes were estimated applying regression equations derived to quantify CO2 storage and uptake per tree; and computations per soil unit area were also performed. Total CO2 storage and uptake by forest landscapes were estimated by extrapolating CO2 storage and uptake per unit area. Results indicated mean CO2 storage per unit area by woody plants and soils was higher in older age classes for the same forest types, and higher in broadleaved than coniferous forests for the same age classes, with the exception of age class II (11-20 years). CO2 storage by broadleaved forests of age class V (41-50 years) averaged 662.0 t/ha (US$331.0 hundred/ha), highest for all forest types and age classes evaluated. Overall, an increased mean CO2 uptake per unit area by woody plants was evident for older age classes for the same forest types. However, decreased CO2 uptake by broadleaved forests at age class V was observed, compared to classes III and IV with an average of 27.9 t/ha/yr (US$14.0 hundred/ha/yr). Total CO2 storage by woody plants and soils in the study area was equivalent to 3.4 times the annual CO2 emissions, and woody plants annually offset the CO2 emissions by 17.7%. The important roles of plants and soils were associated with 39.1% of total forest area in South Korea, and CO2 emissions comprised 62.2% of the total population. Therefore, development of forest lands may change CO2 sinks into sources. Forest landscape management strategies were explored to maintain or improve forest roles in reducing atmospheric CO2 levels.