The present study aims to monitor the long‐term changes in forest structure, productivity, nutrient cycling, and to accumulate ecological information on forest ecosystem in Korea. There are six long‐term ecological research sites and seven flux measurement sites in Korea. The Gwangneung experimental forest (GEF) located in the central cool‐temperate forest sub zone is known as a model site where many interdisciplinary researches have been ongoing actively since mid‐1990s over all other Korea long‐term ecological research sites (KLTER). Collected data and information through monitoring and investigation of changes in forest ecosystem have been stored in a database for analyses. The relative importance of tree species (%) of GEF was in the order Quercus serrata (20) = Euonymus oxyphyllus (20) > Carpinus laxiflora (12). The total biomass and basal area were 249.53 t ha−1 and 26.66 m2 ha−1, respectively. There were 136 taxa with 49 families, with 97 genera, 11 varieties, 3 forma, and 1 subspecies in 1 ha permanent plot. The increase in temperature has been estimated to have negative effects on tree growth. The litter decomposition rate was in the order Cornus controversa < C. cordata < C. laxiflora < Q. serrata. The average litterfall and soil respiration were 5803 kg ha−1 and 8600 kg C ha−1, respectively. Further, the GEF, a KLTER site tended to be almost carbon neutral with an annual growth average of 51,000 ± 78,000 kg ha−1. The data from six LTER sites are digitalized and classified to build data catalogs on the ecological information system. The information on stand dynamics and materials and energy budget in the forest ecosystem is utilized for impact assessment and the study of adaptation strategy for forest ecosystem to climate change.