The fires set for slash-and-burn farming often spread out beyond the farmland, facilitating the invasion of other species into the fire site. Expansion of slash-and-burn farming changes the disturbance regime of the region, often increasing fire frequency. Changes in disturbance regime alters population structure of dominant species if the species has slow growth rate or low fire resistance. Thuja koraiensis is an endemic slow growing conifer in talus areas in mountain or subalpine forests in the Korean peninsula. Due to its site specific characteristics, this species is not adapted to fire frequent areas. T. koraiensis dominated the study site over 200 years. We reconstructed the past disturbance history and the age distribution of the dominant species in the study site using dendroecological approach.
The records showed that the disturbance frequency increased as the disturbance interval from 20-30 years until 19th century to about 10 years in 1900-1950s, which coincided with the slash-and-burn history of the study site which started in early 1900s and lasted until the end of 1950s. During the slash-and-burn farming period, the density of T. koraiensis decreased, while the density of neighboring species (e.g. Betula ermanii and Pinus koraiensis) increased, indicating that fires induced by slash-and-burn negatively affected T. koraiensis. Fire events caused by increasing slash-and-burn farming was too frequent for this slow-growing T. koraiensis to grow above the height of surface fire. Even though surviving T. koraiensis after fire showed the acceleration of height growth, they could not overgrow neighboring species due to their intrinsic small size. This indicated that slow-growing subtree species adapted to low fire frequent environments could not overcome increasing fire frequency although the fire was not severe. Anthropogenic activities changed disturbance regime and facilitated the invasion of other species, altering dominant species in the forest community.