Fire-induced shift from Pinus to Quercus forests: a twenty-year study following the 1996 Goseong forest fire

Background: The 1996 Goseong forest fire, the largest recorded, prompted a debate on the potential for natural forest recovery, leading to the designation of a natural restoration research area. This study mainly aimed to demonstrate the forest's natural regenerative ability in a prefire Pinus densiflora forest that had been affected by a stand-replacing fire. To achieve this, the study tracked the key aspects of the succession process, specifically the formation of vertical structure and changes in species composition. Results: The regenerating vegetation initially passed through stages dominated by herbaceous and shrub layers, then differentiated into the canopy layer, eventually forming the early-stage forest after 20 years. Site A had developed into a forest with an average canopy height of 13.3 m and 73% coverage, while Site B was restored with a canopy height of 10 m and 27% coverage. Tree species of the genus Quercus dominated the canopy layer, occupying 99% of the tree basal area (from 17% prefire). Consequently, the prefire pine forest shifted to a Quercus-dominated forest after secondary succession. Pinus densiflora (83% of the prefire basal area) occupied only 1% after 20 years. Oak species became dominant from the initial stages of regeneration, playing a key role in shaping the early-stage forest structure. The species composition of the regenerating stands was already determined in the initial stage and closely resembled that of 20 years later. Since most species regenerated through resprouting, the understory remained dominated by pine forest companion species. Oak-associated species tended to increase in later stages. No invasive species were observed, and annual plants had low abundance. Conclusions: The study demonstrated the natural regenerative power of the forest following the fire, revealing that it takes around 20 years for a prefire pine forest to be restored an early-stage oak-dominated forest. Quercus trees, particularly Quercus variabilis and Quercus mongolica, regenerated rapidly immediately after fire, contributing to the development of the early-stage forest. Although this study was small in scale, it is a rare study conducted at permanent plots over 20 years, revealing the secondary succession process.