Duryunsan Provincial Park, located in Haenam-gun, Jeollanam-do, is an ecotone situated between warm-temperate and temperate forests, thus making it particularly sensitive to climate change. This study classified the vegetation within the park using Landsat satellite imagery and deep learning techniques to analyze the long-term spatial distribution changes of the warm-temperate evergreen broad-leaved forests over the past 40 years. The results revealed that the forest area expanded from 143.2 ha (4.3%) in the mid-1980s to 191.0 ha (5.8%) by the mid-2020s. Notably, the distribution range shifted beyond specific topographic constraints by spreading into diverse environments with varying elevations, slopes, aspects, and soil conditions. These findings suggest that evergreen broad-leaved forests are increasing in size and are progressively expanding their ecological niche by overcoming their previous environmental limitations. This study provides quantitative evidence of this spatial expansion and serves as a critical baseline for understanding vegetation responses to climate change. Moreover, the case of Duryunsan offers important insights into predicting long-term distributional shifts in Korean warm-temperate forests and establishing effective conservation and management strategies for provincial parks.