We assessed the ecological structure and function of mountain ridges connected to a reserve area, Gwangneung Royal Tomb Forest (GRTF), in central Korea. This site has been strictly preserved since the 15th century. Our objectives were to 1) investigate the interactions between and the influence of a protected old-growth forest on its surrounding forests, and 2) suggest management strategies for forests outside that reserve area. Three ridges were surveyed and divided into two categories -- A and B ridges covered with secondary forests connected to GRTF, and the C ridge, covered with primary forests and plantations within GRTF (from core zone to managed zone). The ridge forests had a characteristic lobe shape. We found no significant decline in species richness (peninsular effect) with distance from GRTF for any tree-layer or herbaceous-layer species on Ridges A or B. However, when only the species that appeared in primary forests on the C ridge were considered, the richness of tree- and herbaceous-layer species was significantly decreased there. This meant that the neighboring forests of GRTF could serve as a buffer zone. Differences were obvious between the two categorized forests in their species composition, species richness, basal area, and regeneration patterns. DCA ordination of quadrats on Ridges A and B showed that Axis 1 was significantly correlated with distance from GRTF, indicating that this protected area affects regeneration within neighboring forests. Thus, reserves are important not only to the conservation of biodiversity, but also to the ecological management of surrounding forests.