Regeneration of Larix sibirica boreal forest patches in the forest-steppe ecotone in Gorkhi Terelj National Park, Mongolia

To demonstrate the dynamics of forest patches in the Mongolian forest-steppe ecotone and examine how forest structure changes with distance from the forest edge, we investigated forest structure and tree age according to two spatial scales: transects and quadrats within transects. The transects shifted with distance across the treeline and we focused on two representative tree species (Larix sibirica and Pinus sibirica) in Gorkhi Terelj National Park. Pure L. sibirica stands were observed in quadrats with a lower maximum tree age; in contrast, P. sibirica occurred only in quadrats with a maximum tree age over 100 years. This result indicated that the forest patches experienced successional changes from L. sibirica to P. sibirica. In all transects, tree stands mainly presented multiaged regeneration patterns. Disturbances such as forest fire may result in the regeneration of younger L. sibirica. The basal area and maximum age increased with increasing distance from the treeline. The increase in the basal area and number of P. sibirica saplings suggested that succession from L. sibirica to P. sibirica was more advanced in the forest interior than at the forest edge. Differences in the disturbance regime may explain the changes in forest structure that occur with increased distance from the forest edge.