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.为阐明蒙古林草交错带（Mongolian forest-steppe ecotone）内森林斑块的动态特征，并揭示森林结构随距林缘距离的变化规律，本研究基于两类空间尺度开展森林结构与树木年龄调查：即样带（transects）尺度，以及样带内部的样方（quadrats）尺度。研究样带沿林线梯度布设，研究区域设于Gorkhi Terelj国家公园（Gorkhi Terelj National Park），聚焦两种代表性乔木树种：西伯利亚落叶松（Larix sibirica）与西伯利亚红松（Pinus sibirica）。 仅在最大树木年龄较低的样方中观测到纯西伯利亚落叶松林分；与之相对，西伯利亚红松仅分布于最大树木年龄超过100年的样方内。该结果表明，研究区内的森林斑块正经历由西伯利亚落叶松向西伯利亚红松的群落演替过程。 所有样带内的林分均以多龄级更新为主要特征。森林火灾等干扰事件可促进西伯利亚落叶松的幼龄个体更新。 林分断面积与最大树木年龄均随距林线距离的增加而递增。 西伯利亚红松幼树数量与林分断面积的增长表明，林内由西伯利亚落叶松向西伯利亚红松的演替进程较林缘更为超前。 干扰制度的差异可解释随距林缘距离增加所发生的森林结构变化。