Abstract:We studied niche characteristics of key arbor tree species including Fraxinus mandshurica, Juglans mandshurica, Phellodendron amurense, Tilia amurensis, Tilia mandshurica, Populus davidiana, Betula platyphylla, Betula costata, Ulmus pumila, Acer mono and Quercus mongolica that represent natural secondary forests in Northeastern China. We conducted these studies at the catchment scale, taking flow accumulation gradient as resource axes, also forest storey as the resource states. Relative flow accumulation ecological amplitude and flow accumulation competition index were proposed to enrich the measurement of niche characteristics. We found that Acer mono, Quercus mongolica and light-demanding pioneer species including Populus davidiana and Betula, platyphylla occupied dominant position in the main storey while the main associated broadleaved tree species of the primary broadleaved-Korean pine mixed forest including Acer mono, Ulmus pumila, Fraxinus mandshurica, and Tilia amurensis occupied dominant position in the succession storey. On the other hand, niche differences between main and succession storey, based on the forest storey resource theory, indicate requirement of tree species for the habitat and the variation trends of this requirement in the succession sere of the natural secondary forest community in this area. We concluded that it was effective to use flow accumulation as a spatial dimension of niche, which aims to illustrate the niche spatiotemporal patterns among different tree species under the topographic and moisture gradients at a catchment scale.