Seed Rain Dynamics And Dispersal Limitations In Mixed Broadleaf-conifer Forest In Changbai Mountain

Seed dispersal is the important way to regenerate for forest and the main measure to self-recolonize and self-repair for forest ecosystem. Seed dispersal limitation determines the dispersal distance in space and the species diversity in community. Based on the data of seeds and seedlings from the long-term observation, this paper researched the seed and seedling dynamics in mixed broadleaf-conifer forests (the Secondary Populus davidiana-Betula platyphylla forests, Secondary conifer and broadleaved mixed forests and Broad-leaved Korean pine mixed forests) in Changbai Mountain, and analyzes the seed dispersal strategies and dispersal limitation, which will supply the theoretical foundation and data support for the community structure dynamics, species biodiversity and species coexistence in mixed broadleaf-conifer forests in Changbai Mountain.From 2006 to 2008, we collected eight families, eleven genus and twenty-two species in total, including Fraxinus mandshurica, Tilia amurensis, Acer, Quercus mongolica, Maackia amurensis and Betula and so on. In general, the seed density was high in every community while the Secondary conifer and broadleaved mixed forest had the highest seed density. In every community, the most proportion is the seeds of Fraxinus mandshurica, Tilia amurensis and Acer. In the Secondary Populus davidiana-Betula platyphylla forests, the seeds of Fraxinus mandshurica accounted for 70% and the seeds of Tilia amurensis occupied 60% in the broad-leaved Korean pine mixed forest and Secondary conifer and broadleaved mixed forest. The trend of seed abundance with the time showed the simple peak curve, but the time of peak was different yearly. The species abundance is no apparent variation with time.The spatial pattern of seeds appeared clustered distribution in part. The distribution of seeds changed dramatically with communities. Seeds disperse widely so that almost all the traps can collect the seeds. Through the research of dispersal capability of several species, it is concluded that most of seeds aggregated around the mother trees and only few seeds could disperse far. The seeds of Fraxinus mandshurica and Acer can be dispersed the whole plots with their wings while the seeds of Tilia amurensis also can spread the whole forests because of its ball shape and large numbers. The seeds of other species have strong seed limitation and establishment limitation.Besides that, the relationship between seed density and seed mass showed negative relevant. The species with larger seeds tend to produce more seeds. The relationship between seed density and seedling density showed negative density-dependent partly like Maackia amurensis,. Abies nephrolepis, Quercus mongolica. However, the species like Fraxinus mandshurica, Tilia amurensis, Acer showed positive correlation between seed density and seedling density.