Seed germination of four tree species responding to environmental heterogeneity Induced by gap characteristics and leaf litter coverage in a secondary forest ecosystem, northeast China

摘要

The characteristics of canopy gaps ( i. e., gap formation and gap sizes) lead to environmental heterogeneity mainly by promoting the fluctuation of light environment and temperature etc. The formation of gaps could also affect litter accumulation on the forest floor. The interaction of litter coverage with the canopy openness variation in gaps produces further fine-scale heterogeneity in germination sites. It has been reported that by providing abundant ecological niches, canopy gaps can facilitate the regeneration of pioneer tree species and the coexistence of various species in secondary forests. Juglans mandshurica, Quercus mongolica and Fraxinus mandshurica are three dominant tree species coexisting in the secondary forests, northeast China. With the increasing demands for timer and other forest products, larch plantations (Larix spp.) have been developed within the secondary forests in northeast China and mosaic plantation/secondary forest landscapes have been formed. Although existing secondary forests are experiencing gap disturbances, the effects of the interaction of litter coverage with gap characteristics on the seed germination of these main tree species are poorly understood.