Seed dispersal and seedling recruitment of trees at different successional stages in a temperate forest in northeastern China

spatial distribution of adult trees in a forest community is determined by patterns of both seed dispersal and seedling recruitment.the objectives of our study were to understand the processes of seed dispersal and seedling recruitment of dominant tree species in a temperate forest of northeastern China and to identify the factors constraining seed dispersal and seedling establishment at different stages of forest succession.Methods During three summer and autumn sessions between 2006 and 2008,altogether 113080 seeds from 22 different tree species were collected in three large field plots representing different for-est types in the Changbai mountain region of northeastern China.the spatial distribution of seed abundance was analyzed using a syrjala test.regeneration success of nine major tree species was assessed using variables defining‘limitations’in‘seeds’and‘seed-ling establishment’.Important Findings We found that seed production fluctuated between years and varied greatly with forest types.Four tree species,Acer spp.,Fraxinus man-dshurica,Tilia amurensis and Betula spp.,had the greatest seed pro-duction and the widest range of seed dispersal,whereas Quercus mongolica showed the most sustained seed production pattern.the spatial patterns of seed abundance differed significantly among forest types and years.the tree species investigated in this study differed in the degree of seed limitation,as well as in limitation of seedling establishment.there were both negative and positive correlations between seed density and seedling density,depending on site and parental tree density.seeds of 16 tree species were found in the Populus davidiana-Betula platyphylla forest(PbF)plot,11 in the conifer and broad-leaved mixed forest(CbF)plot but only 8 in the broad-leaved-Korean pine mixed forest(bKF)plot.the number of seed-contributing species was not only greater in the secondary forests(CbF and PbF plots)than in the primary forest(bKF plot)but was also more variable during the 3 years of assessment.results from the correlations between seed density and seedling occurrence and that between parental tree density or seed weight and dispersal limitation confirm our intuitive expectations,i.e.heavy seeds had greater dispersal limitation but higher establishment success than light seeds.

Stand history is more important than climate in controlling red maple (Acer rubrum L.) growth at its northern distribution limit in western Quebec, Canada

Aims We examined growth of red maple(Acer rubrum l.)to evaluate environmental controls of its northern distributional limit in Eastern North america and its potential response to future climate change.Methods We collected growth data from nine sites located along a 300-km transect(47-49°N),which included frontier population of red maple and covered three bioclimatic domains in western Quebec.We ana-lyzed three growth variables:growth rates during the first 30 years of maple lifespan,cumulative basal area increment(ba I)over the most recent decade(2000-2009)and annual growth rate over the whole tree lifespan ranging from 58 to 112 years.We also examined growth sensitivity to climate by using response function analysis.Important Findingsthree different proxies of maple absolute growth(initial growth rate,ba I during 2000-09 and mean diameter growth rate)indicated a better growth with an increase in latitude.We speculate that stand history effectively overrode the direct effects of colder climate on maple growth along the s-N gradient.regeneration of maple in the southern sites likely occurred in canopy gaps,whereas in the north it was contingent upon large disturbances such as stand-replacing fires,which apparently provided more favorable light environment for maple growth than canopy gaps.the annual growth variability,which reflects effects of annual weather on growth and is largely independent from the absolute growth rate,was significantly affected by monthly climate,suggesting a positive effect of higher summer temperature in the northern part of the transect(48-49°N)and a negative effect of summer drought in the south(47-48°N).In the future,the natural and human disturbance regimes will be dominant controls of the actual biomass productivity of red maple at the northern limit of its present distribution range.Direct effects of climate on maple growth would likely be less important in this context,and will likely entail negative effect of increased summer drought in the southern part of the study area and positive effects of increased temperatures in the north.