Demography and matrix analysis on a natural Pterocarya rhoifolia population developed along a mountain stream

The population structures and dynamics of a dominant riparian canopy species, Pterocarya rhoifolia (Juglandaceae), were analyzed based on the census data collected for the 7 years from 1989 through 1996. A study plot was established over an environmental gradient that included the lower hill-slope, river terrace, and low-level floodplain of a riparian area within a 2.8-ha cool-temperate forest stand. Spatial analyses of the demographic data showed that there were significant differences in recruitment, growth, and death processes among the three habitats. The slope and terrace habitats were the severest for the pre-reproductive stage and recruitment process, respectively. A topographically combined projection matrix was constructed for the life-history processes of the three subpopulations, which clearly revealed that the floodplain and terrace subpopulations constituted the mainland source populations, whereas the slope subpopulation was an island sink population. The whole Pterocarya population linked by seed flow showed an increase in population size (lambda=1.052). The elasticity analysis showed that the sum of the elasticity values was zero, 0.14, and 0.85 in the slope, terrace and floodplain subpopulations, respectively. This fact clearly indicates that the role of the floodplain subpopulation as a source population is six times as large as that of the terrace subpopulation.