Abstract
Horizontal variance of a stand structure and productivity in a tropical foothill rain forest was analysed with the dbh census data obtained from the successive observation for 8 years at a 1-ha forest stand in West Sumatra, Indonesia. Targets of the census were trees over 8 cm in dbh.
Individuals at each dbh class distributed randomly in horizontal pattern. The quadrat method based on the dimensions per some unit area showed that the aboveground biomass was higher aggregated in spatial distribution because of the strong influence of the scattered emergent trees. Main canopy trees being about 35 cm in dbh largely affected the horizontal distribution of leaf biomass and productivity, and the degree of contagion of these values was lower than that of aboveground biomass.
We estimated the stand structure and productivity around 2336 points in a plot, arranging systematically at intervals of 2 m, from the values per projection area of a tree covering each point. Bird’s-eye-view diagrams were presented to visualize the horizontal distribution patterns. The three-dimensional distribution of estimated relative illuminance showed the horizontal and vertical stratification in a 1-ha forest stand. The frequency distribution of biomass, productivity and relative illuminance at lower levels under 20 m in height could be approximated by the log-normal distribution. The coefficient of variance of productivity was higher than those of aboveground and leaf biomass. A simulation of the regeneration process at a gap site in a mature forest reproduced the high variance of productivity.
