No. 1038

Title:

Size distribution changes associated with gap-forming processes - the two-dimensional inhomogeneous Poisson process with Bayesian nonparametric smoothing -

Author(s):

Shimatani Kenichiro(The Institute of Statistical Mathematics)

Key words:

ABIC, allometry, gap dynamics, old-growth forest, patch mosaic, subcanopy

Abstract:

The size structure of a forest tree community reflects its local environmental conditions and changes associating with environmental gradients. Drawing histograms has limited descriptive value when sample sizes are small. Modifying the Bayesian nonparametric smoothing technique described in Sakamoto (1991, Kluwer Academic Publishers), this paper formulates size structure variation along a gradient in the form of a two-dimensional inhomogeneous Poisson process. The model was applied, using both height and diameter at breast height (DBH), to an old-growth forest in which the gap dynamics are primarily controlled by small-scale disturbances. The 142.5m linear plot was established so that it traversed different gap-forming processes, such as gaps older than 40 years and areas of closed canopy. The continuous variation in height structures confirmed the presence of subcanopy strata in the old gaps, and the vertical profiles more sensitively reflected past gap-formation than was achieved by considering diameter distributions. The diameter-height allometry also varied depending on disturbance histories: under closed canopies, trees tended to grow vertically while there was a variety of growth strategies in the old gaps. The inhomogeneous Poisson process with nonparametric smoothing contributed to illustrating a patch mosaic resulted from gap-dynamics in the old-growth forest.