Intraspecific Competition in a Natural Stand of Betula ermanii

Density and size of naturally regenerated Betula ermanii weremonitored for six years in a 100 m² plot located in Hokkaido,northern Japan. Natural thinning of 10- to 15-year-old treesoccurred at a negative exponential rate related to tree volume,demonstrating the –3/2 power rule of self-thinning. Diameterdistributions were unimodal at ages 10–13 years and bimodalat 14 and 15 years. Changes in diameter distribution were accompaniedby changes in structure, from a one- to two-storied stand. Mortalitywas highest among smaller trees and where density was greatest.The spatial distribution of trees changed from random to uniformwith increased stand age. Betula ermanii Cham., Self-thinning, mortality, spatial distribution, size distribution     

Theoretical Relationships Between Mean Plant Size, Size Distribution and Self Thinning under One-sided Competition

As yet there is no comprehensive theory in plant populationecology to explain relationships between mean plant size, sizedistribution and self-thinning. In this paper, a new synthesisof plant monocultures is proposed. If the reciprocal relationshipbetween plant biomass and plant population density among variousstands of even-aged plant populations holds, the same reciprocalrelationship must exist between cumulative mass and cumulativenumber of plants from the largest individual within a population,assuming strict one-sided competition (which is an extreme conditionfor competition for light among plants). The two parametersof the relationship between cumulative mass and cumulative numberwithin a stand both correlate with maximum plant height in thestand. One parameter equals the reciprocal of the potentialmaximum plant mass per area, which is expressed by the productof maximum plant height and dry-matter density. The other parametercorrelates with the potential maximum individual plant mass,which is allometrically related to maximum plant height. Asa stand develops, the growth rate of the smallest individualswill become zero due to suppression from larger individuals,and they will die; i.e. self-thinning will occur. The slopeof the self-thinning line is expressed through the coefficientsof allometry between height and mass and between dry matterdensity and height. When the former coefficient is 3 and thelatter is 0, the gradient exactly corresponds to the value expectedfrom the 3/2 power rule, but it can take various values dependingon the values of the two coefficients. Competition among individualsdetermines size-density relationships among stands, which inturn determine the size structure of the stand. The size structureconstrains the growth of individuals and results in self-thinningwithin the stand.Copyright 1999 Annals of Botany Company. Monoculture, plant population, self-thinning, competition, hierarchy, size-structure.     

Genetic Variation and Population Differentiation in Natural Populations of Cryptomeria japonica

Abstract Sugi (Cryptomeria japonica D. Don) is a valuable tree species in Japan. The present natural distribution is limited to small scattered areas in temperate moist regions, and most of these areas are surrounded by vast artificial plantations. We studied natural populations of C. japonica in an effort to determine the amount and distribution of genetic diversity using 12 allozyme markers. The amount of genetic variation within the species is high (H_T=0.196) but most is found within populations with little among populations (G_ST=0.034) despite their isolated distribution. This pattern of genetic diversity is inferred to be the consequence of the following: (1) the distribution of this species in the past was wider and more continuous than it is now; (2) a high rate of gene flow occurs, perhaps including gene flow between natural populations and plantations; and (3) the long lifespan. However, the distribution of allele frequencies at the 6Pg-1 in northern populations on the side near the Sea of Japan is clearly different from those in other populations. This observation is inferred to result from founding events.