Accounting for competition effects is an essential step in building any stand growth simulator.
However, accurate modelling of competition effects depends upon a clear understanding of quantitative
relationships of various aspects of stand dynamics, including distributional parameters and
spatial statistics. This study addressed four aspects of competition effects: 1) competition effects
on distributional parameter dynamics of tree size variables; 2) inter-specific (loblolly pine vs.
hardwood) and intra-specific competition effects on basal area growth, 3) dynamics of spatial statistical
characteristics of DBH and total height, and their relevance to intertree competition, 4) and
spatial properties of competition measures by available stand simulators for loblolly pine (Pinus
taeda L.) plantations. Competition was found to affect the distribution parameters such as coefficient
of variation, skewness, and the general shapes of distributions for diameter measurements,
total height, crown width and crown height. Competition expedites size differentiation and thereby
increases distribution variability for all variables except crown height. Intertree competition also
drives skewness of these variables negative, although the distributions of crown heights tends to be
more symmetric. Normality assumption generally holds for diameter measurement, but distributions
of total height and crown width deviate from, and those of crown height approach, normality
with intensified competition. A set of competition driven equations was developed for the distribution
parameters and was validated. The differences of distribution parameters among the variables
studied could be attributed to their biological meanings.
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