Spacing and Competition in Natural Stands of Sand Pine

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Abstract
Spacing studies of many even—aged, pure stands of sand pine of various age classes using nearest neighbor distances show that most stands under 23 years old are either aggregated or essentially randomly distributed. Most stands 23 or more years old show significant to highly significant departures toward regular spacing. Information regarding the severity and duration of maximal intraspecific competition between the trees was obtained by measuring nearest neighbor distances to all pines, dead or alive. departure towards more even spacing was shown in nearly every stand when only live trees of the same quadrat were considered. Only stands showing maximal intraspecific competition–those showing a considerable number of dead trees–were studied. In an aggregate stand which showed marked trunk divergence from the center of clumps, distances were measured in the same sample both at breast height and at ground level. The difference in apparent spacing proved highly significant–the breast height measurements being essentially random, the ground level ones highly aggregate. A marked thinning of the understory herbs and shrubs appeared correlated with longer maximal intraspecific competition in one portion of a stand than in another part of the same stand with a dense understory. Correlations between the sum of the squared diameters of nearest neighbors and the distance between them proved positive at the 1% level in three stands, positive at the 5% level in three, and so weakly positive in three as to have little significance. Correlation coefficients were only weakly consistent with stand age, the older stands tending to have the higher correlations.