Pattern of Self‐Thinning in Jack Pine: Testing the Random Mortality Hypothesis

Spatial statistics were used to examine the pattern of self—thinning in a 0.25—ha even—aged (65 yr old), pure stand of jack pine in the boreal forest near Elk Lake, Ontario, Canada. The positions of 459 living and 916 dead trees were recorded and refined nearest neighbor analysis G(W) and second—order spatial statistics L(t) were used to examine distributional deviations from both the Poisson expectation and the hypothesis of random mortality. The results indicate that the initial (live + dead, n = 1375) distribution was locally random. By contrast, the distribution of live trees was locally highly regular, while the dead trees were significantly more clumped than random mortality would dictate. It is suggested that the development of a strong regular pattern in the survivors is attributable to differential mortality involving two distinct competitive phases: an early scramble phase involving two—sided competition for soil resources, and a lager contest phase involving one—sided competition for light. Analysis of L(t) for the live trees indicated a mean "area of influence" for each individual of an °3.5 m radius, suggesting that trees may compete directly only with their immediate neighbor.