Schmid, J.M; Mata, S. A. 1996. Natural variability of specific forest insect populations and their associated effects in Colorado.

Beetle-killed trees in the Front Range of Colorado were observed for their rate and direction of falling. No trees fell within the 2 years following infestation. Thereafter, trees generally fell at the rate of 3-5?40 per year unless winds exceeded 75 mph. Most trees fell to the east and broke off between ground level and 2 feet above ground. Keywords: Dendroctonus ponderosae Hopki ns, Pinus ponderosa Management ImpIicationsForest managers need not be concerned with the falling of beetle-killed ponderosa pine until more than 3 years after infestation. Thereafter, strong winds will blow down many trees when winds exceed 75 mph.

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Ponderosa pine stands were partially cut to various stocking levels at five locations, periodically surveyed, and remeasured during the 20 years after installation. Mean diameter generally increased 2 inches over the 20-year period on most partially cut plots and less than 2 inches on unmanaged controls. Average diameter growth for diameter classes in partially cut plots was generally significantly greater than average diameter growth for the same diameter classes in uncut control plots. Basal area increased 20 to 40 ft 2 /acre in partially cut plots and 5 to 21 ft 2 /acre in unmanaged controls at four locations over a 20-year period. Beetle-caused mortality ranged from 0 to 51 percent of the trees in partially cut plots and from 1 to 77 percent of the trees in control plots although mortality was generally <8 percent in partially cut plots. Beetles attacked trees ranging from 8 to 18 inches in partially cut stands and from 7 to 19 inches in unmanaged stands. Beetles did not exclusively attack >16-inch diameter trees, so some trees >16 inches may be selected as leave trees. However, if an infestation persisted in a stand, trees in diameter classes >16 had the highest percentage mortality. The effectiveness of partial cutting for minimizing mountain pine beetle-caused mortality is influenced by: residual stocking level, size of the partial cut, amount of time since the area was cut, and proximity of beetle populations. Partial cuts of <10 acres may not minimize beetle-caused mortality if the cut stands are surrounded by unmanaged forest. Management to minimize beetle-caused mortality should be considered the top priority in mature ponderosa pine stands.

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The concepts and a procedure for evaluating plant community change using the squared Euclidean distance (SED) resemblance function are described. Analyses are based on the concept that Euclidean distances constitute a sample from a population of distances between sampling units (SUs) for a specific number of times and SUs. With different times, the distances will be intracluster or intercluster. Intercluster distances represent a control treatment. If the communities differ between times, the population will contain clusters (regions of high density with short distances between SUs) that are separated by regions of low density (great distances between SUs). Within-and between-years mean squares from analyses of variance for each species (sp) in the data matrix can be used to compute the intracluster and intercluster mean distances. A multivariate ANOV A gives a test of the hypothesis that the intracluster mean distance is equal to the intercluster mean distance at an overall error rate approximately equal to ex. The statistical distribution of SEDs is the distribution of a linear combination of independent Chi-square random variables. Knowledge of this distribution and use of the usual approximations make the estimation of approximate confidence intervals for the mean intercluster and intracluster distances and their difference possible and reliable. The confidence intervals may be examined and a decision made regarding any indicated change in the community. A simple example is provided to permit study of computational methods.

Three experiments were conducted to evaluate the use of solar radiation for reducing survival of mountain pine beetle populations in infested logs. Ponderosa pine logs were used in experiments 1 and 2 and lodgepole pine logs were used in experiment 3. Experiment 1 comprised three treatments: (1) one-layer solar treatment without plastic sheeting and logs rotated one-third of a turn once a week; (2) two-layer solar treatment with plastic sheeting; and (3) two-layer solar treatment without plastic sheeting. For experiment 2, two additional one-layer treatments were added: one-layer treatment with plastic sheeting and no rotation and a one-layer with no plastic sheeting and no rotation. Experiment 3 included all the above-mentioned onelayer treatments only. For all experiments, brood density per 0.05 m 2 (0.5 ft 2 ) was estimated before and after treatment and analyzed using repeated measures analysis of variance. Subcortical temperatures were monitored in one replicate of all treatments in all experiments. In experiment 2, phloem moisture was monitored before and after treatment in uninfested logs. All treatments in all experiments caused drastic reductions in brood survival. In experiment 1, the one-layer treatment with the logs rotated once a week significantly reduced brood survival compared to the two-layer without plastic sheeting treatment but was not different from the two-layer with plastic sheeting treatment. There were no differences in brood survival after treatment associated with any treatments in experiments 2 and 3. In all experiments brood survival was consistently reduced in the aspects of the logs exposed to the sun. Maximum temperatures were consistently higher in the treatments with plastic sheeting, the exposed surfaces of the logs to the sun, and the upper layer of logs in the two-layer treatments. No differences were detected in phloem moisture content in uninfested logs before and after treatment in experiment 2, suggesting that heat is directly responsible for the observed reductions in survival. We conclude that solar treatments are an effective alternative for reducing mountain pine beetle survival in infested ponderosa and lodgepole pine logs.

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