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Development of a technique for sampling mountain pine beetle populations in lodgepole pine.

University of British Columbia

A technique was developed for sampling the mountain pine beetle, Dendroctonus ponderosae Hopkins, several times during its life cycle for the purposes of estimating within-generation mortality and population trend. The sampling technique is based on a critical study of the density gradients of brood in larval and pupal stages, both vertically and horizontally around the circumference of infested trees. The shape, orientation and size of the optimum sampling unit were investigated by studies of the spatial arrangement of brood, the relationship between edge effect bias and sampling unit shape and size, and by a study of the relationship between total sampling time and sampling unit size. The optimum unit is rectangular, has a width to length ratio of approximately 1:2, and is orientated with long sides perpendicular to the vertical axis of the infested tree. Optimum unit size was approximately eighteen square inches when sampling was at two height levels on the infested stem. A two-stage sampling technique was most appropriate for the sampling problem. The infested surface area of individual trees constituted the primary unit. Variability of brood density estimates between primary units was most efficiently reduced by regression sampling on primary unit size. The variance of brood counts within primary units, on the other hand, was sufficiently reduced by the construction of five within-primary unit strata. Stratum boundaries were determined on the basis of the circular distribution of brood counts (around the stem circumference) and the relationship between brood density and bark thickness. The sampling variances of both attacks and brood counts were related to their respective means by the equation s² = axˉb , where s² = variance/secondary unit. (formula omitted)=mean brood or attack counts/secondary unit and a and b are constants. Therefore, the counts had to be transformed in order to obtain an efficient estimate of the population variance. Taylor's power transformation, sufficiently removed the variance-mean relationship. Population totals (which have to be estimated in order to estimate population trend) were obtained by developing a surface area function to predict infested surface area for individual trees. This surface area function made possible the estimation of partial surface area to any specified height level. The latter property of the function was utilized to estimate within-primary unit stratum sizes. An approximate method of population trend prediction was developed for general insect surveys. This method is based on an estimate of brood density from the d.b.h. region of infested trees and on an estimate of the total infested bole area from a partial surface area table. Population trend is estimated by forming the ratio of the product of total infested surface area and brood density from the d.b.h. level in two successive years.

Text

2011-06-17

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http://hdl.handle.net/2429/35554

Forestry

University of British Columbia

Graduate