Estimating The Rate And Amount Of Tree Loss From Mountain Pine Beetle Infestations

Periodic diameter and basal area growth were determined for partially cut stands of lodgepole pine at five locations over approximately 10 year periods. After cutting, average diameters in the partially cut plots generally increased by 0.8 inches or more, while average diameter in the uncut controls increased by 0.6 inches or less. Diameter growth in the partially cut plots was generally significantly greater than diameter growth in the controls. Individual tree growth is discussed in relation to potential susceptibility to mountain pine beetle infestation. Basal area decreased in three of the four GSL (growing stock level) 40 stands because of windthrow. Basal area generally increased >1.0 ft 2 / acre/year in partially cut plots except in the GSL 40 stands with substantial windthrow and one GSL 100 with an Armillaria infection pocket. Basal area increases in the control plots ranged from 0.2 to 1.1 ft 2 /acre/year, although the one control with a BA growth rate of 1.1 ft 2 /acre/year had a relatively low initial BA. Data from the stands are employed in the susceptibility rating methods of Amman et al.(1977), Shore and Safranyik (1992),and Anhold et al. (1996 to determine stand susceptibility and the results discussed in terms of general applicability of these methods to partially cut stands. Basal area growth is used to estimate the length of time required for various stand densities to reach specific susceptibility thresholds for mountain pine beetle infestation. Several of the GSL 40 stands are not projected to reach the susceptibility thresholds in 100 years because of windthrow. Barring mortality 1%,GSL 80 stands are estimated to reach the basal area threshold of 120 ft 2 per acre in

This study is part of a series of research papers that explore the biological, social, and economic aspects of British Columbia's mountain pine beetle epidemic. The objective of this study is to compare two different approaches for calculating beetle pressure, and to assess the impact these approaches have on the subsequent calculation of risk ratings. To meet this objective, beetle pressure was calculated using the traditional distance-based model, as well as using an alternative density-based model, implemented with a Voronoi tessellation generated from helicopter-GPS point survey data of known beetle infestation locations.--Includes text from document.

Tree losses resulting from infestation by the mountain pine beetle (Dendroctonus ponderosae Hopkins) were measured in two stands of lodgepole pine (Pinus contorta Dougl.) where the beetle population had previously been epidemic. Measurement data showed that larger diameter trees were infested and killed first. Tree losses ranged from 1 percent of trees 4 inches (d.b.h.) to 87 percent of those 16 inches and greater d.b.h. Numbers of adult beetle emergence holes averaged 1.3 per square foot of bark area in trees 7 inches d.b.h. and 62 in trees 28 inches and greater d.b.h. The observations indicate that large infestations of mountain pine beetle depend on the presence of large diameter trees within a stand of lodgepole pine, thus implying that beetle population growth is food-limited.