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Linda Joyce
Rocky Mountain Research Station
240 West Prospect
Fort Collins, CO 80526
Phone: 970-498-2560
 United States Department of Agriculture Forest Service.USDA logo which links to the department's national site.Forest Service logo which links to the agency's national site.
Forest Insects

Issues are bark beetles and seed and cone insects.
Models to estimate probabilities of infestation and extent of mortality based on stand conditions.
Models to define the contribution of insects to fuel loads in forests.
To help define the impact of insects on western forest ecosystems for managing vegetation.
Insects and Fire Tree Mortaliy Insect and Fire Dependent Ecosystems

Geostatistical Approaches in Studying Bark Beetle Ecology

Probability of infestation and extent of mortality models estimate the degree of susceptibility of forest stands to infestation or the amount of expected mortality caused by different bark beetle species. Traditionally, these models are developed using averages across the forest stands or are applied to a management unit regardless of the spatial scale of the original study. Incorporation of spatial information may improve the reliability of these models. In this study, the authors examined the influence of within stand variation of basal area on the distribution of tree mortality caused by the Douglas-fir beetle. The results illustrate how geostatistical techniques can be used to incorporate within-stand variability of Douglas-fir basal area into the process of rating a stand for potential mortality. The results of the geostatistical analyses suggest that after the outbreak, Douglas-fire basal area at specific points is more dependent on adjacent points than before the outbreak. In other words, the beetle increased the within stand continuity of host type (Douglas-fir) basal area. This study, and other recent work, indicates that bark beetles exhibit spatial patterning at the within-stand spatial scale. Developing an understanding of the different spatial scales at which bark beetles operate, both within stand and at the landscape level can help in refining management approaches and explaining their role as disturbance agents. This study demonstrates the value of geostatistical tools to extend our knowledge of bark beetle ecology and to develop improved management strategies.

Negron, J. F., Anhold, J. A., Munson, A. S. 2001. Within-stand spatial distribution of tree mortality caused by Douglas-fir beetle (Coleoptera:Scolytidae). Environmental Entomology. 30: 216-224.

Probability of infestation and extent of mortality models.

Bark beetles are important disturbance agents in the forest ecosystems of the Rocky Mountains. Eruptive populations of bark beetles can cause extensive tree mortality. Although a part of the natural ecosystems, these disturbances can also conflict with certain management objectives. Probability of infestation and extent of mortality models are tool that land managers can use to identify forest stands that may be more likely to b infested by bark beetles or how much mortality may occur. In recent years we have been developing simple models for this purpose for roundheaded pine beetle in New Mexico, Arizona, and Utah; Douglas fir-beetle in the Colorado Front Range, Idaho, Montana, and Wyoming; and pinyon ips in Arizona. We are also developing a system for mountain pine beetle in ponderosa pine in the Colorado Front Range.

Negrón, J.F.; Wilson, J.L. 2003. Attributes associated with probability of infestation by the piñon ips, Ips confusus (Coleoptera: Scolytidae), in piñon pine, Pinus edulis. Western North American Naturalist. 63(4): 440-451.

Negrón J.F., Wilson J.L., Anhold J.A. 2000. Stand conditions associated with roundheaded pine beetle (Coleoptera: Scolytidae) infestations in Arizona and Utah. Environmental Entomology. 29: 20-27.

Negrón, J.F.; Schaupp, W.C.; Gibson, K.E.; Anhold, J.; Hansen, D.; Thier, R.; Mocetini, P. 1999. Estimating extent of mortality associated with the Douglas-fir beetle in the Central and Northern Rockies. Western Journal of Applied Forestry. 14: 121-127.

Negrón, J.F. 1998. Probability of infestation and extent of mortality associated with the Douglas-fir beetle in the Colorado Front Range. Forest Ecology and Management. 107: 71-85.

Negrón, J. 1997. Estimating probabilities of infestation and extent of damage by the roundheaded pine beetle in ponderosa pine in the Sacramento Mountains, New Mexico. Canadian Journal of Forest Research. 27: 1936-1945.

Sequential sampling protocols for estimating brood adult density of Douglas-fir beetle.

Often land managers and forest health specialists are interested in determining population trends of forest insects. We developed a fixed-precision sequential sampling plan for the Douglas-fir beetle in the Colorado Front Range. The plan allows a user to estimate with a known precision the density of brood adults in a stand. The user can also use the ratio of brood adults to attacking adults to determine if the population is increasing or decreasing.

Negrón J.F., Schaupp W.C., Johnson E. 2000. Development and validation of a fixed-precision sequential sampling plan for estimating brood adult density of Dendroctonus pseudotsugae (Coleoptera: Scolytidae). The Canadian Entomologist 132: 119-133.

Fire and insect interactions

Fire and insects are primary disturbance agents in Rocky Mountain forests but little is known about their interactions. In a series of recent studies we have started to quantify fuel loads caused by outbreak populations of the roundheaded pine beetle in the Sacramento Mountain of New Mexico. Preliminary data suggests that stands where outbreaks occurred may have seven times higher fuel loads that unaffected stands. We have also initiated studies in cooperation with Forest Health Protection Staffs to examine the level of fire injury required to kill ponderosa pine and the susceptibility to insects associated with non-lethal fir injury. These studies are being conducted in the Black Hills of South Dakota, Colorado, Arizona, and Montana.

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