|Issues are bark beetles and seed and cone
|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.
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
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:
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.