The Mountain
Pine Beetle or Dendroctonus ponderosae (MPB) is an endemic
species of Western North America; however, it has become the most serious
pest affecting pine tree stands in BC's forests today.
MPB's attack trees during the months of July and August when
the trees are under the greatest stress due to deficiencies
of water. Female beetles fly to a tree and bore through the
bark to the cambrial area where they emit pheremones to attract
males and other females. The insects then mate under the bark
and the female constructs egg galleries, parallel to the grain
of the wood, in the cambrial region. The beetles live through
the winter in the trees as adults and larvae. In general, one
generation of beetles infests one tree per year. During this
period, the adult beetle injects a fungus into the sapwood which
literally stains the wood blue and interrupts the flow of water
to the top of the tree; this combined with the damage caused
by bore holes and egg galleries, eventually kills the host.
One year after attack, the foliage of the pine turns red, however,
by this time the beetles have already moved on to other trees.
Since the early 1990's, a number of factors have contributed
to creating MPB infestations of epidemic proportions in the
forests of northern BC; the catalyst of which has been several
consecutive years of mild winter temperatures. The most effective
natural control of MPB infestations is cold winter temperatures
with sudden cold snaps of -25C in the early fall or late spring
or sustained temperatures below -40C throughout the winter.
Unfortunately this has not occurred in the last several years
in the infested areas. Another natural control for MPB is forest
fires, unfortunately and unwittingly, our ability to effectively
control forest fires over the past 40 years has led to a high
percentage of trees in given stands, living to mature ages.
In the case of lodgepole pine, infestations are most likely
to be successful in stands which are over 80 years old. The
mature forests, besides possibly being unable to effectively
resist infestations, are also more likely to have larger basal
areas, which the mountain pine beetles prefer.
Because lodgepole pine is the predominant pine species in BC,
accounting for almost 24% of the provinces total growing stock,
large investments are being made by the government and industry
to control and manage MPB infestations. Some of the management
methods include: pheromone baiting, removal of specific infested
trees, small and sometimes large scale clear-cut harvesting,
falling and burning of beetle infested trees and mosaic burns,
which are large scale burns of a concentration of infested trees.
Prevention methods include: reduction of tree densities and
establishment of various tree species and ages in newly planted
forest stands. If stands which may be susceptible to infestation
are identified before hand, these and other preventative methods
may be implemented to avoid or minimize the effects of a MPB
infestation. One of the rating systems of susceptiblity to MPB used today is called
a hazard assessment. This tool may be used to identify those
areas where substantial losses of pine to MPB could occur; thus
resources may be targeted to that particular area.
The following project uses a hazard assessment, based on stand
age, density, percent susceptible pine basal area, and location
(figures 1-4), to identify those
areas in part of the Vanderhoof forest district which may be
susceptible to MPB infestation. Both ArcView and IDRISI were
used to produce a hazard map (figure
9) which identifies low, medium and high risk areas.
