The
Mountain
Pine Beetle is a bark beetle native to the the forests of Northwest
North
America. Its current range is from the Pacific Coast to Western South
Dakota
and from Northern British Columbia to Mexico. In its Northern habitats
it can
be found at elevations as low as sea-level, but in the Southern range
it is
restricted to mountain regions higher than 3000 meters (Amman et al.,
1990).
The adult
beetle typically infests its host in July. It makes pitch tubes under
the bark
and constructs long, straight egg galleries (10-120 cm). The eggs hatch
after
10-14 days (Amman et al.,
1990) and during
the late summer the larvae feed on the phloem which is fatal for the
tree (Bentz
et al., 1991).
The
larvae and the beetle
survive the winter under the bark by going through three stages, as
described
by Regniere and Bentz (2007). In the first stage they feed on the
phloem. In
the intermediate stage the beetle voids its guts and eliminates
ice-nucleating
agents from the body as much as possible. Furthermore, it starts
accumulating
cryptoprotectants (alcohol) in the body.
In the final stage the beetle
reaches
its maximum accumulation of cryptoprotectants and is cold-hardened.
With this
technique it can survive temperatures down to -40ºC. The development
continues
in the spring with pupation and in July/August the adult beetle can
jump to the
next host.
This phenologic cycle is
completed under the bark normally in one year, but at low summer
temperatures
it might take two years. There are also examples from low altitude
locations in
California, where the beetle has completed two cycles within one year
(Amman et al., 1990). This may be
one of the future scenarios with a general heating of the climate.
Generally
though, each stage in the life cycle has a threshold temperature which
helps to
synchronize the phenology with the seasonal climate variation (Bentz et
al.,
1991).
Bentz et al.
(2001) suggests that
there is genetic variation within the MPB species associated with the
latitudinal variation, so the life-pattern is not only a matter of
climatic
variables but also genetic variation.
The
MPB has
developed a symbiosis with the blue stain fungi (Grosmannia clavigera).
The beetle
hosts this fungus in its mouth and thus carries it from tree to tree.
The
fungus limits the production of resin in the host tree which is the
pine's only
defence against the beetle infestation. Furthermore, it markedly limits
the
water transportation to the crown, which gradually discolours (Amman
et al., 1990).
The
MPB does have some natural enemies
including other
insects as well as birds (e.g. competition from other beetle larvae;
woodpeckers feeding on the larvae). In addition to this the tree can
increase
the pitch flow if the water supply is adequate. None of these factors
are
adequate to control the beetle at epidemic levels, but at an endemic
level they
do constrain the MPB. The most effective way of controlling it is
silvicultural
methods such as thinning of potential host tree stands and creation of
patches
with different age and species composition (Amman et al., 1990).
Susceptible
Host Trees
Posted by Simon, Dec. 3rd.,
2010
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Most
western pines (sugar pine (Pinus lambertiana), white pine
(Pinus monticola), ponderosa pine (pinus ponderosa), and Lodgepole pine
(Pinus
contorta Douglas ex Louden and Pinus Contorata var. latifolia)) are
susceptible
hosts of the MPB (Amman et al., 1990), but Lodgepole pine (Pinus
contorta
Douglas) and Ponderosa pine (Pinus ponderosae Lawson) are the most
important
host species (Logan and Powell, 2001: 160).
The
fire
suppression that humans have put upon the forests for the
last 100 years could be one of the reasons why the current lodgepole
stand is
more susceptible to MPB attacks. Forest fires are important for
lodgepoles,
since it prepares the seedbed, releases seeds from the serotinous cones
(that
are triggered to release seeds by heat of fire), and eliminates more
shade-tolerant species that would eventually replace the lodgepole pine
(Logan
and Powell, 2001). Furthermore, research point to the fact that pine
trees are
only susceptible to the MPB when they are between 80-160 years old.
Thus, in a
natural BC environment, where wildfires burn down the forest stand on
average
every 60 years, the infested part of the susceptible pine stand will
vary
between 17-25 %. At present the infested part of the susceptible stand
is as
high as 55 % (Taylor & Carrol, 2003: 41).
Climate
Change Impacts
Posted by Simon, Dec. 3rd.,
2010
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According
to the
Intergovernmental Panel on Climate Change (IPCC) climate change is
unequivocal,
thus having a profound effect on several
of the parameters controlling the area suitable for MPB: “At
continental, regional and ocean basin scales, numerous long-term
changes in climate have been observed. These include changes in arctic
temperatures and ice, widespread changes in precipitation amounts,
ocean
salinity, wind patterns and aspects of extreme weather including
droughts,
heavy precipitation, heat waves and the intensity of tropical cyclones”
(IPCC,
2007: 7).
The
current outbreak
is an order of magnitude greater in area than
previous outbreaks, reaching epidemic proportions, spreading
over 4.1x10^6 ha
(41.000 km^2) (Hamann &
Wang, 2006: 2773 after Ebata 2004).
This is mainly due to
an increased area of susceptible hosts
(caused by fire suppression, thus having forests reach older age) and
change in
climate allowing MPB to expand further north and east to areas
previously
uninhabitable (Kurz et al., 2008). The favorable climate is caused by
changes
in:
- Minimum Winter
Temperature
- Average Summer
Temperature
- Spring
Precipitation
- Aridity
Projecting the spread of MBP
and other insect pests in relation to
climate change is often done using General Circulation Models (GCMs),
of which
several have been developed.
However, the application of GCMs has several limitations: the finest
spatial
scale used in these models is often far too coarse to be applied to
ecological
surveys
(Logan et al., 2003: 132). As such interpolation is often necessary,
but local
climate data is to be preferred to limit the amount of uncertainties
and ease
projection of future spread.
According to Hamann
and Wang (2006) British
Columbia (49°-60° latitude) has experienced a
warming similar to that of the predictions from general circulation
models,
around 0.7 °C, why the use of these has been common in many studies of
future
MPB scenarios. Even such a small change has caused severe ecological
and
economic problems, as can be seen be the spread of MPB, a problem that
will be
further discussed later on.
As mentioned elsewhere
the MPBs temperature-controlled development
cycles and lack of diapauses (Logan and Powell, 2001) is highly
dependent upon
changes in temperature. Research suggests (Hamann and Wang, 2006; Logan
et al.,
2003) that this outbreak could be caused by a lack of low winter
minimum
temperatures, which would normally reduce the populations of this
native-insect
pest by killing the beetle. If temperatures drop to less than -40°C even the beetle natural defense mechanisms (as outlined above) can't keep it alive. Higher summer temperatures, especially in
august
where eggs hatch, are also a significant contributor, as well as higher
summer
temperatures allow the MPB to spread to higher altitudes and latitudes. Carroll
et al. (2004) suggests that if minimum 5% of the days in August are at least 18, 3°C warm this increases the risk of epidemic spreading.
Furthermore research
suggests (Carroll et al., 2004) that
reduced amount of precipitation in the late spring / early summer, as
well as a
general warming of the climate (the MPB needs a minimum of 833 degree
days a
year) has further enhanced the spread of the MPB.
To be precise, if precipitation in late spring are below average,
and if there's more than 833 degree days in a year, the risk of an
epidemic spread increases.If precipitation are in late spring are above
average the Lodgepole Pine's natural resistance are enhanced, thus
reducing the risk of an epidemic outbreak.
The death of vast areas of
forest further enhances the impact of
climate change due to emissions of carbon dioxide. Kurz et al. (2008:
987)
estimates that the
impact of beetles on NBP [net
biome production] was projected to reach -20
MtC yr^-1 […]
in 2009.
Cumulative beetle impact over the 21-year simulation period was
projected to be
-270 Mt C” released into
the atmosphere as a result of decaying trees.
That is
roughly one third of British Columbia’s anthropogenic carbon emissions.
Predicting future impacts
Posted by Simon, Dec. 8th.,
2010
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The
future impacts is predicted by data predictions by ClimateBC. The
predictions are based on the scenarios available in the latest IPCC
report (IPCC, 2007).
We have chosen to use the B1 and the A1FI
scenarios for our prediction of future impacts. The B1 predicts the
least change in carbon dioxide levels and temperature, whereas the A1FI, FI meaning Fossil Intensive,
predicts a much bigger change in the two parameters.
As such, it is
hoped that the two scenarios will reflect the upper and lower boundary
of the spread that can be expected in the future.
The CGCM1 model developed by the Canadian Centre for Climate Modeling
and
Analysis www.cccma.bc.ec.gc.ca), and another by the Hadley Centre for
Climate
Prediction and Research
(
www.met-office.gov.uk/research/hadley-centre).
(Logan et al., 2003: 132)
.
“This problem has been addressed through modeling and interpolation
techniques
that project GCM predictions to ecologically meaningful spatial and
temporal
scales”. (Logan et al., 2003: 132)
