Here’s your weekly Science Matters column by David Suzuki with Faisal Moola.
Little bug, big problem
Human beings are obsessed with size. We want bigger cars and bigger
houses, and, of course, men want bigger you-know-whats. But big isn’t
everything. A tiny insect about the size of a grain of rice, the
mountain pine beetle, has devastated British Columbia’s interior pine
forests, threatening enormous social, economic, and ecological
upheaval. The infestation, which is expected to kill close to 80 per
cent of B.C.’s mature pine forests, was caused in large part by global
warming and is now seen as a contributor to the problem that caused its
outbreak in the first place.
How can something so seemingly insignificant cause so much
damage? The mountain pine beetle (Dendroctonus ponderosae) is a
naturally occurring insect that starts its attack when a female uses
its senses to find a pine tree (usually lodgepole) that is at least 80
years old. On finding a mature tree, she bores into it while releasing
a pheromone that attracts male beetles. When the sex-crazed males
arrive, they in turn secrete pheromones that attract more females. The
tree mounts a response by secreting a toxic resin that beats back a few
beetles. But the beetles have another trick up their sleeves – or in
their mouths. They carry spores of a blue-stained fungus, which are
released as they bore into the tree. The fungus puts a stop to the
spread of resin and allows the beetles to keep tunnelling.
The symbiotic relationship between the beetles and fungus doesn’t
end there. The beetles lay eggs under the tree’s bark, and when the
larvae hatch, they feed on the blue fungus until they are mature enough
to leave the now dead tree, carrying the fungus in their mouths.
Under normal conditions, with fewer beetles, many trees could
successfully defend themselves. But industrial forest-management
practices and global warming have helped the beetles thrive.
Forest-fire suppression created a huge supply of the mature lodgepole
that the beetles find so appetizing. And while the spread of beetles
was once held back by cold winters that kill them, warmer temperatures
due to global warming have allowed the insects to survive and
proliferate, and to spread to areas that were once too cold for them.
The devastation caused by the beetles could exacerbate the unnatural
warming that is already occurring. Normally, forests are carbon sinks;
that is, they absorb carbon dioxide, a major greenhouse gas, from the
atmosphere through photosynthesis and store it in plant biomass and
soils belowground. When the trees die, they stop absorbing carbon
dioxide, and as they decompose, they release some of the stored carbon
back into the atmosphere. In attempting to stop the beetles’ spread,
the B.C. government has encouraged forestry companies to clear-cut
large areas of pine forest, even though there are still surviving trees
of other species in the infected stands. However, the hyper pace,
scale, and intensity of this logging threatens to increase greenhouse
gas emissions, as CO2 is released when trees are cut down and
carbon-rich forest soils are mechanically disturbed.
Its effect on climate change isn’t the only reason clear-cutting is
not a good strategy. Clear-cutting kills immature trees and species
such as spruce that aren’t attractive to the beetle. Trees take a long
time to mature to an age at which they become marketable, so if we cut
down all the pine now, many areas of B.C. won’t have much of a forest
industry for 80 years or more, whereas leaving some of the forests to
regenerate on their own would mean the healthy trees that are now
coming up could be ready for harvest much sooner. Areas that have been
clear-cut are also more prone to flooding.
Instead of cutting down the infected forests whole-scale, the B.C.
government must ensure that the response to the crisis doesn’t make a
bad problem worse. Non-pine species shouldn’t be killed, and large
areas need to be set aside to protect the habitat of species that are
vulnerable to logging, and to preserve sensitive sites such as
wetlands, lakes, and rivers.
We should also learn everything we can from this epidemic, as it
likely won’t be the last. Other insects, such as the spruce budworm,
are threatening forests in Eastern Canada, and the pine beetle itself
has already leapt over the barrier of the Rocky Mountains to threaten
the boreal forest that covers most of Northern Canada.
The mountain pine beetle outbreak is a clear example of how our actions
can create ripple effects throughout the environment. Let’s hope that
by the time the pine beetle runs out of trees to attack in B.C., we
will have learned enough to prevent even greater bug-related disasters.
We must also see this as a wake-up call about the dangers of climate
change and the need for industry, citizens, and governments at all
levels to do everything possible to address the problem. Just because
the beetles are small doesn’t mean they are insignificant; it’s not a
matter of size.