Sunday, April 27, 2008

The pine beetle and carbon cycle feedbacks

An important study from in last week’s Nature concluded that the mountain pine beetle infestation that have devastated the forest industry out here has also converted western Canadian forest from a carbon sink to a carbon source. In the simplest possible terms, the beetles kill the trees, decreasing carbon uptake (photosynthesis) and increase carbon loss (decomposition). This is not a new suggestion. The Kurtz et al. paper is, however, the most complete accounting to date.

A lot of people are labelling this a ‘positive feedback’ from climate change (e.g. like how warming melts sea ice, which reduces reflection of solar radiation, which accelerates the warming). The logic is that warmer weather promotes the beetle outbreak, which releases carbon from the forest, which further warms the climate.

The assertion appears correct. But be wary of the hyperbole. Not all positive feedbacks are made equal. There are only so many pines, the beetles can only do so much damage. At some point, they run out of trees to eat, and the infestation recedes. As the authors of the Nature study have said, the betters have almost eaten themselves out of house and home. And re-forestation initiatives could return the forests to being a carbon sink.

The type of positive feedback that should be included in carbon cycle assessments? Yes. Runaway positive feedback that will send the atmosphere to 1500 ppm? Probably not.

There is a sadly ironic policy twist to the beetle infestation. For one, the forests now might pump out more carbon than the entire BC economy, throwing a wrench into regional GHG reduction agreements. The Canadian government lobbied hard to include forest carbon sinks under the Kyoto process, under the expectation that our boreal forest would provide a big carbon credit and reduce the need to address emissions themselves. Safe to say, that stance has softened in recent years.


John Mashey said...

A month ago, we were taking our lunch break from skiing at Big White, and talking with a couple guys who were in the lumber business, and beetles were the #1 topic.

Can you say more about reforestration initiatives? Are there appropriate trees that are more resistant to the beetles?

Simon Donner said...

The pine beetle is a huge subject here, and has been for some time, for obvious reasons. I'm not the expert on the finer details (i teach the carbon cycle, not forestry). One key thing to remember: the beetle affects pines, which are only ~20% of the forests.

There's a recovery effort in BC. As far as I know , there's a big effort towards "reforestation", but that is also business as usual. The companies salvage the infected / dead trees, where possible, and replant, as would happen no matter the source of the disturbance.

John Mashey said...

Ahh, that helps, especially the 20%. Let's hope these antifreeze-laden things don't mutate to eat other trees.

We spend 2-3 weeks a year in B.C., so we're fond of this particular set of trees.

Anonymous said...

this would never have happened in the first place if we would have kept our skies clear of greenhouse gasses. If we had a cold winter, a good portion of these beetles would have died off. we've created a cycle that will eventually let these bugs destroy our forests. the dead trees add CO2 to the atmosphere and eventually the bugs will have no pine to eat and will have to adapt to eat spruce and other trees. the bugs are putting themselves into a cycle because of us.
We need to stop blaming everything on other species, and realize that we are causing all of this,and need to take the responsibility and fix it.
we are destroying everything and ourselves.