According to the draft US National Climate Assessment (Chapter 7 of big pdf), US forests currently absorb about 13% of US carbon emissions. The distribution of this sink (in tonnes of carbon/hectare/year) is as shown above. Clearly the hilly regions of the eastern half of the country are critical, with the Pacific northwest being the second most important region.
The authors project that US forests will become a net source of carbon by mid century due to increases in drought, disease, etc, more than offsetting the benefits of a longer growing season and carbon fertilization.
This may be true - however, I imagine we will also create increasingly large financial incentives to manage forests for carbon storage and this may result in more intensive management of a lot of forests with species explicitly selected for that purpose, and for the changing climate. So I'm not sure this is beyond our control. Forests in the western US are at greatest risk - there is already a lot of wildfire and increasing insect outbreaks there and much more of the west is likely to desertify under climate change.
Plant a tree!! I've planted about thirty in the last five years... yeah, I own five acres, but you can also, for example, buy a live christmas tree and then donate it to the park service to be planted. If you have a regular city lot you can fit in about three good sized trees... I realize this isn't going to save the world, but some studies show that adding 25 or 30% tree cover in urban areas will completely reverse the heat island effect...
ReplyDeleteI don't think the graphic here is very good. I think it overstates the productivity of the north-eastern forests (the only forest I know much about). It looks to me like the map doubles the amount of wood grown/year vs reality.
ReplyDeleteAnd then to the larger issue - forests are only sinks if the wood stay wood. If the tree falls over and rots or gets cut down and burnt the sink becomes a source. The only reason the forests are now sinks is that all those forests were logged many years ago. Young forests suck up a lot of carbon as they grow, older forests in "dynamic balance" do not. What about all the carbon that was released when the forests were first logged?
What percentage of the anthropogenic CO2 emissions of the last 200 years came from forests vs burning fossil fuels. That could give us an idea of what we could reasonably expect to see return to wood in a well managed scenario
Over the past 10 years there has been - and it continues - a massive die off of lodgepole pines across the Rocky Mountain due to warmer winters - the pine borer beetle hasn't been killed during the winter. The White River National Forest, for example, has lost up to 90% of these trees. It is estimated over 700 per acre over 22 million acres across the west...
ReplyDelete"I imagine we will also create increasingly large financial incentives to manage forests for carbon storage and this may result in more intensive management of a lot of forests with species explicitly selected for that purpose, and for the changing climate."
ReplyDeletePossibly, but that path increases the fragility of the forest carbon sink - managed forests consisting of a handful of specific species of tree reduces biodiversity and makes the forest susceptible to large die-offs.
I always wonder at the human "need" to "manage" natural systems - as though they require management when really they simply need to be left alone.
It's impossible to say what future risk our forests are exposed to with climate change.
For example, last year, in northwest Ontario where I live, spring temperatures came so early that trees were "waking up" before the ground had thawed and were therefore deprived of the moisture they required.
The species affected were all coniferous (spruce and fir mostly) and the effect was that whole tracts of boreal forest turned orange with dead needles.
Many of the trees survived and put out new growth, but many were killed.
The phenomenon is know as "winter burn" and a little bit is not that uncommon - but the scale and severity of last year's event was a big surprise.
What other surprises will we see in the coming years I wonder?
http://www.dnr.state.mn.us/fid/june2012/drought.html
For the western forests, add in more than a half-century of misguided forest management -- ie, total fire suppression -- made possible by federal funding. Most of the forests are incredibly overgrown, and with huge fuel loads on the ground. We know better now, but the answer from Washington for the last few decades is "there's not nearly enough money to restore the forests to a natural healthy state."
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