Monday, January 11, 2010

Forests and Carbon in Canada

Deforestation, estimated to be responsible for up to 20 percent of global human generated emissions contributing to climate change, has long been a major focus of climate change policy. Most of the emphasis, however, has been on tropical deforestation. The reasons for this are fairly straightforward: 1) tropical forests are much more effective carbon sinks than are temperate forests (they grow faster and, hence, remove carbon at a more rapid rate) and 2 the volume of forest being cut is larger in the tropics than in temperate regions.

However, recent work by Werner Kurz and others in the Canadian Forestry Service has shifted attention to the forests of British Columbia and surrounding areas which are being devastated by an outbreak of the pine beetle.

According to the Montana Department of Environment, the mountain pine bark beetle (a species native to the region) has benefited from a variety of climate related changes:
1) Prolonged periods of cold weather in the -20 to -40 F range kill pine bark beetle larvae embedded in the thin bark of Lodgepole trees. However, winter weather over recent decades has afforded very few of these extended cold snaps. ... 2)Recent late summer drought conditions have stressed Lodgepole forests. Weakened individual trees have long been known to issue a biological invitation to beetle attack. During its adult mating phase in late summer, adult scout beetles identify weakened trees and issue an aggregating pheromone to other beetles to key-in and attack the tree. The apparent combination of large numbers of drought-weakened trees and the growing population of beetles perpetuates the infestations.

As a result BC's forests, which have traditionally been viewed as a carbon sink, have become a major source of CO2 emissions. As shown in the diagram below, Canadian Forestry estimates now identify the pine beetle infestation as the single largest cause of CO2 emissions in Canada, exceeding by a significant amount the substantially more criticized emissions from the oil sands.

As a result, BC is now embroiled in a policy debate about how to proceed: harvest and burn the wood rapidly (which implies a big hit in short-medium term C02 emissions from the burning in order to get the forest back acting as a carbon sink through active reforestation) versus letting it decay slowly (and, hence, having a lower rate of emissions over a longer period coupled with a longer wait for the forest to return to its role as a carbon sink). The details of these, and other related debates, are nicely summarized in a recent article in the January 9, Globe and Mail, From Green Hero to Carbon Villain.

At a more fundamental level, these developments underscore the uncertainties inherent in attempting to devise a carbon accounting system for a planet that is in the process of profound transformation due to climate change. A few short years of warm winters and dry summers and a whole region goes from being a major carbon sink to a major source of emissions.

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