Tuesday, June 14, 2016

Forest Losses from Fire in Siberia

So I've been granted some funding by the UK Natural Environmental Research Council (NERC) to study Siberian forests that don't recover after a fire. Boreal wildfires have received some press attention lately, namely because of the Fort McMurray fire in Canada earlier this year. Wildfires can be fairly costly when they affect areas of human settlement, but very often they don't, and thousands of square kilometers can burn each year without much reporting in the press.
One of the reasons we often don't worry about such big fires is that they are a natural part of boreal ecology. Boreal forests have adapted to fire disturbance and some boreal species even depend on fire for reproduction. It's true that fires emit carbon, in the form of several greenhouse gases, to the atmosphere. But when forests re-grow after a fire, they take carbon back out of the atmosphere. If the forest returns to its pre-fire conditions, there is no net increase in atmospheric carbon as a result of the fire. So if fires release carbon, and forests that grow back take it up again, why worry about fires at all? Well...

The first problem is that forests often don't return to their pre-fire conditions. Things that affect a forest's ability to grow back include fire severity (which may destroy seeds or allow them to germinate), herbivory (animals eating up recovering plants), and climate/weather conditions (that can help or hinder re-growth). Recovering forests can be different from their pre-fire condition in terms of tree density or species, and this can cause differences in the amount of carbon stored in the new forest (and of course, how much remains in the atmosphere). And it's not just differences in carbon, there's also albedo, or how much of the sun's radiation is reflected back into space without warming up the planet. Some darker trees, such a needleleaf evergreens absorb more heat, just like wearing dark colors on a sunny day. So if a conifer forest is replaced by a light-colored species, the climate effect could be a cooling one!

This NERC project I'll be working on is looking at the most dramatic type of change post-fire, where the stand doesn't come back at all. These areas are replaced with steppe, or grassland, so there's definitely less carbon being stored in the new ecosystem. We don't know yet exactly how often this occurs or why, or what the climate effect will be, but that's what we plan to study over the next few years.

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