Alaska is on fire at the moment.
Well, not all of it, but the state’s wildfire Preparedness Level is at 4. The scale only goes up to 5, so PL 4 means the state is starting to have real trouble dealing with its fires and needs help from other states. For a state, or region to go to Level 4 is not all that unusual–the state and regional wildfire response systems are not designed to be self-sufficient–but the fires are not inconsequential, either. In recent weeks, both forests and tundra in Alaska have burned–and some of the fires have been quite large and dangerous.
Fires are not exactly a new thing in Alaska, but there are more of them now, for a variety of reasons including the current successional stage of previously logged forests, the effects of fire-suppression policies, and, yes, climate change. Alaska’s climate is changing much faster than that of more temperate areas, becoming both hotter and drier. And the fires, in turn, might be causing dramatic changes to both the climate and ecology of the region.
Recent research suggests that larger, more intense and frequent fires might dramatically alter forest compositions that have been stable (despite repeated natural climate changes) for six thousand years–although the forests themselves could then act to slow further changes.
In the interior of Alaska, there are essentially two main types of forest; most areas are dominated by black spruce, berry bushes, and moss, but there are forests of aspen and other deciduous trees as well. Both types of forest burn, perhaps every hundred years or so, but after the fire, the same type of forest eventually grows back. The result is a mosaic of different forest communities that has kept the same pattern since before the pyramids were built. Basically, each forest type produces its own distinctive type of forest floor. Because spruce forest floors are very thick and wet, they don’t burn down to bare soil, whereas the thin deciduous leaf-litter layer does. After a fire, the two different forest floor types guide ecological succession in different directions so that, in time, black spruce and aspen each return to the areas where they grew before.
As Alaska dries out, however, the black spruce forest burns more intensely and more often, destroying its distinctively thick duff. Once the soil is bare, the deciduous trees can move in–and there they stay.
The neat thing about ecology, though, is that nothing is simple–as the number of deciduous groves in interior Alaska increases, it seems likely that the situation will stabilize itself because the deciduous trees do not burn as easily and may act to slow down and break up large fires. These trees are paler in color, too, and they release more water back into the air and so may act to cool the region somewhat. Both effects may act to protect the remaining black spruce forests, at least for a while.
All by itself, changes in the composition of Alaska’s forests is not necessarily a disaster, although we don’t know for sure that it isn’t, either. Both the human cultures in the region and much of its wildlife have developed ways to use both types of forests in different ways, and it is not obvious what changing the proportion and distribution of the two types is going to do. Change is not automatically bad, but the fact that we are changing something this old should certainly give us pause.
Of more obvious, clear-cut concern is the fact that black spruce forests, with their thick, slowly-decaying duff, are a carbon-sink. That is, they take in more carbon than they release and thus are one of the reasons global warming is not worse than it already is. The loss of these duff layers, either because forests convert to deciduous communities or because spruce forests can no longer build up as much duff between more frequent, more intense fires, is already starting to convert Alaska’s forests into a net carbon source.
That’s a problem.
In the tundra
Much of Alaska is still treeless tundra, plant communities dominated by shrubs, mosses, grasses, and lichens. The tundra, too, is a net carbon sink, because huge amounts of organic matter build up in the soil and do not rot. The layers of ligroundving and dead organic matter also insulate the soil, helping to keep the permafrost from melting. The permafrost, in turn, keeps groundwater close to the surface and keeps buried methane trapped. As permafrost melts, some lakes are actually draining away, destroying important habitat for fish and for migratory birds. And, of course, that methane is bubbling up–methane is a much more powerful greenhouse gas than carbon dioxide is.
Alaska’s forests have permafrost as well, but it is discontinuous–rather like big, underground boulders of ice. Beneath the tundra, the permafrost is more like bedrock.
The thing is, when the tundra burns–as it may be doing more often now, in part because northern Alaska is getting more lightening strikes because of its warmer weather–it’s not just the thin living laying but also the soil that goes up in smoke. A tundra fire can release as much carbon dioxide as a forest fire can. Without as much insulation, and given the much darker color of the charred surface, the permafrost beneath can then melt all the faster.
I have written before about how positive feedback loops are anything but positive in the colloquial sense of good or happy. A positive feedback loop is a self-intensifying cycle, such as where rising temperatures melt permafrost, releasing methane, which makes temperatures rise faster, melting more permafrost….
The really scary thing here is that initiating these loops–pushing systems to the point where they start releasing greenhouse gasses–means that even if we stopped burning fossil fuel tomorrow, climate change might continue to get worse. We are losing the option to save ourselves.
That isn’t an argument to give up, of course–no situation is so bad that it cannot be made worse, and that means no situation is so bad that we cannot make things better by our restraint. But it does mean that the hour is later than we might think. The Earth is a live thing, and it has been protecting us from ourselves to some extent–but it won’t do so forever. To those of you who are doing the equivalent of calmly reading the paper while your house burns around you; it is time to get up, now.