I went to a talk last night. It was advertised as being about the importance dead trees; it turned out to be almost entirely about wildfire. This was also very interesting and relevant to my interests, as it relates to ecology, and here’s more or less what I got from the talk last night. (Mostly; some of the bits on dead trees I got from another talk; some of the more editorial comments are mine based on what I’ve learned over the last 6 months about logging and forest ecology.)
The speaker was George Wuerthner, who has been studying forest ecology for years; he’s written (or edited?) a book on wildfire that I want to get my hands on now. He said that even though it was only published a few years ago, that based on what he’s learned since then, there are some things he would rewrite, and that in a few more years, there may well be yet more things he would rewrite, because our understanding of forest ecology is constantly growing and changing what we thought was true. (This theme is one I hear repeatedly re:forest ecology, that we really don’t know a lot, and it is, therefore, kind of foolish to think we know –enough- to truly “manage” and create a healthy forest.)
I would summarize the key points as this:
– Human beings cannot prevent* or stop major fires; major fires are due to weather and climate patterns.
– Forests that burn evolved with wildfire; it is harmful to these systems to NOT let them burn, and that especially means the very large, very severe fires (referred to as “stand replacement,” because these are the fires that kill a majority of the mature trees in the forest).
– Ecologists are more and more into the notion that dead trees in an ecosystem are more valuable to that ecosystem than the living trees; in the West, major fires are one of the major sources for dead trees.
The “model” for forest fires is based on one type of Western forest, and it really isn’t relevant to most other types of forests AND may not even apply to the source as well as previously thought. The model (for what is “desired”) is based on ponderosa pine forests, which have frequent but not very severe fires; mature trees survive them. Most other forests burn rarely, but when they do, they are more likely to burn very severely, with most of the trees being killed. Severe fires will happen in a given place about once every 100-175 years; the likelihood of one of those happening in any given spot is very small. Less severe fires – that kill few trees, and cover <100 acres, happen much more frequently, but that’s not what everyone freaks out about . . . and those less severe fires aren’t as important, ecologically, as the rare, severe fires. (There are some forests where climate patterns are such that they have severe fires even less frequently, like every few hundred years – if left alone, meaning no one intentionally or accidentally sets a fire – certain Native American tribes in Oregon used to intentionally set fires before white people came along and started logging and accidentally setting fires.) There is some evidence that even ponderosa pine forests don’t always fit into their own model, that they, too, have infrequent but severe stand replacement fires.
In the American West, our general climate pattern is wet winters and dry summers. Evergreen conifers grow really well under these conditions, because they can photosynthesize all year – during the wet season; deciduous trees do not do so well, because they can’t get much moisture during the part of the year they have foliage and are actively growing. The West burns, because the hottest part of the year is also the driest. Compare to the East, which gets a pretty uniform amount of precipitation year ‘round, is more humid, and is predominantly hardwood forest (deciduous trees), and (in New England) only very rarely has wildfires. Eastern forests have more rot and decay; the West has fire. (What I’ve learned elsewhere: Some tree species have evolved such that they cannot reproduce without fire; only enough heat will melt the wax on the cones, which lets the seeds out. Other species (Douglas-fir, aspen, alder) prefer or do very well in wide open areas, or the nutrient mix you find right after a fire, to get their start in, and will be the first species to move in post-fire; other species (hemlock) need an established canopy of bigger trees, to create the shade they cannot live without.)
A climate pattern called the Pacific Decadal Oscillation also appears to be connected to the risk of severe (burning many, many acres) fires. The Oscillation refers to changes in the surface temperature of the Pacific Ocean: for many years (20-30 years minimum), it will be cooler in the eastern Pacific and warmer in the west, and then it switches. He had a great chart showing years in which the PDO created overall cooler temperatures, overlaid with a bar graphic of acres burned in a year, and the years in which the major fires happened were in the warmer years; the chart went back to late 1800s or early 1900s and showed that while many of the severe fires happened well before firefighting became refined and competent (which started in the mid-20th century, 1930s or 40s), and before thinning and etc. to prevent fires started – when the PDO swung back to a state that created hotter and drier weather in the PNW, starting in the late 70s/early 80s, we started seeing the same kinds of severe fires we had seen before all those improvements in firefighting and (attempts at) prevention. So it makes it hard to argue that total acreage burned/not burned is related to our technology or techniques.
There are thousands and thousands of small fires every year. They have very little impact on the ecosystem in terms of numbers of acres severely burned; it is only a tiny percentage of all fires that grow to massive size and intensity and have the ability to kill large numbers of trees.
The conditions you need for one of these major fires are: drought/lengthy dry period, high temperatures, strong winds, fuel (trees), and source of ignition. Again, summers in the West are hot and dry. Even in the Coast Range, which gets several feet of precipitation every year, and are pretty damp year round compared to the eastern side of Oregon, those forests can burn some summers, when overall conditions are right, though it’s been decades since the last major fire in the Coast Range). When I drive out to the coast, there are large signs along the road that are set to indicate the current risk of fire, and last summer, there were times I went out and the risk was at Moderate or High. (My limited understanding is that all of the really major fires – burning 100,000 acres or more – in the Coast Range have been caused by human sources of ignition; lightning occurs with rain, so starts very very few.)
In big fires, it is common that the majority of the acreage that burns will often be burned in just a few days (or hours) of the overall length of the fire (which can last weeks), and on those days/hours, the winds were very strong. Human fire control is absolutely no match for those conditions – the fire will go over any kind of fire break, including thinned areas (naturally thinned or human-thinned), clear cuts, etc.; strong winds blow embers far ahead of the actual fire – and the heat from the oncoming fire dries out and heats the area ahead of the active fire, which combines to make conditions even better for the fire to keep advancing. (Fire also moves faster going up a slope than going down a slope.)
The speaker mentioned (and I have read in other accounts of forest fires), how the stories generally end with something like, after days or –weeks- of firefighting, “then the weather turned cool, the winds died down, it started raining, and the fire fighters were able to put the blaze out” . . . because the weather was about to do it anyway. Fires will always eventually go out all on their own, once things are no longer dry and hot enough for it to keep going; in the major blazes, the only way human efforts “put it out” is when the weather is right to allow it to happen.
Most money spent on fighting fires goes to protecting structures.
A better way to prevent houses and towns from going up in flames is to a) not build close to forests; if you’re going to, b) put a metal roof on the buildings, that will do amazing things for the building’s survival: the walls have to be hot enough for long enough to actually ignite, and the heat from a nearby fire often isn’t present for long enough, and hot enough for long enough, to ignite the buildings – but embers blown ahead by the winds WILL set your roof (or nearby vegetation, or piles of firewood, etc.) on fire; and c) keep the area around the house clear of easily-flammable stuff (firewood, trees). Houses burn hotter than trees. He showed some imagery of a neighborhood that was largely destroyed in Colorado due to a nearby fire – all the trees surrounding the remaining foundations survived (they looked like deciduous trees, like people plant in developments), but as houses caught fire, they set their (too-close) neighbors on fire (it looked like typical gross suburban sprawl development, where you have clusters of houses around a little cul-de-sac). The closest forest was like a mile away, but the fire sent embers into the air – and it also burned grassland across the road from the development, showing that clear cuts will not prevent the spread of major fires. (There are many, many examples of major fires that go right through areas that are thinned or even clear cut, they will also cross roads that are wider and better firebreaks than what a crew of people with shovels can create, etc.) Also: city/county/etc. governments could also make zoning and other regulations and laws restricting development or requiring certain things happen (i.e., metal roofs) that would lead to developers and builders creating structures that would either be out of risky areas, or be more able to survive if a fire happened.
Dead trees being a fire risk: not so much. Dead trees, once they have lost all their needles, don’t burn nearly as well as living trees, especially when you are talking conifers, which have needles full of resins. In the summer, living trees can be very dry, especially under drought conditions, so you’ve got all these tiny bits of material, dried out, full of highly flammable chemicals (resins), and that’s going to blaze up much better than a standing dead tree that has lost its needles. This also means that when people say that it’s important to keep areas thinned to prevent beetle outbreaks, because beetle outbreaks kill large areas of trees, and all those beetle-killed trees are a fire risk . . . it’s not quite that straightforward. For a year or two or three, yes, because the dead trees will still have needles on them, and dried out needles burn well, but after those needles fall off, that area is LESS of a fire risk than adjacent forest full of living trees. (And in addition, dead trees are hugely important to many, many species in the forest, so if you prevent the creation of large supplies of dead trees, you’re fucking over the ecosystem.) In addition, the likelihood that any given spot in the forest WILL have a severe burn in a given year is quite small.
Why are dead trees important? Lots of things live in them, or eat them, and then are eaten by other things.
Many bird species are cavity nesters, and need standing dead trees (snags) to build nests in; brown creepers need dead trees with bark still on, but loose enough that they can get under the bark and build their nests. Pileated woodpeckers make pretty big holes in snags, going after insects living in the tree, and then other animals with less impressive wood excavation ability, can take advantage of those holes to make their own nests and shelters.
Martens (related to weasels) need snags that have the right kind of density, because in the coldest parts of winter, they will dig out a shelter inside the tree and be protected from that severe cold. Without that particular kind of snag, you don’t get martens in an area.
So you need not only dead trees, both standing and fallen, you also need a diversity of types of dead trees – killed by different things (beetle-killed trees are way more vulnerable to fungus, which means they decompose faster and differently than fire-killed trees), in different ages of post-death.
Dead trees that fall into streams and rivers are vital for the health of fish communities. They provide shelter for small fish (protection from predators), they cool the water by shading it – water that is too warm will kill fish, and they reduce the erosion of stream banks by slowing the flow of water, especially during high water times. For many, many years, people thought that it was good to “clean up” forests and streams by removing the dead trees . . . and fish declined. Now, science has caught up with what seems like should have been fucking common sense (hello, duh, these forests evolved with trees falling in the water?? how could trees in the water be a bAD THING THE FISH EVOLVED ALONGSIDE THIS), and people are putting dead trees back IN streams and rivers.
Ants live in dead trees, and lots of things eat ants; they are a major food supply for bears. Bears will also hibernate inside large-enough dead trees, especially in areas that don’t have other shelter spaces (caves).
Dead trees are also a really rich source of nitrogen, and some trees won’t grow well, or at all, without a really ample supply of nitrogen – hemlock is one. There are places where you can see a straight line of hemlock trees that started out as seedlings growing on top of a fallen dead tree.
Another interesting thing about stands that have been fire-killed: areas like this are second in biodiversity only to old growth forest. Not IMMEDIATELY post-fire, but in the years after, when plants are moving in, taking advantage of the open canopy, and animals that like the open space, and the snags, and the different plants. These areas are really pretty rare as ecosystems/types of forest, and short-lived, because in 40 years, the seedling trees that started post-fire will have grown tall enough that the area is no longer open, and by 60-80 years, the trees are quite large.
Fish species that are native to the area do not suffer from fires the way that invasive species do; their overall numbers either remain about the same, or they have sometimes shown benefit from fires, whereas non-native species had their numbers decline.
A severe burn will lead to increased runoff and sedimentation in nearby streams, but this only lasts a few years, until plants are well established. Compare to roads that go through forests (there are 1000s and 1000s of miles of logging roads – over 4000 miles in the Mt. Hood National Forest alone), which are a constant and chronic source of sedimentation. Fish cannot recover from constant sedimentation. Salmon, for example, need clean water for successful spawning, or their eggs die – they suffocate – so you will not see significant recovery of salmon unless roads are decommissioned. Sedimentation in the human water supply is also not a good thing.
Thinning to prevent/reduce severe burns is . . . largely a waste of time (except for the logging companies, because they can sell the removed trees). If conditions are right to for a severe fire, it will rip right through a thinned area. In fact, because thinning opens a forest up, that means there are fewer trees to slow down winds (slower wind = less severe fire), and a thinned area will also be drier than a non-thinned area (more wind, and more exposure to the sun). If thinning really were being doing for “forest health,” instead of an excuse for logging companies to make money, then the trees would be cut and LEFT THERE to keep all those nutrients and shelter and etc. there in the forest. The speaker said he’d spoken with someone from the Forest Service and asked the FS person why a thinning was being done miles away from the nearby town – the thinning was supposedly to prevent forest fires becoming severe and threatening the town . . . and the reply was very sheepish, because of course, if you want to prevent a forest fire from burning a town – you start by removing trees close to the town, not miles away; miles away is good for a timber sale, though. (Also: leave a forest alone, and it will thin itself out! There will be a beetle outbreak! Or some sort of viral or fungal infection that kills a stand of trees! Or a fire! It’s like nature is a self-regulating system!!!) (Things I’ve learned recently: The Forest Service releases very short, publicly accessible documents describing why a particular part of the national forest is being proposed for a timber sale, including the reasons; it is entertaining reading, particularly once you have a bit of a sense of what the system is about – timber sales – and how the reasons given are phrased in particular ways. Tortured logic, extremely extremely vague wording . . . it’s really something.)
Thinning also reduces overall genetic diversity in any given area. Thinning to prevent beetle infestations presents a related problem because some trees, when bored into by beetles, will produce a sap that will push beetles out of them – and the trees with those genes will survive the beetle outbreak – but unless you go in and test ALL the trees, and only thin the trees that don’t have that gene, well, the beetles are going to do a better job of selecting which trees pass on the anti-beetle genes.
One of the things he said prevents fires from more widely being considered beneficial for forests is the language that always gets used puts wildfires into negative terms: it was a “catastrophic” or “terrible” fire, we had to go in and “salvage” the dead wood afterwards (as if the dead trees were only valuable by being converted to lumber), we’re “fighting” it, it “raged on and on,” etc. And I understand that from the perspective of a community being literally threatened with burning to the ground, wildfires are terrifying and bad news. In terms of forest health, however, fires are a rejuvenating force.
*Well, we can try to prevent human ignition sources.