2011 was terrible year for wildfires in Arizona. We had several mountain ranges burning at once and huge swaths of forest land were reduced to ash. One fire, the Wallow Fire in eastern Arizona’s White Mountains, became the state’s largest fire on record, eventually spilling over into the western part of New Mexico. Homes and cabins burned as firefighters struggled for a month to get the fire under control. It was bad. Really bad.
There are several obvious losses associated with wildfires in forested areas. U.S. National Forests are in place to protect the nation’s timber resources, and a lot of those were burned away in Arizona’s summer fires. People lost homes and businesses and the state lost some fantastic and popular recreational areas. Many animals were displaced during the fires and several species have probably lost breeding grounds and stops along migration corridors. It’s going to a long time before everything’s back to normal in the burn areas and some areas, where the fires razed all the trees, may never fully return to their pre-fire conditions.
By and large, these obvious costs are the things people associate with wildfires, but the damages wrought by fires are much more widespread. Most people don’t even imagine that fires might impact aquatic systems because water doesn”t burn. However, wildfires can destroy aquatic systems and the insects and other aquatic organisms that depend on them.
Fires damage aquatic systems in many ways. Burned trees leave behind massive amounts of ash. Because the Arizona fires occurred before the summer rains began, all that ash was sitting around waiting to be swept into streams and lakes when the rains came. Increased ash in streams usually causes dissolved oxygen to plummet and can cause other changes to the chemical environment of the water such that insects (and fish and aquatic plants and amphibians) die in mass numbers. Even if some things are able to survive in the new water conditions, they might die off anyway if their foods have been eliminated from the system.
Trees and other vegetation provide stabilization to the soils in forests, holding them in place. When you eliminate the trees, erosion increases dramatically. Soils start to loosen and move about, and rains can get things moving even faster. A lot of this sediment finds its way into streams. Most headwater streams, the sources of streams and rivers, have little sediment and are instead full of large rocks and small boulders. Many insects are adapted to living on or under those rocks and don’t do so well if they’re buried in sand and silt. Sedimentation can therefore eliminate essential habitat for many aquatic invertebrate species. These species will die if conditions do not quickly return to normal. Things rarely return to normal quickly.
Increased erosion leads to another problem: the ability of soils to absorb water decreases dramatically. This means that even gentle rains can sometimes lead to flooding, causing flash flooding in streams. Flash flooding and aquatic insects generally don’t mix (though there are some notable exceptions), and most individuals are swept up in a mass of swirling water full of sand and rocks. These insects are generally ground up into microscopic bits, though a few might be swept out of their habitat and deposited somewhere far downstream. If the habitat conditions in that area aren’t right, they’ll eventually die too.
The loss of vegetation directly impact the stream as well. Shade is eliminated and water temperatures rise. Insects that depend on cold water might not survive. Vegetation is also a very important food source in the headwater regions of streams, providing essential nutrients to the system as leaves and branches fall into the water. When this food source disappears, so do the insects that depend on it.
Then there’s the problem of fire retarding chemicals that firefighters use to bring wildfires under control. These are important tools for fighting fires, but when it rains, the chemicals are flushed into lakes and streams along with the sediment and ash. If a species is sensitive to this sort of pollution, it’s not going to do so well when it’s suddenly swimming in a toxic stew.
So, there are lots of ways that fires cause damage to aquatic systems. There’s still one thing to consider with streams though: the water doesn’t stay in one place. You know what that means: the nasty combination of polluted, low-oxygen water, ash, and sediment doesn’t remain within the burn area. Instead, it flows downstream. Rivers many miles from wildfires might thus suffer due to the fire too. Also, the streams in mountain ranges are often headwater streams, the sources of rivers. Damage to the headwaters of a river can have consequences very far downstream and may even cause damage to an entire watershed.
The fires in Arizona may have caused some very long-term or even permanent damage to some streams impacted by the wildfires this year. Some of the fires ravaged areas that are home to rare or endangered aquatic insects. One species of riffle beetle in the Chiricahuas is ONLY found in one stream in that range. If the fires damaged that stream sufficiently to kill the beetles, it will have caused their extinction. Likewise, the White Mountains are home to a protected springsnail that lived right in the middle of the burn area. Will that species, or the very rare caddisfly known from the area, disappear for good? Even the things that aren’t particularly rare might not reappear after the streams recover. If individuals from other populations are too far away to recolonize the damaged streams, some species might never return to burn area streams.
I think it will be interesting to see what happens to the streams within the burn areas over the next few years. I intend to collect from the White Mountain streams to see how long it takes for the insects in several streams there to recover from the impacts of the Wallow Fire. By comparing what is found in the stream now and into the future to what I’ve collected in the past, I’ll be able to monitor the stream conditions rather effectively over time. I really hope those streams recover! I doubt they will ever be the same again, but I’d hate it if the actions of people destroy species that we’ve barely even begun to understand.