Wildfires and Aquatic Insects


Lightning, one of the main causes of wildfires.

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.


Campfires are a common source of wildfires. An improperly tended fire was the likely cause of the Wallow Fire.

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.

Aspen Fire

The Aspen Fire in the Santa Catalina Mountains, several years ago.

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.


A little wildfire I came across a few years ago. It quickly burned itself out, thankfully.

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.

fire's aftermath

You can see the charred areas where the mesquite trees and agaves burned in the Greaterville Fire in summer 2011. This was one of the little fires.

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.

Three Forks

This area, where the protected springsnail is located, probably doesn't look much like this anymore...

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.


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6 thoughts on “Wildfires and Aquatic Insects

  1. I’m not sure if you’ve read Jaret Diamonds or not. He advocates that controlled fires are the best way to prevent huge fires. He suggests that in the US, in the last few decades, every small fire was put out by helicopters, resulting in overfueled forests. He predicts that with so much fuel in the forests, future fires will be more difficult to contain, and forests find it easier to regenerate from small fires, but they can’t bounce back from the total annihilation of huge forest fires.

    • I haven’t read much Diamond, but he’s right: it’s rather well accepted now that by putting out the little fires, we’ve increased the chance of big wildfires dramatically. Forests are adapted to being burned every few years and our messing with those natural cycles by putting every little fire out means that there are too many trees in our forests and too much leaf litter. Many little fires is a whole lot better than one big fire because those big fires are hot enough to burn the trees whereas the little fires that used to happen every few years just burned the dead trees, thinned out the undergrowth, and burned most of the litter. The little fires provided nutrients for the forest to help it stay healthy while most big wildfires now just destroy everything their paths. Kinda sad really!

  2. I have a single specimen of an undescribed species of jewel beetle collected by a friend a few years ago along Ruby Road in the Atacosa Mountains. The area has burned since, and no more specimens have turned up despite efforts by a number of collectors to find it. I’ve been waiting to describe it hoping more would turn up, but it now looks like I’ll have to do it on this single specimen – the idea of describing an extinct species known from a single specimen is a little depressing.

  3. We struggle with terrible wildfires in Chiang Mai in northern Thailand too. Here they are man-made, an old way of land management, terrible for the soil, for the atmosphere, for the health and for the butterflies! Only via patient information we can overcome. Welcome here to study our gorgeous wild butterflies :)
    Eric & Ketsanee, Dokmai Garden

    • We have the opposite problem in the USA – things that are supposed to burn every few years, systems that have evolved to burn every few years, aren’t being allowed to burn. That means that any fire that does manage to get started causes much more damage to the forest than it should. Forest managers here are starting to do prescribed burns, intentionally burning certain areas, to prevent the bigger, more damaging fires from happening, but a lot of big fires are happening anyway. It’s not a good situation.

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