Wildfire and wild things
Ethan Shaw; Feb 20. 2018
2017 LOS PADRES NATIONAL FOREST FIRE IN LOS ANGELES--Image: Forest Service, USDA-
The aftermath of Southern California's Thomas Fire – at roughly 282,000 acres scorched in December 2017, the biggest in modern Golden State history – has revealed much devastation of human life and property, most recently due to flooding and mudslides provoked by heavy rain on the burn-scape. There have also, however, been a few feel-good nuggets on the post-fire wildlife front: black bears and puma cubs with burned paws and ash-coated barn owls taken into rehabilitation, and the happy news that a California condor pair's chick managed to survive (with singed wingtips) when flames swept through its nesting area in the Los Padres Sespe Condor Sanctuary, home to nearly half the state's free-flying condors.
Fire and critters have also lately been in the news courtesy of a fascinating study published late last year in The Journal of Ethnobiology investigating the so-called "firehawks" of Australia's tropical savannahs. Its authors delved into a phenomenon long known to Aboriginal peoples: raptors plucking flaming or smouldering sticks from bushfires and dropping them in nearby grass, thus sparking a new burn.
To some people who've never experienced one where they live, or where they love to recreate, a big burn can seem a disastrous aberration – and, ala Bambi, nothing but trouble for the creatures caught in its path. The intriguing case of the firehawks (which we'll explore a bit more later) suggests a more complicated story. Most of the world's ecosystems have evolved with fire of one kind or another, and animals have an instinctive (and opportunistic) relationship with it.
Cypress prairie at the Florida Panther National Wildife Refuge. Image: Josh O'Connor/USFWS
Let's have a look at some of what we know about a fire's impact on animals: the bad, the good and the grey areas in between.
Fire in ecosystems: An old story
First though, setting the stage. A remarkable share of ecological landscapes evolved under the regular influence of flame, though what sort of fire, and how frequent, and from what ignition source, vary considerably. Many Mediterranean-zone and semiarid grasslands, shrublands and woodlands burn chronically: from the fynbos of South Africa's Cape region and the eucalypt woods of southeastern Australia to the cerrado savannahs of central Brazil and the California chaparral. But many other plant communities that wouldn't seem terribly flammable at first glance – cold subalpine woods, northern taiga, temperate rainforest – do indeed burn, even if the intervals between fires are sometimes on the order of several centuries, even a millennium.
Lightning conspires with annual dry seasons or periodic droughts to spark wildfires, but we – human beings – are just as important ignition sources in many parts of the world. We've been intentionally starting fires for thousands of years: to improve hunting or herding opportunities, to clear land for agriculture and manage crops. The exact fire regime of a region depends on a whole suite of factors, but generally speaking a place that burns frequently tends to experience low-intensity fires – there's not time in between burns to build up a lot of fuel, basically – while countryside that tends to ignite once every few centuries will nourish bigger, fiercer fires.
An inferno raging through a forest or brushland may look apocalyptic, and some individual animals will perish in it, but such a blaze can also help maintain and rejuvenate the resources local wildlife depends on – and open up crucial opportunities for other species specially disposed to capitalise on the post-fire landscape.
But what about those real-time effects of the leaping flame and billowing smoke? What about the critters that perish, and those that don't?
Mammals
It's often surprising how few medium-sized and large animals appear to die in wildfires. In the mighty conflagrations that roared across Yellowstone National Park in 1988 (and changed wildfire philosophy and policy in the USA), known large-mammal deaths were in the low hundreds: 240 elk, nine bison, four mule deer, a pair of moose – most of them apparently felled by smoke inhalation. Reports of Yellowstone's big beasts running from the big crown fires were scarce; the main reaction was basically indifference. Several radio-collared grizzly bears hung around actively burning areas during the '88 Yellowstone fires, and more than a dozen grizzlies moved right into burned-over zones after the flames subsided. "Bison, elk, and other ungulates grazed and rested within sight of flames, often 100 metres or less from burning trees," noted a United States Forest Service report on the ecosystem impacts of wildland fires.
Bison freaking out (sarcasm!) as the 1988 Yellowstone fires burn. Image: US National Park Service
One basic reason why bigger mammals often escape a fiery death? Well, because they're pretty good at galloping, loping, trotting, even plain sauntering away from flames. The hair of mammals also provides a bit of a buffer against the extreme heat, especially longer and denser fur. This means they can sometimes get away with slipping right across a fire front. (That sort of doubling-back, for example, allowed several woylies – little kangaroo cousins – to remain in their home ranges during a moderate-to-high-intensity burn in a eucalypt forest in southwestern Australia.)
This past December, the manager of the free-roaming American-bison herd in South Dakota's Custer State Park noticed the bovids' shaggy coats seemed to offer some protection during a fierce and fast-moving grassfire: outer guard hairs were burned off, but the "underfleece" beneath provided a shielding layer.
That prairie blaze – which blew up from 4,000 to 35,000 acres on a single night due to winds exceeding 40mph – caused burns severe enough that a number of bison (as well as elk, deer and a feral burro) had to be put down. It goes to show that a swift wildfire can sometimes outpace or outflank even the large and the mobile: whether it's mustangs in the American West or elephants in South Africa, big mammals dosometimes fall victim to flame and smoke.
Elk in woods burned by the 1988 Yellowstone wildfires. Image: US National Park Service
"Large mammal mortality is most likely when fire fronts are wide and fast-moving, fires are actively crowning, and thick ground smoke occurs," the US Forest Service report explained
After the Jasper Fire of 2000 – the largest to impact the Black Hills of South Dakota and Wyoming in modern times – researchers studying pumas in the range found one of their radio-collared cats, an adult female, dead in a mountain draw. They concluded that the puma, which had burned paws and singed whiskers but otherwise minimal external injuries, had asphyxiated, probably on a day when strong south winds had driven the fire front forward at some 15mph – fast enough, they reasoned, to trap the animal in the draw.
Smaller mammals such as rabbits and rodents may also run away ahead of the flame front, or retreat underground. Ventilation is vital, though: mice have been found suffocated post-fire in burrows with only a single entrance.
Some mammals are more vulnerable to fires than others. Koalas, for example, a bit ungainly on the ground and prone to shelter in the canopy, can get in trouble when a bushfire rages through their highly flammable (and fire-dependent) eucalypt woods. Fire can also hit woodrats hard, as those rodents hole up in aboveground nests of grass and other litter – super-combustible homes they're loathe to abandon even when flames start crackling.
Reptiles & amphibians
Like small mammals, reptiles and amphibians may either flee fires or successfully endure them ensconced underground or within crevices, rotten logs and other cool, moist hidey-holes. In 2001, wildfires in New Mexico burned the entire known range of the endangered Jemez Mountain salamander, yet the population survived due to the refuge offered by rock nooks and crannies. Timing's everything, though: snakes in the process of shedding their skin may be less adept at sheltering from a fire.
Birds
Adult birds are pretty well set up to simply fly away from conflagrations, though eggs and chicks are vulnerable: surface or understory fires may destroy nests laid on the ground or in shrubs, while canopy broods go unaffected. (How significant the loss of a nest to fire is can depend on the species: as the US Forest Service notes in its wildfire/ecosystem survey, wild turkeys often don't re-nest if their brood is lost after a few weeks of incubation, whereas another upland game bird, the northern bobwhite, may re-nest several times a season.) In many fire regimes, however, peak burning season occurs after peak nesting.
A black-backed woodpecker enjoys the bounty of a regenerating forest following the Pagami Creek Fire in northern Minnesota. Image: Rich Hoeg/Flickr
Flying birds, well equipped as they are to dodge flames, may – like those big mobile mammals – sometimes be overwhelmed. A 1999 fire in the South Florida Everglades didn't harm two large rookeries of wading birds – even as sawgrass marsh around them burned, the "tree islands" harbouring the rookeries were wet or moated enough to endure – but it did kill 50 white ibises that were likely trapped by heavy smoke while out foraging.
Now, what about those pyromaniacal Aussie raptors? Birds of prey in many parts of the world commonly hunt along and above the fire front, scavenging crispy leftovers and feasting on the small creatures driven ahead of the flames, as well as insects lofted high by the fire thermals. But recent research has investigated the possibility that certain Australian raptors intentionally spread flames to flush out (and fry) more snacks. A National Geographic article on the study quoted a passage from the 1964 life story of an indigenous man named Waipuldanya Phillip Roberts that helped inspire the investigation: "I have seen a hawk pick up a smouldering stick in its claws and drop it in a fresh patch of dry grass half a mile away, then wait with its mates for the mad exodus of scorched and frightened rodents and reptiles. When that area was burnt out, the process was repeated elsewhere."
The researchers delved into traditional knowledge and mythology on the subject and also documented contemporary observations bearing out the firehawk behaviour among three quintessential raptors of Australia's northern savannahs: the black kite, whistling kite and brown falcon. Not everyone's convinced the birds' spreading of fire is intentional – it's also been proposed they accidentally nab smoking sticks in their talons when making unsuccessful predatory strikes – but the research team is continuing its inquiry, and hopes to record the firehawks in action on film.
Invertebrates
It's difficult to summarise what we know about wildfire impacts on invertebrates. Many aboveground insects and arachnids likely perish during fires, although one study* showed both adult acridid grasshoppers and nymphs were quite capable of escaping a savannah fire in Côte d'Ivoire. In many cases, invertebrate numbers and diversity recover quickly in burned zones due to dispersal from neighbouring unburnt habitat (though a recent study on Florida tortoise beetles showed recolonisation can take a good while for some bugs).
Twenty-five years of regrowth following the 1988 "Summer of Fire" Yellowstone wildfires. Image: J Klinger/Flickr
Invertebrates that tunnel into the litter layer or soil probably hold up better in fires, though high-severity burns have been known to destroy even subsurface eggs of mites. (In that case, incidentally, mite populations in the burn area were initially lower than surrounding plots, but by a year and a half post-fire, the burn area supported substantially higher populations than elsewhere, a trend often seen for aboveground invertebrates as well.)
Certain kinds of insects, meanwhile, are actively attracted to fires. Charcoal beetles (Melanophila) sense the heat of wildfires as far as 130 kilometres away and "beeline" for them (if you will) to mate and lay eggs beneath the bark of fire-killed snags. Writing in Bay Nature about the 2013 Morgan Fire near San Francisco, Emily Moskal described firefighters' vivid experiences with hordes of these beetles:
o protect themselves against the darting insects, the firefighters wore bee veils. The beetles emerged from their mating stages in the burned or burning trees to swarm, rising with the smoke and sizzling crackle of extinguished embers. Firefighters recalled that everywhere skin was exposed, beetles scratched and prodded ... [Firefighter Dylan] Jorgensen described a feeling of relentless buzzing in his hair, firefighters "ripping their helmets off like feeling a bee in your shirt," and dancing and shaking to get the beetles off of them.
Other types of wood-boring beetles as well as horntails (or wood wasps) follow the scent of smoke to reproduce in burned forests. "Firebug" is a common shorthand for all of the insects for which wildfires are one big smoking magnet.
Indirectly dangerous
Animals aren't just killed outright by voracious flames and choking smoke. There are also dangers only indirectly related to fire – which would include, for example, the predation inflicted upon those skittering mice and snakes and insects fleeing the fire front.
An endangered Key deer forages in an area burned the previous day in a prescribed fire. Image: Josh O'Connor/USFWS
Creatures retreating from fire face other risks, too. In one instance, a slew of Cape grass lizards were squashed on a gravel road they were crossing to escape a fynbos blaze.
What's more, injury from flames may hamper an animal's ability to obtain food or avoid predators. In early October of last year, a closely monitored male puma in Southern California's Verdugo Mountains turned up dead not long after a 7,000-plus-acre wildfire in the area. While the cause of his death was unclear – a necropsy ultimately ended up finding traces of rat poison in his system – a National Park Service spokesperson told LAist, "We've seen other cases of mountain lions surviving wildfires, and coming away with burned paws that make it difficult for them to hunt and survive."
Fire & wildlife habitat
The real-time deaths and miraculous escapes are the most superficially dramatic wildfire impacts on wildlife, but more significant in the long-term are the habitat changes resulting from burns. As firebugs demonstrate, these changes create opportunities for many animals.
"Fire turns the kaleidoscope of habitat. The post-burn environment favours some species, discourages others, which is why you want lots of patch burns so you have a good churn of habitat," Stephen Pyne, one of the foremost wildfire scholars around (and a former wildland firefighter) told me via email.
Amid the bountiful sunlight and released nutrients of a charred forest or shrubland, grazing animals may prosper; browsers may get their day when early-successional shrubs colonise burns and reign for a few decades. Woodpeckers and other cavity-nesting birds flock to the snags that stud a burned forest. The "case-hardening" by which flames toughen wood means that a fire-killed snag and the downed log it ultimately produces – apartment complex for all kinds of creepy-crawlies – may offer longer-lasting habitat than other deadwood.
A prescribed (or controlled) fire in eastern Oregon. Image: Bureau of Land Management Oregon/Flickr
Fire's impact on habitat varies from fire regime to fire regime, of course. A grass fire creeping across savannah or prairie preserves that ecosystem by killing invading trees and shrubs: many animals of the pre-fire landscape therefore reoccupy it in short order, if not immediately. A huge stand-replacement crown fire in taiga or subalpine forest, by contrast, removes its defining conifers and paves the way for fundamentally different plant communities – brushfields, deciduous woods – that will eventually, maybe a century later, transition back to conifer domination. More specialised animals found in the pre-fire old growth may not reoccupy the site until that happens, but in the meantime, a host of other species will stake their claim.
In the fire-dependent Cape fynbos of South Africa, nectar-eating sugarbirds and orange-breasted sunbirds lose local habitat to fire – it may take some eight years for their preferred nectar-bearing shrubs to reestablish themselves – while insectivorous species such as the Cape rockjumper may prosper on the heels of flame. In the grasslands of southeastern Arizona, cotton rats declined after a fire temporarily reduced the green vegetation they eat, while cotton mice and kangaroo rats increased in the area, likely because of plentiful seeds (their preferred nosh) generated by the forbs colonising the burn-scape.
Roughly speaking, animals specially adapted to fire environments ("pyrophytes"), as well as generalist species, tend to be the short-term "winners" when the smoke clears, while those reliant on habitats or resources that are temporarily destroyed are the "losers". Woodland caribou lose out on winter lichen reserves for a time when their boreal woods burn; white-tailed deer and moose, meanwhile, do well on account of all the abundant post-fire shrubbery.
Beyond the short-term aftermath of burns, it's important to emphasise just how many animals depend on habitats maintained directly by fire. The Kirtland's warbler is a classic North American example. The songbird – restricted to a small breeding range in Ontario, Michigan and Wisconsin, and wintering ground in the Bahamas – nests only in young stands of jack pine: a "serotinuous" tree bearing a large proportion of cones that open only when unsealed by fire. Historically, wildfires perpetuated both jack pine in general and the youthful, scrubby pinewoods the warblers needed; fire suppression has reduced warbler habitat, and prescribed burns (and selective timber harvest) are helping to restore it.
The evolving fire-scape
Part of the crazy complexity of fire ecology is the human element. We're fire animals like none other: our mastery of fire, right up there in our top two or three all-time breakthroughs, didn't just transform our ways of life – it also transformed ecosystems all around the world. Fire is an age-old force on Earth, one we learned to make and manage; for millennia, other organisms have evolved under the rhythms of anthropogenic burning.
Those rhythms, though, have changed considerably across time, as hunter-gatherer burning gave way in many areas to agricultural burning, and, in modern times, as intentional burning gave way to fire suppression. Again, it's complicated, but generally, policies of suppressing fires have built up fuel loads in many flame-adapted ecosystems to the point where they're prone to high-intensity, high-severity burns – as opposed to the low-grade fires that, erupting frequently, once maintained them.
In landscapes subject to institutional fire suppression and not, there's the even greater influence of climate change, which from the American Southwest to the Russian taiga seems to be promoting larger, fiercer and more frequent conflagrations. Climate change is such a planetary-scale, whole-earth-system phenomenon that it's an epic challenge to predict how specifically it'll influence local fire regimes, though more and longer-lasting droughts, higher annual temperatures, receding permafrost, and diminished and faster-melting snowpacks certainly seem to set the stage for more burning. Assessing how wildlife can adapt to an evolving new pattern of wildfire is just one part of the high-stakes puzzle climate change presents.
B;ACK BEAR AND CUB TRAVELING ALONG EDGE OF THE GREAT DISMAL SWAMP REFUGE FIRE
CREDIT-ROB WOOD/USFWS
B;ACK BEAR AND CUB TRAVELING ALONG EDGE OF THE GREAT DISMAL SWAMP REFUGE FIRE
CREDIT-ROB WOOD/USFWS
Our burning behaviour and effects on global climate coincide, of course, with all the other ways we impact wildlife. California condors, for example, have dealt with wildfire in western North America for many millennia; countless nests must have gone up in flames. That's less of an issue when you've got lots of condors, but today, the potential loss of just one nestling – like the chick caught in the Thomas Fire – is a major cause for concern.
"If you have a species tied to a particular place, isolated in a refugia, it may suffer from a big burn that blasts over the site," Pyne said. "Apart from any immediate fatalities, the species won't have any place else to flee to until the original site recovers."
Hemming wildlife into small, isolated patches of habitat surrounded by human development or otherwise unfavourable landscapes makes animal populations more vulnerable to fires, as they may have less ability to seek refuge and food, and fewer source populations for recolonisation. In this way, fires may have contributed to the extinction of the heath hen of eastern North America (a bird dependent on fire to maintain its favoured open habitats) when they broke out in the last remaining stronghold of its hugely reduced range, the New England island of Martha's Vineyard.
Meanwhile, a nearly 50,000-acre wildfire last year in the Pinaleño Mountains of southeastern Arizona killed 217 of 252 known Mount Graham red squirrels, and destroyed many of the rodents' seed caches. Scientists are anxiously hoping enough squirrels survive this winter to give the endangered subspecies a fighting chance in the wild.
If your main takeaway from all of this is that it's tough to generalise about fire impacts on animals – well, you've got it. Flames burn up woodrat nests and yet refresh wildebeest pasture. They destroy the boreal owl's old-growth home while making a new snag-ridden one for some of its close kin. They serve up a smorgasbord for hunting kites and a nursery for charcoal beetles. They pay off for this puma with lots of wild room to roam while mortally threatening that puma living in a pocket refuge walled in by humanity. Wildfire is such a defining element of so many ecosystems around the world that it's impossible to imagine them – and their constituent creatures – without it.
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