I’m sure you all are familiar with the smiling face of Smokey the Bear. There he is, standing, inexplicably in overalls and a ranger hat, carrying a shovel. Usually he’s in the form of a wooden cut-out mounted beside a sign shouting “Only You Can Prevent Forest Fires!”.
The fictional bear tries to instill in us, a sense that wildfires are an evil phenomenon to be feared, prevented, and extinguished on sight (undoubtedly he’ll use his trusty shovel). As a kid, one of the picture books on my shelf was the story of Smokey. Though I don’t remember the whole story, I can vividly recall an illustration showing deer, raccoons, squirrels, birds, and other (always cute) woodland creatures fleeing from an approaching blaze. The not so subtle message: Fire is BAD BAD BAD!
But ol’ Smokey is dead wrong about fire. Without it, much of the wildlife we love, the forests we know, and the landscapes in which we live, would not be the same.
But ol’ Smokey is dead wrong about fire. Without it, much of the wildlife we love, the forests we know, and the landscapes in which we live, would not be the same.
In my last post, I talked about some interesting new research into how fires can impact global climate. But a more direct, and visible impact is that on wildlife.
Fires in the boreal forest open up a lot of country that was previously dense trees and converts it into a series of successional phases. In the year or so immediately following a fire, grasses, forbs, and mosses are the first to reappear. Fireweed is the most noticeable of these, a colorful flower that draws its name from its ability to colonize and thrive in recent burns. Next, shrubs and saplings move in: alders, willows, aspens, and cottonwoods. And eventually, decades later, the spruces will return to push the deciduous vegetation out. Each of these stages plays a role for wildlife. But today, I wanted to talk about the early months and years following a fire, and specifically, how important that period is to a one particular bird.
Perhaps the first critters to make a home in recently burned forest are beetles. Cerambycids (the long-horn beetles) and their smaller counterparts the Scolytids (bark beetles) colonize the recently killed timber within days or weeks of the fire. The adults arrive on the wing, and lay eggs on the dead trees. When these hatch, the young larvae burrow into the wood where they live for up to two years, feeding and growing. Longhorn beetle larvae in particular can grow quite large, up to 50mm. So abundant are these bugs, that if you walk silently through a recently burned forest you can hear their mandibles scratching inside the trees as they grind the wood into digestible pulp.
It’s these larvae that lure in the woodpeckers. Though most species of woodpeckers will happily take advantage of an abundant food source like this, in interior Alaska, there are three that are particularly common in burns: Hairy Woodpecker, Three-toed Woodpecker, and Black-backed Woodpecker. The Black-backed in particular is almost entirely dependent on recent burns. So close is their reliance on fires that there are even reports of Black-backeds moving into burned forest, while the fire is still active.
A project outside of Fairbanks in the mid-90s studied woodpecker abundance and foraging behavior in the years immediately following a burn. Within a few months, the abundance of Black-backed Woodpeckers reached a high of 0.25 birds per hectare. (Though not clinging to every tree, this number would virtually assure a visiting birder the rare opportunity to find a Black-backed.)
Numbers remained high through the first year and into the second but dramatically dropped off in the third year. By the fourth year past fire, Black-backed Woodpeckers had abandoned the burn.
According to the Birds of North America account, Black-backeds likely have a similar life span to that of the closely related Three-toed Woodpecker. Banded Three-toeds have been recaptured up to 8 years after banding, meaning they can live at least that long. So, over the course of its life, a single Black-backed requires at least three separate recently burned areas. If there are low fire periods lasting multiple years, its easy to see this species being forced into sub-optimal habitat, resulting in reduced reproduction and lower survival.
The population dynamics of the species shows this pretty clearly. The Black-backed Woodpecker is what is known as an “irruptive” species. Irruptive is when the population rises in bursts when conditions offer good opportunities for reproduction and then collapses when things aren’t favorable. (This is different from population cycles, which change in predictable patterns). In the years following a big fire season, populations rise, and then decline (or even plummet) when wet years suppress forest fires.
For wildlife, those changes are not just desirable, they are an absolute necessity of survival.
I’m endlessly fascinated by these interactions. Because we humans usually live in the stable environments of towns, cities, and manicured back yards, we often forget that the world is in constant flux, shifting and changing as forest fires sweep across a landscape, floods decimate riverside habitats, storms wipe clear coastlines, or glaciers recede and advance. We tend to view any of these changes as bad things. After all, to us, stability is preferable. But for wildlife, those changes are not just desirable, they are an absolute necessity of survival.
Next time I see a cartoon Smokey, I’m going kick him in the shins.
Information on this post was drawn primarily from:
Murphy, Edward C., and W. A. Lenhausen. 1998. Density and foraging ecology of woodpeckers following a stand-replacement fire. Journal of Wildlife Management. 62(4): 1359-1372.
Dixon, Rita D. and Victoria A. Saab. 2000. Black-backed Woodpecker (Picoides arcticus), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/509
