It’s been some time since my last post here. Other work on photo workshops and tours, travel, global pandemic, writer’s block, and a changing living situation have conspired against me. I have periodically been writing about photography over at my other blog, but I’m afraid my pieces about ecology and wildlife have been pushed to a distant burner. I’m sorry about that.
That said, I’m going to try, (emphasis on “try” I’m not promising anything) to start writing some more here over the next months.
Why now, you ask? Well, due to the pandemic, and some health issues in my family, I’ve spent most of the last year in Colorado. I’ll be here through the winter and spring as well. While I’ve spent a lot of time in the Rockies, it’s come in bits and pieces. A few weeks here, a month or two there. I don’t KNOW this place in the way that I know Alaska. After two plus decades in the far north, studying its birds, other wildlife, and general ecology, I have a solid grasp on that place. But here in Colorado? Sure I can identify the birds that I see, and know most of the trees and wildflowers, but that’s not the same as understanding their seasonal movements, behaviors, and ecology. Living here is like trying to make a good friend out of a passing acquaintance.
I’m living in Salida, right now. It’s a little mountain town about two and half hours west and south of Denver, in the Arkansas River Valley. Two major mountain ranges collide here. The Sawatch Mountains which include the Collegiate Peaks, lies to west and north, while the Sangre de Cristos abut us to the south. East lies a small range of lower, rolling peaks. Every direction I look, mountains.
During my wanderings over the summer I was able to revisit a few places from my past. Mountains I’d climbed and lakes I’d visited as a teenager. There have been changes. More people for one. Colorado’s population has boomed, and the mountains are the recreation area. “Wilderness” has a different definition here than in Alaska. “Wild” places are viewed more as a playground than a temple. While this saddens me to a certain degree, it is a remarkable playground, and I’ve been having fun exploring by bike and foot. Rarely have I found solitude.
Another change has nothing directly to do with Colorado’s booming population: the state of the forests. The amount of beetle-killed spruce and pines is staggering. Vast areas of forest have been killed. Alaska’s forests too have been impacted by beetles. Drive through the Susitna Valley, and you’ll see some areas where 50-70% of spruces have been killed. But here, the beetles impact is on an entirely different scale. Beetles have killed well over 90% of trees in certain areas. I’ve hiked through some stands where it’s a rare to find a living Englemann Spruce.
I didn’t expect that. I knew beetle kill was bad here in Colorado, as it is across much of the mountain west, but seeing it in person… well, it’s hard to ignore.
Spruce bark beetles (Dendroctonus spp.) are thriving in the era of anthropogenic climate change. Previously their populations have been checked by cold, but now warmer winters have allowed the bugs to survive with regularity. The result is millions of dead trees, increased wildfires, and an ecosystem changed to its core.
While books could be written, and probably have, about how this change is impacting the larger ecosystem, I was curious about what’s happened with bird populations.
Woodpeckers seem like a group of birds that would benefit from all those dead trees. Beetles kill the trees, and other wood-boring insects can move in to feast on the dead wood. This, I presume, would mean lots of food and nesting locations for insectivorous, cavity-nesting birds like woodpeckers.
What about other birds? One would think that forest-dwelling birds that rely on living forests would struggle when so many trees are dead or dying due to beetles and wildfire. While those that like a rich understory (newly opened up to sunlight by the dead trees) would probably thrive.
To find out, I dug a bit into the recent scientific literature. And, as always, the answer was not as clear as I might have liked.
Beetle-Kill Forest and Birds
Turns out my hypothesis that woodpeckers would be doing well during these times of heavy beetle-outbreaks is right. More or less. Sort of.
How well a woodpecker is doing depends on the species. That didn’t surprise me. Woodpeckers are not monotypic. Each species has a different foraging behavior, habitat choice, and nesting preference. Species that eat beetles are, not surprisingly, doing well. Generalists, seem indifferent.
All dead forests are not equal. Black-backed Woodpeckers are well-known fire-followers. There are even anecdotes of this species actively flying towards smoke plumes. As most birders will know, to find a Black-backed Woodpecker, you go to the most recent burned forest you can find. Not surprisingly, this species prefers fire to beetle-killed trees.
According to an article by Tingley et al, published in the journal “Forest Ecology and Management”, Black-backed Woodpeckers were almost three times more likely to be found in burned forest than beetle-kill forest.
Other research investigating beetle impacts found some species of woodpeckers responded well to beetle-kill, while others seemed indifferent. Three-toed Woodpeckers, which are closely-related to Black-backeds, were more abundant and productive in beetle-kill areas than in surrounding forest. Downy and Hairy Woodpeckers however, did not show the same relationship.
One paper raised a concerning point: the loss of canopy cover in beetle-kill forests means more direct sunlight, which means more heat, which means nests are at risk of getting overheated, resulting in dead eggs and chicks. Combine that with warmer temperatures, and you’ve got a formula for a lot of failed nests. Any extra success coming from the abundant food, may be countered by an increase in nest failures.
When it comes to woodpeckers, some species appreciate beetle-kill, while others are indifferent. An overall win, I suppose.
What about the other forest species?
I found one paper from Quresh et al. in the journal “Forest Ecology and Management” that provided some insight:
Rather than look at beetle-killed forest in general, the authors distinguished between lodgepole pine and spruce forest. As it turns out, those forest types are as different in death as they are in life.
Quresh et al. found that understory species like Dark-eyed Juncos, aerial insectivores such as flycatchers, and snag-associated species (woodpeckers) responded positively to beetle outbreaks. As time passed since the infestation, bird species richness increased, but ONLY in lodgepole pine forest. Spruce forests showed a negative correlation between species richness and time since the outbreak.
That’s strange, and interesting. Beetle outbreaks could be a good thing for birds, but only in lodgepole pines. Weird.
Here in Colorado, that last bit is probably bad news. From my passing observations, beetles seem to have hit spruce forests harder than lodgepole pines. I wonder what that means for the future?
Take-home messages:
- Black-backed and Three-toed Woodpeckers do well in beetle kill forest, though Black-backeds prefer burns.
- Downy and Hairy Woodpeckers, and Northern Flickers are indifferent.
- As time passes, more species of birds return to beetle-killed lodgepole pine forest, but not to spruce forest.
I didn’t get answers to three questions:
What about species that depend on living trees?
I guess I can take a wild stab at that one, and assume they don’t do well. I doubt warblers who require living conifers for their nests respond well to dead forests.
Since beetle-kill forests are more prone to wildfire, how do birds respond to burned, beetle-killed forest?
Is it the best or worst of both worlds? No idea on that one, but if anyone has an answer, I’d be very curious to know.
What happens when the snags start to fall?
Dead trees don’t stand forever. In wind-prone, subalpine forests, I can only imagine that snag attrition happens quickly. As a recreational user of trails in these areas, I can tell you that the trees are falling quickly. I recently had a dead spruce fall across the trail, just yards in front of me. When they go from standing snags to fallen woody debris, how will the birds respond? We’ll know the answer to that question in few more years.
Conclusion
No matter how we look at it, these huge infestations of beetles, and the resulting dead trees and increased forest-fire risk are not a good thing for wildlife. Some species will temporarily benefit, but eventually all those snags will fall, and the beetles themselves will die off. We’ll be left with something… different.
Perhaps we’ll see a boom in new aspen growth? Or maybe the next decade or two will be filled with rapidly growing willows and alders, the first species in the line of forest succession. Probably, it will be a bit of both.
Earlier this summer, I rode my bike along the Colorado Trail. Segment 2, a bit south and west of Denver, winds through a decade-old burn. The habitat had been Ponderosa Pine forest. While Poderosas area usually resilient to burning, this particular blaze had been hot, and reached the crowns of most of the old pines, killing them. Post-fire few trees remain, replaced by hot, dry, rocky shrubland. Drought and heat-tolerant plants dominate, bearing little resemblance to the open pine woods that stood 15 years before.
It’s not that these changes are inherently bad. Forest fires and beetles have, after all, been passing through our mountain forests for millennia. But they are now more frequent, and more devastating. The mosaic landscape is being replaced by enormous areas engulfed in by massive change. Few areas are stable, which means there are few places of refuge for birds and other wildlife.
I suspect over the coming decades we’ll see waves of species rise, thrive, and then fade as habitats go from living forest, to beetle or fire kill, and then pass through the stages of succession. While likely not “good” from a conservation perspective, it will at the very least be interesting.
References
Hanson and Chi, Black-Backed Woodpecker Nest Density in the Sierra Nevada, California, Diversity 2020, 12(10) 364 https://doi.org/10.3390/d12100364
Kelly et al. Spruce Beetle ourbreaks guide American Three-toed Woodpecker occupancy patterns in subalpine forests. Ibis. 13 March 2018. https://doi.org/10.1111/ibi.12596
Quresh et al. Avian relationships with bark beetle outbreaks and underlying mechanisms in lodgepole pine and spruce-fir forests of Colorado. Forest Ecology and Management Volume 464, 15 May 2020.
Saab et al. Woodpecker nest survival, density, and a pine beetle outbreak. Journal of wildlife mamangement, 11 July 2019. https://doi.org/10.1002/jwmg.21722
Tingley et al. Black-backed woodpecker occupancy in burned and beetle-killed forests: Disturbance agent matters. Forest Ecology and Management Jan 2020 Volume 455.
