Study: Spotted owls compatible with managing forests for fire, drought

Just came across this item from the PSW Research Station…. Key point: Owls look for tall trees, not dense canopies.

Study: Supporting owls compatible with managing forests for fire, drought

For Immediate Release: October 5, 2017

ALBANY, Calif. — In what is believed to be the largest spotted owl study in terms of area analyzed, remote sensing technology is providing a more precise look at habitat preferences for the sensitive species with implications for greater flexibility in forest management.

“For the last 25 years, forests in the western United States have been managed to protect habitat for spotted owls based on ground surveys that were limited by plots with a small sample area and what could be seen from the forest floor,” said Malcolm North, a research ecologist with the U.S. Forest Service’s Pacific Southwest Research Station and lead author of the study. “We’re employing relatively new technology to get a new vantage point into the forest canopy – across an unprecedented amount of terrain – to better understand what that means for spotted owls.”

Using Light Detection and Ranging imaging, or LiDAR, North and colleagues from partnering organizations studied forest attributes across 1.2 million acres, encompassing 316 documented owl territories, along California’s Sierra Nevada. LiDAR uses laser pulses shot from an instrument mounted in an airplane that can measure a forest’s canopy, including tree height, distribution of tree foliage and any forest gaps.

Whereas previous research led to the assumption that spotted owls needed dense canopy cover (generally estimated at 70 percent or greater) across a broad landscape, LiDAR data revealed it’s more the height of the canopy, as opposed to the expanse of it, that matters most to owls.

“Cover of tall trees best predicts California spotted owl habitat,” recently published online by the journal of “Forest Ecology and Management,” reports spotted owls typically were found in forests with high concentrations of tall trees measuring at least 105 feet in height, but preferably taller than 157 feet. Meanwhile, dense stands of trees measuring 52 feet or shorter were generally avoided by the owls.

“We rarely found owls in high canopy cover without tall trees. We also found owls in areas with tall trees but low surrounding density,” North said. “It’s really the big trees that the owls are selecting for.”

The study’s findings could have implications for land management strategies to improve forest resilience to wildfires, drought, insects and diseases. Forests with tree densities greater than historical ranges – especially with high densities of smaller trees – are more susceptible to extreme wildfire behavior or vulnerable to the effects of drought, insect infestations and disease.

“While land managers may have felt compelled to maintain these abnormally high densities to adhere to the 70 percent canopy cover threshold, it might also have placed forests and owls at risk,” North said. “The large trees favored by spotted owls can typically withstand low to moderate wildfires and other disturbances. But when exposed to extreme wildfires from high fuel loads or when their vigor is compromised by too many trees competing on the landscape, these tall trees can become vulnerable.”

Researchers also studied how large openings in the canopy or gaps in the forested landscape, ranging from 0.03 to greater than 2.5 acres, impacted owl use or nest site selection.

“Land managers may have been leery of creating gaps in the landscape because of the reduction in canopy over,” North said. “But other than avoiding placing their nests directly adjacent to a gap, owls showed no difference in the areas they used compared to the surrounding landscape with regard to gaps.”

North and his colleagues’ study comes on the heels of a newly available report synthesizing the last two decades of research pertaining to spotted owls. “The California Spotted Owl: Current State of Knowledge” was made available online by the Forest Service’s Pacific Southwest Research Station. The report represents a comprehensive review by scientists of the ecology, habitat use, population dynamics and current threats to the viability of the California spotted owl.

 

9 Comments

  1. My, my. Sounds a lot like the management history of the red-cockaded woodpecker. “Best available science” (maintaining high B.A.s/reduced harvesting) turns out to be sub-optimal for bird and forest health and devastating for forest-dependent communities.

  2. Study was of California spotted owl living in southern & central California. The fire ecology of these dry forests could not be more different from the wet forests inhabited by its northern spotted owl cousin. No surprise that both subspecies prefer forests with tall trees. The dry forests have fewer short trees in the understory while the wet forests have more understory short trees. Slap-my-forehead-in-amazement!

    • I’m with Andy on this one, many many many apparent scientific disputes are really about “what area was studied” and “what area it applies to”. The Wenatchee is not the Williamette and the coast range is not the Sierra. Now what would be really interesting is to get the scientists who have studied the critter in different places together in one room and see if they could jointly develop an explanation for the differences. Sort of “I found this and you found that, what hypotheses would explain that? What evidence would support those hypotheses? Can we get a grant to figure it out?.”

      But, sadly, there is no current model in Science World that does this (IPCC has some desirable features but is overengineered for our purposes).. would be cool if some Big Funder would take this on- both paying for the meetings and the new studies funded (a carrot). Managers are left with documenting various competing scientific claims, and plaintiffs arguing that they didn’t use the right ones.

  3. So this supports the idea that unnatural accumulations of understory ladder fuels may be removed from sites with a history of frequent low intensity fires without harming owls. Not a surprise if this is what they evolved with (“ecological integrity” one might say). It apparently doesn’t address the question of whether more big trees are better, or how many big trees are enough, and wouldn’t support the idea that reducing the canopy density of large trees would be a good thing for owls (it suggests the opposite).

    This was interesting to me: “While land managers may have felt compelled to maintain these abnormally high densities (of smaller trees) to adhere to the 70 percent canopy cover threshold…” The study isn’t necessarily invalidating the 70% threshold, rather it is questioning the role that smaller trees should play in that. It does raise questions about the threshold if it was established based on the presence of smaller trees.

    • It is more about actual nests than just “tall trees”. Remember, CASPO ‘owl circles’ are probably the most at-risk to stand-replacing wildfires. Yes, there has been some ideas about being able to cut some trees bigger than 30″ but, I doubt such a plan would make it through the courts. I always thought it would be good to have some greater flexibility regarding the diameter limits. There were a ton of older nasty mistletoed white firs that should have been cut on the last project I worked on. I guess the crude science behind diameter limits is the best we have… since 1993.

  4. A) In my research for a distant future post on the NSO I have noticed the following:
    1) When CSO studies by Bond, DellaSala and Hanson say high intensity fire is not a problem, they ignore the evidence to the contrary and they and others on this site jump on board and extrapolate those shaky conclusions to the NSO.
    2) Yet, here we have a relatively high rigor study on the CSO which is being discounted as to it’s suitability for the NSO. All of this after years of claiming that they both had virtually the same nesting and foraging habitats.
    3) When some people go out on a limb their egos just don’t seem to allow them to recognize the point at which the limb will no longer support them.

    B) in regard to John’s comment “It apparently doesn’t address the question of whether more big trees are better, or how many big trees are enough, and wouldn’t support the idea that reducing the canopy density of large trees would be a good thing for owls (it suggests the opposite).”

    My notes on this study from the following sources:
    (ref. 54.2) https://www.fs.fed.us/psw/publications/north/psw_2017_north004.pdf
    (ref. 54.1) https://m.phys.org/news/2017-10-win-win-owls-forest.html
    (ref. 54.3) https://yubanet.com/scitech/study-supporting-owls-compatible-with-managing-forests-for-fire-drought/
    suggest the following answers (emphasis added):
    1) John’s Question: “how many big trees are enough”
    is answered by ““Two lines of evidence, one historical and one derived from our findings in this study, suggest that a focus on preserving patches of large trees rather than canopy cover per se may be more effective. Historical data sets and forest reconstruction studies from the Sierra Nevada consistently suggest active-fire forests on average were dominated by large trees and stands generally had low canopy cover (17–41%) and tree densities (60–328 trees/ha or 24–133 tree/ac)””
    2) “High canopy” (i.e. total canopy) “cover (≥70%) mostly occurs when large tree cover is high, indicating the two variables are often confounded. Our results suggest that the cover of tall trees may be a better predictor of owl habitat than total canopy cover because the latter can include cover in the 2–16 m strata – conditions that owls actually avoid”
    3) ““We rarely found owls in high canopy cover without tall trees. We also found owls in areas with tall trees but low surrounding density,” North said. “It’s really the big trees that the owls are selecting for.”
    “While land managers may have felt compelled to maintain these abnormally high densities to adhere to the 70 percent canopy cover threshold, it might also have placed forests and owls at risk,” North said. “The large trees favored by spotted owls can typically withstand low to moderate wildfires and other disturbances. But when exposed to extreme wildfires from high fuel loads or when their vigor is compromised by too many trees competing on the landscape, these tall trees can become vulnerable.””
    RE John’s Comment: “… wouldn’t support the idea that reducing the canopy density of large trees would be a good thing for owls …” —> Not on nesting sites but it doesn’t preclude patchiness between nesting sites for fire breaks nor reducing density on 2-16m tall trees on nesting sites to eliminate ladder fuels.
    4) “Forests with canopy cover > 70% are not rare, but they usually occur in mixed-conifer forest types and require a combination of high site productivity and/or a long period of fire suppression (Collins et al., 2011).The owl’s documented association with high” (total) “canopy cover conditions has raised one hypothesis that owls have benefited from fire suppression and may presently have more high-quality habitat than would have been present under active-fire forest conditions””

    So I find it very hard to believe those who ignore contradicting evidence and accept anything that agrees with their preconceived/biased notions no matter how limited the study. In my literature search on the NSO I have come across as much variation between and within NSO regions as I have between NSO and CSO research results. It’s a mess – we don’t even know how many NSO there are but we know that there are more than reported because of the sampling methodology being used. We don’t even know if the NSO decrease is really due to Barred Owls since the NSO goes silent in the presence of the BO and often returns to it’s prior site when the BO is removed. Too much misplaced certainty is getting in the way of rigorous research on a meaningful scale. God can not be duplicated and anyone who thinks so knows nothing about the complexity of forest and wildlife science. As to this article, its general precepts appear to me to be consistent with sound fundamental science that should be transferable across subspecies of spotted owls.

  5. It’s quite a leap to get from the LiDar data to the conclusion that logging is compatible with owl conservation. Tree height is an indicator of 3D habitat volume. Also, tree height is associated with relatively dense forest and with stand age which is associated with accumulated dead wood habitat.

    This study does support a recommendation to let forests grow tall, but it does not support any recommendation to reduce the density of forests to benefit owls.

    • Of course, NO ONE is talking about logging ‘owl circles’. Additionally, ALL non-hazardous trees over 30″ in diameter are strictly protected. Besides, what is actually wrong about “thinning from below”, cutting trees which average about 15″ in diameter?

      There is so much about CASPO that isn’t covered in the press and not well understood by some eco-groups. Four main facts that are often not covered are; 1) the birds need BOTH nesting habitat AND foraging habitat to thrive and 2) the birds are quite territorial in occupying their nesting habitat and 3) all the prime nesting habitats are all occupied and protected and 4) Owls need multiple nests in their territory to have offspring every year.

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