Sierra Nevada Lidar Study of Spotted Owls Suggests That Thinning Understory Might Be OK

Here is an interesting story from UCDavis via Treesource.

Remote sensing technology has detected what could be a win for both spotted owls and forest management, according to a study led by the University of California, Davis, the USDA Forest Service Pacific Southwest Research Station and the University of Washington.

For 25 years, many forests in the western United States have been managed to protect habitat for endangered and threatened spotted owls. A central tenet of that management has been to promote and retain more than 70 percent of the forest canopy cover.

However, dense levels of canopy cover leave forests prone to wildfires and can lead to large tree mortality during droughts. Thus, the disconnect between two significant land management goals.

In the study, published in the journal Forest Ecology and Management, scientists found that cover in tall trees is the key habitat requirement for spotted owls — not total canopy cover. It indicated that spotted owls largely avoid cover created by stands of shorter trees.

“This could fundamentally resolve the management problem because it would allow for reducing small tree density through fire and thinning,” said lead author Malcolm North, a research forest ecologist with UC Davis’ John Muir Institute of the Environment and the USDA Pacific Southwest Research Station. “We’ve been losing the large trees, particularly in these extreme wildfire and high drought-mortality events. This is a way to protect more large tree habitat, which is what the owls want, in a way that makes the forest more resilient to these increasing stressors that are becoming more intense with climate change.”

“The analysis helps change the perception of what is important for owls — the canopy of tall trees rather than understory trees,” said co-author and spotted owl expert R.J. Guitiérrez, a professor emeritus at the University of Minnesota. “The results do not mean a forest should be devoid of smaller trees because owls actually use some of those smaller trees for roosting. But it suggests a high density of small trees is likely not necessary to support spotted owls.”

Here’s the study. Of course, the press release format doesn’t cover the usual scientific caveats like they only studied part of California and so on..

I’m interested in how this fits in with what our readers in California have observed.

10 thoughts on “Sierra Nevada Lidar Study of Spotted Owls Suggests That Thinning Understory Might Be OK”

  1. This is like “Duh”, anyone with a lick of common sense knows this. I don’t understand why we have to keep spending money to prove it. It is just more data that managers will be afraid to act on.

  2. It all seems like “water under the bridge”. It probably is too late to do much about the southern Sierra Nevada, as drought and bark beetles have decimated those forests and eliminated the need for thinning. All that is left is for those MILLIONS of dead trees to to burn, at very high intensities.

    Other parts of the Sierra Nevada aren’t seeing enough thinning, and wildfires are also intense, burning through drought-stressed forests. Sadly, there is no political will to do more. We will have to accept the firestorms, burning up “owl circles” and actual nests. Welcome to more gridlock, folks. It is what most people want, despite the serious impacts.

  3. The importance of big trees has always been evident in studies of owl nest stands, prey, and habitat use, the problem has been limited or flawed vegetation data. With Lidar-derived vegetation data, these habitat qualities are pretty clear when looking at the landscape. Dense canopy cover is important, but so are large, complex, mature stands. Now we just need this quality of data on more forests.

  4. There are some aspects and characteristics about spotted owls that need more consideration. Owls (and goshawks) are notoriously lazy in building nests. Of course, last year’s active nest cannot be used for several years, due to the all the bird crap. Nests also need some sort of protection from above, from late-season snowfalls. I’m sure there are a great many stands that have recently become acceptable as “nesting habitat”. They remain unused, because there are no ready-made nests, in those ‘perfect spots’.

    Maybe one of the best things we can do is to encourage owl pairs (and goshawks) to use the habitat by building nests for them. Crews of Wildlife people could be assigned chunks of land, to look for sites to build a nest. I think it would be a relatively small investment to increase populations quicker.

    There can also be some benefit, in some cases, where some light thinning in protected habitat occurs. I worked on one project where we thinned out trees in the 10-14.9 inch size, from underneath large old growth.

  5. This study’s supposed recommendation to reduce understory vegetation in nest patches is NOT supported by the results of this study. This study was about owls’ association with tall tree habitat, not how to perpetuate that habitat.

    The “management implications” state: “To maintain selected habitat in the near-term, management may need to take a more active role reducing stem density in the 2–16 m class and surface fuels in tall tree areas to make these stands more resistant and resilient to drought and high-severity wildfire that can significantly reduce local owl populations.”

    This recommendation is NOT about mimicking the “tall tree” feature of nest sites shown by this study but rather a misguided attempt to save tall trees from fire, but we know that is deeply flawed because ….

    Logging intended to benefit habitat will also reduce the quality of habitat, the analysis must include some evaluation of ecological costs and benefits — e.g., the probability that logging will degrade habitat vs. the probability that fuel reduction treatments will interact favorably with fire and thus benefit habitat. This evaluation requires an estimate of the probability of future wildfire. To assume, as many analyses do, a 100% chance of future wildfire over-estimates the likelihood of treatments will interact with fire, thus over-estimating the ecological value of fuel treatments, and under-estimating the ecological effects of logging on habitat. This is an example of the “base rate fallacy” or “neglecting priors” from Bayesian statistics. The probability of a forest stand NOT burning are far greater than the probability of a forest stand burning. Attempts to address a problem that is unlikely to occur, such as by thinning a forest that is unlikely to burn, runs a high risk that unintended negatives effects will overwhelm improbable beneficial effects.

    Lehmkuhl et al. (2015) found “Tradeoffs between fire resistance and NSO habitat quality are real. Our results demonstrate that balancing the goals of increasing fire resilience while maintaining habitat function, especially nesting and roosting, for the NSO in the same individual stand is a difficult, if not an impossible, task. Even lighter thinning treatments typically reduce canopy cover below 40 percent. The reality is that nesting and roosting NSO habitat is by definition very susceptible to high-severity fire; owl habitat value and fire risk are in direct conflict on any given acre. …” Lehmkuhl, John; Gaines, William; Peterson, Dave W.; Bailey, John; Youngblood, Andrew, tech. eds. 2015. Silviculture and monitoring guidelines for integrating restoration of dry mixed-conifer forest and spotted owl habitat management in the eastern Cascade Range. Gen. Tech. Rep. PNW-GTR-915. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 158 p.

    The Wildlife Society (TWS) peer review of the 2010 Draft Recovery Plan for the Spotted Owl. The draft plan called for extensive logging to reduce fire hazard (“inaction is not an option”). TWS used state-and-transition model to evaluate the effects of opening dry forests to reduce fire hazard versus the effects of wildfire.

    The results of running the model with 2/3rds of the landscape treated leads to open forest becoming predominant after a couple of decades, occupying 51 percent of the forested landscape, while mature, closed forest drops to 29 and 24 percent of the Klamath and dry Cascades forests, respectively (Appendix A, Figure 5, shows the Cascades). Treatments that maintain open forests in 2/3rds of the landscape put such a limit on the amount of closed forest that can occur, even if high severity fires were to be completely eliminated under this scenario, there would only be 35 percent of the landscape occupied by closed forests. In contrast, to the extensive treatment scenario, treating only 20 percent of the landscape reduces mature, closed canopy forest by about 11 percent (Appendix A, Figure 6).
    One justification for the extensive treatment scenario promoted in the 2010 DRRP is that it is needed because of increased fire hypothesized to occur under climate change. By doubling the rate of high severity fire by 2050 with 2/3rds of the landscape treated, closed canopy forest is reduced to 25 percent in the Klamath compared to 60 percent without treatment and 23 percent in the dry Cascades compared to 54 percent without treatment.
    Under what scenario might treatments that open forest canopies lead to more closed canopy spotted owl habitat? The direct cost to close forests with treatments that open them is simply equal to the proportion of the landscape that is treated. This reduction in closed canopy forest can only be offset over time if the ratio of forest regrowth to stand-replacing fire is below 1 (5-8 times more fire than today), and shifts to above 1 with the treatments (and most or all stand replacing fire in treated sites is eliminated, as modeled here). Another scenario that allows closed forests to increase would be if treating small areas eliminated essentially all future stand replacing fire, not only in treated areas, but across the entire landscape. This scenario obviously relies on substantially greater control over fire than is currently feasible, and it would increase impacts of fire exclusion if effective.

    In sum, to recognize effects of fire and treatments on future amounts of closed forest habitat, it is necessary to explicitly and simultaneously consider the rates of fire, forest recruitment, and forest treatment over time, which has not yet been done by the Service.

    The potential impacts of fuel treatments on spotted owls are not considered. … We also know little about the impacts of fire, yet this has been treated as a major threat, leading to proposing more fuel treatments. However, it is uncertain at this time which is a bigger threats, fires or treatments to reduce risk of fires. … If the plan intends to use the best available science to describe ongoing impacts to spotted owl habitat, information and literature about disturbances to reduce fuels should be included.
    … there has been no formal accounting of how closed canopy forests can be maintained with the widespread treatments that are being proposed.

    The Wildlife Society 2010. Peer Review of the Draft Revised Recovery Plan for Northern Spotted Owl. November 15, 2010.

    This analysis is consistent with the findings of Raphael et al (2013) used a state-and-transition model to explore the effects of landscape fuel reduction logging on spotted owls and found:

    Active fuel reduction activities in moderate habitat contributed to substantial short-term (simulation years 0 to 30) population declines under the larger area, higher intensity scenarios. … The combination of BDOW interactions and high-intensity, larger-area treatments contributed to the most substantial NSO population bottlenecks. The combined effects of aggressive fuel reduction treatment approaches and interactions with BDOWs have the potential to contribute to increased extinction risk for NSOs in both analysis areas. … It appears that management regimes that take out owl habitat through treatments (either current or potential future) do not reduce the amount of habitat that is lost to wildfire enough to make up for the habitats lost through treatments.

    Principle Investigator: Dr. Martin G. Raphael. Project Title: Assessing the Compatibility of Fuel Treatments, Wildfire Risk, and Conservation of Northern Spotted Owl Habitats and Populations in the Eastern Cascades: A Multi-scale Analysis. JFSP 09-1-08-31 Final Report, Page 19.

    • I thought there was uncertainty, related to various pieces of research in the Sierra. Or at least that’s what these authors think. Not to diss researchers from western Oregon, but the Sierra is a different kettle of fish, so to speak, than the eastern Cascades.

      Furthermore, there is not a clear understanding of the balance between the potential short-term impacts from treatments and the longer-term benefits provided by introducing landscape heterogeneity (North et al. 2009), reducing potential for severe fire (Ager et al. 2007, Collins et al. 2013), increasing the potential for more desirable fire effects (North et al. 2012), and increasing resilience to climate change (Stephens et al. 2010).

  6. Sorry but, the NSO and CASPO are two different species, with differing habitats.

    Anyway, this study makes no difference, as the Forest Service has already been thinning since 1993. We should be able to see any and all ‘harms’ that come from the current strategies. Same for the benefits.

    Here is a fairly recent example, where I ran the crew. Keep in mind that this is a south-facing slope, where spacing is a bit wider. We took out mostly white fir and incense cedar. We also employed a “clumps and gaps” strategy, including ‘new science’. They are clearly visible.,-120.3315749,342a,35y,270h/data=!3m1!1e3?hl=en

      • One of those old clearcuts is planted with Giant Sequoias (Their shadows confirm that perfect conical shape!). This part of the Amador RD hasn’t seen any green sales in over 25 years. It really needed thinning. They seem to have split the original project into several smaller timber sales. There are some other units around here that we marked but they aren’t cut, in these aerial views.


Leave a Comment