Silviculture and the Northern Spotted Owl

For those of you interested in the NSO, there’s a fine article in the new edition of the Western Forester, an SAF newsletter:

“Potential for Silviculture to Contribute to Conservation of Spotted Owls,” by Larry L. Irwin and Jake Verschuyl

Here’s the concluding chapter (spoiler alert!):

Efforts to model forest succession and likely NSO responses in dry forests under several management scenarios suggest a bleak scenario for owl habitat within the <10 yr window described by the 2011 revised recovery plan. In the short-term or at small spatial scales it is argued that forest-health type thinning would likely result in a decrease in available owl habitat even when compared to habitat lost through catastrophic wildfire during the same time period. After several decades, however, the forests treated silviculturally were considered to have more NSOs than those not treated. A majority of federal scientists now caution, despite acute short-term pressures facing NSOs, that successful management and restoration of dry forests will require a long-term, landscape or eco-regional perspective that involves active silviculture.

The entire article is worth a read. So’s the rest of the same edition.


  1. The authors can be commended for recognizing “The Recovery Plan calls for additional research to determine direct NSO response to variations in vegetation management associated with ecological forestry” (i.e. their pro-logging ideas are untested) and I appreciate that they honestly protray as “philosophy” their speculations about logging and spotted owls, e.g. “we expand on the general philosophy of active management …”

    Maybe because this is a newsletter article and not a science journal, there are no science citations to back up their assertions. Most of their speculations about how logging ~might~ benefit spotted owls is inconsistent with the underlying science.

    For instance, there is no evidence that fragmentation from clearcutting will benefit owls. The evidence the authors may be borrowing from is that owls in some areas of California seem to do well in landscapes that are a mosaic of suitable habitat and non-habitat, but non-habitat is _not_a_synonym_for_clearcuts_, it’s natural non-habitat such as patches of hardwood, shrubs, etc.

    Another example, there is no evidence that logging to open the forest canopy and allow owls to fly and access prey is a good idea. The same opening of the canopy reduces cover and makes owls themselves vulnerable to predators and depletes prey populations. There are no studies of this, but see Wilson, T. 2010. Limiting Factors For Northern Flying Squirrels (Glaucomys Sabrinus) In The Pacific Northwest: A Spatio-Temporal Analysis. PhD Dissertation. Union Institute & University, Cincinnati, Ohio.

  2. What IS known is that owls do not use burned forests for nesting, unless there is no other option. Yes, they do use burned habitats for hunting but, dead forests provide no protection for their nests. Remember, they need a system of nests to continue to reproduce. They also need foraging habitat, to eat and feed their offspring. They need BOTH habitats to survive. They cannot survive with just one of the two.

    • Larry, Again you speak of things you know not of. Owls do in fact use burned forests, and logging to reduce forest density and modify fire behavior provides not net benefit for wildlife that prefer dense forests.

      Clark (2007) looked at post-fire habitat selection by spotted owls after several wildfires in southern Oregon and determined that low severity fire in nesting, roosting, foraging habitat appears to benefit spotted owl occupancy and colonization. “Initial occupancy was positively influenced by the amount of roosting and foraging habitat with low severity burn within the core (β = 0.08, 95% C.I. = -0.02 – 0.17) … Colonization rates were positively influenced by the amount of nesting, roosting and foraging habitat that received a low severity burn within the core (β = 0.08, 95% C.I. = 0.02 – 0.15).” Darren A. Clark. 2007. Demography and Habitat Selection of Northern Spotted Owls in Post-Fire Landscapes of Southwestern Oregon. M.S. Thesis. Oregon State University. Robert Anthony, Advisor. Figure 6.1 shows that nesting, roosting, foraging habitat is used more frequently than random sites even after it has experienced moderate or high severity fire, while areas that were salvage logged were used less frequently than random sites.

      And more importantly, what are you going to do about fire? You can’t predict when, where, and what severity, so any effort to control fire with fuel reduction will need to treat a large fraction of the landscape, far larger than the fires themselves. Since fuel = owl habitat. Logging will adversely affect far more acres than fire will. Conclusion, logging+fire is worse than fire alone.

      The Wildlife Society (TWS) peer reviewed the 2010 Draft Recovery Plan for the Spotted Owl which called for extensive logging to reduce fire hazard. TWS used state-and-transition model to evaluate the effects of opening dry forests to reduce fire hazard versus the effects of wildfire. Here’s along excerpt:

      “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.

      • I would bet that “low-severity burns” in nesting habitats are more rare than the birds, themselves. Just because birds nest in marginal habitats, that doesn’t mean their offspring will thrive. Indeed, owls are so timid, predators meet little resistance (unlike goshawks). What IS clear is that once nest trees are destroyed, the owl’s sustainability takes a very big hit. Sure, it is easy to defend fire impacts on foraging habitats but, any fire that burns in their nesting core areas has potential to result in a devastating crown fire. Coastal ranges have better chances of survival, due to wetter conditions but, predictions say the risk will increase in the coming years.

        What is worse? Careful thinning or probable crown fire? Which is riskier?

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