Forest management for swifts, swallows and big hollow trees?: Guest post by Brandon Keim

Credit to Cornell Lab of Ornithology’s Birds of North America

After Sharon’s post on the Boundary Waters post-blowdown logging project, my first thought was: was it really so necessary to log at all? Blowdowns are habitat, too, and part of natural disturbance cycles that make landscapes richer. Is the need to keep nature subservient so all-consuming, and our regard for the role of dead trees so minimal that we can’t let trees in a water-rich national wilderness fall down?

Many readers here will — perhaps rightly — regard that inclination as unreasonable, or at least knee-jerk. Disturbance doesn’t need to mean megafire. The proscribed fire treatments didn’t apply to the entire blowdown area, just small parts of it, and if I lived in the region then fire prevention would probably be my first priority. I expect that, if we could ask them, the animals living there would feel that way too.

As I Googled blowdown- and disturbance-related terms, I happened across this lovely white paper, “Dead and Dying Trees: Essential for Life in the Forest,” produced by the Forest Service’s Pacific Northwest Research Station. It talks about how not all big dead pieces of wood are the same: living trees with decayed heartwood have exceptional habitat value, as do the dead versions of those trees, which become completely hollow.

I’d known that dead trees with hollows and holes are important, but hadn’t understood the processes that produce this. Guess I’d figured that all big dead trees would become hollow eventually. And of course hollow trees are essential for, among other creatures, purple martins, swallows and swifts — those marvelous birds who provide such a valuable hemisphere-wide pest-eating ecosystem service, and whose populations have been collapsing in large part because there are so few hollow trees on the landscape and the human-built structures they use (i.e., old chimneys) are fast vanishing too.

My question is: do readers here know of forestry projects which specifically account for decaying trees, not just snags and logs in general? And is anyone managing forests with swifts and swallows in mind?

9 thoughts on “Forest management for swifts, swallows and big hollow trees?: Guest post by Brandon Keim”

  1. When I was a marking crew foreman, we started breaking out snag counts into species, just to get a handle of how many “soft” and “hard” snags were being left out there. On salvage projects, there were people who were concerned about the quality of the snags being left, as well as the sizes. One fire salvage project insisted that the biggest and best snags were all to be left in place, if they weren’t hazard trees. Another project wanted 2 large snags and 3 small snags left per acre (I was happy to find the most ‘unmerchantable’ trees to fulfill the requirement). Some wildlife biologists were concerned about my ‘trading’ of wildlife trees when one occupied a necessary landing location, or was a hazard. They wanted nice and straight snags, instead of gnarled and rotting.

    The idea that every acre needs all its snags should not be made into some sort of ‘natural law’. Snag thinning is now the rule, on Forest Service salvage projects. And, yes, some people do not want to see the differences between USFS and private industry salvage practices.

  2. Thanks for sharing that, Larry. Much appreciated.

    A question: what was the rule before snag thinning was the rule on USFS salvage projects?

  3. In a dynamic ecosystem, life may be fleeting but the snags and logs that survive disturbance provide very critical temporal links from one forest stand to the next. Under natural conditions, a forest hands down a large legacy of living and dead material from one stand to another even after an intense disturbance. Even non-stand-replacing disturbance creates pulses of dead material that are critical for forest ecosystems. There are many publications, enumerating the values of dead and decaying wood.
    1. Franklin, J.F., Lindenmayer, D., MacMahon, J.A., McKee, A., Magnuson, J., Perry, D.A., Waide, R., and Foster, D. 2000. Threads of Continuity. Conservation Biology in Practice. [Malden, MA] Blackwell Science, Inc. 1(1) pp9-16.
    2. William F. Laudenslayer, Jr., Patrick J. Shea, Bradley E. Valentine, C. Phillip Weatherspoon, and Thomas E. Lisle Technical Coordinators. Proceedings of the Symposium on the Ecology and Management of Dead Wood in Western Forests. PSW-GTR-181.
    3. Lofroth, Eric. 1998. The dead wood cycle. In: Conservation biology principles for forested landscapes. Edited by J. Voller and S. Harrison. UBC Press, Vancouver, B.C. pp. 185-214. 243 p.
    4. Rose, C.L., Marcot, B.G., Mellen, T.K., Ohmann, J.L., Waddell, K.L., Lindely, D.L., and B. Schrieber. 2001. Decaying Wood in Pacific Northwest Forests: Concepts and Tools for Habitat Management, Chapter 24 in Wildlife-Habitat Relationships in Oregon and Washington (Johnson, D. H. and T. A. O’Neil. OSU Press. 2001)
    5. Stevens, Victoria. 1997. The ecological role of coarse woody debris: an overview of the ecological importance of CWD in B.C. forests. Res. Br., B.C. Min. For., Victoria, B.C. Work. Pap. 30/1997.
    6. Hagar, Joan, 2007, Assessment and management of dead-wood habitat: USGS Administrative Report 20071054, pp. 1-32.
    7. Bruce G. Marcot 2017. Ecosystem Processes Related to Wood Decay. PNW Research Note 576.

    The Forest Service even has a public education program called “Animal Inn” intended to inform the public of the value of dead wood, unfortunately the agencies still don’t fully recognize these values:
    “Nearly a third of all forest creatures depend on standing dead or fallen trees for their survival. ANIMAL INNS provide shelter, nest sites, and feeding areas for over 1200 species of birds, mammals, amphibians, and reptiles; over 60% of which feed on insects. These insect-eating species act as natural biological regulators to dampen the effects of insect outbreaks in forested lands, thereby performing an important ecosystem function. Fish benefit from trees that have fallen into stream channels.” See also:

    In Region 6, virtually all of the forest plans rely on an outdated standards for dead and down wood. New science indicates that species associated with dead wood need more dead trees, and more green trees need to be retained during harvest in order to ensure ongoing recruitment of those dead trees. Unfortunately, the agencies have not amended their forest plans to account for this new information. There is a new tool used to help make decisions related to dead wood, but it is entirely disconnected from any standards.

    See DecAID, the Decayed Wood Advisor for Managing Snags, Partially Dead Trees, and Down Wood for Biodiversity in Forests of Washington and Oregon,

    • In the Sierra Nevada, fires return a lot more often, and wood just doesn’t decay into soil components. They lay around until the next inevitable human-caused wildfire. AND, I’m pretty sure that 100,000,000+ snags is WAY more than wildlife needs. Remember, blackbacked woodpeckers only use freshly-killed trees for 6 years, out of their 8-year lifespan. Yes, of course they adapt when there are fewer wildfires. If the previous decades of intense salvage logging hasn’t killed them off, I’m sure that today’s USFS salvage projects will have no effect on those rare birds.

  4. Brandon asked, “do readers here know of forestry projects which specifically account for decaying trees, not just snags and logs in general? And is anyone managing forests with swifts and swallows in mind?”

    This planner does not recall ever seeing a forest plan provide separate guidance for decaying trees. The newest forest plan, for the Francis Marion in SC, recognizes they are different, but actually explicitly combines them: “Snags OR hollow trees are maintained at a density of approximately 2 to 4 per acre” (my emphasis). The draft EIS for the revised forest plan for the Flathead in MT recognizes the importance of decaying trees, “placing more emphasis on leaving the larger snags and live trees with decay.” However, the draft plan itself does not actually prioritize decay, but rather combines them: “Snags OR decaying and broken-topped live trees greater than 20 inches d.b.h. are present, predominately ponderosa pine or western larch (which have the greatest longevity as snags)…” (my emphasis, though these species selected might promote decay).

    Forest Service policy under the 2012 Planning Rule is to identify ecological conditions necessary for viable populations of at-risk species. Where such species require decaying trees, forest plans should address them. Decay might also be a key ecosystem characteristic to address as part of required ecological integrity.

    Your second question amounts to asking whether swifts or swallows have been identified as at-risk species for forest planning. I know that the black swift is considered at-risk on the Flathead, but the threat and management direction is related to nesting sites near waterfalls rather than loss of decaying trees. That is also what is addressed for black swifts in the 2015 FEIS for the revised plan for the Idaho Panhandle.

    • The vaux swift is also a sensitive species on some national forests, which means existing forest plans in the range of the species should provide habitat for their viability.

  5. Thank you very much Jon, 2ndLaw & Larry. From the sounds of it, many people in the USFS get the importance of big hollow snags, which are preserved unevenly in federally-managed forests and mostly unpreserved in privately-managed forests. (Does that sound about right?)

    I’ll be filing this away for future reference; might be an Old Hollow Tree article somewhere in the making…..

    • In my opinion, all of those ‘soft’ snags are worth so much more still standing than in a cull deck, waiting to be burned. I also see the value in hard snags, too. On private lands, there are still some snags in stream buffers and steep ground.


Leave a Comment