Creating and Maintaining Wildlife, Insect, and Fish Habitat Structures in Dead Wood

Dead wood is an important component of the forest for many species. In many locations, however, the presence of dead wood has declined, and there is a need to make what is left more suitable for the myriad of creatures dependent on this material. In this paper, I will summarize the value of dead wood for these species and describe methods for improving the dead wood component of the forest to meet the needs of a variety of vertebrates and invertebrates. Creating Wildlife Habitat Structures in Snags, Logs, and Stumps In forested ecosystems, habitat diversity is directly related to tree form diversity. Snags are trees, dead or living (living snags are live trees with dead sections) that have been killed or altered by disease, lightning strikes, and wind. Each snag is unique since various factors, such as age, species, location, and cause of mortality or alteration, characterize each snag differently. Snags (standing or downed trees) and other forms of dead or unmerchantable woody structures are recognized by many land managers to benefit wildlife and other biota on forested lands. At least 96 vertebrate species are associated with snags found in forests of Washington and Oregon (Rose and others 2001). A large proportion of forest-associated bird and mammal species require cavities to live in, many provided by snags or other forms of woody debris in various stages of decay. Thomas and others (1979) documented 62 wildlife cavity users in montane forests of northeast Oregon and southeast Washington. To other landowners, snags may represent unclaimed firewood, lightning rods, fire hazard, or loss of potential timber commodity. Many political jurisdictions have forest practice rules or policies requiring prescriptions to retain snags or designate green trees for future snag recruitment in managed landscapes. Wildlife habitat prescriptions, whether they are scientifically based or not, that are implemented and monitored may provide more habitat management options in the future and a more positive effect to increase species diversity and/or abundance as the forest matures. Both dead and living snags are important and offer somewhat different habitats. For example, living snags that retain some lower branches below a sturdy, bare trunk or spike provide ideal protection and support for large predatory birds such as hawks 1 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2 Principal, T.K. Brown & Associates, P0 Box 6252, Bellevue, WA (e-mail: [email protected]) Creating Habitat Structures in Dead Wood—Brown USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 884 and eagles. When a snag is formed abruptly, for example, by wind or lightning, the damaged tissue is quickly colonized by insects and fungi, which in turn provide meals for primary excavators such as woodpeckers and predatory insects. Secondary cavity users such as owls, chickadees, swifts, bats, and bees extend the usefulness of the snag modified by primary excavators. Flaps of loose bark, hollows, and crevices often found in snags are favored bat roosting sites (Tim Brown, pers. obs.). As the snag decomposes and falls to the ground, it will provide shelter, dens and runways for a variety of small mammals and amphibians. Hollow tree trunks, either in the partially standing snag or the downed trunk, creates protective habitat for denning martens (Martes americana), fisher (M. pennanti), coyote (Canis latrans), and raccoon (Procyon lotor). Shrew-moles (Neurotrichus gibbsii), shrews (Sorex sp.), deer mice (Peromyscus maniculatus), salamanders, and frogs may use smaller cavities in the decaying wood for thermal and protective cover, in addition to foraging on the various insect larvae harbored there. Small mammals can act as dispersing carriers for fungi, and if they are using a down log as a runway, their feces deposit fungi, which in turn, recycle nutrients to the soil. The “dead wood” on the ground is a storehouse of energy and nutrients. The decay of this debris steadily contributes to the organic layer of the soil. This organic soil is critical to establishing a fertile medium for supporting a diverse ecosystem of plants, small mammals, amphibians, and invertebrates. The purpose of this paper is to review techniques that I have experimented with in the last 30 years. As a former professional timber industry tree faller, forest firefighter, and owner and operator of a tree-service company, I have witnessed a plethora of wildlife using wood habitat, such as cavities, broken tree-tops, and deep fissures of lightning-struck trees. From these observations, my goal was to create similar habitats using chainsaw and drills. On trees and standing snags, many of the enhancements were performed aboveground anywhere from 2 m to as high as 30 m or more. Although most of the methods described in this paper were employed in the Pacific Northwest, these enhancements should work in other temperate conifer and hardwood forests of the U.S. and overseas. Land managers and their biologists can likely employ most of these techniques presented in this paper by considering the specific type, size, and location of the alteration for the particular target species of their area. Wood Habitat Planning and Retention With skill and planning, forest management activities and wildfires resulting in wildlife habitat loss may be managed to reduce further impact to wood habitat. In all likelihood it will be necessary to prioritize the efforts devoted for snag or other habitat preservation. The following are criteria useful for selection of elements of the landscape to be retained or managed: • Trees or snags with trunks of 30 or more centimeters DBH • Snags providing sites for platform nests • Snags with obvious wildlife holes • Snags with hollows • Snags with conks (indicating soft decay is underway) Creating Habitat Structures in Dead Wood—Brown USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 885 • Downed trees with hollows. To retain snags in proposed logging operation sites, no harvest or no-work zones can be established around designated snag-retention areas. In a forest fire situation, crews, at their discretion, can reduce the potential hazard posed by these trees by routing fire trails around them and establishing no-work zones around each snag. These zones should cover an area with a radius of 1.5 times the height of the snag. The hazard zone can be reduced to acceptable limits by topping threatening snags. Criteria and procedures for any topping should be introduced by the biologist/ecologist of the land management entity and incorporated into the sale administration process. Safety regulatory agencies should participate with the land managers to review topping prescriptions. Topping prescriptions, as well as other restoration techniques, may vary within a planning area depending on, for example, existing stand conditions, snag species, and proposed tree harvest methods. Holistic forest management planning is especially important to foster long-term stand and landscape conditions for wildlife species and other biota associated with snag and down wood habitat. It is apparent that the same features that make the snag an asset for wildlife habitat may be a liability for the forest worker or visitor. Signs of a hazardous tree may include: • A significant lean • A broken top and/or branches that are hanging up in the tree • Snags with hollows • Root or other disease (noted by needle discolor, poor cone production, etc.) • Advanced decay into the bole of the tree • Visible cracks or hollows in the bole of the tree • Visible wildlife excavations