ornia Forest - WORKING TOGETHER FOR HEALTHY FORESTS WINTER 7998 Dead and dying trees: part of a healthy forest Richard Harris and Bill Laudenslayer (although large quantities of these trees There is evidence that "biological "snag" is a standing dead tree. in some forests do suggest a decline in control" by these birds can help keep Snags provide habitat to innum- forest health). In this article, we suggest populations of potentially damaging a few simple guidelines for managing insects, such as bark beetles, below * erable organisms including fungi, insects and other invertebrates, and recruiting snags. epidemic levels. Insect outbreaks often and land animals such as amphibians, Why Are Snags Important? attract cavity nesting birds. Snags are used in numerous other reptiles, birds, and mammals. Probably the single most obvious ways. Woodpeckers and sapsuckers Logs and limbs from snags are reason for a landowner to be concerned communicate by "drumming" on dead important to the forest floor and with snags is because they provide branches. Squirrels and other small streams. As they decay, they release habitat for birds. Some birds, such as mammals use dying and dead trees as nutrients essential to long-term soil sapsuckers and woodpeckers, excavate foraging sites, to store winter food sup- productivity. Down logs and limbs also their own nests in snags (primary cavity provide habitat for many animals in- plies and for roosting and denning. Bats nesters). Other birds occupy abandoned use loose bark and hollow tree trunks cluding salamanders and carpenter ants. nests or natural cavities (secondary for roosting. A myriad of insects use There is a misconception that forest cavity nesters). These secondary nesting dead trees as overwintering sites; some "health" is negatively affected by birds comprise up to one third of the consume portions of dead trees, con- diseased, dying and dead trees. On the breeding birds found in some forests. tributing to the decomposition process. contrary, their presence is an important Most cavity-nesting birds consume The death and eventual falling of component of natural forest ecosystems large quantities of insects each year. (continued on page 4) Stages of snag 1 formation i 1 I ii hi XL i$ Stage 1 Stage 2 Stage 3 Stage 4 Stage 5 Stage 6 Stage 7 Stage 8 Stage 9 Live Declining Dead Loose Bark Clean Broken Decomposed Down Material . Stump I Cooperative Extension -v Non-Profit Org. Environmental Sciences, Policy, & Management US. Postage University of California 163 Mulford Hall Berkeley, CA Berkeley, CA 94720-3114 Permit No. 824 ADDRESS CORRECTION REQUESTED ?J 4 Winter 1998 example, some birds will require snags in open shrub or grass communities. trees provide forest openings that Others avoid snags in the open and will encourage regeneration of shrubs, trees only use those in.the closed forest. and grasses. This leads to improved habitat for species such as deer and Snag Management Guidelines Ecological stewardship should small mammals. include preservation and recruitment of Ecology of Snags snags for the benefit of wildlife and The number of snags in a forest long-term soil productivity. Landowners varies. The creation of new snags must weigh many factors when marag- depends on agents of mortality includ- ing for snags, including fire hazard, ing insects, disease and fire. Tree death hazards posed to developed areas and 3f slopes surrounded by other trees are in the forest is patchy, episodic and trade-offs of productive forestland for at less risk from windthrow than isolat- grouped reflecting the ways in which benefits other than timber production. ed snags on ridgetops. natural disturbances work. There is little reason to remove soft It is not advisable to give general The rate at which a dead tree deteri- snags from a forest provided they are prescriptions for the number and size of orates determines many of its ecological not posing safety or fire hazards. Soft snags without considering the character- properties. Larger diameter trees persist snags have virtually no commercial istics of the stand, including stocking longer than smaller ones. Decay rates value. Hard snags will gradually turn levels and tree species composition and also vary by species. For example, into soft snags so if adequate hard snags requirements of target wildlife species. ponderosa pines generally persist longer are provided, and most soft snags Snag guidelines for particular wild- than white fir of the same diameter. retained, requirements for all snag- life are available (contact Extension Large diameter snags appear to be more dependent species should be met. Forestry). For example, in a ponderosa valuable because they stand longer and In general, it is most beneficial to pine forest, a minimum of 14 snags/100 provide habitat for birds which require provide a wide range of snag species acres with an minimum size equal to or large trees to nest. It is the large trees and size classes. Both coniferous and greater than 20 inches dbh probably and, consequently, large snags that are hardwood snags are useful to wildlife. provides sufficient nesting habitat for becoming more scarce in our forests. For example, large black oak snags are pileated woodpecker assuming large diameter live trees are present and food Hard or Soft extensively used by cavity-nesting birds and small mammals. Of the conifers, supplies are adequate. Snags may be classified as "hard" or ponderosa pine may be preferable to Large snags can often be substituted "soft." Hard snags are essentially sound white fir. Deciduous trees such as aspen, for smaller ones to meet habitat require- wood while soft snags are in an cottonwood and willow are heavily used ments but the reverse is not true. Cau- advanced state of decay. Hardness where available. tion against overly general prescriptions depends on tree species, the nature of Snags should be well-distributed will prevent situations in which either the decay agents and snag age. Some because of the territorial requirements too many or too few snags are provided birds and insects may only excavate in of cavity-nesting birds. Clumping of in a specific forest type on a property. soft snags. Others, including woodpeck- snags in small patches has been shown ers, require hard snags because of the to benefit some species, especially Bottom Line stability they provide for nest cavities. pileated woodpeckers. When selecting Large trees are increasingly scarce in As a snag progresses from hard to soft, specific trees, suitable nest trees are California's forests. Without manage- pieces begin to fall to the ground. indicated by signs of heart rot at the ment to preserve and recruit large trees Eventually, the snag is reduced to a heights and diameters required by the that eventually become snags, important decomposed stump and collection of target animal. Signs of heart rot include: wildlife may disappear from our forests. downed, decayed material-in essence, conks of heart rot fungi, A landowner may find it useful to work ' forest flopr woody debris. broken branch stubs with signs of rot, with neighbors in trying to preserve and Each stage of deterioration has wounds or scars resulting from fire, recruit large diameter snags so that no importance to certain wildlife. Early in lightning or mechanical damage, one person shoulders too much QJa the process when bark loosens, snags discolored or soft, decayed wood burden. Even one large snag over an become important roosting sites for revealed in samples, area of several acres can provide bats. Advanced stages of decay are mod existing woodpecker holes or cavities, significant benefits. important for insectivorous birds and dead areas on living trees. small mammals. (Bill Laudemlayer is Research Wildlife It is wise to consider the position of The successional stage of the com- Biologist, USDA-Forest Service, Pacific a snag in the landscape and in relation munity around the snag also influences Southwest Forest and Range Experiment the way in which they are used. For to other trees. Snags in the lower parts Station, Fresno, CA) After the storm Stow damage can cause significant decay, future storm damage, etc. wash out, erosion, damage to water and problems including: Changes in fish and wildlife habitat fish habitat) Safety hazards (some habitat may be damaged, some a Damaged trees and limbs that'may Economic loss and loss or forest created). fall onto roads or power lines (notify power company) aesthetics Checklist Damaged or blocked roads and a Trees blocking forest access roads culverts Identify high priority problems / Assess the damage Build up of fuel which could result in 01 Immediate safety hazards to people future fire danger / a Walk entire property-preferably or structures / with a forester (wear your hard hat) Potential for future loss due to CI Blocked or damaged ditches, increased susceptibility to insects, / a Make a simple map showing type culverts, and roads (may result in road and extent of damage (blocked roads and trails, trees with broken tops or broken limbs, fallen trees, trees severely Tips for creating snags bent over). Determine objectives Snags may be created from living IRoosting slits and cavity starts may trees if.there is a shortage of safe be added to created snags at the time a Consider salvage harvest of natural snags. Created snags can be of topping or girdling. However, do damaged trees. expected to last for a long period of not put these features, or bird boxes, CI Consider retaining some storm- time. Poor quality or deformed trees, on existing snags. damaged trees and downed debris for such as those with broken tops or large wildlife habitat (see front page article branches, make excellent snags. IRoosting slits may be used by most bats and some birds. The slits should on snags). Snags can be dangerous so locate be at least 8" deep and 2" wide, and 01 Contact a professional consulting them well away from trails, roads, angled sharply upward into the forester for advice.