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A Total Forest Management Plan and Wildland Management Decision Support System
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Dead and Down Wood in the Forest

In every forest there is usually "dead and down" wood. This is primarily standing logs or "snags" and dead trees on the ground. The difference between them may be a mere second, a wind gust. Within this unit and that on snags in general, snags and trees and their cavities for fauna, snags and woody debris in streams, and that on soils there is much overlap. The unit on snags emphasizes their use by animals. The unit on specific gravity of wood relates to weight and to the rate of decomposition of woods.

In warm temperate zone deciduous forests there are about 7.6 to 10.7 metric tons per acre. In a mature Kentucky forest there were 9.7 metric tons per acre of coarse woody debris, the dead and down wood (Shear et al. 1997). This is often about 10 percent of the weight of the overstory. Pine weight on areas is available. By making a count or estimate of the numbers, it is possible to draw many conclusions about a forest stand. The following is our analysis of each stand. After it, we present things that we know or that can be deduced from our present knowledge of wildland and their management needs.

This wood is primarily standing logs or "snags" and dead trees on the ground. Decomposition is clearly of concern.

By making a count or estimate of the numbers of snags, it is possible to draw many conclusions about a forest stand. Snags and down logs have ecological value, enhance soil health, ensure seedling regeneration, retain moisture, control erosion, re-position nutrients in their cycles, and provide many needs of many species of wild animals.

The volume of dead and down wood per acre is expressive of fire-wood and fuel wood potentials, but more importantly, it relates to the conditions of the forest for providing erosion protection, the recharging of nutrients to the soil for the trees and plants that are present, providing homes for many forest mammals, salamanders, snails and other invertebrates, and providing food supplies (insects) for many forest birds and other animals. About 400 cubic feet of wood per acre can be expected on the ground in the average mature hardwood forest of the region.

In warm temperate zone deciduous forests, there are about 7.6 to 10.7 metric tons of such wood per acre. In a mature Kentucky forest there were 9.7 metric tons per acre of coarse woody debris, the dead and down wood (Shear et al. 1997). This is often about 10 percent of the weight of the overstory. The following is our analysis of each stand. After it, we present things that we know or that can be deduced from our present knowledge of wildland and their management needs.

Stand Number	Snags per Acre
126 37 22	4.7 9.6 1.9

Future equations will allow these estimates to be improved.

Tree snags are dead trees that are still standing and are 6 inches or more in diameter and more than 6 feet tall (the wood remaining). They are very important to birds, mammals, and other creatures of the forest. Snags and down logs are important as well to many plant species, including the fungi. They have important effects on the water budget of the forest stand, reduce ground winds, and are the soon-to-fall dead logs of the forest floor. Being midway between the forest and the forest-floor complex, they are invaluable in relation to promoting longterm forest health and sustainability.

In a study in Douglas fir-red alder forests, the biomass of stems and branches of all species was 319.5 Mg/ha in 1985. Since the weight in 1980 was 296.6 Mg/ha, then the rate of stem increments was 4.6 Mg/ha/year. If only the trees surviving to 1985 were counted, the end weight was 287.2 Mg/ha and thus the rate was 6.5 Mg/ha/year. The difference is in the weight results from the death of trees between 1980 and 1985. There was a loss of 2.5% of the trees that substantially reduced the accumulation of stand biomass.To estimate net primary productivity of a stand, the stem increment (e.g., 4.6 needs to have added to it the average annual rate of mortality (e.g., 6.5 - 4.6 = 1.9 Mg/ha/year.) Mortality needs to be added to net stand increments when measured over two points in time (like 1980 and 1985) (Binkley and Arthur 1993). Mortality can be inappropriately included in estimates of net primary productivity.

The ecological processes within the tree that result in dead limbs and fallen trees typically start with a break in the bark. The sequence is well known but complex and the time required differs by species and temperature and moisture at the site. The picture is as follows:

1. In your area there are xxxx species of large animals that use dead trees, trees with significant decay, trees with "witches brooms," hollow logs, snags, and fallen trees.
2. Animals use these for foraging, gaining shelter, nesting, denning, drumming (grouse and woodpeckers), roosting, resting, and above-ground run-ways.
3. About xxxx% of the bird species nesting in Virginia and nearby areas are cavity nesters.
4. Some animals, like the woodpeckers, create cavities for winter roosts and for nesting.
5. These same birds often play an important role (provide a "service"), reducing insect pest populations.
6. Absence of down wood in a forest signifies great disturbance (e.g., fire, fire-wood harvests, grazing, etc.).
7. How many dead logs should there be in a well-managed forest? It depends on the rotation. Studies suggest that as a general rule, at least 3 snags per acre are desirable. It is better if there are more, and those present should be as large as possible for many wildlife benefits. About 10 per acre may be the limit to their realistic benefits in creating a natural, functional forest. When the density is about 10, the distance between the snags will average about 70 feet when they are distributed in a beehive pattern.It should be 15% of the number of stems in the previous 5-year age class. It should be 15% of the number of stems in the previous 5-year age class. Where q = 1.2, and there are 200 stems per acre, then the down logs and snags should number xxxx.

   You have an average of between xx.xplus and minus stems, an average of xxxx stems. A resilient, healthy forest with opportunities for the many, yet unknown processes and functions of the forests are likely to be achieved if the dead wood is over xxxxstems.

8. The estimated volume of dead wood (class 1 and 2) to commercial wood is xxxx. Our first approximation is that this ratio should be about 10%. (The number is under study.) Too small amounts of dead wood suggest nutrients are not being made available for the future forest. Excessive removals may similarly be involved as may past fires. Only when levels are high will there be a rich, diverse fauna.
9. Management is needed for woody components of wildlands. Each alpha-unit has a different rate of production (P) and decay or loss (called respiration, R). Ecologists often look for P/R = 1.0 in wilderness, ancient forest, or undisturbed sites. Your ratio in each stand is approximately as follows:

   Under development: A map of the area showing probable P/R ratios

   Overall, your P/R ratio is 0.XX.

10. There are many areas where trees are not harvested (for many reasons, including slopes are too steep for equipment to operate, erosion potential is too high, color and visual quality will be impaired, etc.). These stands, adjacent or not, are important contributors to the dead and down wood resource of an ownership.
11. The estimated down and dead wood volume is xxxx, xxxx% of the total faunal volume. In general, the greater the volume and the percentage, the more rich will be the animal life over time.
12. The only way to obtain a hollow dead tree is to have one started as a living tree hollowed out by decay.
13. Heart rot fungi do not typically kill trees; hollow trees many provide habitat for years before they eventually die and become hollow snags or fall as hollow logs.
14. Only certain trees form high quality cavities. "Large" is not the only criterion for selecting trees to retain. Large ones of select species need to be retained: oaks, sycamore, and hemlocks.
15. Decay rates differ by sites. Rates are now under study. Class 3 down wood rapidly disappears on low, moist, northerly aspects.
16. About 1.5 large (greater than 24 inches in diameter) hollow trees per acre are needed. Your average is xxxx.
17. Retaining all large hollow trees in managed landscapes can be justified because so little of the landscape has them.
18. Clear-cut silviculture, on typical rotation ages of 50, cannot "produce" large trees. Short rotations cannot produce the number of large hollow trees, well distributed, that are needed for abundant, rich animal and plant populations. We have developed a preliminary list of tree species ranked in order of their probable decay rates and thus tendency to rot in a manner that will produce suitable cavities for the most years.
19. Snags should be retained but, in addition, all these structural classes should be represented across the landscape. A distribution score is: (*mean 30-inch snags per acre - 2* mean condition class) + 1(number of 10-inch or greater / 4 snags) / x 100. Both of the first two measures should be about 1.5 but are usually less; the density is viewed as important as the condition class.
20. Snags should be left in clusters in each stand (at least for safety of workers and area users) . . . but greater abundance will result if they are evenly, systematically spread.

Work with Dead and Down Logs

OSHA rules say that no work shall be conducted within 2 tree lengths (L) of a dead tree or snag. The area (A) influenced by a snag is A = (2L)2TT. A snag is a pre-existing type of tree, not one in the process of being felled. It may be "any dead standing tree" but probably is "any standing, dead, partially dead, or defective (well) tree at least 10 inches in diameter at breast height and at least 6 feet tall." Logging rules say "leave 2-4 snags 15-20" dbh per acre, creating conflicts with OSHA rules, feasible logging, and the role of dead trees in watershed management, the life of wild animals and plants and in ecosystems.

Danger Tree Rule OSHA 29 CFR 1910 (1995, Final Standard)

A danger tree is a standing tree that presents a hazard to employees due to conditions such as, but not limited to, deterioration or physical damage to the root system, trunk, stem, or limbs, and the direction and lean of the tree.

(h.1.vi)

Each danger tree shall be felled, removed or avoided. Each danger tree, including lodged trees and snags, shall be felled or removed using mechanical or other techniques that minimize employee exposure before work is commended in the area of the danger tree. If the danger tree is not felled or removed, it shall be marked and no work shall be conducted within two tree lengths of the danger tree unless the employer demonstrates that a shorter distance will not create a hazard for an employee.

See Decomposition of Forest Litter.

References

Binkley, D. and M. Arthur. 1993. How to count dead trees. Bul. Ecol. Soc. of America 74(1):15-16

Shear, T., M. Young, and R. Kellison. 1997. An old-growth definition for red river bottom forests in the Eastern United States. Rep. SRS-10, Ashville, NC, USDA Forest Service, Southern Research Station, 9pp.

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Last revision July 1, 2004.