1. FOR 274: Forest Measurements
Snags and Downed Wood
Characteristics
Ecological Importance
Snag Classification
Downed Wood Systems
Measuring Downed Wood Loads

2. Snags and Downed Wood: Definitions
Snags: standing dead and dying trees. Must still be attached to the ground through a root system
Downed Woody Material: dead twigs, branches, stems, and boles of trees in all stages of decay. These are often called coarse woody debris (CWD) or large woody debris (LWD).
Although CWD and LWD are widely used the correct management term is downed wood.
Imagine your are asked by a land owner to measure this area – what do you do?

3. Snags and Downed Wood: Importance
Snags and Downed Wood are important components of the fuel’s complex. They are also important for wildlife habitat (woodpeckers, etc) and for nutrient dynamics.
These represent a significant % of the forest biomass (aka fuel loading), accounting for 5-30% in some forests
Downed wood serves the ecosystem by also providing physical protection (barriers limiting trampling) to soils and plants.
Highly decayed (rotten) downed wood can hold water and nutrients during dry periods.
Imagine your are asked by a land owner to measure this area – what do you do?

4. Snags and Downed Wood: Importance
In a recent review of the role of CWD within Rocky Mountain forest ecosystems, Laiho and Prescott (2004) showed that CWD exhibits low nutrient concentrations and very slow rates of decomposition when compared to other litter types. This explains the relatively minor role the CWD plays in the nutrient cycling of nitrogen, phosphorus, potassium, calcium, and magnesium.
However, Laiho and Prescott (2004) did highlight that in situations where the lack of moisture is a limiting factor on plant and microbe production, the presence of the CWD may actually increase forest primary productivity by acting as a moisture or organic soil sink.
Reference:
Laiho, R. and Prescott, C.E (2004) Decay and nutrient dynamics of coarse woody debris in northern coniferous forests: a synthesis, Canadian Journal of Forest Research, 34,
Laiho and Prescott (2004)

5. Snags and Downed Wood: Importance
Many wildlife species are dependent on snags for nesting, denning, foraging, and shelter.
Overstory and understory vegetation influence the structure and function of ecosystems and therefore shape the biota of a forest (Hunter 1999)
Living trees with decay can function as snags within an ecosystem
Broomed trees can provide food, cover, and nesting habitat for many species
Wildlife may use snags for many purposes including nesting, denning, foraging, resting and shelter.
One of the key wildlife uses of snags is by primary cavity excavators. It has been estimated that up to 40% of the bird species in North America are cavity nesters (Evans and Conner 1979). Although some species of primary cavity nesters excavate cavities in living wood, most excavate cavities in either dead wood or through live wood into decaying heartwood. Most primary cavity nesters use only one nest cavity per year, although a few species may use different cavities if they raise more than one brood of young in a year, however additional cavities are often created and used as roost and rest sites (Bent 1939). For many species the creation of a cavity is a required part of the nesting ritual, and therefore are continually producing new cavities within the nesting territory over time. much attention has been given to managing primary cavity nesters based on the assumption that is they are present secondary cavity nesters will have the required habitat they need for survival (Neitro et al. 1985).
Secondary cavity nesters are animals which either use existing cavities opportunistically or rely on existing cavities for nesting or breeding. There are many more species of secondary cavity nesters than primary cavity nesters, and each species has its own requirements for the type of cavity or roost site used (Balda 1973). Unlike primary cavity nesters which are mostly bird species secondary nesters include both birds and mammals.

6. Snags and Downed Wood: Importance
Many taxa use downed wood as plant habitat ‘nurse logs’.
Dennis and Batson (1974): 11 species of herbs restricted to floating logs and stumps in a North Carolina swamp
KcKee et al. (1982): 94-98% of tree seedlings in P.sitchensis-T. heterophylla forests were growing on downed wood

7. Snags and Downed Wood: Formation
Snags and Downed Wood are generally formed as a result of natural or management actions.
Snags are essentially dead trees that are allowed to remain in the stand (typically to enhance habitat)
Downed wood can include slash from forest operations or natural debris, which refers to accumulation of woody material in the absence of harvesting.
Imagine your are asked by a land owner to measure this area – what do you do?

8. Snags and Downed Wood: Formation from Wind
Here are a few examples of the types of damage wind can cause. The picture on the left was taken in Poland, this wind event destroyed over 30,000 ha of forest in 15 mins. You can see from the photo that the fuels complex has greatly changed, how do you think the fire behavior has changed due to this wind event?
The middle picture show an area that is recovering from a combination of a wind event and a wildfire along the blue ridge parkway. In this picture you can see that the combination of these two disturbance agents has shaped a small patch of the landscape. What effects do you think the wind throw had on the ability of fire to spread in this area and how do you think these two disturbances effected the vegetation?
Ok the picture on the right has nothing to do with natural landscapes but it does show that not only is wind a major factor in ecological terms but also in economic terms. Plus I like the picture…
Left Photo – Damage in Pisz Forest Division (Northeast Poland). Strong winds on Jul 4th 2002 destroyed over 30,000 ha of forest in 15 minutes. Poland
Middle Photo - Catastrophic winds, spruce and fir forest, Blue Ridge Parkway, NC.
Right Photo - Blue spruce that failed at the roots in high winds
Photo by: Randy Cyr, GREENTREE Technologies,
Photo by; Gil Wojciech, Polish Forest Research Institute,
Photo by: Joseph O'Brien, USDA Forest Service,

9. FOR 274: Forest Measurements
Snags and Downed Wood
Characteristics
Ecological Importance
Snag Classification
Downed Wood Systems
Measuring Downed Wood Loads

10. Snags: Classification Systems
Snags are generally classified by their amount of decay, their time since death, and whether they have limbs present.
So far we have only discussed the roles of dead fuels as wildlife habitat however as fire mangers we also must think about the role of living trees. Oversotory trees influence the structural and functional characteristics of an ecosystem (Hunter 1999). This influence helps shape the biota of that ecosystem by controlling the distribution and abundance of other taxa. Overstory trees affect the biota by altering light environments, the micro climates in the understory, nutrient cycles and disturbances.
Within the living overstory there are several key features which greatly benefit wildlife species. In particular trees with decay and/or brooms provide important wildlife habitat as well as large dead branches or dead tops. In some cases decay may leave a hollow core in some trees, these trees provide habitat for several wildlife species and are extremely uncommon on the landscape.

11. Downed Wood: Classification Systems
Downed wood are generally classified by the degree to which they are incorporated into the litter and duff and by their decay
So far we have only discussed the roles of dead fuels as wildlife habitat however as fire mangers we also must think about the role of living trees. Oversotory trees influence the structural and functional characteristics of an ecosystem (Hunter 1999). This influence helps shape the biota of that ecosystem by controlling the distribution and abundance of other taxa. Overstory trees affect the biota by altering light environments, the micro climates in the understory, nutrient cycles and disturbances.
Within the living overstory there are several key features which greatly benefit wildlife species. In particular trees with decay and/or brooms provide important wildlife habitat as well as large dead branches or dead tops. In some cases decay may leave a hollow core in some trees, these trees provide habitat for several wildlife species and are extremely uncommon on the landscape.

12. Downed Wood: Classification Systems
Downed wood are generally classified by the degree to which they are incorporated into the litter and duff and by their decay
One of the key factors which will influence plant and animal use of downed logs is the decay state. The figure above shows the decay classification of logs used by the USDA Forest Service common stand exam. In addition to the decay classification the size, distribution and orientation of logs are important to wildlife. In general these factors are more important than the tonnage or volume which we typically use in characterizing woody fuels (Maxwell and ward 1980). In general smaller logs benefit small mammals, amphibians and reptiles, while larger logs benefit other species such as black bear and marten.
In addition to providing habitat downed logs can also be used as foraging sites by many wildlife species. In some cases downed logs may not be directly related to the existence of the predator but will provide habitat for the pray.
Table and Figures from USDA Forest Service common Stand Exam Users Guide

13. Downed Wood: Classification Systems
Degree of decay was determined by a simple 1-5 classification system based on work by Fogel et al 1973, Maser 1979
Degree of decay is determined in a fairly easy method of field observation, based on a range of of physical characteristics such as bark and branch presence, structural integrity, and vegetation establishment.
Table adapted from work by Fogel et al 1973, Maser et al 1979

14. Downed Wood: Classification Systems
Degree of decay was determined by a simple 1-5 classification system based on work by Fogel et al 1973, Maser 1979
Degree of decay is determined in a fairly easy method of field observation, based on a range of of physical characteristics such as bark and branch presence, structural integrity, and vegetation establishment.

15. Downed Wood: The Fogel Classification System
Degree of decay was determined by a simple 1-5 classification system based on work by Fogel et al 1973, Maser 1979
Degree of decay is determined in a fairly easy method of field observation, based on a range of of physical characteristics such as bark and branch presence, structural integrity, and vegetation establishment.

16. Downed Wood: The Maser Classification System
Degree of decay was determined by a simple 1-5 classification system based on work by Fogel et al 1973, Maser 1979
Degree of decay is determined in a fairly easy method of field observation, based on a range of of physical characteristics such as bark and branch presence, structural integrity, and vegetation establishment.

17. Downed Wood: Classification Systems
When considering downed wood for fire management we often talk about the time-lag classes. These classes are based on the time it takes a fuel particle to reach 2/3 of its equilibrium moisture.
Typically:
1 hour; < 0.25 inch diameter
10 hour; 0.25 < X < 1.0 inch diameter
100 hour; 1.0 < X < 3.0 inch diameter
So far we have only discussed the roles of dead fuels as wildlife habitat however as fire mangers we also must think about the role of living trees. Oversotory trees influence the structural and functional characteristics of an ecosystem (Hunter 1999). This influence helps shape the biota of that ecosystem by controlling the distribution and abundance of other taxa. Overstory trees affect the biota by altering light environments, the micro climates in the understory, nutrient cycles and disturbances.
Within the living overstory there are several key features which greatly benefit wildlife species. In particular trees with decay and/or brooms provide important wildlife habitat as well as large dead branches or dead tops. In some cases decay may leave a hollow core in some trees, these trees provide habitat for several wildlife species and are extremely uncommon on the landscape.
The 1 and 10 hour fuels are calculated hourly, while 100 and 1000 hour fuels are calculated on 1 and 7 day averages

18. FOR 274: Forest Measurements
Snags and Downed Wood
Characteristics
Ecological Importance
Snag Classification
Downed Wood Systems
Measuring Downed Wood Loads

19. Downed Wood: Brown’s Transect
We typically calculate surface woody fuel loading via the line intercept method, often called the Brown’s Transect.
Notes:
Include downed woody material under 6 feet in height
Your sampling protocol will determine over what length you tally your 1, 10, 100, and 1000 hour fuels.
Your sampling protocol will determine at what lengths you measure duff and litter depths.
Brown (1974)

20. Downed Wood: Brown’s Transect
In the FIREMON protocol this is how we typically measure the downed wood in the Brown’s transects. The specific location of the duff and litter measurements are arbitrary.
Based on these measurements, we can calculate the fuel loading by fuel lag class. NOTE: many transects are needed to obtain measurements at a high accuracy.

21. Downed Wood: Brown’s Transect
The line intercept method can provide weights and volumes per acre for all diameter size classes. The method also provides depth of fuel and duff at locations along the line.
Main Steps:
Decide sampling length and direction (random)
Run tape for length.
Tally (avoid disturbing the area) small diameters “on way out” and measure large “on way back”
Measure slope
Calculate fuel loading
Brown (1974)

22. Litter and Duff: Depth

23. Downed Wood: Brown’s Transect
Only include a piece of the sampling line intersects the center and if the plane intersects a curved piece twice, count each time
Do not include cones, bark flakes, needles, leaves, grasses, or forbs
Brown (1974)

24. Downed Wood: Brown’s Transect
Include downed woody logs if the center is above the surface. Include twigs and branches if in the litter layer. Include aerial downed wood if below 6 feet above the surface.
YES NO
Also measure the diameter and length of all logs > 3” in diameter. Generally, we also estimate the % of species within the entire sampling frame.
Brown (1974)

25. Downed Wood: Brown’s Transect
120
100 and 1,000 hour
for whole length
S60W
N60W
30 meters long
South
North
10 hour
for 3 m
1 hour
for 1 m
S60E
N60E

26. Downed Wood: Field Sheets and Calculation
Equation for fuel 0 to 3 inches:
Tons/Acre = (11.64 * n * d2 * s * a * c) / L
Equation for fuel 3 inches and greater:
Tons/Acre = (11.64 * Σ [d2]* s * a * c) / L
Where: c = slope correction factor (1 for flat slopes), n = tally for that size class, d2 = mean square diameter, s = specific gravity, L = length of transect, a = non-horizontal angle correction factor.
Brown (1974)

27. Downed Wood: Obtaining the Constants
Many of these constants are found in tables contained in Brown (1974) and more recent works.
Brown (1974)

28. Downed Wood: Slope Factor, c
Brown (1974)

29. Downed Wood: Mean square diameters, d2
Brown (1974)

30. Downed Wood: Specific gravity, s & angle, a
Brown (1974)

31. Downed Wood: Example Calculation
Equation for Transect 1 (50’), 1-hr fuels of PIPO on flat ground:
Tons/Acre = (11.64 * n * d2 * s * a * c) / L
= (11.54 * 7 * * 0.48 * 1 * 1) / 50
= tons / ac
Brown (1974)

32. Downed Wood: Example Calculation 2
Brown (1974)

33. Downed Wood: Photo Guide
In a similar manner to fuel photo guides used to estimate surface and canopy fuel loading, photo guides exist to estimate downed wood.
Degree of decay was determined by a simple 1-5 classification system based on work by Fogel et al 1973, Maser 1979
Degree of decay is determined in a fairly easy method of field observation, based on a range of of physical characteristics such as bark and branch presence, structural integrity, and vegetation establishment.

34. Downed Wood: Photo Guide
Degree of decay was determined by a simple 1-5 classification system based on work by Fogel et al 1973, Maser 1979
Degree of decay is determined in a fairly easy method of field observation, based on a range of of physical characteristics such as bark and branch presence, structural integrity, and vegetation establishment.