The Down Woody Material Indicator on the Allegheny National Forest
Randall S. Morin1, Chris W. Woodall2, Andrew M. Liebhold1, Kurt W. Gottschalk1, and Daniel B. Twardus3
1USDA Forest Service
Northeastern Research Station
180 Canfield St., Morgantown, WV 26505 USA
2USDA Forest Service
North Central Research Station
1992 Folwell Ave., St. Paul, MN 55108 USA
3USDA Forest Service
Northeastern Area State & Private Forestry
180 Canfield St., Morgantown, WV 26505 USA
Abstract
The Forest Inventory and Analysis Program (FIA) conducts a national inventory of all forestland in the US. A subset of the FIA inventory plots are
sampled every year for numerous forest health indicators. Down woody material (DWM) is defined as dead material on the ground in various stages of
decay and is an important component of forest ecosystems. DWM data helps to describe important factors within forests including: quality and structure
of wildlife habitats, structural diversity, fuel loading and fire behavior, carbon sequestration, and storage and cycling of water. The DWM inventory began
in 2001 and is currently implemented in 38 states. The intensified grid of 173 FIA plots on the Allegheny National Forest (ANF) provided a substantial
amount of data for a forest-wide analysis of the DWM data. Loadings of different debris types were characterized and mapped to provide an assessment of
DWM on the ANF.
Introduction
Results Continued
The Allegheny National Forest (ANF) (Figure 1) is
situated in the Allegheny Plateau in northwestern
Pennsylvania. The ANF is dominated by mixed
northern hardwoods including black cherry, red maple,
sugar maple, beech, and oak species. It represents an
important source of high quality veneer-grade logs, but
it is also heavily used for recreation given its proximity
to the densely populated mid-Atlantic region.
Figures 7 and 8 show how DWM fuel components vary by density (basal area/acre) and stand age. Duff and litter
tended to increase with stand age and, to some extent, basal area. As a stand ages and becomes more dense it
follows that increasing litterfall would cause the duff layer to build up. In addition, the thicker overstory would
shade the litter and duff causing decay to be slower. CWD appears to decrease with increasing stand basal area
possibly due to CWD recruitment not by individual tree mortality but by larger stand disturbances. Litter and FWD
levels were similar among age and density classes.
25
25
20
1
FWD < 0.25”
& 0.26”-0.99”
FWD 1.00”2.99”
30°
30°
150°
3
150.1+
0-40
30°
30°
20 ft. s.d.
N
CWD ≥
3.00”
150°
30°
3
30°
150°
b
9
9
CWD Tra n.
FWD Tra n.
150°
Integrated Fuel Depth (ft.)
Integrated Fuel Depth (ft.)
5
4
3
2
1
0
7
6
5
4
3
2
1
0
0.0-75.0
75.1-150.0
150.1+
Basal Area/acre (sq. ft.)
0-40
41-80
81+
Stand Age (years)
Figure 9. Mean values of integrated fuel depth on the ANF
in: (a) basal area/acre classes and (b) stand age classes .
Kriged surfaces were generated to depict the spatial arrangement of fuels and debris (Fig. 10).
CWD ≥
3.00”
3
Ke y
Annular-plo t
150°
150°
CWD Tran.
FWD Tran.
Dist. between su b-plots (2, 3 , and 4) and sub-pl ot center (1): 12 0 ft at angles (deg.) 0, 120, an d
240 respecti vely; dist. be tween subplot center an d micr opl ot ce nter : 12 ft.; shrubs/her bs
sample d on micropl ot. D uff/litter sample d at 14 & 24 ft slo pe dist. on e ach CW D tr ansect.
Dis t. between su b-pl ots (2, 3, and 4) an d sub-pl ot center (1): 120 ft at angles (deg.) 0, 120, and
240 respecti vely; dist. be tween su bpl ot center and micr opl ot ce nter : 12 ft.; de pth/c over age of
shrubs/her bs/duff/litter esti mate d on micr oplot.
Figure 2. 1999 DWM plot layout.
6
M icro-plot
CWD Tran.
FWD Tran.
150°
8
7
Sub-plot
270°
M icro-plot
Dis t. between su b-pl ots (2, 3, an d 4) and su b-pl ot center (1): 120 ft at angles (deg.) 0, 120, an d
240 respecti vely; dist. be tween su bpl ot center and micr opl ot ce nter : 12 ft.; de pth/c over age of
shrubs/her bs/du ff/litter esti mate d on micr oplot.
81+
s.d.= slope dist., h.d.=horizontal dist.
270°
4
Key
Annula r-plot
Sub-plot
FWD 1.00”2.99”
58.9 ft. h.d.
1
s.d.= slope dist., h.d.=horizontal dist.
150°
M icro-plot
150°
FWD < 0.25”
10 ft. s.d. & 0.26”-0.99”
FWD 1.00”2.99”
55 ft. h.d.
270°
270°
Tra nsect Info rmation
30°
FWD < 0.25”
7 ft. s.d. & 0.26”-0.99”
14 ft. s.d.
270°
4
Key
Annular-plo t
2
Transect Informa tio n
41-80
Stand Age (years)
Figure 8. Mean values of DWM variables
on the ANF in stand age classes.
As shown in Figure 9, integrated fuel depth tended to decrease with basal area/acre and stand age. A more
developed herb and shrub layer would be expected in younger less dense stands due to a less developed overstory.
Figure 1. The Allegheny National Forest
is located in northeastern Pennsylvania.
150°
1
CWD
0
75.1-150.0
Figure 7. Mean values of DWM variables
on the ANF in basal area/acre classes .
30°
N
CWD ≥
3.00”
Sub-plot
270°
150°
FWD
Basal Area/acre (sq. ft.)
270°
7 ft. s.d.
s .d.= slope dist., h.d.=horizontal dist.
270°
4
2
14 ft. s.d.
55 ft. h.d.
30°
270°
Litter
10
8
Tra nsect Info rma tio n
Duff
15
5
a
30°
150°
CWD
0.0-75.0
Components estimated by the DWM indicator include: coarse woody debris (CWD), fine woody debris (FWD),
duff, litter, herbs/shrubs, and fuelbed depth. CWD is dead wood greater than 3 inches in diameter; FWD is dead
wood from 0.1 to 2.9 inches in diameter. CWD and FWD are sampled using the line intersect sampling method.
Transects are established on each subplot if the subplot center is accessible and forested. The depth of the duff and
litter layers are important components of fire models used to estimate fire behavior, fire spread, fire effects, and
smoke production. Litter is defined as the loose plant material found on the top of the forest floor where little
decomposition has occurred. Duff is the layer just below the litter; it consists of decomposing leaves and other
organic material. Litter and duff measurements were taken on microplots in 1999 and 2000 and at the 24-foot
location on each transect in 2001 (USDA For. Serv. 2002). An alternative to reporting mean herb/shrub height and
coverage is to incorporate them into a single measure of height termed integrated fuel depth (Woodall and Williams
2004). The DWD plot designs for each of the three years of data collection are shown in Figures 2-4.
270°
FWD
10
0
Down woody material (DWM) is defined as dead material on the ground in various stages of decay and is an
important component of forest ecosystems. DWM data helps to describe important factors within forests including:
quality and structure of wildlife habitats, structural diversity, fuel loading and fire behavior, carbon sequestration,
and storage and cycling of water (USDA For. Serv. 2002).
N
Litter
5
Methods
2
20
Duf f
15
Tons/acre
Tons/acre
The National Forest Health Monitoring Program was
implemented by the USDA Forest Service in 1990 to
monitor, assess, and report upon the status and trends in
forest health across the country. Forest managers on the
ANF recognized the need for a comprehensive survey of
forest health conditions. In collaboration with USDA
Forest Service Forest Health Protection (FHP) and
research staff an intensified grid of 173 Forest Health
Monitoring (FHM) plots was established in 1998.
Methods developed by the National Forest Health
Monitoring Program include the measurement of the
down woody material forest health indicator.
Figure 4. 2001 DWM plot layout.
Figure 3. 2000 DWM plot layout.
Results
Data from the DWM indicator was used to calculate variables that estimate fuel loadings and mass of CWD, FWD,
and total DWD. Total tonnage of DWM broken down into duff, litter, 1-hr fuels, 10-hr fuels, 100-hr fuels, and
1000-hr fuels (also called CWD) is shown in Figure 5. The majority of the tonnage per acre of DWM on the
Allegheny National Forest was comprised of duff (64%).
A comparison of down woody material between plots within the ANF and plots in the rest of Pennsylvania (77
plots) is shown in Figure 6. The mean tonnage per acre of duff and 100-hr fuels were higher on plots in
Pennsylvania outside of the ANF. In contrast, the mean tonnage per acre of 1000-hr fuels was higher on plots
within the ANF. Mean tonnage per acre of litter, 1-hr fuels, and 10-hr fuels were similar on plots within and outside
of the Allegheny National Forest.
1000-HR
20%
30
25
DUFF
1-HR
10-HR
10-HR
3%
100-HR
DUFF
64%
1-HR
1%
1000-HR
20
Tons/acre
LITTER
100-HR
6%
ANF plots
15
Rest of PA plots
10
5
0
LITTER
6%
DUFF
Figure 5. Total DWD broken
down into debris categories .
LITTER
1-HR
10-HR
100-HR
1000-HR
Figure 6. Mean values of DWM variables on
the ANF versus the rest of Pennsylvania .
DWM loadings in tons per acre were broken down by FIA forest type (Table 1). Duff tons per acre were highest in
the eastern hemlock forest type. Decomposition of litter may be slower in hemlock stands because they are
generally darker and moister than hardwood stands. Litter and fine woody debris levels were similar among forest
types. The largest amount of coarse woody debris was recorded in nonstocked stands possibly due to wood left
from harvesting or other disturbance. Among forested stands, the sugar maple/beech/yellow birch forest type had
FIA TYPE
N
DUFF SE LITTER SE FWD SE CWD SE
the highest coarse woody debris levels.
Table 1. Mean values of DWM
variables by FIA forest type .
FHM posters home page
Red maple/upland
Black cherry
Eastern hemlock
Mixed upland hardwoods
Sugar maple/beech/yellow birch
Other
White oak/red oak/hickory
Nonstocked
60
51
14
14
12
12
7
3
18.1
17.8
26.6
14.3
19.0
17.0
12.3
11.2
1.7
1.7
7.7
3.6
4.0
3.1
2.2
3.7
1.9
1.7
1.4
2.0
1.2
2.0
2.4
1.1
0.1
0.1
0.2
0.3
0.3
0.2
0.4
0.0
2.8
2.9
2.6
2.0
3.0
3.6
2.9
3.0
0.2 5.7
0.2 6.0
0.3 4.3
0.4 3.6
0.4 8.3
0.5 5.8
0.4 3.2
0.0 13.1
0.5
0.8
1.2
0.8
1.0
1.2
0.9
9.4
Figure 10. Kriged surfaces of DWM on the ANF.
Literature Cited
U.S. Department of Agriculture, Forest Service. 2002. Forest inventory and analysis national core field guide,
volume 2: field data collection procedures for phase 3 plots, version 1.6. U.S. Department of Agriculture, Forest
Service, Washington Office. Internal report. On file with: USDA, For. Serv., Forest Inventory and Analysis, 201
14th St., Washington, D.C., 20250.
Woodall, C.W. and M.S. Williams. 2004. Sampling protocol, estimation, and analysis procedures for the down
woody materials indicator of the FIA program. USDA For. Serv. Gen. Tech. Rep. NC-xxxx. In press.
FHM 2004 posters