Why Down Wood Percent Cover?
For DecAID, we chose to describe amounts of down wood used by wildlife as percent cover because it is a good metrict to describe the abundance of down wood as it relates to wildlife use (Carey 1995, Carey and Johnson 1995). For many wildlife species down wood provides cover. In our literature review, we found that percent cover was the most common measure used in studies showing wildlife selection of areas with higher amounts of down wood. Volume or biomass may be more relevant measures of ecosystem processes (e.g., nutrient cycling, site productivity, carbon sequestration, fuel loading), but we are opting to emphasize wildlife habitat.
Percent cover is one of the most precise and efficient means of recording down wood (Bate et al. 2002). By laying out a series of randomly placed line transects and measuring the length of the transect that intersects down wood, one can quickly and accurately determine the percent cover. The down wood falling along the transect can be categorized by diameter, species or decay class, further describing the characteristics of the down wood in the area of interest. In contrast, estimates of volume, biomass, pieces per acre or total length require more data collection.
Although volume of down wood tends to be a measurement of down wood amounts that also closely relates to wildlife use it is more complex to measure. Volume requires determining the length, the diameter of both ends of a log or use of a taper equation. Formulas are then used to calculate the volume using these variables. Taper equations will vary by species and decay class of down wood.
Number of down wood pieces per acre may offer the least amount of information when it comes to describing the amount of down wood in an area. Without knowing the length or diameters of the pieces, it has little value in describing wildlife habitat. As an example, 20 pieces of 10 foot logs 4 inches in diameter will have a much lower volume and percent cover than 20 pieces of 80 foot logs greater than 20 inches in diameter, thus resulting in different habitat conditions.
Linear feet of down wood is an often used measurement that also does not fully describe the amount of down wood in an area without knowing the diameters of the down wood being left. As an example, 500 linear feet of 4 inch diameter logs will have a much lower volume and percent cover than 500 linear feet of 20 inch diameter logs, thus resulting in different habitat conditions.
Whereas tons of logs per acre is a common measure used to describe fuel loadings, it is not as closely related to wildlife use and several assumptions and variables must be factored in to determining tons per acre. Weight of logs is based on estimated dry weight and will vary with species and decay class. An “average” species and decay class composition is usually used in tons per acre calculations based on vegetation type.
In order to compare data among studies, down wood data were converted into a common measure of percent cover. The forest inventory down wood data used in DecAID were used to calculate amount of down wood on each plot in terms of percent cover, volume, logs/ha, and linear meters. Regressions were then run on the data to calculate the relationships among 4 measures (see Table 1). Correlations between percent cover, volume, and linear meters/ha were strong. The relationship between percent cover and logs/ha was weak, though still statistically significant. Based on the analysis, when data were reported in the literature in terms of volume or linear meters/ha, we converted it to percent cover using the regression equations and the formula % cover = volume or linear meters/Xvar. Logs/ha data, however, were not converted.
Table 1. Summary of linear regressions for log volume (m3/ha), logs/ha, and linear meters/ha on percent cover of down wood. The X variable is used in the formula to convert the various measures to percent cover (% cover = volume or linear meters/X). Click here for Metric Conversions
| Wildlife Habitat Type | Structural Condition Class | n | r2 for Volume (m3/ha) | X variable for Volume (m3/ha) | r2 for Logs/ha | X variable for Logs/ha | r2 for Linear meters/ha | X variable for Linear meters/ha |
|---|---|---|---|---|---|---|---|---|
| Eastside Mixed Conifer Forest | Small/medium & Larger trees | 3325 | 0.7715 | 24.44 |  | | | |
| Eastside Mixed Conifer Forest | Open canopy | 732 | 0.7864 | 17.89 | 0.3761 | 138.20 | 0.9304 | 574.03 |
| Eastside Mixed Conifer Forest | Small/medium trees | 3009 | 0.7622 | 22.59 | 0.4239 | 125.19 | 0.8929 | 480.51 |
| Eastside Mixed Conifer Forest | Larger trees | 316 | 0.8834 | 28.31 | 0.4637 | 90.84 | 0.8774 | 373.62 |
| Ponderosa pine/Douglas-fir Forest | Open canopy | 494 | 0.8009 | 20.26 | 0.4977 | 205.83 | 0.9199 | 535.48 |
| Ponderosa pine/Douglas-fir Forest | Small/medium trees | 1180 | 0.7733 | 25.36 | 0.2618 | 178.91 | 0.8555 | 462.94 |
| Ponderosa pine/Douglas-fir Forest | Larger trees | 168 | 0.8213 | 24.84 | 0.5576 | 262.18 | 0.8606 | 455.01 |
| Lodgepole Pine Forest | Open canopy | 338 | 0.9146 | 14.16 | 0.1331 | 118.33 | 0.9653 | 637.53 |
| Lodgepole Pine Forest | Small/medium trees | 355 | 0.8635 | 15.36 | 0.6180 | 104.57 | 0.9568 | 612.47 |
| Lodgepole Pine Forest | Larger trees | 9 | 0.7323 | 13.77 | *0.1226 | 123.01 | 0.9586 | 671.44 |
| Montane Mixed Conifer Forest | Small/medium & Larger trees | 1984 | 0.8142 | 26.12 | | | | |
| Montane Mixed Conifer Forest | Open canopy | 355 | 0.8229 | 34.36 | 0.3513 | 85.29 | 0.7582 | 340.11 |
| Montane Mixed Conifer Forest | Small/medium trees | 1560 | 0.8676 | 22.84 | 0.5877 | 96.49 | 0.9165 | 440.59 |
| Montane Mixed Conifer Forest | Larger trees | 424 | 0.9138 | 38.75 | 0.5170 | 70.47 | 0.8778 | 268.63 |
| SW Oregon Conifer-Hardwood Forest | Small/medium & Larger trees | 807 | 0.7738 | 32.53 | | | | |
| SW Oregon Conifer-Hardwood Forest | Open canopy | 132 | 0.8328 | 34.00 | 0.5098 | 127.58 | 0.8331 | 371.87 |
| SW Oregon Conifer-Hardwood Forest | Small/medium trees | 522 | 0.7500 | 30.33 | 0.5629 | 121.19 | 0.8421 | 398.9 |
| SW Oregon Conifer-Hardwood Forest | Larger trees | 285 | 0.8479 | 35.53 | 0.3867 | 91.50 | 0.8207 | 319.1 |
| Westside Lowland Conifer-Hardwood Forest | Small/medium & Larger trees | 1951 | 0.8661 | 43.97 | | | | |
| Westside Lowland Conifer-Hardwood Forest | Open canopy | 286 | 0.7730 | 29.30 | 0.6886 | 143.15 | 0.8512 | 395.13 |
| Westside Lowland Conifer-Hardwood Forest | Small/medium trees | 1171 | 0.8612 | 38.446 | 0.5720 | 83.30 | 0.8069 | 316.23 |
| Westside Lowland Conifer-Hardwood Forest | Larger trees | 780 | 0.8602 | 44.08 | 0.4348 | 71.37 | 0.7981 | 267.78 |
Several examples of down wood of different sizes and what they represent in terms of percent cover are given in Table 2. The conversions from log size to percent cover use the formula: % cover = (((((LED+SED)/2)/12)*L)/43560)*100; where LED=large end diameter (in), SED=small end diameter (in), and L=length (ft). Small end diameter was calculated based on the "rule of thumb" of 1 inch taper per 8 feet of length (Ken Cormier, pers. comm.), and the formula: SED = LED-(L/8).
Table 2. Conversion of individual pieces of down wood to percent cover given large end diameter and length, assuming 1 inch of taper per 8 feet of length.
| Large end diameter (in) | Down wood length (ft) | % cover on per acre basis |
|---|---|---|
| 6 | 20 | 0.018 |
| 8 | 30 | 0.035 |
| 10 | 40 | 0.057 |
| 12 | 20 | 0.041 |
| 12 | 40 | 0.073 |
| 12 | 65 | 0.099 |
| 15 | 20 | 0.053 |
| 15 | 40 | 0.096 |
| 15 | 60 | 0.129 |
| 15 | 75 | 0.148 |
| 20 | 20 | 0.072 |
| 20 | 40 | 0.134 |
| 20 | 60 | 0.187 |
| 20 | 80 | 0.230 |
| 20 | 100 | 0.263 |
| 30 | 20 | 0.110 |
| 30 | 40 | 0.210 |
| 30 | 60 | 0.301 |
| 30 | 80 | 0.383 |
| 30 | 100 | 0.454 |
| 30 | 140 | 0.569 |
| 40 | 20 | 0.148 |
| 40 | 40 | 0.287 |
| 40 | 60 | 0.416 |
| 40 | 100 | 0.646 |
| 40 | 160 | 0.918 |
If trees are to be felled to provide down wood, or left standing to provide down wood at a later time, percent cover contribution of each tree can be estimated using taper equations. Clicking on the wildlife habitat type and subregion below will return a table with rough estimates of percent of an acre covered by different species of trees of given dbh when converted to down wood. The Flewelling Profile Model (Volume Estimator Library, Forest Vegetation Simulator) was used to determine height of a tree to a 5 inch top (12.7 cm). Total height of trees is used in the equations; this variable was estimated by averaging tree height by species and dbh class from inventory data specific to each Wildlife Habitat Type and subregion. The midpoint dbh for each class was input to the model as the dbh. A different version of the Flewelling Profile Model was used for each tree species.
Westside Lowland Conifer-Hardwood Forest - WA Coast
Westside Lowland Conifer-Hardwood Forest - OR Coast
Westside Lowland Conifer-Hardwood Forest - WA W Cascades
Westside Lowland Conifer-Hardwood Forest - OR W Cascades
Southwest Oregon Mixed Conifer-Hardwood Forest
Montane Mixed Conifer Forest
Eastside MIxed Conifer Forest - N Cascades/Rocky Mtns.
Eastside MIxed Conifer Forest - E Cascades/Blue Mtns.
Ponderosa Pine/Douglas-fir Forest
Table 3. Percent of an acre covered by different species of tree of given dbh when the tree is felled to provide down wood for the Westside Lowland Conifer-Hardwood Forest - WA Coast. Blank cells indicate insufficient data were available on tree heights for that species and dbh class.
| DBH (in) | Douglas-fir % cover | Western redcedar % cover | Western hemlock % cover |
|---|---|---|---|
10 |
0.066 | 0.054 | 0.062 |
15 |
0.123 | 0.098 | 0.127 |
20 |
0.204 | 0.161 | 0.212 |
25 |
0.295 | 0.255 | 0.312 |
30 |
0.400 | 0.319 | 0.421 |
35 |
0.536 | 0.431 | 0.535 |
40 |
0.628 | 0.508 | 0.639 |
50 |
0.871 | 0.692 | 0.880 |
60 |
1.169 | 0.921 | 1.050 |
Table 4. Percent of an acre covered by different species of tree of given dbh when the tree is felled to provide down wood for the Westside Lowland Conifer-Hardwood Forest - OR Coast. Blank cells indicate insufficient data were available on tree heights for that species and dbh class.
| DBH (in) | Douglas-fir % cover | Western redcedar % cover | Western hemlock % cover |
|---|---|---|---|
10 |
0.071 | 0.052 | 0.065 |
15 |
0.138 | 0.100 | 0.128 |
20 |
0.239 | 0.163 | 0.210 |
25 |
0.359 | 0.227 | 0.312 |
30 |
0.489 | 0.301 | 0.422 |
35 |
0.594 | 0.389 | 0.541 |
40 |
0.715 | 0.418 | 0.662 |
50 |
0.908 | 0.672 | 0.878 |
60 |
1.102 | 0.878 | |
70 |
1.401 | 1.038 | |
80 |
1.583 | | |
Table 5. Percent of an acre covered by different species of tree of given dbh when the tree is felled to provide down wood for the Westside Lowland Conifer-Hardwood Forest - WA W Cascades. Blank cells indicate insufficient data were available on tree heights for that species and dbh class.
| DBH (in) | Douglas-fir % cover | Western redcedar % cover | Western hemlock % cover |
|---|---|---|---|
10 |
0.074 | 0.054 | 0.062 |
15 |
0.139 | 0.106 | 0.127 |
20 |
0.229 | 0.177 | 0.214 |
25 |
0.332 | 0.259 | 0.300 |
30 |
0.439 | 0.340 | 0.396 |
35 |
0.535 | 0.426 | 0.503 |
40 |
0.685 | 0.538 | 0.590 |
50 |
0.824 | 0.715 | 0.770 |
60 |
1.032 | 0.936 | |
70 |
1.290 | 0.999 | |
80 |
1.464 | 1.254 | |
Table 6. Percent of an acre covered by different species of tree of given dbh when the tree is felled to provide down wood for the Westside Lowland Conifer-Hardwood Forest - OR W Cascades. Blank cells indicate insufficient data were available on tree heights for that species and dbh class.
| DBH (in) | Douglas-fir % cover | Western redcedar % cover | Western hemlock % cover |
|---|---|---|---|
10 |
0.069 | 0.055 | 0.059 |
15 |
0.137 | 0.104 | 0.125 |
20 |
0.232 | 0.173 | 0.213 |
25 |
0.335 | 0.261 | 0.310 |
30 |
0.445 | 0.350 | 0.409 |
35 |
0.546 | 0.415 | 0.518 |
40 |
0.657 | 0.494 | 0.590 |
50 |
0.827 | 0.707 | 0.831 |
60 |
1.045 | 0.894 | 1.046 |
70 |
1.274 | | |
80 |
1.447 | | |
Table 7. Percent of an acre covered by different species of tree of given dbh when the tree is felled to provide down wood for the Southwest Oregon Mixed Conifer-Hardwood Forest. Blank cells indicate insufficient data were available on tree heights for that species and dbh class.
| DBH (in) | Douglas-fir % cover | Ponderosa pine % cover | Western hemlock % cover | White fir % cover |
|---|---|---|---|---|
10 |
0.061 | 0.045 | 0.054 | 0.061 |
15 |
0.120 | 0.104 | 0.117 | 0.125 |
20 |
0.203 | 0.191 | 0.191 | 0.212 |
25 |
0.298 | 0.284 | 0.291 | 0.306 |
30 |
0.398 | 0.403 | 0.396 | 0.405 |
35 |
0.489 | 0.522 | 0.460 | 0.498 |
40 |
0.592 | 0.767 | | 0.577 |
50 |
0.740 | 0.839 | | 0.810 |
60 |
0.951 | 1.094 | | |
70 |
1.139 | | | |
80 |
1.394 | | | |
Table 8. Percent of an acre covered by different species of tree of given dbh when the tree is felled to provide down wood for the Montane Mixed Conifer Forest. Blank cells indicate insufficient data were available on tree heights for that species and dbh class.
| DBH (in) | Douglas-fir % cover | Western hemlock % cover | Mountain hemlock % cover | Western redcedar % cover | Engelmann spruce % cover | Western larch % cover | White fir/Grand fir % cover | Subalpine fir % cover | Western white pine % cover | Lodgepole pine % cover |
|---|---|---|---|---|---|---|---|---|---|---|
10 |
0.056 | 0.053 | 0.045 | 0.048 | 0.064 | 0.076 | 0.056 | 0.055 | 0.055 | 0.064 |
15 |
0.109 | 0.113 | 0.096 | 0.098 | 0.122 | 0.139 | 0.113 | 0.104 | 0.113 | 0.113 |
20 |
0.180 | 0.193 | 0.160 | 0.154 | 0.194 | 0.212 | 0.187 | 0.159 | 0.179 | 0.164 |
25 |
0.261 | 0.287 | 0.231 | 0.234 | 0.271 | 0.283 | 0.266 | 0.214 | 0.269 | 0.202 |
30 |
0.347 | 0.379 | 0.304 | 0.316 | 0.352 | 0.353 | 0.346 | 0.259 | 0.333 | 0.291 |
35 |
0.425 | 0.471 | 0.372 | 0.383 | 0.441 | 0.444 | 0.461 | 0.319 | 0.413 | |
40 |
0.536 | 0.576 | 0.464 | 0.491 | 0.512 | 0.489 | 0.500 | 0.330 | 0.543 | |
50 |
0.667 | 0.747 | 0.617 | 0.677 | 0.661 | 0.630 | 0.760 | | | |
60 |
0.831 | 0.886 | 0.822 | 0.778 | | | | | | |
70 |
1.146 | | | 0.953 | | | | | | |
80 |
1.291 | | | | | | | | | |
Table 9. Percent of an acre covered by different species of tree of given dbh when the tree is felled to provide down wood for the Eastside MIxed Conifer Forest - N Cascades/Rocky Mtns. Blank cells indicate insufficient data were available on tree heights for that species and dbh class.
| DBH (in) | Douglas-fir % cover | Ponderosa pine % cover | Western larch % cover | White fir/Grand fir % cover | Western hemlock % cover | Engelmann spruce % cover | Western redcedar % cover | Western white pine % cover | Subalpine fir % cover | Lodgepole pine % cover |
|---|---|---|---|---|---|---|---|---|---|---|
10 |
0.058 | 0.051 | 0.082 | 0.071 | 0.062 | 0.070 | 0.057 | 0.077 | 0.069 | 0.080 |
15 |
0.108 | 0.105 | 0.146 | 0.133 | 0.117 | 0.131 | 0.102 | 0.140 | 0.126 | 0.131 |
20 |
0.172 | 0.171 | 0.222 | 0.212 | 0.183 | 0.207 | 0.159 | 0.217 | 0.185 | 0.208 |
25 |
0.240 | 0.252 | 0.292 | 0.297 | 0.267 | 0.304 | 0.231 | 0.301 | 0.313 | |
30 |
0.309 | 0.330 | 0.376 | 0.361 | 0.303 | 0.418 | 0.306 | 0.344 | | |
35 |
0.351 | 0.410 | 0.444 | 0.467 | | | 0.361 | | | |
40 |
0.407 | 0.499 | 0.564 | 0.545 | | | 0.487 | | | |
50 |
0.486 | 0.738 | | | | | | | | |
60 |
0.798 | | | | | | | | | |
Table 10. Percent of an acre covered by different species of tree of given dbh when the tree is felled to provide down wood for the Eastside MIxed Conifer Forest - E Cascades/Blue Mtns. Blank cells indicate insufficient data were available on tree heights for that species and dbh class.
| DBH (in) | Douglas-fir % cover | Ponderosa pine % cover | Western larch % cover | Engelmann spruce % cover | White fir/Grand fir % cover | Lodgepole pine % cover |
|---|---|---|---|---|---|---|
10 | 0.052 | 0.046 | 0.076 | 0.066 | 0.051 | 0.066 |
15 | 0.101 | 0.099 | 0.140 | 0.126 | 0.102 | 0.117 |
20 | 0.166 | 0.171 | 0.223 | 0.203 | 0.171 | 0.173 |
25 | 0.241 | 0.253 | 0.304 | 0.289 | 0.246 | 0.217 |
30 | 0.316 | 0.335 | 0.388 | 0.357 | 0.329 | |
35 | 0.380 | 0.420 | 0.477 | 0.474 | 0.411 | |
40 | 0.454 | 0.506 | 0.582 | 0.549 | 0.477 | |
50 | 0.582 | 0.678 | 0.690 | 0.809 | 0.628 | |
60 | 0.731 | 0.786 | | | | |
Table 11. Percent of an acre covered by different species of tree of given dbh when the tree is felled to provide down wood for the Ponderosa Pine/Douglas-fir Forest. Blank cells indicate insufficient data were available on tree heights for that species and dbh class.
| DBH (in) | Douglas-fir % cover | Ponderosa pine % cover | Lodgepole pine % cover |
|---|---|---|---|
10 |
0.045 | 0.041 | 0.056 |
15 |
0.085 | 0.086 | 0.104 |
20 |
0.139 | 0.152 | 0.164 |
25 |
0.208 | 0.228 | 0.233 |
30 |
0.262 | 0.308 | 0.335 |
35 |
0.335 | 0.385 | |
40 |
0.449 | 0.469 | |
50 |
0.630 | 0.660 | |