Detailed Estimates of Old Growth
And Large-Snags on the
Lewis and Clark National Forest
Renate Bush 1,2
Andy Leach3
January 25, 2004
Analysis was done using Forest Inventory and Analysis (FIA) data, see Application of Forest Inventory and
Analysis (FIA) Data to Estimate Amount of Old Growth Forest and Snag Density in the Northern Region of the
National Forest System for an overview on why it is appropriate to use this data for broad-scale analysis. All
forested4 FIA plots that were located on the Lewis and Clark National Forest were used to estimate the
proportion of old growth and density of snags with a minimum diameter breast height of 10.0 inches or larger.
Those FIA plots in which wildfire or harvest have occurred since the 1996-1997 inventory was coded to: (1) not
meet the old growth definition; and (2) represent that there were no snags remaining at these plot locations. This
results in a conservative estimate of old growth and snag density as not all wildfire and harvest activities
remove all old growth and snags on the landscape. The following provides estimates of old growth and snag
density for the Lewis and Clark National Forest, by commercial lands, and by landscapes. Additionally, snag
density is compiled by species cover type.
Estimates of Old Growth and Snag Density for the Lewis and Clark National Forest:
Estimated percentage of Old Growth on all forested lands on the Lewis and Clark National Forest is 12.06%
with a 90% confidence interval of 9.50% to 14.74%. The estimated density of snags is 11.37 per acre with a
90% confidence interval of 8.90 to 14.04 snags per acre.
Estimates of percentage of Old Growth and snag density by Commercial lands and associated 90%
confidence intervals follow.
Ave Snags/Acre ≥ 10" DBH Percent Old Growth Plot Frequency
Number of
90% CI 90% CI 90% CI 90% CI
Commercial Point Point Plots % of the
Lower Upper Lower Upper
Estimate Estimate (Number of Plots
Bound Bound Bound Bound
Subplots)
Noncommercial 9.57 12.85 16.43 10.00 13.30 16.77 176(880) 52.38
Commercial 5.23 8.49 12.14 5.86 9.67 13.83 91(455) 27.08
Estimates of snag density and proportion of old growth and associated 90% confidence interval by
Landscapes follow. These Landscapes are shown in Appendices A and B.
1
USDA Forest Service, Region 1, Forest and Range Management, 200 E Broadway, Missoula, MT, 59801.
2
Forester, Inventory and Analysis.
3
Statistician, USDA Forest Service; Washington Office Inventory and Monitoring Institute/METI; 2150 Centre Ave. Bldg. A., Fort
Collins, CO 80526. 970-295-5731.
4
“..land at least 10 percent stocked, or currently nonstocked but formerly having such stocking, with timber and/or woodland trees,
and where human activity on the site does not preclude natural succession of the forest (i.e., the site will be naturally or artificially
regenerated).” Interior West Forest Land Resource Inventory Field Procedures, 1995-1996.
Ave Number of Snags/Acre ≥
10" DBH Percent Old Growth Plot Frequency
Number of
Landscape 90% CI 90% CI 90% CI 90% CI Percent
Point Point Plots
Lower Upper Lower Upper of the
Estimate Estimate (Number of
Bound Bound Bound Bound Plots
Subplots)
Big Snowy
Mountains 0.00 3.14 6.86 1.82 11.67 23.64 12(60) 3.57
Castle Mountains 0.00 4.36 16.34 0.00 10.00 30.00 6(30) 1.79
Crazy Mountains 1.57 10.08 19.81 0.00 13.33 30.00 6(30) 1.79
Highwood Mountains 0.00 0.00 0.00 0.00 0.00 0.00 3(15) 0.89
Little Belt Mountains 6.98 10.16 13.68 10.39 14.62 19.06 119(595) 35.42
Little Snowy
Mountains 0.00 4.89 14.67 0.00 0.00 0.00 3(15) 0.89
Rocky Mountains 9.91 14.29 19.10 6.67 10.17 13.98 118(590) 35.12
Estimates of snag density and proportion of old growth and associated 90% confidence intervals by
Landscape and Commercial/Non-commercial lands follow.
Ave Number of
Commercial
Snags/Acre ≥ 10" Percent Old Growth Plot Frequency
Number of
Landscape 90% CI 90% CI 90% CI 90% CI Percent
Point Point Plots
Lower Upper Lower Upper of the
Estimate Estimate (Number of
Bound Bound Bound Bound Plots
Subplots)
Big Snowy Mtns 0.00 3.84 10.71 0.00 13.33 33.33 6(30) 1.79
Castle Mountains 0.00 6.53 26.14 0.00 0.00 0.00 4(20) 1.19
Commercial
Crazy Mountains 0.00 4.39 11.21 0.00 6.67 20.00 3(15) 0.89
Highwood Mtns 0.00 0.00 0.00 0.00 0.00 0.00 3(15) 0.89
Little Belt Mtns 5.17 9.05 13.46 6.91 12.13 17.89 61(305) 18.15
Little Snowy
Mountains 0.00 4.89 14.67 0.00 0.00 0.00 3(15) 0.89
Rocky Mountains 0.53 13.06 31.37 0.00 3.64 10.00 11(55) 3.27
Big Snowy Mtns 0.00 2.44 7.17 0.00 10.00 25.71 6(30) 1.79
commercial
Castle Mountains 0.00 0.00 0.00 0.00 30.00 80.00 2(10) 0.60
Non-
Crazy Mountains 0.00 15.77 31.34 0.00 20.00 46.67 3(15) 0.89
Little Belt Mtns 6.34 11.33 17.02 10.70 17.24 24.29 58(290) 17.26
Rocky Mountains 9.84 14.42 19.39 6.97 10.84 14.95 107(535) 31.85
Estimates of snag density and proportion of old growth and associated 90% confidence intervals by 5 th
code HUC follows. These HUCs are shown in Appendices C and D.
Ave Number of Snags/Acre ≥ 10"
dbh Percent Old Growth Plot Frequency
5th Code Number of
90% CI 90% CI
HUC 90% CI Point 90% CI Upper Point Plots Percent of
Lower Upper
Lower Bound Estimate Bound Estimate (Number of the Plots
Bound Bound
Subplots)
1004020110 0.00 2.49 7.48 0.00 13.33 40.00 3 (15) 0.89
3.
Habitat conservation plans/viability
*Refer to the project BE for analysis of effects. Habitat plans and minimum habitat requirements are found in
the Lewis and Clark National Forest Plan. See attachments for goshawk information (maps of territories,
productivity, and active nests).
Historic fire intervals, primarily in the lower elevation dry forest types, maintained a more heterogeneous
condition with open, park-like, stands of fewer, larger trees interspersed with occasional dense patches of
younger trees. Additionally, more frequent fires prevented conifer encroachment into grasslands, shrub-
grasslands, and meadows. Many animal species have historically utilized these habitats to meet a variety of
their life history requirements (e.g., winter range for ungulates, nesting and foraging for passerines). Fire
suppression coupled with livestock grazing has resulted in many stands with overly dense understories, the
loss or reduction in size of grasslands, shrublands, and meadows, a lack of regeneration in aspen stands, and
shifts in plant communities to those that are less fire resistant. Habitat heterogeneity across the landscape and
within stands is desirable to meet the needs of a variety of species. The proposed treatments will contribute to
maintaining historic vegetation structure across the landscape.
4. Big game management
*See BE for effects analysis. Data is provided below.
Percent forest cover of cumulative effects area for elk and project area.
Cover Non-cover Total area
Acres % Acres % Acres
Hunting Districts (HD) 454,254 32 969,811 68 1,424,065
418, 420, 432, 448, 454, and 540
Cumulative effects area - Area 432,715 63 255,78 37 688,593
frequented by elk within HDs
Project area 156,545 73 57,847 27 214,392
Winter range area in and 28,454 26 78,979 74 107,432
adjacent to project boundary
Winter range area in project 13,023 52 12,184 48 25,207
boundary
Compliance With
Management Open Roads Total Area ORD Forest Plan Forest
Area Miles Miles2 Miles/Miles2 Standard Plan Standard
B1 4.0 3.4 1.2 1.5 – 3.0 Yes
B2 21.3 101.9 0.2 1.5 – 3.0 Yes
B3 97.8 31.5 3.1 1.5 – 3.0 No
C1 2.7 1.5 1.7 0.5 – 1.5 No
C2 6.0 5.7 1.0 0.5 – 1.5 Yes
C3 11.9 7.2 1.6 0.5 – 1.5 No
Cumulative Effects Area
Hunting District
418 103.4 96.6 1.1 NA NA
420 33.3 32.5 1.0 NA NA
432 205.0 205.2 1.0 NA NA
448 191.2 174.9 1.1 NA NA
454 120.6 120.4 1.0 NA NA
540 206.3 176.1 1.2 NA NA
Compliance With
Management Open Roads Total Area ORD Forest Plan Forest
Area Miles Miles2 Miles/Miles2 Standard Plan Standard
Total 860.1 805.7 1.1 NA NA
Security area in the project and cumulative effects area for elk (HD=hunting district).
Total
Security % of Area in
Acres Area Acres Security Area
Project Area 214,305 102,494 48
Cumulative Effects
Area
HD 418 81,818 30,692 38
HD 420 36,797 24,337 66
HD 432 153,860 83,801 54
HD 448 158,466 76,782 48
HD 454 77,444 26,053 34
HD 540 117,880 41,136 35
Points related to wildlife, fisheries, and rare plants, from January 20, 2003 letter:
1. copy of BE
2. BE and accompanying maps
3. arche surveys
4. goshawk forms provided
5. Map of timber compartment provided (draw on past harvest).
6. Old-growth map
7. See response to point 2 (November letter).
8. See goshhawk maps.
9. See harvest unit maps with wildlife corridors.
10. See old-growth data.
11. other scoping comments
12. Cumulative effects area varies by species (see attached maps and project file).
13. See old-growth/snag discussion above.
Forest plan standards for snag retention on the Lewis and Clark National Forest are dependent on forest type
(Forest Plan, p. 2-35. Minimum levels may be accomplished by managing for 60% of capacity over 100% of the
forested landscape. Managing for 60% capacity over 100% of the forested landscape would require that a
minimum of 135 snags per 100 acres (10 inches diameter or greater) be retained to meet minimum management
objectives for viable populations of cavity dependent wildlife in the pine forest types common to the project
area. As shown in the table below, snag density estimates within the analysis area exceed snag requirements for
managing cavity dependent species at 100% of the forested landscape.
Density of standing dead trees (snags) on the Jefferson Division
of the Lewis and Clark National Forest by forest type (DeBlander 1996).
Standards Existing condition
Lewis and
Clark
National Lewis and Clark National Forest
Forest Region 1 Jefferson Division
FP Standard Retention Prescription Existing Existing
a b c
Forest Type VRU Snags/acre Snags/acre Snags/acre Snags/acre
Douglas-fir 2 1.35≥10” dbh 1-2>20” dbh 7.13≥10” dbh 0.10>20” dbh
Engelmann spruce 4 1.35≥10” dbh 6-12 total w/ 2>20" dbh 8.24≥10” dbh 1.09 > 20” dbh
Limber pine 7 1.35≥10” dbh All available 3.18≥10” dbh 3.18≥10” dbh
Lodgepole pine 6 1.35≥10” dbh 5-10>10” 5.00≥10” dbh 5.00>10” dbh
Ponderosa pine 1 1.35≥10” dbh 4>20” dbh 1.84≥10” dbh 0.72>20” dbh
Spruce-fir 6 1.35≥10” dbh 5-10>10” 9.72≥10” dbh 9.72≥10” dbh
Whitebark pine 7 1.35≥10” dbh All available 2.70≥10” dbh 2.70≥10” dbh
a
Vegetative Response Unit (VRU) is a combination of potential habitat type, fire group, and slope class.
b
Existing snags/acre is the current snag density relative to the snag standards of the Lewis and Clark Forest Plan.
c
Existing snags/acre is the current snag density relative to the retention prescription of Region 1 of the U.S. Forest
Service.