United States 

Department of 

Agriculture 

Forest 

Service 

Northern 

Region 

200 East Broadway 

P.O. Box 7669 

Missoula, MT 59807 

Forest Health

Protection

Report 03-6 March 2003 

ESTABLISHMENT REPORT FOR DOUGLS-FIR TUSSOCK MOTH 

PERMANENT PLOTS ON THE CLEARWATER NATIONAL FOREST 

Sandy Kegley and Nancy Sturdevant 

INTRODUCTION 

Douglas-fir tussock moth, Orgyia pseudotsugata

McDunnough, outbreaks occur periodically in 

northern Idaho. Outbreaks in northern Idaho are 

synchronized more than 50 percent of the time 

with larger scale western outbreaks. The 

Palouse Ranger District (RD) on the Clearwater 

National Forest has had four recorded outbreaks 

since 1944 including the most recent outbreak 

(Sturdevant 2000, Randall 2001, Randall 2002). 

The next previous outbreak occurred in 1986. 

During the most recent outbreak, 142,000 acres 

were defoliated at its peak in 2001 (Kegley and 

Wulff 2003). 

Though outbreaks usually last for only 2-4 years, 

severe defoliation can cause growth loss, top 

kill, or tree mortality. Growth loss and tree 

mortality have been documented for outbreaks 

in Oregon and California (Wickman 1978 and 

1980) and for one outbreak on the Nez Perce 

National Forest in northern Idaho (Bousfield and 

Ward 1976). There have been no studies that 

have evaluated the effects of tussock moth on 

mature and immature grand fir and Douglas-fir 

forests throughout an entire outbreak cycle in 

northern Idaho. 

After the outbreak in 1986, permanent plots 

were established on the Palouse RD in 1992. 

The objective of establishing permanent plots 

were to measure growth loss, top kill, and tree 

mortality in affected tussock moth areas and to 

observe forest changes as a result of tussock 

moth activity. As forest management objectives 

change, how we view the results of an outbreak 

may also change. Therefore, it is more 

important than ever to focus on the vegetation 

changes as a result of outbreaks versus the 

insects and their damage. 

METHODS 

1992 plots 

Plots were established in 1992 in 4 stands. 

These were mature stands with a high 

component of grand fir and Douglas-fir and were 

not scheduled for harvest for several decades. 

Selected stands varied in habitat type, aspect 

and basal area. Stands were similar in 

topography, slope and elevation (Table 1). 
2 

Table 1. Stand characteristics for Douglas-fir tussock moth plots established in 1992. 

Location Skyline Mission Mtn. Giant White Pine Blakes Fork 

# of plots 10 10 10 10 

Habitat type 591 505 571 508 

Stand aspect SW W NW SW 

Elevation 2500 2500 3000 3200 

Topography Even slope Even slope Even slope Even slope 

Ave. BA per plot 222 317 211 170 

Slope 23 33 32 27 

A series of 10-variable radius (using 40 BAF) 

and 1/100 acre fixed plots were established in 

each stand. Region One timber stand exam 

procedures were used (Timber Management 

Data Handbook 1991). Data recorded on 

variable radius plots were number of trees, plot 

slope, aspect, habitat type, and basal area. 

Data collected on individual trees included 

species, diameter at breast height (d.b.h), tree 

class, tree height, crown ratio, crown class, and 

tree damage. Site trees were selected and 

measured for each stand. On fixed plots, grand 

fir and Douglas-fir regeneration were measured 

and recorded. In addition, five-saplings, at least 

1 foot in height, were permanently tagged on 

each fixed plot. Data on cover type, % cover, 

brush height was also recorded on fixed plots. 

Top-kill and defoliation was measured for all 

mature tagged trees and the five saplings 

permanently tagged. Top-kill was measured as 

a percentage of crown killed. Defoliation for 

both large trees and tagged regeneration was 

measured by crown thirds and in percentages of 

10. Defoliation was measured annually through 

1994. Five pheromone traps for Douglas-fir 

tussock moth were placed in each stand 

between 1992 and 1994. In 1997, 5 years after 

establishment, height, d.b.h., and defoliation on 

mature trees in the variable radius plots were 

remeasured. Height and defoliation of the 

tagged regeneration was also remeasured. 

2001 Plots 

The outbreak that occurred from 2000-2002 was 

very large and severe. However, permanent 

plots we established in1992 experienced only 

light to moderate defoliation during the 2000-

2002 outbreak. In order to obtain information on 

severely defoliated sites and on immature 

stands, additional plots were established in 

2001. 

In October and November 2001, plots were 

established in a heavily defoliated plantation and 

in a surrounding mature stand east of Prospect 

Peak off of road 4709 on the Palouse RD. In the 

plantation, seven 1/50th acre fixed radius plots 

were established 2 chains apart. A total of 101 

Douglas-fir and grand fir were tagged and the 

following data collected: species, d.b.h., and 

percent defoliation. Height was recorded only 

on the first 5 trees in each plot. Douglas-fir and 

grand fir were the only tree species in the 

plantation plots. 

In the mature stand adjacent to the plantation, 

19 variable radius plots were established using a 

20 basal area factor prism. Data taken was 

similar to plots established in 1992. 
3 

Stand Summaries

Location 

Rd.4709 

Mature Stand 

Rd.4709 

Plantation 

Skyline 

Drive 

Mission 

Mountain 

Giant White 

Pine 

Blake’s 

Fork 

TPA of DF * 22.92 278.57 18.73 16.55 16.11 64.02 

QMD DF 22.2 5.24 19.07 20.85 14.38 16.58 

% BA of DF 20 42 31 21 14 80 

TPA of GF 117.67 442.86 81.50 72.45 64.03 28.98 

QMD GF 15.76 3.58 11.56 17.35 13.33 9.51 

% BA of GF 50 58 57 61 39 9 

TPA Larch 62.89 0 0.84 6.67 9.57 4.9 

QMD Larch 13.20 0 20.9 15.45 20.65 12.25 

% BA Larch 19 0 2 5 14 4 

TPA WWP 0.89 0 0 0 3.14 0 

QMD WWP 14.7 0 0 0 10.80 0 

% BA WWP 0.5 0 0 0 2 0 

TPA PP 4.29 0 3.91 5.87 2.73 3.27 

QMD PP 23.86 0 21.66 23.85 11.60 24.07 

% BA PP 5 0 10 10 2 7 

TPA WRC 9.15 0 0 0 11.67 0 

QMD WRC 17.66 0 0 0 18.55 0 

% BA WRC 5 0 0 0 16 0 

TPA WH 0 0 0 0 12.54 0 

QMD WH 0 0 0 0 15.24 0 

% BA WH 0 0 0 0 13 0 

TPA Birch 0 0 0 11.77 0 0 

QMD Birch 0 0 0 7.89 0 0 

% BA Birch 0 0 0 3 0 0 

Total TPA 218 721 105 113 120 101 

Total BA 237 68 102 154 112 92 

* TPA = trees per acre, QMD = quadratic mean diameter of live trees, BA = basal area 

DF = Douglas-fir, GF = grand fir, L = larch, WWP = western white pine, PP = ponderosa pine, WRC = 

western red cedar, 

WH = western hemlock.

In 2001, defoliation, top-kill, and mortality were 

measured for all trees on all plots. This data 

was taken again in 2002, along with a 10-year 

remeasurement of d.b.h and heights of all trees 

on the 1992 plots. A summary of this data will 

be available after a 2003 measurement of 

defoliation, top-kill, and mortality. 

We expect very little, if any, tussock moth 

activity after 2003 for several years. Five years 

following the recent outbreak, in 2007, we hope 

to evaluate the long-term growth effects of 

tussock moth on host trees on all plots. We will 

also measure the effects on subsequent growth 

and survival of non-host trees. 
4 

REFERENCES 

Bousfield, W.E. and J. D. Ward. 1976. 

Observations of impact on the Nezperce 

National Forest caused by the Douglas-fir 

tussock moth. USDA Forest Service, 

Northern Region, State and Private Forestry, 

Missoula, MT 59801. Report 76-9. 

Kegley, S. and Wulff, D. 2003. 2002 North 

Idaho Douglas-fir Tussock Moth Trapping 

System Report. USDA Forest Service 

Northern Region, State and Private Forestry, 

Missoula, MT. FHP Report 03-5. 

Randall, C. 2001. Douglas-fir tussock moth 

biological evaluation, Palouse Ranger 

District, Clearwater National Forest-2000. 

USDA Forest Service, State and Private 

Forestry, Missoula, MT. FHP Report 01-4. 

30 p. 

Randall, C. 2002. Douglas-fir tussock moth 

biological evaluation, Palouse Ranger 

District, Clearwater National Forest-2001. 

USDA Forest Service, State and Private 

Forestry, Missoula, MT. FHP Report 02-5. 33 

p. 

Sturdevant, N. J. 2000. Douglas-fir tussock 

moth in Northern Idaho and Western 

Montana: Current Activity and Historical 

Patterns. USDA Forest Service, Northern 

Region, State and Private Forestry, Forest 

Health Protection, Missoula, MT 59801. 

Report No. 00-12. 

Timber Management Data Handbook. 1991. 

Field Instructions. Stand Examination. FSH 

2409.21h R1 Chapter 400 

Wickman, B. E. 1980. Increased growth of 

white fir after a tussock moth outbreak. J. 

Forestry. 78:31-35. 

Wickman, B. E. 1978. Tree mortality and top-kill 

related to defoliation by the Douglas-fir 

tussock moth in the Blue mountain outbreak. 

USDA Forest Service research paper 

PNW-233.