Reply to: 3420 Date: March 16, 1993Subject:

A Biological Evaluation "A Prelimina~ Validation of a Douglas-fir

Beetle Hazard Rating System, Mountain Home Ranger District, Boise

National Forest."

To:

Chief, WO

Enclosed is a biological evaluation entitled hA Prelimina~ Validation of a

Douglas-fir Beetle Hazard Rating System, Mountain Home Ranger District, Boise

National Forest.h

copies contact: Forest Pest Management

Boise Field Office

1750 Front St. Room 202

Boise, ID 83702

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<17

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~ LAURA B. FERGUSON

,- .Director, State and Private Forestry

Enclosure

cc: -

Forest Supervisors, R-4 ,

District Ranger, Mtn. Home R.D."

Intermountain Research Station, Robert Steele Boise

OFO

TM-R4

State Entomologist, State of Idaho

Canadian Forestry Service,- Victoria., BC

BCC Timber & Wood Products

FPM, MAG

FPM -Rl, R2, R3, RS, R6, RIO

Forestry Sciences Laboratory, INT, Moscow, ID

Library, INT, Ogden, UT

PNW, Portland, OR; PSW, Berkeley, CA; RM, Ft. Collins, CO

State Director BLM, ID

Hugh Homan, Entomology Dept. Univ. of ID
3420

Report No. R4-93-05

March 16, 1993

A PRELIMINARY VALIDATION OF A DOUGLAS-FIR BEETLE HAZARD RATING SYSTEM

MOUNTAIN HOME RANGER DISTRICT, BOISE NATIONAL FOREST 1992 .

Julie C. Weatherby 1

R. W .Thier2

ABSTRACT

Stands in the Burnt Creek/Smith Creek Sa.lvage Sa.le area on the Boise N ationa.l Forest were

hazard rated for Douglas-fir beetle occurrence using 1987 stand exam data. The hazard rating

system developed by R. W. Thier performed well in these stands. High hazard stands had a 67

percent probability of infestation by Douglas-fir beetle during a 2-year period which coincided with

a forestwide outbreak. Only 16 percent of these high hazard stands had significant mortality (> 1

tree/acre). None of the moderate or low hazard stands'sustained significant mortality during the

eva.luation period.

.

1 Entomologist, Forest Pest Management, Intermountain Region, USDA Forest Service.

2 Entomologist, Forest Pest Management, Intermountain Region, USDA Forest Service.

1
INTRODUCTION

Douglas-fir beetle, Dendroctonus pseudotsugae Hopk., is one of several native bark beetles which

is capable of causing mortality in conifer stands in the west. Douglas-fir beetles kill Douglasfirs, preferring mostly mature to overmature large diameter Douglas-firs growing in mixed or pure

stands. Morta.1ity caused by the Douglas-fir beetle is usually not evenly nor randomly distributed

throughout the stand. Usually mortality is concentrated in pockets which range in size from a few

trees to hundreds of trees.

Hazard rating systems have been developed for some of the native ba.rk beetles including mountain

pine beetle, D. ponderosae Hopk., and spruce beetle, D. rofipennis (Kirby), (Amman et a.l. 1977,

Schmid and Frye, 1976). These hazard rating systems attempt to assign a low, moderate or high

risk to stands of timber based upon stand and site characteristics. While a published Douglas-fir

beetle hazard rating is not available, many of the underlying stand and site factors associated with

beetle activity have been described independently. The relationship between Douglas-fir beetle

caused mortality and stand density as a measure of moisture stress and shaded stem environment

has been documented (Furniss 1962 & 1979, Rudinsky 1962 & 1966). Species diversity plays a

role in stand susceptibility and infested spot growth (Furniss et a.l. 1981). Evidence indicates that

most Douglas-firs which die from Douglas-fir beetle attacks exceed 120 years of age -(Furniss et al.

1981 & 1972, Ringold et al. 1965). Predisposing factors such as fire injuries, windthrow, snow

breakage, defoliation and root diseases all influence the probability of occurrence and the intensity

of an outbreak (Berryman and Wright 1978, Furniss 1962, Furniss et al. 1979, R.L. Furniss 1941,

McMullen and Atkins 1962, Vite and Rudinsky 1962).

In 1984 R. W. Thier developed a Douglas-fir beetle hazard rating system which is used by land managers in the Intermountain Region to identify high hazard stands and prioritize treatment. While

this system is based upon published relationships between site and stand factors and associated

damage caused by Douglas-fir beetle, the hazard rating system has never been field validated. In

this paper we describe the results of a preliminary validation.

METHODS

Hazard ratings \vere based on the following stand attributes (Thier, unpublished).

Stand Basal Area -the average basal area in square feet per acre of a.1llive trees.

Proportion of the Stand Basal Area in Douglas-fir -the mean basal area in square feet per

acre of all live Douglas-firs divided by the mean stand basal area.

Average Stand Age -average stand age in years taken from at least two site trees per plot.

A verage Diameter of Douglas-fir Sawtimber -the average diameter at breast height of all

Douglas-firs greater than 9 inches in diameter.

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The ranges in attribute values were divided into discrete classes and a rating value was assigned to

each class.

Attribute Range Rating

Stand Basal Area (ft2jac) 0.5

1.0

1.5

<120

120 -250

>250

Proportion of Stand Basal

Area in Douglas-fir (%)

1.0

2.0

3.0

<25

25 -50

>50

Average Stand Age (years) 1.0

2.0

3.0

<80

80 -120

>120 -

Average DBH of Douglas-fir

Sawtimber (in)

1.0

2.0

3.0

<10

10 -14

>14

We used ava.ilable stand exam data for 64 stands in compartments 503, 505, and 511 in the Burnt

Creek/Smith Creek Salvage Sale Area of the Mounta.in Home Ranger District, Boise National

Forest, to hazard rate stands for susceptibility and vulnerability to Douglas-fir beetle infestations.

Stand exam data were collected in 1987 which coincided with the beginning of an extensive Dougla.sfir beetle outbreak on the Boise National Forest.

Each stand was hazard rated by determining the appropriate attribute rating for each of the four

attributes and summing these attribute ratings to obtain a stand hazard ratirig: Low hazard stands

had ratings ranging from 0 -4, moderate hazard stands had ratings ranging f~om 5 -7, and high

hazard stands had ratings ranging from 8 -11.

Validation of the hazard rating was attempted using 1988 aerial resource photography (1:15,840)

available for the same 64 stands. The imagery was used to identify and compare recent mortality

with the predicted hazard ratings. Stand boundaries were hand transferred from stand maps to

photos. Then the number of red trees assumed to be recent mortality caused by Douglas-fir beetle

and found \vithin each stand boundary were counted under 7X magnification. Red trees visible in

the photos probably died within a 2-year period prior to the photographic mission. We did not

verify the accuracy of the photointerpretation; however, we feel that these mortality estimates are

good relative indicators of Douglas-fir beetle activity in the various stands. Mortality estimates

were converted to trees per acre and subjectively partitioned into three classes (0, <1, >1 treesjac).

i

A chi-square test of significance was used to test whether the three hazard ratings (low, moderate,

high) and the three morta.lity classes (0, <1, >1 trees/ac) are independent.

RESULTS

The total hazard rated area covered 2,559 acres. Seventy six percent of this area (1,944 acres) was

classified as high hazard and 23 percent (596 acres) was classified as moderate hazard. Only one

percent (19 acres) was rated as lo\v hazard.

3
Forty six stands \Vere rated high hazard. Of the 46 stands rated high hazard, 15 were uninfested a.s

determined via. the 1988 aerial photography. Twenty six of these stands lost less than one tree per

acre \vith losses averaging 0.36 trees per acre. Five stands lost more than one tree per acre with

losses averaging 1.80 trees per acre (Table 1.).

Based on the above information high hazard stands had a 67 percent probability of losing some

trees to Douglas-fir beetle. However t only 16 percent of the high hazard stands wi th lossest had

significant losses or \vhat might be termed epidemic losses. For the purposes of this report, epidemic

losses are defined as mortali ty rates of greater than one tree per acre. This rate was selected because

it probably indicates a clustering of mortality indicative of a multiple tree spot or infestation.

Seventeen stands were classified in the moderate risk category. These stands had a 29 percent

probability of losing trees and losses averaged 0.34 tree per acre. Morta.lity rates of less than one

tree per acre are indicative of scattered mortality where a few high risk trees are killed but the

stand is not generally infested \vith multi-tree spots. None of the 17 stands had losses exceeding

one tree per acre (Table 1). .

Only one stand rated a low hazard rating and this stand was uninfested (Table 1).

The null hypothesis ,vas disproved via a significant chi-square test (chi-square = 9.1592 with 4

degrees of freedom, probability level = .0572). Therefore hazard rating classes and mortality

classes are not independent.

Table 1. The number of stands cross tabulated by hazard rating and mortality

class within 1:he Burnt Creek/Smith Creek Salvage Sale Area.

.

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DISCUSSION AND CONCLUSIONS

This hazard rct.ting system performed well in the Burnt Creek/Smith Creek Salvage Sale area.. The

hazard rating system correctly identified the five stands which experienced the greatest losses. It

appears that mortality rates of greater than one tree per acre over a one or two year period are.

probably indicative of epidemic beetle populations, while mortality rates of less than one tree per- acre are probably typical under endemic population levels or background levels. ..

In theory in order to significantly reduce the potential for future Douglas-fir beetle outbreaks, a

large proportion of the area must be managed to reduce the susceptibility. Using this hazard rating

system, high hazard stands could be identified and the rating could be factored into the decision

making proces~; used to prioritize treatments.

t

5
LITERATURE CITED

Amman, G.D.; McGregor, M.D.; Cahill, D.B. 1977. Guidelines for reducing losses

of lodgepole pine to the mountain pine beetle in unmanaged stands in the Rocky Mountains. USDA Forest Service, Gen. Tech. Rep. INT-36. Intermountain Forest and Range

Experiment Station, Ogden, Utah. 19p.

Berryman, A.A.; Wright, L.C. 1978. Defoliation, tree condition, and bark

beetles. In the Douglas-fir tussock moth: a synthesis. M.H. Brookes, R. W. Stark, R. W.

Campbell, eds. USDA Forest Service, Tech. Bull. 1583. p. 81-81.

Furniss, M.M. 1962. Infestation patterns of Douglas-fir beetle in standing and

windthrown trees in southern Idaho. J. Econ. Entomol. 55:486-491.

Furniss, M.M. 1979. An annotated bibliography of the Douglas-fir beetle

(Dendroctonus pseudotsugae Hopkins). USDA Forest Service. Gen. Tech. Rep. INT-48.

Intermountain Forest and Range Experiment Station, Ogden, Utah. 40p.

Furniss, M.M.; Kline, L.N.; Schmitz, R.F.; Rudinsky, J.A. 1972. Tests of three

pheromones to induce or disrupt aggregation of Douglas-fir beetle in live trees. Ann. Entomol. Soc. Am. 65:1227-1232.

Furniss, M.M.; McGregor, M.D.; Foiles, M.W.; Partridge, A.D. 1979. Chronology

and characteristics of a Douglas-fir beetle outbreak in northern Idaho. USDA Forest Service,

Gen. Tech. Rep. !NT-59. Intermountain Forest and Range Experiment Station, Ogden,

Utah. 19p.

Furniss, M.M.; Livingston, R.L.; McGregor, M.D. 1981. Development of a. stand

susceptibility classification for Douglas-fir beetle. In Ha.za.r'd-rating systems in forest insect

pest management: symposium proceedings. R.L. Hedden, S.J. Barras, J.E. Coster, eds. USDA Forest Service, Gen. Tech. Rep. WO-27. Washington DC. p. 115-128. '

Furniss, R.t. 1941. Fire and insects in the Douglas-fir region. USDA Forest

Service, Washington DC. Fire Control Notes 5:211-213.

McMullen, L.H.; Atkins, M.D. 1962. On the flight and host selection of the

Douglas-fir beetle, Dendroctonus pseudotsugae Hopk. (Coleoptera:Scolytidae). Can. Entomol. 94:1309-1325.

Rudinsky, JA 1966 Host selection and invasion by the Douglas-lir beetle,

Dendroctonus pseudotruga, Hopkins, in ,aast.! Douglas-Ii, forests Can. Entomol 9898-

III

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Schmid, J .M.; }"rye, R.H. 1916. Stand ratings for spruce beetles. USDA Forest

Service, Res. Note RM-309. Rocky Mountain Forest and Range Experiment Station, Fort

Collins, Colorado. 4p. -

Vite, J.P.j Rudjnsky, J .A. 1962. Investigations on the resistance of conifers

to bark beetle infestation. XI Int. Congr. Entomol., Vienna. 1960. Sonderdr. Verh. ll:219- 225. .

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