United States Department of Agriculture / Forest Service

Rocky Mountain Research Station

Research Paper RMRS-RP-68

November 2007

The Influence of Partial 

Cutting on Mountain Pine 

Beetle-caused Tree Mortality 

in Black Hills Ponderosa 

Pine Stands

J.M. Schmid, S.A. Mata, R.R. Kessler, and J.B. Popp
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Schmid, J.M.; Mata, S.A.; Kessler, R.R.; Popp, J.B. 2007. The influence of partial cutting on mountain pine 

beetle-caused tree mortality in Black Hills ponderosa pine stands. Res. Pap. RMRS-RP-68 Fort Collins, 

CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 19 p.

Abstract

Ponderosa pine stands were partially cut to various stocking levels at five locations, periodically surveyed, and 

remeasured during the 20 years after installation. Mean diameter generally increased 2 inches over the 20-year 

period on most partially cut plots and less than 2 inches on unmanaged controls. Average diameter growth for 

diameter classes in partially cut plots was generally significantly greater than average diameter growth for the 

same diameter classes in uncut control plots. Basal area increased 20 to 40 ft2

/acre in partially cut plots and 5 to 

21 ft2

/acre in unmanaged controls at four locations over a 20-year period. Beetle-caused mortality ranged from 

0 to 51 percent of the trees in partially cut plots and from 1 to 77 percent of the trees in control plots although 

mortality was generally <8 percent in partially cut plots. Beetles attacked trees ranging from 8 to 18 inches in 

partially cut stands and from 7 to 19 inches in unmanaged stands. Beetles did not exclusively attack >16-inch 

diameter trees, so some trees >16 inches may be selected as leave trees. However, if an infestation persisted in 

a stand, trees in diameter classes >16 had the highest percentage mortality. The effectiveness of partial cutting 

for minimizing mountain pine beetle-caused mortality is influenced by: residual stocking level, size of the partial 

cut, amount of time since the area was cut, and proximity of beetle populations. Partial cuts of <10 acres may 

not minimize beetle-caused mortality if the cut stands are surrounded by unmanaged forest. Management to 

minimize beetle-caused mortality should be considered the top priority in mature ponderosa pine stands.

Keywords: mountain pine beetle, partial cutting, ponderosa pine

Authors

J.M. Schmid, retired Entomologist, Rocky Mountain Research Station, Fort Collins, CO

S.A. Mata, retired Entomologist, Rocky Mountain Research Station, Fort Collins, CO

R.R. Kessler, Consulting Forester, 25240 Ridge View Road, Custer, SD

J.B. Popp, Forestry Technician, Rocky Mountain Research Station, Fort Collins, CO

Cover photo: October 2007 photo of the southside of Odakota Mountain on the 

Black Hills National Forest. Note the abundant number of beettle-killed spots in the 

unmanaged stands above and below the partially cut area and the general lack of 

beettle-killed spots in the partially cut area.
Acknowledgments

R. Cain, Forest Health Management, Lakewood, CO; B. Cook, Timber Staff Officer, Black Hills National Forest, 

Custer, SD; and K. Gibson, Forest Health Management, Missoula, MT, provided critical and helpful reviews of the 

initial draft of the manuscript.

R. King, Biometrican, Rocky Mountain Research Station, Ft. Collins, CO, provided statistical and critical review of 

the manuscript. Over the past 20 years that Mata and Schmid have prepared manuscripts, King has consistently 

provided beneficial reviews that enhanced their manuscripts. For that, they cannot thank him enough.

Contents

Introduction................................................................................................................1

Methods......................................................................................................................1

Plot Information ...................................................................................................2

Bear Mountain 1 Plots .................................................................................2

Border Plots .................................................................................................3

Brownsville Plots..........................................................................................3

Crook Mountain Plots ..................................................................................3

C-C Plot .......................................................................................................3

Results and Discussion............................................................................................3

Diameter Growth .................................................................................................3

BM1 Plots ....................................................................................................4

BOR Plots ....................................................................................................4

BRN Plots ....................................................................................................5

CRK Plots ....................................................................................................6

Basal Area ...........................................................................................................6

MPB-caused Tree Mortality .................................................................................8

Number of MPB-attacked Trees by Year .............................................................9

MPB Population Level Definitions..............................................................10

Proposed MPB Population Level Definitions ............................................. 11

Tree Diameters Attacked by the MPB................................................................12

MPB Susceptibility Thresholds ..........................................................................13

Modifications in MPB Susceptibility Ratings ..............................................15

Management Implications.......................................................................................16

Partial Cutting ....................................................................................................16

Leave Tree Selection.........................................................................................17

Management of Ponderosa Pine Stands...........................................................17

Literature Cited........................................................................................................18

USDA Forest Service RMRS-RP-68. 2007 1

Introduction

The mountain pine beetle (Dendroctonus ponderosae Hopkins) is well known as an important mortality 

agent in unmanaged ponderosa pine (Pinus ponderosa Lawson) and lodgepole pine (P. contorta Douglas) 

stands (Furniss and Carolin 1977). Mountain pine beetle 

(MPB) epidemics have killed millions of trees in ponderosa pine (PP) stands in the Black Hills (see Blackman 

1931, Thompson 1975). Since Thompson’s 1975 report, 

additional epidemics have occurred in each subsequent 

decade. The most recent epidemic, beginning about 1997, 

has caused extensive tree mortality throughout the Black 

Hills with annual mortality averaging about 300,000 

trees per year in 2001, 2002, and 2003 (see Johnson and 

others 2001; Johnson and Long 2003; Schaupp and others 2004). That MPB epidemic continues and shows no 

sign of subsiding.

Most MPB epidemics have originated in even-aged, 

high density stands. Although numerous factors contribute to epidemic MPB populations, over-stocked 

PP stands are the major contributor to MPB epidemics 

(Thompson 1975). Stands with basal areas exceeding 

150 ft2

/acre and average diameters >8 inches are considered highly favorable for MPB epidemics (Sartwell and 

Stevens 1975).

In 1984, the Rocky Mountain Forest and Range 

Experiment Station began a study to determine the relationship between stand density and MPB-caused tree 

mortality in lodgepole (LPP) and PP stands in the central 

Rockies and the Black Hills. The study was conducted 

by establishing sets of plots in susceptible LPP stands 

in Colorado and Wyoming, and PP stands in the Black 

Hills. Beginning in 1985 and continuing for the next 8 

years, sets of plots were established on the Black Hills 

National Forest (BHNF) in South Dakota. This paper reports on diameter and basal area growth, MPB-caused 

mortality by stocking level and by year, and MPB tree 

selection in partially cut and associated unmanaged PP 

stands at five locations in the Black Hills.

Methods

When the study began, even-aged, single-storied 

stands with basal areas (BA) >150 ft2/acre and average 

diameters at breast height (DBH) >8 inches were considered the most susceptible to MPB infestation. Therefore, 

stands with these characteristics were considered most 

preferable for the study. Because of the density of such 

stands, trees with diameters <4 inches were generally 

absent and seedlings, when present, were usually found 

around openings.

Sets of growing stock level (GSL1) plots were installed in susceptible-sized PP stands in the Black Hills 

of South Dakota (Schmid and others 1994). Each set of 

plots usually consisted of four 2.47-acre plots (in other 

words, 10 acres)—three plots partially cut to different 

GSLs and a fourth plot left uncut to serve as a control and 

to represent the unmanaged stand condition. Hereafter, 

we use “control” and “unmanaged” interchangeably, so 

the reader should understand that control refers to the 

unmanaged forest condition. Individual plots within a 

set were generally in the form of a square 100m x 100m 

or a rectangle 80m x 125m.

Although stands with BAs >150 ft2/acre and average 

diameters >8 inches were considered ideal, it became 

apparent that these BA and average diameter characteristics were rarely uniform in 10-acre parcels (in other 

words, for all four plots in a set). One or two plots in a 

set may have occasionally had the initial BA <150 ft2

/

acre or an average DBH <8 inches. Further, as the study 

progressed, pertinent information on the stand density/

MPB relationship appeared to be available from stands 

partially cut under BHNF management plans so a single plot was installed at one location. The C-C plot is 

the exception to the study’s general design of four plots 

per location because only one 2.47-acre plot was established at the C-C location. See separate sections for each 

specific area for more details and exceptions to general 

design.

When the plots were installed, the central 1.235 

acres of each plot was designated as the central inventory plot (CIP). Diameters for all trees >3 inches within 

the CIP were measured at breast height (DBH) to the 

nearest 0.1 inch. DBH and information on the presence 

or absence of MPB, crown form, defects, and diseases 

were also recorded. Following inventory of each CIP, 

GSL, BA, and quadratic mean diameter were calculated. 

Initially, GSLs for plots to be partially cut at each location were assigned on the basis of site index—GSLs of 

60, 80, and 100 when site index was <65, and 80, 100, 

and 120 when site index was >65. Because stand BAs 

were rarely uniform throughout the 10 or more acres in 

the various locations, lower post-cutting stocking levels 

1

 Growing Stock Level (GSL) equals BA when average diameter 

is ≥10 inches. Because GSL and BA are equal when average 

diameter is ≥10 inches, we use GSL and BA interchangeably. 

Although the GSL method is outmoded, the plots were installed 

using it so the results are reported in a like manner.
2 USDA Forest Service RMRS-RP-68. 2007

(GSL 60, GSL 80) were assigned in some instances to 

plots where pre-cutting BA was <150 ft2/acre.

Leave trees within cut plots were selected on the basis 

of DBH, spacing, crown development, and visually apparent good health. Tree selection emphasized leaving 

the best and largest trees as evenly spaced as possible. Smaller diameter trees (<6 inches) were generally 

marked for cutting and eliminated during partial cutting. 

The marking crew tried to leave the GSL for each partially cut plot within +1 ft2

/acre of the designated level 

(for example, a GSL 100 stand would be between 99 and 

101). Metal tags were placed on the designated leave 

trees in the CIP to facilitate record keeping in regard to 

MPB infestation and the determination of individual tree 

growth in subsequent years. Trees in the CIP provided 

growth information and were the basis for DBH and BA 

growth statements for each 2.47-acre plot. When the diameter measurement at remeasurement was less than the 

preceding measurement, we assigned zero growth to that 

tree rather than a negative growth value, because we believe the difference was due to measurement error rather 

than negative growth. Trees dying during the period prior to remeasurement were not included in calculations 

of average DBH and BA at remeasurement.

The remaining 1.235-acre area of each plot surrounding the CIP (in other words, buffer strips) was marked 

and cut to the same GSL as within the CIP. Leave trees 

in the buffers were selected on the same basis as those 

within the CIP but were not tagged. The buffers were 

established in hopes of mitigating mortality caused by 

MPBs emigrating from adjacent plots into plots (treatments) that might not have otherwise occurred.

Subsequent to installation and cutting, plots were 

surveyed for MPB activity and other mortality-causing 

events. Surveys were conducted annually or at 2- to 

3-year intervals depending on MPB activity during the 

previous survey. All trees in the plots were examined for 

the presence of MPB attacks. Trees with MPB attacks 

were classified as “successfully attacked” (tree killed) 

or “pitchout” (a tree that has external evidence of MPB 

attacks, but usually survives the attacks). Our definition 

of pitchout includes trees with attacks on all sides of the 

bole and trees with attacks on just one side of the bole 

(strip attacks). Attacked trees were examined the following year to verify the classification. However, statements 

on the number of MPB-attacked trees per plot and per 

1-inch diameter class are derived only from surveys of 

the CIPs.

Sets of plots were generally remeasured 10 and 

20 years after installation. BAs and quadratic mean diameters were calculated. After the first remeasurement, 

partially cut plots were remarked, at which time GSLs 

for some sets of plots were increased by 10 ft2

/acre (for 

example, a GSL 60 was increased to GSL 70, and so 

forth). GSLs of partially cut plots were increased because we wanted to learn more about the susceptibility 

of stands with GSLs between 80 and 120.

With one exception, partial cutting usually occured 1 

to 2 years after plot installation and the first remeasurment. Thus, diameter and BA growth for the first and 

second decades after installation reflects stand growth 1 

to 2 years at the GSL existing when marked and 8 to 9 

years at the GSL after cutting.

Diameter measurements at installation were sorted 

into 1-inch diameter classes. Each 1-inch class ranged 

from 0.4 less than the specific diameter to 0.5 more than 

the diameter (in other words, the 9-inch class ranged 

from 8.6 to 9.5). One-way analysis of variance was used 

to determine if arithmetic mean DBH growth in the various diameter classes varied significantly among GSLs 

within each diameter class at each location and among 

diameter classes within each GSL at each location. If 

significant variation was found, Tukey’s multiple comparison procedure was used to determine which means 

were significantly different, alpha = 0.05. We did not analyze growth rates at the C-C plot because only one plot 

was present and comparison of the growth rates between 

different stocking levels could not be made.

The number of MPB-attacked trees (successfully attacked and pitchouts) were determined for each 1-inch 

diameter class in each plot and then inserted in a tree 

distribution table for the plot to show the distribution of 

MPB-attacked trees by diameter class. DBH was estimated for the year that each tree was attacked.

The number of successfully attacked trees (pitchouts 

excluded) in each plot was compared against the number 

of live trees in the same plot after installation to determine the percent of MPB-caused tree mortality during 

the 20-year life of the plot. For control plots, the number 

of live trees equaled the number recorded during the initial inventory when the plots were installed. For partially 

cut plots, the number of live trees equaled the number of 

residual trees left after tree selection and marking was 

initially completed.

Plot Information

Bear Mountain 1 Plots

The Bear Mountain 1 (BM1) plots were established 

in June 1986. Three plots were partially cut via horse 

logging to GSL 60, 80, and 100 in June and July 1987, 

while the fourth plot was left uncut at GSL 155. Plots 

were remeasured in late August 1997 and in September 

2006. Stocking levels for the GSL 60, GSL 80, and GSL 
USDA Forest Service RMRS-RP-68. 2007 3

100 plots were increased 10 ft2/acre when they were 

remarked and cut again in 2000. The BM1 plots were 

surrounded by unmanaged stands with densities and tree 

sizes estimated to be about the same as the control plot.

Border Plots

The Border plots (BOR) were established in May 

1986 and were cut in July 1987. Partially cut plots were 

established at GSL 60, 80, and 100. The GSL 60 and 

GSL 80 plots were superimposed on a stand that had 

been previously cut to about BA 80. Plots were remeasured in August 1997 and September 2006. The partially 

cut plots were re-cut in October 1998, at which time the 

GSLs were increased to GSL 70, 90, and 110. The plots 

are surrounded by BHNF that was cut prior to the establishment of the plots. The 5 acres used for the GSL 60 

and GSL 80 was part of this cut. For more information 

on plot location and history, see Obedzinski and others 

(1999).

Brownsville Plots

The Brownsville plots (BRN) were established in 

September 1985. Three plots were cut to GSL 60, 80, 

and 100 in May 1986, while the fourth plot was left uncut 

at GSL 146. Plots were remeasured in September 1995 

and September 2005. GSLs for the GSL 60, 80, and 100 

were raised to GSL 70, 90, and 110, respectively, before 

the plots were scheduled to be re-cut in October 1998. 

The plots are bordered by BHNF land on the west, north, 

and east sides and by an undesignated gravel road on the 

south side. The BHNF land surrounding the plots was 

cut soon after the plots were cut, while the land across 

the road to the south is private and has not been cut.

Crook Mountain Plots

The Crook Mountain plots (CRK) were established in 

March 1985 and were cut in December 1986. Partially 

cut plots were established at GSL 80, 100, and 120 with 

the GSL 120 plot being 20 ft2

/acre greater than the highest GSL in most sets of PP plots established at that time. 

Loggers did not cut all trees marked for cutting on the 

GSL 80 and 100 so those plots actually had GSLs 3 ft2

/

acre greater than our usual upper limit. These trees were 

not incorporated in the GSL values and growth results 

in Obedzinski and others (1999), but are incorporated in 

the GSL values for 1986 and 1996 in this report.

Plots were remeasured in September 1996 and 

September 2006. The partially cut plots were re-cut to 

their designated level in October 1998. Trees left by loggers in 1986 were cut during the second cutting. The 

plots are surrounded by BHNF land on the west and 

north sides and private land on the east and south sides. 

Surrounding BHNF land was cut at the same time the 

plots were cut as part of the Nasty Timber sale, while 

the private land has not been cut. For more information 

on plot location and history, see Obedzinski and others 

(1999).

C-C Plot

The C-C plot was established in 1985 in a stand previously partially cut in a BHNF commerical timber sale 

in 1983. The plot was remeasured on May 16, 1996, 

and on May 15, 2006. It has not been re-cut since it was 

established. In contrast to other sets of plots, only one 

2.47 acre plot was established. The plot was subdivided 

into 10 subplots of equal size. All trees within the plot 

were inventoried and tagged. Analysis of tree inventories for each subplot provides information on variability 

of GSL and BA within the 2.47 acres. The plot is bordered by BHNF on all sides. Lands on the south, west, 

and north sides were cut as part of the 1983 timber 

sale. The east side of the plot is bordered by a 100- to 

200-ft wide strip of uncut PP that separates the plot from 

Highway 385.

Results and Discussion

Diameter Growth

Quadratic mean diameters generally increased about 

2 inches or more over the 20-year periods in partially cut 

plots and <2 inches in control plots (table 1). Part of the 

increase in mean diameters in partially cut plots during 

the second decade resulted from the second cutting that 

occurred after the 10-year remeasurement. Those cuttings generally removed smaller diameter trees, which 

increased mean diameter while maintaining desired GSL 

levels. The decrease in mean diameter on the BM1 control plot from 10 years versus 20 years (table 1) resulted 

from a MPB epidemic. As the epidemic progressed, percent mortality was greater in the larger diameter classes 

so mean diameter decreased.

The interaction between diameter growth and GSL 

was significant in BOR and BRN plots, marginally insignificant in BM1 plots, and insignificant in CRK plots. 

This interaction indicates variation in growth patterns 

for diameter classes among GSLs. With minor exceptions, the growth patterns were:

1) Average diameter growth was not significantly different among diameter classes within each partially 

cut GSL,

2) Average diameter growth was significantly different 

among diameter classes in control (unmanaged) 
4 USDA Forest Service RMRS-RP-68. 2007

plots with the greater rates being in the larger diameter classes, and

3) Average diameter growth in each specific diameter 

class was generally greater in partially cut plots than 

in controls.

BM1 Plots

Average diameter growth in the partially cut plots 

for the 20 years was >2 inches in all diameter classes 

except for two classes in the GSL 60/70 that were represented by only one tree (table 2). Average diameter 

growth in diameter classes in the GSL 60/70 generally 

exceeded 3 inches, while average diameter growth in diameter classes in the control was generally <1.5 inches 

(table 2).

Average diameter growth for the 20 years was not 

significantly different among diameter classes within 

each GSL. For diameter classes 7 to 11 inches, average 

diameter growth was significantly greater in partially 

cut plots than in the same diameter classes in the control. Diameter growth in the 12-inch class could not be 

compared between the partially cut plots and the control because there were no 12-inch trees in the control. 

Average diameter growth for the 13-inch class was not 

significantly different between partially cut plots and the 

control.

BOR Plots

Average diameter growth in partially cut plots for the 

20 years was >2.6 inches in all diameter classes except 

the 15-inch class in the GSL 100/110 that had only one 

Table 1. Quadratic mean diameters by GSL for the Bear Mountain 

1, Border, Brownsville, Crook Mountain, and C-C plots at installation and 10 years and 20 years after installation.

Location Installation 10 years 20 years

Bear Mountain 1

GSL 60/70 11.0 12.6 14.3

GSL 80/90 10.1 11.2 13.0

GSL 100/110 10.5 11.5 12.4

Control 10.0 10.6 10.3

Border

GSL 60/70 10.9 13.1 15.0

GSL 80/90 10.8 12.9 14.7

GSL 100/110 10.7 12.3 13.7

Control 8.9 9.8 10.5

Brownsville

GSL 60/70 12.4 13.8 15.4

GSL 80/90 11.5 12.5 13.6

GSL 100/110 12.8 13.5 14.7

Control 12.7 13.2 13.4

Crook Mountain

GSL 80 13.7 15.3 17.1

GSL 100 11.9 12.8 14.2

GSL 120 13.7 14.9 16.6

Control 12.6 13.3 14.4

C-C Plot

GSL 80 12.8 13.8 14.9

Table 2. Diameter growth by 1-inch diameter class for the Bear Mtn. 1 plots for the 20 years following installation. 

Under each GSL, N equals the number of trees used in calculating mean diameter for each diameter class.

GSL 60/70 GSL 80/90 GSL 100/110 Control

Diameter N X+S.D. N X+S.D. N X+S.D. N X+S.D.

5 1 0.8

6 1 0.6

7 1 3.1 1 2.6 11 0.6+0.4

8 6 3.0+0.8 10 2.6+0.4 15 2.0+0.5 15 1.1+0.4

9 16 3.1+0.5 15 2.9+0.5 19 2.1+0.7 18 1.2+0.7

10 22 3.4+0.6 15 2.5+0.5 21 2.5+0.7 16 1.2+0.5

11 20 3.3+0.6 14 2.4+0.6 16 2.6+0.9 6 1.4+0.9

12 15 3.0+0.6 7 2.6+0.4 6 2.4+0.6

13 2 2.6+0.9 3 2.6+0.3 5 2.2+1.3 4 2.1+0.7

14 3 2.9+0.8 2 3.2+0.4 1 2.7

15 2 3.6+0.1

16 1 1.3

17 1 2.7

18 1 2.7

19

20 1 1.0 
USDA Forest Service RMRS-RP-68. 2007 5

tree (table 3). Diameter growth in the GSL 60/70 and GSL 

80/90 exceeded 3.3 inches in all diameter classes (table 3). 

Average diameter growth in the control was <2 inches in 

all diameter classes except in the 14-inch class.

Average diameter growth for the 20 years was generally not significantly different among diameter classes 

within each partially cut GSL except in the GSL 60/70 

where growth in the 9-inch class was significantly greater than in the 13-inch class, and in the GSL 80/90 where 

growth in the 10-inch class was significantly greater 

than in the 12-inch class. Average diameter growth in 

the control was significantly greater in diameter classes 

>9 inches than in diameter classes <8 inches.

BRN Plots

Average diameter growth in partially cut plots for the 

20 years was >1.7 inches in all diameter classes except 

for a single tree in the 16-inch class in the GSL 80/90 

(table 4). Diameter growth in the GSL 60/70 averaged 

>2.8 inches in all diameter classes. Average diameter 

growth in the control was <1.9 inches in all diameter 

classes, but most classes grew <1.6 inches (table 4).

Table 4. Diameter growth by 1-inch diameter class for the Brownsville plots for the 20 years following installation. Under each GSL, N equals the number of trees used in calculating mean diameter for each 

diameter class.

GSL 60/70 GSL 80/90 GSL 100/110 Control

Diameter N N+S.D. N X+S.D. N X+S.D. N X+S.D.

6 4 0.3+0.6

7 1 0.0

8 4 2.3+0.2 3 0.8+0.6

9 11 2.3+0.6 3 0.3+0.3

10 2 2.8+0.8 22 1.8+0.6 3 2.4+0.3 11 0.8+0.5

11 14 2.9+0.6 35 1.9+0.6 21 1.7+0.6 23 1.2+0.6

12 28 2.9+0.6 29 2.0+0.5 39 1.7+0.6 37 1.2+0.5

13 21 2.8+0.6 19 2.4+0.7 33 1.8+0.5 33 1.4+0.6

14 11 2.9+0.5 5 2.0+0.5 23 2.0+0.5 26 1.4+0.5

15 2 2.9+0.9 2 1.8+0.9 11 1.9+0.7 15 1.6+0.5

16 1 1.2 3 2.0+0.5 13 1.9+0.7

17 1 2.5 1 1.7

18

19 1 0.7

Table 3. Diameter growth by 1-inch diameter class for the Border plots for the 20 years following installation. Under each GSL, N equals the number of trees used in calculating mean diameter for each diameter 

class.

GSL 60/70 GSL 80/90 GSL 100/110 Control

Diameter N X+S.D. N X+S.D. N X+S.D. N X+S.D.

3 2 0.4+0.0

4 6 0.4+0.5

5 14 0.2+0.2

6 38 0.4+0.5

7 1 3.3 57 0.8+0.5

8 5 4.1+0.5 6 3.7+1.1 13 2.6+0.8 79 1.0+0.6

9 15 4.6+1.4 20 4.0+0.5 28 2.9+0.7 86 1.4+0.6

10 21 4.3+0.8 26 4.0+1.0 28 3.1+0.8 70 1.4+0.6

11 19 4.0+0.8 22 3.7+0.7 29 2.3+0.9 44 1.6+0.5

12 19 3.7+1.1 23 3.3+0.7 20 2.6+0.8 35 1.7+0.6

13 10 3.4+1.2 17 3.5+1.0 18 2.8+1.0 13 2.0+0.5

14 4 3.5+0.5 12 2.6+1.1 5 2.4+0.6

15 1 3.7 1 1.6 4 1.8+1.1

16
6 USDA Forest Service RMRS-RP-68. 2007

In partially cut plots, average diameter growth was 

not significantly different among diameter classes in 

each GSL except for the GSL 80/90 where growth in the 

13-inch class was greater than in the 10-inch class. In the 

control plot, average diameter growth in the 6-, 9-, 10-, 

and 12- inch classes were significantly less than in the 

16-inch class.

Average diameter growth in specific diameter classes in partially cut plots varied with respect to average 

diameter growth in the control. For the 10- to 14-inch 

diameter classes, diameter growth in the partially cut 

plots was generally significantly greater than in the control. For the 15- and 16-inch diameter classes, average 

diameter growth was not significantly different than in 

the control.

CRK Plots

Average diameter growth in partially cut plots for the 

20 years was generally >2 inches in all diameter classes 

(table 5). Diameter growth in the GSL 80 was >2.7 inches in all diameter classes except for the 2.4-inch growth 

of the lone 7-inch tree. Average diameter growth in the 

control was <1.8 inches.

In partially cut plots, average diameter growth was 

not significantly different among diameter classes in 

each GSL. Average diameter growth among diameter 

classes in the control was significantly less in the 4- and 

5-inch classes versus the 12- and 15-inch classes.

Comparisons of average diameter growth within specific diameter classes in partially cut plots to diameter 

growth in corresponding diameter classes in the control 

produced mixed results. In the 7- and 8-inch classes, average diameter growth in GSL 100 was greater than in 

the control. In the 10- to 17-inch classes, average diameter growth in the GSL 80 was greater than in the control. 

In the 18- and 19-inch classes, no significant difference 

existed between diameter growth rates in the partially 

cut plots and the control.

Basal Area

BA changed variously among locations and among 

GSLs within locations for the 20-year period (table 6). BA increased at all locations during the first 

decade with increases ranging from 9 to 18 ft2

/acre 

in partially cut plots and from 9 to 19 ft2

/acre in the 

controls. BA in the BM1 control increased more than 

its respective partially cut plots. This greater increase 

was probably due to the greater number of trees existing on that plot—almost twice as many as on the 

respective GSL 80/90.

During the second decade, BAs generally increased 

in plots at the BOR, BRN, CRK, and C-C plot locations, but decreased in three BM1 plots. BA increases 

in the partially cut plots ranged from 10 to 26 ft2

, while 

BAs in the respective controls increased ≤10 ft2

/acre or 

decreased (table 6). In the BM1 plots, the GSL 60/70 

increased 10 ft2

/acre, but the GSL 80/90, 100/110, and 

control all decreased below installation levels because 

of MPB-caused mortality.

Table 5. Diameter growth by 1-inch diameter class for the Crook Mountain plots for the 20 years following 

installation. Under each GSL, N equals the number of trees used in calculating the average diameter for 

each diameter class.

GSL 80 GSL 100 GSL 120 Control

Diameter N X+S.D. N X+S.D. N X+S.D. N X+S.D.

4 6 0.3+0.2

5 6 0.3+0.4

6 1 1.3 7 0.8+1.0

7 1 2.4 7 2.1+0.6 4 0.6+1.0

8 8 2.7+0.4 1 0.0

9 11 2.0+0.8 1 2.4 1 0.8

10 2 3.2+1.3 12 2.1+1.1 4 2.0+1.1 3 0.3+0.4

11 3 3.4+0.2 21 2.0+1.0 5 1.9+0.8 11 1.2+0.7

12 10 3.0+1.1 19 2.0+0.9 7 2.9+0.5 26 1.5+0.9

13 14 2.9+0.7 23 2.1+0.7 24 2.6+0.8 31 1.5+0.6

14 17 2.9+0.8 15 2.0+0.6 30 2.5+0.9 34 1.5+0.7

15 17 3.1+1.0 9 2.6+0.8 13 2.4+0.9 30 1.6+0.6

16 8 3.4+1.1 5 2.3+0.6 20 2.5+1.0 9 1.5+0.4

17 4 3.0+1.0 1 2.1 2 1.8+0.7 8 1.5+0.6

18 1 2.7 1 3.2 1 1.7 4 1.8+0.3

19 1 2.2 1 3.3 3 1.6+0.6
USDA Forest Service RMRS-RP-68. 2007 7

The reader should realize that BAs in the partially cut 

plots at the BM1, BOR, BRN, and CRK locations increased/decreased more in the second decade than can 

be calculated from table 6 because the partially cut plots 

at those locations were cut back to lesser levels after the 

first remeasurement (see methods). Thus, for example, 

reduction of the BM1 GSL 60 from 76.8 to about 70 ft2/

acre would indicate that this plot increased about 10 ft2/

acre (80.7 to 70 ft2/acre) during the second decade rather 

than the 3.9 ft2

/acre as calculated from table 6.

Over the 20 years since installation, BAs in the partially cut plots increased about 20 to 40 ft2

/acre, except 

in the BM1 GSL 80/90 and 100/110 where MPB-caused 

mortality decreased the BAs to below the designated levels (table 6). Simultaneously, BA increases in the BOR, 

BRN, and CRK control plots ranged from 5 to 21 ft2/

acre while the BM1 control decreased to 34 ft2/acre. 

Increases in basal area resulted from growth of the 

residual trees and not from ingrowth. Ingrowth was not 

a contributing factor for BA increases because trees 

<6 inches were usually cut, saplings were generally absent on the plots except for the BRN GSL 60/70 and the 

CRK GSL 80 after 20 years, and we did not measure 

trees <3 inches.

The BM1 plots showed the most dramatic change 

in BAs from the first 10 years compared to the second 

10 years. During the first decade, increases in BAs were 

as good or better than at the other locations. During the 

second decade, the MPB epidemic caused BAs to decrease more than in plots at other locations with BAs 

in the BM1 GSL 80/90, 100/110, and control decreasing 40, 59, and 140 ft2

/acre, respectively. As noted in 

the previous paragraph, decreases were probably greater 

than can be computed from table 6.

The substantial decrease in BA in the BM1 GSL 80/90 

and 100/110 can be misleading from the MPB susceptibility standpoint. As noted in Schmid and Mata (2005), 

the MPB-caused mortality was not uniformly distributed 

throughout the CIPs. Because some parts of the stand 

were unaffected, BAs in those areas exceeded 110 ft2

/

acre. Left to grow without subsequent management, the 

areas could reach the high susceptibility threshold (GSL 

120) relatively soon and thus become potential sites for 

MPB infestations.

BAs in the BRN partially cut plots increased during 

the second decade while the BA in the control decreased. 

The decrease in the BRN control was caused by an incipient MPB epidemic beginning in 1998.

During the second decade, BAs in the CRK plots were 

affected by weather events. Trees with trunks broken below the crowns were observed in all CRK plots, but most 

notably in the GSL 100 and control. This condition was 

attributed to snow/wind storms in 1998, 2001, and 2002. 

The northern Hills commonly receive wet snowstorms 

in the spring and early fall. The wet snow tends to accumulate on the crowns and when accompanied by strong 

winds, causes breakage of the trunk below the bottom of 

the crown. While the loss of the storm-damaged trees reduced the existing BAs and the potential increases in BA 

from annual growth on the damaged trees, BAs in the 

CRK plots were not impacted to the point where BAs 

decreased below their respective GSL at the beginning 

of the decade. However, the BA in the control was significantly impacted such that BA increased only 1.7 ft2

/

acre during the second decade as compared to the 14 ft2/

acre increase during the first decade (table 6).

BA in the C-C plot increased similarly to that for the 

BOR and BRN GSL 80s except BA increases were less 

than at those locations (table 6). More importantly from 

a MPB perspective, BAs within the subplots of the C-C 

plot ranged from 65 to 100 ft2/acre in 1985 and from 80 

to 126 ft2

/acre in 2006 (table 7). If BA 120 is accepted 

as the threshold for high susceptibility to MPB infestation (Schmid and others 1994), then a small part of the 

C-C stand, which presumably was uniformly cut to BA 

80, has become highly susceptible in <20 years. What 

Table 6. Basal Areas by GSL for the Bear Mountain 1, Border, 

Brownsville, Crook Mountain, and C-C plots at installation 

and 10 years and 20 years after installation.

Location Installation 10 years 20 years

Bear Mountain 1

GSL 60/70 60.7 76.8 80.7

GSL 80/90 80.8 98.4 48.9

GSL 100/110 101.5 117.3 58.0

Control 154.7 174.0 34.0

Border

GSL 60/70 60.1 76.9 88.1

GSL 80/90 80.1 97.7 113.2

GSL 100/110 98.3 108.2 124.1

Control 199.1 210.9 220.4

Brownsville

GSL 60/70 60.5 73.6 81.3

GSL 80/90 80.8 93.4 104.8

GSL 100/110 100.7 113.4 126.4

Control 146.1 155.3 150.1

Crook Mountain

GSL 80 84.1 100.2 99.3

GSL 100 104.0 116.4 119.2

GSL 120 119.1 136.8 131.2

Control 158.1 172.1 173.8

C-C Plot

GSL 80 83.6 92.9 102.6 
8 USDA Forest Service RMRS-RP-68. 2007

this means in terms of actual MPB infestation remains 

to be determined. However, this situation appears to be a 

smaller version of the BM1 plots wherein MPBs initially 

infested the most susceptible plot (for example, control) and then spread to adjacent partially cut plots that 

might otherwise have not incurred mortality. Because 

Olsen and others (1996) found MPB infestations were 

predominantly found where stand densities were higher, 

MPBs would most likely infest parts of the C-C stand 

with higher densities and then could cause considerable 

tree mortality in adjacent, less dense parts of the stand if 

the infestation persisted.

MPB-caused Tree Mortality

MPB-caused tree mortality ranged from 0 to 77 

percent per plot for the plots from the five locations 

(table 8). Mortality on the control plots ranged from 1 

to 77 percent (table 8) and the percent mortality in the 

BM1 control exceeded what McCambridge and others 

(1982) found for areas of heavy loss in Colorado’s Front 

Range. Mortality on the partially cut plots ranged from 

0 to 51 percent, but the range in mortality for partially 

cut plots was greatly influenced by what occurred in the 

BM1 plots. If percent mortality for BM1 partially cut 

plots is excluded, then percent mortality for other partially cut plots ranges from 0 to 8 percent (table 8).

By location, percent mortality was greater in the control than in the partially cut plots at BM1, BOR, and 

Table 7. Basal area per acre per 0.25 acre subplots within the 

2.47-acre C-C plot.

Subplot 1985 1996 2006

ft2

/acre 

1 94.2 99.1 108.7

2 84.2 90.5 90.9

3 90.7 104.9 108.6

4 79.6 91.6 101.2

5 65.7 76.8 89.8

6 78.8 90.3 106.8

7 67.4 73.5 80.1

8 100.4 112.5 125.8

9 74.6 86.5 101.6

10 90.8 103.0 112.0

C-C Plot 83.6 92.9 102.6

Table 8. Percent MPB-caused tree mortality by location/GSL for five locations. The data for the C-C plot is derived from 

a 2.47-acre plot, while data for all other locations/GSLs is derived from the CIP (1.25 acre) within each plot. Numbers of trees represent the number of live trees present after partial cutting was completed. Percent mortality in the 

Bear Mtn. 1 GSL 60/70 and 80/90 differs slightly from that presented in Schmid and Mata (2005) because a few trees 

thought to be successfully attacked in the 2004 survey were later determined to be pitchouts.

Location/GSL Number of trees Number of MPB-killed trees Percent mortality

Bear Mtn. 1

GSL 60/70 114 9 8%

GSL 80/90 180 91 51%

GSL 100/110 210 100 48%

Control 351 269 77%

Border

GSL 60/70 115 1 1%

GSL 80/90 155 4 3%

GSL 100/110 195 7 4%

Control 571 32 6%

Brownsville

GSL 60/70 89 2 2%

GSL 80/90 138 2 1%

GSL 100/110 140 0 0%

Control 206 28 14%

Crook Mtn.

GSL 80 101 5 5%

GSL 100 165 7 4%

GSL 120 143 5 3%

Control 224 2 1%

C-C Plot

GSL 80 231 11 5%
USDA Forest Service RMRS-RP-68. 2007 9

BRN locations but slightly less in the CRK control than 

in partially cut CRK plots (table 8). Mortality in the CRK 

control was slightly less because the MPB population 

was subsiding at that location when the plots were installed and only endemic MPB populations were present 

for the 20 years following cutting. Thus, mortality was 

limited to single tree infestations.

The BM1, BOR, and BRN locations were subjected to incipient epidemic and/or epidemic infestations 

in addition to endemic levels of tree mortality. The 

BM1, BOR, and BRN locations developed incipient 

epidemic/epidemic MPB populations during the second 

decade (tables 9, 10, 11), while an incipient epidemic 

population appeared to be developing in the C-C plot. 

Epidemic MPB populations existed at BOR and CRK 

locations when the plots were installed, but apparently 

were collapsing in the general area because high numbers of MPB-attacked trees were not evident 3 to 4 years 

after installation (tables 10, 12).

MPB-caused tree mortality at the BM1 location provides insight into the development of epidemics and 

the relative susceptibility of various stocking levels in 

2.47-acre partial cuts. As the epidemic arose in the Bear 

Mountain area, infestations first developed in the control 

(table 9) and in adjacent unmanaged stands. As the population increased, it spread from the control and adjacent 

unmanaged stands into the buffer strips of the partially 

cut plots even though those areas had reduced stocking 

levels. Two years later, MPB populations moved into the 

CIPs of the partially cut plots (table 9), especially in the 

GSL 80/90 and 100/110 where BAs approached or exceeded 120 ft2

/acre. Thus, partial cuts of 2.47 acres may 

not prevent substantial MPB-caused mortality if the cuts 

are conducted in an otherwise unmanaged forest and/or 

are cut to GSLs >100.

Number of MPB-attacked Trees by Year

From 1991 through 1996, MPB-attacked trees were 

not present on 13 of 17 plots or were limited to 1 to 

2 trees/plot/year on the remaining four plots at the 

five locations (tables 9 through 13). The lack of MPBattacked trees could primarily result from chance, as the 

1.25-acre CIPs may be too small to detect endemic MPB 

populations. However, air temperatures dropped to <-5oF 

on October 30 and 31, and November 2 and 3, 1991, in 

Hill City, SD (Schmid and others 1993). The temperatures were not confined to Hill City but were present 

throughout the Black Hills. Thus, cold temperatures 

likely caused a decrease in MPB populations throughout 

the Hills as evidenced by the general absence of MPBattacked trees in the five locations.

The number of MPB-attacked trees (successful + 

pitchouts) per plot varied by location and year within each 

location. Numbers varied as MPB populations subsided 

or increased. During the first decade following cutting, 

the BOR and CRK locations had >3 MPB-attacked trees 

Table 9. Number of MPB-attacked trees by GSL by year for the Bear 

Mtn. 1 plots.

Year GSL 60/70 GSL 80/90 GSL 100/110 Control

1986

1987 1

1988 1

1989

1990

1991

1992

1993

1994

1995 1 1

1996

1997

1998 5

1999 7

2000 15

2001 1 2 15

2002 29 29 4

2003 8 2 65 215

2004 62 7 14

2005 21

Table 10. Number of MPB-attacked trees by GSL by year for the Border plots.

Year GSL 60/70 GSL 80/90 GSL 100/110 Control

1986 2

1987

1988 1 17

1989

1990 1

1991

1992

1993

1994

1995

1996

1997

1998 2

1999 2 1

2000

2001 1 1

2002

2003 1 1

2004 1 4

2005 1 3

2006 1 8
10 USDA Forest Service RMRS-RP-68. 2007

in at least one plot 1 or more years, while the number 

of MPB-attacked trees in the other 3 locations (BM1, 

BRN, and C-C plot) was 0 to 1 tree per year for all plots 

at each location (tables 9 through 13). Most of the BM1 

and BRN plots had single or no MPB-attacked trees and 

MPB-attacked trees were rarely observed in consecutive 

years (tables 9 and 11). During the second decade for 

the BM1, BOR, and BRN plots, the number of MPBattacked trees increased, especially in the controls where 

three or more trees per plot were evident in 2 or more 

consecutive years. Numbers increased in the C-C plot 

only during the last 2 years.

MPB Population Level Definitions

The number of MPB-attacked trees by year at the 

five locations provides data for further defining endemic 

and epidemic MPB population levels. MPB population 

levels are usually classified as endemic or epidemic. 

Endemic populations are low, relatively static numbers 

of an insect that cause essentially unnoticed or insignificant amounts of defoliation or tree killing (Graham 

and Knight 1965). Endemic MPB populations could be 

visualized as almost undetectable on a landscape basis. 

In contrast, epidemic populations, as evidenced by their 

damage rather than their actual numbers, cause readily noticed or significant amounts of tree damage on a 

landscape scale. Landscape vistas of a MPB epidemic 

are dotted with small and large groups of beetle-killed 

trees.

With respect to MPB populations, Sartwell and 

Stevens (1975) defined the lower limits of MPB outbreaks (= epidemics) as the group killing of three to five 

or more adjacent trees in a single year. Lessard (1982) 

further defined MPB population levels as:

Endemic: <1 infested tree per acre per year,

Increasing or Decreasing: >1 infested tree per acre per 

year or <10 percent of a stand infested over 3 years,

Epidemic: >10 percent of a stand infested over 

10 years.

The Sartwell and Stevens definition has contradictory and biological complications. The dictionary 

defines “outbreak” as a sudden increase in the numbers 

of a harmful organism. After defining the lower limits 

of MPB outbreaks, Sartwell and Stevens subsequently 

indicate that MPB outbreaks rarely develop suddenly. 

If the term is to be applied correctly, then either MPB 

populations must increase rapidly or a more suitable 

term should be used. Although outbreak and epidemic 

are used interchangeably, and epidemic has the same 

contradiction with respect to MPB population increases, 

epidemic seems the preferable term because it contrasts 

with endemic. More important biologically, their definition is stated in terms of MPB-killed trees for a single 

year. Our observations indicate that a single group of 

three MPB-killed trees may indicate the start of a MPB 

Table 11. Number of MPB-attacked trees by GSL by year in the 

Brownsville plots.

Year GSL60/70 GSL 80/90 GSL100/110 Control

1985

1986

1987 1

1988

1989

1990 1

1991

1992

1993

1994

1995

1996

1997 1 1 1

1998 1 1 6

1999

2000

2001 12

2002 4

2003 1 7

2004 2

2005

Table 12. Number of MPB-attacked trees by GSL by year for the 

Crook Mountain plots.

Year GSL 80 GSL 100 GSL 120 Control

1985 3 1 1

1986 4

1987

1988 3 1

1989 2 1

1990

1991

1992

1993

1994

1995

1996 2

1997 1

1998 1

1999 1

2000

2001 2 1

2002

2003 1

2004 1 2

2005

2006 1 1
USDA Forest Service RMRS-RP-68. 2007 11

epidemic if other such groups are simultaneously evident in surrounding and nearby stands. Alternatively, it 

may indicate a 1-year anomaly in the endemic condition 

if similar and/or larger groups are not evident either in 

surrounding and nearby stands or in succeeding years.

Lessard’s definitions are more suitable because they 

incorporate the time factor. However, defining endemic as <1 tree per acre per year may be unsuitable when 

large tracts are considered. Since endemic/epidemic 

populations are commonly judged on a landscape basis, 

Lessard’s definition may be met on a per acre basis, but 

the population level might be otherwise. For example, 

if five groups of five to seven trees per group are present on a tract of 40 acres, then the average number of 

MPB-infested trees would be <1 per acre. However, the 

presence of the five groups with five to seven trees per 

group would not be considered as endemic.

Lessard defines epidemic as the infestation of >10 

percent of the stand over 10 years. Three of the BM1 

plots had more than 10 percent of its trees infested 

in 4 years (tables 8 and 9). While the CIP of a plot is 

only 1.235 acres and may thusly represent only a small 

portion of the landscape, the level of mortality would 

nevertheless be classified as epidemic. In addition, 

MPB populations might cause significant tree mortality for a few years before suddenly decreasing. Should 

that situation be classified as endemic just because the 

infestation did not last 10 years?

Proposed MPB Population Level Definitions

While MPB population level definitions are usually 

generalizations because precise knowledge of population numbers is difficult to obtain, some improvements 

in the definitions can be made. Drawing from the previous definitions and using the frequency of MPB-attacked 

trees per year from our five locations, the following definitions are proposed:

Endemic: usually <1 but occasionally two MPBattacked trees per 5 or more acres per year. Most of 

the time, the number of MPB-attacked trees will be 

<1 tree per 10 or more acres. However, an endemic 

MPB population may attack two adjacent, narrowly 

spaced trees so two trees per 5 acres is recognized as 

being endemic. In endemic situations, one of the two 

trees will probably be a pitchout and pitchouts may 

be found more frequently than successfully attacked 

trees.

Incipient Epidemic: two or more groups of three 

to four MPB-attacked trees per group on 40 to 

320 acres for 2 to 3 consecutive years. The appearance of a single group of three or four infested trees 

in any particular year (for example, Sartwell and 

Stevens [1975] definition) may signal an incipient 

epidemic, but when considered over a landscape of 

20 to 50 acres, it might be a 1-year anomaly. The incipient level represents the transition from endemic 

to epidemic but recognizes that at the beginning 

of an epidemic, MPB populations do not usually 

increase rapidly because the number of trees per 

group increases slowly and infested groups have not 

coalesced.

Epidemic: several groups of four or more MPBattacked trees per group on 20 to 320 acres over 2 to 

3 consecutive years, especially if the number of trees 

per group is increasing and groups are coalescing. 

As for the incipient epidemic definition, the appearance of two to three groups on 50 acres for 1 year 

may be an anomaly, but their continued presence in 

succeeding years indicates otherwise. In contrast to 

the incipient epidemic condition where numbers of 

infested trees are increasing relatively slowly, the 

number of infested trees per group in specific stands 

in the epidemic condition may increase tenfold (as 

evidenced by increases in plots at the BM1 location).

Endemic MPB populations may be easily distinguished from epidemic MPB populations most of the 

time, but the transition from endemic to epidemic, 

which we call incipient epidemic, is difficult to ascertain and may be considered moot from a management 

Table 13. Number of MPB-attacked trees in the C-C plot by 

year.

Year MPB-attacked trees

1985 2

1986

1987

1988

1989

1990

1991

1992

1993

1994 1

1995 1

1996

1997 2

1998 1

1999 1

2000 1

2001

2002 1

2003 2

2004 5
12 USDA Forest Service RMRS-RP-68. 2007

perspective. However, epidemic MPB populations rarely develop rapidly (Sartwell and Stevens 1975), so the 

transition from endemic to epidemic is important to recognize because it provides managers with a grace period 

during which control activities could be initiated before 

substantial tree mortality occurs. The incipient epidemic 

stage represents a last chance for managers to minimize 

MPB-caused mortality.

Similarly, the transition from incipient epidemic to 

epidemic is also difficult to ascertain. However, the epidemic condition might be signified by the appearance 

of infested spots with greater than seven trees per spot, 

or when infested groups appear to be coalescing within 

a stand.

Tree Diameters Attacked by the MPB

MPBs attacked a range of diameter classes in partially cut and unmanaged stands (control plots). Diameters 

of MPB-attacked trees ranged from 8 to 18 inches in 

partially cut stands and from 7 to 19 inches in unmanaged stands (tables 14 through 18). No trees <8 inches 

were attacked in the partially cut stands and no trees 

<7 inches were attacked in the unmanaged stands. No 

trees <7 inches were attacked in the partially cut plots 

because trees <7 inches were generally cut during the 

initial cut.

During the first decade following plot establishment, 

diameters of all MPB-attacked trees in the partially cut 

plots were <15 inches except for two trees in the CRK 

GSL 100/110 that were >16 inches. Thus, 93 percent of 

all attacked trees were <15 inches.

During the second decade, the number of trees per 

diameter class shifted to higher diameter classes as trees 

grew (tables 14 through 18) and slightly greater numbers of trees >16 inches were attacked. The percent of 

MPB-attacked trees per diameter class varied by location. BM1 and BOR plots had >96 percent of the trees 

in diameter classes <15 inches. Some plots at BRN and 

CRK, and the C-C plot, had 25 to 100 percent trees <15 

inches. The differences in the percentage of trees attacked in the <15- versus >16-inch diameter classes in 

the first versus the second decade for BRN, CRK, and 

the C-C plot resulted because the number of attacked 

trees per plot in both diameter categories was relatively small and the number of trees in the larger diameter 

classes increased as trees grew. The differences were not 

attributed to a change in MPB tree selection behavior.

The partially cut and control BM1 plots had 97 percent or more of the MPB-attacked trees in the <15-inch 

diameter classes through 2006. This diameter class distribution of MPB-attacked trees matches that for the 

area of heavy MPB-caused tree mortality in Colorado’s 

Front Range as determined by McCambridge and others 

(1982). The diameter class distribution for the Bear Mtn. 

1 plots is similar to that of Lessard (1982) for epidemic 

conditions in the Black Hills, but not quite comparable 

because Lessard’s diameter range was 7 to 13 inches.

Table 14. Number of trees by 1-inch diameter class for the Bear Mtn. 1 plots. Numbers in parentheses represent the number of MPBattacked trees (successful and pitchouts) in the decade following the year of inventory. The number of MPB-attacked trees in some 

diameter classes may exceed the number of trees in the year of inventory because trees in lesser diameter classes grew into those 

classes before being attacked.

GSL 60/70 GSL 80/90 GSL 100/110 Control

Diameter 1987 1997 2006 1987 1997 2006 1987 1997 2006 1987 1997 2006

5 1

6 1 1. 1

7 5. 4. 4. 1. 21 12.(4) 5

8 9.(1) 2. 30. 2. 30. 5. 67 39.(21) 8

9 19. 6. 1 44.(1) 22. 34.(1) 29.(4) 2 82 74.(50) 14

10 26. 15. 1 44. 46.(20) 3 49. 30.(8) 15 68 73.(62) 18

11 23. 17. 5 30.(1) 47.(26) 10 49. 48.(19) 15 53 64.(49) 12

12 20. 26.(1) 15 18. 22.(18) 22 22. 43.(26) 13 28 37.(50) 8

13 3. 18.(1) 15 5. 20.(13) 11 16. 21.(18) 19 20 26.(31) 1

14 4. 15.(4) 22 4. 10.(10) 10 4. 19.(22) 11 3 11.(14) 2

15 2. 4.(2) 15 1. 4.(4) 5 2. 5.(4) 4 6 5.(9) 2

16 1. 2. 8 2.(2) 3 1.(2) 4 5.(2) 1

17 1. 3. 3 .(1) 2 1 1 .(3)

18 1. 1. 2

19 2 1.(1)

20 1. 2.

21 2
USDA Forest Service RMRS-RP-68. 2007 13

In the MPB literature, MPBs generally attack trees 

>7- to 8-inch DBH in PP and LPP stands. Trees of lesser diameters may be attacked, especially when they are 

intermixed with trees of larger diameter. MPBs killed 

3-inch diameter trees during an epidemic in the Front 

Range of Colorado (McCambridge and others 1982). In 

LPP stands, MPBs usually attack the largest diameter 

trees in a stand and then, if the infestation persists, attack 

progressively smaller diameter trees (Cole and Amman 

1969). This habit prompted researchers to investigate 

the potential of diameter-limit cutting—the cutting of 

all host trees with diameters greater than a specified 

diameter (for example, 10 inches)—as a means of minimizing MPB-caused tree mortality in LPP stands. While 

diameter-limit cutting reduced MPB-caused tree mortality in LPP (McGregor and others 1987), the residual LPP 

stands may be composed of mostly undesirable leave 

trees. In some quarters, this silvicultural treatment also 

raised speculation that the treatment was simply a justification for providing large diameter trees for the timber 

industry.

Diameter-limit cutting has not been a standard treatment in PP stands on the BHNF, and cutting large 

diameter PP to control MPB populations has been 

questioned with regard to some BHNF timber sales. In 

susceptible PP stands in this study, endemic and incipient 

epidemic MPB populations attacked a range of diameter 

classes and did not concentrate solely on the largest diameter classes (tables 14 through 18). Our results agree 

with Olsen and others (1996) who found MPBs did not 

exclusively attack large diameter trees in susceptible 

stands. However, as incipient epidemic MPB populations transition into epidemic populations, the percent of 

MPB-attacked becomes greater in the largest diameter 

classes (table 14) even though the general distribution of 

MPB-attacked trees is predominantly less than 15 inches. Based on this information, silvicultural treatments 

for unmanaged PP stands with endemic or incipient epidemic MPB populations need not be designed to remove 

only the largest trees nor predicated on reasoning that 

MPBs exclusively attack only the largest trees.

MPB Susceptibility Thresholds

When the GSL thresholds for rating the susceptibility of PP stands to MPB infestation were established in 

1994, the lower and upper limits of the moderate hazard level were derived primarily by default (Schmid 

and others 1994). The lack of MPB-caused mortality in 

GSLs between 80 and 120 restricted the definitiveness 

of the limits until future results from plots in GSLs ranging from 80 to 120 would validate or nullify the limits.

Upon first inspection, the number of MPB-attacked 

trees per year for each GSL at the four locations with 

multiple stocking levels (tables 9 through 12) suggests the upper limit for the moderately susceptible 

level (GSL 120) might warrant changing. The number 

of MPB-attacked trees in GSLs between 80 and 120 at 

the BOR and BM1 locations was similar to the numbers in GSLs <80 and even GSLs >120 in most years 

Table 15. Number of trees by 1-inch diameter class for the Border plots. Numbers in parentheses represent the number of MPBattacked trees (successful and pitchouts) in the decade following the year of inventory.

GSL 60/70 GSL 80/90 GSL 100/110 Control

Diameter 1986 1997 2006 1986 1997 2006 1986 1997 2006 1986 1997 2006

3 2. 1. 1.

4 19. 8. 6.

5 30. 21. 14.

6 1 59.(3) 28. 21.

7 1. 6 74.(3) 51.(1) 39.(1)

8 8 13. 20 1. 99.(4) 71.(2) 48.

9 20 29.(1) 41 10. 104.(6) 73. 56.

10 26 9 32. 9 38 20. 6 77.(1) 90.(1) 60.(2)

11 25 6 30.(1) 20 4. 35 33.(1) 12 48.(1) 62.(1) 64.(2)

12 21 27 6. 28.(1) 32 3.(1) 22 37.(3) 32 35. 44.(1) 62.(2)

13 13 27 10. 18. 27 23.(1) 18 24.(1) 27 15. 26. 38.(1)

14 1 20 20. 4. 25 23.(1) 12 21.(2) 33 5. 15. 20.

15 1 10 26. 13 31. 1 9.(1) 18 4. 6.(1) 14.

16 3 15. 5 24. 6. 9 3. 6.

17 1 9. 1 5. 1. 10 1. 2.

18 4.(1) 5. 3 2.

19 1
14 USDA Forest Service RMRS-RP-68. 2007

when MPB populations were endemic. As MPB populations increased, the number of MPB-attacked trees in the 

BOR GSL 100/110 increased just prior to the increase 

in the control, which suggests this GSL may be incorrectly rated as moderately susceptible. Similarly, the 

BM1 GSL 100/110 plot had rates of infestation similar 

to adjacent plots during the first 13 years, but the number of MPB-attacked trees increased beginning in 2001. 

In both plots, however, the BA was >120 ft2/acre when 

MPB-attacked trees increased. Thus, each plot fell in the 

Table 16. Number of trees by 1-inch diameter class for the Brownsville plots. Numbers in parentheses are the numbers of MPBattacked trees (successful and pitchouts) in the decade following the year of inventory.

GSL 60/70 GSL 80/90 GSL 100/110 Control

Diameter 1985 1995 2005 1985 1995 2005 1985 1995 2005 1985 1995 2005

5 2.

6 4. 4. 4

7 1. 1. 0

8 4 3. 3. 1

9 1 13 3. 4.(1) 3. 5

10 3 1. 24 16.(1) 3 6 1. 16.(1) 10.(1) 3

11 15 1. 36 25. 15 24 14. 30. 16.(2) 10

12 33 12. 30 33. 24 39 23. 9 41.(1) 42.(3) 16

13 24 24. 6 21 29. 29 34 35. 26 42.(1) 33.(7) 36

14 11 32.(2) 18 6 16. 25 23 34. 29 29. 35.(6) 27

15 2 13. 23 2 9. 17 11 22.(1) 34 18. 25.(6) 27

16 4. 19 1 4.(1) 9 3 9. 21 14. 14.(3) 20

17 1. 12 1 5 2. 11 1. 10.(1) 8

18 2 1. 1 2 1.(2) 8

19 1 1. 1.(1) 3

20 1 1

Table 17. Number of trees by 1-inch diameter class for the Crook Mountain plots. Numbers in parentheses represent the number of 

MPB-attacked trees (successful and pitchouts) in the decade following the year of inventory.

GSL 80 GSL 100 GSL 120 Control

Diameter 1985 1996 2006 1985 1996 2006 1985 1996 2006 1985 1996 2006

3 2. 1. 1.

4 14. 13. 9.

5 10. 7. 5.

6 1. 2. 2. 1. 10. 10. 6.

7 1. 1. 9. 4. 2. 1. 7. 8. 5.

8 1. 11. 6. 3 3. 2. 2. 3. 1.

9 1. 1. 17. 14. 2 1. 1. 3. 1. 2.

10 3. 17. 16. 8 5. 2. 3. 6.(1) 3.

11 6.(1) 2. 24.(2) 19. 16 8. 5. 2 15. 6.(1) 2.

12 15.(1) 6.(1) 21.(3) 17. 12 11. 9. 4 30. 24. 11.(1)

13 22.(1) 10. 1. 27. 23.(1) 17 29. 7. 1 33. 21. 14.

14 20. 16. 8. 18.(2) 28. 17 38.(2) 29.(1) 6 37. 41. 24.

15 18. 21. 8. 8.(1) 14. 20 18. 37. 22 31. 33.(1) 32.

16 8. 16. 11.(1) 6. 9. 22 21. 21.(3) 16 12.(1) 25. 29.

17 4. 13. 17. 2.(1) 7.(1) 3 3. 17. 28 8. 10. 24.

18 1. 6. 11. 2.(1) 1.(1) 8 1. 7.(1) 12 4. 8. 9.

19 1. 4. 13. 1. 1. 4 1. 13 3. 2. 6.

20 1. 4. 1. 3 2. 4.

21 3. 2 1. 2.

22 1
USDA Forest Service RMRS-RP-68. 2007 15

high susceptibility category even though it was originally designated as GSL 100. The original GSL designation 

no longer described stand density so a lowering of the 

upper limit of the moderate rating does not seem warranted.

Based on the amount of mortality in the BM1 GSL 

80/90 and GSL 100/110, these GSL levels could be 

considered just as susceptible as unmanaged stands. 

However, the susceptibility rating system is based on 

crude probabilities of potential for infestation, not total mortality. In the BM1 plots, the probabilities were 

modified because of the epidemic MPB population in 

surrounding stands (unmanaged and control). In addition, 

the control plot was infested 2 years before infestations 

arose in either the BM1 GSL 80/90 or GSL 100/110. 

Whether the two plots would have been attacked and/or 

exhibited the same level of percent mortality if the plots 

were larger or the MPB population was not in such close 

proximity remains debatable.

The MPB mortality in the two BM1 plots provides 

insight into the crude probabilities of beetle infestation relative to the size of the partial cut. For both plots, 

MPB-attacked trees first showed up in their buffer strips 

where they bordered adjacent unmanaged stands and 

the control. In succeeding years, beetles moved into 

the CIPs of the plots as the MPB infestation persisted. 

The MPB population, being the magnitude that it was, 

overwhelmed trees in the partial cuts. Under these circumstances, partial cutting did not prevent substantial 

mortality.

Modifications in MPB Susceptibility Ratings

Even though the number of MPB-attacked trees in 

the various plots may have resulted from circumstances 

confounding susceptibility so changes in the rating system do not seem warranted, we think modifications are 

in order. Schmid and others (1994) suggested that two 

methods might eventually evolve—one for unmanaged 

stands and one for managed stands. Two methods are 

proposed in hopes of more precisely identifying susceptibility for unmanaged and managed stands.

The method for unmanaged even-aged stands would 

be similar to the Schmid and others (1994) method with 

three susceptibility categories. The limit separating the 

high and moderate susceptibility categories would be 

lowered to GSL 110 while the limit between the low 

and moderate categories would remain the same. In addition, the rating given each stand would correspond 

to the highest GSL found in that stand rather than an 

average of all points sampled. Even though stands are 

relatively even-aged and appear homogeneous, a high 

degree of variability may exist (Olsen and others 1996) 

and that variability in stocking complicates susceptibility ratings when ratings are based on some measure 

of mean stand density. This variation is not a problem 

if GSLs for the various sampling points are within the 

range for the susceptibility category. However, if the 

overall GSL is below the demarcation value between 

two categories, but one sampling point is above the 

same demarcation value, then the stand may be underrated. Under the current method of Schmid and others 

(1994), if overall GSL is 105, but a small portion of the 

stand is at 125, then the stand would be rated moderately susceptible because the overall value was below 

GSL 120, the minimum value for high susceptibility. 

Under the proposed method, the stand would be rated 

high because part of the stand was in the high category. 

This change in the way stands are rated seems justified 

in light of the work of Olsen and others (1996), who 

found MPB infestations associated with high BA but 

not necessarily the highest BA in the stand. Thus, it 

seems logical to expect MPBs to infest parts of a stand 

where the GSL (BA) is greater than the overall average.

The method for managed stands would consist of two 

susceptibility categories—high and low categories separated at GSL 110. GSL 110 is used in this method for 

the same reasons cited for the unmanaged stand method. 

The same concern regarding heterogeneity of stand density is present for managed stands because one subplot 

in the C-C plot exceeded BA 120 while overall BA was 

103 (table 7, 2006 data). Although minimal heterogeneity of stand density would be expected in managed 

Table 18. Number of trees by 1-inch diameter class for the C-C 

plot (2.47 acres). Numbers in parentheses represent the number of MPB-attacked trees (successful and pitchouts) in the 

decade following the year of inventory.

Diameter 1985 1996 2006

5 2.

6 1. 1

7

8

9 2. 2. 1

10 8. 2.

11 39. 11.(1) 5

12 61.(1) 41. 11

13 58.(2) 49.(3) 27

14 37.(1) 60.(3) 57

15 15. 35.(4) 45

16 5. 14.(1) 39

17 3. 7.(2) 14

18 1. 7

19 1. 2. 3

20 3
16 USDA Forest Service RMRS-RP-68. 2007

stands as compared to unmanaged stands, the BHNF’s 

marking procedures may contribute to variation in stand 

densities. If the acceptable range of leave tree densities 

is +10 ft2

 of the desired density level, then the variation 

in stand density as evidenced in the C-C plot is easily 

understood. As with unmanaged stands, managed stands 

with one or more sampling point exceeding GSL 110 

would be classified as highly susceptible even though 

the overall GSL was below 110.

Management Implications

Partial Cutting

The immediate implication of these results is that 

partial cutting unmanaged PP stands can minimize 

MPB-caused tree mortality. While MPB-caused tree 

mortality will not be eliminated in partially cut stands 

(tables 9 through 13), tree mortality can be limited to a 

relatively low level (for example, single trees or pairs 

of trees). Mortality such as that in the partially cut BM1 

GSL 80/90 and GSL 100/110 need not be evident in PP 

stands if stands are regularly managed silviculturally.

MPB-caused mortality in the partially cut plots at the 

various locations indicates that the effectiveness of various levels of partial cutting in preventing high levels of 

tree mortality over the long-term is not influenced solely 

by stand stocking level (residual GSL). The interactive 

effects of the size (acreage) of the cutting, number of 

years since the stand was cut, and proximity of incipient epidemic or epidemic MPB populations to the cut 

stand(s) are also important.

In general, the lower the residual GSL, the greater the 

reduction in subsequent MPB-caused tree mortality over 

the long-term, especially if the area to be cut is relatively 

large and the stand(s) are not silviculturally managed after the initial cut. Based on the results at the BM1 plots, 

unmanaged stands cut to GSLs <75 will sustain significantly less MPB-caused mortality than stands partially 

cut to GSLs >100. The difference in tree mortality for 

GSLs <75 compared to GSLs >100 results from the interrelationships among greater spacing between residual 

trees, less inter-tree competition, and different microclimates. The lower densities also increase the greater 

amount of time required for low density stands (GSL 

<75) versus high density stands (GSL >100) to grow to 

the critical susceptibility threshold.

The greater the size of the partial cut, the lower the 

percentage of subsequent total mortality in the cut stand. 

MPB-caused mortality was about 50 percent in the BM1 

GSL 80/90 and GSL 100/110 over a 20-year period 

primarily because the two stands were surrounded by unmanaged stands and MPBs from those stands moved into 

the partially cut stands. Thus, 2.5-acre partial cuts can 

suffer considerable mortality when surrounded by unmanaged stands. GSL 80 to 100 stands may not initially 

incur substantial tree mortality if the cut area is considerably larger than 2.5 acres (for example, >10 acres). 

Mortality would probably be confined to the boundaries 

between the cut stand and adjacent unmanaged stands. 

However, the low potential for MPB-caused mortality 

in GSLs of 80 to 100 in larger cutting areas may be lost 

as years since the initial partial cutting increase. GSLs 

of 80/90 can grow to exceed BAs of 120 in 20 to 30 

years (Obedzinski and others 1999) or, as the C-C plot 

shows, more than BA 120 in parts of the stand if spacing 

is not properly addressed (table 7). GSLs of 100/110 can 

exceed BA 120 in 10 to 20 years (table 6, Obedzinski 

and others 1999). Both GSL levels thus reach the GSL 

120 threshold for MPB infestation relatively quickly. If 

GSL 110, as proposed in this report, is accepted as the 

new threshold for high susceptibility, then GSL 100/110 

stands would be near or at that level after their initial 

cutting.

If stands are partially cut to GSLs >100, the stands 

may sustain a low level of MPB-caused tree mortality 

(percent) as long as epidemic MPB populations are not 

present in the immediate vicinity. If epidemic populations 

are present, such stands could lose more than 50 percent 

of their trees, especially if the acreage of the partially cut 

stand(s) is <3 acres and it is surrounded by unmanaged 

stands. Moreover, stands partially cut to GSL >100 are 

just below the current susceptibility threshold of 120 and 

can grow to that level in 10 to 20 years (see Obedzinski 

and others 1999) so MPB-caused mortality in such areas 

should be expected within 15 years.

General statements regarding partial cutting are useful, 

but forest managers need more specific recommendations. When this study began in the Black Hills, Floyd 

Fowler, Timber Management Officer, Nemo district, 

BHNF, stated, “We know we can reduce MPB-caused 

tree mortality to a negligible level if we greatly reduce 

the stocking level of unmanaged stands. What we need 

to know is the greatest level of stocking we can carry 

without sustaining substantial MPB-caused mortality.” 

His question is not simply answered, because specific 

recommendations for maintaining minimal MPB-caused 

mortality in a particular stand(s) for >20 years encompass a multitude of considerations, including:

1) Management objectives,

2) Stand reentry period,

3) Reaction time of management (time period between the appearance of incipient epidemic MPB 
USDA Forest Service RMRS-RP-68. 2007 17

populations and when control efforts are initiated in 

the stand[s]), and

4) Factors influencing the effectiveness of partial cutting previously discussed.

Assuming a relatively large contiguous tract of forest 

is to be partially cut and stand(s) within are to be managed to maintain high stocking levels of mature trees, 

then partial cutting to GSL 90 to 100 could be recommended as long as incipient epidemic MPB populations 

are absent. If incipient epidemic MPB populations are 

present in surrounding stands and management cannot initiate future control efforts within a year, then 

GSLs <80 would be a better recommendation. Despite 

the threat of MPB populations in adjacent tracts, forest 

managers may still opt to cut to GSL 90 to 100 if they 

can initiate control operations within a year or reentry is 

scheduled within a few years.

If the tract to be cut is relatively small (for example, 

2 to 5 acres) and surrounded by unmanaged forest, then 

partial cutting to GSL 90 to 100 would not be generally 

recommended as a long-term solution. This is especially 

pertinent for private landowners whose holdings consist 

of a few acres bordered by unmanaged forest. It is highly probable that their tract could be decimated by MPB 

populations from adjacent stands (as in the BM1 plots) 

before control efforts could be initiated on surrounding 

lands. In this case, partial cutting to a GSL <75 would be 

more advisable.

The former, long-standing BHNF policy of partial 

cutting stands to BA 80 will probably keep such stands 

free of epidemic MPB populations for 10 to 15 years following cutting. However, as evidenced by results from 

the C-C plot (table 13), stands of BA 80 (GSL 80) may 

begin to sustain more than endemic MPB mortality 15 

to 20 years after the initial cutting. Such stands should 

be closely monitored after 15 years, especially if additional cutting is not initiated or planned during that time. 

Further, uniform spacing is not always achieved during 

the leave tree selection/marking process. Uneven spacing 

leads to microcosm stands of 110 to 120 BA within the 

overall stand (table 7) that become more susceptible to 

MPB infestation and may lead to more extensive MPBcaused tree mortality. This may explain why stands cut 

to GSL 80 are exhibiting MPB infestations before their 

normally scheduled reentry.

Leave Tree Selection

The distribution of MPB-killed trees by diameter class 

within the partially cut and associated unmanaged stands 

(tables 14 through 18) has implications regarding leave 

tree selection for proposed silvicultural treatments in unmanaged stands. In unmanaged susceptible PP stands on 

the BHNF, endemic and incipient epidemic MPB populations attacked a range of diameter classes and did not 

concentrate exclusively on the largest diameter classes 

(tables 14 through 18). Thus, harvesting the three to four 

largest diameter classes within an unmanaged stand (for 

example, trees in diameter classes >16 inches) during 

an initial partial cut does not necessarily reduce stand 

susceptibility if the stocking level after cutting is GSL 

>100, as a substantial number of susceptible-sized trees 

(10 to 15 inches) would still exist in most stands. Further, 

susceptibility of partially cut stands will not automatically increase even though some trees >16 inches are 

left because large diameter trees in such stands would 

not be expected to be attacked more readily than trees 

with 10 to 15 inch diameters. However, if susceptible 

stands are partially cut to a GSL >100, and an epidemic 

MPB population is present, then most trees in the large 

diameter classes may be killed because MPB-caused 

mortality (percentage-wise) would be highest in the 

largest diameter classes if the epidemic persists in the 

stands. Obviously, removal of trees in the largest diameter classes before a MPB epidemic occurs will ensure 

that such trees will be harvested when their value is 

greatest and will eliminate such trees from being major 

contributors to future MPB generations. Nevertheless, if 

the largest trees are the most desirable for regeneration 

production or other management objectives, then leaving some of them is warranted as long as the trees are in 

apparent good health.

Management of Ponderosa Pine Stands

The greater implication of these results is the management of PP stands to minimize MPB-caused mortality in 

relation to the BHNF Management Plan. Graham and 

Knight (1965) succinctly state that forest insect management is an integral part of forest management. The 

most important aspect of managing mature PP stands 

on the BHNF is minimizing MPB-caused mortality. If 

forest managers are to achieve long-term multiple objectives, managers need to assume that minimization of 

MPB-caused mortality is the primary objective in stands 

where incipient epidemic MPB populations arise and 

should temporarily relegate other objectives to secondary status until the immediate threat from epidemic MPB 

populations has been eliminated. While this approach 

may be contrary to the principle of multiple use and 

many objectives within the BHNF Plan, it is essential to 

achieving many of the Plan’s long-term multiple objectives. Allowing MPB populations to expand beyond the 
18 USDA Forest Service RMRS-RP-68. 2007

incipient stage will prevent achievement of most other 

management objectives.

To illustrate how reticent MPB management causes 

objective achievement failure, consider the recent MPB 

epidemic in the Beaver Park area of the Sturgis watershed. In 1996, MPB populations began increasing in 

Beaver Park SW of Sturgis, SD (Allen and others 2002). 

In subsequent years, MPB populations continued to increase with more than 100,000 trees attacked in 2000 

(Allen and others 2002). Due to legal restraints, the 

BHNF was unable to conduct silvicultural treatments in 

the area. MPB-caused tree mortality became so extensive 

that “entire hillsides are now completely devoid of large 

trees” (Allen and others 2002). Areas exhibiting this degree of mortality “may take 80 to 100 years before a 

mature forest is present again” (Allen and others 2002). 

When this level of stand mortality occurs, achievement 

of other objectives is extremely unlikely. For example, 

loss of the overstory will eliminate the “thermal cover” 

for wild ungulates. Death of mature trees will eliminate the habitat for red squirrels and roosting sites for 

wild turkeys. MPB-killed trees increase dry fuel loads 

and thereby increase the potential for severe fires if 

fires start. Increased runoff and the possibility of flooding may temporarily occur on hillsides devoid of trees. 

Thus, failure to address incipient epidemic MPB populations can substantially affect the achievement of other 

objectives well beyond the immediate objective of dealing with MPB populations.

Once PP stands reach the susceptible condition for 

MPB attack, maintaining minimal MPB-caused mortality must become of primary concern and the concern 

must extend well beyond an initial single partial cut. A 

single partial cut to GSL 80 in susceptible stands may 

suffice for a number of years, but waiting another 20 to 

30 years to make the regeneration cut may not be prudent. As shown in Obedzinski and others (1999) and 

in this report, PP stands may again become susceptible 

in 10 to 20 years just through natural growth. Further, 

microcosm stands with densities greater than the overall average stand density may be inadvertently created 

within large tracts during the marking process for the 

initial partial cut (table 7). These microcosm stands may 

become highly susceptible well before overall stand susceptibility exceeds the high susceptible threshold or the 

stand is silviculturally revisited. Constant silvicultural 

action is a must if the BHNF is to ever extricate itself 

from the periodic appearances of MPB epidemics in its 

timber managed areas.

Literature Cited

Allen, K.K.; Schaupp, W.C., Jr.; Long, D.F. 2002. Evaluation 

of mountain pine beetle activity in the Beaver Park area 

of the Black Hills National Forest. Biological Evaluation 

R2-03-03. Golden, CO: U.S. Department of Agriculture, 

Forest Service, Rocky Mountain Region, Renewable 

Resources. 14 p.

Blackman, M.W. 1931. The Black Hills beetle (Dendroctonus 

ponderosae Hopk.) New York State College of Forestry 

Tech. Bull. 36. 97 p.

Cole, W.E.; Amman, G.D. 1969. Mountain pine beetle 

infestations in relation to lodgepole pine diameters. Res. 

Note INT-95. Ogden, UT: U.S. Department of Agriculture, 

Forest Service, Intermountain Forest and Range Experiment 

Station. 7 p.

Furniss, R.L.; Carolin, V.M. 1977. Western forest insects. 

Miscellaneous Publication No. 1339. Washington, D.C.: 

U.S. Department of Agriculture, Forest Service. 654 p.

Graham, S.A.; Knight, F.B. 1965. Principles of forest 

entomology. 4th Edition. McGraw-Hill Inc. xii + 417 p.

Johnson, E.; Schaupp, W.E., Jr.; Long, D.F. 2001. [Letter 

to Forest Supervisor]. October 12. 3 p. On file at: U.S. 

Department of Agriculture, Forest Service, Black Hills 

National Forest, Custer, SD.

Johnson, E.; Long, D.F. 2003. [Letter to Forest Supervisor]. 

January 7. 3 p. On file at: U.S. Department of Agriculture, 

Black Hills National Forest, Custer, SD.

Lessard, G. 1982. Factors affecting ponderosa pine stand 

susceptibility to mountain pine beetle in the Black 

Hills 1981. Technical Report R2-26. Lakewood, CO: 

U.S. Department of Agriculture, Forest Service, Rocky 

Mountain Region, Timber, Forest Pest, and Cooperative 

Forestry Management. 16 p.

McCambridge, W.F.; Hawksworth, F.G.; Edminster, C.B.; 

Laut, J.G. 1982. Ponderosa pine mortality resulting from 

a mountain pine beetle outbreak. Res. Pap. RM-235. 

Fort Collins, CO: U.S. Department of Agriculture, Forest 

Service, Rocky Mountain Forest and Range Experiment 

Station. 7 p.

McGregor, M.D.; Amman, G.D.; Schmitz, R.F.; Oakes, R.D. 

1987. Partial cutting lodgepole pine stands to reduce 

losses to the mountain pine beetle. Can. J. For. Res. 17: 

1234-1239.

Obedzinski, R.A.; Schmid, J.M.; Mata, S.A.; Olsen, W.K.; 

Kessler, R.R. 1999. Growth of ponderosa pine stands in 

relation to mountain pine beetle susceptibility. Gen. Tech. 

Rep. RMRS-GTR-28. Fort Collins, CO: U.S. Department 

of Agriculture, Forest Service, Rocky Mountain Research 

Station. 13 p.

Olsen, W.K.; Schmid, J.M.; Mata, S.A. 1996. Stand 

characteristics associated with mountain pine beetle 

infestations in ponderosa pine. Forest Science 42: 

310-327.

Sartwell, C.; Stevens, R.E. 1975. Mountain pine beetle in 

ponderosa pine: prospects for silvicultural control in 

second-growth stands. Journal of Forestry 73: 136-140.
USDA Forest Service RMRS-RP-68. 2007 19

Schaupp, B.; Johnson, E.; McConnell, T. 2004. [Letter to Forest 

Supervisor]. April 26. 3 p. On file at: U.S. Department of 

Agriculture, Forest Service, Black Hills National Forest, 

Custer, SD.

Schmid, J.M.; Mata, S.A. 2005. Mountain pine beetlecaused tree mortality in partially cut plots surrounded by 

unmanaged stands. Res. Pap. RMRS-RP-54. Fort Collins, 

CO: U.S. Department of Agriculture, Forest Service, Rocky 

Mountain Research Station. 11 p.

Schmid, J.M.; Mata, S.A.; Obedzinski, R.A. 1994. Hazard 

rating ponderosa pine stands for mountain pine beetles 

in the Black Hills. Res. Note RM-529. Fort Collins, CO: 

U.S. Department of Agriculture, Forest Service, Rocky 

Mountain Forest and Range Experiment Station. 4 p.

Schmid, J.M.; Mata, S.A.; Olsen, W.K.; Vigil, D.D. 1993. 

Phloem temperatures in mountain pine beetle-infested 

ponderosa pine. Res. Note RM-521. Fort Collins, CO: 

U.S. Department of Agriculture, Forest Service, Rocky 

Mountain Forest and Range Experiment Station. 10 p.

Thompson, R.G. 1975. Review of mountain pine beetle and 

other forest insects active in the Black Hills: 1895 to 

1974. Forest Pest Management Special Report R2-75-1. 

Lakewood CO: U.S. Department of Agriculture, Forest 

Service, Forest Pest Management. 35 p.
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