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SUSCEPTIBLE TO ATTACK BY THE SOUTHWESTERN PINE _

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Donald A. Pierce ; "

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Station Paper No. bay August 1961.

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uf ROCKY MOUNTAIN FOREST AND RANGE EXPERIMENT STATION a" =<
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Raymond Price, Director *_Fort Collins, Colora#de-

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United States
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\CLASSES OF PONDEROSA PINE IN NEW MEXICO AND ARIZONA
SUSCEPTIBLE TO ATTACK BY THE SOUTHWESTERN PINE
eat ual eae ASSOCIATED BARK BEETLES \v

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Donald A. |Pierce, Entomologist

Rocky Mountain Forest and Range Experiment Station!

GlORNe aes N T S

Page
Methods of tests in Southwest MCC tE oe Meine = 02 ems 118) NO 4
Results e e e e } e e e e e ae e e es e e e e 4
Total mortality by tree class . . . . «6 « «© -« 7
Total mortality by vriskiclass. 3. «.« se. © « «) © aU
Insect-caused mortality by tree classes oF Maret > 8
Insect-caused mortality by risk classes niet Mier tte 8
DISCUSS LON: 3) ie. aos Miowepyel Me one ele Osh UTIs Qe at. vero ine 8

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li Central headquarters maintained in cooperation with Colorado
State University at Fort Collins. The study was completed at the Sta-
tion's Forest Insect Laboratory at Albuquerque, New Mexico.

CLASSES OF PONDEROSA PINE IN NEW MEXICO AND ARIZONA
SUSCEPTIBLE TO ATTACK BY THE SOUTHWESTERN PINE
BEETLE AND ASSOCIATED BARK BEETLES
by
Donald A. Pierce, Entomologist

Bark beetle control in the United States is largely done by direct methods.
These include: (1) Killing the overwintering brood by felling, peeling, and burn-
ing the bark of infested trees; (2) salvage logging the infested trees from the
woods, the wood is utilized, and the insects are killed in the refuse burner or
mill pond; and (3) spraying either the standing or felled infested tree with
insecticides.

These methods are effective, but results may be temporary and not
directed at the cause of the insect outbreak. An ideal way of keeping bark
beetle populations under control would be by silvicultural methods based on
a susceptibility classification system.

The aim of the system is to sort the trees in a stand accorcing to their
susceptibility to bark beetle attack. Trees classed as high-risk can be
removed by a sanitation-salvage cutting that captures the loss and possibly
prevents outbreaks. The success of the system is dependent on three things:
(1) The species of bark beetles involved prefer trees of low vigor; (2) low-vigor
trees can be recognized in the stand and their characteristics defined; and (3)
the high-risk trees constitute a low percentage of the stand that can be removed
without upsetting the ecology of the residual stand.

Keen! in 1936 and Salman and Bongberg=! im 1942 developed systems that
proved to be highly successful against the western pine beetle (Dendroctonus
brevicomis Lec.) on the inland ponderosa pine stands of California and Oregon.
Because of the similarity of the habits of the southwestern pine beetle (Dendroc-
tonus barberi Hopk. ) to those of the western pine beetle, ind similarity of the
pine stands, it was only natural that the methods be tested in the ponderosa pine
stands of the Southwest. Such tests were started in 1952 when a Forest Insect
Laboratory, a field unit of the Rocky Mountain Forest ge Range Experiment
Station, was established at Albuquerque, New Mie sic or

2/ Keen, F. P. Relative susceptibility of ponderosa pines to bark-beetle

attack. Jour. Forestry 34: 919-927, illus. 1936.

3/ Salman, K. A., and Bongberg, J. W. Logging high-risk trees to con-
trol insects in the pine stands of northeastern California. Jour. Forestry 40:
533-539. 1942,

4/ Mortality plots were established by J. W. Bongberg and R. K. Bennett
in 1953 and 1954.

Keen's classification as modified by Thomeon for the Southwest used
4 age groups each of which is divided into 4 vigor classes resulting in a total
of 16 age and vigor divisions (tables 1 and 2). The age groups are determined
on the basis of d.b.h., bark color and surface texture, shape of the top, and
the branching habit. The vigor classification groups trees into classes accord-
ing to their relative rates of growth, from the best represented by A to the
poorest represented by D. Size of crown and the abundance and condition of
the needles are the best indicators of vigor.

Table 1. --Description of Keen's age classes as modified by Thomson for the Southwest
Character d Class 1 j Class 2 : Class 3 ; Class 4
Maturity Young Immature Intermediate - Mature -overmature
mature
Age Usually less than Usually less than Approximately 150- Approximately 225
75 years 150 years 225 years years and over
Diameter breast Under 12 inches Seldom over 24 Usually less than Usually large
high inches 36 inches
Bark color Dark gray to Black to dark Reddish brown Reddish brown to
black reddish brown shading to black yellow
in the top
Bark plates No plates, rough Ridges or very Moderately large Plates usually very
bark, deeply narrow plates plates between wide, long and
furrowed with between the the fissures smooth
narrow ridges fissures

between fissures

Tops Usually pointed Pointed or slightly Usually pyramidal Usually flat and

rounding; never flat or rounded, occa- making no further
sionally pointed height
Branches Upturned and Mostly upturned and Upturned in upper Mostly large
whorls distinct whorls distinct for third of crown; drooping, gnarled

upper half of crown, those in the middle or crooked; whorls
flattening out with horizontal, and indistinct and
less distinct whorls drooping in lower incomplete
in lower half third of crown

Salman and Bongberg defined four risk groups (table 3). Characters used
in defining risk are concerned with the apparent health or vigor of the crown
as evidenced by the foliage, twigs, and branches. Factors of age, crown form,
and crown position do not enter into their appraisal of risk.

As stated by Miller and Keene! the essential difference between the two
systems is one of distinguishing inherent vigor (Keen's classes) from current
health (risk ratings).

5/ Thomson, Walter G. A growth rate classification of southwestern
ponderosa pine. Jour. Forestry 38: 547-553, illus. 1940.

6/ Miller, J. M., and Keen, F. P. Biology and control of the western
pine beetle. U. S. Dept. Agr. Misc. Pub. 800, 381 pp., illus. 1960.

Table 2. --Description of Keen's crown vigor classes as modified by Thomson for the Southwest

Character Class A Class B Class C

Class D

Fair to moderately Fair to poor vigor

vigorous

Crown vigor Full, vigorous

Crown length 55 percent or Less than 55 percent, Either short (from

and width more of the but 35 percent or 20-25 percent of the
total height more of height of the height of the tree,
of the tree; tree, or a longer if foliage is of
average width crown if narrow or average thrift) or
or wider somewhat thin; either long, sparse and
short wide crowns or narrow
long narrow ones
Foliage Usually very Usually thrifty, of Usually short and
dense and full to medium from medium to
thrifty, the density and of poor density; of
individual average length normal length and
leaves being density when
of average confined to top
length or longer third of tree
Position Usually Usually codominant Usually inter -
isolated or but often isolated mediate or some-
dominant or dominant times codominant,
but rarely isolated
Diameter Large for age Above average for Usually below

age average

Usually of very poor
vigor

Less than 20 percent
of the total height of
tree; often quite thin
and sickly

Usually short and of
poor to very poor
density, very sparse
and scattered or only
partially developed

Usually suppressed or
intermediate or if
dominant or codominant
it is suffering from
some vigor=-reducing
ailment such as severe
insect attack, lightning
strike, or very old age

Usually decidedly
subnormal, but very
old and damaged trees
are often of large
diameter

Table 3. --Descriptions of Salman and Bongberg's risk ratings

Risk rating

Symptoms

Risk I--Low risk

Risk II--Moderate risk

Risk III--High risk

Risk IV--Very high risk

Full-foliaged, healthy-appearing crowns. Foliage of healthy appearance,
needles usually long and coarse, color good dark green. Practically all
twigs with normal foliage complement. No weakened parts of crown.

Fair to moderately healthy crowns, imperfect in spots. Foliage mostly
healthy, needle length average or better, color fair to good. Some twigs
or branches may lack foliage, but such injur, should not be localized to
form definite ''weak'"' spots in crown.

Crowns of fair to poor health, somewhat ragged or thin in parts of crown.
Foliage in parts of crown thin, bunchy, or unhealthy; needles average to
shorter than average in length; color fair to poor. Some to many twigs or
branches lacking foliage, some to many twigs or branches fading or dead.
Small localized weakened parts of crown usually present.

Crowns in poor condition, ragged or thin, often showing evidence of active
insect infestations in upper parts. Foliage thin or bunchy, needles short

or sparse, color poor. Twigs and branches dead or dying, parts of crown
definitely weakened. Active top-killing or partial infestations often present.

METHODS OF TESTS IN SOUTHWEST

During the 1953 and 1954 field seasons, forty 10-acre plots were estab-
lished in virgin ponderosa pine stands in Arizona and New Mexico. Table 4
gives the plot locations and information on the stands. Figure 1 shows a typical
plot and how the trees were numbered.

Table 4. --Summary of plot locations and stand characteristics

beehin toare 3 lOwaere Volume per acre Trees per acre
plote Lowest i Highest : Average : Lowest : Highest : Average

Number ---- Boardfeet ---- = ----- Number - - - - -

Navajo Indian Reservation 20 4,197 16, 067 8,914 9.9 40.2 21.4
National forests:

Apache 7 5,451 11, 966 8,429 15.5 39.3 26.4

Kaibab 4 17, 293 19, 274 18, 225 37.0 46.0 39.5

Santa Fe 3 4, 828 22,521 13, 496 24.8 33.6 30.0

Sitgreaves 4 6,765 17,955 12, 388 17.4 34.9 26.6

Coconino 2 9, 684 12, 243 10, 963 24.9 36.2 30.5

Plot boundaries were marked with aluminum paint and each ponderosa
pine tree 11.6 inches d.b.h. and over was numbered. Each tree was rated by
Keen's Tree Classification System and also by Salman and Bongberg's Risk-
Rating System. In addition, the d.b.h. height and volume were obtained for
each tree.

The plots were examined each year from 1956-59 by a crew of three men
to determine the amount of mortality caused by the southwestern pine beetle
and associated bark beetles.

RESULTS

During the 5-year period of the study, 223 trees died on the plots. Bark
beetles alone killed 126 trees (tables 5 and 6); lightning, wind, and pathological
agents accounted for the remainder.

In volume, total loss amounted to approximately 119, 000 board feet of
ponderosa pine timber on 400 acres during the 5-year period, an average of
nearly 60 board feet per acre per year. The bark beetle-caused loss amounted
to approximately 66, 000 board feet (tables 5 and 6).

The basis for the susceptibility of a class is the percent of trees killed in
the class. In making a selective cut to remove expected mortality from a stand,
it would be best to select trees in classes that sustain a high percent of loss and
contain a small percentage of the total living stand.

Navajo

--A typical plot with trees numbered with aluminum paint.

Figure 1

Indian Reservation, Arizona.

Table 5. --Insect-caused mortality over 5-year period grouped by tree classes

Portion of ' : Portion of ; * Portion vol- * Portion of
1 Live and : Q pri * : Volume : :
Tree class stand by Dead trees © risk class ume loss total vol-
:deadtrees : .. : 3 : Ios £5 :
risk class ; i dead i . inclass _ ume loss
Number Percent Number Percent M b.m. Percent Percent
HIGH RISK:
4D 90 0.9 14 15.6 8.2 14.8 12.4
3D 405 39 26 6.4 O5 9.4 14,4
2D 152 Wee} 4 2.6 1.0 6.4 ile 5
1D 7 sol 1 14, 3 0 0 0
4C 461 4.4 14 3.0 iG 3.4 17.0
3C 1, 658 15.9 Sil 1.9 14.8 Coe 22.4
LOW RISK:
2C 1, 187 11.4 10 0.8 1.3 of 2.0
1C 78 8 1 1.3 20 6 ol
4B 731 7.0 9 aye, 9.6 1.4 14.5
3B 1, 868 17.9 8 4 5.8 oy) 8.8
2B 1,475 14.2 3 674 6 G2 09)
1B 180 Ie 0 0 0 0 0
4A 347 S68 2 55 2.6 3.9
3A 704 6.8 3 4 1.4 a8} Po i
2A 923 8.9 0 0 0 0 0
1A 146 1.4 0 0 0 0 0
a ee
Total or average 10, 412 100.0 126 U2 66.0 Ne '7e 100.0

rr rrr

1 Categories of high and low risk as defined by Keen (see footnote 7).
2 50 bd. ft. loss in this class.

Table 6. --Insect-caused mortality over 5-year period grouped by risk classes

2 Portion of ' * Portion of * ; Portion vol-' Portion of
3 : Live and : : Eee : Volume =: :
Risk class stand by Dead trees risk class ume loss total vol-
: dead trees : 3 g : : loss So ers B
risk class © ‘ dead ; . in class , ume loss
Number Percent Number Percent M b.m. Percent Percent
4 241 Zed 38 15.8 18.3 17.9 Cithetts
3 817 7.8 24 2.9 16.0 4.6 24.3
2 3, 183 30.6 41 1.3 20.2 5) 30.6
1 6,171 59.3 23 4 Niles) 68) 17.4
Total or average 10, 412 100.0 126 liv 66.0 Ned 100. 0
Cumulative
risk class
4 241 Ze3) 38 15.8 18.3 17.9 27.7
4+ 3 1, 058 10.1 62 5.9 34.3 (uskO 52.0
4+ 342 4,241 40.7 103 2.4 54.5 25 JI 82.6

TOTAL MORTALITY BY TREE CLASSES

Table 7 is a summary of the total mortality data by each tree class.
Classes 1C and 4B were placed in the low-risk category even though they
showed a fairly high percentage of class killed. Had the study been more
extensive and continued several more years, these classes would probably
have been in the low-risk group.

Table 7. --Mortality by all causes over 5-year period grouped by tree classes

* Portion of ' * Portion of * beorton vol="" Portion of
Q F : : 7 wWolume a: :
Tree class! Eivevends stand by ~~ Deadtrees ~ risk class 1 ume loss ~ total vol-
si ideaiditrees! js!) os 5 : : Oss Bg 8
‘ riskclass | “dead : . inclass ~ ume loss
Number Percent Number Percent Mb.m. Percent Percent
HIGH RISK:
4D 90 0.9 22 24.4 14.9 27.0 W255
3D 405 3.9 41 10. 1 12.4 L204 10.4
2D 152 Nas) 7 4.6 M74 fiche: 1.0
1D 7 5 il 1 14, 3 20 Bi3 0
4C 461 4.4 30 655 24.7 7.6 20.8
3C 1, 658 NEG) Bi) Saul fail best 3.03 18,
LOW RISK:
2C Ly LS 7; 11.4 16 IN} 4.0 ey 3.4
1c 78 at Zi 6 wl Meal ae)
4B 731 to) 20 enh 20.4 Sa trees
3B 1, 868 17.9 15 8 10.3 1.6 8.7
2B 1,475 14.2 6 4 4 aie oie
1B 180 tent! 1 ots .6 4.8 ce)
4A 347 353 6 EAT? 6.9 1.8 5.8
3A 704 6.8 3 4 1.0 oo .8
2A 923 8.9 1 6 dl se are 5
1A 146 1.4 0 0 0 0 0
ee ee Se ee ee ee ed ee
Total or average 10,412 100.0 213) Zak 118.8 360 100.0

1 Categories of high and low risk as defined by Keen (see footnote ti)
g & Yi
2 50 bd. ft. loss in this class.

Of the total stand involved in the study, 26.7 percent fell into the high-
risk category. During a 5-year interval, approximately 74.9 Mb.m. or
63.0 percent of the total volume loss occurred in this group.

TOTAL MORTALITY BY RISK CLASSES

Table 8 is a presentation of the total mortality data by the risk-rating
system.

Risk class 4 contained only 2.3 percent of the green stand, but 25.6 per-
cent of the volume loss, amounting to approximately 30.4 Mb.m., which
occurred during the 5-year period. Risk classes 4 and 3 combined contained

47.6 percent of the total volume loss or approximately 56.6 Mb.m. in only
10.1 percent of the living stand.

Table 8.--Mortality by all causes over 5-year period grouped by risk classes

Li Be ; Portion of : ; Portion of d Valurse ‘ Portion vol- * Portion of
Risk class i Be “standby ‘ Deadtrees * riskclass ° “ume loss ~~ total vol-
:deadtrees : _. fs g is loss Abas .
i * risk class A a dead i . in class _ ume loss
Number Percent Number Percent Mb.m. Percent Percent
4 241 2.3 BM 23.7 30.4 29.8 25.6
3 817 7.8 47 5.8 26.2 To 22.0
2 3, 183 30.6 67 (oi ° 36.9 2.8 Shale al
1 6,171 59.3 52 8 25153. ere (Alles)
Total or average 10, 412 100.0 223 Zeid 118.8 3.0 100.0
Cumulative
risk class
4 241 2 57 OSS 1 30.4 29.8 25.6
4+ 3 1, 058 10.1 104 9.8 56.6 12.7 47.6
4+34+2 4, 241 40.7 171 4.0 93:5 5.3 78.7

INSECT-CAUSED MORTALITY BY TREE CLASSES

Arranging the insect-caused mortality by tree classes (see table 5), 44.7
Mb.m. of the volume loss fell in the high-risk category. These classes would
isolate 67.7 percent of the volume loss caused by bark beetles from 26.7 per-
cent of the stand in the 5-year period.

INSECT-CAUSED MORTALITY BY RISK CLASSES

Risk class 4, with 2.3 percent of the living stand, sustained a loss of
17.9 percent of its volume and 27.7 percent of the total volume loss due to bark
beetles (see table 6). Risk classes 4 and 3 combined accounted for 52.0 per-
cent of the volume loss (34.3 Mb.m.) in 10.1 percent of the living stand.

DISCUSSION

cen tested the two methods of tree selection in a study in Oregon.
The results of the present study were similar to those reported by Keen. In
the following tabulation the two studies are compared on the basis of bark
beetle-caused mortality only. The comparison shows the percentage of trees
killed and percentage of the living stand in the high-risk category:

7/ Keen, F. P. Ponderosa pine tree characteristics indicative of
high risk to pine beetle attack. U. S. Forest Serv., Calif. Forest and Range
Expt. Sta., Prog. Rpt. (1938-52). 50 pp. 1954. [Unpublished report. ]

Portion of tree Portion of green

in high tand in high
Rating method joss ip beh as ee 8
risk classes risk classes
(Percent) (Percent)
8
Keen's tree classes:—
Oregon 66.8 34.8
Arizona and New Mexico 9/ (ot Zoe
Salman and Bongberg's risk
classes 3 and 4:
Oregon 65.5 19516
Arizona and New Mexico 52.0 OER

It appears the identification of susceptible trees was better in the Arizona
and New Mexico study than in the Oregon study. It must be kept in mind, how-
ever, that the Oregon study lasted 10 years. If the Arizona and New Mexico

studies were continued, a larger percentage of the mortality would come from
the lower risk classes.

It appears from the data obtained in the foregoing study that both methods --
a marking system based on Keen's Tree Classification as modified by Thomson,
and Salman and Bongberg's Risk-Rating System--can be adapted to marking
ponderosa pine stands in the Southwest.

g/ All D crowns and classes 4C and 3C.

9/ This study used Keen's tree classes as modified by Thomson (see
footnote 5).

Agriculture --- CSU, Ft. Collins a 9 2

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