GROWTH OF

SELECTIVELY CUT PONDEROSA PINE STANDS

IN THE UPPER COLUMBIA BASIN

Agriculture Handbook No. 39

UNITED STATES DEPARTMENT OF AGRICULTURE

Forest Service August 1952
GROWTH OF

SELECTIVELY CUT PONDEROSA PINE STANDS

IN THE UPPER COLUMBIA BASIN

By ARTHUR L. ROE, forester

Northern Rocky Mountain Forest and Range Experiment Station,

Forest Service

CONTENTS

Page

[ntroduction 1

How the data were analyzed 3

Growth of residual trees 4

Number and size 4

Site productivity and age 5

Precipitation 6

Vigor 9

Reliability of the data 9

Ingrowth 9

Mortality 11

The growth tables and how to use them 11

General estimates 11

Page

Adjusting growth estimates for additional variables 16

Limitations on use of tables 20

Silvicultural significance of the findings— 20

Intensity of cutting 20

Growth of resei-ve stands by average

stand age and site quality 22

Selecting trees to reserve from cutting— 23

Length of cutting cycle 25

Summary 26

Appendix 28

INTRODUCTION

Timber-management planning for the sustained production of

ponderosa pine requires a knowledge of growth rates, responses to

cutting, desirable cutting cycles, cutting practices, and regeneration requirements. In recent years, partial cutting has been widely

practiced in ponderosa pine forests,^ shorter cutting cycles have

been viewed with more favor, and residual trees selected with considerable care. These practices result, of course, in uneven-aged

residual stands to which normal yield tables for even-aged timber

do not apply. Because forest managers have expressed a need for

information that will help them predict growth for selectively cut

uneven-aged ponderosa pine, data obtained from a study of westem Montana stands are presented here. It is believed, however,

that these data apply equally well to stands in eastern Washington,

north Idaho, and British Columbia.

The growth of uneven-aged ponderosa pine has been studied by

several methods. Krauch (7)^ used a diameter-accretion method

by which growth was computed for individual trees, and the aggregate represented stand growth. While this method accounted

for variation in individual tree growth, other important variables

were not considered. Hanzlik (3) adapted "growth percent" to

predicting increment for residual stands, but concluded that it

^ Presentation of this report is not necessarily an endorsement of partial

cutting in mature and overmature ponderosa pine.

' Italic numbers in parentheses refer to Literature Cited, on inside of back

cover.
2 HANDBOOK 39. U. S. DEPARTMENT OF AGRICULTURE

could not be used to predict future volume accurately since it is a

function that decreases as age increases. He reduced the error

from this source by introducing the principle of interpolating for

future growth percent. Dunning (2) applied growth percent to

residual trees in four vigor groups, which he had classified according to external characteristics.

Later studies were based on correlations that included a larger

number of variables. Thus, Meyer (9) showed that growth after

logging varies by size of reserve stand, elapsed time since logging,

site quality, stand structure, degree of release, and mortality.

Lexen (8) found a significant correlation between growth of the

reserve stand and average diameter of the trees ; ingrowth from

pole-size trees was not considered to be important in the first cutting cycle. Initial reserve volume and elapsed time since cutting

were highly important variables in preliminary yield tables developed by Hornibrook (^) for selectively cut stands in the Black

Hills ; site, number of poles in the reserve stand, and stand structure were also considered. And Briegleb (1) computed growth

rate for individual trees in virgin stands in the Pacific Northwest

by. diameter and Keen tree classes (6), and converted the results

to stand growth rates following logging. These rates were then

adjusted according to factors derived from basic growth measurements made by Meyer in selectively cut stands : stand density and

release (percent of stand cut), site quality, number and size of

pole trees in the reserve stand, and mortality. Thus, the past

studies shovv^ that growth of residual stands depends on many

factors.

Basic data for this study were obtained during the 1947 field

season on 60 half-acre, temporary, sample plots on 21 cut-over

areas located throughout western Montana. The sampled stands

ranged in volume from approximately 500 to 10,000 board feet an

acre. Because growth was considered only for stands that had

been cut once, it is not known to what extent the data apply to

reserve stands after repeated cuts. Elapsed time since cutting on

the sample plots varied from 5 to 50 years: 2 plots, 5 years; 9

plots, 10 years; 6 plots, 15 years; 5 plots, 20 years; 6 plots, 25

years; 11 plots, 30 years; 3 plots, 35 years; 5 plots, 40 years; 13

plots, 50 years.

The follov/ing information was recorded for each half-acre plot :

1. Diameter of all trees 7.6 inches in diameter at breast height

and larger, measured with a tape.

2. Total height of all trees 7.6 inches d. b. h. and larger, measured with Abney level and tap«.

3. Merchantable heights of all trees 10 inches d. b. h. and larger,

measured with an Abney level and tape.

4. Increment by 5-year periods, for 20 years before logging as

well as for all elapsed time after logging, averaged for cores from

two opposite sides of all trees, 7.6 inches d. b. h. and larger.

5. Keen tree class of all ponderosa pine trees 7.6 inches d. b. h.

and larger, estimated at the time of examination.

6. Keen tree class at the time of logging, estimated for all ponderosa pine trees 7.6 inches d. b. h. and larger.
GROWTH OF SELECTIVELY CUT PONDEROSA PINE Q

7. Vigor and tree description of all trees other than ponderosa

pine 7.6 inches d. b. h. and larger.

8. Species of all stumps.

9. Diameter and height of all stumps, measured with a tape.

10. D. b. h. and merchantable length of bole of all logged trees,

measured with tape where these dimensions could be determined

from stumps, long butts, top remains, or other evidences.

11. Species of all post-logging dead trees 7.6 inches d. b. h. and

larger.

12. D. b. h. and total and merchantable length of all post-logging dead trees, measured with a tape.

13. Time of death to nearest 5 years, and cause of death where

possible to determine, for all post-logging dead trees.

14. Site index, determined from trees dominant or codominant

prior to cutting, or very young unsuppressed trees in more heavily

cut stands.

On smaller plots within the half-acre sampling units, the following additional data were obtained :

1. Diameters and species of pole-size trees on i/io-acre plots.

2. Sizes, ages, and species of saplings and seedlings on five

4-milacre plots distributed around the centers of the major plot

locations.

As a result of this study, yield tables have been constructed

from which two kinds of estimates can be made: (1) A general

estimate of growth for residual stands on areas where typical or

average conditions prevail, to be used principally for broad planning; and (2) a more precise prediction of growth, which includes adjustments for stand competition, site index, and maturity.

In addition to the yield tables, silvicultural information of considerable practical importance resulted.

HOW THE DATA WERE ANALYZED

Diameter changes by 5-year periods, based on increment core

records and bark thickness curves, were computed, and heights

were estimated from height over diameter curves prepared by

site classes. Individual tree volumes on the plots were determined

from tables currently in use in the region, and then summed to

reconstruct the stand volumes by 5-year intervals. Growth was

separated into three categories for analysis: Growth of residual

trees that were 9.6 inches d. b. h. or larger at time of logging;

ingrowth or volumes of trees that grew into the 10-inch d. b. h.

class after logging ; and mortality, which is negative growth.

Nearly all of the sampled stands included Douglas-fir trees

growing in mixture with the ponderosa pine ; Douglas-fir averaged

23 percent of the basal area on the plots. In analyzing the data,

volumes for the two species were pooled without distinction. Because an admixture of Douglas-fir in ponderosa pine stands is

typical in the Upper Columbia River Basin and growth rates of

these species when in mixture do not differ greatly, separate

analyses would probably not have significantly increased the reliability of the findings. Separate analyses would also have greatly

complicated the computing as well as use of the results.
4 HANDBOOK 39, U. S. DEPARTMENT OF AGRICULTURE

Growth of Residual Trees

Residual saw-timber trees and poles were observed separately

because (1) the two differ in age and growth rates as well as in

size, (2) ingrowth accrues in units of whole tree volumes and

tends to be erratic, and (3) ingrowth «varies greatly from stand to

stand ; this variation depends principally on the amount of advance

reproduction present at the time of logging rather than on numbers and sizes of residual trees.

Four steps were followed in analyzing reserve tree growth.

(1) Gross board-foot growth was related to reserve-stand basal

area by computing a separate regression for each 5-year period.^

(2) A first estimate of plot growth was then read from the regressions, and ratios of relative growth rates obtained by dividing

estimated plot growth into actual plot growth. (3) Multiple regressions of relative growth rates on 10-foot, site-index classes

and Keen's age classes (6) were computed, from which adjusted

relative growth rates were derived. This step was taken after

a study of these factors revealed a significant multiple correlation.

(4) Adjustments of growth in the 7th, 8th, 9th, and 10th 5-year

periods after logging were made. A study of the influence of

growing season precipitation (April-August) on growth, by

graphic methods, showed that this step was necessary.

Number and Size

Analysis of the effect of number and size distribution of residual

trees shov/ed that gross board-foot growth correlates better with

reserve-stand basal area than with reserve-stand board-foot volume. Because of differences in diameter distribution and number

of trees per acre, stands of equal board-foot volumes frequently

have different basal areas. Thus, stands of small trees show a

greater basal area than stands having the same board-foot volume

per acre in larger but fewer trees. Stands composed of numerous

trees of small diameter tend to grow faster.

The correlation of reserve-stand basal area and growth was

further studied by relating board-foot growth per acre to reservestand basal area separately for each 5-year period after logging.

In light reserve stands, the growth rate of individual trees was

high but diminished with increased reserve-stand volume. This

demonstrates the effect of competition. Trees in stands with light

reserve, therefore, grow faster than trees in relatively wellstocked, heavy reserve stands. The trend of periodic growth by

elapsed time after logging showed that 5-year board-foot increment per acre increases rapidly to the 3rd and 4th 5-year periods.

In later periods, increment declines progressively.

Although growth correlates better with reserve-stand basal

area than with board-foot volume of reserve, the latter has considerable utility in predicting growth because it is a more commonly available statistic. Some of the prediction methods pre-

^ Since the relationship between reserve-stand basal area and periodic

growth was linear in the early periods and did not tend to become curvilinear

until the 9th and 10th periods, a more complex method of analysis was not

justified.
GROWTH OF SELECTIVELY CUT PONDEROSA PINE 5

sented later therefore are based on board-foot reserve. Although

predictions based on board-foot reserve are less precise than those

using basal-area reserve, they are reasonably accurate for large

areas containing a variety of stand conditions.

Site Productivity and Age

Productivity of a given area, as expressed by site-quality classes

or site index, has long been recognized as a variable affecting

growth rates. Each of the sample plots was classified according

to Meyer's site index on the basis of average age and total height

of dominant and codominant trees (appendix table 11, 10). Site

index for the plots at 100 years ranged from as low as 52 feet to

as high as 92, and the average for all plots was 71 feet. Grouping

of the plots by Meyer's interregional ponderosa site-quality classes

(appendix table 12) placed 98 percent of them in classes III, IV,

and V. Stands on sites of high quality grow more rapidly, of

course, than those on poor sites, and growth estimates must therefore be adjusted for such variations.

Growth rate varied by 12 percent between adjacent site classes

with the higher site class growing faster than the lower by that

amount in each case. Because the study included only stands

ranging from site index 52 to 92 feet (site classes III-VI), it is

not known to what extent adjustment factors can safely be applied to stands outside of that range. The 12 percent difference

closely approaches the 15 percent found in the Pacific Northwest

by Briegleb (1).

In the analysis, age was found to be another factor strongly

inñuencing the growth rate. Young trees grow faster than old

ones. Thus, age of the reserve stand affects the relative growth

rates. To determine the average physical age of uneven-aged

ponderosa pine stands in actual years would be difficult. Therefore, to provide a simple means of quickly assessing the relative

age of these stands, the Keen system of tree classes was used.

Keen's tree classification (6), which is commonly used in the

northern Rocky Mountain region, distinguishes four classes of

physiological age. They are designated as class 1, young blackjacks usually less than 80 years of age; class 2, immature trees

still making rapid growth, approximately 80 to 180 years of age ;

class 3, mature trees, approximately 180 to 300 years ; and class 4,

overmature trees 300 years or more in age. The use of Keen age

reduces need for increment borings and difficult, time-consuming

annual ring counts to determine age. Because Keen age classes

and growth showed a straight-line relationship for the stands

studied, average age was quickly approximated by taking an

average weighted by the number of trees in each of the individual

Keen age classes of a group of sample trees. The average age

class of the stands from which the data were collected was 2.4,

indicating an age nearly midway between classes 2 and 3. Average age class on individual plots ranged from 1.0 to as high as 4.0.

The adjustment factor between any two adjacent Keen standage classes was found to be 30 percent. Thus a stand in age class

3 grows 30 percent less than a stand in age class 2, providing other
Q HANDBOOK 39. U. S. DEPARTMENT OF AGRICULTURE

conditions are equal. The 30-percent factor is applicable to the

full range of age classes because all ages were represented in the

sample data.

Precipitation

The effect of precipitation partially obscures the true trend of

growth response after logging. In general, growth slows down

during drier periods and accelerates during wetter periods. Consequently, abnormal precipitation tends to exaggerate the effects

of logging in some instances and nullify it in others. To remove

this masking effect and provide average growth rates for approximately normal precipitation, it was necessary to evaluate the influence of rainfall and adjust the growth rates. The influence of

rainfall was first observed in the data for the period 1943-47

(fig. 1)."* Almost without exception, grovv^th accelerated in that

period, independently of elapsed time after logging or plot condition.

To facilitate comparison of growth on all plots, as influenced

by precipitation and time since logging, the curves in figure 1 are

brought to the left in figure 2 so that all plots have a common base

line for the 1st 5-year period. Also, each curve in figure 2 reflects

the wet cycles and dry cycles experienced by the plots the curve

represents. For example, on the 13 50-year plots growth from the

1st period to the 4th was made when annual growing-season precipitation was above average; from the 5th to the 8th, when

precipitation was below average; and in the 9th and 10th, above

average. Thus, in using all the curves, we find that from the 1st

to the 6th 5-year period the number of plots representing growth

in wet and dry cycles was nearly equal. On the average, there;

fore, abundance of precipitation did not have a net effect on

growth. However, during the 7th and 8th periods, the number

of plots representing grovd:h in dry cycles was greater than that

representing wet-cycle growth; and in the 9th and 10th periods,

only wet-cycle growth was represented. Thus, growth fluctuations

in the last 4 periods were attributed mainly to the effects of precipitation.

In making the adjustment for more abundant or less abundant

precipitation for the 7th to 10th periods, the average growth pattern for the 13 plots that had been cut 50 years prior to measurement was used. It was believed that the effect of logging release

on those plots had largely diminished. If the decline in growth

rates during the 7th and 8th 5-year periods had continued, growth

in the last period would have been only 87 percent of what was

^ Precipitation statistics in figure 1 are based on records of western Montana weather stations at locations reasonably similar to, although somewhat

lower in elevation than, ponderosa pine stands. Most of the records were not

continuous for the whole 50-year period, and records from only 2 to 8 stations were used for different 5-year periods. Although the records show

trends in only a general way, they support observations that 1918-37 was a

generally dry period. April through August probably does not correspond

exactly to the period when rainfall has its greatest inñuence on growth of

ponderosa pine, but it is believed to be approximately correct; a detailed

study would have been outside the scope of the project. Because the precipitation data are relatively crude, it is not possible to determine the statistical

significance of the correlation.
GROWTH OF SELECTIVELY CUT PONDEROSA PINE

600

y^ 10

U 0

1

ii-i

^^^

I

^

1^ 1-1=1-1 ^

ii=l=i=B I I

1898- 1903- 1908- 1913- 1918- 1923- 1928- 1933- 1938- 1943-

1902 1907 1912 1917 1922 1927 1932 1937 1942 1947

FIVE-YEAR PERIODS

LEGEND

A 13 50-yeor plots £

B 5 40-year plots F

C 3 35-yeor plots 6

D 11 30-year plots H

I

6 25-year plots

5 20-yeor plots

6 15-year plots

9 lO-yeor plots

2 5-yeor plots

First five-year period otter logging

FIGURE 1.—Five-year periodic growth and growing season precipitation for

ponderosa pine sample plots, 1898-1947.

found. Even though the 9th period included only growth made

during wetter than average years, it continued the slight downward trend. However, the decline ended abruptly in the sudden

increase of growth in the 10th period which is believed to be at

least partly an accumulated or delayed effect of the increased precipitation during the 9th period. The downward trend displayed
8 HANDBOOK 39, U. S. DEPARTMENT OF AGRICULTURE

by the 7th to 9th periods was probably a normal decline owing to

increasing competition after logging. Therefore, a line paralleling that trend was fitted between the points of the 7th, 8th, 9th,

and 10th periods (fig. 2). In this way, above-average growth in

the 10th period was leveled off against below-average growth in

the other periods. As a consequence of this analysis, growth in

the 7th, 8th, and 9th periods was raised by approximately 4 percent, and growth in the last period was reduced to 89 percent of

the actual. These adjustment factors were applied to all of the

plots. *

600

500

Ci

5 400

Ci

§

et

I

300

200

100

LEGEND

— Growth during drier periods

—' Growth during wetter periods

3 4 5 6 7 8

FIVE-YEAR PERIODS SINCE LOGGING

10

LEGEND

A 13 50-yeor plots £

B 5 40-year plots F

C 3 35-yeor plots G

D 11 30-year plots H

I

6 25-year plots

5 20-year plots

6 15-year plots

9 lO-yeor plots

2 5-year plots

FIGURE 2.—Growth of ponderosa pine sample plots, by 5-year periods since

logging, with an adjustment for precipitation for the 50-year plots.
GROWTH OF SELECTIVELY CUT PONDEROSA PINE 9

Vigor

The correction for average stand age according to the Keen

tree-classification system largely accounted for differences in

vigor and left comparatively little pure-vigor effect for separate

correlation. After adjusting for stand age, however, attempts to

correlate board-foot growth with tree vigor were unsuccessful

because of the correlation of age and vigor in the basic data. The

analysis method used was not sensitive enough to separate pure

age and vigor effects from their interaction.

Vigor classes A and B included 64 percent of the basal area of

ponderosa pine trees on the sample plots—13 percent in class A

and 51 percent in class B which was approximately the average.

Twenty-nine percent was in class C and 7 percent in class D.

Since the vigor of reserve stands will improve under intensive

management, future volume predictions based on data in this

study may underestimate growth if there is a larger percentage

of high-vigor trees than shown here. On the other hand, an overestimate may result if a stand is of less than the average vigor.

Reliability of the Data

By correlating gross growth with reserve-stand basal area, 48

to 63 percent of the total variation of growth within 5-year

periods was removed. Adjustment for the additional variables of

site and age accounted for 70 to 77 percent of the variation. Some

of the remaining unaccounted variation probably was due to the

effect of precipitation, for which an adjustment was also made as

described earlier.

To evaluate the efficiency of these data for predicting growth,

fiducial limits were computed for the regressions of periodic

growth on reserve-stand basal area in the 1st, 5th, and 10th 5-year

periods, respectively. The solid lines in figure 3 show computed

average growth and the dotted lines outline the fiducial limits or

confidence bands at the 95-percent level. The probabilities are 95

out of 100 that the true regression lines for the stands studied

fall within the confidence bands shown.

Ingrowth

Trees below 9.6 inches d. b. h. in a reserve stand contribute

board-foot volume for the first time when they reach the 10-inch

class. Because of the highly variable nature of ingrowth on a

per-acre basis, computation of average ingrowth per acre seems

pointless. To use such average figures in growth predictions

would introduce large errors into the estimates. However, knowledge of the approximate rate of ingrowth expected is important

because it helps to determine the rate at which the old stand may

be cut. The average volume of pole-size trees was, therefore,

determined by 5-year periods and 1-inch d. b. h. classes for trees

of average age and vigor. These volumes can be applied to the

actual number and size of poles in a stand to determine the volume

of ingrowth expected in future periods.

In collecting the field data, trees that contributed to ingrowth

were taken as they were found, and an attempt w^as made to ac-
IQ HANDBOOK 39, U. S. DEPARTMENT OF AGRICULTURE

1.000

800

600

400

200 -^

PERIODIC SROWTH 45 - 50 YEARS

AFTER LOGGIN 6

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PERIODIC SROWTH 20 - 25 YEARS ^>

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RESERVE

FIGURE 3.—Fiducial limits of regression lines.

count for small dead trees. The ingrowth tables presented later,

therefore, represent average net growth to the extent that the

field measurements were accurate and representative. However,

it is probable that conditions will be found where exceptional

numbers of small saplings exist in dense thickets. In such instances, growth will be far slower and mortality far higher than

indicated in the tables. In future volume predictions, therefore,

these small trees should be eliminated, but only when they occur

in numerous thickets.
GROWTH OF SELECTIVELY CUT PONDEROSA PINE U

Mortality

Although mortality is a highly important factor in timber management, its erratic occurrence from acre to acre makes the

achievement of a high degree of accuracy in predicting such losses

difficult. Over large areas, hov^ever, average values should approximate true values except in instances of catastrophe, such as

insect epidemics or violent storms. Even though average mortality figures are sometimes inaccurate, adjustment for this factor

will generally give the results of growth computations more

realism than if it is ignored. In the analysis of the data presented

here, mortality was handled as a percentage loss of gross growth.

No attempt was made to determine the growth on the dead trees

from the time of logging until death. However, in order to give

the results of the analysis the smoothing inñuence of data from a

large area, mortality data from a 2,000-acre selective cutting in

Lick Creek on the Bitterroot National Forest were included.

An attempt was made to correlate mortality with reserve-stand

volume and 5-year periods after logging, but the experimental

error was so high that the correlations were not statistically significant. Consequently, mortality was computed as an average

percent of the gross growth and found to be 15 percent, which

agreed with that found in the Pacific Northwest (9). Under good

management, it is probable that much of the mortality will be

anticipated and the trees harvested before they die or lose their

value. In such instances, growth predictions may underestimate

actual growth to some extent.

THE GROWTH TABLES AND HOW TO USE THEM

General Estimates

Growth can be estimated as an average figure that is applicable

to average or typical residual stands. The average volume per

acre of residual ponderosa pine, by reserve-stand classes and

5-year intervals after cutting is shown in tables 1 to 3. Because

mortality has been deducted, the volumes given are net. Table 1

represents growth estimates for typical or average site-class conditions on cut-over areas, and tables 2 and 3 show values for site

classes IV and V, respectively. The values given in these tables

can be converted to other site classes by using a 12-percent adjustment factor. For example, a value in site class IV when

multiplied by 112 percent is converted to a corresponding value

for site class III

In order to use tables 1 to 3, the board-foot volume of a reservestand (trees 10 inches d. b. h. and larger at logging) and site

class 5 are the only stand statistics needed. As an example of how

to use the tables, assume that selective cutting in a ponderosa pine

stand averaging site class IV left a reserve of 4,500 board feet per

acre, and that the predicted volume of this stand in 30 years is

required. (1) Enter table 2 at the 4,500 board-foot reserve-stand

' Site classification tables are presented in the appendix, p. 28.
12 HANDBOOK 39, U. S. DEPARTMENT OF AGRICULTURE

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]_g HANDBOOK 39, U. S. DEPARTMENT OF AGRICULTURE

class (interpolate between 4,000 and 5,000 board feet) ; (2) read

the values in the 30-year column. The volume will be 6,920 board

feet 30 years after logging, representing a net growth of 2,420

board feet (6,920 bd. ft. -4,500 bd. ft.) in 30 years, or 80.7 board

feet periodic annual growth. Ingrowth must be computed independently because it is not included in these tables.

Adjusting Growth Estimates for Additional Variables

To refine the growth prediction, the following information will

be needed :

1. A stand table of the residual trees in the 1-inch d. b. h. class

and larger. Do not include exceptional numbers of small trees that

occur in numerous dense thickets. Occasional thickets, which are

typical of overmature stands in western Montana, should be included.

2. Basal area of the reserve stand 9.6 inches d. b. h. and larger.

3. Site index (height in feet of the average dominant and codominant trees at 100 years—see appendix tables 11 and 12).

4. Age of residual trees, based on a sample of residual trees

classified by Keen tree classes.

After basal area has been derived from the stand table, summarize the survey data from the cut-over stand, as in the following

example :

1. Volume, 5,000 board feet.

2. Basal area, 50 square feet.

3. Site index, 70 feet at 100 years (site class V).

4. Keen age, 2.6.

5. Cutting cycle, 35 years.

Growth is then computed as follows:

1. Derive gross growth by reading from table 4 for the correct

basal area (50) and cutting cycle (35). In this instance, gross

growth is 4,850 board feet. Interpolate when values are intermediate to those shown in the table.

2. Obtain a correction factor (94 percent) for age (2.6) and

site index (70) from table 5. This reduces growth to 4,559 board

feet (4,850 X 0.94).

3. Take out mortality with the 15 percent average found in the

study. 4,559 - (0.15 X 4,559) or 4,559 X 0.85 = 3,875 board feet.

This is net growth of the residual trees. If a more exact mortality correction factor is available for a particular stand, it should

be used instead of the 15 percent average.

4. Sum the reserve stand volume and net growth to obtain net

volume of the residual trees at the end of the cutting cycle—

5,000 + 3,875 = 8,875 board feet per acre. Periodic annual

growth is 3,875/35 = 111 board feet.

5. Set up a stand table for determination of ingrowth, using

field survey data, as shown in the following tabulation :
GROWTH OF SELECTIVELY CUT PONDEROSA PINE 17

D.b,h. class Trees per acre^

(inches) Ponderosa pine Douglas-fir

5 0.19 2.75

6 — 2.17

7 .37 1.90

8 — 1.28

9 .92 .83

Total 1.48 8.93

* Trees in the 1- to 4-inch d.b.h. classes not recorded in this instance because,

as shown in tables 7 and 8, ponderosa pine and Douglas-fir do not attain

merchantable size in 35 years.

TABLE 5.—Correction percentages for effect of age and site index upon

board-foot growth of selectively cut ponderosa pine stands

Average age

Average site index

(Keen class)

50 60 70 80 90

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

Percent

125

122

118

116

112

110

106

104

100

98

95

92

89

86

83

80

77

74

70

68

65

62

59

56

53

50

47

44

41

38

35

Percent

133

130

127

124

121

118

115

112

109

106

103

100

97

94

91

88

85

82

79

76

73

70

67

64

61

58

55

52

49

46

43

Percent

142

138

136

133

130

127

124

120

118

114

]

112

108

105

102

100

97

94

90

87

84

81

78

75

72

69

63

60

57

54

51

Percent

150

147

144

141

138

135

132

129

126

123

120

117

114

111

108

105

102

99

96

93

90

87

84

81

78

75

72

69

63

60

Percent

158

155

152

149

146

143

140

137

134

131

2.0- 128

2.1 - 125

2.2 122

2.3

2.4 _

119

116

2.5 113

2.6- - _ . 110

2.7 107

2.8

2.9- —

3.0

104

101

97

3.1

3.2

3.3

3.4

3.5

3.6

3.7

3.8

95

92

89

86

83

80

77

74

3.9

4.0

71

68
18 HANDBOOK 39, U. S. DEPARTMENT OF AGRICULTURE

6. Compute ingrowth from tables 6, 7, and 8 and the stand

table prepared in step 5. Tables 6, 7, and 8 show the board-foot

volume of pole-size trees by 5-year intervals after logging. In

our problem, both ponderosa pine in site class V and Douglas-fir

are present. Therefore, values are taken from table 7 for ponderosa pine and from table 8 for Douglas-fir. Values, read from

the proper diameter class and 5-year interval in the table, should

be multiplied by the number of trees in the corresponding diameter class in the stand table. Thus, in the example there is 0.37

ponderosa pine tree per acre in the 7-inch d. b. h. class. A volume

of 41 board feet is shown in table 7 for the volume of a 7-inch tree

35 years after logging. This volume multiplied by the number of

trees per acre in the stand table will give the volume per acre

TABLE 6.—Volume, Soribner n¿Ze, for individual pole-size ponderosa pine trees

in selectively cut stands, by d. b. h, classes, site-quality class IV {site

index 78y

D.b.h. Volume per tree after an interval of—

class

at time

of cutting

(inches)

5

years

10

years

15

years

20

years

25

years

30

years

35

years

40

years

45

years

50

years

3

4

5

6

7

8

9

Bd.ft.

27

Bd.ft.

27

41

Bd.ft.

37

56

Bd.ft.

37

53

70

Bd.ft.

31

50

68

89

Bd.ft.

28

45

63

81

104

Bd.ft.

27

40

57

74

94

118

Bd.ft.

32

46

64

83

104

134

Bd.ft.

28

40

55

72

92

115

144

Bd.ft.

31

45

59

77

96

124

154

^ These volumes are for trees 9.6 inches d. b. h. and larger ; they have been

reduced by 5 percent to account for average mortality of poles in the stand.

TABLE 7.—Volume, Scribner rule, for individual pole-size ponderosa pine trees

in selectively cut stands, by d. b. h. classes, site-quality cUiss V (site index 6J^)^

D. b. h. Volume per tree after an interval of—

class

at time

of cutting

(inches)

5

years

10

years

15

years

20

years

25

years

30

years

35

years

40

years

45

years

50

years

4

5

6

7

8

9

Bd.ft.

18

Bd.ft.

37

Bd.ft.

24

39

Bd.ft.

19

33

49

Bd.ft.

27

42

58

Bd.ft.

19

34

50

69

Bd.ft.

26

41

58

78

Bd.ft.

19

32

48

64

82

Bd.ft.

26

38

52

67

86

Bd.ft.

21

30

42

56

71

93

* These volumes are for trees 9.6 inches d. b. h. and larger; they have been

reduced by 5 percent to account for average mortality of poles in the stand.
GROWTH OF SELECTIVELY CUT PONDEROSA PINE 19

TABLE 8.—Volume^ Scribner rule, for individual pole-size Douglas-fir trees in

selectively cut ponderosa pine stands, by d. b. h, classes, site-quality classes

IV 2nd V

D.bh. Volume per tree after an interval of—

class

at time

of cutting

(inches)

5

years

10

years

15

years

20

years

25

years

30

years

35

years

40

years

45

years

50

years

1

2

3

4

5

6

7

8

9

Bd.ft.

21

Bd.ft.

28

Bd.ft.

27

35

Bd.ft.

27

34

43

Bd.ft.

25

32

41

48

Bd.ft.

27

32

40

48

55

Bd.ft

25

31

39

45

53

60

Bd.ft.

27

32

39

45

50

58

65

Bd.ft.

28

33

40

47

52

59

65

71

Bd.ft.

25

32

39

45

50

57

64

70

76

^ These volumes are for trees 9.6 inches d. b. h. and larger; they have been

reduced by 5 percent to account for average mortality of poles in the stand.

(41 X 0.37 = 15.17 bd. ft.). A tabulation like the following will

result when volumes for the other diameter classes have been

computed.

D.bJi.

class

(inches)

5 ___

6 ___

Net ingrowth per acre^

Ponderosa pine

(bd. ft.)

'0.00

7 15.17

8 —

9 71.76

Douglas-fir

(bd. ft.)

85.25

84.63

85.50

67.84

49.80

Total 86.93 373.02

^ The products derived are net because average mortality has been deducted

from pole volumes in the tables.

' Negative value because a 5-inch ponderosa pine does not attain merchantable size in 35 years (table 7).

7. Obtain total volume of the stand 35 years after logging by

summing the volume of residual trees and ingrowth. The computations for this and the periodic annual growth follow :

Board feet

Volume of residual trees at end of 35-year cutting cycle 8,875

Ingrowth :

Ponderosa pine : 87

Douglas-fir 373

Total predicted volume of stand 10 inches d.b.h. and larger at end of

35-year cutting cycle 9,335

Periodic annual growth :

3,875 bd. ft. + 87 bd. ft. + 373 bd. ft.
2Q HANDBOOK 39, U. S. DEPARTMENT OF AGRICULTURE

Limitations on Use of Tables

Two limitations, which the user should remember, apply to prediction of growth from the tables presented here. One pertains

to the species composition of stands. Since sample stands contained, on the average, 77 percent ponderosa pine and 23 percent

Douglas-fir by basal area, the tables should be used only for stands

that are predominantly ponderosa pine. The other limitation applies to predicting growth in stands that have been cut two or

more times. An estimate from the tables should not be applied

directly to a cut-over stand unless growth has dropped back to

about the prelogging rate. When a stand is still benefiting from

the stimulating effect of thinning caused by a previous logging,

its initial growth rate at the time of the second cutting will be

higher than the one given in the tables. Therefore, the tables

will generally underestimate growth after a second cutting. If an

adjustment is made for higher initial growth, the accuracy of the

estimate will be improved but the degree of improvement and the

reliability of the estimate will be unknown.

The values in tables 1 to 4 should not be extended to predict

growth in stands more heavily stocked than shown in the tables.

It is probable that growth in such stands is severely retarded by

the greater stand density.

SILVICULTURAL SIGNIFICANCE OF THE FINDINGS

The results obtained in this study, aside from their value for

predicting growth, have some important silvicultural implications.

Forest managers will find the data useful in evaluating (1) the

effect of various intensities of cutting upon growth of reserve

stands, (2) the growth response by stands composed of trees of

differing age and vigor and on lands of varying degrees of site

quality, (3) the fitness of trees to reserve from cutting, and (4)

the relative merits of various cutting cycles.

Intensity of Cutting

The quantity of growing stock left on cut-over areas determines in a large measure the amount of growth that can be expected for the next two or three cutting cycles. Low-volume reserve stands grow less than heavier reserve stands. For example,

table 1 shows that the residual trees in a typical 2,000-board-foot

reserve stand will reach a volume of 3,380 board feet in 30 years,

but a 10,000-board-fóot reserve stand will increase to 14,260 board

feet in the same time. In other words, the light stand will add

only 46 board feet per acre per year of periodic growth as contrasted with 142 board feet in the heavier stand.

However, board-foot growth on reserve stands does not represent the maximum potential growth return from the soil. Reserve

stands are usually understocked because logging has removed part

of the stand. Moreover, they usually contain mature and overmature trees that are incapable of growing as fast as younger

trees. Cutting off the old trees and starting a new fully stocked
GROWTH OF SELECTIVELY CUT PONDEROSA PINE £1

stand of young trees would, over the rotation period, probably

yield the highest mean annual growth.

On the other hand, several advantages will be gained by leaving

residual trees. Relatively high board-foot growth rates may be

obtained from such growing stock following logging until the

younger age classes begin to produce merchantable volume. Thus,

cuts can be taken at relatively short intervals. The growth obtained on the old boles yields high-quality wood because these

stems lave been pruned naturally, and a large portion of the new

growth will be in the form of clear wood. In addition, the residual trees provide a source of seed for natural regeneration of

the stand.

Cutting should be heavy enough to make possible the prompt

establishment of adequate numbers of seedlings, provide conditions for seedling development, and yet leave enough reserve trees

for one or more cuts during the next 20 to 50 years. The following tabulation shows the reproduction success obtained on 300

4-milacie plots sampled in this study.

T,r 1 r -77, Percent of plots stocked Number of residual trees per ^-^^ ^^^ ^^ ^^^^ seedlings and

acre 10 inches d.b.h. and larger saplings per acre

Ponderosa pine Douglas-fir

Under 10 , 20 40

10-19 26 39

20-29 56 44

33 or more 20 60

Two-thirds of the pine and three-fifths of the Douglas-fir reproduction shown was established subsequent to cutting; therefore,

these figures reflect largely the influence of the density and composition of the residual stand. The residual trees were mainly

ponderosa pine with less than one-third of the board-foot volume

in Douglas-fir. However, because Douglas-fir is a very aggressive

seed producer, that species became established in proportionately

greater quantities than ponderosa pine.

The tabulation indicates that 20 to 29 ponderosa pine trees per

acre (3,500 to 5,400 bd. ft.) bore suflScient seed to stock a majority ol the areas sampled to the extent of 300 or more seedlings

and saplings per acre. Less than 20 trees per acre apparently did

not produce enough ponderosa pine seed to counteract negative

factors in seedling establishment as successfully. Reserve stands

contaiaing from 30 to 53 trees per acre, with volumes ranging

from about 6,300 to 9,700 board feet, showed much less general

stocking of ponderosa pine but much more general stocking of

Dougla3-fir. Thirty to fifty-three trees per acre, therefore, appears to be the threshold above which conditions favor a greater

seedling establishment rate for Douglas-fir than for ponderosa

pine. Evidently ponderosa pine seedlings did not survive as well

in heavj reserve stands as they did in somewhat lighter tree cover.

In typical western Montana ponderosa pine stands, a reserve of

about 5,000 board feet per acre will provide (1) an adequate seed

source, (2) conditions favoring survival of ponderosa pine seed-
22 HANDBOOK 39. U. S. DEPARTMENT OF AGRICULTURE

lings, and (3) moderately good growth rates in the residual timber. The study indicates that larger reserve volumes aie likely

to encourage establishment of Douglas-fir instead of pine. Of

course, special reproduction measures, such as seedbed preparation coordinated with a seed crop and rodent control can assist in

establishing pine, but without seedbed preparation Doyglas-fir

will probably dominate the reproduction in heavier stands.

Not all ponderosa pine stands contain enough thrifty trees to

justify leaving large reserves. Many old stands support few

trees that are suitable to reserve for an appreciable length of time.

In such instances, the chief silvicultural job is to regenerate the

stand as quickly as practicable. Where large areas of such stands

exist, a light salvage cut can be made first, harvesting high-risk

trees and opening up the stand to easy access for later salvage.

The residual stand can then be removed within a 20- to 30-year

period. If reproduction does not become established during the

period of removal, other measures such as planting will be necessary. Since growth on these old stands will probably be low,

reserving such trees serves mainly to (1) spread the cut of old

timber to fill in gaps in age-class distribution, (2) protect the old

stand from loss while placing a larger area under management,

and (3) maintain a seed source for regenerating the stand.

Growth of Reserve Stands by Average Stand Age and Site Quality

Average stand age and quality of site strongly influence the

growth of residual stands. In general, the younger the stand and

the better the site, the smaller the reserve stand which is required

to produce a given quantity of growth. Table 9 shoVs the

amounts of reserve-stand growing stock required to produce a

periodic annual growth of 100 board feet for different ages and

sites. The selection of 100 board feet annual growth was arbitrary and should not be construed as a general goal. Oil some

sites the objective may be to obtain considerably higher growth,

while on other sites, 100 board feet may be too optimistic, depending upon the stand condition.

TABLE 9.—Reserve stand needed to obtain 100 bd. ft} jyeriodic annual frowth

per acre in 30 years, by age class ayid site quality

Age classof

reserve stand

Volume of residual trees per acre

Site III Site IV Site 7

1

2

Bd. ft.

2,600

3,700

5,400

8,400

Bd, ft.

3,000

4,200

6,400

10,500

Bd.ft

3,400

4,900

3

4

7,600

C)

^ Includes average periodic annual ingrowth of 14 board feet per acre.

- Age class is determined as an average Keen age class weighted by the

numbers of trees 9.6 inches d. b. h. and larger in each of the individual Keen

age Masses comprising the sample.

A stand considerably in excess of 40,000 board feet would be needed here.
GROWTH OF SELECTIVELY CUT PONDEROSA PINE 23

The table shows that only about one-half as much reserve volume will be needed in age-class 1 stands as in age-class 3 stands

to produce a periodic annual increment of 100 board feet per acre

in a 30-year cutting cycle. Thus, for example, on site IV land,

a 3,000-board-foot age-class 1 stand will produce the same growth

as a 6,400-board-foot age-class 3 stand. However, reserve stands

comprised of all age-class 1 trees are rare. The majority of the

stands have enough older trees in them to raise the average age

of the reserve stand to at least class 2. On the other hand, it is

also unlikely that reserve stands comprised of all age-class 4 trees

will occur because large old overmature trees are usually removed

in cutting. Thus, the average age of most reserve stands will fall

between age classes 2 and 3. The trees in this study averaged 2.4.

In age classes between 2 and 3, reserve stands ranging from 4,550

board feet per acre on site III up to 6,250 board feet per acre on

site V will be required to produce 100 board feet per acre periodic

annual increment for 30 years after logging.

The study indicates the value of concentrating intensive forest

management on the better sites. For example, an age-class 3 reserve stand having a volume of 5,400 board feet on site III land

will produce as much growth (100 board feet per year) as a stand

of 7,600 board feet of the same age on class V site. Thus, approximately 40 percent more volume is required on site V than on site

III for the same production. Whenever the forest manager has a

choice between encouraging growth by silvicultural measures on

less productive or more productive lands, he will be wise to concentrate first on the better sites.

Selecting Trees to Reserve From Cutting

Reserve-stand growth comprises the aggregate growth of all

the individual trees in the stand. Therefore, the age and vigor of

the trees have an important bearing on the reserve-stand growth

rate. High growth rates can be obtained by reserving, where

practicable, young vigorous trees. Reserving trees capable of

growing rapidly and producing quality material is the responsibility of the tree marker.

Ponderosa pine trees tend to grow in a groupwise pattern with

small even-aged patches varying in size from a small fraction of

an acre to several acres scattered through the stand. Variation

in the ages of these small groups creates the uneven-aged condition

that is characteristic of virgin ponderosa pine stands. The wellqualified marker will vary his marking with the conditions he

encounters as he works through the stand. Marking may vary

from clear cutting groups comprised of old low-vigor trees to

thinning of bull pine groups and release of poles and saplings.

The marker must have enough knowledge of individual tree

growth to choose intelligently in the various kinds of groups

encountered.

Growth rates of ponderosa pine residual trees vary greatly.

Variation may be due to several causes such as competition and

site quality, but a large part of it is caused by differences in age

and vigor of the trees. Diameter grovv^th in the first decade after
24 HANDBOOK 39. U. S. DEPARTMENT OF AGRICULTURE

TABLE 10.—Diameter-breast-high growth for 10-year period before logging

and after logging^ by Keen tree class

Vigor class Unweighted

average

Age class

A B C D

. ÍPrelogging

\ Postlogging

2 ÍPrelogging

(Postlogging

Q ÍPrelogging

(Postlogging

4 ÍPrelogging

) Postlogging

Unweighted ÍPrelogging

average (Postlogging

Inches

1.60

1.99

1.35

1.91

.97

1.88

^72

^88

1.16

1.54

Inches

1.25

1.65

.99

1.26

.74

1.14

.60

.70

.90

1.19

Inches

0.81

1.09

.69

1.11

.54

• .90

.42

.46

.62

.89

Inches

0.64

.97

.56

.70

.44

.69

.38

.35

.50

.68

Inches

1.08

1.42

.90

1.24

.67

1.03

.53

.60

.80

1.07

Basis : 926 sample trees.

^ No 4A trees were obtained in the sample,

were obtained by extrapolation.

Values shown for this class

logging may vary from as low as 0.35 inch per decade to as high

as 1.99 inches per decade (table 10). Table 10 shows the diameter

growth of 926 ponderosa pine trees for 10 years before and 10

years after logging in relation to the Keen tree classification.

Growth varied inversely with age, but directly with vigor. Thus,

as age increases growth decreases, and as vigor declines growth

decreases.

Residual trees also vary in their ability to respond to release.

The response or increase in growth rate due to logging release is

represented by the difference between prelogging and postlogging

diameter growth rates shown in table 10. Trees in age-classes 1,

2, and 3 responded well, but those in age-class 4 responded only

a little in actual board-foot growth. Trees in the A vigor class

showed the best response in board-foot growth, while trees in

class D showed the least. Based on past growth, the lower vigor

trees make the largest percentage-wise response. The response

of the trees to logging, however, is not as important to the marker

as the total growth expected on the trees after logging. It is interesting to note that the average response of age-class 3 trees in

the A, B, and C vigor classes about equals the class 1 and 2 trees

(table 10). The total growth after logging, however, is different

because the trees in the younger age classes were making better

growth before as well as after logging.

The expected growth rate after logging provides a better criterion to use for selecting trees to reserve from cutting than the

response to release does. In the following tabulation, Keen tree

classes have been arranged in four groups of expected diametergrowth rates for the first decade after logging. The marker will

find this information helpful, along with other considerations, in

making his selections of trees to cut and trees to leave.
GROWTH OF SELECTIVELY CUT PONDEROSA PINE £5

Range of

diameter-growth rate Keen tree cla^s

(inches)

1.6-2.0 lA, 2A, IB

1.1-1.5 3A, 2B, 3B, IC, 2C

.6-1.0 [ID, 3C, 4A, 2D, 4B, 3D]

0.0- .5 [4C, 4D]

The tree classes in the right-hand column are arranged in descending order by growth rates. The brackets include those

classes in which the trees grew less than the average. On the

basis of this tabulation, trees in the groups showing the lower

growth rates should be designated for cutting first. The trees

within the brackets might be cut leaving only those which are

expected to grow average or better. The extent to which other

trees might be cut, or trees in classes within the brackets left,

would depend upon the condition of the stand in other respects.

Markers should not adhere strictly to vigor and age classes when

selecting reserve trees, but should also consider quality, form,

insect and disease susceptibility, and other important silvicultural

characteristics. In many instances, trees in the A vigor class

have large crowns extending far down the bole. Such trees will

not produce high-quality lumber, yet they will grow at fast rates.

The marker will face situations where volume growth should be

sacrificed for quality growth. One of the objectives of silviculture

is to improve quality; therefore, when selecting trees to reserve,

the marker should appraise the quality of the stem and form of

the tree before considering expected growth rates.

Length of Cutting Cycle

The length of the cutting cycle bears upon the growth to be

obtained. Ponderosa pine trees respond very well to release.

Trees that have been suppressed for many years take advantage

of additional growing space provided by cutting. Dominant and

codominant trees will continue high growth rates longer when

root competition is reduced. On the average, the effect of logging

release lasts for about 30 years, after which growth falls off to

prelogging rates. By that time, the growing space is occupied by

the spreading roots and crowns of residual trees, pole-size trees,

saplings released by logging, new reproduction, and other vegetation. Competition is then reñected in reduced growth rates (fig.

4). Periodic growth rates therefore indicate that 20- to 30-year

cutting cycles will yield the maximum growth on residual trees

in average stands.

Density of the reserve stand inñuenced the length of the cutting

cycle. The smallest reserve stands (1,000 board feet or less)

showed little if any decline in board-foot volume increment during

the 50-year postlogging period. Apparently 50 years is too short

a period for these light stands to reoccupy the land fully. In the

heavier reserve stands volume increment by 5-year periods increased rapidly to the second decade but dropped off significantly

to the third decade. This trend became more pronounced with

increasing reserve volume.
26 HANDBOOK 39. U. S. DEPARTMENT OF AGRICULTURE

ki

0 8

0.7

tr 0.6

tu

0.5

<^ 0.4

Qi 0.3

Ci.

0.2

TIME OF LOGGING

^

\^:'Ñ^ ^^^\K .....

Î

à

I

1 1É

\v^1

i 1fc

m

e

5-10 É

YRS. B

0-5

EFORE

0-5

YEAF

5-10

ÍS AFT

10-15

ER LO

15-20

GGING

20-25 25-30 30-35 35-•40 40-45 45-50

FIGURE 4.—Diameter growth by 5-year periods before and after logging.

Shorter cutting cycles provide an opportunity to anticipate

mortality and to harvest trees before they die. This study showed

an average mortality rate of 15 percent of the gross annual

growth. While cutting cycles shorter than 30 years may not increase the growth rates of individual trees materially, they provide an opportunity to salvage trees that are about to die. Thus,

while individual tree growth may not be affected, the total yield

of wood will be increased by the amount of annual mortality

prevented through cutting. However, we need to learn the characteristics by which we can more effectively identify the trees

that are about to die (insects, root rots, senility, etc.). "California risk marking'' represents an attempt to identify short-term

mortality for purposes of salvage (5). The system gives rules for

judging likelihood of survival by such signs as color and length

of needles, needle retention, and dead twigs and branches or weak

spots in the crown. With a more discerning selection of trees to

cut, mortality will be reduced and yields increased.

SUMMARY

A study of cut-over ponderosa pine stands in western Montana

was made in 1947 to learn of growth responses to different intensities of cutting, and to obtain information concerning the best

methods of cutting in mature and overmature stands. Although

the study was conducted in western Montana, it is believed that

the results apply equally well to the Upper Columbia Basin.

Sixty half-acre temporary sample plots, with volumes from approximately 500 to 10,000 board feet an acre, were studied.
GROWTH OF SELECTIVELY CUT PONDEROSA PINE 27

Growth was considered only for stands that had been cut once,

and elapsed time following cutting varied from 5 to 50 years. The

effects of the following factors on per-acre growth were evaluated: Volume, number, and size of residual trees in reserve

stands; site quality and stand age class; growing-season precipitation; vigor; ingrowth; and mortality.

Eight tables for predicting growth after cutting were developed.

The first predicts growth by 5-year periods on the basis of reservestand board-foot volume for average site conditions; the second

and third distinguish two degrees of site productivity. Estimates

obtained from these three tables do not take into account the important factors of stand age, and number and size of residual

trees. Therefore, the predictions are suitable only for relatively

large areas where variations tend to compensate. Tables 4 and 5

are used together to predict growth with considerably greater precision. Reserve stand is measured in terms of basal area to

evaluate number and size of trees more accurately than when

reserve stand is expressed in terms of board-foot volume. Adjustments for stand age and site quality are provided. Mortality can

be deducted either with an average factor (15 percent) or from

data based on the user's knowledge. Tables 6 to 8 give data for

estimating ingrowth separately on the basis of number and size

of poles present at time of logging.

The principal conclusions of the study concerning silvicultural

implications follow :

Residual stands of ponderosa pine of about 5,000 board feet per

acre in the Upper Columbia Basin will yield moderate growth and

provide suitable overstory conditions and seed production for

seedling establishment.

Younger, relatively thrifty stands on better sites grow much

faster than older stands on poorer sites. On site IV, a Keen ageclass 2 reserve stand with a volume of 4,200 board feet per acre

will grow as much in 30 years as a 7,600-board-foot reserve in a

Keen age-class 3 stand on site V. Silvicultural efforts should be

concentrated first on encouragement of relatively young trees on

better sites.

Diameter growth rates of individual ponderosa pine trees vary

from as low as 0.35 inch per decade to as high as 1.99 inches per

decade during the first 10 years after logging. The variation is

caused largely by the age and vigor of the trees. Tables are pre-,

sented that show the relationship of growth rates to Keen tree

classes. Markers should reserve the trees that will grow most

rapidly, after first considering quality and form.

Cutting cycles of 20 to 30 years will sustain high growth rates

on individual trees. However, more frequent cutting will aid in

reducing losses by permitting the identification and utilization of

trees that are likely to die within a relatively few years. Short

cutting cycles should be the rule. Light reserve stands will require longer cutting cycles than heavy reserve stands.
28 HANDBOOK 39, U. S. DEPARTMENT OF AGRICULTURE

APPENDIX

TABLE 11.—Height of average dominant and codominant trees by age and

site index (10)

Age (years)

Height, by site index—

40 50 60 70 80 90 100 110 120 130 140 150 160

20

Feet

6

11

16

21

26

30

34

37

40

42

44

45

46

47

48

48

49

49

50

Feet

9

15

22

28

34

39

43

47

50

53

55

57

59

60

61

62

63

63

64

Feet

12

20

28

35

42

47

52

57

60

63

66

69

71

73

75

77

78

79

80

Feet

16

26

35

43

50

56

61

66

70

74

77

80

83

86

89

91

93

95

97

Feet

20

32

42

51

58

64

70

75

80

84

88

92

96

99

102

105

108

110

112

Feet

25

38

49

58

66

73

79

85

90

95

100

104

108

112

116

119

122

125

128

Feet

30

44

55

65

73

80

88

94

100

106

111

116

121

125

129

133

136

139

143

Feet

35

51

63

73

81

89

97

104

110

116

122

128

133

138

143

147

151

154

157

Feet

40

57

70

80

90

98

106

113

120

127

133

139

145

161

156

161

165

169

172

Feet

45

64

77

89

99

108

116

123

130

137

144

151

157

163

169

174

179

183

187

Feet

50

70

85

97

107

116

124

132

140

147

154

161

167

173

179

184

189

194

198

Feet

55

77

93

105

115

125

133

142

150

158

165

172

179

185

191

196

201

205

209

Feet

60

30

40-

84

ion

50 113

60

8o~"rii'~iiir"

90

124

134

143

152

100

110

160

168

120

130

150~'I"~I~IIIII

160 -

175

182

189

195

201

170 206

180

190

211

216

200 220

TABLE 12.—Site-quality classification for ponderosa pine, with corresponding

heights at maturity in terms of logs (10)

Site-quality class

Site index

[at 100 years]

Logs in dominant trees

Central value Range

at maturity ^

TT ''''"''" T"'"" "

Feet

120

106

92

78

64

50

36

Feei

+113

99-112

85-98

71-84

57-70

43-56

43-

Number

10 or more.

8 to 9.

III . 7.

5 to 6.

3 to 4. VÎ - 2.

VII 2-.

^ Estimated in terms of 16-foot logs to 8-inch top. Maturity is assumed to begin at the age

of 250 years.

U. 8. GOVERNMENT PRINTING OFFICE: 1952 204388

For sale by the Superintendent of Documents, U. S. Government Printing Office

Washington 25, D. C. - Price 15 cents
LITERATURE CITED

(1) BRIEGLEB, PHILIP A.

1945. CALCULATING THE GROWTH OF PONDEROSA PINE FORESTS. U. S.

Forest Serv., Pacific Northwest Forest and Eange Expt.

Sta., Portland, Oreg., 60 pp. [Processed.]

(2) DUNNING, DUNCAN.

1922. RELATION OF CROWN SIZE AND CHARACTER TO RATE OF GROWTH

AND RESPONSE TO CUTTING IN WESTERN YELLOW PINE. Jour.

Forestry 20: 379-389, illus.

(3) HANZLIK, E. J.

1927. MORE ABOUT GROWTH PERCENT. Jour. Forestry 25: 443-447,

illus.

(4) HORNIBROOK, E. M.

1939. PRELIMINARY YIELD TABLES FOR SELECTIVELY CUT STANDS OF

PONDEROSA PINE IN THE BLACK HILLS. Jour. Forestry 37:

807-812, illus.

(5) JOHNSON, PHILIP C.

1951. APPLICATION OF RISK RATINGS FOR WESTERN PINE BEETLE CONTROL IN THE INLAND EMPIRE. Northwest Sci. 25 (1) : 32-37.

(6) KEEN, F. P.

1943. PONDEROSA PINE TREE CLASSES REDEFINED. Jour. Forestry 41:

249-253.

(7) KRAUCH, HERMAN.

1922. THE USE OF DIAMETER AGE CHARTS IN YIELD STUDIES. JOUR.

Forestry 20: 390-392, illus.

(8) LEXEN, BERT.

1939. GROWTH FOLLOWING PARTLY CUTTING IN PONDEROSA PINE.

Jour. Forestry 37: 943-946, illus.

(9) MEYER, WALTER H.

1934. GROWTH IN SELECTIVELY CUT PONDEROSA PINE FORESTS OF THE

PACIFIC NORTHWEST. U. S. Dept. Agr. Tech. Bui. 407, 64 pp.,

illus.

(10)

1938. YIELD OF EVEN-AGED STANDS OF PONDEROSA PINE. U. S. Dept.

Agr. Tech. Bui. 630, 60 pp., illus.