...~.. United States

1£ ~b' Department of

r:,~j Agriculture

Forest Service

Pacific Southwest

Research Station

Research Paper

PSW-RP-212

Incidence and Effects of

Endemic Populations of

Forest Pests in Young

Mixed-Conifer Forests

of the Sierra Nevada

Carroll B. Williams David L. Azuma George T. Ferrell
Williams, Carroll B.; Azuma, David L.; Ferrell, George T. 1992. Incidence and effects of endemic populations of forest

pests in young mixed~coniferforests ofthe Siena Nevada. Res. Paper PSW~RP~212. Albany, CA: Pacific Southwest

Research Station, Forest Service. U.S. Department of Agriculture; 8 p.

Approximately 3.200 trees in young mixed~conifer stands were examined for pest activity and human-caused or

mechanical injuries, and approximately 25 percent of these trees were randomly selected for stem analyses. The examination

of trees felled for stem analyses showed that 409 (47 percent) were free of pests and 466 (53 percent) had one or more pest

categories. Incense~cedar contained the fewest number of pests with 133 out of 193 trees (69 percent) free of pests, and 60

trees or.31 percent with one or more pests. White fir and ponderosa pine trees had the highest percentage of pests and

mechanical injuries: 64 percent(252 trees outof395), and 62 percent (93 trees out of 151), respectively. Top injury and dise'!se

were the two most frequent pest/damage categories recorded among all tree species. White fir seemed most susceptible to a

large number ofdiseases, particularly wetwood and leafy and dwarfmistletoes. White pine blister rust and cedar rust were the

most frequent diseases recorded on sugar pine and incense-cedar. respectively. Most diseases were in the early stages of their

infections. Bark beetles were an important pest category for white fir, ponderosa pine, and incense-cedars. Mechanical or

human-caused injuries ranged from 6to II percent ofthe damage records among all mixed-coniferspecies. Nevertheless, pest

damage on most trees was relatively minor throughout the young mixed-conifer stands and seemed to have little effect on

height and basal area increment. Tree mortality averaged a little over 3 percent. The data indicate the potential problems for

older mixed-conifer stands, and they identify white fir as the tree species particularly susceptible to pests and human-caused

damage.

Retrieml Terms: Pest Damage Inventory, mixed-conifers. white fir, ponderosa pine, incense-cedar, sugar pine, Douglas-fir,

forest insects. forest pathogens. top injury, mechanical injuries

The Authors:

Carroll B. Williams is adjunct professor offorestry, University ofCalifornia, Berkeley. David L. Azuma is a mathematical

statistician in the Watershed Management/Inland Fishery Research Unit at Station headquarters in Albany, California. George

T. Ferrell is a research entomologist at the Station's Conifer Regeneration Research Unit in Redding, California.

Acknowledgments:

We thank K. LeRoy Dolph for providing the data and Sylvia R. Mori and Sandy Young for theirstatistical and editorial

review, respectively, of the manuscript.

Cover-White flf poles killed by 5col)'tlls ventralis.

Publisher:

Pacific Southwest Research Station

Albany, California 94710

(Mailing address: P.O. Box 245, Berkeley, CA 94701-0245

Telephone: 510-559-6300)

May 1992
Incidence and Effects of

Endemic Populations of

Forest Pests in Young

Mixed-Conifer Forests

of the Sierra Nevada

Carroll B. Williams

Contents

David L. Azuma George T. Ferrell

In Brief ii

Introduction I

Methods 1

Study Area 1

Plot Selection 1

Stand and Tree Measurements and Evaluations of Damage 2

Analysis of Data 2

Results and Discussion 2

Pest Incidence 011 Standing Trees 2

Pest Incidence on Felled Trees 3

Height Growth and Site Index Values 6

Basal Area InCrell1ent 6

Tree Mortality 6

Discussion 8

References 8

USDA Forest Service Res. Paper PSW-RP-212. 1992.
In Brief . ..

Williams, Carroll B.; Azuma, David L.; Ferrell, George T. 1992.

Incidence and effects of endemic populations of forest

pests in young mixed-conifer forests of the Sierra Nevada.

Res. Paper PSW-RP-212. Albany, CA: Pacific Southwest

Research Station, Forest Service, U.S. Department of Agriculture; 8 p.

Retrieval Terms: Pest Damage Inventory, mixed-conifers, white

fir, ponderosa pine, incense-cedar, sugar pine. Douglas-fir, forest insects, forest pathogens, top injury, mechanical injuries

Forest pest managers need to assess growth losses and

tree mortality caused by forest pests under non-outbreak conditions. A Pest Damage Inventory (PDI) system, developed by

forest entomologists and pathologists of the Pacific Southwest

Region of the USDA Forest Service, was used to code insect

pests and disease-causing agents and rate the severity of pestcaused and human-caused injuries to forest trees in young

mixed-conifer stands occupying the mid-elevations on the

west slope of the Sierra Nevada. Approximately 3,200 mature

trees, generally less than 80 years of age, were examined and

877 of these trees were randomly selected for stem analyses.

Information on pest and various injuries recorded on the trees

after they were felled for stem analyses showed a substantial

increase in the number of pests and injuries compared to that

recorded on the same trees before felling. Forty-seven percent

of the felled trees were free of pests, whereas 53 percent had

exhibited one or more pest categories. Obviously, the felled

trees allowed a much closer examination of the tree stems

which revealed pests and injuries that were either missed on

standing trees or could not be seen, e.g., heart rot and wetwood.

Since the felled trees provided the most accurate information,

the bulk of the data analyses focused on these trees.

White fir and ponderosa pine trees exhibited the highest

percentage of pests and mechanical injuries: 64 percent and 62

percent, respectively, of these trees had one or more pests.

Field crews recorded a total of 414 instances of pest damage

on 252 white fir trees with pests; 120 trees had two pests, 34

trees had three pests, and six trees had four pests. The most

frequent damage observed on white fir were top injuries (96

records), wetwood (96 records), and attacks by the fir engraver (Sco!ylus ventralis Le C.) (69 records). The most frequent pest combinations on white fir were fir engraver and

wetwood (29 records) and fll·engraver and top injuries (16 records).

The examination of 93 ponderosa pines with pests yielded

120 records of pest presence/damage or pest categories. Twentythree trees had 32 pest categories, and four trees had three pest

categories. Top injuries (49 records) was the most frequent

ii

damage observed on ponderosa pine followed by some moderate defoliation caused by sawflies (II records). Bark beetles

(9 records), mechanical injuries (8 records), and smog (7

records) also damaged pines. Bark beetles and top injury was

the most frequent pest combination with four records.

Incense-cedars contained the fewest number of pests or

pest categories, with 69 percent of incense-cedar trees free of

pests and 31 percent with one or more pests. A total of 72 pest

records were compiled on the 60 incense-cedar trees with

pests. Eleven trees had two pest categories and one tree had

three pest categories. The most frequent damage was caused

by flatheaded borers (18 records), followed by cedar rust (16

records), top injury (eight records), and mechanical injuries

(eight records). F01ty-five pest records were listed for 27

sugar pine pest-damaged trees. Fourteen trees had two pest

categories, and three trees had three pest categories. Top injury (13 records) and blister rust (12 records) were the most

frequent damage observed on sugar pines. Twenty pest records

were made on 16 Jeffrey pine trees with visible damage. Four

trees had two pest categories, and top injury was the most

frequent type of damage observed. Twenty-three pest records

were catalogued on 18 Douglas-fir trees with visible damage.

Four trees had two pest categories, and one tree had three

pest categories. An unknown canker, top injury, and mechanical injuries were the most frequent types of damage

recorded on Douglas-fir trees.

In general, top injury was the most frequent pest category

recorded among all tree species, and was particularly noticeable for ponderosa and Jeffrey pines. Disease was the second

most frequent pest category recorded in the study; however,

most diseases seemed to be in the early stages of their infection. White fir seemed most susceptible to a large number of

diseases, particularly wetwood and leafy and dwarf mistletoes. White pine blister rust and cedar rust were the most

frequent diseases recorded on sugar pine and incense-cedar,

respectively. However, no bole infections were seen on any of

the sugar pines. Insects, primarily bark beetles, was an important pest category for white fir, ponderosa pine, and incense-cedars.

Height increment for the past 20 years was measured on

all stem analysis trees and was the dependent variable used to

test variability in pest classifications. No significant variations

were detected in height growth rates and total height among

the various pest classifications. Comparisons of the last 10

years of basal area increment among trees placed in various

pest classes indicated no significant variation for Douglas-fir,

white fir, sugar pine, and Jeffrey pine. There was significant

variation in basal area increment among the pest classes for

incense-cedars and ponderosa pines. Nevertheless, pest damage on most trees was minor throughout the study stands, and

USDA Forest Service Res. Paper PSW-RP-212. 1992.
we doubt that pest incidence and damage had a real impact on

basal area increment. Tree mortality averaged 3.16 percent for

young mixed-conifer stands. Bark beetles and root diseases

were the pests most frequently associated with the mortality

on white fir and ponderosa pine.

The low incidence of tree mortality and the relatively

minor effect of endemic pest activities on tree growth recorded in these studies are not surprising given the fact that the

studies were limited to young-growth mixed conifer stands

,

USDA Forest Service Res. Paper PSW-RP-212. 1992.

whose basal areas were largely composed of trees 80 years old

or younger at breast height. The trees were able to repel the

bark beetle attacks and many of the important disease pests in

these young stands were in the early stages of their infections,

and would not be expected to have much current impact on

tree health and growth. Nevertheless, the data indicate the

potential problems for older mixed-conifer stands. They identify white fir as the tree species particularly susceptible to

pest- and human-caused injuries.

iii
Introduction

O ~tbr~aks of forest pe~ts, including bark b~etles, defoliat~

mg Insects, dwarf mlstletoes and root dlseases, can reduce tree growth and cause widespread tree mortality. However,

little is known about the effects of non-outbreak or endemic

levels of these pests on trees and forest stands. Forest pest

managers have long understood the need for assessing growth

losses and mortality caused by forest pests under non-outbreak

conditions in forest stands. But they have found the task impossible without: (I) a system of identifying various pests and

agents that cause damage to trees and rating the severity of the

damage, and (2) knowledge of the growth potential of forest

stands on various sites.

Porest entomologists and pathologists of the Pacific Southwest Region of the USDA Forest Service have developed the

Pest Damage Inventory (PD!) system to identify, measure, and

evaluate pest-caused damage (Byler 1975, 1978). The I'D! provides a system of coding insect and disease-causing pests, injuries and abiotic diseases, and guidelines to rate the severity of

their damage. A well-trained observer is needed to identify the

pests, as well as abiotic diseases and types of injuries, on the

basis of various symptoms, some of which are very subtle. The

PDI system has been used to measure tree mortality caused by

all pests (pest complex) on major tree species, and to determine

the incidence of pests and the severity of their damage to tree

growth (Byler 1975, 1978).

A 1977 inventory of pest damage on the Barton Flats Compartment on the San Bernardino National Forest provided substantial evidence that pests such as dwmf mistletoes, root diseases, and specific insects have profound long-term effects on

tree growth. At 167 study points, the to-year cubic volume

growth for sites that had insect and disease problems (74 sites)

was 68 percent of that for sites with no problems (93 sites)

(Anon. 1977, Byler 1978). For the individual trees with pests,

the growth rate was 56 percent of that for healthy trees. Furthermore, the growth of healthy trees on sites that had pests was only

89 percent of that for healthy trees on non-pest sites, indicating a

site difference as well (Anon. 1977).

Studies to develop equations that predict tree growth in

mixed-conifer stands in the Sierra Nevada provided an 0ppOltunity to assess the chronic or low-level effects of forest pests and

pest complexes on tree growth and mortality in the same stands

(Dolph and Amidon 1979). These equations describe the relationship of variables which have a significant effect on an individual tree's height and diameter growth (Dolph 1988a, Dolph

1988b).

This paper reports the results of an effort to identify the

forest pests endemic to mixed-conifer stands in the Sierra Nevada and to assess their effects on tree growth and mortality.

USDA Forest Service Res. Paper PSW-RP~212. 1992.

Methods

Study Area

The study area occupied the mid-elevations on the west

slope of the Sierra Nevada, extending approximately 350 miles

north to south from 40'00' to 35'25' N. latitude (Dolph and

Amidon 1979). Data were collected within the boundaries of six

National Forests extending from the northern boundary of the

Plumas National Forest southward to the southern boundary of

the Sequoia National Forest, and included the Tahoe, Stanislaus,

and Sierra National Forests. The elevationallimits of the mixedconifer type vary with changes in latitude and aspect within

these National Forests. Most of the type is found between 3000

and 7000 ft (900 and 2 I30 m) elevation, below the red til' (Abies

magnifica A. Murr.) andlodgepoJe pine (Pinus contorla Doug!.

ex Loud.) types and above the drier foothill types. It reaches its

best development on sites along the west side of the Sierra

Nevada with abundant winter precipitation followed by long,

warm growing seasons.

The tree species which comprise the mixed-conifer type are

California white Jir(Abiesconcolorvar./owiana [Gord.] Lemm.),

incense-cedar (Libocedrus decurrens Torr.), Douglas-fir

(Pseudotsuga menziesii [Mirb.] Franco), ponderosa pine (Pillus

ponderosa Dougl. ex Laws. val". ponderosa), and sugar pine

(Pinus lamberriana Doug!.). Jeffrey pine (Pinusjeffreyi Grev. &

BalL) is an associate at upper elevations and replaces ponderosa

pine on serpentine soils. Hardwood associates are California

black oak (Quercus kelloggii Newb.), Pacific madrone (Arbutus

menziesii Pursh), tanoak (LithoCOllJIIS densiflorus [Hook. and

Am.] Rehd.), and Pacific dogwood (Cornus ",mallii Audubon)

(Helms 1980).Mixed-conifer stands occur as variable mixtures

of species or as small groups of single species.

Plot Selection

Young-growth natural stands which fit the definition of

Sierra Nevada Mixed-Conifer Type (Tappeiner 1980) were randomly sampled throughout the western slopes of the Sierra

Nevada. Starting with a randomly selected point, plot locations

were established using the Pacific Southwest Region's five-plot

cluster arrangement (U.S. Dept. of Agriculture, Forest Service

1986). Each sample location consisted of five plots arranged in

an L-shape with plot centers 132 feet apart along north and east

compass lines. Each plot was evaluated for study suitability by

the following criteria:
1. Young-growth-No more than 25 percent of the trees

tallied were older than 80 years at breast height.

2. Mixed-conifer type-No more than 20 percent of the

trees tallied were conifer species other than those characteristic

of the mixed-coni fer type. Evidence of white fir regeneration in

the stand or surrounding area was required also.

3. Homogeneous site-No more than one distinct soil type,

slope percentage, or aspect was present on a O.2-acre circular

plot around the plot center (radius 52.7 ft).

4. Untreated stand-No evidence of silvicultural treatment during the 10 years before measurement. A cluster was

retained as a suitable sample point if two or more plots met

the above criteria.

Stand and Tree Measurements and

Evaluations of Damage

Basal area per acre was detellllined from each plot center by

counting all "in" trees with a wedge prism. The Basal Area

Factor (BAF) of prism selection procedure followed that described in the Pacific Southwest Region forest inventory handbook and is based on the number of trees counted with a BAF 20

prism (U.S. Dept. Agriculture, Forest Service 1986). Using the

selected prism all tally trees 1.0 inch (2.5 em) d.b.h. and larger

were listed on a tally sheet, and the following characteristics and

measurements were recorded for each.

1. Species.

2. Diameter at breast height (d.b.h.) (outside bark) in inches.

3. Position, damage, defect, and tree class.

4. Age at breast height.

5. Total height from base to tip of tree, in feet.

6. Height to base of live crown, in feet.

7. Type and extent ofinsect and disease symptoms using the

California Pest Damage InventOly (PDl) system (Byler 1975, 1978).

One increment core was used to measure radial growth on trees

3.0 to 5.9 inches (7.6 to 15.0 em) d.b.h. and at least 10 years old

at breast height (4.5 ft [1.4 m] above the ground on the uphill

side of the tree). Two cores taken at right angles were used to

measure radial growth for trees greaterthan 6 inches (15.2 cm) d.b.h.

An average of two trees per plot, selected at random from

the prism tree tally sheet, were felled, and the additional following data were recorded:

1. Total stem length in feet, excluding the current

season's growth.

2. Height growth in feet during the last two 10-year

growth periods.

3. Bark thicknesses in inches along the stem.

4. Type and extent ofinsect and disease symptoms using the

PDI system. The pest information was recorded separately for

the same tree, once before it was felled and again after it was felled.

Analysis of Data

All tree records were collated by species, National Forests,

and numbers and identities of pests and other injuries as defined

by the PDl system. Additionally, all tree records separated by

2

species were divided into qum-tiles according to their diameter

measurements, resulting in four diameter classes. For example,

diameter class 1 for white fir consisted of the quarti Ie of the

white fir population with the smallest diameter measurements,

and diameter class 4 comprised the quartile with the largest

diameters. In a similar manner tree heights and height increment

data from the stem analyses records were llsed to produce four

height classes and determine site indices.

General Linear Models of the Statlstical Analysis System

(SAS) (the SAS Institute Inc., Box 8000, Cary, NC 275 11-8000)

were used to examine the variability oftree basal area and height

increments by pest classification, diameter classes, height classes,

and site classes, National Forests, and their various interactions.

The natural log of 10-year basal area growth was the dependent

variable.

Results and Discussion

Pest Incidence on Standing Trees

Approximately 3,200 plot trees were examined in six National Forests for signs of pest activity and human-caused or

mechanical injuries, and rated by the codes of the PDI system.

The PDI code, as used in this report, identifies pests as pest

categories and ti'equency of pest occurrence as pest records. A

pest category refers to a particular species or species group of

insects/diseases, or to an abiotic disease or type of injury. A pest

category such as insects will contain a number of recorded

instances of an insect's presence or activity (pest records) for a

particular tree species. There may be more than one species of

insects recorded in the insect pest category.

We use the term "Pest Classes" to refer to the number of

pests or pest categories a tree may have. Trees in thls study were

rarely found to be affected by more than three pest categories, so

we established four pest classes which ranged from "0" (free of

pests) to "3" (three or more pest categories). Using this nomenclature, the "0" Pest Class is synonymous with "0" Pest Category, whereas Pest Class "3" would contain three or more pest

categories. Of the 3,200 plot trees, 1,980 trees (62 percent )were

recorded as free of pests and injuries ("0" Pest Category). Trees

free of pests grouped by species ranged from 68 and 70 percent

for incense-cedar and Douglas-fir, respectively, down to 52 and

53 percent for white fir and sugar pine, respectively (fable 1).

Of these plot trees 877 were randomly selected for stem

analyses. Pest information was recorded twice for trees selected

for stem analyses, once before felling, and again after felling

(table 1). In the examination for signs of pest activities and

human-caused and mechanical injuries before the trees were

felled, 633 (72 percent) were recorded as free of pests and other

injuries; 244 (28 percent) were rated as having one or more pests

USDA Foresl Service Res. Paper PSW-RP-212. 1992.
and injuries (table 1). Trees rated as free of pests and injuries

("0" Pest Category/Class) ranged from 82 percent for standing

incense~cedarto 68 percent for white fir. Conversely, the percent

of trees with one or more pests ranged from 32 percent for white

fir to 18 percent for incense-cedar.

Pest inventory records of the trees selected for stem analyses before they were felled are samples of the records for all plot

trees and generally are expected to be representative of the larger

data set. Yet, a comparison oftwo sets of records shows that only

the numbers of pest categories for Douglas-fir trees were similar

(tahle 1). There seemed to be differences among the two data

sets for other tree species-ponderosa pine, Jeffrey pine, sugar

pine, white fir, and incense-cedar. Generally the standing trees

selected for stem analysis exhibited much lower incidence of

pest ancl mechanical injuries than did the larger set of standing

plot trees. These data suggest either some bias towards pest-free

trees or a Hawed procedure in the selection ofstem analysis trees.

The question of whether trees selected for stem analysis

belong to the same population as trees not selected for stem

analysis was examined by comparing the latest 10-year basal

area increments of trees selected for stem analysis with those of

trees not selected for stem analysis. Data describing the average

of the latest 10-year basal area increment for all trees, standing

plot trees, and felled stem-analysis trees were summarized by

plot and cluster. The 95 percent confidence interval for the

difference between the means of the logarithm (base 10) of the

basal area increment for all species of stem-analysis vs. the

standing trees was (-.026, .247). Because this interval contains

zero, a difference in the basal area increment is not detectable at

the .05 level. A simi lar comparison was done on each species.

White fir was the only species to show a significant difference.

The 95 percent confidence interval for the difference between

stem-analysis and standing white tir trees wa's (.06, .34), which

indicates that the stem-analysis trees on the average had a larger

basal area increment than did the standing trees. There may have

been some bias in the sampling procedure on white fir stemanalysis trees. White fir also had the largest sample size between

the individual species for the stem-analysis trees. The possibility

of a sampling bias on the white fir stem-analysis trees was not

incorporated in fUl1her analysis.

Pest Incidence on Felled Trees

Information on pest and various injuries recorded on 875

treesl after they were felled showed a large increase in the

number of pests and injuries compared to those recorded before

felling (table 1). The felled trees allowed a much c1osel" examination of the tree stems and showed that many signs of pest

activities and various injuries were missed on the standing trees.

Some of the differences are due to pests or injuries that cannot be

'Two tree records were lost.

Table l-Comparisolls oftrees ill pest and no~pest categories among all study trees

Number of Number of trees with

Tree species Trees with no pests Trees with pests pest I or more pest categories Total

!l0. pc/ no. pet categories 1 I 2 I 3 I 4 pests

Douglas-fir

Standing' 30 71 12 29 8 12 0 0 0 12

Felled' 24 57 18 43 9 13 4 1 0 24

All trees~ 101 70 44 30 - - - -

Ponderosa pine

Standing 108 72 43 28 12 37 6 0 0 55

Felled 58 38 93 62 24 66 23 4 0 124

All trees 333 58 232 42 - - - -

Jeffrey pine

Standing 24 77 7 23 6 7 0 0 0 7

Felled 15 48 16 52 9 12 4 0 0 20

All trees 75 55 61 45 - - - -

Sugar pine

Standing 44 70 19 30 9 18 2 0 0 22

Felled 36 57 27 43 13 10 14 3 0 47

All trees 112 53 100 47 - - - -

White fir

StJ:mding 270 68 125 32 22 106 18 1 0 164

Felled 143 36 252 64 30 92 120 34 6 458

All trees 907 52 848 48 - - - - -

Incense-cedar

Standing 157 82 35 18 6 34 I 0 0 36

Felled 133 69 60 31 14 48 11 I 0 73

All Trees 452 68 213 32 - - - - -

lTrees selected lor stem analyses.

~AnaJyses of pest categories were not made for all trees since the felled trees provided the most accurate information.

USDA Forest Service Res, Paper PSW~RP~212, 1992. 3
seen on standing trees (e.g., heart rot and wetwood) or are Table 2-Pest Stl11l11lalY by tree species ulidJorest

difficult to see on standing trees (e.g., top injuries).

The examination of felled trees showed that 409 (47 per- Pest category 3 Pct

cent) were free of pests and 466 (53 percent) had one or more

pest categories (table J). Incense-cedar contained the fewest -----------------------NI/l/lher ------------------------

number of pests or pest categories with 133 out of 193 trees (69 Douglas-fir

No pests II 7 0 () () 6 24 51

percent) free of pests, and 60 trees (3 I percent) with one or more Top injury 0 4 0 () 0 I 5 II

pests. White fir and ponderosa pine trees had the highest per- Other injllries~ 3 I 0 0 () I 5 II

centage of pest and mechanical injuries: 64 percent (252 trees Insects 0 0 0 0 0 I I 2

out of 395), and 62 percent (93 trees out of lSI), re- Diseases,1 2 9 () 0 0 I 12 26

Unknown damage () 0 0 0 0 () 0

spectively (Iable f). Total 47 A comparison of the pest data recorded on the trees selected

for stem analyses before and after they were felled shows that Ponderosa pine

the number of trees identified as having pests increased substan- No pests 16 10 2 5 II 4 58 33

Top injury 10 7 7 18 7 11 49 28

tially after felling, and that the total number of recorded pests Other injuries 6 2 0 I I 0 10 6

doubled (Iable f). It was much easier to see and identify pest Insects S I 2 2 12 0 25 14

activities and other injuries, particularly multiple pests and pest Diseases II 4 0 5 4 I 25 14

associations, after the trees were felled (table 1). Records taken Unknown damage 4 7 () 0 0 0 II 6

on standing trees revealed few pest-damaged trees with multiple Total 178

pests, whereas the records for felled trees showed that 61 percent Jeffrey pine

of the pest-injured white fir trees, 63 percent of the sugar pine, No pests 2 () 13 () () () 15 43

and 29 percent of the ponderosa pine had two or more pests/ Top injury 2 () 9 0 0 0 II 31

Other injuries 0 () 2 11 0 0 2 6

injuries (Iable f). Only 20 percent of the pest-damaged incense- Insects I 0 0 I 2 () 4 II

cedars had two or more pests/injuries. Diseases I () I 0 I 0 3 9

The overall incidence of pests by tree species was similar Unknown damuge 0 () 0 0 () () 0

for both sets of records. Before felling, 22 different pest catego- Total 35

ries were identified on white fir, followed by 12 for ponderosa Sugar pine

pine. Jeffrey pine and incense-cedar had the fewest number of No pests 10 5 2 12 4 3 36 44

pests (6). After the trees were felled, we were able to see and Top injury 2 2 I 5 3 0 13 16

Other injuries 4 () I 2 I () 8 10

identify 30 kinds of pests on white fir and 24 on ponderosa pine. Insects () 0 0 2 I 0 3 4

The number of pest categories recorded on incense-cedar in- Diseases' 4 II 0 I I 3 20 24

creased from 6 to 14. Douglas-fir and Jeffrey pine had the fewest Unknown damage I 11 0 0 I 0 2 2

pest categories (9). This may be due to the smaller number of Totul 82

trees for these species. However, it is clear that the pest inven- White fir

tory records for the felled trees provide the most accurate infor- No pests 59 15 25 16 II 17 143 26

mation on the incidence of pests and various injuries in young Top injury 39 II 7 19 14 II 101 18

forests of mixed conifers. Other injuries5 20 2 5 2 3 0 32 6

Insectsf> 36 13 5 9 4 29 96 17

There is evidence ofsubstantial variability among trees free Discases 33 II 7 17 12 2 82 15

of pests and those with pests between National Forests. For Wetwood 12 40 5 () 0 37 96 17

example, the percent of white fir in the "0" Pest Category Unknown damage 2 0 0 () 0 () 0

averages 26 percent of all pest categories over the six National Total 553

Forests. But white firs in the "0" Pest Category averaged only 16 IncenscMcedar

and 18 percent of all pest categories in the Plumas and Stanislaus No pests 67 8 13 27 15 3 133 65

National Forests, respectively, and 46 percent of all pest catego~ Top injury 3 I I I 2 0 8 4

des on the Sequoia National Forest (fable 2). In contrast, in- OLher injuries 5 2 0 0 I 11 8 4

Insects' 15 0 () 0 3 0 18 9

cense-cedar in the "0" Pest Category averaged 65 percent of all Diseases~ 13 7 4 6 7 I 38 19

pest categories for the six National Forests. Trees in this cat- Unknown damage 0 0 () 0 () 0 0 0 -

egory ranged from 65 to 79 percent of all classifications of the Total 205

Eldorado, Sequoia, and Sierra National Forests, and was 44

percent on the Plumas National Forest. The four tree records for IForests: 3 = Eldorado. [I = Plumas, 12 = Sequoia, 15 = Sierra, 16 =

the Tahoe National Forest were too few to merit con- Stanislaus. 17 = Tahoe.

sideration (Iable 2). ~Mcchanic,ll and hUlllun-caused injuries (4 of 5).

Of aU the tree species, white fir appeared most susceptible ,1Unknown canker comprised 9 of the 12 disease pests.

'Blister rust comprised [2 of 20 records of diseases.

to damage from insect and disease pests and human-caused and 'Largely human-caused injuries and frost cracks.

mechanical injuries. Field crews recorded 30 pest categories (,Largcly Ill" engraver.

with a total of 414 instances of pest damage on 252 white fir 7Flatheaded borers.

trees; 120 trees had two pests, 34 trees had three pests, and six ~Cedar rust comprised 16 of the 38 records of diseases.

4 USDA Forest Service Res. Paper PSW-RP-212. 1992.
trees had four pests. Those pest categories or pests with five or

more records of the pest's presence/damage were top injury, 96

records; wetwood, 96 records; fir engraver (Scalytus velltralis

Le C.), 69 records; leafy mistletoe (Phoradendron bolleanllll1),

20 records; frost cracks, 17 records; human-caused and mechanical injuries, 12 records; root disease (Heterobasidioll

anllasum), 11 records; dwmfmistletoe (Arceuthobium abietillum),

1I records; bole canker, seven records; needle miners, seven

records; unknown defo] iator, seven records; branch nagging, six

records; Cytospora abietis, six records; Douglas-fir tussock moth

(Orgyia pseudotsligata), five records; unknown canker, five

records. The most frequent pest combinations observed on white

fir were fir engraver and wetwood, 29 records; fir engraver and

top injury, 16 records; and top injury and wetwood, 15 records.

A large number of pest categories and injuries were also

recorded on ponderosa pine: 24 pest categories and 120 records

of pest presence/damage on 93 trees. Twenty-three trees had two

pest categories, and four trees had three pest categories. Pest

categories or pests with five or more records were top injury, 49

records; sawflies, 11 records (all on the Stanislaus National

Porest); human-caused and mechanical injuries, eight records;

smog damage, seven records (all on the Plumas National Porest); white scale, five records. Bark beetles (DelldroctollliS

brevicomis, D. pcmderosae and D. valens) were on nine records.

D. brevicomis and top injury were the most frequent pest combination (four records).

Field crews compiled 14 pest categories and 72 pest records

on 60 incense-cedar trees. Two pest categories were found on 11

trees, and one tree had three pest categories. Pest categories with

five or more records were: insects (flatheaded borers), 18 records;

cedar rust (Gymnosporangium libocedrus), 16 records; top injury, eight records; human-caused and mechanical injuries, eight

records; and hemt rot, five records.

ThiIteen pest categories with 45 pest presence/damage records

were listed for 27 sugar pine trees. Fourteen trees had two pest

categories, and three trees had three pest categories. Pest categories with five or more records were top injury, 13 records; blister

rust (Cronartium ribicola), 12 records; human-caused and mechanical injuries, seven records. The most frequent pest combinations were: top injury and mechanical injury, three records; D.

ponderosae and top injury, three records; and top injury and

blister rust, with two records.

Nine pest categories with 20 instances of pest presence/

damage were recorded on 16 Jeffrey pine trees. Four trees had

two pest categories. Top injury contained 11 pest records and

was the only pest category with more than two records. Nine pest

categories with 23 pest records were also cataloged on J8 Douglas-fir trees. Four trees had two pest categories and one tree had

three pest categories. Pest categories with five or more records

were: unknown canker, nine records; top injury, five records;

human-caused and mechanical injuries, five records. The most

frequent pest combination was the unknown canker and top

injury on two of the records.

In general, top injury was the most frequent pest category

recorded among all tree species, and was particularly noticeable

for ponderosa and Jeffrey pine (table 2). A top-injury rating

included any form of top injury that occurred at any time of the

USDA Forest Service Res. Paper PSW-RP-212. 1992.

tree's development, and includes spike tops, broken tops, multiple tops, and regrown tops. However, for stem-analysis trees,

this category was restricted mainly to regrown tops, because

trees with multiple, spike, or broken tops were dismissed as

being unsuitable for stem analysis. It is practically impossible to

determine the cause of an old top injury, but possible causes are

damage by wind, snow, and from falling trees, or branches of

other trees. Western spruce budwonn and Douglas-fir tussock

moth can caLIse substantial top injury, including stem dieback, to

white fir and Douglas-fir trees that is usually clearly seen. In

contrast, the western pine shoot borer (Eucosma sOllomana)

injures the terminals of ponderosa and Jeffrey pines, substantially reducing height growth, but the top injury is more subtle

and not seen as clearly as that caused by other insects. Imperfections in the PDI rating system may not allow for the impact of

top injury on growth to be determined. Nevertheless, there should

be an effect on height growth of the tree.

Disease was the second most frequent pest category recorded on mixed-conifer tree species (table 2). Of all the tree

species, white fir seemed most susceptible to a large number of

diseases, including wetwood and leafy and dwmf mistletoes.

Wetwood was so extensive among the trees that some field

crews stopped recording it, so the incidence of wetwood was

much greater than the 96 records suggest. The mistletoe infections were generalJy light, and occurred mostly in the upper

crown at the base of branches next to the bole. Because of their

locations in the inner parts of the crown, these infections were

difficult to spot from the ground. Douglas-fir was particularly

susceptible to cankers. The most common were small limb

cankers and were classified as unknown. These were usually

very old, and the causes were not detenllined. White pine blister

rust and cedar rust were the most frequent diseases recorded on

sugar pine and incense-cedar, respectively (table 2). These infections were considered minor. Most of the sugar pines infected

with blister rust had spindle-shaped limb cankers some distance

from the bole. On some trees, infections between 4 and 24 inches

from the bole were observed. No bole infections were seen on

any of the trees.

Insects, primarily bark beetles, were an imp011ant pest category of white fir, ponderosa pine, and incense-cedars. Attacks

by fir engravers, top injuries, and diseases were the most frequent pest categories for white fir. Sixty-nine of the 96 insect

records were unsuccessful attacks by fir engravers, usually in

the form of strip kills. Attacks by tir engravers were frequently

associated with wetwood (29 records) and top injury (16 records)

in white firs. All the insect records on incense-cedar were for

flatheaded borers (Buprestidae). These were on trees growing

very slowly in stagnated groups. Unsuccessful attacks by the

western pine beetle (Dendrocfol1us brevicomis), mOllntain pine

beetle (D. ponderosae), and red turpentine beetle (D. valens)

comprised nine of the 25 insect records for ponderosa pine.

Sawflies (Neodipriol1 sp.) and white scale comprised II and five

of the remaining insect records, respectively, on ponderosa pine.

Logging and mechanical injuries ranged from six to 11 percent

of the damage records among mixed-conifer species.

5
Height Growth and Site Index Values

Stem analyses of felled trees allowed the calculation of site

index values for each tree species (Dolph 1988a) and comparisons of height growth rales and total heights among trees with

various pest classifications (Dolph 1988b). Descriptive statistics

for the site index values show that ponderosa pine, while fir,

Douglas-fir, and sugar pine trees comprised the dominant forest

canopies across all site classes of mixed-conifer forests (table 3)

(Dolph 1988a, 1988b). Douglas-fir exhibited the best height

growth rates on the poorest sites (site class 4) with a range of

height of 39 to 65 feet at age 50 years. White firs exhibited a

range of heights of 28 to 59 feet and ponderosa pine a range in

heights of22 to 59 feet at age 50 011 these sites (table 3). Incensecedars showed the poorest growth on site class 4, with a range of

heights of 12 to 38 at age 50 yenrs. Ponderosa pine and white fir

trees showed the highest height growth rates on the best sites

(site class 1) with ranges in heights of 97.5 to 127 feet and 90 to

134 feet, respectively, at age 50 yeal~. Douglas-fir and sugar

pine trees ranged in heights from 90 to I II feet and 88 to 109

feet, respectively, at age 50 on these sites. Incense-cedars and

Jeffrey pines showed the poorest relative growth on these sites

and ranged in heights from 63 to 94 feet and 58.7 to 95 feet,

respectively, at age 50 on site class I (table 3).

The felled trees of each National Forest were divided nccording to height and placed into qumtiles (four height classes).

Height increment for the past 20 years was measured on all

stem-analysis trees and was the dependent variable used to test

variability in pest classifications among the height classes for the

various tree species and National Forests. We did not detect any

significant variation in height growth rates and total height mnong

the various pest cla<;sitications. Trees with two or more pests tended

to be the Imger trees; most likely they were also the older trees.

Basal Area Increment

We calculated the natural log of the last 10 years of basal

area increment for all the study trees, and using the Bonferroni

"T" tests we compared thislO-year basal area increment for

each tree species by diameter, site class and pest classes. As has

already been reported, basal area increment differed significantly at the 0.05 percent level among diameters and site classes

for all tree species (Dolph 1988a). However, there was no significant variation in basal area increment among trees placed in

the various pest classes for Douglas-fir, white fir, sugar pine and

Jeffrey pine (fable 4). For some reason incense-cedars placed in

Pest Classes" I" and "3" grew signiticantly faster than those in Pest

Classes "0" and "2" (table 4). Ponderosa pines placed in Pest Cla"es

"0" and "1" grew significantly faster than those in Pest Class "2"

(fable 4). Nevertheless, pest damage on all tree species was minor

throughout the study stands, and we doubt that pest incidence and

damage had a real impact on basal area increment.

Tree Mortality

Out of 3,255 tree records examined among the six National

Forests, 103 were dead, resulting in a mortality average of 3.16

percent for young mixed-conifer stands (table 5). According to

these tree records, tree mortality ranged from 0.49 percent for

the Plumas National Forest to 6.89 percent for the Stanislaus

National Forest (table 5). The percent of tree mortality by species also varied greatly among the National Forests (table 6).

However, the major species which comprise the mixed-conifer

type-white fir, ponderosa pine, and incense-cedar-had 35, 26,

and 21 percent, respectively, of the total mortality for the six

National Forests (table 6). The largest number of dead trees in

the study plots was encountered on the Plumas National Forest;

about half were white tiro Bark beetles and root diseHses, primarily Heferobasidioll annOSUnl, were the pests most frequently

associated with the mortality on white fir and ponderosa pine.

6

Table 3-Descriptive statisticsfor site illdex va/llesl

Max.

Species height3

feet jeet jee! feet fee! feet

White fir 316 75.84 1.23 28.00 59.25 74.00 90.00 134.00

Incense-cedar 225 50.96 1.12 12.00 38.00 51.00 63.00 94.00

Ponderosa pine 149 79.38 1.88 22.00 59.00 81.00 97.50 127.00

Sugar pine 94 72.38 2.07 19.00 55.00 71.00 88.25 109.00

Jeffrey pine 36 53.94 2.22 23.00 46.25 52.50 58.75 95.00

Douglas-fir 58 75.60 2.32 39.00 65.00 76.00 90.00 111.00

IHeight at age 50 years.

2Mean Standard Error

'Site index values are dividcd into four classes from MIN to MAX.

i.e.: Sitc Class 4 = (MIN, QI)

Site Class 3 = (QI' Q:!)

Sitc Class 2 = (Q:!. Ql)

Site Class I = (Ql' MAX)

4Median Hcight

USDA Forest Service Res. Papcr PSW-RP-2l2. 1992.
Table 4--Comparison oflog 10~year basal area illcremellts ofstudy trees

by species and pest classes

Table 5-1ncidence ofmortality ill youlig-mature trees ill the mixedcOllifer stands ofsix NatiOllal Forests'

Item Forest code~

3 I II I 12 I 15 I 16 I 17 I Total

Total trees 1346 481 402 509 430 358 3526

Missing trees 80 71 27 39 9 45 271

Total deud 45 2 7 14 29 6 103

Percent dead 3.55 .49 1.87 2.98 6.89 1.92 3.16

lDetermll1ed by subtracting the number of mIsSing trees hom the llumberof

total trees and using the result as the divisor of totul dead.

2Forests: 3 = Eldorado, II =Plumas. 12 = Sequoia, 15 = Sierra. 16 =

Stanislaus, 17 = Tahoe.

Table 6-1llcidellce ofmortality ill young-mature mixed-collifer stallds by

tree species alld National Forest

Forest code '

Tree species 3 I II I 12 I 15 I 16 I 17 ITotal

Douglas-fir

Number dead I 0 0 0 I 0 2

Percent of total 2.22 16.67 2

Ponderosa pine

Number dead 12 I 2 5 7 0 27

Percent of total 16.67 50 28.57 35.71 24.14 26

Jeffrey pine

Numberdeud 5 0 2 0 0 0 7

Percent of 101<1l 11.11 28.57 7

Sugar pine

Number dead I 0 0 4 5 0 10

Percent of total 2.22 28.57 17.24 10

White fir

Number dead 22 0 2 I 5 6 36

Percent of total 48.89 28.57 7.14 17.24 100 35

Incense-cedar

Number deud 4 I I 4 12 0 22

Percent of total 8.89 50 14.29 28.57 41.38 21

Total dead 45 2 7 14 30 6 104

lForests: 3 = Eldorado, II = Plumas, 12 = SequOIa, 15 = SIerra, 16 =

Stanislaus. 17 = Tahoe.

'Alphu = 0.05, Confidence = 0.95, DF = 107, MSE = 0.279511; Cntlcal

Value ofT = 2,68819.

2Number of Douglas-fir trees in Pest Classes 0, 1,2, and 3 are 95. 30, 2, and

I, respectively.

'Alpha = 0.05, Confidence =0,95. DF =449, MSE =0.450443; Critical

Value ofT = 2,65000.

4Number of Ponderosa pine trees in Pest Classes 0, 1,2, and 3 are 323, 142.

23. und 5. respectively.

'Alpha = 0.05, Confidence = 0.95.

bNumber ofJeffrey pine trees in Pest Classes 0, 1,2, ,md 3 are 62, 36. 4. and

2, respectively.

7Alpha = 0.05, Confidence =0.95, DF = 138, MSE =0.257813; Critical

Value ofT = 2.67682.

xNumber ofsugur pine trees in Pest Classes 0, 1,2, and 3 are 109,60,6, and

I, respectively.

'!Alpha = 0.05, Confidence = 0.95, DF = 1438, MSE = 0.365309; Critical

Value ofT = 2.64191.

IONumber of white fir trees in Pest Classes O. I, 2. and 3 are 897,442, 119,

and 31, respectively.

"Alpha =0.05, Confidence =0.95, DF = 584. MSE =0.415485; Critical

Value ofT = 2.64728.

'~Number of incense-cedar trees in Pest Classes O. 1.2. and 3 are 482, 122,

20, and 4, respectively.

Lower Difference Upper SignifTree species Pest confidence between confidence icance at

classes limit means limit 0.05 limit

Douglas-fir' 1-0' -0.12195 0.17569 0.47333 NS

1-2 -0.57121 0.46670 1.50461 NS

1-3 1.28209 2.72680 4.17151 * 0-2 -0.72446 0.29101 1.30649 NS

0-3 1.12244 2.55111 3.97979 "" 2-3 0.51947 2.26010 4.00073 *

Ponderosa pine' 0_1 4 -0.10964 0.06944 0.24852 NS

0-3 -0.36012 0.44140 1.24292 NS

0-2 0.12625 0.51008 0.89391 * 1-3 -0.43732 0.37196 1.18123 NS

1-2 0.04088 0.44064 0.84040 * 3-2 -0.80892 0.06868 0.94628 NS

Jeffrey pine' 3_2b -1.1314 0.1975 1.5265 NS

3-0 -0.7476 0.3549 1.4573 NS

3-1 -0.4532 0.6616 1.7765 NS

2-0 -0.6343 0.1573 0.9490 NS

2-1 -0.3447 0.4641 1.2729 NS

0-1 -0.0148 0.3068 0.6283 NS

Sugar pine7 2_0x -0.21246 0.35749 0.92743 NS

2-1 -0.20123 0.38073 0.96269 NS

2-3 1.86275 3.33082 4.79888 * 0-1 -0.19524 0.02324 0.24173 NS

0-3 1.60795 2.97333 4.33872 * 1-3 1.57964 2.95009 4.32053 *

White fir'> 3-0 10 -0.07435 0.21735 0.50906 NS

3-2 -0.09571 0.22628 0.54826 NS

3-1 -0.04593 0.25075 0.54742 NS

0-2 -0.14686 0.00892 0.16471 NS

0-1 -0.05941 0.03339 0.12619 NS

2-1 -0.14044 0.02447 0.18938 NS

Incense-cedarl1 3- I 12 -0.20223 0.66484 1.53190 NS

3-0 0.10195 0.95867 1.81540 * 3-2 0.15060 1.08522 2.01985 * 1-0 0.12090 0.29384 0.46678 * 1-2 0.00874 0.42039 0.83204 * 0-2 -0.26285 0.12655 0.51594 NS

..

USDA Forest Service Res. Paper PSW-RP-212. 1992. 7
Discussion

Pest/Damage inventory records taken on standing trees provide a good approximation of the incidence of pest activities and

other injuries in young mixed-conifer forests. However, those

records taken from felled trees provide the most accurate information. White til' was the tree species most slisceptible to insect,

disease and human-caused injuries. Only 26 percent of the white

firs on the study plots were free of pests and injuries. The most

frequent records were for top injuries, wetwood, and the fir

engraver. Approximately 33 percent of the ponderosa pines

were free of pests and injuries, and top injury was the most

frequent injury recorded. Incense-cedar was the tree species that

exhibited the least number of pests and injuries; approximately

65 percent of the trees were free of pests and injuries. Flatheaded

borers and cedar rusts were the pests most frequently encountered on incense-cedar in the study plots.

The pests and humanwcaused injuries seemed to have very

little effect on tree growth and mortality in the study stands. The

low incidence of tree mortality and the relatively minor effect of

endemic pest activities on tree growth recorded in these studies

are not surprising given the fact that the studies were limited to

young-growth mixed-conifer stands whose basal area is largely

composed of trees less than or equal to 80 years old at breast

height. The exclusion of older stands resulted in many five-point

clusters in the study stands having fewer than five plots, as well

as relatively low incidence of pests and tree mortality. However,

there were a number of trees much older than 80 years at breast

height. Much of the variability in basal area increment among

pest classes is largely due to these trees.

Our observations of many of the important disease pests in

the study stands showed that they were in the early stages of their

infections, and would not be expected to have much current

impact on tree health and growth. For example, white pine

blister rust infections were located on the branches of sugar

pines and had not progressed to the boles where they would have

had greater impact on tree growth and mortality. Symptoms of

root and stem diseases were not as readily seen in the study

stands as they are in much olderstands. Root and especially stem

diseases are major pests in mature and old-growth stands of

coniferous forests, and the cUl11ulative effects of the spread and

development of their infections predispose infected trees to

attack by bark beetles. There were frequent associations between

fir engraver and wetwood and top injury for white fir, western

pine beetle and top injury for ponderosa pine, and t1atheaded

borers and cedar rust for incense-cedars.

8

Endemic levels of pests require a substantial amount oftime

for their cumulative effects to have any significant impact on

forest trees and stands, and the studies reported here indicate that

mixed-coni fer stands 80 years of age and younger are too young

to show these effects, Nevertheless, the data indicate the potential problems for mature and older mixed-conifer stands. They

identify white fir as the tree species particularly susceptible to

pests and human-caused injury. Under uneven-aged forest management with frequent stand entries white fir would become the

predominant tree species in mixed-conifer forests. The results of

this study suggest that a forest in which white fir is the dominant

forest tree would be severely affected by pests and mechanical

injury and would most likely produce low yields.

References

Anon. 1977. Inventory or the Barton Flats Compartmcnt, San Bcrnardino

Nalional FOI'est. U.S. Dept. Agriculture, Forest Service. Repon on filc,

Forest Pest Management, State and Private Forestry, Forest Service, Regionnl Office, 630 Sansome S1.. San Francisco, CA.

Byler, James W. 1975. Pest damagc inventory. In: Proceedings of joint

meeting of twcnty-sixth annual forest insect work conference and (wentysccond western international forest disease work conference: 1975 February 23-28; Monterey, CA; 30-35.

Byler. James W. 1978. The pest damage inventory in CalifOl'nia. In: Scharpf,

Robert F.; Parmeter, John R., Jr., tech. coords. Proceedings of the symposium on dwarf mistletoe control through forest management; 1978 April

11-13; Berkeley, CA: Gen. Tech. Rep. PSW-31. Berkeley, CA: Pacific

Southwest Forest and Range Experiment Station. Forest Service, U.S.

Departmcnt of Agriculture; 162-171.

Dolph, K. Leroy. 1988a. Pl'cdiclion of periodic basal area increment for

.voung~growth mixed conircrs in the Sierra Nevada. Res. Paper PSW190. Berkeley, CA: Pacific Southwest Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture; 20 p.

Dolph, K. Leroy. 1988b. Prcdicting height increment of young-growth

mixed conifcrs in thc Sierra Nevada. Res. Papcr PSW-191. Berkeley,

CA: Pacific Southwest Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture: 7 p.

Dolph, K. Leroy; Amidon. Elliot L. 1979. Predicting growth of mixcdconircr species in the Sierra Nevada: rationalc ::lI1d mcthods. Res. Note

PSW-339. Berkeley. CA: Pacific Southwest Forest and Range Experiment

Stntion, Forest Service. U.S. Department of Agriculture; 7 p.

Helms, John A. 1980. The Calirornia region. In: Barretl. Jolm W.. cd.

Silviculrure of fhe United States. New York: John Wiley and Sons;

391-446.

Tappeiner, John c., 11. 1980. Sicrra Ncvadn mixed conifer. In: Eyre. F.B.. cd.

Forest cover types of the United States nnd Canada. Washington. DC:

Society of American Foresters; I 18-119.

U.S. Department of Agriculture. Forest Service. 1986. R~5 Foresl Service

Handbook 2409.21 b., Timber managemcnl plan invcntory handbook.

San Francisco, CA.

USDA Forest Servicc Res. Paper PSW-RP-212. 1992.
The Forest Service, U.S. Department of Agriculture, is responsible for Federal leadership in forestry.

It carries out this role through four main activities:

• Protection and management of resources on 191 million acres of National Forest System lands

• Cooperation with State and local governments, forest industries, and private landowners to help

protect and manage non-Federal forest and associated range and watershed lands

• Participation with other agencies in human resource and community assistance programs to

improve living conditions in rural areas

• Research on all aspects of forestry, rangeland manugement, and forest resources utilization.

The Pacific Southwest Research Station

• Represents the research branch of the Forest Service in California, Hawaii, American Samoa

and the western Pacific.

Persons of any race, color, national origin, sex, age, religion, or

with any handicapping conditions are welcome to use and enjoy

all facilities, programs, and services of the U.S. Department of

Agriculture. Discrimination in any fOlm is strictly against agency

policy, and should be reported to the Secretary of Agriculture,

Washington, DC 20250.
Research Paper

PSW-RP-212

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