Vegetation Trends in a Young

Conifer Plantation after Grazing,

Grubbing, and Chemical Release

Philip M. McDonald Gary O. Fiddler Peter W. Meyer

United States

Department

of Agriculture

Forest Service

Pacific Southwest

Research Station

Research Paper

PSW-RP-228-Web
Pacific Southwest Research Station

Forest Service

US Department of Agriculture

Abstract

McDonald, Philip M.; Fiddler, Gary O.; Meyer, Peter W. 1996. Vegetation trends in a

young conifer plantation after grazing, grubbing, and chemical release. Res. Paper

PSW-RP-228-Web. Albany, CA: Pacific Southwest Research Station, Forest Service,

U.S. Department of Agriculture; 17 p.

A 3-year-old Jeffrey pine (Pinus jeffreyi Grev. & Balf.) plantation in northern California

was released by grazing with sheep for 5 years, manual grubbing for 3 years, and applying

a herbicide 1 year. These treatments plus an untreated control provided an opportunity to

evaluate density and developmental trends for the pine, shrub, and grass components of

the plant community during 1986-1994. Creating a near free-to-grow condition by applying

Velpar herbicide modified the plant community by controlling the shrubs, reduced

cheatgrass in the second and third years, and caused mean pine diameter, foliar cover, and

height to be significantly greater than counterparts in all other treatments. Grazing caused

two significant, but opposing changes in the plant community. Nipping of twigs by sheep

stimulated foliar cover of snowbrush to more than three times that of similar plants in the

control. Grazing significantly reduced greenleaf manzanita cover. Grubbing a 4-foot

radius around pine seedlings, and grazing with sheep did not increase Jeffrey pine

development relative to the control. Because of this ineffectiveness, the efficacy of grazing

as a silvicultural tool is questioned and suggestions for its betterment are presented.

Retrieval terms: density, development, grasses, pines, sheep, shrubs

The Authors

Philip M. McDonald is a research forester assigned to the Station’s Vegetation

Management Research Unit, with headquarters at Redding, Calif. (2400 Washington

Avenue, Redding, CA 96001). Gary O. Fiddler is a silviculturist with the Silviculture

Development Unit, Pacific Southwest Region, USDA Forest Service, stationed at Redding,

Calif. Peter W. Meyer is a culturist on the Milford Ranger District, Plumas National Forest.

Publisher:

Albany, California

Mailing address:

PO Box 245, Berkeley CA

94701-0245

510 559-6300

http://www.pswfs.gov

July 1996
Vegetation Trends in a Young Conifer Plantation after

Grazing, Grubbing, and Chemical Release

Philip M. McDonald Gary O. Fiddler Peter W. Meyer

Contents

In Brief . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

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

Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Location and Site Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Study and Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Plant Diversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Snowbrush . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Greenleaf Manzanita . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Cheatgrass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Combined Forbs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Jeffrey Pine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Treatment Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Discussion and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

USDA Forest Service

Pacific Southwest

Research Station

Research Paper

PSW-RP-228-Web

July 1996
In Brief

A major development in managing natural resources is the increasing emphasis

on ecosystems and the many species in the plant community. Much needs to be

learned about the shrubs, forbs, and grasses that currently have no recognized

value. Key to this need is the realization that each species has intrinsic worth, not

necessarily for wood or wood products, but as food for wildlife, to fulfill the

variety and contrast requirements of pleasing scenery, or as components in

ecosystems that the manager wishes to sustain or enhance. This study, conducted

in northern California in 1986-1994, provides some knowledge on the species

composition and early development of a pine plantation and the plant

community that ensued after a wildfire. An untreated control, manual grubbing,

herbicide application, and grazing with sheep provided a wide range of

treatments and an opportunity to study the density and development of planted

pines, shrubs, forbs, and grasses in a natural and manipulated condition.

The early natural plant community that developed after the wildfire was

composed of snowbrush, greenleaf manzanita, several grasses, and more than 20

forbs. Planted Jeffrey pines and invading cheatgrass soon became major

components of this community. By study end in 1994, total plant density in the

control was more than 189,000 plants per acre, 97 percent of which were

cheatgrass. Total foliar cover was 49 percent, a proportion that recognizes the

small contribution to aboveground biomass typical of grasses.

For treated plots, plant density and cover varied significantly. If the treatment

was the soil-active herbicide, Velpar, applied to the full 0.5-acre plots, plant

competition was reduced and the pines developed significantly better in

diameter, foliar cover, and height than seedlings in other treatments. Less

competition for critical site resources, and specifically a low number of shrubs

and grasses for the first 3 years, are the likely reasons. When the treatment was

manual grubbing a 4-foot radius around Jeffrey pine seedlings for the first 3

years of the study, the density of greenleaf manzanita and forbs was larger than

in any other treatment, although not significantly so. Development of pine

seedlings in the grubbed treatment did not differ significantly from counterparts

in the control.

For grazed treatments, little effect of foraging by sheep for the first 5 years of

the study was found. Of note was that the sheep actually stimulated snowbrush

plants to develop significantly more cover than in any other treatment. More

cheatgrass resided in grazed plots although it did not differ significantly among

treatments. Pine seedling development in grazed plots did not differ significantly

from seedlings in the control.

Because results from this and another grazing study in northern California

showed no significant improvement in pine seedling development, the use of

grazing as a silvicultural release tool should be questioned. As currently

practiced, grazing with sheep does not meet critical tenets of vegetation

management. Competing vegetation is not being manipulated soon enough or

strongly enough to be effective. Some suggestions for enhancing grazing as a

silvicultural release tool are presented.

McDonald, Philip M.; Fiddler,

Gary O.; Meyer, Peter W. 1996.

Vegetation trends in a young

conifer plantation after grazing,

grubbing, and chemical release.

Res. Paper PSW-RP-228-Web.

Albany, CA: Pacific Southwest

Research Station, Forest Service,

U.S. Department of Agriculture;

17 p.

Retrieval terms: density, development, grasses, pines, sheep,

shrubs

USDA Forest Service Res. Paper PSW-RP-228-Web. 1996. iii
USDA Forest Service Res. Paper PSW-RP-228-Web. 1996. 1

Introduction

As the USDA Forest Service embraces the philosophy of ecosystem

management and increasingly incorporates it into management plans, a

disturbing weakness and a major need are recognized. The weakness is that very

little is known about the shrubs, forbs, and grasses in the community; the need is

for knowledge on silvicultural treatments that will provide specific plant

communities at given times in the future. And because of differences in plant

species composition and structure, the number of plant communities is huge,

and because the number of environments in which they grow also is large,

providing knowledge to fulfill this need is a major task.

The silvicultural treatments can be used for a variety of reasons: to create a

future forest; provide an economic crop; encourage forbs and grasses in a

plantation environment that provide seeds needed to sustain a desired species of

wildlife; or simply to make possible a broad base of species and age classes so

that forest stands will be in position to provide a broad range of amenities and

commodities for future use.

Of the silvicultural treatments investigated in this study, the least

information is available on grazing with sheep. Indeed, “forest managers’

acceptance of sheep as a biological tool is currently limited by lack of sitespecific data detailing the ecological and economic costs and benefits associated

with prescription sheep grazing in forests” (Sharrow 1994). Young conifer

plantations often contain palatable shrubs and herbaceous plants that provide

forage for grazing animals until the tree crowns close and shade out the lower

vegetation. Utilizing this forage, or transitory range as it sometimes is called, is

increasing worldwide (Oregon State University 1983). Providing forage and

wood constitutes a joint production strategy that gives the landowner income

from the animals while the forest is developing (Ritters and others 1982). Sheep

often are the grazing animals selected because they are well-suited to the dry,

rough, and often shrub-inhabited terrain typical of plantations in the western

United States. In general, weight gains and number of lambs have been

satisfactory (Hall and others 1959, Sharrow and Rhodes 1983). And through

proper herding techniques, the sheep can be controlled to minimize damage to

conifer seedlings (Fullmer 1987, McDonald and Fiddler 1993). That sheep

consume competing vegetation is generally accepted. For example, “Plenty of

evidence supports the use of livestock grazing as a useful management tool to

reduce unwanted vegetation in plantations” (Allen 1987).

Several recent studies with the herbicide Velpar, used in young conifer

plantations in northern California (McDonald and Fiddler 1990, McDonald and

others 1994) and elsewhere in California (Ballew 1991), have shown that it

historically has controlled grasses, forbs, shrubs, and hardwoods during the

establishment period. Other plantation release studies with herbicides and manual

release (grubbing) have consistently shown that the treated plot must have at

least a 5-foot radius to provide significant control of competing vegetation,

principally shrubs and hardwoods (McDonald and Fiddler 1986, 1990).

This paper documents trends in vegetation after a wildfire, after the planting

of Jeffrey pine seedlings, after the installation of a wide range of treatments, and

after grazing was terminated. Cost data also are presented so that the manager

can determine the cost effectiveness of each treatment.
2 USDA Forest Service Res. Paper PSW-RP-228-Web. 1996.

Methods

Location and Site Characteristics

The study site was located on the Milford Ranger District of the USDA Forest

Service’s Plumas National Forest, about 20 airline miles southeast of Susanville,

California. The area was burned in a 5,700-acre lightning-caused wildfire known

as the Elephant Burn in 1981. Before burning, the site was occupied by a mixed

conifer forest composed mostly of Jeffrey pine (Pinus jeffreyi Grev. & Balf.),

California white fir (Abies concolor var. lowiana [Gord.] Lemm.) and occasional

incense-cedar (Libocedrus decurrens Torr.). Snowbrush (Ceanothus velutinus

Hook.), squawcarpet, C. prostratus Benth.), and greenleaf manzanita

(Arctostaphylos patula E. Greene) were common shrubs. A few species of forbs and

grasses were present in more open areas.

After burning, the plant community consisted of these shrub species, but no

conifer seedlings—no seed source remained. Many of the shrubs originated from

the root crown and, fueled by the established root system, grew rapidly.

Seedlings of these and a few other species also were present, originating from

dormant seeds in the soil. Grasses, chiefly of the genera Bromus, Achnatherum

(formerly Stipa), Sitanion, and Poa, became abundant quickly as did forbs of the

genera Phacelia, Epilobium, Agoseris, Collinsia, and Paeonia.

Site quality of the study area is low (IV) with conifers growing well for the

first 30 years and then slowly thereafter. Dominant Jeffrey pines average 70 feet

tall at a breast-height age of 100 years (Meyer 1938). The study area is located at

an elevation of 6,600 feet on a northwest aspect with a slope of about 15 percent.

The soil, which is of the Haypress series (Entic Haploxeroll) that formed in

residuum weathered from granitic rocks, is moderately deep (30 inches),

somewhat excessively drained, and has a texture of loamy coarse sand

throughout. Large rock outcrops are common (fig. 1). Annual temperatures range

from a high of 70 oF to a low of -25 oF. Average annual precipitation is 32 inches

with 80 percent falling as snow. Summer drought and drought years are common

with 1987-1992 and 1994 being particularly dry.

Figure 1—Overview of the study area.

Note the large granite rocks, recently

grubbed Jeffrey pines, and developing

plant community. June 1985.
USDA Forest Service Res. Paper PSW-RP-228-Web. 1996. 3

Study and Design

The study presents density and development data on pine seedlings and shrubs,

forbs, and grasses collected from 1986 through 1994. It includes information

gathered on plants developing naturally (control) and after several treatments.

The year after the fire (1982), the area was logged by tractor, and all

merchantable trees were removed. Jeffrey pine seedlings from the Placerville

Nursery were then planted in spring 1983. They had spent 2 years in the nursery

and were large and healthy. Spacing was 10 by 10 feet. In August 1985, each

seedling was released by hand-grubbing a 4-foot radius around it. Consequently,

when we began the study in 1986, the Jeffrey pine seedlings had developed with

the natural post-burn plant community for three growing seasons.

The band of sheep initially consisted of 1,000 ewes and 23 rams, all

experienced with wildland conditions. They were trucked to an area near the

study site, unloaded, and allowed to browse for a week to become accustomed to

the wildland environment (fig. 2). Then, under the vigilant eye of a Basque

shepherd and three sheep dogs, they were guided through about a 400-acre area

that included the study site. The study site was grazed each year from 1986

through 1990. At least 1,000 sheep were present each year, with over 1,500 in

1987. The daily routine began at about 5:30 a.m. with the sheep foraging through

an area for 5 hours and then bedding down in a shaded area having water. This

was repeated from 4 to 8 p.m. each evening. The band passed through the study

site at least 10 times each summer. The length of the grazing season depended on

the availability of water. The sheep usually arrived at the study site from midMay to mid-June and departed around October 1. If the water sources dried up,

the sheep were moved out earlier. They departed August 24, 1990, for example.

The experimental design was completely randomized with four treatments

and three replications. Treatments were grazing (no fence), manually maintaining

a 4-foot radius (fence), applying Velpar (fence), and control (fence). The 4-foot

tall fence, which was installed shortly before the study treatments were applied,

was constructed of hog wire and maintained each year to exclude the sheep. The

4-foot radius, initially installed in fall 1985, was maintained each year for the first

3 years (1986-1988) by grubbing new plants within the radius and clipping plant

Figure 2—These sheep have just

been offloaded from the trucks and

are beginning to graze near the

study area.
4 USDA Forest Service Res. Paper PSW-RP-228-Web. 1996.

parts that leaned into it (fig. 3). Near free-to-grow replications (plots) were

created by applying Velpar L1 one time in mid-October 1986. Velpar is a soilactive herbicide. It was applied from a backpack apparatus and a carbon-dioxide

pressurized boom at the rate of 2 pounds acid equivalent per acre (fig. 4). Nozzles

on the boom were the same as those used in helicopter applications; therefore, the

rate of application and droplet size were similar. The boom, which covered a 9-

foot swath, was held about 12 inches above the shrubs, and the spray was

directed downward. Trial runs with water determined the proper walking speed

needed to apply the correct amount of herbicide to each plot. The entire plot and

half the buffer were sprayed. Application took place in clear, calm weather

between 8 and 9 a.m. PST.

The cost of installing each treatment was calculated from hourly records and

a wage of $8.74 per hour, the rate for a WG-1 laborer, U.S. Department of Labor,

as of June 1993.

Each plot was roughly rectangular and consisted of about 0.5 acre with at

least 40 seedlings surrounded by two rows of buffer (seedlings receiving similar

treatment). About 20 healthy seedlings, identified as potential crop trees, were

flagged. As their name implies, these were thrifty seedlings that had good

potential of becoming harvestable trees. Small, misshapen and discolored

seedlings were excluded—their chance of being alive at the end of the study was

remote, given the large populations of rapidly growing shrubs and grasses. For

each of the sample seedlings, stem height and stem diameter at 12 inches above

mean groundline were measured. The seedlings also were checked for possible

injury by sheep, herbicide, and other agents.

Sampling intensity for shrubs, forbs, and grasses was five randomly selected

subplots in each plot. Subplots were centered around Jeffrey pine seedlings.

They were square and contained 1 milacre (0.001 acre). The most abundant

species were measured for density, foliar cover (the sum of shadows that would

be cast by leaves and stems of individual species expressed as a percentage of the

land surface [Daubenmire 1968], and average dominant height (average of the

three tallest stems measured from mean groundline to bud). Less abundant

species were not measured, but noted in a species list.

Figure 3—A Jeffrey pine seedling in

the center of a 4-foot grubbed area.

A few grasses and forbs are invading

the treated area.

1This paper neither recommends

the pesticide uses reported nor

implies that the pesticides have

been registered with the appropriate governmental agencies.
USDA Forest Service Res. Paper PSW-RP-228-Web. 1996. 5

Vegetation was measured in late summer/fall 1986-1988, 1990, and 1994, and

data were statistically analyzed each year. To test for treatment effects and

significant differences among treatments, one-way analysis of variance of

treatment means (fixed model, Steel and Torrie 1980) and Tukey tests were the

analytical tools (Wilkinson 1989). Significance in all tests was at a = 0.05. Data

were gathered from permanent plots measured each year, and where analyses of

means from repeated measurements are concerned, the data are not truly

independent. The levels or type I errors given for various tests apply to each

measurement and year separately.

Results

Manipulating vegetation in young conifer plantations involves more than just

reducing the density and development of the tallest and most competitive plant

species. Large numbers of shorter plants may be just as capable of capturing

available resources and limiting conifer seedling survival and growth. Because

we wanted to denote vegetative trends associated with grazing and other

treatments, we quantified several growth parameters not only of Jeffrey pine, but

also of two aggressive shrub species and one abundant alien, but naturalized,

grass species. We also listed all the plant species in our area at the beginning and

end of the study, and noted the effect of treatment on plant diversity.

Plant Diversity

At the beginning of the study in 1986, the plant community consisted of 4 shrubs,

24 forbs, and 8 graminoids. At the study’s end in 1994, 4 shrubs, 22 forbs, and 6

graminoids were recorded (table 1). Seven species that were present in 1986 were

not found in 1994 and three species found in 1994 were not recorded in 1986. At

the end of the study, the number of shrub, forb, and graminoid species by

treatment was:

Treatment Number

Grazed 5 years .................... 21

Grubbed 3 years ................. 17

Velpar 1 year ....................... 14

Control ................................. 21

Figure 4—Applying Velpar herbicide

from a backpack and boom apparatus.

The man in the background is moving

to another swath width as a guide to

ensure that areas are not doubletreated or missed.
6 USDA Forest Service Res. Paper PSW-RP-228-Web. 1996.

In the plots treated by Velpar, the tree crowns were so full that they often

touched the ground and occupied almost all of the area. Little unshaded ground

was available for forbs and grasses. Lack of available space also characterized the

manually grubbed 4-foot radius plots. Here the combination of tree crowns in the

plots and shrub crowns leaning into the plots from 1991 to 1994 was the probable

cause of the lower number of species in this treatment at the end of the study.

Snowbrush

In fall 1986, plants of this fast-growing evergreen shrub varied from almost 700

to 2,400 per acre (table 2). About half were sprouts from root crowns, and half

originated from dormant seeds in the soil. Their crowns covered from 1 to 3

percent of the plot area, and their height ranged from 0.3 to 1.3 feet. In the Velpar

treatment, a few short plants from seed were recorded. These plants died the

following spring when their roots grew deep enough to encounter the herbicide—

a process that was repeated in 1987 but not thereafter. Plant density and

development did not differ among treatments.

In 1987, mean snowbrush density, foliar cover, and height increased in all

treatments except Velpar. Mean foliar cover was significantly greater in grazed

than in Velpar treatments—a trend that remained constant throughout the study.

By 1990 mean foliar cover of snowbrush in grazed plots was significantly larger

than in any other treatment. By 1994, mean foliar cover in grazed plots was three

times greater than in the control. Grazing actually stimulated foliar cover of

Table 1—Plant species in each treatment, Elephant Burn, Plumas National Forest, California, 1994

Species Control Grazing Grubbing Velpar

5 years 3 years 1 year

Shrubs Arctostaphylos patula X XX–

Ceanothus prostratus – X XX

Ceanothus velutinus X X XX

Purshia tridentata X – ––

Forbs Achillea millefolium X – ––

Agoseris spp. – – X –

Anaphalis margaritacea X – ––

Apocynum androsaemifolium – – XX

Collinsia parviflora X XX–

Cryptantha spp. X – – –

Epilobium spp. X X X X

Eriogonom parishii X X ––

Hypochaeris spp. – X – –

Linanthus ciliatus X – ––

Lotus spp. X X – X

Mentzelia congesta – – X–

Mimulus spp. – X – X

Montia spp. X X X X

Navarretia spp. X X – X

Paeonia brownii X X XX

Penstemon heterodoxus X – ––

Phacelia hastata – X XX

Stephanomeria spp. – X X –

Tragopogon dubius X X XX

Wyethia mollis – X ––

Graminoids Achnatherum occidentalis X X XX

Bromus tectorum X X XX

Carex spp. X X X –

Muhlenbergia filiformis X – ––

Poa spp. – – – X

Sitanion hystrix X XX–
USDA Forest Service Res. Paper PSW-RP-228-Web. 1996. 7

snowbrush. The sheep would browse only the tender twigs and the flowers. Each

twig then developed several buds that produced more twigs that led to horizontal

expansion of the plants. Another agent that affected snowbrush was the

California tortoise shell butterfly (Nymphalis californica Boisduval) (fig. 5).

Infestation by larvae occurred from June 20 to July 20, 1987, when almost every

plant in the study area was denuded (fig. 5). Most plants responded by producing

a few leaves that were promptly eaten by the sheep before they fully developed.

Little long-term effect from this defoliation could be discerned, however, and the

large amount of nutrient-rich frass provided by the larvae probably enhanced

shrub growth the following year.

The overall trend for snowbrush was an increase in density and development

for all treatments (except Velpar) through 1990 and then a decrease in density

and foliar cover in 1994. The decrease in density was caused by mortality to

young snowbrush seedlings that could not compete with snowbrush sprouts,

pine seedlings, and other shrubs and grasses. The decrease in plant cover in

grazed and control treatments probably was caused by the cumulative effect of

the drought years. Almost every large plant had one or more dead or dying

stems in each clump.

Greenleaf Manzanita

In fall 1986, plants of this hardy evergreen shrub varied from 200 to more than 700

per acre (table 3). Most plants were sprouts from root crowns, except in the 4-footradius plots maintained for 3 years where new seedlings from dormant seeds in

the soil represented the species. Aggregate crown development, as quantified by

Table 2—Average density, cover, and height of snowbrush, Elephant

Burn, Plumas National Forest, California, 1986-1994

Year Treatment Density Cover Height

Plants/acre pct ft

1986 Grazed 5 years 2,400 a1 3 a 0.9 a

Grubbed 3 years 2,267 a 1 a 0.8 a

Velpar 1 year 733 a 1 a 0.3 a

Control 667 a 1 a 1.3 a

Standard error 991 1.2 0.24

1987 Grazed 5 years 3,867 a 14 a 1.6 a

Grubbed 3 years 2,467 a 5 ab 1.3 a

Velpar 1 year 67 a 0 b 0.1 a

Control 1,867 a 5 b 1.6 a

Standard error 979 2.4 0.27

1988 Grazed 5 years 4,533 a 18 a 1.9 a

Grubbed 3 years 3,000 a 5 ab 1.8 a

Velpar 1 year 0 a 0 b .0 a

Control 2,000 a 8 ab 2.1 a

Standard error 1,014 3.2 0.13

1990 Grazed 5 years 4,600 a 33 a 2.2 a

Grubbed 3 years 3,133 ab 8 b 1.8 a

Velpar 1 year 0 b 0 b .0 a

Control 2,000 ab 14 b 2.4 a

 Standard error 797 3.8 0.27

1994 Grazed 5 years 3,000 a 30 a 2.3 a

Grubbed 3 years 1,867 a 8 b 1.9 a

Velpar 1 year 0 a 0 b .0 a

Control 1,267 a 10 b 2.4 a

Standard error 700 2.9 0.21

1For each year, treatment means in each column followed by the same

letter do not differ significantly according to a Tukey Test ( α = 0.05).
8 USDA Forest Service Res. Paper PSW-RP-228-Web. 1996.

foliar cover, was poor (1 percent), and height was average (0.6 to 1.2 feet) for this

site. In the Velpar treatment, a few small plants from seed were recorded. These

died the following spring when their roots encountered the herbicide in the soil.

No manzanita seedlings were found on Velpar plots after 1986.

Although greenleaf manzanita is given only a marginally palatable

designation (USDA Forest Service 1947), it was browsed heavily by the sheep

each year. Indeed in 1987, utilization was visually rated at 75 percent of greenery.

The trend of increasing manzanita density in radius plots continued through

1990 but then declined slightly. In general, manzanita height was similar among

treatments throughout the study and no statistical differences were noted. None

Figure 5—(A) Tent and larvae of

the California tortoise shell butterfly

in a snowbrush crown. (B) Severely

defoliated snowbrush plant in study

area. Fall 1987.

A

B
USDA Forest Service Res. Paper PSW-RP-228-Web. 1996. 9

was found for plant density as well. Only for foliar cover in 1990 and 1994 were

statistical differences found; significantly more cover was present in the control

than in grazed plots.

Cheatgrass

Cheatgrass (Bromus tectorum L.) is an annual alien species that invaded North

America from Eurasia in 1889-1894 and spread throughout what is now its

naturalized range by 1928 (Mack 1981). It has several adaptations that allow it

to effectively colonize and become established in disturbed areas. It produces

huge seedcrops, has an extensive root system, a high root-shoot ratio,

capability for root growth in cold soils, and maturity early in the growing

season (Jackson 1985).

By spring 1986 when we began the study, cheatgrass had spread throughout

the study area. In general, it was well established, but differed somewhat in

density and distribution (table 4). Density values ranged from 200 to 702,000

plants per acre and foliar cover from 0 to 15 percent. Both density and foliar

cover increased and decreased yearly, and no chronological trend was noted. A

general trend was that density and cover were greater in the less intensive

treatments (grazed, control) than in the more intensive treatments (grubbed

radius, Velpar). Of particular note was the relatively low density values of

cheatgrass in the Velpar treatment through 1988 followed by a huge increase.

This abrupt change in density suggests that the herbicide was present and

effective in the soil through 1988 but not thereafter.

Table 3—Average density, cover, and height of greenleaf manzanita,

Elephant Burn, Plumas National Forest, California, 1986-1994

Year Treatment Density Cover Height

Plants/acre pct ft

1986 Grazed 5 years 467 a1 1 a 1.2 a

Grubbed 3 years 733 a 1 a 0.7 a

Velpar 1 year 200 a 0 a 0.2 a

Control 333 a 1 a 0.6 a

Standard error 360 0.5 0.36

1987 Grazed 5 years 733 a 1 a 1.3 a

Grubbed 3 years 867 a 2 a 1.0 a

Velpar 1 year 0 a 0 a .0 a

Control 867 a 1 a 1.4 a

Standard error 392 0.8 0.41

1988 Grazed 5 years 867 a 1 a 1.4 a

Grubbed 3 years 1,267 a 2 a 1.3 a

Velpar 1 year 0 a 0 a .0 a

Control 1,200 a 2 a 1.6 a

Standard error 482 1.0 0.45

1990 Grazed 5 years 600 a 1 a 1.6 a

Grubbed 3 years 1,465 a 2 ab 1.5 a

Velpar 1 year 0 a 0 a .0 a

Control 1,600 a 5 b 2.2 a

Standard error 601 0.9 0.41

1994 Grazed 5 years 467 a 2 a 1.5 a

Grubbed 3 years 1,400 a 4 ab 1.8 a

Velpar 1 year 0 a 0 a .0 a

Control 933 a 7 b 2.1 a

Standard error 427 1.0 0.24

1

For each year, treatment means in each column followed by the same letter

do not differ significantly according to a Tukey Test ( α = 0.05).
10 USDA Forest Service Res. Paper PSW-RP-228-Web. 1996.

Combined Forbs

Forbs in the study area seemed to be distributed in two ways, depending on

species and treatment. Some species tended to be scattered with a few plants here

and there regardless of treatment. Others were present in widely scattered

aggregations in specific treatments. Some species preferred openings, however

small; others found the shade of taller plants to provide a desirable environment.

Several species favored the continuously disturbed environment of the grubbed

radius plots, but few could compete in the Velpar plots dominated by the fullcrowned Jeffrey pines.

Data from 1990 serve as an example of forb density and development. At no

time during the study did we find statistically significant differences among

treatments. In 1990, mean density of combined forbs ranged from 3,133 plants per

acre in grazed plots to 6,000 plants per acre in grubbed radius plots (table 5).

Average foliar cover ranged from 0 to 2 percent, and mean height spanned the

0.2- to 0.5-foot range.

Jeffrey Pine

Survival of Jeffrey pine seedlings varied only slightly among treatments during

the 1986-1994 period. At the end of the study, survival was 100 percent in grazed

and grubbed radius treatments, 93 percent in Velpar plots, and 92 percent in the

control. Pocket gophers (Thomomys spp.) were the principal cause of mortality. In

Table 4—Average density, cover, and height of cheatgrass, Elephant

Burn, Plumas National Forest, California, 1986-1994

Year Treatment Density Cover Height

Plants/acre pct ft

1986 Grazed 5 years 8,067 a1 1 a 0.6 a

Grubbed 3 years 200 a 0 a 0.7 a

Velpar 1 year 5,467 a 0 a 0.5 a

Control 153,467 a 9 a 0.9 a

Standard error 60,718 3.0 0.13

1987 Grazed 5 years 15,800 a 4 a 0.9 a

Grubbed 3 years 1,200 a 1 b 1.1 a

Velpar 1 year 1,667 a 0 b 0.9 a

Control 89,733 b 12 c 1.1 a

Standard error 17,305 0.5 0.11

1988 Grazed 5 years 57,067 a 6 ab 0.9 a

Grubbed 3 years 3,800 b 1 a 0.9 a

Velpar 1 year 7,333 b 3 a 1.2 a

Control 68,267 a 10 b 1.0 a

Standard error 11,228 1.7 0.08

1990 Grazed 5 years 702,200 a 14 a 1.2 a

Grubbed 3 years 80,600 a 3 a 1.0 a

Velpar 1 year 316,867 a 11 a 1.3 a

Control 411,533 a 15 a 1.0 a

Standard error 188,447 4.9 0.07

1994 Grazed 5 years 251,000 a 8 a 0.9 a

Grubbed 3 years 148,000 a 3 a 0.7 a

Velpar 1 year 147,000 a 3 a 0.8 a

Control 184,000 a 7 a 0.7 a

Standard error 45,059 2.2 0.06

1

For each year, treatment means in each column followed by the

same letter do not differ significantly according to a Tukey Test

( α = 0.05).
USDA Forest Service Res. Paper PSW-RP-228-Web. 1996. 11

spite of resident deer (Odocoileus spp.), rodents, and other animals, damage to

pine seedlings was minimal. The only browsing damage noted was in 1987 when

the sheep nipped a few lateral buds in the grazing treatment. No damage from

the herbicide was observed.

Statistically significant differences among treatments for pine stem diameter

first showed up in fall 1988 (table 6). Seedlings in the Velpar treatment were

larger than counterparts in grazed and control areas. This trend continued

thereafter as seedlings in herbicide-treated plots had significantly larger

diameters at 12 inches above mean groundline than seedlings in all other

treatments. Statistically significant differences for foliar cover and height first

Table 5—Average density, cover, and height of combined forbs, Elephant

Burn, Plumas National Forest, California, 1990

Treatment Density Cover Height

Plants/acre pct ft

Grazed 5 years 3,133 a1 0 a 0.2 a

Grubbed 3 years 6,000 a 1 a 0.4 a

Velpar 1 year 4,800 a 2 a 0.5 a

Control 5,733 a 0 a 0.5 a

Standard error 2,658 0.6 0.18

1For each year, treatment means in each column followed by the same

letter do not differ significantly according to a Tukey Test ( α = 0.05).

Table 6—Average diameter, height, and cover of Jeffery pine, Elephant Burn, Plumas

National Forest, California, 1986-1994

Year Treatment Diameter Cover Height

inches pct ft

1986 Grazed 5 years 0.4 a1 0 a 0.9 a

Grubbed 3 years 0.4 a 1 a 1.0 a

Velpar 1 year 0.4 a 1 a 1.1 a

Control 0.5 a 0 a 1.0 a

Standard error 0.05 0.3 0.14

1987 Grazed 5 years 0.4 a 3 a 1.3 a

Grubbed 3 years 0.5 a 3 a 1.6 a

Velpar 1 year 0.7 a 4 a 1.8 a

Control 0.5 a 3 a 1.6 a

Standard error 0.07 0.7 0.21

1988 Grazed 5 years 0.5 a 5 a 1.5 a

Grubbed 3 years 0.7 b 6 a 2.2 a

Velpar 1 year 1.2 b 11 a 2.6 a

Control 0.6 a 5 a 2.0 a

Standard error 0.11 2.1 0.30

1990 Grazed 5 years 0.9 a 5 a 2.3 a

Grubbed 3 years 1.3 a 8 ab 3.2 ab

Velpar 1 year 2.6 b 19 b 5.2 b

Control 1.1 a 8 ab 2.9 a

Standard error 0.23 2.6 0.52

1994 Grazed 5 years 1.9 a 19 a 4.7 a

Grubbed 3 years 2.4 a 17 a 5.8 a

Velpar 1 year 4.6 b 72 b 10.5 b

Control 2.2 a 25 a 5.2 a

Standard error 0.40 7.4 0.93

1For each year, treatment means in each column followed by the same letter do not

differ significantly according to a Tukey Test ( α = 0.05).
12 USDA Forest Service Res. Paper PSW-RP-228-Web. 1996.

Figure 6—Relative development of

Jeffrey pine and surrounding plant

community, by treatment, fall 1994.

(A) Velpar herbicide, (B) 4-foot radius

grubbed three times, (C) control, (D)

grazed 5 years.

A B

C D
USDA Forest Service Res. Paper PSW-RP-228-Web. 1996. 13

showed up at the next measurement in 1990. By study end, mean foliar cover and

height of seedlings in the Velpar treatment were significantly larger than

seedlings in all other treatments (fig. 6). In fact, herbicide-treated seedlings had

92 percent more girth and 324 percent more cover, and were 81 percent taller

than seedlings in the next closest treatment.

Treatment Costs

The cost of grazing with sheep was considered to be zero. The money paid by the

permittee equaled the Forest Service’s cost of inspecting the area and moving the

sheep to the allocated area each year. The cost of manually grubbing a 4-foot

radius around conifer seedlings for 3 years involved two components: removing

plants, and clipping plants that leaned into the radius. For the first year, both

grubbing and clipping were required; by the third year, retreatment consisted

almost entirely of clipping. Grubbing a 4-foot radius three times proved expensive.

Applying Velpar was inexpensive although the chemical itself was costly:

Treatment Dollars per acre

Grazed 5 years - - - - - - - - - - - - - 0

Grubbed 3 years - - - - - - - - - - 420

Velpar 1 year

Chemical - - - - - - - - - - - - - 75

Application - - - - - - - - - - - - 27

Discussion and Conclusions

The individual treatments comprising this study, applied in an area burned by

wildfire, provide a means for portraying plant succession in a natural state

(control), after an effective plot-wide second disturbance (herbicide), after an

ineffective, small-scale disturbance that was applied continuously for 3 years (4-

foot radius grubbed), and after an ineffective area-wide disturbance that took

place continuously for 5 years (grazing by sheep). Ecologists, foresters, wildlife

biologists, ranchers, and others should find the interrelationship of snowbrush,

greenleaf manzanita, cheatgrass, forbs, and ponderosa pines (tables 2-6) useful

because of the wide range of disturbance.

When we began this study in fall 1985, treatment “effectiveness” was geared

mostly to increasing growth of the conifer seedlings. They were the economic

crop. Money had been spent to gather their seeds, propagate them in nurseries,

and plant them where a new forest was desired. The effect of grazing was

unknown but suspected to be moderate/low in effectiveness; Velpar was known

to be an effective herbicide; grubbing a 4-foot radius, which was thought to be a

large treated area at that time, was given moderate to high marks; and no

treatment (control) would provide no effect.

In 1986, the first year of the study, most plant species were well established,

but not fully so. Some bare area remained and colonization, at least through

1990, resulted in increasingly higher densities of shrubs, graminoids, and forbs.

After 1990, mean plant density and foliar cover tended to decrease although

height increased slightly. Too many plants per unit area and the effect of

cumulative drought are possible reasons for this decrease.

By the end of the study, vegetation in the various treatments ranged from

more than 256,000 plants per acre in grazed areas to 150,000 plants per acre in

Velpar areas. More than 97 percent of this vegetation was cheatgrass. This high

percentage tended to mask species/treatment relationships. However, noting

treatments with “most” and “least” amounts of specific vegetation helps portray

them. Of all the treatments, grazing resulted in the most snowbrush and
14 USDA Forest Service Res. Paper PSW-RP-228-Web. 1996.

cheatgrass, the smallest Jeffrey pines, and a tie with the control for the highest

number of plant species. The 4-foot radius plots that were grubbed for 3 years

had the most manzanita and forbs. The Velpar plots had the least snowbrush,

manzanita, and cheatgrass, the largest Jeffrey pines, and the lowest number of

plant species.

Averaging 10.5 feet in height and 4.6 inches in diameter, the Jeffrey pine

saplings in the Velpar treatment constituted the tallest vegetation in the area—

4.3 times taller than the tallest shrubs. The effect of the herbicide-treated

environment was to provide a plant community of tall, vigorous, wide-crowned

trees that were growing at the potential of the site. This treatment, however, did

not provide an environment that was totally free of vegetation. Cheatgrass was

present. And although this grass used site resources, the vigorous growth of the

pines suggests that its effect must have been small. Furthermore, the grass could

have interfered with the germination of dormant shrub seeds in the soil

(McDonald 1986). Excluding the aggressive shrubs with their high resource use

would be a net gain.

A principal tenet in vegetation management is that treatment be applied as

soon as possible after disturbance, and before the competing vegetation can

become established. In this study, naturally occurring vegetation was present for

4 years before the treatments were applied, and planted pine seedlings had to

endure competition from it for 3 years. Plainly, competing vegetation was well

established before the study began, and the need for strong treatments that

would remove competing vegetation from enough area for enough time to

release the conifer seedling was obvious.

Previous work has shown that the minimum area needed to allow

statistically significant conifer seedling development (relative to a control) is a 5-

foot radius (Fiddler and McDonald 1984, McDonald and Fiddler 1989). Smaller

radii do not provide a nursery-grown conifer seedling enough time to develop

its root system well enough to get to, and stay in, a zone of adequate soil

moisture. The better adapted, naturally occurring shrubs and grasses with

faster-developing and more massive root systems (Jackson 1985, Logan 1983,

McDonald 1982, McDonald and Fiddler 1989, Mooney and Dunn 1970) reach the

zone of adequate soil moisture first, use the moisture, and deny it to the conifer

seedlings. The grubbing and grazing treatments were ineffective because too

much well-established competing vegetation remained.

Another important tenet of vegetation management is that, to have value,

release must be effective soon after treatment. Otherwise, the competing

vegetation has even more time to develop and capture site resources. The herbicide

treatment, by virtue of the near free-to-grow environment that it created, allowed

pine seedling diameter to become significantly larger than that of seedlings in the

control three growing seasons after treatment. This duration is about as soon as

can be expected, given the 3-year delay between planting and treatment.

An objective of this study was to quantify the recovery of the vegetation

after the sheep were removed. Recovery from grazing can happen only if

damage, and particularly chronic damage, has occurred. The only damage that

we could detect was minor—manzanita cover with grazing was significantly

lower than that in the control. Consequently, quantifying recovery was not

possible because there was virtually no damage to recover from.

Heightened public concern and increased restrictions on use of herbicides

have caused many natural resource managers to look for other methods to

control unwanted vegetation in young conifer plantations. Livestock grazing

has been suggested as an alternative silvicultural tool (Doescher and others 1987,

Sharrow and others 1989, Thomas 1984). Wray (1987) claimed that sheep “graze

off unwanted brush, help trees grow, save money, and provide fertilizer in the

bargain.” In spite of this belief, a key question remains: Do sheep consume
USDA Forest Service Res. Paper PSW-RP-228-Web. 1996. 15

enough competing vegetation to significantly enhance the growth of the planted

conifer seedlings? Are they an effective vegetation management tool? Although

studies in the moist Oregon Coast Range indicated that diameters of Douglas-fir

(Pseudotsuga menziesii [Mirb.] Franco) seedlings increased by 7 to 14 percent in

grazed areas as compared to ungrazed controls (Sharrow and Leininger 1983), a

more recent study in summer-dry northern California showed that 10 continuous

years of grazing deerbrush (Ceanothus integerrimus H. & A.) by sheep did not

significantly increase diameter or height of ponderosa pine seedlings (McDonald

and Fiddler 1993).

Because this study and another (McDonald and Fiddler 1993) did not

demonstrate a significant gain in ponderosa and Jeffrey pine seedling growth,

the use of sheep as a release tool for silviculturists seems questionable. Current

grazing practice has several weaknesses, at least as practiced in northern

California. To begin with, sheep are seldom used the first season after logging or

burning—the perception is that not enough forage is present and that damage to

planted conifer seedlings will be severe. In addition, when sheep are used in

subsequent growing seasons, the timing is poor. Traditionally, they feed at lower

elevations until the forage is gone, then they are trucked to higher elevations in

the forest zone. Usually this is too late. Most of the early, tender, and more

nutritious growth has become hard and mature, or eaten by other herbivores.

And even when the sheep are present for wildland grazing, the tendency is to

herd them to the most nutritious forage, and remove them before secondary

species and plant parts are all that remain. The end result is that grazing is too

little, too late, and utilization is never high enough to make a significant

difference in the competitive ability of the shrubs, forbs, and grasses.

Plainly, the basic tenets of vegetation management must be met if grazing by

sheep is to become a viable silvicultural alternative. This means the sheep must

be allowed to graze new plantations as soon as possible—preferably during the

first growing season after planting. And they should be brought to the plantation

each spring as soon as possible to utilize the vegetation before carbohydrate

reserves are replenished. Once there, the sheep should be held in the area to

graze as much vegetation as possible even if it means consuming less than prime

forage. If these conditions cannot be met, the range deteriorates, or damage to

conifer seedlings becomes intolerable, then grazing with sheep will be recognized

as an inviable tool for enhancing conifer seedling growth.

Grazing, however, still should be considered from the viewpoint of the other

return from the land—the sheep—and more specifically their wool, meat, and

lambs. The owners’ records indicate that each ewe gained an average of 126

pounds during the summer. About 20 percent of ewes had twins. More than

once, the owner indicated that he was pleased with grazing in the area, and

protested vigorously when he could not return.

The cost data presented in this study reflect the interplay between amount

and size of competing vegetation and the cost of controlling some of it. For

manual release, the dollars spent achieved little gain; for applying herbicide, a

large gain resulted; for grazing, little gain and no cost characterized the treatment.

The grazing, grubbing, and herbicide treatments in this study created two

vegetative assemblages that probably will lead to different plant communities in

the future. The future community on herbicide-treated areas likely will be

primarily Jeffrey pine with scattered plants of cheatgrass and a few forbs. The

crowns of the pines will close in the near future and even fewer plants with less

biomass will be present. The potential for a fully stocked forest developing in the

shortest time possible is high. The other treatments will lead to a plant

community composed of pines and shrubs with grasses and a few forbs in small

openings or under crowns. The time it will take to become a forest will be longer

and the tree canopy likely will be more open.
16 USDA Forest Service Res. Paper PSW-RP-228-Web. 1996.

References

Allen, Barbara H. 1987. Livestock grazing as a vegetation management tool. In: Proceedings, 8th

annual forest vegetation management conference; 1986 November 5-6; Sacramento, CA. Redding,

CA: Forest Vegetation Management Conference; 43-55.

Ballew, Larry. 1991. Biodiversity: benefits of Velpar L herbicide on conifer growth and range and

wildlife habitat. In: Proceedings, 12th annual forest vegetation management conference; 1991

May 14-16; Redding, CA. Redding, CA: Forest Vegetation Management Conference; 10-15.

Daubenmire, R.F. 1968. Plant communities: a textbook on plant synecology. New York: Harper and

Row; 300 p.

Doescher, Paul S.; Tesch, Steven D.; Alejandro-Castro, Mabel. 1987. Livestock grazing: a silvicultural

tool for plantation establishment. Journal of Forestry 85(10): 29-37.

Fiddler, Gary O.; McDonald, Philip M. 1984. Alternatives to herbicides in vegetation management:

a study. In: Proceedings, 5th annual forest vegetation management conference; 1983 November

2-3; Sacramento, CA. Redding, CA: Forest Vegetation Management Conference; 115-126.

Fullmer, Donald G. 1987. Sheep grazing for plantation release. A Foresthill Ranger District case

study. In: Proceedings, 8th annual forest vegetation management conference; 1986 November 5-

6; Sacramento, CA. Redding, CA: Forest Vegetation Management Conference; 149-163.

Hall, F.C.; Hedrick, D.W.; Keniston, R.F. 1959. Grazing and Douglas-fir establishment in the

Oregon white oak type. Journal of Forestry 57(2): 98-103.

Jackson, Louise E. 1985. Ecological origins of California’s Mediterranean grasses. Journal of

Biogeography 12: 349-361.

Logan, Robert S. 1983. Agro-forestry: growing trees, forage, and livestock together. Extension

Circular 1114. Corvallis: Oregon State Univ.; 4 p.

Mack, Richard N. 1981. Invasion of Bromus tectorum L. into western North America: an ecological

chronicle. Agro-ecosystems 7: 145-165.

McDonald, Philip M. 1982. Adaptations of woody shrubs. In: Hobbs, S.D.; Helgerson, O.T., editors.

Proceedings of a workshop on reforestation of skeletal soils; 1981 November 17-19; Medford, OR.

Corvallis, OR: Forest Research Laboratory, Oregon State Univ.; 21-29.

McDonald, Philip M. 1986. Grasses in young conifer plantations—hindrance and help. Northwest

Science 60(4): 271-278.

McDonald, Philip M.; Abbott, Celeste S.; Fiddler, Gary O. 1994. Response of young ponderosa

pines, shrubs, and ferns to three release treatments. Western Journal of Applied Forestry

9(1): 24-28.

McDonald, Philip M.; Fiddler, Gary O. 1986. Release of Douglas-fir seedlings: growth and

treatment costs. Res. Paper PSW-182. Berkeley, CA: Pacific Southwest Forest and Range

Experiment Station, Forest Service, U.S. Department of Agriculture; 9 p.

McDonald, Philip M.; Fiddler, Gary O. 1989. Competing vegetation in ponderosa pine plantations:

ecology and control. Gen. Tech. Rep. PSW-113. Berkeley, CA: Pacific Southwest Forest and

Range Experiment Station, Forest Service, U.S. Department of Agriculture; 26 p.
USDA Forest Service Res. Paper PSW-RP-228-Web. 1996. 17

McDonald, Philip M.; Fiddler, Gary O. 1990. Ponderosa pine seedlings and competing vegetation:

ecology, growth, and cost. Res. Paper PSW-199. Berkeley, CA: Pacific Southwest Research

Station, Forest Service, U.S. Department of Agriculture; 10 p.

McDonald, Philip M.; Fiddler, Gary O. 1993. Vegetative trends in a young conifer plantation after

10 years of grazing by sheep. Res. Paper PSW-RP-215. Albany, CA: Pacific Southwest Research

Station, Forest Service, U.S. Department of Agriculture; 9 p.

Meyer, Walter H. 1938. Yield of even-aged stands of ponderosa pine. Tech. Bull. 630. Washington,

DC: Forest Service, U.S. Department of Agriculture; 59 p.

Mooney, Harold A.; Dunn, E. Lloyd. 1970. Convergent evolution of Mediterranean-climate

evergreen schlerophyll shrubs. Evolution 24: 293-303.

Oregon State University. 1983. Foothills for food and forests. In: Hannaway, D.B., ed. Proceedings

of an international symposium; 1983 April 25; Corvallis, OR. College of Agriculture Science. 2,

Oregon State Univ. Beaverton, OR: Timber Press; 383 p.

Ritters, Kurt; Brodie, J. Douglas; Hann, David W. 1982. Dynamic programming for optimization of

timber production and grazing in ponderosa pine. Forest Science 28(3): 517-526.

Sharrow, Steven H. 1994. Sheep as a silvicultural management tool in temperate conifer forest.

Sheep Research Journal (special issue).

Sharrow, Steven H.; Leininger, Wayne C. 1983. Forage preferences of herded sheep as related to

brush control and seasonal browsing damage to Douglas-fir regeneration. In: Progress Report

1982. Project Number 0066. Corvallis: Oregon Agricultural Experiment Station; 42 p.

Sharrow, S.H.; Leininger, W.C.; Rhodes, B. 1989. Sheep grazing as a silvicultural tool to suppress

brush. Journal of Range Management 42(1): 2-4.

Sharrow, Steven H.; Rhodes, Bruce. 1983. The effect of grazing sheep on clearcuts in Oregon’s

Coast Range and its impact on big game habitat. In: Progress Report 1981-1982. Project Number

0066. Corvallis: Oregon Agricultural Experiment Station; 42 p.

Steel, Robert C.D.; Torrie, James H. 1980. Principles and procedures of statistics. 2nd ed. New York:

McGraw-Hill Book Company; 218-220.

Thomas, David F. 1984. The use of sheep to control competing vegetation in conifer plantations.

In: Proceedings 5th annual forest vegetation management conference; 1983 November 2-3;

Sacramento, CA. Redding, CA: Forest Vegetation Management Conference; 138-143.

USDA Forest Service. 1947. Standard symbols and use factors. Region 5, Division of Range

Management; 31 p.

Wilkinson, L. 1989. SYSTAT: The system for statistics. Evanston, IL: SYSTAT, Inc.

Wray, Pat. 1987. Sheep. An alternative to herbicides? American Forests 93(3/4): 34-35, 79.
The Forest Service, U.S. Department of Agriculture, is responsible for Federal Leadership

in forestry.

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