Development of a Mixed Shrub–

Tanoak–Douglas-fir Community in

a Treated and Untreated Condition

Philip M. McDonald Gary O. Fiddler

Treated

Untreated

United States

Department

of Agriculture

Forest Service

Pacific Southwest

Research Station

Research Paper

PSW-RP-225-Web
Abstract

McDonald, Philip M.; Fiddler, Gary O. 1996. Development of a mixed shrub–tanoak–

Douglas-fir community in a treated and untreated condition. Res. Paper

PSW-RP-225-Web. Albany, CA: Pacific Southwest Research Station, Forest

Service, U.S. Department of Agriculture; 16 p.

On a medium site in northern California, a tanoak-mixed shrub community was

given several treatments (manual release two and three times, a combination chainsaw

and cut surface herbicide treatment, two foliar herbicides, and a tank mix of the two

herbicides) to study its development in both a natural (control) and treated condition.

The herbicides were 2,4-D, Garlon 3A, and Garlon 4, each applied two times. Survival

of planted Douglas-fir seedlings was recorded for 11 years and growth was quantified

for 9 years after the last treatment application. In addition to Douglas-fir, data are

presented individually for the two most abundant species (tanoak and snowbrush),

for greenleaf manzanita, and for the hardwood tree and shrubs combined. At the

study’s end in 1992, combined vegetation in the control had a mean density of 1,800

plants per acre, foliar cover of 23,700 ft2

 per acre, and height of 11.2 feet. In contrast,

combined tree and shrubs in the most effective treatment for controlling them—cut

and spray Garlon 3A—had a mean density of 150 plants per acre, foliar cover of 150

ft2

 per acre and height of 5.9 feet at study end. And because competition for site

resources was low, Douglas-fir seedlings developed best in this treatment. Mean

Douglas-fir diameter was 4.6 inches at 12 inches above mean ground line, height

averaged more than 21 feet, and mean foliar cover was 39,850 ft2

 at the end of the study.

The cost was $227 per acre. The treatment response data, cost information, and plant

community relationships provide the forest land manager with knowledge on how to

attain some specific plant communities in the future, and their developmental

potentials.

Retrieval Terms: Douglas-fir seedlings, manual and chemical release, northern

California, shrubs, tanoak sprouts

The Authors

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

Management Research Unit (2400 Washington Ave., Redding, CA 96001). Gary O.

Fiddler is a silviculturist assigned to the Timber Resource Planning Unit, Pacific

Southwest Region, USDA Forest Service, with headquarters in San Francisco, and

stationed at Redding, Calif. (2400 Washington Ave., Redding, CA 96001).

Pacific Southwest Research Station

Forest Service

US Department of Agriculture

Publisher:

Albany, California

Mailing address:

PO Box 245, Berkeley CA

94701-0245

510 559-6300

http://www.pswfs.gov

August 1996
Contents

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

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

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

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

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

Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

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

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

Tanoak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Snowbrush . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Greenleaf Manzanita. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Combined Tree and Shrubs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Douglas-fir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Plant Moisture Stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Production and Cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Discussion and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Development of a Mixed Shrub–

Tanoak–Douglas-fir

Community in a Treated and

Untreated Condition

Philip M. McDonald Gary O. Fiddler

Pacific Southwest

Research Station

USDA Forest Service

Research Paper

PSW-RP-225-Web

 August 1996
4 USDA Forest Service Research Paper PSW-RP-225. 1996.

Development of a Mixed Shrub–Tanoak–Douglas-fir Community McDonald and Fiddler

In Brief

Most conifer plantations in California are located in areas

that have been created by wildfire or timber harvest. In

many instances, the preharvest stands are devoid of conifers

or poorly stocked with them and have a large component of hardwoods

and shrubs. A forestry goal is often to create a new stand with a higher

conifer component. How to limit the hardwoods and shrubs in the new

stand is a problem, especially on steep ground, because few treatment

alternatives are available. Falling the hardwoods and burning them and

the conifer slash is the most practical. If this technique is effective, the

soil surface is mostly bare mineral soil with scattered burned logs on it. If

the broadcast burn takes place in the spring when the debris and litter

layers are dry, but the organic material next to the soil is wet, an

unburned layer remains to protect the soil, at least for a year or two.

Bare mineral soil does not last long, however, because many native

hardwoods and shrubs have a regeneration strategy of rapid expansion

after disturbance (Grime 1979). This is manifest in extensive sprouting

from the root crown or burl. Each sprout captures a portion of the parent

tree’s root system, and fueled by water and nutrients from it, develops

rapidly. Rapid regrowth and concomitant capture of site resources

combine to make establishment and subsequent development of conifer

seedlings difficult, if not impossible.

In this atmosphere of burgeoning competition, natural conifer

seedlings from seed produced by adjacent trees would have difficulty

becoming established. Planted conifer seedlings would fare no better. If

conifers are to regain their place as the dominant vegetation,

manipulation by humans has to be done. Specifically, the hardwood and

shrub sprouts have to be reduced in number and vigor. Treating them as

soon as possible after broadcast burning is cost effective. Early treatment

denies competing plants the chance to recover from damage sustained in

harvesting and site preparation. It also prevents them from using the

high levels of site resources typically present after disturbance. And

because they are young and small, they are easier to treat at a lower cost.

The two manual treatments, three chemical treatments, and combination

of manual and chemical treatment evaluated in this study created a plant

community dominated either by planted Douglas-fir, or with various

proportions of Douglas-fir, tanoak, and snowbrush. Several other shrubs,

forbs, and grasses were present, but never became abundant.

The most effective treatments (chainsaw and spray cut surfaces with

Garlon 3A herbicide two times, and foliar spray with 2,4-D plus Garlon 4

two times) created a plant community whose foliar cover was 99 and 95

percent Douglas-fir at the end of the study. A moderately effective

treatment, such as manually releasing a 5-foot radius around Douglas-fir

seedlings three times, led to a community whose foliar cover had the

proportion of 33 percent tanoak, 14 percent snowbrush, and 53 percent

Douglas-fir seedlings at the study’s end. Applying no further treatment

after broadcast burning, as in the control, created a plant community

whose foliar cover was evenly distributed among tanoak, snowbrush,

and Douglas-fir. The future of this community, however, is in doubt as

the Douglas-fir seedlings are so slender that they would fall over if not

supported by the shrubs and hardwoods. Precedent suggests that the

Douglas-fir component here is likely to be much reduced in the future.

iii

McDonald, Philip M.; Fiddler,

Gary O. 1996. Development of a mixed shrub

–tanoak–Douglas-fir community in a natural and

treated condition. Res.

Paper PSW-RP-225. Albany, CA: Pacific Southwest Research Station,

Forest Service, U.S. Department of Agriculture; 16 p.

Retrieval Terms: Douglas-fir

seedlings, manual and chemical

release, northern California,

shrubs, tanoak sprouts

USDA Forest Service Research Paper PSW-RP-225. 1996.
USDA Forest Service Research Paper PSW-RP-225. 1996. 5

Development of a Mixed Shrub–Tanoak–Douglas-fir Community McDonald and Fiddler

Consequently, the trend in the control is toward a plant community much like

that before harvest or one composed primarily of hardwoods and shrubs.

The most effective treatments in this study led to a full component of rapidly

growing Douglas-firs with potential to create a stand composed of mostly

conifers. The moderately effective treatments created a mixed stand of

vegetatively propagated tanoak trees, snowbrush shrubs, and slower growing

planted Douglas-fir seedlings. The untreated control promoted a stand composed

mostly of hardwoods and shrubs. These different plant communities,

developmental potentials, and associated treatment costs give the forest land

manager of the future choices for manipulating the vegetation in the landscape.

And if one treatment is not politically or economically desirable, another

treatment may attain the desired condition.

iv USDA Forest Service Research Paper PSW-RP-225. 1996.
USDA Forest Service Research Paper PSW-RP-225-Web. 1996. 1

Development of a Mixed Shrub–Tanoak–Douglas-fir Community McDonald and Fiddler

As ecology becomes more important in forestry, knowledge about plantspecies and plant communities that develop naturally or after a deliberate

manipulation is increasingly needed. Manipulation could be for a variety of

reasons: to create a future forest, to provide an economic crop, to grow plants

along with trees whose seeds would be critical to wildlife, or simply to provide a

broad base of species and age classes and thus be able to provide values and

commodities that will be needed in the future. In forestry, much knowledge has

been generated on economic species (conifer trees), but little is available on the

currently uneconomic hardwoods, shrubs, forbs, and grasses.

What is known is that growth of Douglas-fir (Pseudotsuga menziesii [Mirb.]

Franco) seedlings can be reduced to a fraction of their potential by competing

vegetation, and that dramatic increases have occurred when this vegetation was

removed. Gratkowski and Lauterbach (1974) recorded height increases of 170 to

255 percent for Douglas-fir seedlings 6 years after herbicide release in the Cascade

Range of Oregon. The competing vegetation was primarily the tall variety of

Ceanothus. Peterson and Newton (1982) measured third-year growth of 5-yearold Douglas-fir seedlings growing with Ceanothus and several herbs. Volume

growth of treated conifers was 258 percent greater than untreated seedlings when

shrubs were controlled and 415 percent greater when both shrubs and forbs were

effectively treated. McDonald and Fiddler (1986) found that the mean diameter of

Douglas-fir seedlings (measured at 12 inches above mean ground line) in the

most effective of several treatments was 86 percent greater than that of untreated

seedlings after 5 years. Competition in this instance also was mostly from a

species of Ceanothus. Several other studies have shown dramatic increases in

growth of Douglas-fir seedlings after release from other vegetation, particularly

sprouting hardwoods (McDonald and others 1994, Tappeiner and others 1992).

In ecosystem management, every combination of every species could have

value at some place in the landscape at some time. The chief of the USDA Forest

Service, Jack Ward Thomas, acknowledged that we have much to learn about

ecosystems, but “we have no option but to move forward on the basis of what we

know.” Furthermore, “We must quickly adapt to new information and new

understanding as it becomes available” (Thomas 1994). A strong need to develop

new information on individual species and their interrelationships is implicit.

To increase knowledge about the ecology of several widespread plant species

and a plant community that is commonplace in California and Oregon,

information was collected on the species composition and developmental

potentials of vegetation reoccupying a clearcut-harvested and broadcast-burned

area in northern coastal California. Data were gathered both for vegetation

developing naturally in an untreated control and for vegetation that was

manipulated deliberately by several manual and herbicide treatments. Planted

Douglas-fir seedlings were part of both plant communities. Natural seedlings

had little chance of becoming established. This, one of the earliest studies that we

installed, was part of a National Forest Service Administrative Study on

alternative release methods (Fiddler and McDonald 1984).

This paper reports results on the competitive interaction of vegetation in a

recently disturbed plant community. It portrays the growth dynamics of

vegetatively propagated trees and shrubs and suggests that these dynamics, plus

those of planted Douglas-fir seedlings, limited other plant species from becoming

established or developing well. The study describes the density and development

of the most abundant hardwood and shrub species and quantifies the growth of

Introduction
2 USDA Forest Service Research Paper PSW-RP-225-Web. 1996.

Development of a Mixed Shrub–Tanoak–Douglas-fir Community McDonald and Fiddler

the Douglas-fir seedlings. Timing of treatment effectiveness and cost of the

treatments is also presented. The variety of species proportions, growth

potentials, costs, and treatments provide ecosystem managers with choices that

should be useful in the future.

Methods

Location and Site Characteristics

The study area, located on the Gasquet Ranger District of the Six Rivers National

Forest, was about 10 airline miles east of Crescent City, California. It comprised

about 60 acres in two homogeneous units about 2 miles apart. Before clearcutharvesting in 1978-79, the area supported a patchy stand of Douglas-fir

intermixed with hardwoods and clumps of tall shrubs. After the merchantable

conifers were harvested, the hardwoods, which were 3 to 6 inches in diameter,

were cut. They and the conifer slash were broadcast burned in fall 1979. Most of

the slash and hardwoods were consumed, leaving a soil surface that was mostly

mineral soil with scattered burned logs on it.

The area was planted at an 8- by 8-foot spacing in February 1981 with 2-0

Douglas-fir seedlings from the USDA Forest Service’s Humboldt Nursery. Because

damage from deer (Odocoileus spp.) was common in the area, each seedling was

fitted with a 24-inch vexar leader protector. Although a good job of planting was

done, survival in the fall of 1981, when we began the study, was 70 percent.

The plant community when the study began consisted mostly of plants that

originated from root crowns and dormant seeds in the soil. Many hardwood and

shrub burls were present, which promptly sprouted. Rapidly growing sprouts

comprised the early after-burning plant community. The second summer after

site preparation, shrub seedlings and a few forbs from windblown seeds became

established. In addition to the planted Douglas-fir seedlings, the most abundant

vegetation in the plantation was tanoak (Lithocarpus densiflorus [Hook. & Arn.]

Rehd.) and snowbrush (Ceanothus velutinus var. hookeri M. Johnston) with

greenleaf manzanita (Arctostaphylos patula E. Greene) a distant second.

Oregongrape (Berberis spp.), yerba santa (Eriodictyon californicum [Hook. & Arn.]

Torrey), and beargrass (Xenophyllum tenax [Pursh] Nutt.) (family Liliaceae) were

locally dense. A few forbs and bracken fern (Pteridium aquilinum [L.] Kuhn var.

pubescens L. Underw.) were widely scattered throughout the study area. No

grasses were recorded.

Snowbrush, which formerly was called Ceanothus velutinus var. laevigatus,

has recently been given a new variety name (hookeri) (Hickman 1993). It is found

near the Pacific coast from northern California northward to British Colombia. It

grows at low elevations, and differs from the inland variety, primarily by its

taller stature. Although common in many conifer plantations in California and

southern Oregon, ecological information, particularly density and development

data, are needed for it (Conard and others 1985). Variety hookeri is a hardy, fastgrowing shrub with many adaptations (Hanes 1981, McDonald 1982) that help it

to be a strong competitor to conifer seedlings in plantations. Mature plants form

large burls with dormant buds that sprout vigorously if the aboveground plant

parts are damaged. The species also produces large and frequent seedcrops. Fire

stimulates germination, but disturbance without fire can lead to the presence of

seedlings (Conard and others 1985).

Based on the height-age relationship of Douglas-fir, site quality of the study

area before burning is medium (King 1966). The soil is derived from Mesozoic
USDA Forest Service Research Paper PSW-RP-225-Web. 1996. 3

Development of a Mixed Shrub–Tanoak–Douglas-fir Community McDonald and Fiddler

sedimentary rocks and classifies taxonomically as Haploxeralfs, Haploxerults,

and Xerochrepts. The soil is best characterized as rocky, well drained, and with

only a small amount of clay in the profile. The elevation is 2,550 feet, slopes range

from 25 to 80 percent, and the aspect is southeast. Precipitation averages about

110 inches per year, with about 75 percent falling as rain. In spite of heavy annual

rainfall, the summers are dry with little precipitation falling between June and

mid-September.

Study and Design

This study presents data on Douglas-fir seedlings, a hardwood, two shrubs, and

the hardwood and shrubs combined collected during 1982-1992. It includes

information gathered on plant species developing naturally in the control and

after receiving a range of release treatments.

The experimental design was randomized block with four blocks and seven

treatments per block. Thus, each treatment was replicated four times. A replicate

(plot) consisted of one-fourth acre on which were about 40 Douglas-fir seedlings

surrounded by two or three rows of buffer (seedlings receiving similar treatment).

Treatments and installation dates were:

• Manual release (pull and chainsaw)

5-foot radius two times, August 1981, October 1982

5-foot radius three times, August 1981, October 1982, April 1984

• Chemical release

2,4-D, two times, entire plot, September 1981, May 1984

2,4-D plus Garlon 4, two times, entire plot, September 1981, May 1984

Garlon 4, two times, entire plot, September 1981, May 1984

• Manual and chemical release

Chainsaw and Garlon 3A, two times, entire plot, September 1981, May 1984

• Control

Treatments were not considered complete until repeat applications had been

performed.

The manual release treatments were designed to test the effect of removing

competing vegetation two and three times from a fixed radius around crop trees.

Because small snowbrush seedlings were intermixed with taller vegetation, they

were hand-pulled before the sprouts were cut with chainsaws. For manual and

chemical release, the vegetation was first cut by chainsaws as close to ground

level as possible and then followed (within 0.5 hour) by chemical application to

the cut surfaces. Vegetation was sheared if leaning into the 5-foot radius or into

the plot.

The chemical treatments were the herbicides 2,4-D (ester), the amine form of

Garlon (3A), and the ester form of this same chemical (Garlon 4).1 When the study

began, 2,4-D was the foliage-active herbicide most often applied to forest

plantations in California, and Garlon was a new cut-surface and foliage-active

herbicide recommended for use in young conifer plantations threatened by broad

sclerophyll vegetation. Sclerophyllous vegetation is characterized by species

having tough leathery leaves that do not wilt, and that often have waxy or

pubescent coverings. The 2,4-D and two formulations of Garlon were applied

directly to the vegetation from backpack sprayers. Garlon 4, with and without

2,4-D, and 2,4-D alone were mixed with water and diesel oil. Garlon 4 and 2,4-D

were combined and applied as a tank mix, not one chemical followed by the

other. Garlon 3A was mixed only with water. Because the chemicals were aimed

1This paper neither recommends

the pesticide uses reported nor

implies that the pesticides have

been registered by the appropriate governmental agencies.
4 USDA Forest Service Research Paper PSW-RP-225-Web. 1996.

Development of a Mixed Shrub–Tanoak–Douglas-fir Community McDonald and Fiddler

directly at the competing vegetation, the likelihood of chemical drift was minimal.

The Douglas-fir seedlings were not covered during treatment.

The cost of each treatment both initially and for retreating was calculated

from hourly records and the current wage—$8.74 per hour—the rate for a WG-1

laborer, U.S. Department of Labor, as of June 1993.

Sampling

In each plot, 20 Douglas-fir seedlings that qualified as potential crop trees were

identified and tagged. As “crop tree” implies, these were well developed

seedlings that had good potential of becoming harvestable trees. On each sample

seedling, stem diameter and height were measured. Diameters were recorded at

12 inches above mean groundline. The seedlings were checked for injury from

chemicals, animals, and insects.

Sampling intensity for evaluating other vegetation and foliar cover of

Douglas-firs in the control was five randomly selected subplots in each plot.

Subplots were centered around Douglas-fir seedlings in all treatments. For plots

where the entire area was treated (manual plus chemical, chemical, and control),

a square 1 milacre (0.001 acre) frame was used. For manually released radius

plots, sampling took place only in the treated area. Vegetation was 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 ground line to bud).

To statistically test for treatment effects and significant differences among

treatments, a two-way analysis of variance of treatment means (mixed model, no

interaction [Steel and Torrie 1980]) and a Tukey test were used (SAS Institute Inc.

1988). It was assumed that the block-treatment interaction equalled zero.

Statistical significance in all tests was at α = 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 α levels or

type I errors given for various tests apply to each measurement and year

separately.

To quantify plant diversity, all species were recorded when the study began

and at the end of the study.

Internal moisture stress of Douglas-fir seedlings and tanoak sprouts was

determined to help explain growth differences among treatments that became

apparent early in the study. Snowbrush was evaluated for internal moisture

stress, but only in the control. Xylem sap tension was measured with a Scholander

pressure chamber (Scholander and others 1965) on August 25, 1984, a typical

cloudless day near the end of summer. At this time of year, the seedlings should

have been under maximum physiological stress because of high moisture deficits.

Sampling of sap tension began just after dawn and continued through late

afternoon. Time and distance considerations mandated that only one replication

be sampled. For this reason and because of the ever-changing amount of xylem

sap tension in the plant, no statistical analysis of differences among treatments

was attempted. Sampling intensity was three randomly selected seedlings of each

species in each treatment. Consequently, three twigs of each species were tested in

the pressure chamber at five measurement times throughout the day. Each twig

was placed in a sealed plastic bag to minimize moisture changes while en route to

the pressure chamber. The elapsed time between cutting and placement in the
USDA Forest Service Research Paper PSW-RP-225-Web. 1996. 5

Development of a Mixed Shrub–Tanoak–Douglas-fir Community McDonald and Fiddler

chamber did not exceed 3 minutes. Every third sample was measured twice in the

chamber as a check on technique and working order of the equipment. “Plant

moisture stress” is expressed in atmospheres (Waring and Cleary 1967) because it

is a direct reading and familiar to foresters and biologists.

Results

Plant Diversity

The plant community at the beginning of the study consisted of planted Douglasfir, three species of hardwoods, six species of shrubs, eight forbs, one fern, and no

grasses. Seeds of bull thistle (Cirsium vulgare [Savi] Ten.), woolly mullein

(Verbascum thapsus L.), willow herb (Epilobium spp.), and groundsel (Senecio spp.)

blew in on the wind in the fall and settled in pockets in the soil or caught on

minor protrusions from it. Seedlings from these species and a few others formed

the forb component of the plant community. Not until about midway through the

study was grass noticed. It tended to be widely scattered in the study area. After

11 years the community consisted of the same species with one additional shrub

and one species of grass. However, the forbs, grass, and some of the shrubs were

so few and small that they were difficult to find. Douglas-fir, tanoak, snowbrush,

greenleaf manzanita, and, in places, bracken fern so dominated the plantation

that plants of other species were becoming both diminutive and scarce.

Tanoak

This hardwood tree species was present in all plots and was by far the most

abundant of the arborescent vegetation. After cutting and burning, each stump

sprouted, and by the end of the first growing season in 1982, tanoak clumps in the

control averaged 900 per acre with foliar cover of 3,850 ft2 per acre and an average

height of 3.2 feet (table 1). By the end of the study in 1992, tanoak clump density

decreased by 6 percent, but mean foliar cover had increased by 205 percent to

11,750 ft2 per acre, and average height by 244 percent to 11.0 feet.

On treated plots in 1992, tanoak density was lowest in plots treated by cutting

plus Garlon 3A and with Garlon 4, and highest in plots treated by manual release

three times, applying 2,4-D, and in the control (table 2). These differences were

statistically significant at the 5 percent level. Tanoak foliar cover in cut and spray

(Garlon 3A) plots, 2,4-D plus Garlon 4, and Garlon 4 alone differed significantly

from clumps in the control. Tanoak clump height did not differ significantly among

treatments.

Snowbrush

The presence of variety hookeri in the study area was in the form of numerous root

crown sprouts, seedlings from seeds in the soil, and possibly seedlings from new

seeds carried into the area by birds and rodents.

In fall 1982, density of snowbrush plants in the control was 950 plants per

acre with only 150 ft2 of foliar cover and 2.3 feet of height (table 1). By fall 1992,

density had decreased 5 percent but mean foliar cover and height had increased

manyfold, to 11,850 ft2 per acre and 11.5 feet, respectively.

On treated plots in fall 1992, density of snowbrush was significantly lower

in plots treated by cut and spray (Garlon 3A) and Garlon 4 than in the control

(table 2). For foliar cover, all three treatments with Garlon were significantly

lower than for counterparts in the control. Snowbrush height did not differ

significantly among treatments.
6 USDA Forest Service Research Paper PSW-RP-225-Web. 1996.

Development of a Mixed Shrub–Tanoak–Douglas-fir Community McDonald and Fiddler

Greenleaf Manzanita

This evergreen, normally fast-growing shrub was expected to be the most

abundant woody species in the plantation. After site preparation, viable seeds in

the soil usually germinate by the thousands. But that did not happen in this

study. Virtually all plants originated from root crown sprouts. In the control,

mean plant density, which was low to begin with, decreased 67 percent to only 50

plants per acre (table 1). Foliar cover began low and ended low. Mean height

increased from 0.6 to 5.8 feet during the study.

For the various treatments, low density and development values were

characteristic. Manzanita density and height did not differ significantly among

treatments (table 2). For all chemical treatments and manual release to a 5-foot

radius three times, the manzanita plants were either absent or so small that they

had less than 0.5 ft2 cover. These treatments differed significantly from manual

release two times and the control.

Combined Tree and Shrubs

Most early seral vegetation in young plantations in California and Oregon almost

always consists of mixtures of vegetation that include grasses, forbs, shrubs, and

hardwoods. Rarely is this vegetation dominated by a single class of plants

(McDonald and Radosevich 1992), or by plants from a single regeneration strategy,

in this instance rapid expansion of vegetatively produced sprouts (Grime 1979).

Table 1—Density, cover, and height, with standard errors (SE), of tanoak, snowbrush, greenleaf manzanita,

and combined tree and shrubs in the control, 1982-1992

Species and Year Density SE Cover SE Height SE

------ Plants/acre ------ ---------- Ft2/acre --------- -------- Ft ------

Tanoak

1982 900 301 3,850 728 3.2 0.4

1984 1,000 253 8,250 824 4.9 0.5

1987 950 225 10,400 1,513 6.7 1.0

1992 850 163 11,750 1,967 11.0 1.5

Difference (pct)1 −6 +205 +244

Snowbrush

1982 950 449 150 98 2.3 0.2

1984 950 181 1,400 251 2.5 0.3

1987 900 172 7,900 1,373 6.3 1.0

1992 900 158 11,850 2,127 11.5 1.7

Difference (pct)1 −5 +7800 +400

Greenleaf Manzanita

1982 150 202 50 102 0.6 0.2

1984 150 123 300 94 1.4 0.3

1987 200 92 100 219 3.2 0.1

1992 50 57 100 57 5.8 0.2

Difference (pct)1 −67 +100 +867

Combined Tree and Shrubs

1982 2,000 712 4,050 733 2.3 0.3

1984 2,100 346 9,950 886 4.0 0.4

1987 2,050 326 18,400 2,105 6.3 0.9

1992 1,800 237 23,700 2,661 11.2 1.3

Difference (pct)1 −10 +485 +387

1Difference between 1982 and 1992 values expressed as a percent increase or decrease.
USDA Forest Service Research Paper PSW-RP-225-Web. 1996. 7

Development of a Mixed Shrub–Tanoak–Douglas-fir Community McDonald and Fiddler

Table 2—Density, cover, and height of tanoak, snowbrush, greenleaf manzanita, and combined tree and

shrubs in treated and control plots, Six Rivers National Forest, 1992

 Species and Treatment Density Cover Height

Plants/acre Ft2/acre Ft

Tanoak

Manual

5-ft radius two times 637.ab1 6,571.ab 8.5 a

5-ft radius three times 1,081.a 7,902.ab 8.1 a

Chemical

2,4-D 850.a 4,850.ab 8.3 a

2,4-D + Garlon 4 450.ab 350.a 5.4 a

Garlon 4 150.b 2,100.a 7.0 a

Manual and chemical

Cut and spray (Garlon 3A) 0 b 0.a .– a

Control 850 a 11,750.b 11.0 a

Standard error 163 1,967 1.5

Snowbrush

Manual

5-ft radius two times 166 .ab1 3,105 .ab 9.0 a

5-ft radius three times 416 .ab 3,382 .ab 10.2 a

Chemical

2,4-D 300 .ab 2,450 .ab 11.5 a

2,4-D + Garlon 4 250 .ab 1,200 .a 7.2 a

Garlon 4 50 .a 100 .a 14.5 a

Manual and chemical

Cut and spray (Garlon 3A) 50 .a 150 .a 7.6 a

Control 900 .b 11,850 .b 11.5 a

Standard error 158 2,127 1.7

Greenleaf Manzanita

Manual

5-ft radius two times 111 .a1 333 .a 4.4 a

5-ft radius three times 111 .a 28 .b 1.4 a

Chemical

2,4-D 0 .a 0 .b –.a

2,4-D + Garlon 4 0 .a 0 .b –.a

Garlon 4 50 .a 0 .b 2.5 a

Manual and chemical

Cut and spray (Garlon 3A) 100 .a 0 .b 5.0 a

Control 50 .a 100 .a 5.8 a

Standard error 57 57 0.6

Combined Tree and Shrubs

Manual

5-ft radius two times 917 .ab1 10,009 .a 7.9 a

5-ft radius three times 1,608 .a 11,312 .ab 8.3 a

Chemical

2,4-D 1,150 .ab 7,300 .a 8.4 a

2,4-D + Garlon 4 700 .ab 1,550 .a 6.3 a

Garlon 4 250 .b 2,200 .a 9.1 a

Manual and chemical

Cut and spray (Garlon 3A) 150 .b 150 .a 5.9 a

Control 1,800 .a 23,700 .b 11.4 a

Standard error 237 2,661 1.4

1

For each species and combination, treatment means in each column followed by the same letter do

not differ statistically at the 0.05 level.
8 USDA Forest Service Research Paper PSW-RP-225-Web. 1996.

Development of a Mixed Shrub–Tanoak–Douglas-fir Community McDonald and Fiddler

In fall 1982, mean density of combined tree and shrubs in the control was

2,000 plants per acre with more than 4,000 ft2 of foliar cover and 2.3 feet of height

(table 1). By fall 1992, density had decreased 10 percent, but cover and height had

increased 485 and 387 percent, respectively (table 1).

Among treatments in 1992, the same relationships found for tanoak and

snowbrush were generally present: for density, the treatment having the most

shrubs was the control; the least, cut and spray with Garlon 3A and Garlon 4

(table 2). For foliar cover, the control had 23,700 ft2 per acre with the next closest

amounts being in the two manually released radius treatments. Significantly

more cover occurred in the control than in any other treatment except 5-foot

radius three times. No significant difference among treatments occurred for

height of combined tree and shrubs.

Douglas-fir

Total mortality of Douglas-fir was two seedlings from 1982 through 1992. Survival

after the initial losses in 1980-1981 averaged 99 percent with no statistically

significant differences among treatments. Despite the presence of deer, and a few

sightings of rabbits and a bear early in the study, damage to Douglas-fir seedlings

also was negligible. The vexar protectors caused minor early distortion to a few

leaders, which was not discernible by the end of the study.

Statistically significant differences among treatments for Douglas-fir showed

up first for foliar cover in 1984 (table 3). Foliar cover was significantly greater in

plots treated by 2,4-D plus Garlon 4 than in manually released treatments. By fall

1987, statistically significant differences among treatments were present for foliar

cover, stem diameter at 12 inches above mean ground line, and stem height (fig.

1). This trend continued through 1992. In 1992, mean stem diameter of Douglasfir seedlings treated by cut and spray (Garlon 3A), 2,4-D plus Garlon 4, and

Garlon 4 alone differed significantly from seedlings in the control. Foliar cover

also followed this trend. For mean height of Douglas-fir seedlings, only those in

the cut and spray (Garlon 3A) treatment differed significantly from counterparts

in the control. The treatment that led to the greatest Douglas-fir growth was to

spray freshly cut surfaces with Garlon 3A. The gain from this treatment relative

to the control was striking—1.8 times for height, 2.4 times for diameter, and 3.6

times for foliar cover.

The ratio of Douglas-fir height to diameter reinforces the differences among

treatments. For instance, the Garlon 3A and Garlon 4 treatments resulted in heightdiameter ratios that were generally lowest in the study, suggesting that stem

diameter expanded faster than stem height. Manual release two times and control

plots generally had the highest ratios, suggesting that stem diameter expanded

slower than stem height.

Plant Moisture Stress

Of the five treatments tested, postdawn minimum moisture stress of tanoak was

lowest (4.3 atmospheres) in the manual release two times treatment, intermediate

(4.8 atmospheres) in the Garlon 4 treatment, and highest (7.3 atmospheres) in the

control (fig. 2). Maximum moisture stress was greatest in the control (18.5

atmospheres) and least in 2,4-D (11.0 atmospheres) and Garlon 4 (11.7

atmospheres) treatments. Maximum stress was first noted in the third round of

sampling (12:10-1:00 p.m. PST) for all treatments except the control in which it

occurred in the fourth round at 2:46 p.m. PST. Tanoak sprouts in the control had

the highest internal moisture stress of all treatments in every round of sampling.

For the seven treatments tested, postdawn minimum moisture stress of

Douglas-fir seedlings was lowest (6.0 atmospheres) in the cut surface treatment

with Garlon 3A, intermediate (8.3 atmospheres) where radii were manually
USDA Forest Service Research Paper PSW-RP-225-Web. 1996. 9

Development of a Mixed Shrub–Tanoak–Douglas-fir Community McDonald and Fiddler

released twice, and highest (15.8 atmospheres) where manually released three

times (fig. 2). Maximum moisture stress was generally lowest in treatments where

herbicides were used (15 to 18 atmospheres) and highest in manual release three

times and the control (23 to 24 atmospheres). From 8:35 a.m. to 4:57 p.m. PST,

Douglas-fir seedlings in the control endured higher stress than counterparts in

any other treatment.

Internal moisture stress of snowbrush sprouts was quantified only in the

control, and registered 13.5 atmospheres of stress at 5:48 a.m., reached 23.3

atmospheres at maximum (12:52 p.m.), and tapered off at 21.8 atmospheres at 5:31

p.m. PST (fig. 2).

Table 3—Stem diameter, height, and foliar cover of Douglas–fir seedlings, by treatment, Six Rivers National Forest, 1982–1992

Treatment 1982 1984 1987 1992

Diameter ----------------------------- inches --------------------------

Manual

5–ft radius two times – 0.59 a1 1.47 ab 3.02 ab

5–ft radius three times – 0.52 a 1.49 ab 2.95 ab

Chemical

2,4–D – 0.72 a 1.87 ab 3.55 ab

2,4–D + Garlon 4 – 0.82 a 2.11 a 4.50 a

Garlon 4 – 0.61 a 1.64 ab 4.05 a

Manual and chemical

Cut and spray (Garlon 3A) – 0.80 a 2.17 a 4.64 a

Control 0.24 0.52 a 1.08 b 1.96 b

Standard error – 0.08 0.19 0.36

Height ------------------------------- feet -----------------------------

Manual

5–ft radius two times – 2.95 a 6.99 ab 15.64 ab

5–ft radius three times – 2.81 a 7.05 ab 14.65 ab

Chemical

2,4–D – 3.29 a 8.60 ab 18.18 ab

2,4–D + Garlon 4 – 3.81 a 9.16 ab 19.91 ab

Garlon 4 – 2.81 a 7.11 ab 17.94 ab

Manual and chemical

Cut and spray (Garlon 3A) – 3.32 a 9.90 a 21.55 a

Control 1.50 3.07 a 6.06 b 12.08 b

Standard error 0.34 0.83 1.68

Cover ----------------------------- ft2/acre -------------------------

Manual

5–ft radius two times – 1,130 .a 3,770 .b 16,552 .bc

5–ft radius three times – 1,275 .a 4,325 .b 12,504 .bc

Chemical

2,4–D – 1,850 .ab 10,900 .ab 26,400 .ab

2,4–D + Garlon 4 – 2,850 .b 13,850 .a 35,895 .a

Garlon 4 – 1,950 .ab 8,050 .b 37,750 .a

Manual and chemical

Cut and spray (Garlon 3A) – 2,550 .ab 16,400 .a 39,850 .a

Control 700 1,900 .ab 4,500 .b 10,950 .c

Standard error 309 . 1,647 . 1,422 .

1

For each year, treatment means followed by the same letter do not differ significantly

at the 0.05 level.
10 USDA Forest Service Research Paper PSW-RP-225-Web. 1996.

Development of a Mixed Shrub–Tanoak–Douglas-fir Community McDonald and Fiddler

A

D E

B
USDA Forest Service Research Paper PSW-RP-225-Web. 1996. 11

Development of a Mixed Shrub–Tanoak–Douglas-fir Community McDonald and Fiddler

Figure 1—Relative development of Douglas-fir seedlings and other

vegetation by treatment in fall 1987: (A) cut and spray entire plot with

Garlon 3A, (B) manually release a 5-foot radius around Douglas-fir

seedlings two times, (C) manually release a 5-foot radius around Douglasfir seedlings three times, (D) apply 2,4-D to entire plot, (E) apply 2,4-D

plus Garlon 4 to entire plot, (F) apply Garlon 4 to entire plot, and (G)

untreated control.

F

C

G
12 USDA Forest Service Research Paper PSW-RP-225-Web. 1996.

Development of a Mixed Shrub–Tanoak–Douglas-fir Community McDonald and Fiddler

Production and Cost

Chainsawing hardwood and shrub sprouts and treating the freshly cut surfaces

with Garlon 3A twice, and manually releasing 5-foot radii around Douglas-fir

seedlings two times were expensive. Manually releasing 5-foot radii around

seedlings 3 times was even more expensive. Directed foliar sprays with chemicals

was the least expensive:

Treatment Production rate Cost

Laborer

hours/acre Dollars/acre

Manual release (pull and chainsaw)

5-foot radius, 2 times 23 201

5-foot radius, 3 times 34 297

Manual and chemical release

Cut + Garlon 3A, 2 times, entire plot 26 227

Chemical release

2,4-D, 2 times, entire plot 9 79

2,4-D plus Garlon 4, 2 times, entire plot 9 79

Garlon 4, 2 times, entire plot 9 79

Cost is for labor only and does not include overhead or chemicals. If the cost of

the chemicals was included, $10 should be added to the cost per acre for 2,4-D, $70

for Garlon 3A, $40 for 2,4-D + Garlon 4, and $75 per acre for Garlon 4.

Discussion and Conclusions

With an annual precipitation average of 110 inches and mild temperatures,

revegetation of the disturbed study area was dynamic. Stimulated by cutting and

broadcast burning, dormant buds on root crowns of tanoak, snowbrush, and

greenleaf manzanita quickly produced numerous sprouts. These grew rapidly,

fueled by energy stored in the root crown and root system. Bull thistle, woolly

mullein, willow herb, and groundsel became locally abundant in pockets, but in

Figure 2—Diurnal trend of internal moisture stress by treatment on August 25, 1984 in (A) tanoak sprouts, and (B) Douglas-fir seedlings. Standard errors

applicable to differences between treatments could not be estimated.

5-ft radius 2 times

5-ft radius 3 times

2,4-D

Garlon 4

Control

Pacific standard time

A

35

30

25

20

15

10

5

0

4 6 8 10 N 2 4 6

Plant moisture stress (atmospheres)

5-ft radius 2 times

5-ft radius 3 times

2,4-D

Garlon 4

Control

35

30

25

20

15

10

5

0

4 6 8 10 N 2 4 6

Plant moisture stress (atmospheres)

B

Cut & spray (Garlon 3A)

2,4-D Garlon 4

Pacific standard time
USDA Forest Service Research Paper PSW-RP-225-Web. 1996. 13

Development of a Mixed Shrub–Tanoak–Douglas-fir Community McDonald and Fiddler

general never became dense throughout the study area. The grass species invaded

in midstudy and were too late to expand their population beyond scattered

plants. By the end of the study 20 plant species had been noted. This number is

low relative to that found in other studies (17 to 41 species) in our National

Administrative Study in young conifer plantations (McDonald and Fiddler 1993).

As noted by Sousa (1984), large individual size just after disturbance is

advantageous to a plant for procuring available resources. Certainly, having

direct vascular connection to part of a huge parent root system, such as found in

root crown sprouts, qualifies as “large.” Plant species that germinate from seeds

have little chance of competing for long with such individuals. It is soil moisture

that they cannot compete for—the limiting environmental factor in most of

California. Consequently, forbs, grasses, slower-growing shrubs, and shrubs

from seeds in this study never had the opportunity to become abundant. Their

presence was relegated to relatively small areas where tanoak and snowbrush

were less frequent. Here they persisted.

Analysis of the first full data set in 1982 showed that tanoak and snowbrush

constituted more than 92 percent of total competing plant density and 99 percent

of foliar cover in the control. Both were the tallest vegetation in the plantation.

Density of both species was remarkably stable, each declining by only about 5

percent at the end of the study in 1992. Foliar cover of tanoak and snowbrush

followed a steadily increasing trend, with both species over 11,700 ft2 per acre in

1992. Height of both species was similar in trend and final amount—more than 11

feet tall. Greenleaf manzanita density and foliar cover, however, were low

throughout the study.

Development of Douglas-fir seedlings in the control was governed by heavy

competition and lower available soil moisture. The likelihood of being

overtopped by the burgeoning tanoak and snowbrush sprouts was high. In this

situation, Douglas-fir seedlings typically sacrifice crown and needle development

for height growth. Consequently, their form tended to be tall and thin with

narrow crowns. Many seedlings were so thin that they needed support from

nearby shrubs and hardwood trees. By the study’s end, Douglas-fir seedlings in

the control averaged about 2 inches in diameter, 12 feet in height, and had more

than 10,900 ft2 of foliar cover per acre. These values denote a 7 percent advantage

in height over combined tanoak and shrubs, but a 116 percent disadvantage in

foliar cover. The sacrifice of support and photosynthetic surface area cannot

continue, and at some point the rate of height growth will decline (Wagner 1994).

If the height growth rate of competing plants does not decline, most of the

Douglas-fir seedlings will eventually die.

In contrast to Douglas-fir seedlings in the control, growth of Douglas-fir in

the most effective treatment (cut and spray with Garlon 3A) was characterized by

robust diameter (4.64 inches), well developed crowns (39,859 ft2 ), and tall trees

(21.55 feet). The odds for their survival and continued growth are high.

At the end of the study in fall 1992, the various treatments had all reduced the

hardwood tree and shrub components of the plant community to some degree.

Average density, cover, and height of combined tree and shrubs were less in all

treatments relative to the control. With the exception of 2,4-D, treatments that

involved chemicals were more effective than chain sawing vegetation in a 5-foot

radius. From previous studies, we found that the minimum effective radius was 5

feet—any lesser radius did not give the conifer seedlings time to develop the

deep and extensive root system necessary to secure adequate soil moisture for

growth at the potential of the site (Fiddler and McDonald 1984, McDonald and

Fiddler 1989). Because the 5-foot treated radius in this study was only moderately

effective at best, a wider radius seems logical. Jaramillo (1988) found that 8-foot
14 USDA Forest Service Research Paper PSW-RP-225-Web. 1996.

Development of a Mixed Shrub–Tanoak–Douglas-fir Community McDonald and Fiddler

and even 12-foot treated radii significantly improved height and diameter growth

of Douglas-fir seedlings growing with sprouting trees and shrubs in southwestern

Oregon. For this plant community, however, the tradeoff between effectiveness

of an expanded radius and its cost is unknown.

For just the chemical treatments in this study, none differed statistically from

the other. Differences were not significant among treatments for combined

vegetation or for Douglas-fir seedlings. Thus, the decision to apply a given

chemical should be decided on other than biological reasons.

The cost and production data gathered in this study reflect the aggressive

nature of the hardwood tree and shrub sprouts. Their hardiness and ability to

withstand natural and human-caused perturbations mandated that at least two

treatment applications be applied. For manual release, the tanoak and shrub

sprouts were only cut off, not severed below the root crown. They and new

sprouts from formerly dormant buds on the burl sprouted after site preparation

and after each retreatment. The amount of vegetation in the prescribed radius

decreased a little with each successive treatment, but the amount of vegetation

that was leaning into the radius also increased. Thus the total amount of vegetation

that was removed probably did not differ much after each treatment. This total is

reflected in the large number of hours expended and the highest cost in the study.

For chemical release, the retreatment cost was about half that of the initial cost

because much less vegetation had to be treated the second time.

The timing of treatments in this study was adequate, but could have been

improved to maximize effectiveness. Competing vegetation is best controlled

when the interval between disturbance and becoming established is short

(McDonald and Oliver 1984, McDonald and Fiddler 1989). The first 3 years are

important; the first year is critical. Seedlings need freedom to vigorously expand

their root systems in an ever-increasing volume of soil. In a southern Oregon

study, for example, roots of Douglas-fir seedlings were excavated and carefully

measured relative to the amount and position of roots from competing vegetation.

Results showed that the Douglas-fir roots expanded greatly in biomass and

volume of soil occupied in the near-absence of competing vegetation, but

developed scarcely at all if roots of competing species were present (Tesch and

Hobbs 1989). In our study, the initial treatments were applied soon after site

preparation and the interval between manually retreating the 5-foot radii was

correct. For the chemical treatments, the 2-year interval between the initial

treatment and retreatment could have been shortened by 1 year.

A continuing objective of the National Administrative Study on vegetation

management is to determine the timing of treatment effectiveness. In general, the

faster the occurrence of a statistically significant difference between a treatment

and the control, the more effective the treatment. When competition is controlled,

stem diameter usually is the conifer parameter that differs significantly first. In

this study, however, foliar cover of Douglas-fir seedlings became significant first.

Achieving significance in fall 1984, or four growing seasons after planting,

probably is about as fast as can be expected, given the aggressive nature of the

competing vegetation in this study.

Doing a good job of site preparation and then believing that sufficient conifer

seedling growth will result is not realistic. As noted earlier, shrub density and

development in the control were such that Douglas-fir seedlings there were tall

and thin with little girth or crown development. Although almost all seedlings

are alive, their future is uncertain and probably precarious.

A primary goal of vegetation management is to manipulate the after-site

preparation plant community to alter the trajectory of its succession. More
USDA Forest Service Research Paper PSW-RP-225-Web. 1996. 15

Development of a Mixed Shrub–Tanoak–Douglas-fir Community McDonald and Fiddler

specifically, it focuses on restoring dominant species, usually one or more

conifers, to their natural place in the community. This means having the desired

number of conifer seedlings present and developing well. But as they are

developing, at least until the crowns close, many other species of plants usually

become present. In this study, however, only two other species developed well—

tanoak and snowbrush. Other species were not abundant initially, or became

established too late to garner enough site resources to grow well. Because

Douglas-fir seedlings are present in all treatments, another influence on

secondary succession has been introduced. Where the Douglas-fir seedlings grow

well, the competing vegetation will develop poorly; where the competing

vegetation develops well, the Douglas-fir seedlings will grow poorly. Thus,

secondary succession in this study is manifest in different proportions of the

same species, each with a different developmental potential.

In the future, ecosystem managers will need to create specific plant

communities at specific times in the landscape. Having a choice of species

proportions, growth potentials, and costs, as well as a range of treatments to attain

them, should prove valuable.

References

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the genus Ceanothus in western forest ecosystems. Gen. Tech. Rep. PNW-182. Portland, OR:

Pacific Northwest Forest and Range Experiment Station, Forest Service, U.S. Department of

Agriculture; 72 p.

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Row; 300 p.

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

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1248-1254.
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