United States 

Department 

of Agriculture 

Forest Service 

Pacific Southwest 

Research Station 

Research Paper 

PSW-RP-243 

Ecology and Development of Douglas-fir 

Seedlings and Associated Plant 

Species in a Coast Range Plantation 

Philip M. McDonald Gary O. Fiddler 
Publisher 

Albany, California

Mailing address: 

PO Box 245, Berkeley CA

94701-0245 

(510) 559-6300 

http://www.psw.fs.fed.us 

December 1999 

Pacific Southwest Research Station 

Forest Service 

U.S. Department of Agriculture 

Abstract 

McDonald, Philip M.; Fiddler, Gary O. 1999. Ecology and development of Douglas-fir 

seedlings and associated plant species in a Coast Range plantation. Res. Paper PSWRP-243. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. 

Department of Agriculture; 18 p. 

On an average site in northern coastal California, a tanoak-mixed shrub community was 

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

chainsaw and cut surface chemical treatment; two foliar chemicals; and a tank mix of the 

two chemicals) to study its development over an 11-year period in both a broadcast-burned

(untreated control) and released (treated) condition. The chemicals were 2,4-D, Garlon 3A,

and Garlon 4, each applied two times. In addition to Douglas-fir, data are presented

individually for the four most abundant and well distributed species (tanoak, hairy

manzanita, huckleberries, and rhododendron), and for these plus two more of the tallest

and most abundant (but poorly distributed) species (snowbrush, elderberry) combined. At

the study's end in 1991, combined shrubs in the control had a mean density of 4,733 plants

per acre, foliar cover of 16,800 ft

2 per acre, and height of 9.5 feet. In contrast, combined 

shrubs in one of the most effective treatments for controlling them-2,4-D-had a mean

density of 2,000 plants per acre, foliar cover of 2,600 ft2 per acre and height of 5.5 feet at the

end of the study. Here, mean Douglas-fir diameter was 4.0 inches at 12 inches above mean 

ground line, height averaged 18.7 feet, and mean foliar cover was 34,800 ft2 per acre. The 

cost (including chemical) was $77 per acre. The biological and economical data in this

paper provide the ecosystem manager, wildlife biologist, and fuels manager with

knowledge on how to attain plant communities with different density and development

potentials, and the cost of creating them. 

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

northern California, plant community

Authors 

Philip M. McDonald and Gary O. Fiddler are Research Forester and Supervisory Forester, 

respectively, assigned to the Station's Western Forest Management Research Unit, at the

Silviculture Laboratory, 2400 Washington Ave., Redding, CA 96001. 
Ecology and Development of Douglas-fir 

Seedlings and Associated Plant 

Species in a Coast Range Plantation 

Philip M. McDonald Gary O. Fiddler 

Contents 

In Brief....................................................................................................................ii 

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

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

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

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

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

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

Soil Moisture Tension ..................................................................................... 5 

Plant Moisture Stress......................................................................................... 5 

Plant Diversity ................................................................................................ 6 

Tanoak ............................................................................................................. 6 

Hairy Manzanita ............................................................................................. 8 

Huckleberries ................................................................................................... 9 

Rhododendron ...............................................................................................10

Combined Shrubs ...........................................................................................10

Salal ................................................................................................................10

Douglas-fir .....................................................................................................10

Production and Cost .......................................................................................13

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

References.............................................................................................................17

Pacific Southwest 

Research Station 

USDA Forest Service 

Research Paper 

PSW-RP-243 

December 1999 
In Brief... 

McDonald, Philip M.; Fiddler, Gary O. 1999. Ecology and development of Douglas-fir

seedlings and associated plant species in a Coast Range plantation. Res. Paper PSWRP-243. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. 

Department of Agriculture; 18 p. 

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

northern California, plant community As ecosystem management increasing

ly becomes the operational paradigm for 

managing federal forest land, the art and science of vegetation management will 

have an increased role. Especially needed is information on currently uneconomic 

species and their interrelationships in the plant community. In ecosystem 

management, every combination of species could have value at some place in the 

landscape at some time. In a young conifer plantation, for example, the worth of 

the small trees and the wood products that eventually come from them has long 

been recognized. And, with ecosystem management, the seed from a common 

herbaceous species in the plantation that is critical to a threatened species of 

wildlife could also be regarded as being equally worthwhile. 

Most conifer plantations in California are located in areas that were 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 management goal often is 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 has proved to be a practical technique for preparing the site for 

planting. Site preparation often gives the planted conifer seedlings at least 

temporary relief from competing vegetation. 

But not in this 11-year study in northern coastal California. Competition 

from such rapidly growing species as tanoak, snowbrush, rhododendron, 

huckleberries, and hairy manzanita, was both rapid and heavy. Plainly, release 

of the plantation was needed if the Douglas-fir seedlings were to grow at the 

potential of the site. Consequently, three manual treatments (chain saws and 

shears), three chemical treatments, and a combination manual and chemical 

treatment were installed to evaluate their effect on the species composition, 

density, and development of the ensuing plant community. In general, the 

chemical treatments and manual release three times were the most effective 

treatments; manual release one and two times, and the uncut control were the 

least effective. The chemical treatments cost roughly one-sixth that of the manual 

release treatments. 

At the end of the study in 1991, the plant community in the various treatments 

was comprised almost entirely of vegetatively propagated hardwood trees and 

shrubs with only a few forbs and no grasses. All were present in all treatments, 

with fewer and smaller plants in the most effective treatments, and more and 

larger ones in the least effective treatments. Thus, the resulting plant communities 

can be characterized as having different proportions of the same species. 

Douglas-fir was present in all communities as well. However, in the most 

effective treatments, it had a statistically larger mean foliar cover than in the least 

effective treatments, and in one of them it had a statistically larger stem diameter 

at 12 inches above mean groundline. Results from this study should be useful to 

several disciplines in natural resource management. Ecologists now have data on 

the early species composition, density, and development of the plants in this 

community, wildlife biologists can infer browse and seed production, and fuel 

managers can quickly multiply the foliar cover and height values to arrive at 

cubic volume estimates by species. 

ii USDA Forest Service Research Paper PSW-RP-243. 1999. 
Introduct

ion 

Significant public sentiment, expressed through recent polls, newspaper articles, 

and proposed legislation, seems to favor maintaining the inherent productivity 

of the forest so that it can provide a full range of amenities and commodities for 

future generations. Emphasis is being placed on ecosystems and especially on 

ecosystem components and processes. Sometimes, ecosystems need to be nudged 

a bit. Large burned areas that once were forest, for example, may have no tree 

seed source, and centuries can pass before a forest becomes established. And 

areas where tree seeds fall on land already occupied by vigorous plant species 

constitute another example where scores of years can elapse before the traditional 

tree species again clothe the land. In these instances, ecosystem processes can be 

speeded up by manipulating a key component like plant species. Manipulation 

could be for a variety of reasons: to create a future forest, to provide an economic 

crop, to grow plants critical to wildlife along with trees, or simply to provide a 

broad base of species and structures that provide values and commodities that 

will be needed in the future. In forestry, much knowledge has been generated on 

economic species such as conifer trees, but little is available on the currently 

uneconomic hardwoods, shrubs, forbs, and grasses. 

What is known is that the growth of Douglas-fir (Pseudotsuga menziesii 

[Mirb.] Franco) seedlings can be reduced to a fraction of its potential by 

competing vegetation, and that dramatic increases have occurred when this 

vegetation was removed. Results from a "sister" study about 15 miles southeast 

of this one on a similar site, but with no fog and a less complex plant community, 

indicated major gains from reducing the amount and size of competing 

vegetation. Average diameter of Douglas-fir seedlings at 12 inches above mean 

ground line in the most effective treatment (cut and spray with Garlon 3A) was 

137 percent greater relative to the least effective treatment (the control), stem 

height was 78 percent larger, and foliar cover was 264 percent greater (McDonald 

and Fiddler 1996). 

Results from a more widespread area show a similar trend. 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-year-old 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; 

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 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). 

To increase knowledge on the ecology of several plant species in a shrub-rich 

community in a somewhat unique environment characterized by long, hot, dry 

summers, and morning fog, information was collected on the species composition 

and developmental potential of vegetation reoccupying a clearcut-harvested and 

broadcast-burned area in northern coastal California. Data were gathered for 

vegetation developing naturally after broadcast burning (control) and for 

vegetation that was manipulated deliberately by several manual and chemical 

treatments. Planted Douglas-fir seedlings were part of both plant communities. 

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 

USDA Forest Service Research Paper PSW-RP-243. 1999. 1 
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 the Douglas-fir seedlings. Timing of treatment effectiveness and 

cost of the treatments is also presented. The variety of treatments, plant numbers, 

growth potentials, and costs, provide ecosystem managers with informed 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 northeast of Crescent City, California, 

and about 9 miles due east of the Pacific Ocean. Before clearcut-harvesting in 1977, 

the area supported a patchy stand of mature Douglas-fir trees with scattered 

Port-Orford-cedar (Chamaecyparis lawsoniana [A. Murr.] Parl.), western hemlock 

(Tsuga heterophylla [Raf.] Sarg.), and western redcedar (Thuja plicata Donn ex 

D.Don). Hardwood species, scattered in a lower stratum as single trees or as 

small aggregations, were tanoak (Lithocarpus densiflorus [Hook. & Arn.] Rehd.) 

and a few Pacific madrone (Arbutus menziesii Pursh), and giant chinquapin 

(Castanopsis chrysophylla [Dougl.] A. DC.). Scientific names of tree species are 

from Little (1979), and for all other vegetation from Hickman (1993). Shadetolerant shrubs, common in the understory, were California huckleberry 

(Vaccinium ovatum Pursh), red huckleberry (Vaccinium parvifolium Smith) and 

rododendron (Rhododendron macrophyllum D.Don). Salal (Gaultheria shallon Pursh) 

and bracken fern (Pteridium aquilinum [L.] Kuhn var. pubescens L. Underw.) were 

widely scattered throughout the area. This vegetation assemblage best fits the 

tanoak series and the tanoak/evergreen huckleberry-Pacific rhododendron 

association (U.S. Department of Agriculture 1996). 

Merchantable conifers and hardwoods larger than 12 inches in breast-height 

diameter were harvested in summer 1977. Site preparation began in fall 1977 

with the felling of all remaining hardwood and conifer stems. These, plus the 

logging slash, were broadcast-burned in April 1978. The burn was effective, and 

almost all small material was consumed, leaving a soil surface of mostly mineral 

soil and scattered burned logs. 

The area was planted at an 8- by 8-foot spacing in March 1979 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 tall vexar leader protector. Although a good 

job of planting was done, survival in the fall of 1980 was 62 percent. 

When the study began in 1981, the plant community consisted mostly of 

species that originated from root crowns and rhizomes in the soil (fig. 1). Also 

Figure 1 

Rapidly growing clumps of 

hardwoods and shrubs are visible 

throughout this part of the study 

area in fall 1983, six growing 

seasons after site preparation. 

2 USDA Forest Service Research Paper PSW-RP-243. 1999. 
Figure 2 

Components of the plant 

community in the study area in fall 

1983 included tanoak and hairy 

manzanita (left side of photo), 

rhododendron (center) and 

huckleberries and manzanita (right 

side). 

present were numerous seedlings of hairy manzanita (Arctostaphylos columbiana 

Piper) (fig. 2) from dormant seed in the soil, and forbs from windblown seeds 

such as fireweed (Epilobium spp.), sow thistle (Sonchus spp.), and ragwort 

(Senecio spp.). The most abundant residual forbs were bear-grass (Xenophyllum 

tenax [Pursh] Nutt.) (family Liliaceae) and a tall lily (Lilium spp.) No grasses 

were recorded. In addition to the two species of huckleberries, rhododendron, 

and salal, other shrub species of lesser size or abundance were Oregon grape 

(Berberis spp.), blue elderberry (Sambucus mexicana C. Presl), blackcap raspberry 

(Rubus leucodermis Torrey & A. Gray), thimbleberry (Rubus parviflorus Nutt.), 

cascara (Rhamnus purshiana DC.), snowbrush (Ceanothus velutinus Hook. var. 

hookeri M. Johnston), and blue blossom (Ceanothus thyrsiflorus Eschsch.). Based on 

the height-age relationship of Douglas-fir, site quality of the study area is 

medium (McCardle and others 1961). The geology of the area consists of Jurassic 

sediments with some marine sedimentary deposits. The soil is complex and best 

described as being deep (2 to 10 feet), reddish in color beneath a dark brown 

surface layer, and contains only a small percent of rock. Soil texture varies from 

loam to clay-loam. The suggested soil association is described as Aiken-SkalanGoldridge. The average elevation of the study is 1,500 feet, slopes vary from 10 

to 50 percent, and aspect includes north, south, and east. Precipitation averages at least 

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. A temperature-ameliorating influence is fog, which 

occurs at night and in the morning of 30 to 40 days during the summer of each year. 

Study and Design 

This study presents data on Douglas-fir seedlings, hardwoods, and shrubs that 

were collected during 1981-1991. It includes information gathered on plant 

species developing in the control and after receiving a range of release

treatments. 

The experimental design was randomized block with four blocks and eight 

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

(plot), which was about one-seventh acre in size, consisted of approximately 14 

Douglas-fir seedlings surrounded by two or three rows of buffer (seedlings 

receiving similar treatment). Treatments and installation dates were:

Manual release (chainsaw and shears) 

5-foot radius one time, July 1981, 

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

5-foot radius three times, July 1981, October 1982, March 1984 

USDA Forest Service Research Paper PSW-RP-243. 1999. 3 
Chemical release 

2, 4-D, two times, entire plot, April 1981, April 1984 

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

Garlon 4, two times, entire plot, April 1981, April 1984 

Manual and chemical release 

Chainsaw & 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 one, two and three times from a fixed radius around crop 

trees. 

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 also was mixed with water and diesel oil. Because the chemicals 

were aimed directly at the competing vegetation, the likelihood of chemical drift 

was minimal. The Douglas-fir seedlings were not covered during treatment. 

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. For all treatments, vegetation was 

sheared if leaning into the 5-foot radius or designated measurement area. 

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

from hourly records and $8.74 per hour-the rate for a WG-1 laborer, U.S. 

Department of Labor, as of June 1993. 

Sampling 

In each plot, 8 to 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 at 12 inches above mean groundline, and total height 

were measured. The seedlings were checked for injury from chemicals, animals, 

and insects. Sampling took place in fall 1981, 1984, 1987, and 1991. 

Sampling intensity for evaluating other vegetation in all treatments and 

foliar cover of Douglas-fir 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 (chemical, manual plus chemical, and 

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

plots, sampling took place only in the treated radius. 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 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 1

This paper neither recommends treatments, a two-way analysis of variance of treatment means (mixed model, no the pesticide uses reported nor

implies that the pesticides have interaction, [Steel and Torrie 1980]) and a Tukey test were used (SAS Institute 

been registered by the appro- Inc. 1988). It was assumed that the block-treatment interaction equaled zero. priate governmental agencies. Statistical significance in all tests was at α= 0.05. Data were gathered from

4 USDA Forest Service Research Paper PSW-RP-243. 1999. 
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. 

Soil moisture tension was measured using a single junction, screen-cage 

thermocouple psychrometer by a cooperator

2

 during early summer-fall of 1982. 

Data (in atmospheres) were recorded on the 15th of each month from May 

through October in four treatments (manual release one time, 2,4-D, Garlon 4, 

and control) in one replication at the 24-inch soil depth. 

Internal moisture stress of planted Douglas-fir seedlings, tanoak sprouts, 

and hairy manzanita seedlings was determined to help explain growth 

differences that became apparent among treatments early in the study. Internal 

moisture stress also was denoted for huckleberry, but only in the control. Xylem 

sap tension was measured with a Scholander pressure chamber (Scholander and 

others 1965) on August 23, 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 

per treatment 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 change while enroute to the pressure chamber. The elapsed time 

between cutting and placement in the 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 is 

familiar to foresters and biologists. 

Results 

In this study, we wished to portray developmental relationships and treatment 

effects for all species possible. These included tanoak, hairy manzanita, the two 

huckleberries, rhododendron, and planted Douglas-fir. Information on these 

species, as well as that on soil moisture and internal plant moisture stress, help 

explain why the Douglas-fir seedlings survived and developed as they did. 

Soil Moisture Tension 

To gain insight into the amount of moisture available during the growing season 

relative to use by shrubs, hardwoods, and Douglas-fir seedlings, soil moisture 

was quantified. 

At the 24-inch depth, soil moisture tension in May was less than one 

atmosphere in all treatments. In general, it increased through August, peaked in 

September, and declined in October. Peak tension was highest (7.4 atmospheres) 

in the control, followed by Garlon 4 (6.2 atmospheres) and 2,4-D (4.1 atmospheres), 

and was lowest in plots released manually one time (2.1 atmospheres). 

Plant Moisture Stress 

To gain insight into the potentially ameliorating effect of summer fog on internal 2

Data from Daniel R. Sendek, 

water relationships in various plant species during the typical long dry Humboldt State University, 

Mediterranean summer, plant moisture stress was quantified in the same Arcata, CA. May 1983, on file, 

Pacific Southwest Research replication as soil moisture. Station, Redding, Calif. 

USDA Forest Service Research Paper PSW-RP-243. 1999. 5 
Plant 

moisture stress of tanoak sprouts was quantified in six of the eight 

treatments, with manual release three times and cut and spray with Garlon 3A 

excepted. Of the six treatments, predawn minimums ranged from a low of 4.2 

atmospheres in plots manually released two times to 6.5 atmospheres in the 

manual-release-one-time treatment and control (fig. 3). Internal moisture stress 

then increased in all treatments (except manual release two times) through the 

11:30 a.m. to 1:00 p.m. PST period, peaked at this time with values of 8.3 to 16.5 

atmospheres, and then declined to values of 7.0 to 11.8 atmospheres in the 4:20 to 

5:00 p.m. period. For the five timespans sampled, plant moisture stress was lowest 

for tanoak in plots treated by manual release two times and 2,4-D plus Garlon 4, 

and highest in treatments that were manually released one time and in the control. 

Of the seven treatments tested (manual release three times was the 

exception), predawn minimum moisture stress of hairy manzanita seedlings was 

lowest in plots treated with Garlon 4 and cut and spray (Garlon 3A) at 3.5 

atmospheres and highest in plots that were manually released one time at 7.5 

atmospheres (fig. 3). Plant moisture stress then increased in all treatments, peaked 

between 10:25 a.m. and 3:40 p.m. PST with values that ranged from 11.8 to 21.5 

atmospheres, and then declined to values of 6.5 to 17.2 atmospheres in late 

afternoon. For the five timespans sampled, plant moisture stress was lowest 

most often for hairy manzanita in plots treated with 2,4-D, and consistently 

highest in those that were manually released one time. 

Plant moisture stress of Douglas-fir also was evaluated in seven of the eight 

treatments with manual release three times being the exception. Predawn 

minimum moisture stress of this conifer was lowest in plots treated by cut and 

spray (Garlon 3A) at 4.5 atmospheres, and highest in counterparts in the control 

at 12.8 atmospheres (fig. 3). Plant moisture stress then increased in all treatments, 

peaked between 10:00 a.m. and 3:45 p.m. PST with values that ranged from 16.7 

to 23.2 atmospheres, and then declined to values of 12.5 to 19.5 atmospheres in 

late afternoon. For the five timespans sampled, plant moisture stress was lowest 

most often for Douglasfir in plots treated by cut and spray (Garlon 3A), and 

highest most often for this conifer in the control. 

Internal moisture stress of the huckleberries was quantified only in the 

control, where it registered 4.8 atmospheres of stress at 6:00 a.m. PST, reached 

17.0 atmospheres at peak (12:01 p.m.), and declined to 14.8 atmospheres at 4:40 

p.m. PST. 

Plant Diversity

In addition to the planted Douglas-fir seedlings, the natural plant community 

near the beginning of the study consisted of 2 species of conifers, 3 species of 

hardwoods, 12 shrubs, 10 forbs, 1 fern, and no grasses for a total of 28 species 

(table 1). After 10 years, the community consisted of no naturally established 

conifer seedlings, the same 3 species of hardwoods, 3 more species of shrubs, 6, 

less species of forbs, and no grass for a total of 23 species. Two hardwood species 

(Pacific madrone, giant chinquapin), 2 forb species (vetch, unknown), and 8 

species of shrubs (blackcap raspberry, blue blossom, cascara, coyotebrush, 

deerbrush, Oregon grape, rose, and thimbleberry) were scarce in the study area. 

Tanoak 

Although harvesting and site preparation removed many above-ground tanoak 

stems, a host of root crowns remained at or just below the soil surface. After 

cutting and burning, many stumps or burned root crowns sprouted, and by 1981 

tanoak clumps in the control averaged 950 per acre with foliar cover of 2,500 ft2 

per acre and an average height of 3.8 feet (table 2). By the end of the study in 1991, 

tanoak clump density had increased by 5 percent to 1,000 per acre, mean foliar 

cover increased by 191 percent to 7,267 ft

2 per acre, and a

verage height had 

increased by 197 percent to 11.3 feet. 

6 USDA Forest Service Research Paper PSW-RP-243. 1999. 
Figure 3 

Diurnal trend of internal moisture 

stress by treatment on August 25, 

1984 in (A) tanoak sprouts, (B) 

hairy manzanita seedlings, and (C) 

planted Douglas-fir seedlings. 

Standard errors applicable to 

differences between treatments 

could not be estimated. 

USDA Forest Service Research Paper PSW-RP-243. 1999. 7 
On treated plots in 1991, tanoak density ranged from 148 to 1,146 plants per acre, 

foliar cover from 800 to 7,267 ft

2 per acre, and height from 6.5 to 11.3 feet 

(table 3). Although tanoak clumps were taller and wider in the control, no 

statistical differences were found. 

Hairy Manzanita 

Typical of disturbance-enhanced Arctostaphylos species, hairy manzanita 

produced thousands of seedlings from dormant seeds in the soil. In fall 1981, 

density of this manzanita in the control averaged 8,350 plants per acre with 6,100 ft2 

of foliar cover and 2.7 feet of height (table 2). By fall 1991, average plant density in 

the control had decreased 66 percent to 2,800 plants per acre and mean foliar 

cover had decreased by 6 percent, to 5,733 ft2 per acre, but mean height had 

increased 167 percent to 7.2 feet. 

On treated plots in fall 1991, density of hairy manzanita ranged from 333 

plants per acre in plots treated by 2,4-D and cut and spray (Garlon 3A) to over 

5,600 plants per acre in plots that were manually released one and two times 

(table 3). However, these differences were not statistically significant at the 5 

percent level. In terms of foliar cover, plants in plots treated with 2,4-D, 2,4-D + 

Table 1-Natural vegetation in study plots, Signal Plantation, Six 

Rivers National Forest, California, 1982-1991 

Common name 1982 1991 

Conifers 

Douglas-fir 

Western hemlock 

Hardwoods 

Tanoak

Pacific madrone

Giant chinquapin 

Shrubs 

Elderberry

Rhododendron

Salal 

California huckleberry 

Red huckleberry

Blackcap raspberry 

Thimbleberry

Cascara

Deerbrush 

Coyotebrush 

Oregon grape 

Snowbrush 

Blue blossom

Rose 

Hairy manzanita 

Forbs 

Beargrass 

Fireweed 

Vetch 

Groundsel 

Ragwort 

Lily 

Sow thistle 

Hawkweed 

Unknown 

Unknown 

Fern 

Bracken fern 

Total 

X -

X -

X X 

X X 

X X 

X X 

X X 

X X 

X X 

X X 

X X 

X X 

X X 

X 

- X 

X X 

X X 

X X 

- X 

X X 

X X 

X -

X X 

X -

X -

X X 

X -

X -

X X 

X -

X X 

28 23 

8 USDA Forest Service Research Paper PSW-RP-243. 1999. 
Garlon 4, and cut and spray with Garlon 3A averaged significantly less cover than 

counterparts on plots that were manually released one and two times. Foliar cover of 

plants treated with the ester form of Garlon (Garlon 4) or manually cut three times did 

not differ significantly from plants in the control. Manzanita height ranged from 

4.2 feet in plots treated with 2,4-D to 7.2 feet in the control, but did not differ 

significantly among treatments. 

Huckleberries 

These shade-enduring species were well distributed throughout the study area, had 

relatively low density and cover values, and indicated no statistical 

differences among treatments. Originating mostly from below-ground organs, 

Table 2-Average density, cover, and height, with standard errors (SE), of tanoak, 

hairy manzanita, huckleberries, rhododendron, and combined shrubs in the control, 

1981-1991 

Year Density SE Cover SE Height SE 

Tanoak 

1981 

1984 

1987 

1991 

Plants/acre 

950 320 

1,050 395 

1,100 404 

503 

Ft

2

/acre Ft 

2,500 1,323 3.8 0.5 

5,150 1,731 6.3 1.0 

4,600 1,169 7.8 1.1 

7,267 1,967 11.3 1.6 

+191 +197 

6,100 2,255 2.7 0.5 

9,800 2,895 4.3 0.6 

14,050 3,198 6.0 0.8 

5,733 3,291 7.2 1.0 

-6 +167 

750 150 2.7 0.2 

1,350 568 3.6 0.1 

1,550 457 4.3 0.6 

933 481 5.0 0.3 

+24 +85 

800 408 2.4 0.3 

1,400 683 3.0 0.1 

1,250 585 3.9 0.3 

1,800 1,102 5.2 0.8 

+122 +116 

8,000 2,020 2.8 0.5 

12,850 1,773 4.3 0.4 

19,150 3,113 5.9 0.9 

16,800 4,084 9.5 2.4 

+110 +239 

1,000 

Difference1 

(pct) +5 

Hairy Manzanita 

1981 8,350 1,323 

1984 7,400 1,556 

1987 5,700 1,601 

1991 2,800 1,039 

Difference1 

(pct) -66 

Huckleberries 

1981 450 96 

1984 950 492 

1987 750 419 

1991 933 353 

Difference1 

(pct) +107 

Rhododendron 

1981 300 173 

1984 450 320 

1987 400 271 

1991 600 416 

Difference1 

(pct) +100 

Combined Shrubs 

1981 9,300 1,248 

1984 9,050 1,791 

1987 7,100 1,865 

1991 4,733 1,618 

Difference1 

(pct) -49 

1

Difference between 1981 and 1991 values expressed as a percent increase or decrease. 

USDA Forest Service Research Paper PSW-RP-243. 1999. 9 
they increased in number and size in the control, however. From 1981 to 1991, 

mean density increased by 107 percent from 450 to 933 plants per acre, foliar 

cover by 24 percent from 750 to 933 ft2 per acre, and height by 85 percent from 2.7 

to 5.0 feet (table 2). 

On treated plots, huckleberry density ranged from 133 to 1,333 plants per acre, foliar 

cover from 0 to 1,733 ft2 per acre, and height from 1.3 to 5.3 feet (table 3). 

Rhododendron 

Density and development of this evergreen, shade-enduring species was much 

like that of the huckleberries. It also originated from belowground organs. In the 

control, mean plant density, foliar cover, and height all increased during the 

study: density by 100 percent from 300 to 600 plants per acre, foliar cover by 122 

percent from 800 to 1,800 ft2

 per acre, and height by 116 percent from 2.4 to 5.2 

feet (table 2). 

In the various treatments, low density was characteristic of rhododendron. 

Mean density varied from 111 to 702 plants per acre (table 3), foliar cover from 

111 to 2,366 ft2 per acre, and mean height from 3.3 to 5.6 feet. No significant 

differences were found among treatments for this species. 

Combined Shrubs 

This category includes species that had the tallest and most numerous plants. It 

consisted of the two species of huckleberries, hairy manzanita and 

rhododendron, plus two others (snowbrush and elderberry), that were so poorly 

distributed that they could not be presented individually. 

In fall 1981, density of combined shrubs in the control averaged 9,300 plants 

per acre with 8,000 ft2

 of foliar cover and 2.8 feet of height (table 2). By fall 1991, 

density had decreased 49 percent, but cover and height had increased 110 and 

239 percent, respectively. 

Among treatments in 1991, the highest density of combined shrubs was 

recorded on plots that were manually released one and two times (7,172 and 

7,578 plants per acre) and the lowest was on plots treated with herbicides and 

those manually released three times (867 to 3,400 plants per acre) (table 3). 

However, no differences were statistically significant. For foliar cover, the highest 

values occurred on plots manually released one and two times (20,701 and 

24,176 ft2

 per acre), and the lowest on plots treated with 2,4-D and the Garlon 

compounds (2,133 to 7,000 ft2 per acre). Some of these relationships were 

statistically significant (table 3). Average height of combined shrubs ranged from 

9.5 feet in the control to 2.8 feet in plots treated with 2,4-D + Garlon 4, but no 

differences were statistically significant. 

Salal 

The relatively small plants of salal were inconspicuous relative to the other much 

taller shrubs, and were not sampled until 1991. In this study, salal was relegated 

to the lowermost stratum of the understory. Here it persisted with slender 

upright stems and large leaves in almost total shade. Among the various 

treatments, average density ranged from more than 6,000 to 17,700 stems per 

acre (table 4), foliar cover from 0 to more than 1,180 ft2

 per acre, and height from 

0.4 to 2.6 feet. No significant differences among treatments were found. 

Douglas-fir 

As noted earlier, survival of Douglas-fir seedlings in fall 1980 was 62 percent. 

Mortality had occurred in all treatments with slightly more in the control and in 

plots manually released one time. After we began the study, mortality continued 

with 1 seedling noted as dead in 1982, 1 in 1983, 5 in 1987, and 27 in 1991. 

Mortality appeared to be unrelated to treatment, with death attributed to the 

general effects of competition. 

10 USDA Forest Service Research Paper PSW-RP-243. 1999. 
Table 3-Average density, cover, and height of tanoak, hairy manzanita, 

huckleberries, rhododendron, and combined shrubs in treated and control plots, Six 

Rivers National Forest, 1991 

Treatment Density 

Plants/acre 

Tanoak 

Manual 

5-ft radius one time 148 a1 

5-ft radius two times 739 ab 

5-ft radius three time 1,146 b 

Chemical 

2,4-D 267 ab 

2,4-D + Garlon 4 600 ab 

Garlon 4 533 ab 

Manual and chemical 

Cut and spray (Garlon 3A) 400 ab 

Control 1,000 ab 

Standard error 199 

Hairy Manzanita 

Manual 

5-ft radius one time 5,915 a 

5-ft radius two times 5,619 a 

5-ft radius three times 1,553 a 

Chemical 

2,4-D 333 a 

2,4-D + Garlon 4 733 a 

Garlon 4 1,933 a 

Manual and chemical 

Cut and spray (Garlon 3A) 333 a 

Control 2,800 a 

Standard error 1,290 

Huckleberries 

Manual 

5-ft radius one time 628 a 

5-ft radius two times 1,035 a 

5-ft radius three times 739 a 

Chemical 

2,4-D 1,333 a 

2,4-D + Garlon 4 1,000 a 

Garlon 4 1,200 a 

Manual and chemical 

Cut and spray (Garlon 3A) 133 a 

Control 933 a 

Standard error 442 

Rhododendron 

Manual 

5-ft radius one time 628 a 

5-ft radius two times 702 a 

5-ft radius three times 111 a 

Chemical 

2,4-D 333 a 

2,4-D + Garlon 4 267 a 

Garlon 4 267 a 

Manual and chemical 

Cut and spray (Garlon 3A) 200 a 

Control 600 a 

Standard error 179 

Combined Shrubs 

Manual 

5-ft radius one time 7,172 a 

5-ft radius two times 7,578 a 

5-ft radius three times 2,403 a 

Chemical 

2,4-D 2,000 a 

2,4-D + Garlon 4 2,000 a 

Garlon 4 3,400 a 

Manual and chemical 

Cut and spray (Garlon 3A) 867 a 

Control 4,733 a 

Standard error 1,468 

Cover Height 

Ft2

/acre Ft 

1,109 a 7.2 a 

4,547 a 8.6 a 

5,286 a 8.9 a 

2,200 a 6.5 a 

800 a 7.5 a 

1,133 a 6.5 a 

1,533 a 8.3 a 

7,267 a 11.3 a 

1,348 1.5 

17,892 b 6.5 a 

16,931 b 7.0 a 

5,804 ab 6.4 a 

600 a 4.2 a 

1,333 a 4.6 a 

5,933 ab 6.1 a 

800 a 4.3 a 

5,733 ab 7.2 a 

2,785 0.9 

444 a 3.3 a 

518 a 3.5 a 

111 a 2.9 a 

1,733 a 5.3 a 

267 a 1.3 a 

733 a 3.2 a 

0 a 2.2 a 

933 a 5.0 a 

607 0.8 

2,366 a 4.8 a 

1,183 a 5.0 a 

111 a 5.6 a 

267 a 3.4 a 

533 a 3.3 a 

333 a 4.2 a 

400 a 3.8 a 

1,800 a 5.2 a 

680 0.3 

20,701 c 5.6 a 

24,176 c 6.5 a 

6,026 ab 5.2 a 

2,600 a 5.5 a 

2,133 a 2.8 a 

7,000 ab 5.5 a 

2,533 a 6.4 a 

16,800 bc 9.5 a 

3,135 2.7 

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. 

USDA Forest Service Research Paper PSW-RP-243. 1999. 11 
Damage to Douglas-fir seedlings was noted only if the terminal shoot and 

bud were killed. It occurred throughout the study period and consisted of 3 

seedlings that had been browsed and 23 seedlings whose tops had died for 

unknown reasons. Damage appeared to be independent of treatment or year of 

occurrence. However, in almost every instance, the seedlings developed a new 

top and were alive at the end of the study. 

By 1984, horizontal and vertical development of Douglas-fir seedlings was 

beginning to differ among treatments, especially on plots treated with chemicals 

versus those manually released one time and in the control (fig. 4). Statistically 

Table 4-Average density, cover, and height of salal in treated and control 

plots, Six Rivers National Forest, 1991 

Treatment Density Cover Height 

Plants/acre Ft

2

/acre Ft 

Manual 

5-ft radius one time 14,694 a1 333 a 0.8 a 

5-ft radius two times 11,497 a 1,183 a 1.9 a 

5-ft radius three times 6,155 a 1,054 a 2.6 a 

Chemical 

2,4-D 11,867 a 333 a 1.6 a 

2,4-D + Garlon 4 17,700 a 400 a 0.5 a 

Garlon 4 15,000 a 0 a 1.0 a 

Manual and chemical 

Cut and spray (Garlon 3A) 6,400 a 0 a 0.4 a 

Control 8,133 a 400 a 2.6 a 

Standard error 9,867 375 0.9 

1Treatment means in each column followed by the same letter do not differ statistically at the 0.05 

level. 

Figure 4 

A difference in growth between 

Douglas-fir seedlings in the Garlon 

4 treatment (A) and the manualrelease, one-time treatment (B) 

was visible in fall 1983. 

Figure 4A Figure 4B 

12 USDA Forest Service Research Paper PSW-RP-243. 1999. 
significant differences among treatments for Douglas-fir were first realized in 1987 

when mean foliar cover of seedlings in plots treated with 2,4-D was significantly 

greater than for counterparts in plots manually released one time (table 5). By 1991, 

seedlings in all chemical treatments had significantly more foliar cover than in 

plots released one time and in the control. The difference was striking--29,133 to 

37,750 ft

2 per acre vs 10,831 to 11,467 ft2 per acre, or two to three times more cover. 

Significant differences in stem diameter of Douglas-fir were not found until 1991 

when seedlings in plots treated by cut and spray (Garlon 3A) had a significantly 

larger average diameter at one foot of height than counterparts in the control (4.2 

vs 2.4 inches) (table 5). No significant difference among treatments was found for 

stem height during the study. Overall, the consistently poorest treatments for 

enhancing Douglas-fir development were manual release one time and the control. 

Production and Cost 

Manually cutting vegetation in a 5-foot radius around Douglas-fir seedlings was 

expensive, even if done only once. And manually cutting a 5-foot radii around 

Douglas-fir seedlings two and three times was even more expensive. Chainsawing hardwood and shrub sprouts and treating the freshly cut surfaces with 

Garlon 3A twice, also was costly. Applying foliar sprays with chemicals was the 

least expensive: 

Treatment Production rate Cost 

Laborer hours/acre Dollars/acre 

Manual release (chainsaw and shears) 

5-foot radius, 1 time 

5-foot radius, 2 times 

5-foot radius, 3 times 

Chemical release 

2,4-D, 2 times, entire plot 

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

Garlon 4, 2 times, entire plot 

Manual and chemical release 

Cut + Garlon 3A, 2 times, entire plot 

36.0 315 

51.0 446 

59.6 521 

6.5 67 

6.5 67 

6.5 67 

39.6 346 

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 

Soil moisture tension in the four treatments tested, especially at the 24-inch 

depth, was low through June 15 and then increased rapidly through August 15 as 

plant roots and evaporation depleted the moisture in the soil. Tension peaked 

September 15, and then declined through October 15, probably because of a 

combination of upward moving water in the soil, fall rain, and less transpirational 

and evaporative demand. 

For internal plant moisture stress and its precursor--soil moisture--the 

limiting environmental factor in most of California, predawn minimum values 

and peak maximum values are useful for indicating differences among treatments 

and species (tanoak, hairy manzanita, and Douglas-fir). Treatments with a large 

amount of vegetation (control and 5-foot radius one time, for example) had the 

highest predawn and peak moisture stress, and those treatments with the least 

vegetation (chemicals) in general had the lowest predawn and peak moisture 

stress. For the three species tested, the highest predawn value was for Douglas-fir, 

USDA Forest Service Research Paper PSW-RP-243. 1999. 13 
Table 5-Average stem diameter, height, and foliar cover of Douglas fir seedlings, by 

treatment, Six Rivers National Forest, 1981-1991 

Treatment 1981 1984 1987 1991 

Diameter (inches) 

Manual 

5-ft radius one time 0.45 al 0.99 a 1.85 a 2.89 ab 

5-ft radius two times 0.41 a 1.00 a 2.00 a 3.33 ab 

5-ft radius three times 0.49 a 1.14 a 2.29 a 3.88 at 

Chemical 

2,4-D 0.40 a 0.96 a 2.10 a 4.00 at 

2,4-D + Garlon 4 0.39 a 0.80 a 1.90 a 3.46 ab 

Garlon 4 0.43 a 1.00 a 2.11 a 3.74 ab 

Manual and chemical 

Cut and spray (Garlon 3A) 0.34 a 0.90 a 2.17 a 4.18 b 

Control 0.47 a 0.93 a 1.50 a 2.38 a 

Standard error 0.04 0.10 0.21 0.34 

Height (feet) 

Manual 

5-ft radius one time 2.21 a 4.51 a 8.61 a 14.34 a 

5-ft radius two times 1.50 a 4.74 a 9.51 a 16.96 a 

5-ft radius three times 2.25 a 5.11 a 10.72 a 19.07 a 

Chemical 

2,4-D 1.80 a 4.89 a 9.86 a 18.66 a 

2,4-D +Garlon 4 1.77 a 3.79 a 8.25 a 14.70 a 

Garlon 4 2.14 a 4.82 a 9.68 a 17.30 a 

Manual and chemical 

Cut and spray (Garlon 3A) 1.82 a 3.88 a 8.96 a 17.24 a 

Control 2.52 a 5.30 a 9.00 a 14.42 a 

Standard error 0.35 0.71 0.97 2.04 

Cover (ft2 /acre) 

Manual 

5-ft radius one time 111 a 1,747 a 5,295 a 10,831 a 

5-ft radius two times 305 a 2,911 a 8,012 ab 12,790 ac 

5-ft radius three times 111 a 2,967 a 9,482 ab 28,132 bc

Chemical 

2,4-D 200 a 3,500 a 18,950 b 34,800 b 

2,4-D + Garlon 4 150 a 3,050 a 14,000 ab 29,133 b 

Garlon 4 1,300 a 4,950 a 16,000 ab 37,750 b 

Manual and chemical 

Cut and spray (Garlon 3A) - 2,650 a 15,600 ab 33,867 b 

Control 750 a 3,950 a 8,450 ab 11,467 a 

Standard error 447 872 2,383 3,123 

1

For each year, treatment means followed by the same letter do not differ significantly at the 0.05 level. 

followed by tanoak, and hairy manzanita. For maximum moisture stress, the 

highest value was for Douglas-fir, hairy manzanita, and tanoak. 

The diameter growth values in table 5 and the plant moisture stress curves in figure 

3 show that the most-- and least--effective treatments for Douglas-fir seedlings were cut 

and spray with Garlon 3A, and control, respectively. Given that photosynthesis begins 

to decrease in Douglas-fir seedlings at 8 atmospheres (Cleary 1971), seedlings treated 

by cut and spray with Garlon 3A maintained a positive carbon balance for at least an 

hour early in the morning, but seedlings in the control were unable to do so. This onehour difference could be important as it constituted an energy input rather than a 

drain. Furthermore, seedlings in the control had to endure many more hours at a 

higher level of moisture stress than were counterparts in the cut and spray plots. 

Fertile soil, mild temperatures, and copious precipitation combined to make 

the vegetation in this study the most dynamic that we have encountered in the 42 

studies in our vegetation management research program. Altogether, the 18 

species of hardwoods and shrubs formed a dense mass of developing vegetation 

14 USDA Forest Service Research Paper PSW-RP-243. 1999. 
t

hat so occupied the site and so captured the available resources, that little 

opportunity existed for additional species, especially forbs and grasses, to become 

established. The few forbs that did invade the area were present only as 

individuals and in small aggregations for a short time. The two most abundant 

forbs, present at the end of the study, were bear-grass and a tall lily. Bear-grass, 

which is not a grass at all, but a vigorous forb that arises from woody, tuber-like 

rhizomes, produces a tall flowering stalk every 3 to 7 years. Like most lilies, the 

one in this study also originates from a large bulb. These forbs persisted because 

of their ability to develop from large below-ground structures that had sufficient 

energy to produce stems that were tall enough to compete with the shrubs. 

Opportunistic bracken fern developed well in scattered areas, particularly where 

the shrubs had been reduced in density and size by chemicals. 

When the study began, we noted 28 species; when it ended, we found only 23 

species. This number is low relative to that found in other studies (17 to 46 

species) in our National Administrative Study Program in young conifer 

plantations (McDonald and Fiddler 1993, 1997). 

The developmental trajectories of the vegetation in this study indicated the 

critical need to grow as tall as possible, as fast as possible. Fueled by the energy 

stored in the root crowns and root systems of parent plants, and stimulated by 

cutting and broadcast burning, dormant buds quickly produced numerous 

sprouts. These grew rapidly in height and width. Vertical development of 

hardwoods, shrubs, ferns, and forbs was more than 2 feet when the study began, 

with large and consistent increases thereafter. By the end of the study, no species 

was less than 5 feet tall, and blue blossom and snowbrush were over 30 feet tall. 

In places, bracken fern reached 5 feet in height, and even vetch adopted a tall and 

skinny form. 

By the end of the study, much of the soil surface was covered with vegetation. 

In fall 1981 or after the first year of study, horizontal development of the shrubs 

and tanoak in the control totaled 10,500 ft

2

 per acre and that of Douglas-fir 750 ft2 

per acre. At the end of the study, the foliar cover of tanoak averaged 2,293 ft

2

 per 

acre, the shrubs 16,800 ft

2

, and Douglas-fir 11,467 ft

2

 per acre. Foliar cover of salal 

added another 400 ft2 per acre, for a combined total of 30,960 ft2 per acre. This 

equates to 71 percent of each acre being cast in solid shadow, independent of the 

additional cover provided by the rare and poorly distributed species. 

Unlike the developmental pattern of the hardwoods and shrubs in the control 

of the "sister" study 15 miles away, where just two species (tanoak and 

snowbrush) dominated the plant community at the end of the study, the pattern 

in this study was one of no clear dominance pattern, but excellence in density, or 

cover, or height by several species. Competition to Douglas-fir seedlings was not 

by one or two species, but by most of them together. 

Although Douglas-fir seedlings in the control were impacted by heavy 

competition and lower available soil moisture, their development was still 20 percent 

taller than their tallest rival (tanoak). Thus, the consequence of the competing 

vegetation was not so much the danger of overtopping Douglas-fir, but more a 

slowdown in its total development, especially of foliar cover. When foliar cover of 

Douglas-fir at the end of the study in each treatment was compared to that in the 

most effective treatment (Garlon 4), the relative proportion (in percent) was: 

5-ft radius one time 29 

5-ft radius two times 34 

5-ft radius three times 75 

2,4-D 92 

2,4-D + Garlon 4 77 

Cut and spray (Garlon 3A) 90 

Control 30 

Plainly, foliar cover of Douglas-fir seedlings was much poorer in the lessfrequent radius treatments and in the control. USDA Forest Service Research Paper PSW-RP-243. 1999. 15 
In contrast to these ineffective treat

ments, the growth of Douglas-fir seedlings 

in 1991 in the most effective treatments (for diameter, cut and spray with Garlon 

3A; for height, 5-ft radius 3 times; and foliar cover, Garlon 4) was characterized 

by robust diameter (4.18 inches), tall trees (19.07 feet), and well developed 

crowns (37,750 ft

2

 per acre). The odds are for continued rapid growth in these 

treatments. 

The cost and production data reflect the capability of the many fast-growing 

sprout stems of the hardwoods and shrubs in this study, Their dynamic nature 

mandated that they be treated at least two times. 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 below-ground structures developed 

rapidly after the first release, but less rapidly after successive treatments because 

of competition from Douglas-fir. However with time, more vegetation leaned 

into the plots and had to be clipped. 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 for treatments with manual release and 

the highest costs in the study. For chemical release, the retreatment cost was 

about equal to that of the initial cost because the amount and size of vegetation 

was about the same. 

A continuing objective of the National Administrative Study Program on 

vegetation management is to determine the timing of treatment effectiveness. 

Based on results from the many studies in this program, some trends are 

emerging. In general, the faster the occurrence of a statistically significant 

difference in conifer seedling growth between a treatment and the control, the 

more effective the treatment. Lack of an early statistical difference occurs when 

the vegetation in an ineffective treatment slows the growth of the conifer 

seedlings relative to their counterparts in the control. When competition is 

controlled, stem diameter usually is the first conifer variable to differ 

significantly. In this study, however, foliar cover of Douglas-fir seedlings in the 

most effective treatment in 1987 (2,4-D) versus the least significant treatment (5-

foot radius, one time) became significant first. Achieving significance in fall 1987, 

or nine growing seasons after planting, is late relative to other studies in our 

vegetation management study program. This was because of the effective 

competition present even in the best treatment. 

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

seedling growth will result is not realistic. Release is needed. Site preparation 

also is needed. Stein (1995) noted that certain site preparation treatments, 

particularly those involving broadcast burning and herbicides, significantly 

enhanced Douglas-fir seedling growth for the first 10 years in Oregon Coast 

Range plantations. The early survival of Douglas-fir seedlings in this study, 

including that in the control, was probably due to site preparation. 

A primary goal of vegetation management is to manipulate the plant 

community to alter the trajectory of its succession. 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 (fig. 5), usually when competing species are absent or developing 

poorly. In this study, however, almost all species that were present at the end of 

the study were developing well. Where the Douglas-fir seedlings were growing 

well, the competing vegetation was growing well, albeit with lesser numbers and perhaps with a bias toward the most shade-tolerant species. Where the Douglasfir seedlings were growing poorly, the competing vegetation was also growing 

well, albeit with a slight bias toward higher numbers of slightly larger plants. 

Thus for the next several decades, the composition of the plant community is not 

likely to change very much. Regardless of treatment, secondary succession during 

this period will be manifest in different numbers and sizes of the same species. 

With time, however, the increasing size of the Douglas-fir trees and their 

capability to capture light, soil moisture, and nutrients, will influence the plant 

16 USDA Forest Service Research Paper PSW-RP-243. 1999. 
Figure 5 

Reducing competition in the highly 

competitive plant community of 

this study allowed Douglas-fir 

seedlings to establish their root 

systems and begin to grow rapidly. 

community. Certainly the larger firs will negatively affect the development and 

eventually the species composition of plants in the understory before their 

slower-growing counterparts.

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

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

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

prolong them, should prove valuable. 

References 

Cleary, Brian D. 1971. Theeffect of plant moisture stress on the physiology and establishment of 

planted Douglas-fir and ponderosa pine seedlings. Corvallis, OR: Oregon State University; 85 

p. Dissertation. 

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

and Row; 300 p. 

Gratkowski, H.; Lauterbach, P. 1974. Releasing Douglas-firs from varnishleaf Ceanothus. Journal 

of Forestry 72(3): 150-152. 

Hickman, James C., ed. 1993. The Jepson manual, higher plants of California. Berkeley: University 

of California Press; 1400 p. 

Little, Elbert L., Jr. 1979. Checklist of United States trees (native and naturalized). Agric. Handb. 

541. Washington, DC: Forest Service, U.S. Department of Agriculture; 375 p. 

McCardle, Richard E.; Meyer, Walter H.; Bruce, Donald. 1961. The yield of Douglas fir in the 

Pacific Northwest. Tech. Bul. 201 (rev.). U.S. Department of Agriculture; 74 p. 

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. 

USDA Forest Service Research Paper PSW-RP-243. 1999. 17 
McDonald, Philip M.; Fiddler, Gary O. 1993. Feasibility of alternatives to herbicides in young 

conifer plantations in California. Canadian Journal of Forest Research 23: 2015-2022. 

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. Berkeley, CA: Pacific 

Southwest Research Station, Forest Service, U.S. Department of Agriculture; 15 p. 

McDonald, Philip M.; Fiddler, Gary O. 1997. Vegetation trends in a young ponderosa pine 

plantation treated by manual release and mulching. Res. Paper PSW-RP-234. Berkeley, CA: 

Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; 15 p. 

McDonald, Philip M.; Fiddler, Gary O.; Harrison, Henry R. 1994. Repeated manual release in a

young plantation: effect on Douglas-fir seedlings, hardwoods, shrubs, forbs, and grasses. Res. 

Paper PSW-RP-221. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. 

Department of Agriculture; 11 p. 

Petersen, Terry D.; Newton, Michael. 1982. Growth of Douglas-fir following release from 

snowbrush and forbs--implications for vegetation management of brushfields. Res. Note 

RM-82-8. Milltown, MT: Rocky Mountain Timberlands Research and Development, Champion 

International Corporation; 9 p. 

SAS Institute, Inc. 1988. SAS procedures guide, release 6.03 edition. Cary NC: SAS Institute, Inc. 

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plants. Science 148: 339-346. 

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

McGraw-Hill Book Company; 218-220. 

Stein, William I. 1995. Ten-year development of Douglas-fir and associated vegetation after 

different site preparation on Coast Range clearcuts. Res. Paper PNW-RP-473. Portland, OR: 

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Tappeiner, John C., II; Newton, Michael; McDonald, Philip M.; Harrington, Timothy B. 1992. 

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in northwestern California. R5-ECOL-TP-009. Pacific Southwest Region, Forest Service; 537 p. 

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1248-1254. 

18 USDA Forest Service Research Paper PSW-RP-243. 1999. 
The Forest Service, U.S. Department of Agriculture, is responsible for Federal leadership 

in forestry. It carries out this role through four main activities: 

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

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United States 

Department of Agriculture Forest Service Pacific Southwest Research Station Research Paper PSW-RP-243 

Ecology and Development of Douglas-fir Seedlings and Associated Plant Species in a Coast Range Plantation