United States

Department 

of Agriculture

Forest Service

Pacific Southwest

Research Station

Research Paper

PSW-RP-248

Development of a Mixed-Shrub–Planted

Ponderosa Pine Community on a Poor

Site After Site Preparation and Release

Philip M. McDonald
USDA Forest Service Research Paper PSW-RP-248. 2003. 1

Pacific Southwest Research Station

Forest Service

U.S. Department of Agriculture

Abstract

McDonald, Philip M. 2003. Development of a mixed-shrub—planted ponderosa pine

community on a poor site after site preparation and release. Res. Paper PSW-RP248. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department

of Agriculture; 28 p. 

On a poor site in northern California, a mature brushfield was treated in various ways

that left initial density categories of light, medium, and heavy shrubs. Density, foliar

cover, and height of seven shrub species (alone and combined) and ponderosa pine

seedlings in these categories were quantified from 1967 through 1978. Heretofore, density and development data for five of the seven shrub species were unavailable. From the

beginning to the end of the study, vegetation in the plantation was subjected to damage

from insects, disease, snow, wind cupping, winterburn, a parasitic vine (dodder), and

application of an herbicide. In general, greenleaf manzanita, which was the most abundant shrub species in the study area, prospered, as did bitter cherry, choke-cherry, and

Fremont silk tassel; huckleberry oak endured; and bush chinquapin and mountain

whitethorn declined. Among shrub categories at the end of the study in 1978, the density of combined shrubs ranged from 19,800 to 8,300 plants per acre; foliar cover from

14,000 ft2 to 8,900 ft2 per acre, and height from 2.8 to 2.5 feet. Ponderosa pine seedlings

began to recover from damage in 1974, and because upturned branches had replaced

dead and damaged tops, seedling form improved. Pine seedlings growing with a low

amount of competition were significantly taller and had more foliar cover than counterparts with heavy competition in 1974, a finding that continued for foliar cover through

1978. 

Retrieval terms: competition, northern California, plant community development, ponderosa pine seedlings, poor site, silviculture

The Author

Philip M. McDonald was, until his retirement, a research forester assigned to the

Station’s Western Forest Management Research Unit, 2400 Washington Ave., Redding,

CA 96001; e-mail: pmcdonald@fs.fed.us.

Publisher

Albany, California

Mailing address:

PO Box 245, Berkeley

CA 94701-0245

(510) 559-6300

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

July 2003
i

Contents

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

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

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

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

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

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

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Plant Diversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Effect of Release Spray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Greenleaf Manzanita . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Mountain Whitethorn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Huckleberry Oak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Bush Chinquapin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Bitter Cherry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Western Choke-Cherry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Fremont Silk Tassel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Combined Shrubs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Ponderosa Pine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Discussion and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Development of a mixed-shrub—planted

ponderosa pine community on a poor

site after site preparation and release

Philip M. McDonald

Pacific Southwest

Research Station

USDA Forest Service

Research Paper

PSW-RP-248

July 2003
In Brief. . .

McDonald, Philip M. 2003. Development of a mixed-shrub—planted ponderosa pine

community on a poor site after site preparation and release. Res. Paper PSW-RP248. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department

of Agriculture; 28 p.

Retrieval Terms: competition, northern California, plant community development, ponderosa pine seedlings, poor site, silviculture

Ideally, each land type or segment of commercial forest land in California will

provide valuable amenities and commodities, and serve as a needed

species/structure/age component of an ecosystem. But for the land manager to

obtain the desired amenities and commodities, knowledge is needed on what

plant species are present, how they develop, which ones dominate, and what

effect currently undesirable species have on desired species. When such knowledge is available for all, or at least most of the segments, ecosystem management

will become both easier and sustainable. Silviculture research can provide some

of this knowledge. Natural revegetation of a treated brushfield on a poor-quality, ridge-top site in northern California, and planted ponderosa pine seedlings

serve as the setting for this study, and provide answers to some of the above

questions. The answers pertain only to this particular segment of forest land

and to others having a similar environment. 

The objectives for this 12-year (1967-1978) study were threefold: (1) to identify the plant species on study plots and denote changes in species richness during the study period; (2) to quantify density, foliar cover, and height of principal

shrubs, and density and height of abundant forbs, ferns, and grasses; (3) to quantify foliar cover and height of ponderosa pine seedlings, denote their recovery

from several forms of damage, and determine their interaction with shrubs in

three initial density categories of light, medium, and heavy shrubs.

For the first objective, species richness decreased from 29 to 26 species. At

the end of the study in 1978, the natural plant community consisted of 1 conifer,

1 hardwood, 10 shrubs, 12 forbs, 1 grass, and 1 fern. For the second objective,

greenleaf manzanita was the most abundant species and had the highest density and foliar cover of the seven shrub species that were quantified. Greenleaf

manzanita and bitter cherry, choke-cherry, and Fremont silk tassel generally

increased in density, cover, and height in all three of the initial density categories, and will be present in the plant community of the near future. The status

of huckleberry oak in the future plant community is unclear. Average density

and foliar cover values suggest that this oak is maintaining its position in the

community, but its low average height makes it vulnerable to taller shrubs and

pines. Mountain whitethorn and bush chinquapin had generally declining values in most density categories and probably will have only a minor presence in

the plant community of the future. Because these seven shrub species dominate

both vertically and horizontally, other species of shrubs, forbs, ferns, and grasses probably will be sparse and poorly distributed in the near future. 

For objective three, only 12 percent of ponderosa pine seedlings perished

during the study in spite of the harsh ridge-top environment. Pine foliar cover

and stem height increased steadily throughout the study in all three initial shrub

density categories. By the end of the study, mean pine foliar cover ranged from

12,550 ft

2 per acre in the low shrub category to more than 5,900 ft2 per acre in the

high shrub category. Values for average height in similar categories were 8.1 to

5.8 feet. From the beginning to the end of the study, ponderosa pine seedlings

were beset by damage from snow, wind cupping, winterburn, insects, disease, a

parasitic vine (dodder), and application of an herbicide that was applied in

October 1967 to release the plantation from competition. Rare was the year that

at least some damage did not occur. The resiliency of the pine seedlings was

USDA Forest Service Research Paper PSW-RP-248. 2003. iii
remarkable, and after upturned branches replaced dead and deformed tops, it

was difficult to tell that damage had occurred on many of the seedlings. By the

end of the 1974 growing season, the relationship of the pines to the competing

shrubs was becoming clear. Where competition was low, the pines had significantly more foliar cover and height than pines in the high shrub density category; where competition was intermediate, as in the medium shrub category, the

pines also had significantly more foliar cover than counterparts in the high shrub

category. Graphs of pine cover and height showed a clear trend of increasing

growth with decreasing amounts of shrubs.

Silviculturists have many techniques to manipulate unwanted vegetation,

and to nudge an area with low plant diversity and little vertical structure toward

one with a more natural species composition and a more variable structure. Site

preparation, which tends to lessen the number and size of mature competing

plants, and plantation release, which often lessens the effect of new or reestablished competing plants, aid in the establishment of a desired species by increasing the amount of available site resources. An arborescent species, ponderosa

pine, which historically had been part of the plant community, was not present

in the mature brushfield when this study was installed. Now it is present and

growing well, at least where the competing shrubs are of low and medium density. As a young pine stand with 26 other species of vegetation, it forms a specific vegetative assemblage about which some information is now available and

whose developmental trajectory can be postulated. Because the pines provide

contrast to the mature stand of trees nearby, they have amenity value. Because

they could eventually become a crop of timber and wood products, they have

commodity value as well.

iv USDA Forest Service Research Paper PSW-RP-248. 2003.
Introduction The practice of silviculture in the era of ecosystem management needs not

only to employ its traditional emphasis on trees, but also to concentrate on

lesser vegetation, particularly on land disturbed both naturally and by humans.

Manipulating lesser vegetation could be for a variety of reasons: to help create a

future forest, to enhance stream flow, to provide an economic crop, to grow

plants whose seeds or browse would be critical to wildlife, or simply to have

present a broad base of species and age classes, and thus be able to provide

amenities and commodities that will be needed in the future.

Broadening the art of vegetation management to include detailed information on lesser vegetation is increasingly recognized. Gordon (1979) recommended that foresters begin to build a database for vegetation that is expected in

specific areas. Hungerford (1986) stated, “research is needed on seed dissemination and establishment requirements for many species.” Wagner and Zasada

(1991) noted that forest managers across North America need to consider the

potential effect of noncrop vegetation on nearly every acre of newly forested

land. Rietveld (1992) advocated an increased demand for diverse tree and shrub

nursery stock, especially for species that provide food and shelter for wildlife.

Aune and others (1993) suggested that greater within-stand species variation

will be desired in the future and “the growing and planting of high quality

seedlings of hardwood trees, shrubs, and other flowering plants is now expanding to meet multi-resource objectives.” O’Hara and others (1994) stated that

future forestry must embrace “a mix of commercially valuable and nonvaluable

species.” McDonald and others (1996) noted a weakness and a need when

beginning ecosystem management in areas that had or should have a forest on

them. The weakness is that “very little is known about the shrub, forbs, and

grasses in the community.” The need is for “knowledge on silvicultural treatments that will provide desired plant communities at specific times in the

future.”

Ecosystem managers of the future are going to need a tremendous amount of

data (McDonald 1999). Information on plants, animals, fish, insects, fungi, and

even genes will be needed in order to effectively practice ecosystem management.

For plants, knowledge about species composition, density, and development

often is unavailable not only for individual species, but also for the community in

which they grow. In this study, seven common and widespread shrub species

were quantified and evaluated both ecologically and for competitive potential.

These were greenleaf manzanita (Arctostaphylos patula Greene), mountain

whitethorn (Ceanothus cordulatus Kellogg), huckleberry oak (Quercus vaccinifolia

Kellogg), bush chinquapin (Chrysolepis sempervirens [Kell.] Hjelmq.), bitter cherry (Prunus emarginata [Hook.] Walp.), western choke-cherry (Prunus virginiana L. var.

demissa [Nutt.] Torrey), and Fremont silk tassel (Garrya fremontii Torrey). No

density or developmental information could be found for five of the seven

shrub species that were studied. Realistically, ecosystem management can best

be accomplished if discrete units of land are identified and studied. These discrete units, called segments or land types (Miles and Goudey 1997), are the

smallest units identified in the hierarchical framework of ecological units.

When knowledge about many land types is available, not only will ecosystem

management be enhanced on each, but it will be improved even more because

these types can be joined and relationships at larger scales ascertained.

Although some anecdotal information has been recorded, knowledge about

individual plant species in specific plant communities on poor sites is largely

unavailable. Changes in species composition, density, and growth are often lacking, especially over a 5-year or longer period. The effect of these plant species on

planted ponderosa pine seedlings, whether alone or combined, and the pine’s

effect on them also are poorly quantified.

USDA Forest Service Research Paper PSW-RP-248. 2003.

1
This paper reports the recovery of individual shrub species, combined

shrubs, and planted ponderosa pine seedlings at various intervals during a 12-

year (1967-1978) period in three initial shrub density categories; documents

changes in plant species composition; quantifies density, foliar cover, and height

of principal shrubs; and quantifies foliar cover and height of ponderosa pine

seedlings.

Methods

Location and Site Characteristics

The study area, called the Sugarloaf plantation, is located on the Downieville

Ranger District of the USDA Forest Service’s Tahoe National Forest in T20N,

R9E, sections 13 and 14, Mt. Diablo meridian. It is situated about 6 airline miles

northwest of the town of Downieville, and is located in a 750-acre brushfield.

The area burned in 1924 and has been undisturbed since then. One small grove

of large ponderosa pines (Pinus ponderosa Dougl. ex Laws. var. ponderosa) was

located in a portion of the brushfield, but no other evidence was found to indicate that the area had been other than a brushfield for scores of years. 

Before the study began, the vegetation consisted of mature shrub species

that ranged from 3 to 8 feet tall (fig.1). Most abundant was greenleaf manzanita

with mountain whitethorn, bush chinquapin, and huckleberry oak less abundant, but well distributed throughout the area. Western choke-cherry, bitter cherry, and Fremont silk tassel also were common, but less well distributed.

Bracken fern (Pteridium aquilinum [L.] Kuhn var. pubescens L. Underw.), two

perennial forbs, and no grasses were noticed in a pretreatment (fall 1962) survey

(Bradshaw 1962). Scientific and common names of trees are from Little (1979)

and all other vegetation follows the nomenclature of Hickman (1993).

Deer (Odocoileus spp.), rabbits (Sylvilagus spp.), and coyotes (Canis spp.)

were common in the study area, but other than occasional nipping of some of the

shrubs, damage was negligible. 

Site quality of the study area is low with height of dominant mixed conifers

averaging about 50 feet in 50 years (Biging and Wensel 1984). Because of its

ridge-top location, the study area is subjected to high amounts of insolation and

strong winds. The elevation is about 5,500 feet and the topography is gently

undulating with slopes of less than 15 percent. The soils are derived from vol2 USDA Forest Service Research Paper PSW-RP-248. 2003.

Figure 1—A portion of the study

area before site preparation in

1962.
canic flows, are 2 to 36 inches deep, and generally quite stony and droughty.

Occasionally, small rocky outcrops and bare gravelly areas are present. The

growing season is about 90 days. Mean annual precipitation is about 80 inches

with most falling as snow.

Precipitation for the January-through-June period was evaluated each year.

Years with an above average amount of precipitation were 1967, 1969, 1973, and

1978. Years with below-average precipitation occurred in 1966, 1968, 1971-72,

and 1976-77; and years with average precipitation were 1970, 1974, and 1975. 

An early study on site preparation (Buck and Baron 1961), installed in spring

1962 through fall 1963, involved a combination of mechanical and chemical

applications at different times of the year (spring and fall). The mechanical treatment involved pushing the mature shrubs into windrows with tractors equipped

with a straight blade and a brushrake. The goal was to remove the shrub root

crowns, but this was impossible in places because of rocks and shallow soil.

About 2 inches of soil were moved, and some of it was deposited in the

windrows, particularly where the blade was used. The windrows were burned

shortly after piling. Two herbicides (2,4-D and 2,4,5-T) also were applied with a

power sprayer as a tank mix in spring and fall in conjunction with the mechanical treatments. The treatments were applied in 12 rectangular blocks, each

about 5 acres (330 by 660 feet), sandwiched between the windrows. Some treatments were effective and some were not. The net effect of all the treatments was

to create a large area covered with a wide range of shrub densities that were

ideal for a study whose aim was to quantify subsequent plant community-ponderosa pine relationships.

Ponderosa pine seed was from the correct zone, and seedlings were grown

in the Placerville Nursery for 1 year. They were planted in spring 1964 at an

intended spacing of 8 by 8 feet, which became 6 by 8 feet in places (McDonald

and Oliver 1984). The weather was ideal for early seedling establishment, with

rain falling before, during, and after planting. Survival after 2 years was 91 percent (McDonald 1966). 

Study and Design

The current study began in summer 1965 when transects, perpendicular to planted rows of pines, were drawn on maps at 20-foot intervals in each of the 12

blocks. Two transects in each were randomly chosen and laid out on the ground.

These became the center lines of sample plots. Each plot was then evaluated for

shrub density and categorized as light, medium, or heavy. Consequently, six

plots had a heavy shrub density, ten had a medium density, and eight had a

light shrub density. At least 15,000 plants per acre separated the light, medium,

and heavy designations. In effect, each category became a treatment.

Each sample plot was rectangular and contained 24 to 31 seedlings, averaging 27, surrounded by several rows of similar seedlings. No plots were located

close to the windrows or near the corridors at the ends of the planted rows.

Sample seedlings had to appear healthy and none that were small, misshapen, or

discolored were selected. These would have been removed in the first thinning.

On each of the sample seedlings, stem height (fig. 

2) and 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]) were measured. These

seedlings also were checked for possible injury from both biotic and abiotic

sources. Damage was recorded only if the seedling stem was injured or the top

was killed. Sampling for shrubs and other vegetation was by four systematically selected subplots located near the center of each plot. Subplots were square

and contained 1 milacre (0.001 acre or 43.56 ft

2

). The most abundant species were

measured for density, foliar cover, and height. More specifically, density was

the number of plants on each subplot, presented on a per-acre basis. Foliar cover

was an ocular estimate, checked by a foot-square wire frame and a measuring

USDA Forest Service Research Paper PSW-RP-248. 2003.

3
tape, and also presented on a per-acre basis. If less than 0.5 ft2

, foliar cover was

denoted as a trace (T). Height was calculated as the average of the three tallest

stems per species in the milacre subplots. It was measured from mean ground

line to top of plant.

Sampling

Detailed sampling of pine seedlings and woody vegetation by species did not

begin until 1966, but these data are not presented here because of lingering

effects from the site preparation spraying. Consequently, sampling of the most

abundant species began in 1967 and took place in late summer or early fall at

various yearly intervals, which were close together early in the study and

widened at the end. All species on study plots were recorded at the beginning

and end of the study, and some of the forbs, ferns, and grasses were quantified

at the end of the study in 1978.

Early surveys showed that total shrub density was huge (up to 97,000 plants

per acre) and shrub growth was vigorous. Thus, a decision was made to release

the pines from the shrubs in early October 1967. Sampling had already been

completed. Release involved aerially spraying the study area with 2,4,5-T at a

rate of 3 pounds acid equivalent per acre.

Because the three treatments (categories) had an uneven number of plots in

them, an unbalanced form of analysis of variance was used, along with a

Bonferroni “t” test (SAS Institute 1988). Significance in all tests was at a= 0.05.

The a levels (type I errors) given for comparing means apply to each measurement time separately. 

Results

Plant Diversity

The natural plant community on all plots in 1967 consisted of 29 species including 1 conifer, 1 hardwood, 11 shrubs, 15 forbs, and 1 fern. At the end of the

study in fall 1978, the plant community was composed of 1 conifer, 1 hardwood,

10 shrubs, 12 forbs, 1 graminoid, and 1 fern, for a total of 26 species. The total

number of plant species recorded during the study period was 32 (table 1). The

graminoid (Achnatherum nelsonii [Scribner] Barkworth), which is a species of 

4 USDA Forest Service Research Paper PSW-RP-248. 2003.

Figure 2—Measuring height on a

ponderosa pine seedling in a low

shrub density area, September

1965. Note the rocky soil.
Table 1—Natural vegetation in study plots, Sugarloaf plantation, Tahoe National Forest, 1967-1978

Vegetation Scientific Common 1967 1978

category name name

Conifers

Abies concolor var. lowiana California white fir X X

Hardwoods

Quercus kelloggii California black oak X X 

Shrubs

Arctostaphylos patula greenleaf manzanita X X

Amelanchier utahensis service-berry X X

Ceanothus cordulatus mountain whitethorn X X

Chrysolepis sempervirens bush chinquapin X X

Garrya fremontii Fremont silk tassel X X

Prunus emarginata bitter cherry X X

Prunus virginiana var. demissa western choke-cherry X X

Quercus vaccinifolia huckleberry oak X X

Ribes roezlii Sierra gooseberry X X

Rosa gymnocarpa wood rose X --

Symphoricarpos mollis creeping snowberry X X

Forbs

Calyptridium umbellatum pussypaws X X

Eriophyllum lanatum woolly sunflower X X

Eriophyllum spp. woolly sunflower X X

Gayophytum diffusum --- X X

Kelloggia galioides --- X --

Lilium washingtonianum Washington lily X X

Lupinus spp. lupine -- X

Nama lobbii purple mat X X

Penstemon spp. beardtongue X X

Smilacina racemosa false Solomon’s seal X X

Solanum xanti nightshade X --

Trientalis latifolia starflower -- X

Unknown --- X --

Unknown --- X --

Unknown --- X --

Unknown --- X X

Unknown --- X X

Graminoids

Achnatherum nelsonii needlegrass -- X

Fern

Pteridium aquilinum var. bracken X X

pubescens

USDA Forest Service Research Paper PSW-RP-248. 2003. 5
needlegrass, is common at lower elevations, but was not present in the study

area before site preparation. It became established near the road that passed

through the plantation, and eventually spread into the study plots (fig. 3).

Pickups and cattle trucks travel this road and seed probably blew off them. In

1978, several classes of non-woody and semi-woody vegetation were present on

the milacre subplots. Their mean density and height were:

________________________________________________

Category Density Height

____________________________________________________________

plants/acre ft

Most abundant forbs 12,459 0.7

Woolly nama 3,302 0.3

Bracken fern 1,417 1.1

Needlegrass 4,323 1.8

____________________________________________________________

Because plants were poorly distributed, standard errors are meaningless and

not presented. 

Woolly nama (Nama lobbii A. Gray) is a prostrate perennial that becomes

established on bare areas in bright sunlight (fig. 4). It spreads rapidly from elongating roots and forms dense masses of vegetation. These dense masses suppress germination of dormant shrub seeds in the soil, and serve as a means of

biological control. Hence, it was sampled separately. However, it was impossible

to delineate a “plant” because of its spreading habit. Consequently, density for

this species is conservative and defined as number of clumps, rather than number of plants. Bracken fern spreads across the landscape from underground rhizomes and defining a “plant” also is difficult. Hence, its density was recorded in

terms of number of fronds. 

Dodder (Cuscuta spp.), which is an annual parasitic vine, became present in

the plantation in 1966 and became dense in places. It tended to form a net over

some plants, particularly greenleaf manzanita, and killed several of them. By the

end of the study, however, it had almost disappeared from the study area.

6 USDA Forest Service Research Paper PSW-RP-248. 2003.

Figure 3—Invasion of needlegrass

in the study area.
Effect of Release Spray

The effect of the October 1967 release spray is best described as variable both as

to area and plant species affected (tables 2-9). Some portions of the study area

were not affected; some were moderately influenced; and a small portion, particularly where the soil was poorest, was heavily affected. In affected portions of

the plantation, mountain whitethorn was damaged most with greenleaf manzanita second. Many plants of these two species died. Bush chinquapin and

huckleberry oak lost almost all of their leaves and stems, but resprouted at

ground line in most instances. Fremont silk tassel lost most of its outer leaves,

but the inner leaves were untouched. Only a few plants of these species died

from the spray. Western choke-cherry was only lightly affected by the spray and

bitter cherry was unaffected. Dieback and sprouting from the root crown almost

always resulted. Woolly nama and dodder virtually disappeared from the study

area, but reappeared the next year and colonized vigorously for 2 additional

years. 

Visual observations and diary records noted that the timing of death differed among species as well. Most mountain whitethorn plants died outright,

although a few sprouted from ground line the next spring. In contrast, greenleaf

manzanita continued to die from spray damage through 1970. Some plants died

outright, others died back to ground line, and still others lost most of their leaves

and stems. Many lingered in this condition for 2 or 3 years. Some recovered and

some died. Mortality of manzanita was greatest the first year after spraying and

tapered off during the next 2 years. For mountain whitethorn, density decreased

53 percent between 1967 and 1970; for greenleaf manzanita, the decrease in density was 56 percent. Certainly, some of this decrease can be ascribed to mortality from spraying, but not all. Early density values for some species were

high—too high. They are unsustainable and high natural mortality during the

first few years is the normal trend. Corresponding decreases in foliar cover for

whitethorn and manzanita were 46 and 57 percent, respectively. Because plants

tend to become larger from the beginning, foliar cover tends to increase. Thus,

the decrease in foliar cover during the first few years is likely to be more a consequence of the spraying than is density.

USDA Forest Service Research Paper PSW-RP-248. 2003. 7

Figure 4—This ponderosa pine

seedling is surrounded by woolly

nama and a few shrubs.
Table 2—Average density, foliar cover, and height of greenleaf manzanita by shrub category, Sugarloaf plantation, Tahoe National Forest, 1967-1978

Year Category Density Cover Height

plants/acre ft2/acre ft

1967 High 64,783 a1 2,900 a 0.8 a

Medium 26,580 b 1,400 b 0.8 a

Low 7,975 c 588 c 0.8 a

Root mse2 10,300 885 0.29

F 35.60 7. 88 0.51

P 0.001 0. 001 0.679

1969 High 29,917 a 1,250 a 0.8 a

Medium 12,670 a 740 a 0.8 a

Low 5,613 a 238 a 0.5 a

Root mse 15,999 994 0.35

F 3.02 1. 62 1.65

P 0.054 0. 216 0.210

1971 High 26,317 a 3,483 a 1.3 a

Medium 12,750 a 2,430 a 1.3 a

Low 5,325 a 688 a 1.1 a

Root mse 14,615 2,203 0.46

F 2.78 2. 06 0.62

P 0.068 0. 138 0.608

1974 High 21,733 a 6,100 a 2.2 a

Medium 11,180 a 4,930 ab 2.1 a

Low 6,500 a 1,575 b 1.6 a

Root mse 11,625 2,941 0.75

F 2.46 3. 29 1.19 

P 0.094 0. 042 0.339

1978 High 16,583 a 9,183 a 3.1 a

Medium 8,980 a 7,980 a 3.1 a

Low 5,812 a 2,437 b 2.8 a

Root mse 8,218 3,675 0.79

F 2.32 4. 97 0.94

P 0.105 0. 010 0.440

1 For each year, treatment means in each column followed by the same letter do not differ significantly according to a Bonferroni test (a = 0.05). 2 Root mse is root mean square error.

8 USDA Forest Service Research Paper PSW-RP-248. 2003.

Greenleaf Manzanita

This evergreen, fast-growing shrub was the most abundant species in the plantation. After site preparation, viable seeds in the soil germinated by the thousands, and averaged more than 64,000 plants per acre in the high shrub category.

Corresponding values in the medium and low shrub categories were 26,580 and

7,975 plants per acre, respectively. These values differed statistically (p = 0.001)

(table 2). Manzanita density in the high and medium categories then decreased

markedly through the end of the study in 1978. In the low category, however,

density decreased through 1971 and then increased. Foliar cover was more consistent among shrub density categories. In all three categories it decreased

through 1969 and then increased through 1978. For the high category foliar
USDA Forest Service Research Paper PSW-RP-248. 2003. 9

averaged 2,900 ft2 in 1967 and increased 217 percent through 1978; for the medium category, it was 1,400 ft2 in 1967 and increased 470 percent; in the low category, foliar cover of manzanita in 1967 averaged 588 ft2 per acre and increased

314 percent through 1978. In general, foliar cover differed statistically between

the high and low shrub density categories during the study. Mean height of

manzanita generally increased throughout the study in all three categories. It

ranged from 0.8 foot in 1967 to about 3 feet in 1978 with no statistical difference

among categories.

Mountain Whitethorn

Although never abundant, this species was well distributed throughout the

study area and was an important part of the shrub community. In 1967,

whitethorn density averaged between 350 and 925 plants per acre among shrub

categories (table 3). Density then declined through 1969, recovered slightly in

1971, and decreased drastically between 1974 and 1978. In 1978, density averaged between 100 and 312 plants per acre in the three shrub categories. The

trend in foliar cover was to decrease in 1969, and to recover somewhat by the

end of the study. In 1978 foliar cover averaged between 330 and 917 ft2 per acre

among shrub categories. Height of mountain whitethorn generally increased

during the study, and in 1978 ranged between 1.3 and 1.9 feet. At no time did

mean density, foliar cover, or height differ statistically among shrub categories. 

Huckleberry Oak

This oak is a small, compact, deciduous shrub, 1 to 4 feet tall, that inhabits

mountain ridges and rocky areas at higher elevations. It extends from southern

Oregon southward in the North Coast and Klamath Mountains and through

the Sierra Nevada to the vicinity of Yosemite National Park (McMinn 1939,

Pavlik and others 1991). In 1967, mean density of this oak ranged from 88 to 840

plants per acre among shrub categories (table 4). In 1978, density ranged from

162 to 950 plants per acre among shrub categories with no real trend in intervening years. Foliar cover also showed no meaningful trends and ranged from 250

to 860 ft2 per acre in 1967 to 188 to 1,000 ft2 per acre in 1978. For all density

classes, mean height ranged from an average of 1.8 feet in 1967 to an average of

1.3 feet in 1978. No statistical differences were found among shrub categories for

density, foliar cover, or height during the 1967- to 1978-period. 

Bush Chinquapin

This low, spreading, evergreen shrub, 1 to 8 feet tall, often forms thickets on dry

mountain ridges and in rocky places in open forests in several mountain ranges

in California, western Nevada, and southern Oregon (McMinn 1939). In this

study, mean density generally declined in all density classes between 1967 and

1978 (table 5). In 1978, statistically more plants per acre were present in the

medium category than in the low category (322 versus 62 plants). Foliar cover

decreased erratically in the high and low density categories, and then after an

early decline, increased steadily in the medium category. In 1978 it ranged from

600 ft2 per acre in the high category to 1,944 ft2 per acre in the medium category. Height generally increased throughout the study in all density categories,

and by the study’s end ranged from 2.6 to 4.5 feet.

Bitter Cherry

This cherry, one of seven species in California, is a deciduous shrub, 4 to 12 feet

tall, that often forms dense thickets in the Coast Ranges and the mountains of

the Sierra Nevada (McMinn 1939). Average density of this species in 1967 
10 USDA Forest Service Research Paper PSW-RP-248. 2003.

Table 3—Average density, foliar cover, and height of mountain whitethorn by shrub category, Sugarloaf

plantation, Tahoe National Forest, 1967-1978

Year Category Density Cover Height

plants/acre ft2/acre ft

1967 High 350 a1 50 a 0.5 a

Medium 630 a 510 a 0.8 a

Low 925 a 725 a 1.8 a

Root mse2 927 869 0.34

F 0.49 0. 72 2.09

P 0.694 0. 553 0.155

1969 High 200 a T3 a 0.5 a

Medium 210 a 320 a 0.9 a

Low 500 a 412 a 0.9 a

Root mse 541 530 0.45

F 1.71 0. 78 0.80

P 0.198 0. 519 0.536

1971 High 300 a T a 0.7 a

Medium 400 a 400 a 0.8 a

Low 588 a 825 a 1.0 a

Root mse 676 985 0.39

F 0.57 0. 93 0.93

P 0.641 0. 444 0.481

1974 High 467 a 500 a 1.1 a

Medium 400 a 250 a 0.7 a

Low 500 a 400 a 1.0 a

Root mse 700 601 0.47

F 0.04 0. 29 0.46

P 0.987 0. 832 0.724

1978 High 150 a 917 a 1.9 a

Medium 100 a 330 a 1.9 a

Low 312 a 750 a 1.3 a

Root mse 331 1,272 0.63

F 1.02 0. 39 0.54

P 0.406 0. 760 0.681

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

significantly according to a Bonferroni test ( a = 0.05). 2 Root mse is root mean square error.

3 T equals trace.
Table 4—Average density, foliar cover, and height of huckleberry oak by shrub category, Sugarloaf plantation,

Tahoe National Forest, 1967-1978

Year Category Density Cover Height

plants/acre ft2/acre ft

1967 High 717 a1 833 a 3.2 a

Medium 840 a 860 a 0.4 a

Low 88 a 250 a 1.8 a

Root mse2 900 1,043 2.14

F 1.27 1. 23 1.28

P 0.310 0. 324 0.352

1969 High 550 a 417 a 1.2 a

Medium 560 a 410 a 0.5 a

Low 88 a 125 a 0.7 a

Root mse 728 844 0.33

F 0.98 0. 54 3.38

P 0.422 0. 663 0.084

1971 High 550 a 1,200 a 1.2 a

Medium 490 a 930 a 1.0 a

Low 88 a 250 a 0.9 a

Root mse 728 1,515 0.25 

F 0.93 0. 77 1.42

P 0.442 0. 522 0.325

1974 High 1,000 a 1,717 a 1.5 a

Medium 600 a 960 a 1.2 a

Low 88 a 250 a 1.2 a

Root mse 1,120 1,744 0.29

F 0.89 0. 86 1.59

P 0.462 0. 477 0.302

1978 High 950 a 1,000 a 1.6 a

Medium 750 a 930 a 1.5 a

Low 162 a 188 a 0.9 a

Root mse 1,102 1,372 0.34

F 0.73 0. 63 2.88

P 0.548 0. 605 0.142 

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

significantly according to a Bonferroni test (a= 0.05). 2 Root mse is root mean square error.

USDA Forest Service Research Paper PSW-RP-248. 2003. 11
Table 5—Average density, foliar cover, and height of bush chinquapin by shrub category, Sugarloaf plantation, Tahoe National Forest, 1967-1978

Year Category Density Cover Height

plants/acre ft2/acre ft

1967 High 333 a1 1,217 a 1.3 a

Medium 788 a 750 a 0.9 a

Low 290 a 1,250 a 1.2 a

Root mse2 1,048 1,830 0.51

F 0.49 0. 14 0.62

P 0.695 0. 933 0.627

1969 High 283 a 333 a 1.0 a

Medium 210 a 250 a 1.0 a

Low 625 a 538 a 1.6 a

Root mse 988 797 0.64

F 0.34 0. 22 0.66

P 0.799 0. 880 0.629

1971 High 200 a 500 a 2.2 a

Medium 210 a 700 a 2.1 a

Low 662 a 1,100 a 2.3 a

Root mse 1,043 1,674 0.99

F 0.43 0. 16 0.03

P 0.735 0. 921 0.990

1974 High 200 a 767 a 2.5 a

Medium 180 a 1,100 a 2.5 a

Low 62 a 625 a 3.5 a

Root mse 336 2,182 0.35

F 0.69 0. 16 5.37

P 0.566 0. 922 0.305

1978 High 167 ab 600 a 3.1 a

Medium 322 a 1,944 a 2.6 a

Low 62 b 875 a 4.5 a

Root mse 297 3,038 1.46

F 5.25 0. 42 1.41

P 0.008 0. 742 0.440

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

significantly according to a Bonferroni test (a = 0.05). 2 Root mse is root mean square error.

12 USDA Forest Service Research Paper PSW-RP-248. 2003.
ranged from 267 plants per acre in the high shrub category to 562 per acre in the

low shrub category, and in general increased throughout the study period (table

6). In 1978, density ranged from 960 to 1,783 plants per acre. Foliar cover

increased erratically throughout the study in the high density category andsteadily in the medium and low categories. At the study’s end, mean foliar cover

was 300 ft2 per acre in the high category and 2,000 or more square feet per acre

in the medium and low categories. Mean height ranged from 2.3 to 3.3 feet at the

end of the study. No statistical differences were found among shrub categories

for density, foliar cover, or height during the study period.

Western Choke-Cherry

Like bitter cherry, this species is one of the seven species of Prunus in California.

It is an erect deciduous shrub, 3 to 12 feet tall, that is widely distributed throughout the mountains of California (McMinn 1939). Average density, foliar cover,

and height of this species all increased erratically in all density classes from the

beginning of the study in 1967 to its end in 1978 (table 7). At the end of the study,

density ranged from 90 to 262 plants per acre, foliar cover from a trace to 1,962

ft2 per acre, and height from 0.4 to 5.4 feet. The lower number reflects the height

of new recruits entering the medium shrub category. Mean height was statistically lower than counterparts in the high shrub category.

Fremont Silk Tassel

This erect, evergreen shrub, which grows in chaparral and forest areas in most

mountain ranges in California (McMinn 1939), ranges from 4 to 10 feet tall. It

resembles greenleaf manzanita in many ways, except that it has dark green

leaves arranged opposite each other on the stem. No plants were present during

the study in the high density category (table 8). In the medium and low categories, density ranged from 112 to 340 plants per acre in 1967 to 175 to 340 plants

per acre in 1978. Only in the low category was density increasing. Mean foliar

cover in the medium category decreased initially and then increased to 950 ft2

per acre in 1978. It was 750 ft2 per acre in the low category at the beginning and

end of the study. Height increased in both the medium and low categories

throughout the study, and was about 2.8 feet tall in 1978. 

Combined Shrubs

When combined, the seven principal shrub species in this study constituted a

hardy, vigorous, dominant component of the plant community. Initial mean densities of 66,533 plants per acre in the high category and 29,240 plants per acre in

the medium category generally decreased throughout the study and ended with

19,800 and 11,542 plants per acre, respectively (table 9). Density in the low category decreased through 1971 and then increased to more than 8,300 plants per

acre, which was a decrease of 18 percent from the initial value (10,625 plants per

acre). The trend in foliar cover was consistent in all categories: decreasing in

1969 and then steadily increasing through 1978. For the high category, foliar

cover averaged 5,333 ft2 per acre in 1967 and increased 135 percent by the end of

the study in 1978. In the medium category, cover in 1967 was 4,370 ft2 per acre

and in 1978 was 14,184 ft2 per acre for a 225 percent increase. For the low category, cover increased 94 percent to 8,962 ft2 per acre through 1978. Average height

increased over initial values in all categories and by the end of the study ranged

from 2.5 to 2.8 feet.

USDA Forest Service Research Paper PSW-RP-248. 2003. 13
Table 6—Average density, foliar cover, and height of bitter cherry by shrub category, Sugarloaf plantation,

Tahoe National Forest, 1967-1978

Year Category Density Cover Height

plants/acre ft2/acre ft

1967 High 267 a1 83 a 0.7 a

Medium 560 a 400 a 1.0 a

Low 562 a 288 a 1.3 a

Root mse2 1,251 944 0.53

F 0.10 0. 22 0.71

P 0.957 0. 883 0.584

1969 High 267 a T3 a 1.1 a

Medium 540 a 650 a 1.7 a

Low 825 a 688 a 2.1 a

Root mse 1,577 1,615 0.68

F 0.16 0. 30 0.88

P 0.920 0. 827 0.525

1971 High 233 a 267 a 1.2 a

Medium 530 a 1,020 a 1.5 a

Low 900 a 1,350 a 2.3 a

Root mse 1,590 2,674 1.19

F 0.26 0. 19 0.54

P 0.852 0. 900 0.668

1974 High 667 a 333 a 1.5 a

Medium 880 a 1,430 a 1.6 a

Low 1,325 a 1,588 a 2.9 a

Root mse 1,881 3,477 1.04

F 0.17 0. 17 1.19

P 0.916 0. 914 0.391

1978 High 1,783 a 300 a 2.5 a

Medium 960 a 2,050 a 2.3 a

Low 1,562 a 2,000 a 3.3 a

Root mse 2,243 4,086 1.25

F 0.20 0. 27 0.47

P 0.895 0. 847 0.716 

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

significantly according to a Bonferroni test (a= 0.05). 2 Root mse is root mean square error.

3 T equals trace.

14 USDA Forest Service Research Paper PSW-RP-248. 2003.
Table 7—Average density, foliar cover, and height of western choke-cherry by shrub category, Sugarloaf

plantation, Tahoe National Forest, 1967-1978

Year Category Density Cover Height

plants/acre ft2/acre ft

1967 High 83 a1 250 a 2.0 a

Medium 0 a 0 a -

Low 175 a 775 a 2.7 a

Root mse2 256 885 1.06

F 1.36 2. 12 0.33

P 0.284 0. 130 0.667

1969 High 83 a 167 a 2.4 a

Medium 20 a 10 a 2.0 a

Low 200 a 275 a 2.3 a

Root mse 223 360 0.42

F 2.35 1. 82 0.04

P 0.104 0. 175 0.879

1971 High 83 a 417 a 2.8 a

Medium 0 a 0 a -

Low 150 a 688 a 2.2 a

Root mse 160 879 0.49

F 2.05 1.90 14.05

P 0.140 0.162 0.185

1974 High 83 a 583 a 3.2 a

Medium 20 a T3 a 0.2 a

Low 250 a 1,312 a 2.8 a

Root mse 238 1,542 0.28

F 2.05 1. 79 33.80

P 0.139 0. 181 0.126

1978 High 167 a 550 a 5.4 b

Medium 90 a T a 0.4 a

Low 262 a 1,962 a 2.9 a

Root mse 300 2,092 0.49

F 1.46 1. 98 30.31

P 0.256 0. 149 0.010

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

significantly according to a Bonferroni test (a= 0.05). 2 Root mse is root mean square error.

3 T equals trace.

USDA Forest Service Research Paper PSW-RP-248. 2003. 15
Table 8—Average density, foliar cover, and height of Fremont silk tassel by shrub category, Sugarloaf plantation, Tahoe National Forest, 1967-1978

Year Category Density Cover Height

plants/acre ft2/acre ft

1967 High 0 a1 0 a -

Medium 340 a 450 a 1.1 a

Low 112 a 750 a 1.3 a

Root mse2 663 1,018 0.15

F 0.80 1. 92 1.50

P 0.501 0. 160 0.308

1969 High 0 a 0 a -

Medium 340 a 350 a 1.3 a

Low 112 a 500 a 1.3 a

Root mse 662 633 0.27

F 0.80 2. 41 0.02

P 0.501 0. 097 0 .903

1971 High 0 a 0 a -

Medium 340 a 520 a 1.7 a

Low 112 a 1,125 a 1.7 a

Root mse 663 1,159 0.61

F 0.80 2. 97 0.01

P 0.507 0. 056 0.956

1974 High 0 a 0 a -

Medium 340 a 850 a 2.0 a

Low 188 a 50 a 1.8 a

Root mse 671 1,311 0.54

F 0.90 1. 96 0.26

P 0.459 0. 152 0.645

1978 High 0 a 0 a -

Medium 340 a 950 a 2.8 a

Low 175 a 750 a 2.9 a

Root mse 665 1,390 0.59

F 0.79 2. 00 4.17

P 0.516 0. 147 0.136

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

significantly according to a Bonferroni test (a= 0.05). 2 Root mse is root mean square error.

16 USDA Forest Service Research Paper PSW-RP-248. 2003.
USDA Forest Service Research Paper PSW-RP-248. 2003. 17

Table 9—Average density, foliar cover, and height of combined shrubs by shrub category, Sugarloaf plantation, Tahoe National Forest, 1967-1978

Year Category Density Cover Height

plants/acre ft2/acre ft

1967 High 66,533 a1 5,333 a 1.2 a

Medium 29,240 b 4,370 a 0.8 a

Low 10,625 c 4,626 a 1.0 a

Root mse2 10,230 1,018 0.15

F 34.78 1. 92 1.50

P 0.001 0. 160 0.308

1969 High 31,300 a 2,167 a 1.0 a

Medium 14,550 a 2,730 a 0.9 a

Low 7,962 a 2,776 a 1.1 a

Root mse 16,548 633 0.27

F 2.56 2. 41 0.02

P 0.083 0. 097 0.903

1971 High 27,683 a 5,867 a 1.3 a

Medium 14,720 a 6,000 a 1.4 a

Low 7,825 a 6,025 a 1.5 a

Root mse 15,371 1,159 0.61

F 2.21 2. 97 0.01

P 0.118 0. 056 0.956

1974 High 24,150 a 10,000 a 1.8 a

Medium 13,600 a 9,520 a 1.8 a

Low 8,913 a 6,500 a 2.1 a

Root mse 12,285 1,311 0.54

F 2.18 1. 96 0.26

P 0.123 0. 152 0.645

1978 High 19,800 a 12,550 a 2.6 a

Medium 11,542 a 14,184 a 2.5 a

Low 8,347 a 8,962 a 2.8 a

Root mse 8,592 1,390 0.59

F 2.40 2. 00 4.17

P 0.098 0. 147 0.136

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

significantly according to a Bonferroni test (a= 0.05). 2 Root mse is root mean square error.
Ponderosa Pine

Pine seedlings led a precarious existence during most of this study and were

constantly recovering from a host of biotic and abiotic agents. Destructive biological agents were humans, insects and disease; abiotic agents were wind and

snow. Damage by humans was caused by the release spray. An unknown tip

moth killed the tops of ponderosa pine seedlings in 1969, 1970, and 1976.

Damage was confined to small, weak seedlings that were shaded by the surrounding shrubs. Death almost always resulted. Snow mold (Neopeckia colteri

[Pk.] Sacc.) killed several pine seedlings in 1967 and 1968 and damaged others

in 1969. Damage seemed to relate more to the persistent snowdrifts of a cool,

late spring than to a winter with a heavy snow pack. 

Wind in this ridge-top study was strong and pervasive. Its damage took

the form of wind cupping and winterburn. Wind cupping causes a funnelshaped depression in the soil around seedling stems. Normally, when this happens, the depression is small, and little or no damage results. In this study,

however, the depression was so large that many pine seedlings leaned 60

degrees or more (fig. 5). Years 1966 and 1970 were particularly bad for wind

cupping. Most pines eventually recovered, but some developed a crooked bole.

Winterburn takes place when the ground is frozen, water uptake is low, and

strong winds dehydrate the needles, especially in the upper part of the seedling.

This took place in 1969, 1970, and 1974. Its effect was to weaken most of the

seedlings and kill a few of them. Damage from snow took the form of weighting down pine branches and boles to the point that the branches were actually

pulled out of the bole or the boles were either split open or broken off (fig. 6).

Snow damage occurred in the plantation where large drifts were formed. In the

spring, the snow became ice and its weight was tremendous. Many seedlings

were deformed from this damage and some eventually died. This form of damage was prevalent in 1971 and 1978. 

Damage from the aerially applied herbicide was worse the first season after

spraying (1968), and continued for the next 2 years. Not many seedlings died,

but many were deformed. Some lost their tops and others formed a spindleshaped leader with a few twisted needles on top. Most of these tops died. On

many seedlings, a branch turned upward and became a new bole. 

Diary entries noted “seedlings recovering from damage” almost every year.

In 1974, the comment was that “pine seedlings are beginning to look like young

trees” (fig. 7). In 1978 observers noted that “for the first time, the area is beginning to look like a plantation.” This was because the proportion of deformed

pines had lessened dramatically in every shrub density category: 

Pine seedling mortality during the 12-year study by shrub category was high, 7

percent; medium, 16 percent; and low, 9 percent. Overall, mortality was 12 percent, making survival 88 percent. The primary cause of seedling mortality was

injury-related/competition-induced drought. From mid-July to the first rain in

the fall, the soil was dry and its moisture content was at or below the wilting

point. Shrubs often lost most of their leaves and pines all but current-year needles by mid-August. 

18 USDA Forest Service Research Paper PSW-RP-248. 2003.

_____________________________________________

Category 1974 1978

_____________________________________________

- - - - - -percent - - - - -

High 25 7

Medium 24 2

Low 19 3

_____________________________________________
USDA Forest Service Research Paper PSW-RP-248. 2003. 19

Figure 5—Because of wind cupping at the base of the stem, this

pine seedling has a severe lean, May

1970.

Figure 6—Typical snow damage to

a ponderosa pine seedling in the

study area, September 1978.

Figure 7—Now straight and tall,

the pine on the right once had a

damaged stem, August 1974.
20 USDA Forest Service Research Paper PSW-RP-248. 2003.

Figure 8—A contrast in ponderosa pine foliar cover in 1978 (A)

low initial shrub density, and

(B) high initial shrub density. (The

tip of one pine is just to the right of

the man’s shoulder.)

A

B
Average foliar cover of pine seedlings in all three shrub categories increased

steadily throughout the study period (table 10). Values in 1978 by shrub category

were high, 5,933 ft2 per acre; medium, 7,780 ft2 per acre; and low, 12,550 ft2 per

acre. By fall 1974, pine cover in the low shrub category was significantly larger

than that in the high and medium categories. In 1978, foliar cover of pines in the

low shrub category was significantly greater than that of counterparts in the high

category (fig. 8). This relationship is likely to continue (fig. 9). Height also

increased steadily in all categories from 1967 through 1978, when pines in the

high shrub category averaged 5.8 feet tall; those in the medium category, 6.2 feet;

and those in the low category, 8.1 feet tall (table 10). In 1974, pine height in the low

shrub category was significantly greater than that of counterparts in the high

category. This relationship not only is likely to continue, but it also is likely to

accelerate (fig. 10), and to again become statistically significant as it was in 1974.

USDA Forest Service Research Paper PSW-RP-248. 2003. 21

Figure 9—Trend of average foliar

cover in three initial shrub density

categories for ponderosa pine

seedlings, Sugarloaf plantation,

Tahoe National Forest, 1967-1978.

Figure 10—Trend of average stem

height in three initial shrub density

categories for ponderosa pine

seedlings, Sugarloaf plantation,

Tahoe National Forest, 1967-1978.
Discussion and Conclusions

Recovery was an important and ongoing process for almost all the vegetation in

the study area. Pines in particular, and shrubs to a lesser extent, were recovering

from some form of damage almost every year. Even bracken fern was affected.

Wind cupping in 1967 had many ferns lying on their side. Notable was the almost

complete recovery of the vegetation in 1978. Diary records noted the “unbelievable recovery of the pines” and the healthy appearance and vigorous growth of

the shrubs. Indeed, “enormous” seed crops of bitter cherry, choke-cherry, greenleaf manzanita (fig. 11), Fremont silk tassel, and bush chinquapin were noted that

fall.

The overall effect of the October 1967 release spray with the herbicide 2,4,5-

T is best described as marginal. Timing, not the herbicide, was the primary reason for its ineffectiveness. First of all, the shrubs had grown for several years

after the site preparation spray and were large and healthy. Had the release

spray been applied in 1965, when the shrubs were still recovering from the first

spray, the release spray probably would have been more effective. Secondly, the

release spray was applied too late in the fall. Best results generally are attained

when shrubs such as these are actively growing and transpiring (Stewart and

others 1984). At the elevation of the study site, temperatures were becoming

low in October, and most plants were hardened off and in a ready-for-winter

mode. Many had lost at least some of their leaves and bitter cherry had lost all

of its leaves. Although mountain whitethorn was affected most by the spray

and thousands of greenleaf manzanita plants were damaged or killed, the overall effect of spraying on the shrub community was small. For example, before

spraying in 1967, mountain whitethorn constituted about 2 percent of the

total shrub community and retained this proportion in 1970. Greenleaf

manzanita constituted about 93 percent of the community in 1967 and 89

percent in 1970. These proportions, however, are close, but only approximate, because recruitment from the seed bank in the soil took place each

year, especially where mortality was heavy and the ground had become

devoid, or nearly devoid, of vegetation. New shrub seedlings, mostly of

manzanita, emerged by the hundreds. Many died, but those that did live

became established and lowered mortality. 

22

Figure 11—A heavy seed crop on

greenleaf manzanita in the study

area, September 1978.
Most plant species recovered by regrowth from burls or rhizomes plus a

few recruits from seed. Greenleaf manzanita, however, recovered almost entirely by producing new seedlings from dormant seed in the soil. Diary records

noted many new seedlings of this species each year from 1967 through 1972. 

Ecologically, tables 2 through 

9 provide within-species and among-species relationships that suggest trends in early plant succession and the composition of the

future plant community. Greenleaf manzanita was the most abundant species

before the study began and continued to be the most abundant species at the end

of the study. Its early densities in the high shrub category (64,783 plants per acre)

and medium category (26,580 plants per acre) were not sustainable, and density

continued to decline to a more sustainable level (16,583 and 8,980 plants per acre,

respectively) in 1978. The release spray probably did little more than reduce

inevitable mortality. Even with the decline, manzanita density in all categories

was 70 to 84 percent of total shrub density at the end of the study. Foliar cover was

affected by the release spray as well, but that too was inconsequential. In 1978,

foliar cover of manzanita ranged from 73 percent of total shrub cover in the high

category to 27 percent in the low category. At the end of the study, density was

lower, but foliar cover and height were higher. Altogether, greenleaf manzanita

should be both abundant and dominant in the study area for years to come.

Of all the shrub species, bitter cherry was the only one to increase in density, foliar cover, and height in all categories during the study. It was unaffected by

biotic and abiotic agents, as well as the release spray, and showed large increases in cover in the medium and low categories. Western choke-cherry also was

increasing in most categories during the study. It recovered from the release

spray of 1967 and browsing in 1971 and was the tallest shrub in the study.

Fremont silk tassel also recovered from the release spray, and in general was

maintaining its density and foliar cover, and was increasing slightly in height.

All three of these species should be present in the future plant community in the

study area. 

The future of huckleberry oak in the future plant community is not clear.

From the beginning to the end of the study, its density, foliar cover, and height

were generally increasing in the high and medium categories, but cover and

height were decreasing in the low category. Its low average height in all categories (0.9 to 1.6 ft) in 1978 makes it vulnerable to increasing shade from taller

shrubs and pines.

Mountain whitethorn appears to be the least competitive of the shrub

species in the study. Its decreasing density from beginning to end of study in all

three shrub categories and mixed gains and losses in foliar cover suggest that it

will be relegated to only a minor presence in the plant community of the future.

Bush chinquapin is another species with similar trends during the study period,

and it too appears to be in decline. However, its robust height (2.6 to 4.5 feet)

should help it to retain its presence in the plant community of the future.

For combined shrubs, some relationships are noteworthy. Foliar cover, which

is recognized as providing a conservative expression of horizontal development,

was low. At the end of the study, foliar cover ranged from 21 percent in the low

category to 33 percent in the medium category. Crowns of the most abundant

species, greenleaf manzanita, tended to be narrow and skimpy, with bare ground

between them. It is likely on this poor site that shrub roots of manzanita and

other species had larger radii than crowns and that they were present beneath

much of this bare area. Another finding noted in diaries and to some extent in

the data was that where manzanita was abundant and well developed, other

shrub species were less abundant and poorly developed. For example, in the high

category in 1978, shrubs other than manzanita had an average cover value of 8

percent relative to manzanita’s 21 percent; in the low category, however, shrubs

other than manzanita had an average value of 15 percent while manzanita had a

USDA Forest Service Research Paper PSW-RP-248. 2003. 23
cover value of only 6 percent. Indeed, foliar cover of bush chinquapin, bittercherry,

and western choke-cherry was higher in the low category than in the high category at the end of the study.

Not only was foliar cover low, so was average height. Height values of combined shrubs of 2.5 to 2.8 feet in the three shrub categories in 1978 do not accurately portray the amount of competition that the shrubs gave to the pine

seedlings. Although all the shrubs furnish competition, the tallest and widest

ones probably furnish more. In this study, the tallest plants of most shrub species

ranged from 4 to 7 feet (fig. 8B).

“Remarkable” best describes pine survival and recovery from damage.

From 1966 through 1978, 88 percent of pine seedlings in the study survived in 

spite of almost chronic damage by a host of biotic and abiotic agents. Dead tops

and crooked stems were common during the study, but many seedlings turned

a branch upward and it became the new bole. Damage decreased from 23 percent of living trees in 1974 to 4 percent of living trees in 1978. 

By 1974, the effect of competition on pine seedlings was becoming manifest

among the three shrub density categories. Not only were differences among density classes becoming statistically significant (table 10), but trends in foliar cover

and height were strengthening (figures 9 and 10). The slope of the fitted curves

of pine foliar cover and height in the low shrub category in 1978 is greater than

that of the curves in the medium category, indicating that the separation in

growth will continue. The slope of the curve for foliar cover in the medium

shrub category and its separation from the high category indicate that increasingly better growth will accrue to pines in the medium category as well. Plainly,

the lower the amount of competition, the better the growth of ponderosa pine

seedlings. Where the site preparation trials were effective, the competition was

reduced early in the life of the seedlings, and that gave them an advantage that

was maintained throughout the study. 

The future of the pine seedlings in the high shrub category is problematical.

The slope of the curves in figures 9 and 10 indicate an upward trend, but the

photo (fig. 8B) indicates heavy competition and skinny pine stems and narrow

crowns. Tall, skinny stems are typical of pine seedlings striving to remain taller

than the competition. To do so, stem diameter, crown development, and needle

number and length are sacrificed to bolster stem height. This sacrifice is not sustainable, however, and at some point height growth slows, the pine seedlings

become shaded, and soon die. Thus, height alone is a poor indicator of future

pine seedling growth. In a similar study on a poor site (McDonald and Abbott

1997), the already-slow growth rate of pines with heavy competition continued

for another 14 years, and was below minimum acceptable growth standards.

On a harsh, dry site in southwestern Oregon, Hanson (1997) studied the

relationship between various densities of whiteleaf manzanita (Arctostaphylos

viscida C. Parry) and the growth of ponderosa pine seedlings over a 13-year period. His data indicated that the biomass of whiteleaf manzanita expanded each

year from seed during this period and will continue to do so for years to come.

For pine seedlings, he found that the variation in height growth among the several manzanita densities correlated to both timing of departure and degree of

departure from shrub-free conditions. In general, pines growing with manzanita continued to fall behind those without manzanita each year. He postulated

that this trend in growth will continue until the trees reach economic maturity.

Without release, trees growing with manzanita probably will grow slowly or

succumb, leaving a near-continuous manzanita brushfield. 

Vegetation managers never cease to look for “good” plant species that

suppress “bad” species, and thus serve as a biological control. In the case of

woolly nama, it had strong potential to be a good species because it virtually

eliminated the aggressive shrub species. However, it requires full sunlight.

Decline is inevitable as crowns of other vegetation develop and coalesce. Nord

24 USDA Forest Service Research Paper PSW-RP-248. 2003.
and Leiser (1974) noted that woolly nama grew well and formed dense cover

in full sunlight. In this study, milacre subplots that initially had a dense cover

of this species remained free of woody shrubs for the length of the study.

Thus, woolly nama is worth considering as an early, but ephemeral, biological control species. 

Before this study began, the area was a brushfield, and likely would have

remained a brushfield for scores of years. The shrubs were large, well established, and covered the area to the point that access was limited. After site

preparation, the planting of ponderosa pine seedlings, and their recovery

from a release spray and several damaging agents, the area is poised to

become a forest, at least in that area where competition was low. By reestablishing ponderosa pine, an important arborescent component has been

restored to the plant community. 

USDA Forest Service Research Paper PSW-RP-248. 2003. 25

Table 10—Average foliar cover and height of ponderosa pine seedlings by shrub category,

Sugarloaf plantation, Tahoe National Forest, 1967-1978

Year Category Cover Height

ft2/acre ft

1967 High 100 a1 0.9 a

Medium 170 a 1.1 a

Low 312 a 1.1 a

Root mse2 331 0.30

F 0.92 1.08

P 0.451 0.380

1969 High 667 a 1.7 a

Medium 660 a 1.6 a

Low 775 a 2.0 a

Root mse 394 0.48

F 1.78 0.71

P 0.182 0.557

1971 High 1,083 a 2.3 a

Medium 1,280 a 2.4 a

Low 2,162 a 3.0 a

Root mse 997 0.66

F 1.70 2.02

P 0.198 0.144

1974 High 2,300 a 3.4 a

Medium 3,250 a 3.8 ab

Low 5,912 b 4.9 b

Root mse 2,126 1.04

F 3.85 2.66

P 0.025 0.076

1978 High 5,933 a 5.8 a

Medium 7,780 ab 6.2 a

Low 12,550 b 8.1 a

Root mse 3,993 1.84

F 3.70 2.57

P 0.029 0.083

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

do not differ significantly according to a Bonferroni test (a= 0.05). 2 Root mse is root mean square error.
26 USDA Forest Service Research Paper PSW-RP-248. 2003.
References

Aune, Philip S.; Diaz, Nancy; Fiske, John; and others. 1993. Report on silvicultural practices in the

Pacific Northwest and Northern California. Unpublished report on file at Pacific Southwest

Research Station, USDA Forest Service, Redding, CA; 8 p.

Biging, Greg S.; Wensel, Lee C. 1984. Site index equations for young-growth mixed conifers of

northern California. Res. Note 8. Berkeley, CA: Department of Forestry and Resource

Management, University of California; 13 p. 

Bradshaw, K.E. 1962. Vegetation investigation of Sugarloaf site preparation plots, Downieville

Ranger District, Tahoe National Forest. Unpublished report on file at Pacific Southwest

Research Station, USDA Forest Service, Redding, CA. 

Buck, John M.; Baron, Frank J. 1961. Work plan for administrative tests, Tahoe site preparation and

planting project. Unpublished report on file at Pacific Southwest Research Station, USDA

Forest Service, Redding, CA.

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

and Row; 300 p.

Gordon, Donald T. 1979. Successful natural regeneration cutting in California true firs. Res. Paper

PSW-140. Berkeley, CA: Pacific Southwest Forest and Range Experiment Station, Forest Service,

U.S. Department of Agriculture; 14 p.

Hanson, Thomas J. 1997. Growth of plantation conifers and whiteleaf manzanita in southwest

Oregon. Corvallis: Oregon State University; 210 p. Ph.D. dissertation.

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

California Press; 1400 p.

Hungerford, Roger D. 1986. Predicting response of understory vegetation to stand treatment: consequences for multiresource management. In: Proceedings of a workshop on management of

small-stem stands of lodgepole pine; 1986 June 20- July 2; Fairmont Hot Springs, MT. 118-136.

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.

McDonald, Philip M. 1966. Brushfield reclamation: second-year results from a study of reforestation with ponderosa pine are encouraging. Res. Note PSW-118. Berkeley, CA: Pacific Southwest

Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture; 8 p.

McDonald, Philip M. 1999. Diversity, density, and development of early vegetation in a small

clear-cut environment. Res. Paper PSW-RP-239. Albany, CA: Pacific Southwest Research Station,

Forest Service, U.S. Department of Agriculture; 22 p.

McDonald, Philip M.; Abbott, Celeste S. 1997. Vegetation trends in a 31-year-old ponderosa pine

plantation: effect of different shrub densities. Res. Paper PSW-RP-231. Albany, CA: Pacific

Southwest Research Station, Forest Service, U.S. Department of Agriculture; 35 p.

McDonald, Philip M.; Fiddler, Gary 0.; Meyer, Peter W. 1996. Vegetation trends in a young conifer

plantation after grazing, grubbing, and chemical release. Res. Paper PSW-RP-228. Albany,

CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; 17 p.

McDonald, Philip M.; Oliver, William W. 1984. Woody shrubs retard growth of ponderosa pine

seedlings and saplings. In: Proceedings of the 5th annual forest vegetation management conference; 1983 November 2-3; Sacramento, CA. Redding, CA: Forest Vegetation Management

Conference; 65-89. 

McMinn, Howard E. 1939. An illustrated manual of California shrubs. San Francisco: J.W. Stacey

Inc.; 689 p.

Miles, Scott R.; Goudey, Charles B. 1997. Ecological subregions of California. RS-EM-TP-005. San

Francisco: Pacific Southwest Region, Forest Service, U.S. Department of Agriculture.

Nord, Eamor C.; Leiser, Andrew T. 1974. Woolly nama. In: Schopmeyer, C.S., tech. ed. Seeds of

woody plants in the United States. Agric. Handb. 450. Washington, DC: US. Department of

Agriculture; 551-552.

O’Hara, Kevin L.; Seymour, Robert S.; Tesch, Steven D.; Guldin, James M. 1994. Silviculture and our

changing profession. Leadership for shifting paradigms. Journal of Forestry 92(1): 8-13.

Pavlik, Bruce M.; Muick, Pamela C.; Johnson, Sharon; Popper, Marjorie. 1991. Oaks of California.

Los Olivos, CA: Cachuma Press Inc.; 184 p.

Rietveld, W.J. 1992. Conservation forestry: an idea whose time has come, again. Tree Planters’

Notes 43(3). Summer.

USDA Forest Service Research Paper PSW-RP-248. 2003. 27
SAS Institute, Inc. 1988. SAS procedures guide, release 6.03 edition. Cary, NC: SAS Institute, Inc. 

Stewart R.E.; Gross, L.L.; Honkala, B.H. 1984. Effects of competing vegetation on forest trees: a bibliography with abstracts. Gen. Tech. Rep. W0-43. Washington, DC: Forest Service, U.S.

Department of Agriculture.

Wagner, Robert G.; Zasada, John C. 1991. Integrating plant autecology and silvicultural activities

to prevent forest vegetation management problems. The Forest Chronicle 67(5): 506-513.

28 USDA Forest Service Research Paper PSW-RP-248. 2003.
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Research PaperPSW-RP-248

Development of a Mixed-Shrub–Planted Ponderosa Pine

Community on a Poor Site After Site Preparation and Release