United States

Department 

of Agriculture

Forest Service

Pacific Southwest

Research Station

General Technical Paper

PSW-GTR-190

Ecology and Manipulation of Bearclover

(Chamaebatia foliolosa) in Northern and

Central California:The Status of Our

Knowledge

Philip M. McDonald Gary O. Fiddler Donald A. Potter
Abstract 

 McDonald, Philip M.; Fiddler, Gary O.; Potter, Donald A. 2004. Ecology and manipulation of bearclover (Chamaebatia foliolosa) in northern and central California: The 

status of our knowledge. Gen. Tech. Rep. PSW-GTR-190. Albany, CA: Pacific Southwest 

Research Station, Forest Service, U.S. Department of Agriculture; 26 p.

Long the bane of foresters, but of interest to ecologists, bearclover inhabits thousands of 

acres of forest land in northern and central California. Little quantification of its recovery 

after disturbance is available because knowledge on the morphology of flowers, seeds, 

and rhizomes is fragmented, and physiological processes, especially plant moisture and 

photosynthetic relationships, are unknown. Consequently, most of the dozens of treatments 

that have been tried to manipulate bearclover have failed. Bearclover’s rhizomes efficiently 

gather soil moisture and together with high rates of photosynthesis promote rapid growth 

and site capture. Using all available water limits species richness, and the plant community in established stands is limited to a few hardy species. Above-ground stem density of 

bearclover also is high. Because of nearly total site capture both above and below ground, 

successful long-term manipulation of bearclover is limited. The most effective treatments 

are those that kill bearclover rhizomes, and herbicides such as Roundup and Velpar are 

effective. In local environments, treatments such as the winged subsoiler and perhaps 

repeated fire at the time of flowering may prove to be effective. However, no treatment 

completely eliminates bearclover, and it persists as part of the plant community.

Retrieval Terms: bearclover, morphology, plant community, species development, vegetation 

management

The Authors

Philip M. McDonald was, until his retirement, a Research Forester with the Pacific Southwest Research Station’s Western Forest Management Unit, 2400 Washington Avenue, 

Redding, CA 96001: e-mail: pmcdonald@fs.fed.us. Gary O. Fiddler is a silviculturist with 

the Ecosystem Conservation Staff, Pacific Southwest Region, USDA Forest Service, San 

Francisco, and stationed at Redding, CA. Donald A. Potter is a zone ecologist with the Stanislaus National Forest, USDA Forest Service, Sonora, CA 95370: e-mail: dpotter@fs.fed.us.

Pacific Southwest Research Station

Forest Service

U.S. Department of Agriculture

Publisher

Albany, California

Mailing address:

PO Box 245, Berkeley CA 

94701-0245

(510) 559-6300

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

March 2004
USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. i

Ecology and Manipulation of Bearclover 

(Chamaebatia foliolosa) in Northern and 

Central California: The Status of Our 

Knowledge

Philip M. McDonald Gary O. Fiddler Donald A. Potter

Contents

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

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

Location and Site Characteristics ........................................................................1

Ecology .....................................................................................................................4

Morphology......................................................................................................4

Physiology........................................................................................................6

Plant Diversity .................................................................................................7

Plant Development..........................................................................................8

Manipulation ..........................................................................................................8

Manual..............................................................................................................9

Mulching...........................................................................................................9

Mechanical .....................................................................................................10

Burning ...........................................................................................................13

Herbicides.......................................................................................................15

Cost..................................................................................................................20

Discussion and Conclusions ..............................................................................20

References..............................................................................................................25

Pacific Southwest 

Research Station

USDA Forest Service

General Technical Paper

PSW-GTR-190

March 2004
i

i USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 

In Brief. . .

McDonald, Philip M.; Fiddler, Gary O.; Potter, Donald A. 2002. Ecology and ma-

nipulation of bearclover (Chamaebatia foliolosa) in northern and central 

California: The status of our knowledge. Gen. Tech. Rep. PSW-GTR-190. 

Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Depart-

ment of Agriculture: 26 p.

Retrieval Terms: bearclover, morphology, plant community, species development, 

vegetation management

Bearclover, which is a widespread and well-adapted shrub in the northern and 

central Sierra Nevada and southern Cascades of California, is an enigma to ecolo-

gists and foresters. It produces an abundance of flowers, which presumably lead 

to seed, but very few seedlings have been observed. Its rhizomes, which extend 

the species over the landscape, seem to grow rapidly in some environments but 

not in others. Disturbance seems to aid the spread of rhizomes, but bearclover 

on the edges of plots treated with a variety of herbicides has not expanded for a 

decade or more. Bearclover fixes nitrogen, which should benefit conifer seedlings, 

but most die when this shrub is nearby.

Answers to these perplexing enigmas, plus a chronological history of the 

many vegetation management techniques that have been attempted to manipulate 

bearclover, comprise the bulk of this paper. Understanding the functions of the 

various plant organs and internal physiological processes helps to explain why 

some manipulative treatments have failed and others have succeeded.

The morphology and physiology of bearclover combine to enable it to out-

grow most other plant species and to capture a site. In the spring, the dense mass 

of rhizomes efficiently gathers moisture, and the plant uses it to attain maximum 

photosynthesis and early growth. In midsummer, when soil moisture is low, bear-

clover plants endure high internal moisture stress, reduced photosynthesis, and 

low growth rates. The strategy of maximizing early growth, using all available 

soil moisture, and then withstanding the environmental stress of summer and fall 

denies soil moisture to competing plants, including conifer seedlings, and helps 

to ensure their absence.

Because of bearclover’s long and consistent record of endangering young 

conifer plantations, silviculturists have applied a large number and variety of 

treatments to manipulate it both for site preparation and for plantation release. 

These include manual methods (hand grubbing), mulching (sheets of plywood, 

paper/fiberglass/asphalt sandwiches, black plastic, polypropylene), mechanical 

techniques (rotary mowers, dynamite, disking, plowing, ripping, subsoiling, ter-

racing), burning (different dates and intensities), and herbicides (2,4-D; 2,4,5-T; 

Roundup; Garlon; Hexazinone; and others). Many combinations of the above 

also were attempted. Some treatments were outright failures; most provided a 

short-term increase in conifer seedling survival, but not growth; and a few were 

effective. Those that were effective enhanced not only survival, but also seedling 

stem and crown growth. Many treatments looked promising at first, but too often 

bearclover reinvaded and the conifer seedlings stopped growing and died after 

a few years.

Because the below-ground reproductive system of bearclover is extensive, 

deep in the soil, and primed for regrowth, it is not enough to simply damage it. 

Most of the roots and rhizomes have to be killed. Because selective herbicides do 

this, they appear to be the primary means for manipulating bearclover. Reducing 

bearclover density allows enough time for conifer seedlings to survive, grow at an 

acceptable rate, and become trees. However, even the most effective herbicides do 

not completely eliminate bearclover, and it remains on the site, albeit at a lower 

density, contributing to the diversity of the plant community. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 1

Introduction

In this age of ecosystem management, every plant species has value as an integral 

component of an ecosystem, as sustenance for animals, or even as a provider of 

medicines or food for humans. To fully practice their art, ecosystem managers are 

going to need information—lots of information—on every plant species in their 

area of responsibility. Because detailed information on many, indeed most, plant 

species is absent or widely scattered, this will be a huge job. This paper on bearclover (Chamaebatia foliolosa Benth) (fig. 1) is a start.

Bearclover, which is a member of the family Rosaceae, is a perennial evergreen 

shrub that is endemic to northern and central California. Its two other common 

names, bearmat and mountain misery, are often found in the literature. Bearclover 

has long been regarded as a strong competitor to natural and planted conifer seedlings, and most of the work on it has been done in an attempt to increase survival 

and growth of these seedlings.

Unfortunately, research on the ecology and manipulation of this shrub is scant 

and information is fragmented. Most information was anecdotal or from small 

unreplicated studies. Later larger, more detailed studies were installed, and results from them are becoming available. Nevertheless, most of the work has been 

concentrated at a few locations where the trials have been case histories. If there 

is a strength, it is that most of the major components of bearclover morphology, 

physiology, and manipulation have been examined, albeit not in depth. Thus, the 

silvicultural concepts and principles presented in this paper have support, but the 

data are site-specific in many instances.

The objectives of this paper are to bring together available ecological and 

silvicultural information on bearclover and specifically to show how the species’ 

external organs and internal processes make it a formidable competitor to other 

plant species. A related objective is to translate this knowledge into methods and 

techniques that can be used to manipulate the development and density of bearclover to accomplish the establishment of more desirable species.

Location and Site Characteristics

Bearclover is prevalent on south- and west-facing slopes at elevations between 

1,000 and 6,000 feet in the Sierra Nevada of California and, to a lesser extent, on 

Figure l—A 4-year-old patch 

of bearclover with typical fernlike foliage and showy flowers.
2 USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 

lower slopes in the southern Cascade Range (Hickman 1993, Little 1979). This 

shrub is capable of occupying almost all aspects, site qualities, and soil types 

within its natural range (Potter 1976). However, it is less common on north and 

east aspects, mostly because conifer and hardwood stands are more dense on these 

aspects and more fully occupy the sites. With the exception of isolated stands near 

Burney in Shasta County, near Greenville in Plumas County, and in Kern County 

in southern California, most stands of bearclover are located between Yuba and 

Tulare Counties in the Sierra Nevada (fig. 2) (Potter 1976). 

This shrub develops best in partial shade but grows well in a sunlit environment. In shady environments, it has sparser foliage and taller stems. Overall, it is 

a remarkably persistent species and, once established, maintains its presence for 

long periods of time.

Bearclover occupies areas that range from small patches to hundreds of acres 

and, in places, forms almost pure stands (fig. 3). Individual bearclover plants are 

short in comparison to associated shrub species, and rarely do plants exceed 1.5 

feet in height. Disturbance, such as that from fire or logging, aids the species by 

removing taller trees and shrubs, thus providing additional site resources.

Challenge

Chaix

Gold Note

Penmoke

Stanislaus

100 50 0 100 Miles

Legend

BEAR CLOVER

COUNTIES

Figure 2—Schematic of bearclover natural range and study areas.
USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 3

Because of its broad elevational range and ability to develop well in a wide 

range of environments, vegetative associates are numerous. The most common 

tree associates are ponderosa pine (Pinus ponderosa Dougl. ex Laws. var. ponderosa), 

incense-cedar (Libocedrus decurrens Torr.), and California black oak (Quercus kelloggii Newb.), followed by interior Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco 

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

sugar pine (Pinus lambertiana Dougl.). Common shrubs include those in the genera 

Arctostaphylos, Ceanothus, Chrysothamnus, Rhamnus, Ribes, Rubus, and Toxicodendron. Abundant annual and perennial herbaceous plants are of the genera Cirsium, 

Epilobium, Eriophyllum, Galium, Lotus, Madia, Potentilla, Vicia, and Viola. Grasses 

tend to be common associates of bearclover, and some of the most abundant species are in the genera Bromus, Elymus, and Festuca. Introduced cheatgrass (Bromus 

tectorum L.) often invades recently disturbed stands of bearclover. 

This shrub appears to be virtually immune from attack by insects and disease; 

drought, heat, frost, and other abiotic agents rarely kill the plant. Seeds and leaves 

are beneficial to wildlife. Potter (19911) placed numerous seeds on a board in the 

forest and left them exposed overnight. All had disappeared by morning; rodents 

were the likely culprits. Browsing by deer has been observed, particularly in the 

spring or after a recent burn when tender new growth is available (Adams 1969, 

Gibbens and Schultz 1963). Additional attributes are erosion control, use as a medicine by Native Americans (Anderson 1997), and as a source of dark, tasty honey.

Information and data for this paper have been gathered from numerous 

sources throughout the range of the species and from four recent studies. These 

studies are entitled Chaix, Challenge, Gold Note, and Penmoke. All were located in 

northern and central California in the Sierra Nevada Range. They were established 

in clearcuttings that had been created by timber harvest and site preparation. 

Site preparation involved removing the unmerchantable conifer and hardwood 

trees, as well as logging slash and shrub clumps, with a bulldozer and piling this 

material into windrows for eventual burning. The study areas were located at 

moderate elevations, on medium slopes, with average or above site quality, and 

plentiful rainfall (table 1). Gold Note (McDonald and Fiddler 1999) and Penmoke 

(McDonald and Everest 1996) had substantial bearclover populations, and Chaix 

(McDonald and others 1999) and Challenge (McDonald 1999) had more diverse 

plant communities not dominated by bearclover.

Figure 3—A mature bearclover stand in partial shade. Note 

the high density of bearclover 

and the lack of other plant 

species.

1

Unpublished data on file at 

the Stanislaus National Forest, 

Sonora, Calif.
4 USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 

The Chaix, Gold Note, and Penmoke study areas had three to six replications, 

including a control, and all had planted ponderosa pine seedlings growing in 

them. The Challenge study area differed from the others in that it was not replicated and had natural pine regeneration. In each replication, there were at least 

five permanent milacre (0.001 acre) plots on which vegetation was periodically 

measured. Because individual bearclover “plants” were impossible to determine, 

stems were carefully counted on each plot and presented as a per-acre value. Foliar cover was estimated to the nearest square foot, recorded as a per-acre value, 

and then converted to a percentage. If less than 0.5 square foot, foliar cover was 

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

stems on a sample plot. One factor common to all areas where bearclover is found 

is the Mediterranean climate, which is characterized by long, hot, dry summers 

and cool, wet winters. May through September often are rainless. In this climate, 

almost all plant species have adopted a strategy to grow as fast as they can as soon 

as they can, and to set seed before the onset of summer drought.

Ecology

Morphology

Extensive literature and numerous observations describe the propensity of bearclover to produce abundant flowers almost every year. The flowers are white to 

cream colored, small, and showy, suggesting that insects are the primary pollinators. At the Challenge Experimental Forest in north-central California, time of 

flowering for bearclover was recorded in 1976 and 1979 at 2-week intervals. This 

highly productive site is located at the 2,750-foot elevation. Flowers were first produced from May 7 to May 25 and last produced from September 10 to September 

15 (McDonald 19802). However, one or two plants were still flowering in early 

November. In partial shade on the Stanislaus National Forest in central California, 

again on a highly productive site, peak flowering occurred from May 26 to June 12, 

1989, and within a week of these dates for the next 2 years (Weatherspoon 1989).

Thousands, if not millions, of seed are produced, but bearclover seedlings are 

rarely seen. After many hours of searching on hands and knees, no seedlings were 

found on study plots in clearcuttings in several study areas in northern California. 

However, in another study in central California, where bearclover was growing 

beneath a partial overstory of ponderosa pines, more than 50 new bearclover 

seedlings were found at three locations over a 3-year period (Everest 1996). The 

seedlings were present in both burned and unburned plots during March through 

June, and many were beneath mature bearclover plants. Seedlings were 0.5 to 1.5 

inches tall, and some still had the remains (cotyledons) of the seeds attached (fig. 

4). Sixteen of these seedlings were flagged in 1996 and searched for in September 

2001. No trace of any seedling was found, and competition from the mature plants 

was the likely cause of mortality. 

Table 1—Physical characteristics of study areas in the northern and central Sierra Nevada of 

California

Study Site quality Slope Elevation Average annual

 precipitation

pct ft inches

Chaix High 23 3,700 50

Challenge High 20 2,750 68

Gold Note High 20 4,000 40

Penmoke Medium 15 5,000 55

2 Unpublished data on file, Pacific 

Southwest Research Station, 

Redding, Calif.
USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 5

Reigel (l991) germinated bearclover seed in a greenhouse and found 93 percent germination. After 6 months, survival was described as high. The growth 

pattern of bearclover seedlings (from seed) is to initially form a taproot and then 

to produce lateral rootlets. Tappeiner (1989) collected seed from mature bearclover 

plants in central California and grew seedlings in the laboratory. Rhizomes were 

not produced during the first 3 years. 

In 1978, Potter3 tested the sprouting ability of severed pieces of bearclover. He 

built wooden boxes, filled them with soil, screened them to be sure no bearclover 

was present, and then buried pieces of living bearclover roots and rhizomes in 

them. Many pieces sprouted at the nodes and turned the soil surface in the boxes 

“green.” On the Eldorado National Forest, Lyons (1913) noted that bearclover 

seedlings grow from 3 to 5 inches tall the first season, then branch out, and grow 

very slowly in height thereafter. For immature plants, stem elongation is rapid 

in the spring, with most growth accomplished while soil moisture is present. For 

mature plants, height growth virtually ceases, and crown expansion is lateral, provided that space is available. Many plant stems die after age 12 and are replaced 

by new shoots from the root crown. On the Stanislaus National Forest, Wulff 

(1914) counted rings on bearclover stems and found their age to vary between 9 

and 18 years.

Bearclover produces new leaves each year, retains its old leaves for about 2 

months, and then sheds them (Rundel and others 1981). Thus the stem is always 

clothed. Leaves are heavily scented, glandular, and have a fern-like structure. 

They are produced on short flexible stems that arise from below-ground organs. 

The glandular secretion has been described as highly resinous, hydrophobic, 

and amounting to about 140 pounds per acre in a medium density stand (Fredrickson 1994). Large numbers of stems (up to 104 per square foot; Munns 1922), 

relatively high volume (5,316 ft3/acre at age 4; Lanini 1981), and rapid growth 

(6 to 8 inches the first year after disturbance) virtually exclude colonization by 

other plant species. 

The root system consists of an extensive network of rhizomes 4 to 16 inches 

below the soil surface and taproots that often extend to depths of 6 feet or more 

(Potter 1976). Fredrickson (1994) dug trenches through bearclover stands and 

mapped rhizomes on the sidewall. He found that most rhizomes were located 

in the surface 12 inches of soil with statistically fewer in the 12- to18-inch strata. 

Munns (1922) excavated part of a bearclover root system and sketched the density 

and distribution of the roots (fig. 5). Lateral extension of rhizomes from mature 

Figure 4—Tiny just-emerged 

bearclover seedlings with cotyledons still attached. Distance 

from the base of the cotyledon 

to top of most developed plant 

is 1 inch.

3

Unpublished data on file at 

the Stanislaus National Forest, 

Sonora, Calif. 
6 USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 

plants in undisturbed areas is reported in general as slow (Coombes and McHenry 

1984, Potter 1976), but rapid after disturbance, especially burning (Rundel and others 1981). Several investigators (Fredrickson 1994, McDonald and Fiddler 1999, for 

example) have noted that sprouting, which occurred in disturbed areas, stopped 

abruptly at the edge of the treated zone. But whether slow or rapid, extension over 

time is impressive. One rhizome in a previous study was traced horizontally for 

almost 90 feet (Munns 1922).

To study rhizome elongation, two 10-foot-long permanent transects with 11 

evenly spaced metal pins were installed in a clearcutting in central California in 

fall 1986 (McDonald and Fiddler 1999). Logging slash, unmerchantable trees, and 

shrubs had been pushed into windrows and burned. Both transects were located 

in the middle of an area of bare ground with a patch of bearclover at least 3 feet 

away. On one transect the bearclover grew uphill toward the transect; on the other, 

downhill. The slope was about 12 percent. After each growing season, a pin was 

placed on the bearclover stem nearest the corresponding metal pin on the transect. 

The 11 distances from transect pin to pin were averaged each season to arrive at 

the amount of annual rhizome elongation.

After three successive growing seasons, bearclover rhizome extension, as denoted by above-ground stems, was 29.7 inches if growing uphill and 9.6 inches if 

extending downhill. Growth was best the second year and virtually nonexistent 

the third growing season. During the fourth season, tiny new bearclover plants 

appeared within the bare area. Pulling on them revealed that they originated from 

deep in the soil, apparently from structures deeper than the rhizomes whose elongation we were quantifying. The study ended at this point. Fredrickson (1994) 

also noted the propensity of bearclover to sprout in the centers of disturbed areas, 

presumably from underground roots.

Physiology

Near Nevada City in the north central Sierra Nevada, Lanini (1981) measured 

internal moisture (xylem sap tension) and photosynthesis of bearclover from June 

through October 1979. Xylem sap tension increased from about -1.5 MPa in June 

to -4.0 MPa in September (MPa = megapascals; 1 = 10 bars), indicating the plants’ 

capability to withstand very high levels of moisture stress. Relative to other shrub 

species in the plant community (manzanita, ceanothus), bearclover had the highest internal moisture stress of any species, and these values occurred earlier in the 

growing season. As xylem sap tension increased, photosynthesis decreased from 

27 to about 7 mg of CO2 per dm2 per hr. Thus, bearclover apparently uses much 

of the available soil moisture early in the spring to attain a maximum amount of 

photosynthesis at the expense of reduced photosynthesis and growth later in the 

Figure 5—Typical rhizome/

root system of bearclover 

(Munz 1922).
USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004.

7

season. Ramifications of this relationship are twofold: (1) the species apparently 

has efficient stomatal control, and (2) bearclover causes rapid soil depletion that 

limits the amount of moisture available to other species.

Tappeiner and Radosevich (1982) also studied soil moisture in the same gen-

eral area and emphasized that high pre-dawn xylem sap tension was found for 

bearclover as the season progressed from spring through summer, thus indicating 

a rapid depletion of available soil moisture.

Two other competitive mechanisms involving physiology include the pro-

duction of nodules on fine roots that are probably active nitrogen fixers, and 

allelopathy, or the ability of one plant species to inhibit the development of a plant 

part or interfere with a metabolic process in another species.

Heisey and others (1980) found direct evidence of nitrogen fixation on nodu-

lated bearclover plants in an area with little organic matter on the soil surface 

because of an intense forest fire a decade earlier. No nodulation was found in an 

undisturbed area nearby that had a deep organic layer. They noted that nodulation 

was uncommon on nonleguminous plants, especially among the Rosaceae (which 

includes bearclover). Furthermore, in cross-section, the nodules were strikingly 

similar to those of snowbrush (Ceanothus velutinus Hook., family Rhamnaceae) 

(Furman 1959) and to those of deerbrush (Ceanothus integerrimus Hook.& Arn.) 

(Newcomb and Heisey 1984)—two common associates of bearclover.

In a relatively pure stand at the 5,300-foot elevation in Sequoia National Park 

in central California, Rundel and others (1981) evaluated the effect of seasonal 

burning on the productivity and nutritional response of bearclover. They found 

that the burning of above-ground biomass and litter produced large deposits of 

nutrient-rich ash on the soil surface that was rapidly mineralized into the upper 

soil horizon. Although nitrogen and phosphorus were lost due to volatilization, 

the net above-ground uptake immediately following the spring burn was nearly 

three times greater than for the adjacent unburned control over the same period.

Allelopathy has been noted visually in the field (Potter 1976) and in the labo-

ratory (Powers 1972). In the latter study, viable seeds of four conifer species were 

sown in intact layers of soil and organic matter carefully gathered from beneath 

pure bearclover stands. The intact layers were brought into the laboratory and 

maintained in a controlled atmosphere. Analyses of conifer seed germination and 

root length suggested that chemical growth inhibitors were produced by the foli-

age of bearclover.

Plant Diversity

After disturbance, such as from fire or site preparation, species composition of 

the bearclover community tends to be highly variable. Some species arise from 

root crowns or rhizomes, some from windblown seeds, and still others from dor-

mant seeds in the soil (Grime 1979). The distribution of plant species ranges from 

clumpy for some species to random for others. Number of species depends on 

several factors, including the degree of disturbance, time since disturbance, avail-

ability of invading propagules, and rapidity of colonization by early invaders. 

Herbaceous species often contribute most to species richness just after disturbance. 

However, because bearclover recovers rapidly from disturbance and tends to form 

dense stands, its very presence tends to lower species richness quickly. Invading 

species are often relegated to bare areas among bearclover clones. However, a few 

species such as bull thistle (Cirsium vulgare [Savi] Ten.) and death camas (Zigadenus 

exaltatus Eastw.) grow well in bearclover stands apparently because of the ability 

to grow tall early in the season (McDonald and Everest 1996).

For the four recent studies, the number of plant species was recorded for four 

to eleven growing seasons after disturbance (table 2). Species numbers ranged from 

13 at Gold Note to 62 at Challenge. Where bearclover is the dominant species, at 

least in terms of density and foliar cover, the number of species tends to be low 
8 USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 

initially and to remain low. For example, both density and foliar cover were high at 

Gold Note, and number of species after the first growing season was 12 and after 

eleven seasons was 13. A likely reason is that bearclover dominated below-ground 

after site preparation and dominated both above- and below-ground shortly after. 

Other species could not compete.

Plant Development

Data from the four recent studies noted earlier portray developmental trends 

in bearclover density, foliar cover, and height. Initial bearclover density values 

(reported one to three growing seasons after site preparation) ranged from an 

average of 630 stems per acre at Challenge to 152,200 per acre at Gold Note (table 

3). Ending values ranged from 2,267 stems per acre at Challenge to 282,000 per 

acre at Penmoke. Initial foliar cover ranged from a trace at Challenge to 20 percent 

at Gold Note. Ending values spanned the range of 1 percent at Challenge to 63 

percent at Penmoke. Of interest is that foliar cover at Gold Note increased from 20 

percent to 57 percent after five growing seasons and then decreased to 36 percent 

after 11 seasons. The decline probably can be attributed to competition from the 

ponderosa pine seedlings. Bearclover height averaged about 0.6 foot initially on 

all study areas and ranged from 0.6 to 1.4 feet by the end of the studies.

Manipulation

Foresters began studying bearclover in California in 1911 (Munns 1922). Early 

studies, usually in areas having natural conifer regeneration (Tappeiner and Helms 

1971 for example), detailed the capability of bearclover to recover rapidly from 

natural disturbance and to restrict the establishment of conifer seedlings. Observers noted that conifer seeds often were caught in the dense foliage of bearclover 

crowns and never reached the ground. Those that did reach the ground had difficulty penetrating the deep litter layer. Once in mineral soil, competition for site 

resources among the mass of bearclover roots was fierce. Rarely could conifer 

seedlings become established, and for those that did, growth was poor. Death 

almost always was ascribed to competition-induced drought.

Planted conifer seedlings often fared no better, and as noted by Potter (1985) 

survival often was less than 20 percent where bearclover was the primary competitor. Height growth almost universally was described as inadequate. Foresters 

often were surprised how fast bearclover recovered after fire or disturbance. Areas 

that were visually devoid of bearclover turned green after a few months. Worse, 

ineffective treatments that provided only temporary or partial control actually 

rejuvenated bearclover and increased its potential to dominate. For example, Tappeiner and Radosevich (1982) concluded that after 19 years, bearclover appeared 

to be more dense and vigorous on plots sprayed with a mixture of herbicides than 

on those receiving no treatment.

Over the past 65 years, an amazing variety of treatments has been employed to 

control bearclover in young conifer plantations. Herbicides were suspended by the 

Table 2—Number of species by vegetation category after various numbers of growing seasons, northern and 

central California, 1980-1996

Study Growing Conifers Hardwoods Shrubs1 Forbs Graminoids Fern Total

area seasons

Chaix 6 1 4 8 41 6 1 61

Challenge 5 3 2 12 38 6 1 62

Gold Note 11 1 0 5 4 3 0 13

Penmoke 4 3 2 4 5 4 1 19

1

Includes bearclover
USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 9

USDA Forest Service in March 1984 in response to Federal court rulings (Click and 

others 1989). This moratorium was lifted in January 1991, but during the 7-year 

interval, the variety of treatments used by vegetation managers increased even 

more. Most of these were performed “to buy time” for planted conifer seedlings 

until better techniques became available.

Techniques for manipulating bearclover are placed in five categories: manual, 

mulching, mechanical, burning, and herbicides. Sometimes two or more categories were involved. These combinations are presented in the category having the 

last treatment.

Manual

Manual techniques generally are those that are performed by hand. They can be 

used in both site preparation and plantation release, but most often are used in 

release. Techniques include grubbing small plants with hand tools, or severing 

larger plants with power tools. Both operations can be done one or more times. 

Steepness of slope is not a limiting factor.

On the Stanislaus National Forest, Potter (1985) reported that several attempts 

had been made to hand-grub bearclover in plantations including a 4-foot circle 

around individual conifer seedlings. Within a year, new sprouts occupied nearly 

100 percent of the grubbed area. On the Eldorado National Forest, Parsons (1991) 

observed that “lots of manual release is being performed here.” Like so many 

other trials when only the above-ground portion of bearclover was removed, the 

treatment appeared to be effective at first, but soon failed. Click and others (1994) 

recommended that manual release not be done “even as a last resort.”

Mulching

The first attempt to control bearclover with mulches took place in Eldorado 

County in the late 1950s and early 1960s (Potter 1985). Large (4- by 8-foot) sheets 

of plywood were laid over existing bearclover plants. One year later the bearclover 

was dead aboveground and soil moisture had increased beneath the plywood. 

The plywood was then removed, and a few years later the area was again covered 

with bearclover. More trials with different mulches took place in the early 1980s in 

Stanislaus County. Newspapers, black plastic in 4- by 8-foot segments, and heavy 

Table 3—Average density, foliar cover, and height of bearclover on four study areas in northern and 

central California, 1976-1996

Study area Year Density Foliar cover Height

Mean SE1 Mean SE Mean SE

Number/acre pct ft 

Chaix 1992 28,067 8,156 11 3 0.6 0.1

1995 45,625 8,803 10 2 0.6 0.1

Challenge 1976 630 73 T2 - 0.5 0.1

1980 2,267 301 1 - 0.7 0.1

Gold Note 1986 152,200 38,504 20 3 0.6 0.1

1990 152,333 32,119 57 3 0.8 0.1

1996 117,200 21,803 36 3 1.4 0.1

Penmoke 1991 - - - - - -

1994 282,000 85,000 63 26 1. 2 0.2

1

SE = Standard error

2

T = Trace
10 USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 

kraft paper/fiberglass/asphalt sandwiches were tried, but all were expensive to 

install and maintain. These materials also broke down rapidly and were subject 

to tearing by sharp stems, cattle, and deer.

Another mulching study took place in Eldorado County in 1991 on land that 

was occupied by bearclover and scattered ponderosa pines (McDonald and Everest 1996) and then logged and broadcast-burned. Mulches were made of woven 

black polypropylene, 5 feet square (fig. 6), and applied around planted ponderosa 

pine seedlings and over bearclover stubs soon after the burn. Each mulch was 

held in place with nine 8-inch, flat-headed U-shaped pins. Several mulches were 

lifted in September 1994 and rhizome development examined to shovel depth (8 

inches). The soil was bone-dry. Living rhizomes were numerous in the soil beneath 

the mulches. No new roots had developed at rhizome nodes, however. Where 

above-ground stems had burned, a new white horizontal rhizome was present 

at the nearest node on some plants. Occasionally, this rhizome gave rise to a new 

plant at the slit where the pine seedling came through the mulch. Just beneath the 

mulches were rhizomes with chlorotic leaves that had obviously been pushing 

against the mulches. These were dying from heat conducted from the mulch to 

them. The combination of burning and mulching was judged as ineffective because the rhizomes were still present and competitive belowground, and the pine 

seedlings were obviously stressed and growing poorly.

Mechanical

As its name implies, this treatment involves the use of techniques or large machines that either scrape off undesired plants above ground or gouge them out 

or tear up their roots or rhizomes below ground. Mowing, dynamiting, disking, 

plowing, subsoiling, and terracing have all been attempted to lessen the competitiveness of bearclover. Most have been used in site preparation, and several have 

been employed many times in a variety of soils and slopes. Foresters reasoned that 

they could reduce much of bearclover’s competitiveness if they could damage the 

top 18- to 24-inches of its root system. Soil disturbance was a constant concern, and 

steps were taken to minimize it. Leaving untreated (filter) strips on the contour 

was one example.

Potter (1976) noted that mowing bearclover with a rotary-type mower had 

been tried several times. Plants were cut as close to the ground as possible. Apparently, the treatment was successful in some cases and not in others. No mention of 

Figure 6—Five-foot-square sheets 

of woven black polypropylene surrounded by 4-year-old bearclover 

on the Eldorado National Forest. 

The pine seedling in the center of 

the mat has died.
USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 11

what constituted success was noted or how long after treatment the assessment 

was made.

A more controversial attempt to dislodge bearclover both above- and belowground employed the use of dynamite. The goal was to build small terraces or 

openings in established bearclover by blasting, and then to plant conifer seedlings 

in the cleared areas (Potter 1985). As might be expected, much bearclover remained 

and rapidly invaded the cleared areas.

Vegetation managers have long observed that old skid trails through bearclover, which gouged the soil for 2 to 4 feet, often created areas where conifer 

seedlings had become established and grown well. Based on these observations, 

treatments that disturbed bearclover’s root system such as disking, plowing, and 

subsoiling were thought to have potential. Slopes of up to 35 percent can be treated 

with these techniques.

One of the early trials that disturbed bearclover belowground took place on 

the Stanislaus National Forest (Stowell and Lloyd 1935). A Caterpillar “fifty” tractor and an angled blade were used to clear mature bearclover in strips on relatively 

flat ground (fig. 7). The strips were about 9 feet wide and about 2 feet apart. All 

topsoil to a depth of 6 inches was piled in the narrow intervening strips. Ponderosa 

pine and sugar pine seedlings (1-1) were planted and seed-spotted in one to three 

rows in each strip. Rodents were controlled with poisoned grain. Although results 

were not presented, the authors noted ominously that “bearclover sprouts had 

appeared over the entire eradicated area.”

Another early trial also took place on the Stanislaus National Forest in 1952 

(Adams 1969). A heavy disk was used but was ineffective because new sprouts 

from rhizomes quickly regained control of the site. Another trial, which took place 

on the Stanislaus National Forest in 1955, was reported by Potter (1976). It involved 

using a disk that had 22-inch blades and weighed 8,000 pounds. After 3 years, 

ponderosa pine seedling height growth (40 inches) and survival (73 percent) were 

promising. However, 18 years later the plantation was judged a failure due to poor 

pine survival and lack of growth. In another trial, a heavy agricultural disk with 

six 18-inch blades was pulled behind a tractor (Potter 1985). Although the blades 

tore up the bearclover, small pieces of rhizomes sprouted, and a vigorous stand of 

bearclover was present one year later.

In June 1988, Craig (1989) used a more involved technique to control mature 

bearclover in a loamy-sand soil. He employed a heavy disk (18-inch blades) with 

Figure 7—An early attempt 

to control bearclover on the 

Stanislaus National Forest was 

with a tractor and blade, June 

1934.
12 USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 

one pass up and down the slope and another pass across the slope. Because grasses 

and forbs invaded the area and were considered a threat to planted ponderosa 

pine seedlings, the site was again disked in April 1989. This was a light disk that 

went about 6 inches into the soil. It was effective for removing competing vegetation, including severed pieces of bearclover rhizomes, and was judged as being 

a critically needed step. Although no long-term results are available, the appearance of the area and the early growth of the pine seedlings indicate the technique 

is promising. 

A variation of disking was to use it in combination with the spraying of herbicides. This was attempted several times on the Stanislaus National Forest in the 

1960s with mixed results (Adams 1969). The herbicides were esters of 2,4-D and 

2,4,5-T.4 

Plowing was another early technique employed to control bearclover. Potter 

(1985) noted that a single-tooth agricultural plow was used to create a furrow that 

would be beneath the majority of the rhizomes. Conifer seedlings would then be 

planted in the bottom of the furrow. Unfortunately, vigorous sprouts from severed 

rhizomes and roots quickly developed, and the plantation failed after 2 years. 

Contour ripping of bearclover roots belowground was first tried in Amador 

County in fall 1960 using a D-9 bulldozer with a two-shank road ripper attached 

to the rear (Adams 1969). Natural regeneration of ponderosa pine in the disturbed 

area was described as “more than adequate,” but seedling growth and the status of 

the plantation at a later date were not mentioned. Another method of mechanical 

site preparation is ripping with a winged subsoiler (fig. 8). This machine differs 

from a conventional ripper in that each of the three shanks has a winged shoe 

about 20 inches across that resembles a delta wing on an airplane. Each shank is 

adjustable for depth, and each can trip (raise) when a large boulder or stump is 

encountered. Operational depths range from 12 to 34 inches (Nelson 1990). The 

winged subsoiler also is pulled behind a heavy tractor and is applicable on slopes 

up to 30 percent. One advantage of this machine is that bearclover rhizomes tend 

to travel up the shanks and are pulled from the ground.

Rutty (2002) stressed the importance of using the winged subsoiler in the 

summer when the soil is dry. Dry soil breaks into large clods and in turn breaks 

up the bearclover rhizomes in them. Without soil moisture, the rhizomes dry out 

and die; with soil moisture, they readily sprout. Soil permeability and root growth 

also are improved.

In July 1988, Nelson (1990) investigated the applicability of the winged subsoiler to control bearclover on the Eldorado National Forest and compared it to 

standard disking. The study was performed on soils having a variety of textures 

and on slopes that ranged from 5 to 30 percent. Cross-ripping (two-way) was superior to one-way contour ripping because the operator could get closer to stumps 

and other obstacles and more of each acre could be treated. After 15 months, reinvasion of bearclover was minimal, especially in fine textured soils. It was not as 

effective in coarse textured, rocky soils. Nelson also noted that use of the winged 

subsoiler provided superior short-term control of bearclover and made it vulnerable to subsequent treatments.

Click and others (1994) discussed a two-step site preparation method using a 

large tractor pulling a machine with subsoiler shoes followed by a smaller cultivator-like machine equipped with five to seven shanks. The objective was to smooth 

the furrows created by the large machine and to control invading forbs, grasses, 

and sprouting pieces of bearclover. Even with this rather intensive treatment, they 

noted that conifer seedling survival was highly variable (30 to 90 percent) because 

of competition from invading plants. Further, they cautioned that the long-term effectiveness of the method was unknown. However, Campodonico (2002) reported 

good survival and pine height growth on the Stanislaus National Forest on slopes 

of 20 to 35 percent 10 years after treatment with a similar double-pass technique.

4 This paper neither recommends 

the pesticide uses reported 

nor implies that the pesticides 

have been registered by the 

appropriate governmental 

agencies.
USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 13

An even more intensive treatment to control bearclover belowground was 

terracing (fig. 9), which was tested extensively on the Stanislaus National Forest 

(Potter 1976). In general, the technique was applicable on slopes between 15 and 

40 percent. Below 15 percent, not enough excavation occurred, and over 40 percent 

too much soil was removed. In both instances, much topsoil was lost (Potter 1985). 

Delapp (1975) prepared operational guidelines for the design and construction of 

terraces, as well as considerations for soil erosion, and stocking/spacing arrangements for planted conifer seedlings.

Potter (1976) noted that terracing often gave conifer seedlings a 5- to 7-year 

headstart, and in a few instances, particularly on highly productive sites, they 

maintained acceptable height and diameter growth rates. However, bearclover 

eventually invaded the site. For example, areas terraced and planted in 1959 were 

totally covered with bearclover in 1976 (Potter 1985). Results from extensive terracing trials conducted from 1955 (Adams 1969) through the early 1980s have 

followed the pattern of planted conifer seedlings growing well at first and then 

slowing as competition from bearclover increased.

Burning

Like most plant species in California that are short and have major reproductive 

capability from underground organs, bearclover is both susceptible to fire and 

enhanced by it. The species has several structural and chemical characteristics 

that lead to its flammability. Bearclover is well adapted to burning, with many 

anecdotal accounts of the species burning within a few hours of a rain storm or 

with snow still on the ground. Furthermore, the species has finely dissected leaves 

and fine branch structure that provide high surface-to-volume ratios and good 

convective air circulation. The foliage also has a high ether extractive content that 

reaches a peak of 7 to 9 percent in late summer (Rundel and others 1981).

Figure 8—Shanks and 

blades of the winged subsoiler.
14 USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 

Silviculturists have long noted that burned snags and logs often were present 

in the healthiest of bearclover stands. They also noted that burns typically were 

hot in these stands and that bearclover recovery often was delayed. The first trial 

that used burning to control bearclover occurred in 1911, when Munns (1922) began a study in a naturally burned area on the Stanislaus National Forest. By 1921, 

bearclover was considered dense on more than 71 percent of the area. The only 

area that was free of bearclover was occupied by a dense stand of trees.

A somewhat unique burning technique was to treat individual stems (sprouts) 

of bearclover with a blow torch (Potter 1985). This usually was done after site 

preparation. Although no followup information on effectiveness or cost was 

found, the area was soon fully occupied by bearclover. 

The combination of burning followed by an application of herbicide was 

studied extensively in the 1960s on the Stanislaus National Forest (Adams 1969). 

The fires were of both natural and prescribed origin. The herbicides used the 

most were 2,4-D and 2,4,5-T applied with a mist blower or back-pack sprayers at 

various rates and times of the year. In general, summer application was the most 

effective. Less sprouting occurred and lower dosages could be applied at this time. 

However, higher dosages were effective with application in the fall. Although this 

combination treatment was described as being effective and giving good control 

of bearclover, some trials gave mediocre results and at least one was a failure. Of 

note was that grasses often invaded the treated areas and became quite dense.

Almost all early trials with controlled burning were performed in the spring or 

fall— a time when the risk of escape was low (fig. 10). Potter (1985) noted that after 

burning resprouting was vigorous and, furthermore, that the general consensus 

among silviculturists was that burning does not control or eliminate bearclover, 

but rather stimulates it (Potter 1976). Rundel and others (1981) found that while 

spring (pre-growing season) and fall (post-growing season) fires stimulated regrowth, summer burns (mid-growing season) appeared to inhibit regrowth for 

at least 2 years.

Weatherspoon and others (1991) expanded this finding and, in a preliminary 

study, noted that although bearclover did not respond much differently among 

burning dates in a single growing-season, it recovered much more slowly after a 

second growing-season treatment (actually a manual grub because of inadequate 

fuel) applied the next summer. Results after a third successive growing-season 

burn continued the trend of slowing recovery (Weatherspoon 2002). An additional 

Figure 9—An 8-year-old terrace on the Stanislaus National 

Forest. Although ponderosa 

pine survival is good, crown 

development and growth are 

poor.
USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 15

finding was that burning in mid-June was more effective than burning in mid-May 

or mid-August— a finding that corresponded to the time of peak blooming. Some 

evidence also suggested that bearclover was stressed more by the combination of 

resource drain by overstory trees and burning than from burning alone.

Herbicides

Many factors influence the ability of a herbicide to control undesirable vegetation. 

These include the ability of the herbicide to penetrate the leaves, the availability of 

enough water in the leaves and stems to translocate the herbicide to the intended 

plant part, and the capability of the herbicide to effectively damage the plant to the 

point that it becomes moribund. Several morphological and physiological factors 

are important and relate to plant size and leaf age. It stands to reason that small 

plants are more easily affected than large plants: they have less biomass and less 

sprouting potential. Recently developed leaves have not had time to develop thick 

epidermal layers or oily and waxy coverings and therefore are more easily penetrated by the herbicide. They also are developing at a time when internal moisture 

levels and photosynthesis are high, and thus translocation and assimilation of the 

herbicide are increased.

A definitive physiological study on bearclover was performed by Lanini 

(1981), who found that this shrub was sensitive to soil moisture and photosynthesis. Photosynthesis was reduced more than 50 percent as water stress increased 

throughout the season. A reduction in bearclover cover was correlated to lower 

photosynthesis, especially for the two most effective herbicides, glyphosate 

(Roundup) and triclopyr (Garlon), with water stress providing a smaller (but 

positive) correlation coefficient.

The first attempt to control bearclover with herbicides took place on the Stanislaus National Forest in 1945 (Schubert 1955). Mature plants were sprayed with 

2,4-D at five different concentrations on four different dates spanning May through 

October. In general, topkill was achieved, but resprouting took place and rendered 

the treatments ineffective. Many trials with other herbicides have since taken place 

(Adams 1969, Coombes and McHenry 1984, McHenry and others 1980, Potter 

1985). Results were mixed: some trials aided site preparation but not plantation 

release; some were effective for release in the spring, others in the fall; many were 

only moderately effective; some were totally ineffective. Observations at specific 

sites with specific environments, short-term studies, and unreplicated trials added 

Figure 10—Fall burning in a 

mature stand of bearclover.
1

6 USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 

confusion. A general conclusion was that a single application of a herbicide was 

ineffective. For example, a long-term study, begun in 1961 on a good site in Eldo-

rado County, concluded that after 19 years, no adverse effect to bearclover had 

resulted from either a single herbicide application with 2,4-D and 2,4,5-T or com-

petition from the planted ponderosa pine seedlings (Tappeiner and Radosevich 

1982). However, some findings common to these early studies are important: (1) a 

short-term increase in conifer seedling survival often occurred but was misleading 

because no stimulus in seedling height growth took place, (2) topkill of bearclo-

ver by herbicides—even almost 100 percent topkill—did not indicate an effective 

treatment, and (3) herbicides were more effective for treating bearclover in late 

spring/early summer and less effective in early spring or late summer, although 

higher dosages seemed to increase effectiveness at these times.

One trial that provided effective control of bearclover began in Eldorado 

County in 1961. It involved spraying once with 2,4-D and 2,4,5-T, hand clipping 

sprouts during spring 1962, and installing a 4.9-foot-deep polyethylene-lined 

trench around the plots (Tappeiner and Radosevich 1982). After 19 years, no bear-

clover was present on these intensively treated areas.

More recent studies with new herbicides like hexazinone (Velpar, Pronone), 

glyphosate (Roundup, Accord), and Escort proved to be more effective. Hexa-

zinone is a soil-active herbicide; glyphosate and Escort are foliage-active. These 

later studies also differentiated between undisturbed, mature bearclover, usually 

growing under a scattered overstory, and newly-sprouted bearclover, usually in 

young conifer plantations.

On the Blodgett Experimental Forest in northern California, Heald (1987) 

found that Roundup effectively controlled mature, 6-inch-tall bearclover in a 

partially shaded environment. In central California, Jackson and Lemon (1988) ap-

plied Roundup herbicide several times during the year and found that a May-June 

application was the most effective. An October application was surprisingly effec-

tive as well. May-June was the time of full flowering and adequate soil moisture, 

and October corresponded to the time of carbohydrate movement to the roots. 

These authors recommended that this herbicide be used before timber harvest, 

which suggested that at least a partial overstory of trees was present. Ballew (1989) 

found that a mature bearclover stand had too much biomass to be successfully 

treated with a single application of herbicide. He recommended that bearclover be 

treated with Garlon or Roundup followed by an application of Velpar. Velpar was 

particularly effective because it killed bearclover sprouts as well as the inevitable 

grasses and forbs.

Herbicide technology, especially for application in young conifer plantations, 

continued to improve as new herbicides, new information on rates and appli-

cations, and more knowledge on the fate of herbicides in the environment was 

developed. Johnson (1988) showed that Pronone controlled bearclover in Eldorado 

County for at least 2 years after site preparation in a young conifer (ponderosa 

pine and Douglas-fir) plantation. No crop phytotoxicity was detected. On the 

Eldorado National Forest, Fredrickson (1994) demonstrated that Roundup inhib-

ited the sprouting of bearclover for up to 5 years after treatment. He also noted 

that treated areas were quickly occupied by grass. In central California, Garlon 4 

herbicide at 1 percent and 2 percent with 1 percent Mor-Act as a surfactant and 

Garlon 3A at 1 percent and 3 percent with Mor-Act provided excellent control of 

bearclover when applied in November (Anonymous 1994).

On the Eldorado National Forest northeast of Jackson, California, McDonald 

and Everest (1996) conducted a more intensive study involving a tank-mix of two 

herbicides followed a few months later with a third herbicide. The tank-mix was 

1.5 percent Accord, 1 percent Garlon 4, Bivert adjuvant, and a surfactant, applied 

in August 1991. The second herbicide was Pronone 10G (20 pounds per acre hexa-

zinone) applied in November 1991. In fall 1994, mean density, foliar cover, and 

height of bearclover in treated plots and control (fig. 11) were:
USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 17

In 1994, 100 percent of planted ponderosa pine seedlings in the herbicide plots 

had survived, and mean stem diameter and height were more than twice as large 

as counterparts in the control. Cheatgrass invaded in 1992 and in 1994 numbered 

more than 743,000 plants per acre in the control and more than 130,000 plants per 

acre in the herbicide plots.

Another study in central California strived to evaluate the long-term effect 

of three herbicides on bearclover. The herbicides were Roundup, Velpar L, and 

Escort (fig. 12). After 11 years, bearclover density ranged from more than 7,700 

plants per acre with Roundup to more than 117,000 plants per acre in the control,5

foliar cover varied from a trace with Roundup to more than 36 percent in the control (fig. 13), and height differed from 0.8 foot with Roundup to more than 1.4 feet 

in the control. Velpar L ranked a close second to Roundup in effectiveness, with 

Escort being a distant third. Roundup and Velpar L produced values that differed 

significantly from those in the control at the 5 percent level. Grasses, chiefly of 

the genera Achnatherum and Bromus (including B. tectorum), invaded the study 

area and were highest in the Roundup plots (618,600 per acre), next highest in the 

Escort plots (493,660 per acre), and lowest in the Velpar plots (194,100 per acre). 

Of interest is that after 5 years, grass density in the Velpar plots was about 26,000 

plants per acre, and in the Roundup and Escort plots more than 2 million and 1 

million plants per acre, respectively.

At the 3,200-foot elevation in Calaveras County, Potter (1997) reported results 

of trials with nine herbicides after 7 years. Different dosages, tank-mixes, and times 

of year were part of the study. Herbicides that were effective in reducing bearclover 

below pretrial conditions and substantially below the control were Velpar L applied in the fall and Escort at 4 ounces per acre. Virtually no herbicides completely 

controlled annual grasses. Even the most effective herbicides did not eliminate 

bearclover, and substantial numbers were present after 7 years.

Treatment Density Foliar Cover Height

Mean SE Mean SE Mean SE

stems/acre pct ft

Herbicide 3,667 3,371 1 <1 0.7 0.07

Control 282,000 85,000 63 26 1.2 0.20

Figure 11—Sampling is a 

big job: every bearclover stem 

inside this milacre frame will 

be counted to arrive at density 

values.

5

Unpublished data on file, 

Pacific Southwest Research 

Station, Redding, Calif.
18 USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 

Figure 12—Applying an herbicide with a carbon dioxide 

pressurized boom in central 

California. The man in the background is standing at the edge of 

the swath.

Figure 13—Effect of Roundup 

herbicide (A) and Velpar herbicide 

(B) relative to control (C) on 

newly-sprouting bearclover after 

11 years.

A
USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 19

B

C
2

0 USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 

Cost

The cost of manipulating bearclover over the years has varied tremendously 

from $70 per acre for plowing in 1975, to $500 per acre for dynamiting in 1985, to 

$300 per acre for hand grubbing in 1994. Because many of the older treatments 

were ineffective or expensive, costs are presented only for those treatments 

judged as having the highest potential for effectively manipulating bearclover. 

In 2002 these were winged subsoiler, successive growing-season treatments 

(burns), and herbicides.

The cost of the winged subsoiler depends on whether one or two passes are 

made, steepness of slope, and other considerations. Campodonico (2002) found 

that a two-pass operation on steep slopes cost about $300 per acre. Because bear-

clover can be burned at low-risk times of the year, the cost of successive controlled 

burns should require a minimum of cleared lines and standby equipment and 

crews. The cost should be low initially and decrease each year. Weatherspoon 

(2002) suggested that about $50 per acre for the first burn was reasonable, with 

the cost decreasing to about half that after two burns.

The two most effective herbicides for controlling bearclover are Velpar (6

qt/ac) and Roundup (1.5 qt/ac). Aerially applied Velpar costs about $92 per acre 

for both the chemical and its application, and backpack application costs about 

$110 per acre for both. Aerially applied Roundup costs about $30 per acre for both 

chemical and application, and the cost of backpack application is $92 per acre for 

both. Although Escort was moderately effective in one study, it is not registered 

in California.

Discussion and Conclusions A major need in forest silviculture and ecology today is to develop knowledge on 

the plant community that develops after different levels of natural and humancaused disturbance. More specifically, knowledge is needed on the changes in the 

community over time. The density and growth of individual species and their 

eventual ascendance or decline, a process called plant succession, are particularly 

important. Equally important is to recognize the changes to plant communities 

brought about by different levels of human-caused disturbance. Such levels, 

termed treatments, often alter the rate of plant succession but seldom have longterm effects on the eventual species composition of the community.

Unfortunately, the development of knowledge on plant species composition 

and development after disturbance generally is limited and often tied to competi-

tive species that limit the survival and growth of economic species. Such is the 

case for bearclover, which is notorious for its limiting effect on conifer seedling 

survival and growth. Understanding the morphology and physiology of bearclo-

ver, relating them to the capture of site resources and plant growth, and tying such 

knowledge to a range of treatments is a major emphasis of this paper.

Much is known; more knowledge is needed. The production and fate of bear-

clover seed are a case in point. Thousands of seeds are produced, but how many 

are sound and how many of them reach the soil? Once in the soil, do they die or do 

they form a seedbank? Given the overwhelming success of vegetative propagation 

and the likelihood that extensive areas are of the same genotype, it is possible that 

some mechanism to discourage fertilization or seedling development would be 

present. In a controlled test, Powers (1971) collected pollen from several bearclover 

plants on the Challenge Experimental Forest and observed that the grains germi-

nated on the stigmas of other bearclover plants, but did not develop further. It is 

possible that these plants were all from one clone and were incompatible. Perhaps 

interclonal pollination is needed. A larger question concerns the size and age of 

bearclover clones. Are patches or stands made up of one or several individuals? 

No information is available on this subject.
USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004.

21

Knowledge is needed not only on seed, but on rhizomes as well. From the 

rhizome transect study in central California (McDonald and Fiddler 1999), bear-

clover rhizomes elongated for 2 years after disturbance, developed very little the 

third year, and then occupied new territory from deep underground structures the 

fourth year. From the study in Eldorado County with small mulches (McDonald 

and Everest 1996), the poor growth of the ponderosa pine seedlings was attributed 

to the capture of soil moisture by roots and rhizomes located deep in the soil. Con-

nection to rhizomes outside the mulches also was likely. 

All of this adds to the confusion on when, where, and how bearclover spreads 

over the landscape. Distinguishing between mature undisturbed bearclover stands 

and young disturbed stands could be useful. Numerous observers have noted the 

remarkable lack of mature bearclover extension into treated areas, and the lack of 

extension of rhizomes from disturbed areas into undisturbed areas. It is likely that 

mature bearclover, which is characterized by already-developed dense masses of 

roots and rhizomes, allocates most of its energy to crown development, and rhi-

zome extension is relegated to only a few inches each year. Mature bearclover has 

to be damaged before it grows rapidly. In contrast, newly disturbed stands, which 

are characterized by scattered stems aboveground and an in-place root system 

belowground, vigorously extend rhizomes from those near the soil surface and 

from roots located deep in the soil. The sporadic nature of rooting from side nodes 

of extending rhizomes could be a response to a strategy of first allocating energy 

to rhizome tips and then to the development of side rhizomes. 

Silviculturists have long been intrigued by the idea that damaging competing 

plants when their food reserves are low is the best time to treat them. Food reserves 

tend to be lowest at the time of peak growth or at the time of peak flowering. For 

bearclover, this would be June-July in most instances. If bearclover were treated for 

three or more successive summers, would the effect of low carbohydrate reserves 

be compounded to the point that the plant would be seriously affected? Studies 

by Rundel and others (1981) and Weatherspoon and others (1991) showed that 

regrowth of bearclover is slowed after successive mid-summer treatments, and 

after three such treatments, vigor appeared to be low. But low enough to allow 

conifer seedlings to grow at the potential of the site? Presumably, more succes-

sive treatments would lower bearclover reserves even more. Cost could eventually 

become prohibitive. An additional problem with burning is obtaining enough fuel 

to carry the fire in successive years. 

Because the techniques for treating bearclover are many and the variations and 

combinations are even more numerous, an at-a-glance table is presented (table 4). 

Of interest is that all of the treatments have broad to moderate application, and 

every treatment has at least one limitation. No treatment is immune to causing too 

much disturbance to the environment, or being too costly, or not being socially ac-

ceptable, or simply being limited by the steepness of slope or rocky ground. Risk, 

regulation, lack of fuel for subsequent burns, or creating conditions that will be 

difficult to manage in the future are additional limitations. However, it is impor-

tant to note that this is a generalized table and exceptions can occur where local 

conditions of soil, microclimate, and vegetation occur. Cost also is a wide-ranging 

variable that could be modified by local conditions. 

In spite of the limitations, two treatments stand out as being effective. These 

are subsoiling and herbicides. A third that has potential for being effective is suc-

cessive growing-season treatments (burns). All three are based on the fact that to 

be effective it is necessary to treat the entire plant; above- and below-ground plant 

parts need to be killed. Just damaging them is not enough. 

Additional discussion on some of the treatments, old and new, follows: 

Most of the mechanical methods are limited by slope, large rocks in the soil, and 

stumps, boulders, rock outcrops, and residual vegetation that block the path of the 

machines. This causes a significant portion of each acre to not be treated. Worse, 
22 USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 

these untreated areas serve as sources of propagules that eventually reinvade the 

treated areas.

For terracing, the difficulty of managing the stand in the future may be as 

much a detractor of the method as are soil disturbance and possible loss in site 

productivity. Although growth of some conifer seedlings is negatively affected, 

others reach a size at which they will need to be commercially thinned and eventually harvested. How and where to lay out roads, thin, and harvest could be a 

major logging and engineering problem in the future. How best to treat terraces 

covered by bearclover is another challenge. 

Just as burning was most effective when performed during mid-summer, so 

is the application of most of the herbicides. Mid-summer is the time when photosynthesis and internal moisture levels in bearclover are high. Thus, the herbicide 

is readily absorbed by the plant and transported to the site within the plant where 

it is active.

Bearclover is notorious for being a strong competitor in young forest plantations. Such plantations occur after various combinations of logging, burning, 

and site preparation and are characterized by bare mineral soil, planted conifer 

seedlings, and few competing plants above ground. Below ground, however, the 

rhizomes of bearclover are mostly unscathed and in position to capture critical 

soil moisture. Even if fragmented, the rhizomes quickly develop into new plants. 

In this competition-free environment, site resources are plentiful and bearclover 

becomes a vigorous competitive species.

Consequently, the species that become associates of the after-disturbance 

bearclover plant community must be able to compete aggressively for site 

resources both above and below ground. Few species are able to do this and, as 

noted at Gold Note and Penmoke, species richness tends to be low almost from the 

beginning. However, with distance from the heart of bearclover’s range, species 

Table 4—Summary of treatments on bearclover and their comparative effectiveness

Treatment and variation Application Limitation Effectiveness1

Manual

Hand grubbing Broad Cost Ineffective

Mulching

Various materials Broad Cost Ineffective

Mechanical

Mowing Broad Cost, terrain Ineffective

Dynamiting Broad Cost, disturbance Ineffective

Disking Moderate Terrain, disturbance Moderate2

Plowing Moderate Terrain, disturbance Ineffective

Subsoiling Moderate Terrain, disturbance Effective

Terracing Moderate Terrain, disturbance, cost, management Ineffective2

Burning

One growing season Broad Cost, risk Ineffective

Two+ growing seasons Broad Cost, risk, adequate fuel Moderate3

Herbicides

2,4,5-T Broad Social pressure, regulation Effective

Escort Broad Social pressure Effective

Roundup Broad Social pressure, grass invasion Effective

Garlon Broad Social pressure Effective

Velpar Moderate Social pressure Effective

1

Density of bearclover reduced to the point that conifer seedlings can become established and grow at the potential 

of the site.

2

Can be effective on gentle-moderate slopes and coarse-textured soils.

3

Moderate rating on the basis of promise; not enough trials to be certain. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 23

richness increased as noted at Chaix and Challenge. Although the four study 

areas had a varied and rapidly developing plant assemblage, the composition of 

the community differed. In addition to bearclover and ponderosa pine seedlings, 

which were common to all four study areas, the Challenge vegetation consisted 

of forbs, grasses, shrubs, and hardwoods; Chaix had a similar mix; Gold Note 

was predominately bearclover, manzanita, and a few forbs; and Penmoke was 

primarily bearclover, a few forbs, and cheatgrass.

Based on the density and development of the various species in stands that 

have received both site preparation and release (tables 2,3), composition of the typical bearclover community in the near future can be ascertained. Certainly, the main 

constituents will be bearclover and conifer seedlings, with whiteleaf manzanita a 

lesser component. The forbs will be few and consist of those species that can persist 

in a shady, competitive environment. Grasses also will be present, initially in large 

numbers and then declining as taller vegetation develops. 

Almost inevitably, treatments that disturb bearclover cause the density of various grass species to increase. Whether site preparation or release, and regardless 

of type of treatment, the grasses invade. On the Stanislaus National Forest, a study 

was designed to specifically test the effect of grasses on bearclover regrowth.6 The 

study area burned in a wildfire in late summer 1987 and was seeded to annual rye 

grass that fall. A vigorous stand of grass became established in 1988, and a myriad 

of seed was produced. Each of these seeds produced a plant in 1989 (fig. 14) and 

by that fall numbered over 10 million per acre. Thus bearclover had to sprout and 

regrow at this high level of competition.

Results from the measurement of study plots in fall 1992 showed a dramatic 

decrease in number of stems of both bearclover and rye grass (table 5). Although 

both species maintained their initial height values, the density of grass actually fell 

Figure 14—At age 2, bearclover is able to grow and 

dominate in a dense stand of 

seeded rye grass.

6 Study entitled “Effect of herbicides and seeded grass for controlling bearclover in a young 

ponderosa pine plantation on 

the Stanislaus National Forest.” Philip M. McDonald and 

Gary O. Fiddler. 1989. On file 

at Pacific Southwest Research 

Station, Redding, CA. (Study 

area destroyed by forest fire 

in 1996.)

Table 5—Average stem density and height of bearclover and annual rye grass, Stanislaus 

National Forest in 1989 and 1992

Year Bearclover Grass

Density Height Density Height

Mean SE1 Mean SE Mean SE Mean SE

stems/acre ft stems/acre ft

1989 339,900 12,200 0.8 0.1 10,489,000 805,000 1.6 0.1

1992 9,867 1,555 0.9 0.1 9,133 1,711 1.6 0.1

1

SE = Standard error
24 USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 

below that of bearclover in 1992, indicating that the grass population was being 

stressed by the bearclover. This and all the other studies in which grass was monitored, strongly suggest that bearclover is virtually immune to competition from 

grass, regardless of species or seed origin (natural or artificial seeding). Nevertheless, grass of one species or another will continue to be an associate of bearclover 

and persist in small openings between the bearclover plants.

In the heart of bearclover’s natural range, natural plant succession in disturbed 

stands is characterized by an onrush of bearclover sprouts, annual grasses from 

seed, and other shrubs, particularly those of the genera Arctostaphylos and 

Ceanothus, from dormant seeds in the soil. Species from these categories capture 

site resources early and establish dominance at an early age. Such species expand 

their populations rapidly and cumulate at ages 4 to 7 in very high densities. 

These high density levels are unsupportable and the number of plants per acre 

declines, but foliar cover and height increase. Grass density generally decreases 

first because of pressure from the shrubs (including bearclover). During the longer 

term, bearclover becomes ever more dominant, and plant species richness declines. 

Biotic agents and abiotic forces have little effect, and the bearclover community 

adds new meaning to the word “stable.” After 19 years, even ponderosa pine 

seedlings had no adverse effect on bearclover (Tappeiner and Radosevich 1982).

Given this stability and a much longer timeframe, has bearclover been markedly affected by the activities of humans? Based on extensive observations and 

inquiries throughout the Eldorado National Forest, Lyons (1913) noted that bearclover has not extended its natural range for many years. However, he noted that 

a “considerable increase in the density of the stands” has occurred on both private 

and government lands that have burned over. The extent of bearclover over the 

landscape probably did not change much until the advent of herbicides in the 

1960s. But what about since then? Probably the best answer, is “somewhat,” but 

only temporarily. Not all areas in a plantation are treated, and islands of bearclover remain. In addition, a few deep roots, which escape damage from herbicides, 

apparently lead to new invaders in a few years. Consequently, bearclover density 

may be affected locally, but its presence across the landscape remains constant 

over longer time frames. A large wildfire like the Stanislaus complex of 1987 is an 

example. It destroyed thousands of acres of pine plantations which converted to 

vigorous stands of bearclover in a few years. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-190. 2004. 25

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General Technical Paper

PSW-GTR-190

Ecology and Manipulation of Bearclover (Chamaebatia foliolosa) in Northern

and Central California:The Status of Our Knowledge