Through natural selection over

thousands of years, many

species of shrubs and grasses are

superbly adapted to dominate in

newly disturbed areas. In many

instances, they are better adapted

than the nursery-grown pines and

firs that are outplanted over the

landscape, minus part of their

root systems. 1 Bearclover

(Chamaebatia foliolosa Benth) and

cheatgrass (Bromus tectorum L.)

are two such species.

Bearclover is an evergreen

perennial shrub that is prevalent

between the 1,000- to 6,000-foot

elevation in the central Sierra

Nevada of California. It excels on

south slopes and in open stands.

In the typical California

environment of summer drought

and limited soil moisture, the root

system of bearclover is key to its

success as a species. The root

system consists of an extensive

network of roots and rhizomes 4

to 16 inches below the soil

surface with sinker roots that

often extend to depths of 6 feet.

After fire or other disturbance, the

plants resprout from adventitious buds at nodes along the

rhizomes, and produce a dense

stand. Additional competitive

mechanisms include capability

to fix nitrogen,2 to reproduce

from seed, and potential for

allelopathy.3

Bearclover is a serious

competitor to conifer regeneration. Indeed, if bearclover is

present, survival and growth of

conifer seedlings is poor,4,5,6 and

the plantation often fails.

Cheatgrass is an introduced

annual species that invaded North

America from Eurasia in the 1889-

1894 period and by 1928 had

spread throughout what is now

its naturalized range.7 It has

several adaptations that allow it

to effectively colonize and become

established in disturbed areas. It

produces huge seedcrops, has an

extensive root system, a high rootshoot ratio, capability for growth

in cold soils, and matures early in

the growing season.8 Because

survival is high and appears to be

independent of density, 9

cheatgrass tends to saturate an

area. A community of low

diversity often results.

Because of its many and

effective adaptations to a wide

range of environmental

conditions, cheatgrass can be a

major cause of failure in conifer

plantations. However, if the soil

is deep, and the newly planted

conifer seedlings are provided 1

or 2 years of competition-free

growth, their roots can occupy the

deeper soil layers, stay in a zone

of adequate moisture, and

increase in number and volume.

Dense stands of grasses can

exclude more aggressive shrub

species if the grasses become

established first.10

This note reports a study in

central California on the response

of young ponderosa pines,

bearclover, and cheatgrass to two

United States

Department of Agriculture

Forest Service

Pacific Southwest

Research Station

P.O. Box 245

Berkeley, California 94701-0245

http://www.pswfs.gov

Research Note

PSW-RN-419-Web

July 1996

Response of Young Ponderosa Pines,

Shrubs, and Grasses to Two Release

Treatments

Philip M. McDonald Glen A. Everest

McDonald, Philip M.; Everest,

Glen A. 1996. Response of

young ponderosa pines, shrubs,

and grasses to two release

treatments. Res. Note PSWRN-419. Albany, CA: Pacific

Southwest Research Station,

Forest Service, U.S. Department of Agriculture; 8 p.

To release a young pine

plantation on a medium site in

central California, herbicides

and mulches were applied soon

after planting to study their

effectiveness. Bearclover is an

aggressive shrub species that

resprouts from rhizomes after

disturbance, and must be

controlled if young conifer

seedlings are to become

established. After 4 years,

resprouting bearclover plants

numbered 282,000 per acre in

the control, but less than 4,000

per acre in the plots treated by

herbicides. Mean foliar cover

was 63 percent versus 1 percent

for control and herbicide plots,

respectively. Ponderosa pine

seedlings were significantly

taller, had larger mean

diameters, and survived better

in the herbicide treatment than

counterparts in mulched plots

and control. The 5-foot square

mulches were ineffective for

controlling bearclover.

Cheatgrass invaded the

plantation in the second year,

and after 2 more years became

abundant in herbicide plots

(743,667 plants per acre) and

plentiful in the control (130,300

plants per acre).

Retrieval Terms: competition,

plant development, northern

California, replacement species,

vegetation management
2 USDA Forest Service Res. Note PSW-RN-419-Web. 1996

release treatments—applying herbicides and a mulch—and their effect on the

capability of planted pines to become established and develop well.

Methods

The study area was located on the Eldorado National Forest’s Amador Ranger

District, about 35 miles northeast of Jackson, California. Before logging, it was

primarily a dense stand of bearclover with large ponderosa pines (Pinus ponderosa

Dougl. ex Laws. var. ponderosa) scattered throughout. An occasional blackened

stump suggested that the area had burned previously. After logging, the site was

prepared for planting by broadcast burning in early March 1991. The foliage of

bearclover had enough oils and aromatic chemicals to burn in the winter after a

period of warm dry weather. After burning, almost all vegetation was consumed,

and the surface was mostly mineral soil with only stubs of bearclover remaining

aboveground.

Ponderosa pine seedlings (1-0) from a local seed source were grown in the

USDA Forest Service’s nursery at Placerville, Calif., and planted by auger in

March 1991 at a 10- by 10-foot spacing. Pine seedling height averaged 0.6 feet

above mean ground line.

Site quality of the study area is medium with height of dominant ponderosa

pines averaging about 40 feet in 50 years.11 The soil, which is closely related to

the Chaix series, was formed from material weathered from granitic rock.

Taxonomically it is a dystric xerochrept, and is skeletal and well drained. The soil

texture is coarse sandy loam, at least 4 feet deep. The elevation is about 5,000 feet,

the slope ranges from 10 to 25 percent, and the aspect is south. Yearly

precipitation averages 55 inches with about 70 percent falling as snow.

Temperatures range from 20 

°

F to 95 

°

F. The growing season is about 120 days.

The experimental design in this study consisted of three treatments each

replicated four times in a complete randomized block design. A treatment

plot consisted of about one-sixth acre on which were 30 pine seedlings

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

treatment). The treatments were:

• Herbicide sprayed from backpack apparatus in August 1991 with a

tankmix of 1.5 percent Accord,12 1.0 percent Garlon 4, Bivert adjuvant,

and a surfactant to kill bearclover sprouts. Pronone 10G (20 pounds/acre

[2 pounds/acre hexazinone]) was applied in November 1991 to limit

grasses and forbs.

• Mulches made of woven black polypropylene, 5 feet square, applied

around pine seedlings and over bearclover stubs, June 1991. Held in

place with nine 8-inch, flat-headed, “u”-shaped metal pins.

• Control (no treatment after site preparation).

In each plot, 20 healthy pine seedlings were selected for study and given a

metal tag. Each seedling was measured after the first growing season in 1991 and

after the fourth season in 1994 for stem height and diameter. Diameter was

recorded at 12 inches above mean groundline. The seedlings were checked

periodically for possible injury from animals, insects, and herbicides.

The sampling intensity for measuring other vegetation in the herbicide

treatment and the control was five randomly selected subplots in each plot. No

subplots were installed in the mulch treatment because each mulch was assumed

to completely exclude competing vegetation. Subplots were centered around

ponderosa pine seedlings. They were square and contained 1 milacre (0.001

acre). Because very little vegetation was present in 1991, detailed sampling took

place only in 1994. Furthermore, only bearclover and cheatgrass were sampled as

all other species were too few to analyze.
USDA Forest Service Res. Note PSW-RN-419-Web. 1996

3

To test for treatment effects and significant differences among treatments,

two-way analysis of variance (mixed model, no interaction)13 and Bonferroni

tests were the analytical tools.14 We assumed that the block-treatment interaction

equalled zero. Unfortunately, three treatments were missing in two plots,

resulting in an unbalanced design. Significance in all tests was at α = 0.05. To

approximate a more normal distribution, the survival data were transformed by

arcsin15 before analysis of variance.

Bearclover and cheatgrass were sampled for density in terms of number of

plants per milacre plot and expanded to a per-acre basis. Because new entities of

bearclover arise from belowground structures, defining a “plant” was necessary.

Excavation and pulling on new stems showed rhizomes to vary widely in depth,

length, and origin. Plants from rhizomes consisted of a single stem or a clump of

stems. Determining individual plants was impossible. Consequently, single stems

and small clumps of stems were counted as one bearclover plant. Determining

the density of cheatgrass also was difficult. Plants were so numerous and so close

together that it was almost impossible to determine individual plants. We took

an inordinate amount of time to do so. Foliar cover (the sum of shadows that

would be cast by leaves and stems of each species expressed as a percentage of

the land surface)16 and average dominant height (average of the three tallest

stems measured from mean groundline to top of plant) also were recorded for

both species. Other species were not measured but noted in a species list.

Data for pines were gathered from permanent plots measured each year, and

where analyses of means from repeated measurements are concerned, the data

are not truly independent. The α levels or type I errors given for various tests

apply to each measurement and year separately.

Results

Plant Diversity

Within study plots, almost all species other than bearclover and cheatgrass were

scarce and small. The total number of plant species found in the study area from

1991 through 1994 was 19. In 1994, these species consisted of three naturally

seeded conifers, two hardwoods, four shrubs, five forbs, one fern, and four

grasses. In June 1992, a species of trefoil (Lotus spp.) and bull thistle (Cirsium

vulgare [Savi] Ten.) were present in study plots and abundant outside of them.

The tender green seed heads of the bull thistles were being destroyed by the

larvae of the painted lady butterfly (Vanessa cardui) to the point that virtually no

seed was produced. This thistle was scarce in 1993. In summer 1994, only a few

plants of trefoil were present and then only in the herbicide plots. One species

that grew well among the bearclover plants was a death camas (Zigadenus

exaltatus Eastw.). Apparently, its large bulb and tendency to grow taller than

bearclover gave it a competitive edge.

Bearclover

Burned in early March, bearclover did not sprout above ground until the middle

of June. By the end of the growing season in 1994, mean height was 1.2 feet in the

control and 0.7 feet in herbicide plots (table 1). Only a few young plants were

present in the herbicide treatment and most had only one stem. Density of plants

in the control was more than 282,000 per acre with cover of 63 percent.

 Because rhizome development beneath mulches is unknown, we lifted

several mulches in 1994 and dug up the bearclover rhizomes with a shovel.

Rhizomes were prolific beneath the mulches and crisscrossed below the soil

surface under them. No new roots had developed at rhizome nodes, however.

Where aboveground stems had burned, a new white horizontal rhizome was

present at the nearest node on some plants. In a few instances this rhizome had

resulted in a new plant that had developed in the center slit near the pine
4 USDA Forest Service Res. Note PSW-RN-419-Web. 1996

seedling. Beneath the mulches that we lifted were several shoots of bearclover

having flattened stems and chlorotic leaves that obviously had been pushing

against the mulches. These were beginning to die from heat absorbed by the dark

mulch and conducted to them.

Cheatgrass

Although not observed in study plots in 1991, this grass was becoming well

established in bare places in 1992. By the end of 1994, cheatgrass was abundant in

herbicide-treated plots with a mean density of more than 743,000 plants per acre

and foliar cover of 22 percent (table 1). More than 130,000 plants per acre were

present in the control, but mean foliar cover was only 3 percent.

Ponderosa Pine

Fierce competition from bearclover in the control caused significant mortality of

ponderosa pine seedlings by fall 1994. Survival of pines in the herbicide treatment

(100 percent) was significantly higher than for pines in the control (73 percent) or

surrounded by mulches (77 percent) (fig. 1). No damage from insects, browsing,

or herbicides was noticed.

Because a majority of ponderosa pine stems were shorter than 12 inches in

1991, mean pine diameter is presented only for 1994. Analysis of variance

indicated that pines in the herbicide treatment were significantly larger in

diameter (1.8 inches) than counterparts in the control (0.5 inches) or with mulches

(0.5 inches) (fig. 2). The mean height relationship for ponderosa pine in 1994 was

similar to that for diameter. Pines were significantly taller in the herbicide

treatment (4.3 feet) than in the control or mulched plots (2.0 feet) (fig. 3).

Discussions and Conclusions

Among the many widespread aggressive shrub species that negatively impact

young ponderosa pine plantations in the Sierra Nevada of California, bearclover

is probably the toughest. Its large and well developed root system and abundant

shoot growth enable the species to fully occupy the site both above and below

ground. Because of this, most attempts to establish conifer plantations in

bearclover have failed. This failure has challenged foresters, and led them to

investigate a wide range of site preparation and release techniques. These include

manual release (grubbing and chainsawing), mechanical release (discing and

bulldozing), dynamiting to create small openings, mulching (sheets of plastic

and plywood), prescribed burning (one or more times, various months), and

applying herbicides (alone and mixed). Except for the herbicide 2,4,5-T, these

Table 1—Growth parameters of bearclover and cheatgrass in herbicide plots and

control. Amador Ranger District, Eldorado National Forest, 1994.

Species and Growth Herbicide Control

Parameter Mean SE Mean SE

 Bearclover

 Density (no./acre) 3,667 3,371 282,000 85,000

 Foliar Cover (pct) 1 <1 63 26

 Height (ft) 0.7 0.07 1.2 0.2

 Cheatgrass

 Density (no./acre) 743,667 299,360 130,300 68,700

 Foliar Cover (pct ) 22 3 3 <1

 Height (ft) 1.0 0.3 1.4 0.6
USDA Forest Service Res. Note PSW-RN-419-Web. 1996 5

Figure 1—Average ponderosa

pine survival by treatment in 1991

and 1994. Standard errors were

2.52 percent in 1991 and 3.84

percent in 1994. For each year,

treatment means followed by the

same letter do not differ significantly at the 5 percent level.

Figure 2—Average ponderosa

pine stem diameter at 1 foot above

mean groundline in 1994. The

standard error was 0.1 inch.

Treatment means followed by the

same letter do not differ significantly at the 5 percent level.

Figure 3—Average ponderosa

pine height in 1991 and 1994.

Standard errors were 0.08 feet

in 1991 and 0.24 feet in 1994.

For each year, treatment means

followed by the same letter do

not differ significantly at the 5

percent level.

Control

Mulch

Herbicide

1991 1994

Year

Height (pct)

2

3

4

5

1

0

a

a a

a

a

b

Control

Mulch

Herbicide

1994

Year

Diameter (inches) 1.0

1.5

2.0

0.5

0.0

a a

b

Control

Mulch

Herbicide

1991 1994

Year

Survival (pct) 100

50

0

a

a a a

a

b
6 USDA Forest Service Res. Note PSW-RN-419-Web. 1996

trials were inconsistent and ineffective. The plant community that replaced

bearclover was often a dense stand of grasses or ferns. These species also proved

to be severe competitors to conifer seedlings. After 2,4,5-T became unavailable in

the early 1970’s, it was not until the mid-1980’s that new herbicides were found

which killed the entire bearclover plant and not just its crown. But herbicides are

not always socially acceptable and new variations of old techniques continue to

be tested.

One of these techniques is mulching. Common knowledge suggests that

surface dressings such as mulches will not be effective on rhizomatous species.

But will they be effective after a high-consumption burn has killed the stems and

crowns of the plant? More specifically, will the combination of burning and

mulching provide the necessary competition-free space to allow ponderosa pine

seedling roots to develop enough volume and depth to capture adequate soil

moisture to grow well? Results from this study showed that small mulches did

not. Furthermore, mulches probably would not be effective, even if they were

larger.

Because bearclover rhizomes beneath mulches had no new roots at nodes

after four growing seasons, we questioned their source of nourishment. And

because the nodes had no roots and hence no water absorption capability, we

strived to explain the obviously poor development of the ponderosa pine

seedlings in the mulch treatment. The most likely answer consistent with our

observations was that roots or rhizomes located much deeper in the soil were

extracting soil moisture and denying it to the pines. Nourishment of bearclover

probably came from plants outside the mulches as well. Plainly, much more

research is needed on the extent and depth of this species’ root system, as well as

on rhizome stimulation and development. Keying treatment to bearclover

phenology needs more work as well.

The constant, perhaps annual, pressure of new bearclover plants against the

mulches again demonstrated the need for a tough, heat-absorbing, well anchored

mulch.17

Because it significantly reduced the bearclover population and delayed the

cheatgrass invasion, albeit for only 1 year, the herbicide treatment in this study

was effective.

The ability of cheatgrass to compete with bearclover and ponderosa pine

seedlings also was investigated. In the control, which was characterized by high

bearclover density and foliar cover, cheatgrass density was relatively high (more

than 130,000 plants per acre), but foliar cover was low (3 percent). Plants were

slightly taller in the control, probably because they were forced to reach for

adequate sunlight. Consequently, the competitive strategy (or competitive

weakness) of this grass, at least for the first few years, was to maintain a

considerable presence in dense bearclover, but not to develop well horizontally.

After a delay of 1 year, cheatgrass colonized the herbicide plots and

developed rapidly. By fall 1994, density of this grass was more than 743,000

plants per acre and foliar cover was 22 percent. With an average diameter of 1.8

inches and height of 4.3 feet, the pines were developing well also. Furthermore,

visual evidence showed that the length of pine stem between branch whorls was

increasing each year, indicating healthy seedlings and continued potential for

good growth. Little evidence was present to suggest that cheatgrass was

negatively affecting this growth, most likely because the pine roots were able to

get to and stay in a zone of adequate soil moisture. By the time the cheatgrass

community had developed, the pine roots were below cheatgrass roots and pine

crowns were above cheatgrass stems and leaves. Once again, the value of

providing conifer seedlings with 1 to 3 years of little or no competition

1

 was

demonstrated.

Did the high cheatgrass density in herbicide-treated plots directly inhibit

bearclover and indirectly enhance pine growth? Density of bearclover was low

in the herbicide treatment and all plants were sprouts—none were from seed. Yet
USDA Forest Service Res. Note PSW-RN-419-Web. 1996 7

bearclover just outside the plots was flowering profusely and surely must have

been producing seed, some of which was disseminated in the study plots. In

another study, new bearclover seedlings were found at three locations, over a 2-

year period, in both burned and control plots, during March through June.18 The

dense grass may have denied this form of regeneration to bearclover and

indirectly aided the growth of the pine seedlings. Another possibility is that no

bearclover seed or new seedlings would have been present in herbicide plots in

any case.

Before site preparation, the study area was occupied by a few large ponderosa

pines and a dense stand of bearclover. It was characterized by limited accessibility

and productivity, at least for wood products from trees. After site preparation

and planting with ponderosa pine seedlings, the bearclover again became

abundant. So did cheatgrass, although its development differed widely between

the untreated control and the herbicide-treated plots. In the herbicide plots a

future ponderosa pine forest is likely. In the mulched plots and control, the pines

are dying and developing poorly. Here, the future plant community will

probably consist of pines and abundant bearclover.

End Notes and References

1

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

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

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

2

Heisey, R.M.; Delwiche, C.C.; Virginia, R.A.; Wrona, A.F.; Bryan, B.A.1980. A new nitrogen-fixing

non-legume: Chamaebatia foliolosa (Rosaceae). American Journal of Botany 67(3): 429-431.

3

Potter, Donald A. 1976. Ecology of bear clover. In: Bear Clover Conference, March 17, 1976. Sonora,

CA; 1-4.

4

Munns, E.N. 1922. Bear clover and forest reproduction. Journal of Forestry 20: 745-754.

5Potter, Donald A. 1985. Control of bear clover. In: Proceedings of the 6th annual forest vegetation

management conference. 1984 November 1-2; Redding, CA; 144-150.

6

Tappeiner, J.C.; Helms, J.A. 1971. Natural regeneration of Douglas-fir and white fir on exposed

sites in the Sierra Nevada of California. American Midland Naturalist 86: 358-370.

7Mack, Richard N. 1981. Invasion of Bromus tectorum L. into western North America: an ecological

chronicle. Agro-ecosystems 7: 145-165.

8

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

Biogeography 12: 349-361.

9Pyke, David A.; Novak, Stephen J. 1994. Cheatgrass demography—establishment attributes,

recruitment, ecotypes, and genetic variability. In: Monson, Stephen B.; Kitchen, Stanley G., eds.

Proceedings of a symposium on the ecology and management of annual rangelands; 1992 May

18-22; Boise, ID. Gen. Tech. Rep. INT-GTR-313. Ogden, UT: Intermountain Research Station,

Forest Service, U.S. Department of Agriculture; 12-21.

10McDonald, Philip M. 1986. Grasses in young conifer plantations—hindrance and help. Northwest

Science 60(4): 271-278.

11Dunning, D.; Reineke. 1933. Preliminary yield tables for second growth stands in the California

pine region. USDA Technical Bulletin 354; 23 p.

12This note neither recommends the pesticide uses reported nor implies that the pesticides have been

registered by the appropriate governmental agencies.

13Steel, Robert C.D.; Torrie, James H. 1980. Principles and procedures of statistics. 2nd ed. New

York: McGraw-Hill Book Company; 218-220.

14SAS Institute, Inc. 1988. SAS procedures guide. Release 6.03 edition. Cary, NC: SAS Institute, Inc.

15Snedecor, George W. 1956. Statistical methods. 5th ed. Ames: The Iowa State College Press; 316-

319.

16Daubenmire, R.F. 1968. Plant communities: a textbook on plant synecology. New York: Harper

and Row; 300 p.

17McDonald, Philip M.; Helgerson, Ole T. 1990. Mulches aid in regenerating California and Oregon

forests: past, present, and future. Gen. Tech. Rep. PSW-123. Berkeley, CA: Pacific Southwest

Research Station, Forest Service, U.S. Department of Agriculture; 19 p.

18Weatherspoon, C. Phillip. Pacific Southwest Research Station. USDA Forest Service, Redding,

Calif. [Personal communication with Philip M. McDonald]. July 1995.
The Authors

Philip M. McDonald, a research forester, and Glen A. Everest, a forestry

technician, are assigned to the Pacific Southwest Research Station’s Vegetation

Management Research Unit at the Silviculture Laboratory, 2400 Washington

Avenue, Redding, CA 96001.

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