Mechanical and Chemical Release in a12-Year-Old Ponderosa Pine PlantationGary O. Fiddler Philip M. McDonald

United StatesDepartmentof Agriculture

Forest Service

Pacific SouthwestResearch Station

Research PaperPSW-RP-232

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

AbstractFiddler, Gary O.; McDonald, Philip M. 1997. Mechanical and chemical release in a 12-

year-old ponderosa pine plantation. Res. Paper PSW-RP-232. Albany, CA: PacificSouthwest Research Station, Forest Service, U.S. Department of Agriculture; 12 p.

A 12-year-old ponderosa pine plantation on the Tahoe National Forest in northernCalifornia was mechanically treated with a Hydro-Ax in an attempt to increase the survivaland growth of the planted seedlings. Other release methods were not feasible because theshrubs in the mixed-shrub community (greenleaf manzanita, mountain whitethorn,bittercherry, coffeeberry) were too large (3 to 5 feet tall) and well developed. Additionaltreatments were a chemical treatment, in which 2,4-D was applied to a portion of the studysite that had been treated with the Hydro-Ax 1 year previously, and control. Elevengrowing seasons after treatment (1993), average pine crown cover was statistically higherin the mechanical treatment (Hydro-Ax alone) than in the control. This was the onlysignificant enhancement of pine growth by the Hydro-Ax alone. Mean pine diameter andheight did not differ statistically from the control after 11 years. In contrast, the Hydro-Axplus herbicide (chemical) treatment statistically increased pine crown cover, height, anddiameter over the Hydro-Ax alone and the control. Mean crown cover was 104 percentgreater in the treated trees than for pines in the control, height was 45 percent greater, anddiameter was 47 percent greater. Relative costs were $225 per acre for the Hydro-Ax alone(mechanical) and $273 per acre for the Hydro-Ax + herbicide (chemical). Altogether, themost cost-effective treatment was Hydro-Ax + herbicide.

Retrieval Terms: cost, growth, mechanical release, mechanical and chemical release,ponderosa pine, shrub sprouts

The AuthorsGary O. Fiddler is a silviculturist assigned to the Silviculture Development Unit,

Pacific Southwest Region, USDA Forest Service, with headquarters in San  Francisco, andstationed at Redding, Calif. Philip M. McDonald is a research forester assigned to theStation’s Vegetation Management Research Unit, with headquarters at Redding, Calif.

Publisher:Albany, California

Mailing address:PO Box 245, Berkeley CA

94701-0245

510 559-6300

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

April 1997

Pacific Southwest Research StationForest ServiceUS Department of Agriculture

Mechanical and Chemical Release in a12-Year-Old Ponderosa Pine Plantation

Gary O. Fiddler Philip M. McDonald

Contents

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

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

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

Study Location and Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Treatments and Study Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

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

Ponderosa Pine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Bittercherry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Greenleaf Manzanita . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Whitethorn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Coffeeberry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Combined Shrubs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Grass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Cost and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Discussion and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Pacific SouthwestResearch Station

USDA Forest ServiceResearch PaperPSW-RP-232

 April 1997

USDA Forest Service Res. Paper PSW-RP-232. 1997.

In Brief...Fiddler, Gary O.; McDonald, Philip M. 1997. Mechanical and chemical release in

a 12-year-old ponderosa pine plantation. Res. Paper PSW-RP-232. Albany,CA: Pacific Southwest Research Station, Forest Service, U.S. Department ofAgriculture; 12 p.

Retrieval Terms: cost, growth, mechanical release, mechanical and chemicalrelease, ponderosa pine, shrub sprouts

Ecosystem management is emerging as the current approach to themanagement of natural resources on National Forests. In forest management,

this translates into the need to know more about species other than the morecommonly studied wood producers, such as commercial conifers andhardwoods. Values like wildlife habitat and scenic diversity have a prominentposition in ecosystem management. Regardless of the desired products,manipulation of plant communities is often required to meet these future needs.Manipulation requires a healthy plant community to work with. This northernCalifornia study, located on the Nevada City Ranger District of the TahoeNational Forest, provides knowledge on species composition and developmentin a ponderosa pine plantation after a release treatment. An untreated control,mechanical release (Hydro-Ax alone), and chemical release (Hydro-Ax +herbicide) are contrasted.

In 1982 at age 12, when the study began, the ponderosa pine plantation waspart of a plant community composed of the planted pines and four shrub species.Grass was almost nonexistent. There were more than 10,000 woody plants peracre on the site. Shrub foliar cover exceeded 19,000 square feet, and height variedfrom 1 to 3 feet. Ponderosa pine height ranged from 6 to 7 feet, and crown coverfrom 12 square feet to 14 square feet per tree. Conifer stocking averaged morethan 200 trees per acre. The most common woody shrub was mountainwhitethorn, with greenleaf manzanita a close second. A release treatment wasapplied to this plantation at the end of the 12th year.

Eleven growing seasons after this release, the plant community consisted ofthe same species that had been present before treatment, with the exception of asignificant increase in the grass population, primarily in the chemical treatmentand control. Grass density exceeded 1,246,000 plants per acre in the chemicallytreated areas. Greenleaf manzanita had replaced mountain whitethorn as themost abundant woody shrub. Ponderosa pine height had at least doubled in alltreatments. Crown cover of ponderosa pine had increased significantly frompretreatment values, and now ranged from 47 to 96 square feet per tree. In thecontrol, density and height of the woody shrubs increased during the studyperiod, but foliar cover decreased by more than 50 percent.

The mechanical treatment alone did not significantly increase conifer growthover that in the control except for crown cover. In year 11, pine height anddiameter were not significantly different between these two treatments. But theherbicide in conjunction with the Hydro-Ax increased all parameters of pinegrowth over that in the other treatments. This significant increase in pine growthcost 21 percent more than the mechanical treatment alone. Mechanical releasealone is an ineffective treatment for releasing plantations of this age.

1USDA Forest Service Res. Paper PSW-RP-232. 1997.

Introduction

Conifer plantations are an important component in ecosystem management,just as they are in forest management. In the latter, these plantations are

the beginning point for all forest management that will follow, whether thismanagement takes the form of release, precommercial or commercial thinning,pruning, or other cultural activities leading up to final harvest of the stand. Inecosystem management, these plantations furnish some of the building blocksthat will be molded and manipulated into the types of stands required tosatisfy future needs. These needs may take the form of wildlife habitat,vegetative diversity, scenic values, or other more commodity-oriented values,such as wood production.

The establishment of plantations is often not an easy task. Almost all newplantations in California will be invaded by weeds in the form of hardwoods,woody shrubs, grasses, and forbs (Fiddler and McDonald 1990). This invasionusually occurs early in the life of the plantation, and without proper releasetreatments, the competition between the planted conifers and these weedscontinues until crown closure. That this competition is detrimental to survivaland growth of the planted conifers is well established (Gjerstad and Glover 1992,Stewart and others 1984). Another accepted research finding is that in order forthe planted conifers to develop at or near the potential of the site, they must bereleased from competing vegetation early in the life of the plantation, probablyin the first or second year after the conifer seedlings are outplanted (McDonald1982, McDonald and Fiddler 1986, Newton and Preest 1988).

Despite these findings, many untreated plantations that are 10 years ofage or older can be found in the western United States. What should be donewith them? If they are left to grow in an untreated condition, loss of growthor death is likely. Ponderosa pine (Pinus ponderosa Dougl. ex Laws. var.ponderosa) has demonstrated its ability to survive despite extremecompetition, but at the cost of decreased growth. The fact that pine saplingsare taller than the surrounding vegetation does not guarantee that theponderosa pines are growing at the potential of the site. Considering all thesefactors, should these older plantations be released?

If the answer is yes, a release method must be chosen. Several of the morecommonly used methods are not effective when the competing vegetation is asold and well developed as that found in this study. Manual methods areprohibitively expensive when trying to control older weeds, and grazing bycattle or sheep is at best marginally effective. Even herbicides alone are ineffectivefor controlling tall, well-developed shrubs.

The most commonly used release treatment in older plantations on NationalForest land in northern California uses a mechanical chopper, similar in principleto a lawn mower, which cuts the vegetation close to the ground and leaves thechopped stems and leaves on site. The question is: does this operation reduce thecompeting vegetation long enough to increase the growth of the conifer saplings?

This paper reports on the effectiveness of mechanical chopping as a releasetreatment. In addition, a treatment in which the mechanically cut shrubs weresprayed with a herbicide 1 year after cutting was evaluated. Cost and productiondata are included for all treatments. Pine growth response in diameter, height,and crown cover to these treatments and an untreated control, as well asresponses of the treated and untreated shrub community, are reported.

2 USDA Forest Service Res. Paper PSW-RP-232. 1997.

MethodsStudy Location and EnvironmentThis study is part of a National Administrative Study on vegetation managementin young conifer plantations started in 1980 in northern California (Fiddler andMcDonald 1984). The study area, known as Big Tunnel, is located on the NevadaCity Ranger District of the Tahoe National Forest, about 20 miles east of NevadaCity, Calif. Before timber harvest, the study site supported a forest of ponderosapine, California white fir (Abies concolor var. lowiana Gord. Lemm.), and incense-cedar (Libocedrus decurrens Torr.). The understory consisted of scatteredindividuals of greenleaf manzanita (Arctostaphylos patula Greene), mountainwhitethorn (Ceanothus cordulatus Kell.), and California black oak (Quercus kelloggiiNewb.). Forbs and grasses were small and few in number.

After timber harvest in 1970, logging slash and woody shrubs were pushedinto windrows with a brushrake and burned. Ponderosa pine seedlings from alocal seed source were raised at the Forest Service nursery at Placerville, Calif.,and hand planted as 1-year-old, bare-root stock in May 1971. A spacing of 10 by10 feet resulted in about 430 planted trees per acre. Survival at the end of the firstgrowing season was 90 percent.

In early 1983, 13 years after site preparation, the area had a dense cover ofgreenleaf manzanita, mountain whitethorn, bitter cherry (Prunus emarginataDougl.), and coffeeberry (Rhamnus purshiana DC.) resulting mostly from newseedlings and sprouts from plants in the previous stand. Height of this coverranged from 1 to 3 feet. The most common shrubs were greenleaf manzanita andwhitethorn. Grass (mostly Acnatherum sp. Hickman 1993) was present on the site,but in fairly small numbers.

Elevation of the study site is 4600 feet with slopes of 5 to 10 percent, andaspects of northeast, northwest, and south. The climate is characterized bywarm, dry summers and cool, moist winters. Mean annual precipitation variesfrom 35 to 70 inches with about 50 percent falling as snow. The mean Januarytemperature is 35 oF, mean July temperature is 70 oF, and the mean annualtemperature varies from 50 to 58 oF. The frost-free season is from 130 to 225 days.

The soil is of the McCarthy series. It is moderately deep, well drained andformed from material weathered from andesitic mudflows. The soil is sandyloam or loam throughout, and may be gravelly or cobbly.

Based on the height-age relationship of dominant mixed conifer trees, sitequality of the study area before harvesting was 40 feet in 50 years (Dunning andReineke 1933). As a whole, the study area is remarkably uniform in terms ofslope and site quality.

Treatments and Study MethodsThe study, begun in fall 1982, includes data recorded through 11 growing seasons.

The experimental design was complete randomized block with one 3-leveltreatment. Differences among treatments were detected by analysis of varianceand Tukey tests. Because information is gathered from permanent plots, the dataare not truly independent from year to year. The α levels or type I errors apply toeach measurement and year separately. The overall error rate could increase by asmuch as the given amount for each measured variable each year.

Treatments, each replicated three times (3 blocks), included mechanical,chemical (mechanical plus a herbicide), and a control. A replicate consisted ofabout one-seventh acre on which 30 to 40 ponderosa pine saplings weresurrounded by two or three rows of buffer (saplings receiving the sametreatment). Twenty of these pines per replication were flagged formeasurement of height, stem diameter at 4.5 feet above mean ground line, and

3USDA Forest Service Res. Paper PSW-RP-232. 1997.

crown cover. Those chosen were thrifty saplings that had good potential ofbecoming harvestable trees; small, misshapen and discolored saplings werenot part of the study.

Sampling intensity for competing vegetation was nine randomly selectedplots in each replication. Plots were centered around conifers and were 1 milacre(0.001 acre) in size. Competing vegetation was measured for density and averagedominant height (average of the three tallest stems measured from mean groundline to bud). Foliar cover (the sum of shadows that would be cast by leaves andstems of individual species expressed as a percentage of the land surface[Daubenmire 1968]) was determined by ocular estimate. Values less than 0.5square foot per species in each plot were not recorded.

Mechanical treatment consisted of cutting the woody shrubs with a Hydro-Ax1—a machine with a large rotary cutting head in which there are twofree-swinging blades (fig. 1). The cutting head is mounted on a vehicle similar insize to a medium-sized log skidder. The Hydro-Ax resembles a common rotarylawnmower, but cuts an 8-foot swath. With experienced operators, as was thecase on the study, the Hydro-Ax works efficiently on slopes up to about 40percent, and production rates of 3 to 4 acres per day are common. Current (1995)costs range from $135 to $225/acre. Severed material remains in place. Cuttingwas done September 1982.

Chemical treatment consisted of applying 3 pounds acid equivalent of 2,4-D2

in 10 gallons of solution per acre to the foliage of sprouting shrubs the first yearafter cutting. The herbicide was applied in July 1983 using a carbon dioxidepressurized boom. Nozzles on the boom were the same type as those used inhelicopter application; hence, rate of application and droplet size were similar tothose used in helicopter application of herbicides. The boom, which covered a 9-foot swath, was held about 12 inches above the shrubs, and the spray wasdirected downward. The system was calibrated using trial runs with water to

1Trade names and commercialproducts are mentioned solelyfor information. No endorse-ment by the U.S. Department ofAgriculture is implied.

2This paper neither recommendsthe herbicide uses reported norimplies that the herbicides havebeen registered by the appro-priate governmental agencies.

Figure 1—A Hydro-Ax showingcutting head.

4 USDA Forest Service Res. Paper PSW-RP-232. 1997.

determine the proper walking speed at which to apply the correct amount ofherbicide to each replication. The entire seventh-acre replicate, plus half of thewidth of the buffer, was sprayed. The area treated around each pine had at leasta 5-foot radius. Workers guided the applicator at each side of the swath to ensureeven coverage and no overlap.

A control served to show the response of naturally developing vegetationand its effects on the ponderosa pines.

Production data were gathered for each treatment. The basis for productionwas hourly records; the basis for costs was $90.00 per hour (the 1995 rate forequipment of the type used on the study) and $11.13 per hour (the rate for aLaborer-1, U.S. Department of Labor, as of June 1995).

Statistical analysis of density, cover, and height of combined shrubs testedwhether the treatments differed from the control and each other, and whetherthey continued to do so in spite of shrub regrowth.

ResultsAs forest management moves toward ecosystem management, knowledge andinformation on the dynamics and composition of plant communities,  in additionto the conifer component, become desirable. Results are most useful whenpresented both for individual and groups of species, because competition to theconifer saplings results from the interaction of the different species found in theweed community, not from individual members of it. Data on survival, stemdiameter, height, and cover are presented for the planted ponderosa pine saplings,and information on density, foliar cover, and height for bittercherry, greenleafmanzanita, whitethorn, coffeeberry, combined shrubs, and grass is reported.

Ponderosa PineNo ponderosa pine saplings died during the life of the study (1982 to 1993). Anearly concern about damage to the conifers from flying debris generated by theHydro-Ax proved to be unwarranted. In addition, no damage to conifers fromthe machine itself was noted.

The gouty pitch midge (Cecidomyia piniinopis) attacked the conifers in 1985,causing branch flagging in 1986. Only the tips of the affected branches showedany damage. Trees in each treatment were attacked by this insect; those in thechemical treatment were attacked the fewest number of times. Studies located onsites similar to Big Tunnel have experienced damage from the gouty pitch midge(McDonald and Oliver 1984), but damage and loss of growth in this studyappeared minimal (Schultz 1986).

Differences among treatments in ponderosa pine crown cover were evident in1983, the first growing season after initial treatment. Tukey analysis showed coverof the pines was significantly larger (p < 0.05 unless otherwise stated) in themechanical treatment than in the control (table 1). The chemical was applied in July1983, after the growing season was over; therefore, only two of the treatmentscould affect conifer growth in 1983: the mechanical treatment and the control. By1985, however, pine diameter and height were significantly greater in the chemicaltreatment than in the control. This difference continued through 1993. In 1986, pinecover in the chemical treatment was larger than in the control and continued thisway through 1993. In 1986, pine diameter in the chemical treatment becamesignificantly larger than in the mechanical treatment, a trend that continuedthrough 1993. By 1988, pine height in the chemical treatment exceeded that in themechanical treatment and continued through 1993. Pine height was never greaterin the mechanical treatment than in the control. In 1986 and 1988, pine diameterwas significantly greater in the mechanical treatment than in the control, but thisdifference had disappeared by 1993.

5USDA Forest Service Res. Paper PSW-RP-232. 1997.

BittercherryDensity and height of this species never differed significantly among thetreatments during the study  (table 2). Density in the control increased to a high of2,037 plants per acre in 1985, but decreased to 1,133 plants by study end in 1993.Height in the control increased from 3.9 feet to 4.3 feet, a gain of 11 percent. For1985, 1986, and 1988, bittercherry foliar cover was significantly smaller in thechemical treatment than in the control. This difference had disappeared by 1993.Foliar cover was never significantly different between the mechanical treatmentand the other two treatments. In general, this species showed a trend of relativelyconstant density, decreasing foliar cover, and slightly increasing height. Themore robust plants that had existed early in the study were declining andbecoming tall and spindly with sparse foliage.

Greenleaf ManzanitaExcept for whitethorn, greenleaf manzanita was the most abundant shrub specieswhen the study started. By 1988, it was the most common woody shrub in thestudy. In the control, density generally increased throughout the study and was66 percent larger by 1993 (table 3). Density was significantly less in the chemicaltreatment than in the mechanical treatment starting in 1985 and continuingthrough 1993. Density never differed between the mechanical treatment and thecontrol. Foliar cover in the control increased from 6,037 square feet per acre in1983 to 9,333 square feet per acre in 1986 before declining to 6,867 square feet peracre by 1993, a net gain of 14 percent. Foliar cover was significantly less in thechemical treatment than in the control in 1985, 1986, and 1988, but by 1993 therewere no differences among the three treatments. The mechanical treatment and

Table 1—Average diameter, crown cover, and height of ponderosa pine,Big Tunnel Plantation, Tahoe National Forest, California, 1983-1993

Year Treatment Diameter Cover Height

inches ft2/tree ft

1983 Mechanical 1.55 a1 13.86 a 6.98 aChemical .00 o2

Control 1.33 a 11.67 b 6.70 aStandard error 0.05 0.28 0.17

1985 Mechanical 2.43 ab 24.91 a 8.75 abChemical 2.94 a 27.93 a 9.89 aControl 2.02 b 18.53 a 8.24 bStandard error 0.10 1.91 0.26

1986 Mechanical 2.87 a 33.78 ab 9.68 abChemical 3.60 b 41.22 a 11.11 aControl 2.40 c 24.55 b 9.12 bStandard error 0.09 3.02 0.31

1988 Mechanical 3.77 a 41.68 ab 11.99 aChemical 4.83 b 52.35 a 14.53 bControl 3.07 c 31.43 b 11.12 aStandard error 0.08 3.74 0.45

1993 Mechanical 7.56 a 67.76 a 18.99 aChemical 9.51 b 96.20 b 24.19 bControl 6.49 a 47.23 c 16.68 aStandard error 0.32 3.52 0.87

1For each year, treatment means in each column followed by the sameletter do not differ significantly according to a Tukey Test (α = 0.05).

2Treatment not complete until chemical applied.

6 USDA Forest Service Res. Paper PSW-RP-232. 1997.

Table 2—Average density, cover, and height of bittercherry, Big TunnelPlantation, Tahoe National Forest, California, 1983-1993

Year Treatment Density Cover Height

plants/acre ft2/acre ft

1983 Mechanical 2,889.a1 1,333 a 1.97 aChemical 2,481 a 704 a 1.63 aControl 1,444 a 2,185 a 3.88 aStandard error 866 315 0.65

1985 Mechanical 3,111 a 1,963 ab 3.40 aChemical 1,296 a 296 a 2.05 aControl 2,037 a 3,074 b 4.11 aStandard error 825 402 0.66

1986 Mechanical 2,741 a 2,037 ab 4.10 aChemical 1,222 a 111 a 2.26 aControl 1,444 a 3,333 b 4.85 aStandard error 544 481 0.76

1988 Mechanical 2,926 a 1,592 ab 4.94 aChemical 1,074 a 0 a 3.37 aControl 1,555 a 2,148 b 4.96 aStandard error 556 368 1.05

1993 Mechanical 2,667 a 267 a 4.13 aChemical 1,733 a 0 a 4.12 aControl 1,133 a 733 a 4.31 aStandard error 596 249 0.52

1For each year, treatment means in each column followed by thesame letter do not differ significantly according to a Tukey Test (α =0.05).

Table 3—Average density, cover, and height of greenleaf manzanita, BigTunnel Plantation, Tahoe National Forest, California, 1983-1993

Year Treatment Density Cover Height

plants/acre ft2/acre ft

1983 Mechanical 5,000.a1 2,370 a 1.09 aChemical 5,259 a 2,481 a 1.04 aControl 3,444 a 6,037 a 3.94 bStandard error 763 1,255 0.40

1985 Mechanical 4,852 a 4,000 ab 2.27 aChemical 1,037 b 259 a 0.74 bControl 3,592 a 8,814 b 4.24 cStandard error 499 1,129 0.28

1986 Mechanical 4,481 a 4,592 ab 2.75 aChemical 926 b 111 a 0.91 bControl 3,444 ab 9,333 b 4.50 cStandard error 541 1,203 0.22

1988 Mechanical 4,852 a 4,444 ab 3.66 aChemical 814 b 0 a 1.66 bControl 3,407 ab 7,703 b 5.03 cStandard error 550 1,298 0.26

1993 Mechanical 9,733 a 3,200 a 3.90 aChemical 1,400 b 0 a 2.02 bControl 5,733 ab 6,867 a 5.15 aStandard error 1,263 1,792 0.35

1For each year, treatment means in each column followed by the sameletter do not differ significantly according to a Tukey Test (α= 0.05).

7USDA Forest Service Res. Paper PSW-RP-232. 1997.

the control never differed in foliar cover. Mean height increased throughout thestudy in the control, resulting in a gain of 31 percent. Height in the chemicaltreatment was significantly less than in the control in every year of the study.There was also a significant difference in this parameter between the chemicaltreatment and the mechanical treatment in every year except 1983. Heightdiffered between the mechanical treatment and the control in every year except1993. Without treatment, this species tended to increase in density, foliar cover,and height throughout the study. With mechanical treatment, trends in density,foliar cover, and height were similar to those in the control; but when a herbicidewas applied to the cut shrubs, density and foliar cover declined.

WhitethornThis was the most abundant plant species when the study began but relinquishedthis position in 1988. Density increased from 3,778 plants per acre in 1983 to 4,533in 1993 in the control (table 4). Height showed a net gain of only 3 percent despitelarge increases during the middle years of the study. Foliar cover decreased from8,888 square feet per acre in 1983 to 1,200 square feet per acre by the close of thestudy, a decrease of 86 percent. There were never any significant differencesamong treatments in density or cover. Differences in height among the treatmentsbegan to disappear by 1988 and had completely disappeared by 1993. During thestudy, this species tended to increase in density and slightly in height, butdecrease greatly in foliar cover.

CoffeeberryAs was the case with whitethorn in the control, density and height of this speciesshowed a net increase during the study, but foliar cover decreased significantly(table 5). Density increased 236 percent, height increased 20 percent, and foliar

Table 4—Average density, cover, and height of whitethorn, Big TunnelPlantation, Tahoe National Forest, California, 1983-1993

Year Treatment Density Cover Height

plants/acre ft2/acre ft

1983 Mechanical 3,000.a1 3,481 a 1.09 aChemical 3,518 a 3,000 a 1.09 aControl 3,778 a 8,888 a 2.78 bStandard error 389 192 0.03

1985 Mechanical 2,741 a 5,666 a 2.33 aChemical 2,148 a 2,259 a 1.38 bControl 3,888 a 8,407 a 3.04 cStandard error 358 1,443 0.09

1986 Mechanical 2,778 a 4,963 a 2.62 aChemical 1,963 a 1,519 a 1.47 bControl 3,592 a 6,703 a 3.16 cStandard error 390 1,059 0.08

1988 Mechanical 2,667 a 2,815 a 3.29 aChemical 1,926 a 666 a 2.00 bControl 3,148 a 3,852 a 3.28 aStandard error 410 759 0.15

1993 Mechanical 3,200 a 1,067 a 2.95 aChemical 3,067 a 0 a 2.60 aControl 4,533 a 1,200 a 2.86 aStandard error 505 590 0.16

1For each year, treatment means in each column followed by the sameletter do not differ significantly according to a Tukey Test (α = 0.05).

8 USDA Forest Service Res. Paper PSW-RP-232. 1997.

cover decreased 92 percent. Density showed no significant differences amongtreatments until 1993, at which time there was a difference between the chemicaltreatment and the control. A difference in foliar cover in 1985 between thesesame two treatments had disappeared by 1986. In 1985, a significant difference inheight among treatments was recorded. This difference disappeared in 1986. In1988, there was a significant difference in height between the mechanical and thechemical treatment. This difference was gone by the end of the study in 1993.

Combined ShrubsAs noted earlier, competition to the conifer seedlings results from the interactionof the different species in the plant community. Data on a combination of shrubspecies best show this relationship. The density, foliar cover, and height of thefour shrub species present in all replications  (greenleaf manzanita, whitethorn,bittercherry, and coffeeberry) were aggregated and presented as “combinedshrubs” (table 6).

In the fall of 1983, after one full growing season, combined shrubs in thecontrol numbered 10,073 plants per acre, had 19,517 square feet of foliar cover,and were 3.3 feet tall. By the end of the 1993 growing season, density in thecontrol had increased 60 percent to 16,133 plants per acre. During this sameperiod, height had increased to 3.8 feet, a 14 percent increase. But foliar coverhad decreased to 9,000 square feet per acre, a decline of 54 percent. Density in thechemical treatment was significantly less than in the mechanical treatment everyyear of the study, except 1983; by 1993 density in the chemical treatment wassignificantly less than in both other treatments. Foliar cover in the control wassignificantly larger than in the other treatments through 1986, but by 1988, foliarcover in the mechanical treatment did not differ significantly from that in the

Table 5—Average density, cover, and height of coffeeberry, Big TunnelPlantation, Tahoe National Forest, California, 1983-1993

Year Treatment Density Cover Height

plants/acre ft2/acre ft

1983 Mechanical 8,925.a1 1,518 a 1.61 aChemical 3,074 a 1,037 a 1.27 aControl 1,407 a 2,407 a 2.28 aStandard error 4,298 200 0.93

1985 Mechanical 5,666 a 2,185 ab 2.89 aChemical 667 a 333 a 1.96 bControl 3,333 a 2,333 b 3.44 cStandard error 1,499 391 0.05

1986 Mechanical 3,741 a 2,556 a 3.84 aChemical 555 a 259 a 2.50 aControl 3,370 a 2,296 a 3.73 aStandard error 1,142  550 0.29

1988 Mechanical 2,852 a 1,407 a 4.33 aChemical 518 a  74 a 2.23 bControl 1,889 a 1,444 a 4.02 abStandard error 643 365 0.38

1993 Mechanical 2,733 ab 0 a 3.54 aChemical 1,467 a 0 a 1.85 aControl 4,733 b  200 b 2.74 aStandard error 614 0 0.56

1For each year, treatment means in each column followed by the sameletter do not differ significantly according to a Tukey Test (α = 0.05).

9USDA Forest Service Res. Paper PSW-RP-232. 1997.

control; foliar cover in the chemical treatment was significantly less than in theother treatments in 1985, 1986, and 1988. By 1993 there was no significantdifference in foliar cover among the treatments. Height increased every year inthe chemical treatment and was always significantly shorter in this treatmentthan in the other two, except in 1983, when it did not differ from that in themechanical treatment. Heights in the control and the mechanical treatmentpeaked in 1988, at which time they began to decline. From 1986 through the endof the study, height in the control and the mechanical treatment did not differ.

GrassGrasses were not an important component of the study area before the studybegan. Their numbers were few and the grasses were small and scattered. Thissituation did not change until 1985, when grass density showed a significantincrease in the chemical treatment. A density in excess of 14,000 plants per acrewas recorded at the end of this growing season (table 7). This significant differencein density between the chemical treatment and the other two treatmentsdisappeared in 1986 and 1988. However, in 1993, density differed significantlybetween the chemical and mechanical treatments. Density never differed betweenthe control and the mechanical treatment. Foliar cover and height never differedsignificantly among the treatments. The grass component reached a height ofalmost 3 feet before declining to less than 1 foot by 1993. This component, whosenumbers were so small at the start of the study as to be considered minor, had1,246,667 plants per acre by 1993 in the chemical treatment. There was a steadyincrease in density in the chemical treatment for every year of the study. Thisincrease resulted in 85 times more grass plants in 1993 than in 1985.

Table 6—Average density, cover, and height of combined shrubs (greenleafmanzanita, whitethorn, bittercherry, coffeeberry), Big Tunnel Plantation,Tahoe National Forest, California, 1983-1993

Year Treatment Density Cover Height

plants/acre ft2/acre ft

1983 Mechanical 19,813.a1 8,703 a 1.37 aChemical 14,332 a 7,222 a 1.23 aControl 10,073 a 19,517 b 3.28 bStandard error 4,491  390 0.33

1985 Mechanical 16,369 a 13,813 a 2.66 aChemical 5,148 b 3,148 b 1.30 bControl 12,850 ab 22,628 c 3.73 cStandard error 2,055  528 0.18

1986 Mechanical 13,740 a 14,147 a 3.26 aChemical 4,666 b 2,000 b 1.51 bControl 11,851 ab 21,665 c 4.00 aStandard error 1,435 1,130 0.22

1988 Mechanical 13,295 a 10,258 a 4.02 aChemical 4,333 b  741 b 2.08 bControl 9,999 b 15,147 a 4.34 aStandard error  857 1,185 0.30

1993 Mechanical 18,333 a 4,533 a 3.58 aChemical 7,667 b  0 a 2.48 bControl 16,133 a 9,000 a 3.75 aStandard error 1,113 1,790 0.20

1For each year, treatment means in each column followed by the sameletter do not differ significantly according to a Tukey Test (α = 0.05).

10 USDA Forest Service Res. Paper PSW-RP-232. 1997.

Cost and ProductionCost data for the chemical and mechanical treatments were obtained frominspection reports that were compiled during the execution of the service contractunder which the work was accomplished. Equipment production rates forapplying the treatments came from Nevada City Ranger District records. Costand production data for herbicide application came from project records.

Although based on rates for smaller areas, the cost and production ratesgathered from this study compared favorably with rates generated by contractsfor similar work on large areas awarded on several National Forests in northernCalifornia. These data were expected to be similar because both the contracts andthis study shared similar terrain, woody plant species, treatment types, andworker motivation.

The chemical treatment was more expensive than the mechanical treatmentbecause of chemical cost and labor required to apply the herbicide:

Treatment Production rate CostHours/acre Dollars/acre

Mechanical 2.5 225Chemical 5.5 273

Dollars per acre are for labor, equipment time, and chemical; they do not includeoverhead. Costs are updated to 1995 rates for labor and equipment of the typeused on the study.

Table 7—Average density, cover, and height of grass, Big Tunnel Planta-tion, Tahoe National Forest, California, 1985-1993

Year Treatment Density Cover Height

plants/acre ft2/acre ft

1985 Mechanical 1,555.a1 222 a 1.92 aChemical  14,739 b 2,666 a 2.76 aControl     0 a  0 a .—Standard error 1,559 931 .—

1986 Mechanical 1,259 a  37 a 1.05 aChemical 209,423 a 2,296 a 1.84 aControl     0 a 0 a .—Standard error  95,376 802 .—

1988 Mechanical 1,481 a 0 a 1.00 aChemical 383,702 a 1,370 a 2.30 aControl 1,481 a 0 a 0.90 aStandard error  97,809 446 .—

1993 Mechanical     0 a 0 a .—Chemical 1,246,667 b 0 a 0.59 aControl  44,000 ab 0 a 0.85 aStandard error 107,970 0 .—

1For each year, treatment means in each column followed by the sameletter do not differ significantly according to a Tukey Test (α = 0.05).

11USDA Forest Service Res. Paper PSW-RP-232. 1997.

Discussion and ConclusionsConifer plantations function as the building blocks for both forest and ecosystemmanagement. Both management strategies require thrifty stands of trees (usuallyconifers) that can be manipulated into the species composition and standstructure needed for future uses. Growth of these plantations has to be at anacceptable rate, that rate depending on future needs, whether the final product isa tangible commodity such as boards or an amenity such as scenic value. Thesestands must be thrifty if they are to survive for the many decades required toproduce these desired results. To remain thrifty, most plantations in northernCalifornia must be released at least once during their lifetime; the best time forthis release is early in the life of the plantation, usually within the first 1-3 yearsafter outplanting. But often, the most opportune time for release is lost, andmanagers must consider how to treat older plantations. The size and amount ofwoody shrubs in these older plantations dictate mechanical treatment of somekind. Manual treatments are too expensive, and grazing and chemical treatmentsare usually not effective in controlling plants of this size.

Eleven growing seasons after treatment, mechanical release applied to a 12-year-old ponderosa pine plantation increased crown cover of the conifer saplingsby 43 percent over that in the untreated control. Cost of this mechanical treatmentwas $225 per acre. Pine height and diameter were not significantly differentbetween the mechanically treated areas and the control after the 11 growingseasons. In a variation to the mechanical treatment, herbicide was applied to thesevered shrubs 1 year after the cutting operation. This herbicide application,including chemical and labor to apply the chemical, cost $48.29 per acre. The costof the herbicide application added to the cost of mechanically cutting the shrubstotaled about $273 per acre. This additional $48 per acre resulted in a significantdividend to the growth of the conifers. By 1993, pine crown cover in the chemicaltreatment was significantly larger than in the other two treatments, increasing by104 percent over the control and 42 percent over the mechanical treatment  alone.Pine diameter and height also differed significantly in the chemical treatmentwhen compared to the other treatments. Diameter in the chemical treatment was47 percent larger than in the control and 26 percent larger than in the mechanicaltreatment. Pine height was 45 percent greater in the chemical treatment than inthe control and 27 percent greater in the chemical treatment than in themechanical treatment.

Grass plants, in large numbers, became established in the chemical treatmentearly in the study. Grass is shorter and probably less competitive to conifer treesof the size in the study than the woody shrubs that it replaced. Less competitionmeant more site resources would be available to the pine saplings.

For these plantations, releasing with mechanical treatment alone resulted ina significant increase in ponderosa pine cover, with no increase in coniferdiameter or height. This significant increase in crown cover did not appear untilthe 11th year after treatment. When the mechanical treatment was enhanced byapplying a herbicide 1 year later, at an additional cost of 21 percent, allparameters of pine growth were significantly increased over those in both themechanical treatment alone and in the control. Mechanical release alone was notan effective or cost-efficient release method for these older plantations.

The Big Tunnel site indicated that untreated and mechanically treated ponderosapines survived for at least 11 years, but whether they would grow to the size neededto meet future demands is doubtful. Ecosystem management and forest managementdepend upon building blocks being more predictable than this.

12 USDA Forest Service Res. Paper PSW-RP-232. 1997.

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

and Row; 300 p.

Dunning, D.; Reineke, L.H. 1933. Preliminary yield tables for second-growth stands in theCalifornia pine region. Tech. Bulletin FS-354. Washington, DC: Forest Service, U.S. Departmentof Agriculture; 23 p.

Fiddler, Gary O.; McDonald, Philip M. 1984. Alternatives to herbicides in vegetation management: astudy. In: Proceedings of the 5th Annual Forest Vegetation Management Conference; 1983 November2-3; Sacramento, CA.   Redding, CA: Forest Vegetation Management Conference; 115-126.

Fiddler, Gary O.; McDonald, Philip M. 1990. Manual release contracting: production rates, costs,and future. Western Journal of Applied Forestry 5(3): 83-85.

Gjerstad, Dean H.; Glover, Glenn R. 1992. Abstracts: international conference on forest vegetationmanagement—ecology, practice, and policy. 1992 April 27-May 1; Auburn, AL. Report 1992: 1.Auburn, AL: Auburn Univ. School of Forestry; 140 p.

McDonald, Philip M. 1982. Adaptations of woody shrubs. In: Hobbs, S.D.; Helgerson, O.T., eds.Proceedings of a workshop on reforestation of skeletal soils; 1981 November 17-19; Medford,OR. Corvallis, OR: Forest Research Laboratory, Oregon State Univ.; 21-29.

McDonald, Philip M.; Fiddler, Gary O. 1986. Release of Douglas-fir seedlings: growth andtreatment costs. Res. Paper PSW-182. Berkeley, CA: Pacific Southwest Forest and RangeExperiment Station, Forest Service, U.S. Department of Agriculture; 9 p.

McDonald, Philip M.; Oliver, William W. 1984. Woody shrubs retard growth of ponderosa pineseedlings and saplings. In: Proceedings of the 5th Annual Forest Vegetation ManagementConference; 1983 November 2-3; Sacramento, CA. Redding, CA: Forest Vegetation ManagementConference; 65-89.

Newton, Michael; Preest, David S. 1988. Growth and water relations of Douglas-fir seedlingsunder different weed control regimes. Weed Science 36: 653-662.

Schultz, David. 1986. Biological evaluation of Big Tunnel Plantation, Nevada City Ranger District.Rep. 86-31. San Francisco, CA: Pacific Southwest Region, Forest Service, U.S. Department ofAgriculture; 3 p.

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

The Forest Service, U.S. Department of Agriculture, is responsible for FederalLeadership in forestry. It carries out this role through four main activities:

• Protection and management of resources on 191 million acres of National ForestSystem lands

• Cooperation with State and local governments, forest industries, and private landownersto help protect and manage non-Federal forest and associated range and watershed lands

• Participation with other agencies in human resource and community assistance programsto improve living conditions in rural areas

• Research on all aspects of forestry, rangeland management, and forest resources utilization.

The Pacific Southwest Research Station• Represents the research branch of the Forest Service in California, Hawaii, American

Samoa, and the western Pacific.

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