USDA

United States

Department

of Agriculture

Forest Service

Pacific Southwest

Research Station

Timing and Duration of Release Affect

Vegetation Development in a Young

Ponderosa Pine Plantation

Research Paper

PSW-RP-245 Philip M. McDonald Gary O. Fiddler
Publisher

Albany, CaBfornia

Mailing address:

PO Box 245. Berkeley CA

94701-0245

(510) 559-6300

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

January 200 I

Pacific Southwest Research Station

Forest Service

U.S. Department of Agriculture

Abstract

McDonald, Philip M.; Fiddler, Gary O. 2001. Timing and duration of release

affect vegetation development in a young ponderosa pine plantation. Res.

Paper PSW-RP-245. Albany, CA: Pacific Southwest Research Station, Forest

Service, U.s. Department of Agriculture; 15 p.

The density and development of greenleaf manzanita, other shrubs, and

graminoids were evaluated in a young ponderosa pine plantation on a poor site

in northern California from 1988 through 1997. Manual grubbing to a 5-foot

radius created treatment regimes that lasted for 3 to 6 years and vegetation

recovery times of 4 to 10 years. The duration and timing of the grubbing

constituted the treatments. Greenleaf manzanita was the dominant shrub in the

former brushfield and again dominated after site preparation and release. In

1988 its density in the control averaged 123,500 plants per acre; in 1997 density

had declined to 44,450 plants per acre, but its foliar cover had increased to 34,600

ft' per acre and its height to 3.2 feet-values that were significantly larger than

counterparts in any other treatment. Early release provided pine seedlings with a

Significant advantage in average height and diameter if continued each year for

the first 3 years and first 6 years. However, manually grubbing the last 3 of the

first 6 years gave no biological advantage and was more expensive. Delaying

grubbing for the first 3 years and then grubbing each year for the next 3 years

(years 4 through 6) also provided pine seedlings with a significant growth

advantage over counterparts in the control, but was expensive. Delayed grubbing

usually is biologically ineffective, but on poor sites such as this, any release is

beneficial.

Retrieval Terms: competing vegetation, northern California, plant succession,

ponderosa pine seedlings, poor site, timing of release

The Authors

Philip M. McDonald is a research forester with the Station's Western Forest

Management Research Unit, 2400 Washington Ave., 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, Vallejo, CA

and stationed at Redding, CA.
Timing and Duration of Release Affect

Vegetation Development in aYoung

Ponderosa Pine Plantation

Philip M. McDonald

Contents

Gary o. Fiddler

Pacific Southwest

Research Station

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

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

Methods 2

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

Study and Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4

Sampling 4

Results 5

Plant Diversity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 5

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

Other Shrubs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 7

Graminoids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 7

Forbs 7

Ponderosa Pine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 8

Production and Cost. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 11

Discussion and Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 12

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 14

USDA Forest Service

Research Paper

PSW-RP-24S

January 200 I

ii

.' . In Brief...

McDonald, Philip M.; Fiddler, Gary O. 2001. Timing and duration of release

affect vegetation development in a young ponderosa pine plantation. Res.

Paper PSW-RP-245. Albany, CA: Pacific Southwest Research Station, Forest

Service, U.S. Department of Agriculture; 15 p.

Retrieval Terms: competing vegetation, northern California, plant development,

ponderosa pine seedlings, poor site, timing of release

Density and development of greenleaf manzanita and several other shrubs

and grasses that invaded a young conifer plantation were studied on a poor site

at mid-elevation (4,750 feet) in northern California. In addition, survival and

growth of planted ponderosa pine seedlings were quantified in four release

treatments relative to this vegetation. A major influence on all the vegetation was

the environment of the site, which is best characterized as harsh because of the

rocky, droughty soil, exposed west aspect, and incessant wind.

This study differs somewhat from most studies that evaluate alternatives for

controlling competing vegetation in young conifer plantations. In this study, we

wished to document the recovery of the vegetation after a series of manipulations

that were applied at different times and continued for various durations. We

hypothesized that the amount of vegetation and when it was present, relative to

site preparation and release, would affect the various species in the community

and in turn affect the conifer seedlings. Thus, the manual grubbing and fertilizer

that we applied served only to accomplish the treatments. The different times of

application, their duration, and the plant community recovery times were the

treatments. These were:

• Treat first 6 years (1988-1993), develop naturally last 4 years: T-first-6

• Fertilize first year, treat first 6 years (1988-1993), develop naturally last 4

years: F-first-6

• Treat first 3 years (1988-1990), develop naturally last 7 years: T-first-3

• Delay 3 years, treat next 3 years (1991-1993), develop naturally last 4

years: T-second-3

• No treatment after site preparation, develop naturally entire 10 years of

the study (1988-1997): ControL

A greenleaf manzanita brushfield begets a greenleaf manzanita brushfield in

spite of a good job of site preparation and release. This shrub was by far the most

abundant and dynamic natural species in the study area. In the first growing

season after treatment, density of greenleaf manzanita in the control was 123,500

plants per acre or 40 times more than that of the other shrubs and graminoids

combined. When the study ended 10 years later, manzanita density. (44,450

plants per acre) was 5 times greater, but its foliar cover (1,600 ft' per acre in 1988

and 34,600 ft' per acre in 1997) had increased from 11 to 23 times greater than the

other shrubs and grasses combined. Among treatments at the end of the study,

greenleaf manzanita was significantly taller and wider in the control than in all

others.

Graminoids, chiefly needlegrass, were significantly more dense in the Tfirst-3 treatment than in the control at the end of the study-confirming the

inverse relationship between grasses and shrubs noted in earlier studies.

USDA Forest Service Res. Paper PSW-RP-245. 200 I.
For ponderosa pine seedlings, immediate release for the first 3 and 6 years

provided a significant increase in average stem diameter and height over

counterparts in the control three growing seasons after treatment, and continued

throughout the lO-year study. Grubbing each year for the first 6 years was not

justified either biologically or economically. Delayed release, as in the T-second3 treatment, also resulted in significantly larger stem diameters and more foliar

cover than for pines in the control at the end of the study. This is contrary to

findings in other studies and was not anticipated. However, a similar study has

shown that on a poor site, the need for release is so strong that any release,

regardless of timing, duration, or vegetation recovery time, is beneficial.

USDA Forest Service Res. Paper PSW-RP-245. 200 I.
Introduction

One farmer sows the barley soon

His neighbor sows them late,

But both see the charlock grow

As was theirfather's fate.

(Van der Zweep 1981)

The early plant community typical of young plantations often is composed

of competitive species (as evidenced by charlock), is diverse, and often variable

because of different historical events (fire, windthrow), different regeneration

strategies (seed and seedling banks, wind-borne seeds, rapid growth above and

below ground; Grime 1979), and different successional mechanisms (facilitation,

tolerance, inhibition; Connell and Slatyer 1977). Many species from many

categories of vegetation, including conifers, hardwoods, shrubs, grasses, forbs,

and ferns, comprise the plant community (McDonald 1999, McDonald and

Fiddler 1993). Through natural selection over millions of years, many species are

superbly adapted to dominate in newly disturbed areas. Land recently prepared

for planting is nearly ideal: soil moisture levels are high and nutrients generally

are plentiful. Competition to newly-planted conifer seedlings almost always

develops quickly and becomes formidable. Seedling death or a slowed growth

rate is the usual consequence of not treating the developing vegetation.

Clearly, the plant community needs to be manipulated to achieve conifer

survival and development goals. One method to achieve this is to reduce the

presence or vigor of the competing plants-a process called plantation release.

But when should release be implemented, and how long should it be continued?

Early studies provided some information on the lag between the visible decline

of conifer seedlings and the effect of competing vegetation. Bentley (1967)

recorded "noticeably lower vigor" of ponderosa pine (Pinus ponderosa Dougl. ex

Laws. var. ponderosa) seedlings after four growing seasons on a poor site in

northern California, even though the shrubs had been effectively treated with

herbicide the previous year. In another northern California study on a good site,

naturally seeded ponderosa pine seedlings growing with rapidly developing

vegetation first showed signs of competition three growing seasons after site

preparation (McDonald and Radosevich 1992). Fewer, shorter, and lighter

colored needles became noticeable at this time. By the time the pines show visible

signs of competition, it is too late. Several years of reduced growth ensue even if

the pines are released immediately. This growth was not recovered for at least 31

years on a poor site (McDonald and Abbott 1997).

When does the effect of competition on planted conifer seedlings first become

manifest? That depends on the kind, amount, and spacing of the competing

species and also on the productivity of the site. Only one definitive study could

be found. On a productive site in northern California, Radosevich (1984)

evaluated the competitive interaction between greenleaf manzanita

(Arctostaphylos patula Greene) and ponderosa pine seedlings in an experiment

having several proportions of seedlings and shrubs. During the first growing

season, no interference was observed between shrubs and seedlings, even though

about 60 times more growth in terms of biomass took place on the shrubs than on

the pines. Interference apparently began the second growing season. After three

growing seasons, shrub growth was still about 35 times greater than pine seedling

growth, but pine growth had decreased on all plots where manzanita was

present. Also, after three seasons, manzanita was beginning to limit its own

growth, especially where it was more abundant.

Although some empirical evidence is available, the relationship of the timing

of release to the onset of competition on sites of different productivity is largely

unknown. Effective timing of release could depend on the kind of plant species,

the abundance of each, and their rate of development. Timing of release could

USDA Forest Service Research Paper. PSW·RP-24S. 2001.
2

also be manifest in any ofseveral comparisons, such as immediate versus delayed

release or releasing for one timespan versus another. At some point, delayed

release might not be more effective than never releasing, or releasing each year

for several years might not be more effective than releasing for 1 or 2 years,

depending on when the release took place. As part of a National Forest Service

administrative study on alternative release methods (Fiddler and McDonald

1984), data were gathered from 1988 to 1997 on vegetation developing ~ftet site

preparation in a control and on vegetation manipulated deliberately by fertilizing

and by grubbing. Time of release, duration of release, and the timespan after

release, or more specifically the "vegetation recovery times after disturbance by

site preparation and release/' were the treatments.

This paper reports the biological and economical results of these treatments

in terms of the recovery of the plant community 2, 5, and 10 years after

manipula tion, and it quantifies the survival and growth of the ponderosa pine

seedlings after immediate and delayed release.

Methods

Location and Site Characteristics

The study area is located on the Mt. Shasta Ranger District of the USDA

Forest Service's Shasta-Trinity National Forests in T41N, R4W, sections 27 and

28. It is about 4 airline miles north of the town of Mt. Shasta and on a gentle slope

at the base of the mountain that has a similar name. Before the study began, the

area was a brushfield, and probably had been for scores of years. It had not

always been a brushfield, however, as an occasional hard, blackened log

indicated that at least some trees were present long ago. Scattered trees on a

nearby hillside also suggest a past forest and provide clues as to the species

makeup of the stand. Ponderosa pine probably was the most abundant species,

followed by incense-cedar (Libocedrus decurrens Torr.) and California white fir

(Abies coneolor var. lowiana [Gord.] Lemm.). Scientific names of trees are from

Little (1979) and for all other plant species from Hickman (1993).

Before the study began, the mature brushfield consisted of 4- to 5-foot tall

plants of greenleaf manzanita and snowbrush ICeanothus velutinus Dougl. ex

Hook.), with occasional bitler cherry (Prunus emarginata [Hook.] Walp.),

bitterbrush (Purshia tridentata (Pursh) DC., and rabbitbrush (Chrysothamnus spp.).

Prostrate mahala mat (Ceanothus prostratus Benth.) also was present but limited

to small open areas among shrub clumps.

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

averaging about 50 feet in 50 years (Biging and Wensel 1984). The site is best

described as harsh for the establishment and growth of conifer seedlings. The

soil, which is closely related to the Neer series, is a skeletal, mesic Andie

Xerochrept. Itwas formed in material weathered from volcanic ash and deposited

over extrusive igneous rocks. It has a gravelly sandy loam texture and is about 3

feet deep. Large stones, gravel, and sand are abundant throughout. The elevation

is about 4,750 feet, the slope averages 10 percent, and the aspect is west. The area

is reasonably uniform with respect to slope, aspect, and soil. Precipitation

averages about 40 inches per year, with about 60 percent falling as snow.

Temperatures range from 20 of to 85 of with the average annual temperature

being 48 OF. The growing season is about 100 days. Downslope-winds off of Mt.

Shasta are common in all seasons of the year.

Shrubs in the study area were pushed into windrows with a brushrakeequipped tractor in spring 1986 and burned in the fall. Very little soil was

displaced, and the windrows could scarcely be seen a few years later. The area

also was cross ripped (perpendicular to slope) at about 10-foot intervals in the

summer of 1986 !fig. 1). This operation broke up the dense mass of rocks and

shrub roots and served to loosen the soil. It also created depressions

perpendicular to the primary wind direction that filled with snow in the winter.

USDA ForeSt Service Research Paper. PSW~RP·245. 2001.
Ponderosa pine seedlings were raised in the Placerville Nursery and planted

in the depresssions created by the ripper in spring 1987. Spacing was 10 by 10

feet. Mortality of seedlings in all study plots at the end of the first growing

season was estimated at less than 5 percent. The plant community when the

study began consisted almost entirely of plants that had originated from dormant

seeds in the soil and from windblown seeds. Virtually no competition from

sprouting root burls was present. In addition to the planted ponderosa pine

seedlings, the early plant community consisted almost entirely of greenieaf

manzanita seedlings (fig. 2) and a few plants of the other shrub species noted

earlier. A few grasses !fig. 3) and forbs also were present.

Insects were commonplace in the plantation and affected the growth and

form of the pine seedlings. The principal species were the pine needle-sheath

miner (Zelleria haimbachi Busch) (Stevens 1959) and the. gouty pitch midge

(Cecidoymia piniinopis Osten Sacken) (Bedard and others 1989). Several animals,

including ground squirrels (Spermophilus spp.) and rabbits (Lepus spp.), were

occasionally seen in the study area.

USDA Forest Service Research Paper. P5W-RP-HS. 2001.

Figure I-A portion of the study

area showing the depressions

perpendicular to the slope made

by the ripper.

Figure 2-This 4Myear_old

ponderosa pine seedling in the

control is surrounded by greenleaf

manzanita plants from seed.

3
Figure 3-A typical T-first-6

subplot in fall 1990. Stems of

needlegrass are readily seen.

4

Study and Design

The experimental design was completely randomized with five treatment

categories, including a control and four replications, each referred to as a "plot."

A replicate (plot) was rectangular and consisted of about 0.1 acre on which were

about 40 ponderosa pine seedlings surrounded by at least 2 rows of buffer

(seedlings receiving similar treatment). The study began in 1988 and ended in

1997. Treatments and treatment dates were:

• Treat first 6 years (1988-1993), develop naturally last 4 years: T-first-6

• Fertilize first year, treat first 6 years (1988-1993), develop naturally last 4

years: F-first-6

• Treat first 3 years (1988-1990), develop naturally last 7 years: T-first-3

• Delay 3 years, treat next 3 years (1991-1993), develop naturally last 4 years:

T-second-3

• No treatment after site preparation, develop naturally entire 10 years of the

study (1988-1997): Control.

Treatment consisted of grubbing all vegetation in a 5-foot radius around

selected pine seedlings with hand tools. The cost of each treatment both initially

and for retreatment was calculated from hourly records and $8.74 per hour-the

rate for a WG-1Iaborer, u.s. Department of Labor as ofJune 1993. No allowance

for travel, equipment, or overhead was included. The fertilizer, which was

applied in early summer 1987, was a slow-release variety and contained 14

percent each of nitrogen, phosphorus, and potassium. Each sampled seedling

received 76 grams of fertilizer in a 6-inch deep hole located about 4 inches uphill

from it.

Sampling

Of the 40 ponderosa pine seedlings in each plot, 25 that appeared to have

good potential of becoming harvestable trees were selected and tagged. Chlorotic

and misshapen seedlings that would be removed in the first precommercial

thinning were excluded. Stem diameter (recorded at 12 inches above mean

USDA Forest Service Research Paper. PSW-RP-245. 200 I.
groundline), stem height, foliar cover (the sum ofshadows that would be cast by

leaves and stems of individual species expressed as a percentage of the land

surface [Daubenmire 1968]), and needle length were measured on each.

Unfortunately, limitations in budget and staffing affected sampling, and some

remeasurements were not taken. All vegetation was periodically checked for

injury from abiotic agents, animals, and insects.

Sampling intensity for evaluating vegetation other than pines was five

randomly selected subplots in each plot. Subplots were centered around

ponderosa pine seedlings and encompassed 1 milacre (0.001 acre). The most

abundant species were evaluated for density, foliar cover, and average dominant

height (average of the three tallest stems measured from mean ground line to

bud). More specifically, number of plants in each subplot were counted, foliar

cover was visually estimated, and height was measured with a graduated pole.

Because treatment in the T-first-6 and F-first-6 subplots was intensive and

continuous, revegetation and competition to pine development were considered

to be minor. Hence, data on manzanita, other shrubs, and graminoids were not

recorded in these treatments during the study.

To test for treatment effects and significant differences among treatments,

one-way analysis of variance of treatment means (fixed effect model; Steel and

Torrie 1980) and Tukey tests were applied (SAS Institute Inc. 1988). Statistical

significance in all tests was at 0: = 0.05. Data 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 0: levels or type I errors

given for various tests apply to each measurement period and year separately.

To quantify plant diversity, all species were noted on study plots when the

study began and when it ended.

Results

Plant Diversity

Most early seral vegetation in young plantations in California and Oregon

consists of a mixture of shrubs, forbs, and grasses, often from seed and from

sprouts. In this study, only two classes of vegetation were prominent-shrubs

and grasses. Conifer seedlings and forbs had either a minor presence or an

ephemeral one. Revegetation ofstudy plots was by 25 speciesfrom 2 regeneration

strategies (Grime 1979). These were persistent seed bank (dormant seeds in soil)

and wind-blown seeds.

With minor exceptions, the natural plant species in the study area were

found in all treatments. The plant community on all plots at the end of the first

growing season after treatment in 1988 consisted of 19 species and at the end of

the study in 1997 was 16 species. The natural plant community at the beginning

of the study consisted of no conifer seedlings, 7 species of shrubs, 10 forbs, and 2

graminoids. By the end of the study, vegetation in the study plots included a few

natural seedlings of 2 conifer species (ponderosa pine, California white fir), 7

shrubs, 5 forbs, and 2 graminoids. Those forbs that remained were notably few

and small. No alien species were found during the study in spite of musk thistle

(Carduus nutans 1.) being present in the nearby area.

Greenleaf Manzanita

This evergreen, fast-growing shrub was remarkable for its early abundance

and its dominance in the study area. Early observers consistently noted "myriads

ofseed capsules and new plants" and"countless numbers of tiny new seedlings"

on study plots. Manual grubbing, which removed scores of manzanita plants

each year, seemed to facilitate a new crop of seedlings the following year.

Average density of greenleaf manzanita in the control was highest initially

(1988) at 123,500 plants per acre and declined steadily to 44,450 plants per acre

ten growing seasons after treatment (1997) (table 1). Foliar cover and height

USDA Forest Service Research Paper. P5W-RP-245. 2001. 5
increased steadily throughout the study period and reached 34,600 ft' per acre

and 3.2 feet tall in 1997. During the 10-year study, the average number of

manzanita plants in the control decreased by 64 percent, but average foliar cover

increased by more than 21 times and height by more than 6 times.

Among the three treatments where vegetation was quantified, more greenleaf

manzanita plants (44,450 per acre), significantly more foliar cover (34,600 ft' per

acre), and Significantly taller plants (3.2 feet) were present in the control than in

any other treatment at the end of the study (table 2). Significantly lower mean

density, foliar cover, and height values occurred in the T-second-3 treatment

than in the T-first-3 treatment.

Table 1-DensitY,foliar cover, and height, with standard errors (5E), ofgrecnleafmanzanita, other shrubs, and

grasses in the control, northern California, 1988-1997

Species Year

Greenleaf manzanita 1988

1990

1992

1997

Other shrubs 1988

1990

1992

1997

Graminoids 1988

1990

1992

1997

Density SE Cover SE Height SE

---plantslacre---- ------ft2facre----- --------It------

123,500 10,728 1,600 183 0.5 0.1

101,800 13,041 16,200 2,986 1.4 0.1

66,450 3,928 21,350 2,815 2.0 0.1

44,450 4,023 34,600 1,472 3.2 0.1

1,600 510 50 50 0.3 0.1

3,000 469 1,400 82 1.1 0.1

2,550 574 1,450 310 1.5 0.2

1,950 263 1,500 238 2.4 0.4

1,450 741 100 58 1.5 0.1

13,300 4,394 900 300 1.6 0.3

14,700 5,730 200 200 1.5 0.2

6,850 3,193 TI T 1.1 0.1

ITrace.

Table 2-Average density, joliar cover, and height of greenleaf manzanita, other shrubs, and graminoids, by

treatment, northern California, 1997

Species

Greenleaf

manzanita

Other shrubs

Graminoids

Treatment

Treated first 3 years

Treated second 3 years

Control

Standard error

F ratio

P value

Treated first 3 years

Treated second 3 years

Control

Standard error

F ratio

P value

Treated first 3 years

Treated second 3 years

Control

Standard error

F ratio

P value

Density Cover Height

plants/acre ft 2

1acre ft

32,200 a1 12,550 b 2.6 b

1,500 b 1,650 c 1.8 c

44,450 a 34,600 a 3.2 a

5,374 2,164 0.2

16.95 60.19 22.97

0.0009 0.0001 0.0003

1,200 a 900 a 2.0 a

1,200 a 650 a 0.8 b

1,950 a 1,500 a 2.4 a

295 251 0.3

2.14 3.03 9.32

0.1730 0.0988 0.0064

21,350 a 400 ab 1.2 a

12,100 ab 900 a 1.5 a

6,850 b T' b 1.1 a

3,072 219 0.1

5.71 4.26 2.88

0.0250 0.0500 0.1079

6

IFor each species or combination, treatment means in each column followed by the same letter

do not differ statistically at the 0.05 level.

2Trace.

USDA Forest Service Research Paper. PSW~RP~245. 200 I.
Other Shrubs

Of the six shrub species, other than greenleaf manzanita, that were present

from the beginning to the end of the study, bitterbrush was by far the most

common and the most evenly distributed. Rabbitbrush and squaw carpet were

the next most abundant. However, even when combined, the other shrubs were

few and their foliar cover and height were low relative to greenleaf manzanita.

Average density of other shrubs in the control was 1,600 plants per acre in

1988, peaked at more than 3,000 plants per acre in 1990, and declined steadily to

1,950 plants per acre in 1997 (table 1). Foliar cover and height increased steadily

from 50 to 1,500 ft' per acre and from 0.3 to 2.4 feet tall, respectively, at the end of

the study. For the 10 years of the study, the average number of other shrubs in

the control increased by 22 percent, average foliar cover increased by 30 times,

and height increased by 8 times.

Among treatments, the plotsthat had the longestrecovery time since disturbance

(the control) had the highest average density (1,950 plants per acre), highest foliar

cover (1,500 it' per acre), and highest average height (2.4 feet) (table 2). However,

average height of the othershrubsin the control differed significantly only from that

in the T-second-3 treatment. If time since disturbance was 7 years, as in the T-first-3

treatment, or 4 years, as in the T-second-3 treatment, mean density and foliar cover

did not significantly differ between them, but height did. Other shrubs were

significantly taller in the T-first-3 plots (2.0 feet) than counterparts in the T-second-3

plots (0.8 foot).

Graminoids

As early as October 1987, a few plants of needlegrass (Achnatherum nelsonii

[Scribner] Barkwort) (formerly Stipa; Hickman 1993) and cheatgrass (Bromus

teetorum L.) were recorded as invading the study plots. They were noted as

increasing in June 1988 and invading newly-grubbed plots in 1990. By fall 1990,

the established needlegrass clumps were described as "difficult to grub out."

Some cutting of grass by rodents was noted in fall 1987 and 1990.

Graminoids in the control numbered 1,450 per acre in 1988 with only minor

amounts of foliar cover (table 1). However, by 1990, density had increased to

more than 13,000 plants per acre with 900 ft' of foliar cover per acre and an

average height of 1.6 feet. By 1992, density had peaked at 14,700 plants per acre

before declining to 6,850 plants per acre at the end of the study in 1997. Average

foliar cover and height also declined and by the end of the study were only a

trace and 1.1 feet, respectively.

Among treatments in fall 1997, the treatment with the longest time since

disturbance (control) had Significantly lower density (6,850 plants per acre) than

counterparts in the T-first-3 treatment (21,350 plants per acre) that had 7 years

since last disturbance, and it had significantly less foliar cover than plants in the

T-second-3 treatment (900 ft2 per acre) that had 4 years since disturbance (table 2).

Average height did not differ statistically among treatments.

Forbs

Although too few and poorly distributed to analyze statistically, the forbs in

the study area contributed in a small way to the plant community. The most

abundant species were from the genera Lilium and Phaee1ia. The forbs never

formed patches ofsingle species, as is common in newly disturbed areas. Rather,

they tended to occur as single plants Or in aggregations of 5 to 10. By the end of

the study, forbs were found on only 12 of the 100 milacre subplots, numbered 460

per acre, and had only a trace of foliar cover and an average height of 0.8 foot.

Most were present beneath crowns of the largest trees or in small openings

among the manzanita plants.

USDA Forest Service Research Paper. P5W-Rp·245. 200 I. 7
Ponderosa Pine

Life for ponderosa pine seedlings in this plantation is best described as a

struggle. Damage has been almost continuous and from several sources. As early

as January 1988, about 15 percent of the pine seedlings in the study area were

noted as damaged by winterburn. Winterburn occurs when the ground is frozen,

no water intake by the plant is possible, and the wind pulls most of the moisture

from the needles. Of the damaged seedlings, a few had 50 percent of foliage

browned, but most had about 30 percent. Severe damage from winterburn also

was noted in 1993 and 1994. In August 1993, pines in the control were recorded

as dying from suppression. By August 1994, many trees in the control were either

dead or had dead tops. Winterburn and suppression were the likely causes.

Insect damage was first noted in the summer of 1995 when the tips of pine

branches were browned"on everything sticking out of the brush." The survey of

1996 recorded increased mortality and at least some insect damage on 80 percent

of pines in the study area. By fall 1997, the combination of winterburn,

suppression, and insects had killed, damaged, or reduced the growth of almost

all pines in the control. Unfortunately, almost all pines in one plot in the T-first-3

treatment were decimated by insects. Dead and deformed tops, brown needles,

narrow crowns, and a general lack of vigor characterized the pines in this plot.

Mortality of pine seedlings began in 1993 and continued through 1997. Insect

attack on the already suppressed and winterburned seedlings apparently was

too much, and the seedlings perished from the combination of causes (fig. 4). At

the end of the study, percent survival by treatment was:

Treatment

T-first-6

F-first-6

T-first-3

T-second-3

Control

Average

95

85

95

97

57

Standard error

2

6

2

3

14

An analysis of variance of transformed (arcsin) values indicated thatsurvival

was significantly higher in all treatments than in the control.

Among treatments, 24 to 67 percent of surviving seedlings were deformed.

Values did not differ among treatments at the 5 percent level. "Deformed" was

defined as death of the terminal shoot and replacement by one or more shootsan event that caused a crooked stem. Percent deformed with standard errors by

treatment was:

Treatment

T-first-6

F-first-6

T-first-3

T-second-3

Control

Average

29

41

49

24

67

Standard error

10

8

20

10

6

8

Average stem diameter, measured at 12 inches above mean groundline, first

differed significantly in 1990 when pines in the T-first-6, F-first-6, and T-first-3

treatments differed significantly from pines in the control !table 3). By the end of

the study in 1997, average diameter of pines in the T-first-6 and T-first-3

treatments continued to differ significantly from those in the control, but the

diameter of seedlings in the F-first-6 treatment no longer differed significantly

from those in the other treatments. The diameter of pines in the T-second-3

treatment also differed significantly from counterparts in the control. In 1997,

pine diameter ranged from 3.7 inches in the T-first-6 treatment to 1.4 inches in the

control.

USDA Forest Service Research Paper. PSW-RP-245. 2001.
Mean stem height also first differed significantly among treatments in 1990

and among the same treatments as stem diameter. By the end of 1997, however,

the only significant differences in stem height were between pines in the T-first6 and T-first-3 treatments (8.7 and 8.3 feet, respectively) and the control (3.6 feet)

(table 3).

Foliar cover relationships, which suffered from missing data early in the

study, became meaningful in 1992 when average values in the T-first-3 treatment

(11,100 ft' per acre) differed significantly from those in the control (2,500 ft' per

acre) (table 3). In 1997, however, foliar cover in the T-first-6 (27,700 ft' per acre)

and T-second-3 (22,050 ft' per acre) treatments differed significantly from

counterparts in the control (3,400 ft2 per acre). The heavy insect damage in one

plot of the T-first-3 treatment decreased foliar cover and caused a lower treatment

mean.

Table 3-Average stem diameter and height, foliar cover, and needle length of ponderosa pine seedlings, by

treatment, northern Califomia, 1988-1997

Treatment

Treated first 6 years

Fertilize, treat first 6 years

Treated first 3 years

Treated second 3 years

Control

Standard error

F ratio

Pvalue

1988

0.39 a1

0.42 a

0.44 a

0.33 a

0.35 a

0.03

1.91

0.1684

1990 1992 1997

Diameter (inches)

1.15 a 2.05 a 3.70 a

1.08 a 3.02 ab

1.20 a 2.07 ab 3.36 a

0.70 b 1.49 be 3.21 a

0.68 b 1.02 e 1.40 b

0.06 0.14 0.37

15.61 13.56 5.51

0.0001 0.0004 0.0062

-----------------------------------Height ifeet)--------------------------------

Treated first 6 years 0.79 a 3.00 a 5.11 a 8.68 a

Fertilize, treat first 6 years 0.72 a 2.98 a 6.83 ab

Treated first 3 years 0.85 a 3.11 a 5.22 a 8.34 a

Treated second 3 years 0.79 a 2.28 b 3.73 ab 7.44 ab

Control 0.79 a 2.18 b 2.83 b 3.58 b

Standard error 0.05 0.14 0.36 1.06

F ratio 1.15 9.39 10.18 3.70

P value 0.3719 0.0005 0.0013 0.0274

----------------------------Foliar cover ift2 per acre)-----------------------

Treated first 6 years

Fertilize, treat first 6 years

Treated first 3 years

Treated second 3 years

Control

Standard error

F ratio

P value

200 a

250 a

67.7

0.27

0.6202

2,950 a

2,400 a

211

3.39

0.1151

11,100 a

6,750 ab

2,500 b

1,48J

8.43

0.0087

27,700 a

16,800 ab

20,100 ab

22,050 a

3,400 b

3,667

55.08

0.0096

------------------------------Needle length (inches)-----------------------

Treated first 6 years 6.07 a 7.53 a 7.04 a

Fertilize, treat first 6 years 6.11 a 7.28 a

Treated first 3 years 6.05 a 7.55 a 6.54 a

Treated second 3 years 5.94 a 5.74 b 6.75 a

Control 5.62 a 5.39 b 4.56 b

Standard error 0.16 0.18 0.22

F ratio 1.54 33.14 25.34

Pvalue 0.2418 0.0001 0.0001

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

level.

USDA Forest Service Research Paper. PSW-RP-245. 200 I. 9
Figure 4-Mortality of

ponderosa pine seedlings on a

poor site: (A) pine height growth

becomes less and less relative to

that of the manzanita; (8) insects

kill the top and upper branches of

weakened seedlings; and (C) even

though well above the manzanita,

the seedling is dead by age 10.

A

B

10 USDA Forest Service Research Paper. PSW-RP·245. 2001.
Needle length, which was used as an indicator of future treatment

effectiveness, first differed statistically among treatments in 1990 (table 3).

Average needle length of pines in the T-first-6, F-first-6, and T-first-3 treatments

were significantly longer than those in the control. By fall 1992 (the last year that

data were taken), needles were significantly longer in the T-first-6, T-first-3, and

T-second-3 treatments than in the control. Needle length ranged from 4.6 to 7.0

inches among treatments.

Production and Cost

The amount of time to manually grub a 5-foot radius around each pine

seedling was relatively small when the competing vegetation was young and not

yet established. Because grubbing in the T-first-6 and T-first-3 treatments was

performed annually, each subsequent grub took about the same amount of time.

With time, however, more and more plants, particularly shrubs on subplot

edges, expanded their root crowns into the treated space or had stems that

leaned into it, which required additional labor to remove. Consequently,

grubbing the last year in the T-first-6 treatments and the T-second-3 treatment

was more time consuming. Total time to grub the treatments was:

C

Treatment

T-first-6

T-first-3

T-second-3

Time (hours)

52.2

24.9

63.8

Grubbing the vegetation in the T-second-3 treatment was very difficult.

Four-year-old manzanita plants often had roots that exceeded 5 feet in length.

Grass plants did not have long horizontal roots, but large masses of spreading

roots. Both had to be loosened around their perimeter first and then grubbed out.

If placed on a per-acre basis, the T-first-6 and F-first-6 treatments each cost about

$130 per acre, the T-first-3 treatment about $62, and the T-second-3 treatment

more than $159 per acre to manually grub.

USDA Forest Service Research Paper. PSWMRpM245. 2001. II
Figure 5-Ten years after

treatment, this ponderosa pine in

the T~first-6 treatment is still

benefitting from shrub removal as

shown by the vegetation-free area

beneath the tree crown.

12

Discussion and Conclusions

Before this study began, the area was a brushfield composed primarily of

greenleaf manzanita and a few other species of shrubs. Ten years after site

preparation, the plant community in the control is approaching pre-study

conditions. It consists of short, discolored, and deformed ponderosa pine

seedlings whose crowns are just above a near-solid mass of shrubs. With a

combined density of more than 46,000 plants per acre, foliar cover of '36,100 ft2

per acre and a height of 3 feet, the shrubs will again dominate in the near future.

Although perennial needlegrass is present, its future among and under the

shrubs is precarious.

In plots with a longest treatment duration (6 years), the pines generally were

taller and wider than pines in the other treatments. The crowns of pines in the Tfirst-6 treatment were closing or had closed at the end of the study, and the

competing vegetation was leaning away from them toward the sunlight. The

needlegrass component of the community in this treatment is likely to decline

and be relegated to only a trace in the near future (McDonald and Abbott 1997).

Timing of competition is important. A large number of competing plants

early in the study constitutes more competition to the pine seedlings than does a

large number of plants after the pines have become established. The T-first-6

treatml'nt and the control are an example. In the T-first-6 treatment, each crop of

shrubs was eliminated before it could become established and competitive; in the

control, the shrubs became established, developed well, and significantly reduced

pine growth. At the end of the study, the pines in the T-first-6 treatment were

negatively impacting the shrubs that were present (jig. 5); in the control the

shrubs were negatively impacting the pines.

USDA Forest Service Research Paper. PSW·RP~245. 200 I.
McDonald and others (1992) showed that ponderosa pine needle length is a

good indicator of pine growth, and thus was a useful gauge of treatment

effectiveness in the future. More specifically, l-year-old needles, measured 2 to 4

years after treatment, were strongly related to treatment response for at least 7

years after treatment. Seven years was the longest timespan evaluated. In this

study, needles measured 2 and 5 years after the treatment began accurately

portrayed pine growth-treatment relationships. In 1992, the longest needles were

on pines in released treatments, and the shortest were in the unreleased control.

In the T-first-3 and T-second-3 plots, which had a short treatment duration (3

years), but varying times since disturbance (7 and 4 years), the treatment area at

the end of the study consisted of pines in the center of little circles inhabited by

shrubs and graminoids in a sea of taller shrubs. The 5-foot treatment radius was

no longer 5 feet because of the growth of adjacent vegetation. In a few instances,

the treated circles were becoming difficult to see-a process that will accelerate

in the near future. Nevertheless, the pines are likely to dominate here, albeit with

a lower growth rate than that of counterparts with less competition.

By the end of the 1990 growing season, pine diameter, height and needle

length in the T-first-3 treatment were Significantly larger than counterparts in the

control, and continued throughout the study. Foliar cover of pines, which

significantly differed from those in the control in 1992 did not differ from them in

1997. Apparently, the large number of manzanita and grass plants that invaded

after the last grubbing was beginning to have an effect.

The growth of pines in the T-second-3 treatment was better than expected. A

possible reason involves the competitive interaction between shrubs and

perennial grass. Results from a long-term study nearby (McDonald and Abbott

1997) showed that perennial needlegrass had lower density and development if

growing with shrubs. However, the number of new shrubs from dormant seeds

in the soil was much less if grass was present. Close examination of table 2

indicates low values of greenleaf manzanita density, foliar cover, and height in

the T-second-3 treatment and relatively high values for grass density and height.

Perhaps the graminoids negatively affected the shrubs and the shrubs negatively

affected the graminoids, both to the benefit of the pines. A more compelling

reason is that when the need for release is strong, as it is on poor sites, any release

is helpfUl (Fiddler and McDonald 1999). Timing of release, duration of release

and vegetation recovery times are secondary.

A major reason for analyzing and presenting the results of this study in

terms of time since disturbance and duration of treatments was to reinforce the

hypothesis, based on findings in earlier studies (McDonald and Fiddler 1990,

1995), that early release is more cost-effective than repeated release or delayed

release. Delaying release almost always means larger plants and often large,

deep masses of roots. The T-first-3 and T-second-3 treatments were a direct test

of early versus delayed release. Biologically the two treatments did not differ

statistically from each other. But economically they did. Manual grubbing in the

T-first-3 treatment cost less than half of that in the T-second-3 treatment.

The role of the slow-release fertilizer that was applied in June 1987 is not

clear. Diary records indicated that no effect was visible the following year, but by

fall 1990, "needles were noticeably greener on fertilized trees." By June 1996,

needles on fertilized seedlings were described as more numerous, longer, and

with better color than those in other treatments-a finding that was repeated in

the 1997 measurements. Thus, the needle characteristics suggested good growth,

but average diameter, foliar cover, and height, although about twice that of the

control, did not differ significantly from it.

The different treatments, which spanned plant recovery times of 4 to 10

years, created similar plant communities, but with different amounts of the same

species that further differed in terms of development. Although the community

has not changed greatly, one major component-ponderosa pine--now is part of

USDA Forest Service Research Paper. P5W-RP-245. 200 I. 13
14

the community. These seedlings, other than in the control, are plentiful,

established, and have potential to outgrow the competing vegetation. Restoring

the arboreal component, which historically has been part of the community,

should create a forest stand, and a more desirable and sustainable vegetative

assemblage.

References

Bedard, William D.; Robertson, Allen S.; Ferrell, George T. 1989. Growth los5 in sapling ponderosa

pine associated with injury caused by gouty pitch midge. In: Alfaro, ReneK.; Glover, S.C.,

eds. Proceedings of etmeeting of the IUFRO working group on insects affecting reforestation;

1988 July 3~9; Vancouver, British Columbia, Canada. Victoria, British Columbia, Canada: Forestry

Canada, Pacific Forestry Centre; 196~204.

Bentley, }.R. 1967. Brushfield reclamation in California. In: Proceedings of a sympOSium on

herbicides and vegetation management in forest, ranges, and noncrop lands. Corvallis, Oregon.

Oregon State University; 186-195.

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

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

Management, University of California; 13 p,

Connell, J.H.; Slatyer, R.O. 1977. Mechanisms of succession in natural communities and their role

in community stability and organization, American Naturalist 111: 1119-1144.

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

and Row; 300 p.

Fiddler, Gary 0,; McDonald, Philip M.1984. Alternatives to herbicides in vegetation management:

a study, In: Proceedings, 5th annual forest vegetation management conference; 1983 November

2-3; Sacramento, CA. Redding, CA: Forest Vegetation Management Conference; 115-126.

Fiddler, Gary 0,; McDonald, Philip M. 1999. Treatment duration and time since disturbance affect

vegetation development in a young ponderosa pine plantation. Res, Note PSW-RN-424.

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

Sp.

Grime, J,P. 1979. Plant strategies and vegetation processes. New York: John Wiley and Sons; 222 p.

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

of California Press; 1400 p.

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

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

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

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

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

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

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

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

McDonald, Philip M.; Fiddler, Gary 0. 1990. Ponderosa pine seedlings and competing vegetation:

ecology, growth, and cost. Res. Paper PSW-199. Berkeley, CA: Pacific Southwest Research

Station, Forest Service, U.S, Department of Agriculture; 10 p.

McDonald, Philip M.; Fiddler, Gary 0, 1993. Feasibility of alternatives to herbicides in young

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

McDonald, Philip M.; Fiddler, Gary O. 1995. Development of a mixed shrub-ponderosa pine

community in a natural and treated condition. Res. Paper PSW-224. Berkeley, CA: Pacific

Southwest Research Station, Forest Service, U.S. Department of Agriculture; 18 p.

McDonald, Philip M.; Radosevich, Steven R. 1992. Chapter4. General principles of forest vegetation

management. In: Black, Hugh c., tech. ed. Silvicultural approaches to animal damage

management in Pacific Northwest forests. Gen. Tech, Rep. PNW-GTR-287. Portland, OR: Pacific

Northwest Research Station, Forest Service, U.S. Department of Agriculture; 67-91.

McDonald, Philip M.; Skinner, Carl N.; Fiddler, Gary O. 1992. Ponderosa pine needle length: an

early indicator of release treatment effectiveness, Canadian Journal of Forest Research 22: 761-

764.

Radosevich, Steven R 1984. Interference of shrub and tree species: a research approach.

Unpublished draft supplied by author.

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

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

McGraw-Hill Book Company; 218-220.

USDA Forest Service Research Paper. PSW-RP-245. 2001.
Stevens, Robert E. 1959. Biology and control of the pine needle~sheathminer (Zelia ria haimbachi

Busch). Tech. Paper 30. Berkeley, CA: Pacific Southwest Forest and Range Experiment Station,

Forest Service, U.S. Department of Agriculture; 20 p.

Van der Zweep, Wybo. 1981. Golden words and wisdom about weeds; weeds in proverbs,

quotations, verse and prose. Weeds Today. (Fall): 19~21.

USDA Forest Service Research Paper. PSW-RP·24S. 2001. IS
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Research Paper

PSW-RP-245

v+s

,~""''';<,~

Timing and Duration of Release AffectVegetation

Development in aYoung Ponderosa Pine Plantation