Plant Community Development After 28

Years in Small Group-Selection Openings

United States

Department

of Agriculture

Forest Service

Pacific Southwest

Research Station

Research Paper

PSW-RP-241

Philip M. McDonald Phillip E. Reynolds

1973

1991

1965
Abstract

McDonald, Philip M.; Reynolds, Phillip E. 1999. Plant community development after 28

years in small group-selection openings. Res. Paper PSW-RP-241. Albany, CA: Pacific

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

Thirty openings, 9, 18, and 27 meters in diameter, were created by group-selection harvest

on a high quality site in northern California in 1963. In 1991, or 28 years after site

preparation, the plant community in the openings had stabilized at 55 species. A major shift

was from annuals to perennials. New seedlings of ponderosa and sugar pine were able to

become established for the first 15 years and those of Douglas-fir and California white fir

for the first 25 years. Density and development of conifer and hardwood saplings, shrubs,

forbs, graminoids, and ferns were examined for differences in openings size and aspect. In

general, plants in almost all classes of vegetation were more numerous and developed

better in the larger openings and on the south aspect. Tanoak was an exception, with

significantly more seedlings in the smallest opening size and on the north aspect. After 28

years, conifer and hardwood saplings averaged more than 25,230 per hectare, and shrubs,

forbs, graminoids, and ferns averaged more than 220,700 per hectare. Conifer and

hardwood species grew two to four times faster in height the last 18 years than during the

first 10 years. The tallest saplings were 9 to 12 meters in height after 28 years.

Retrieval Terms: group selection, mixed-conifers, plant community dynamics, regeneration,

Sierra Nevada, silviculture

The Authors

Philip M. McDonald is a research forester with the Pacific Southwest Research Station’s

Western Forest Management Research Unit, 2400 Washington Ave., Redding, CA 96001.

Phillip E. Reynolds is a research forester with the Great Lakes Forestry Centre, Canadian

Forest Service, Natural Resources Canada, 1219 Queen St., East, Sault Ste. Marie, Ontario,

Canada P6A 5M7.

Publisher

Albany, California

Mailing address:

PO Box 245, Berkeley CA

94701-0245

(510) 559-6300

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

December 1999

Pacific Southwest Research Station

Forest Service

U.S. Department of Agriculture

Metric-English Conversions

________________________________________________________________

From To Operation

Centimeter (cm) Inch x 0.39

Hectare (ha) Acre x 2.47

Kilometer (km) Mile x 0.62

Meter (m) Foot x 3.28

Millimeter (mm) Inch x 0.039

Square meter Square foot x 4.36

per hectare (m2/ha) per acre
Plant Community Development After 28 Years in

Small Group-Selection Openings

Philip M. McDonald Phillip E. Reynolds

Pacific Southwest

Research Station

USDA Forest Service

Research Paper

PSW-RP-241

December 1999

Contents

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

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

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

Species and Site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Treatments, Measurements, and Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

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

Plant Community Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Age Distribution of Conifer Seedlings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Conifer and Hardwood Saplings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Shrubs, Forbs, Graminoids, and Ferns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

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

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
USDA Forest Service Research Paper. PSW-RP-241. 1999.

In Brief...

McDonald, Philip M.; Reynolds, Phillip E. 1999. Plant community development after 28

years in small group-selection openings. Res. Paper PSW-RP-241. Albany, CA: Pacific

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

Retrieval Terms: group selection, mixed-conifers, plant community dynamics, regeneration,

Sierra Nevada, silviculture

The trend toward forest management methods that are perceived as more gentle

on the land, its vegetation, and its creatures continues to grow. Sustaining

ecosystems and maintaining ecosystem components are key to modern forest

practice. The group-selection cutting method, which involves the removal of

trees in small aggregations, promotes a landscape that has the appearance of

continuous forest cover with small openings. Such openings can resemble those

created when wildfire creeps through a stand and flares through tree crowns in

areas of heavy fuels. Because it has this natural counterpart, limits the harvest to

a small fraction of the trees in a stand at any one time, and promotes many age

classes, the group-selection method is regarded as both gentle on the land and

one that promotes a complex stand, resilient to major damage.

The group-selection cutting method is perhaps the least used and poorest

understood of all the silviculture regeneration harvesting methods.

Consequently, some knowledge gaps exist, and one of the most serious is a lack

of long-term information on plant species composition, succession, and

development within the small openings inherent to the method.

In 1963, 48 small openings, 9, 18, and 27 meters in diameter, were created by

timber harvest on the Challenge Experimental Forest in northern California. The

dominant overstory species in the study area was ponderosa pine. A gentle

scraping with a bulldozer bared the soil and created a seedbed that was receptive

to colonization by tree, shrub, and herbaceous species. All vegetation had to

become established and develop in an environment characterized by openings

that were impacted by roots and crowns of adjacent trees.

In 1991, 30 openings (10 of each diameter) were remeasured. Conifer and

hardwood saplings, shrubs, forbs, graminoids, and bracken fern were sampled

in each opening for density and height. Root-collar diameter was recorded for

conifers and hardwoods, and all plant species in the openings were listed.

Results from this study showed that the number of plant species increased

from 40 in 1973 to 55 in 1977 and remained at 55 in 1991. The plant community in

1991 consisted of 5 conifers, 5 hardwoods, 16 shrubs, 24 forbs, 4 graminoids, and

1 fern. Almost all were perennials.

Unlike even-aged silvicultural regeneration methods where the first few

seedcrops stock the land, many seedcrops are effective for establishing

regeneration in group-selection openings. Ponderosa pine and sugar pine

seedcrops were effective for the first 15 years after site preparation; Douglas-fir

and California white fir seedcrops provided new seedlings for an additional 10

years.

In 1974 the total number of conifer and hardwood seedlings was almost

27,800 per hectare with stand composition of 71 percent ponderosa pine, 16

percent tolerant conifers, and 13 percent hardwoods. In 1991 the total number of

conifer and hardwood saplings was more than 25,230 per hectare with stand

composition of 22 percent ponderosa pine, 37 percent tolerant conifers, and 41

percent hardwoods. Thus, the composition of the stand has shifted toward the

more tolerant conifers and hardwoods at the expense of ponderosa pine.

Comparative height values support this trend. Among the five conifer species

and the combined hardwoods, ponderosa pine ranked no better than fourth in

average sapling height in 1973 and 1991 and for tallest trees in 1991. However, in

ii
USDA Forest Service Research Paper. PSW-RP-241. 1999.

spite of the large decrease in ponderosa pine numbers, this species will continue

to be a significant component of the stand, particularly near centers of larger

openings.

Size of opening and aspect had a major influence on plant density and

development. In general, almost all statistically significant differences for all

classes of vegetation were between the largest opening sizes and the smallest and

between the north and south aspect. Plainly, more plants, and plants that

developed better, occurred in the larger openings and on south aspects. Tanoak

was a partial exception, having significantly more plants in the smallest opening

size and on a north aspect, but developing better in both mean height and rootcollar diameter on south aspects.

Several shrub species that develop rapidly and reach large size in more sunlit

environments did not grow well in group-selection openings. This finding

suggests that vegetation managers can use the environment, especially

components like shade and organic material, to control undesirable vegetation;

thus, indirect methods can be added to their repertoire of vegetation control

techniques. We also found that because the entire 9-m opening probably was

impacted by shade and roots from adjacent trees, and conifer and hardwood

sapling growth was poorest in 9-m openings, this size of opening probably is too

small for operational application in group-selection cutting.

Finally, the density and development data for the conifer and hardwood

saplings, plus the finding that their growth rate was two to four times faster the

second 18 years than the first 10 years, suggest that this application of groupselection cutting will produce a spatially distinct age class. Furthermore, it shows

promise as a way to convert from essentially a ponderosa pine stand to a mixed

conifer-hardwood stand.

iii
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PSW-RP-241

Research PaperResearch StationPacific SouthwestForest Serviceof AgricultureDepartmentUnited States

Small Group-Selection OpeningsPlant Community Development After 28 Years in
USDA Forest Service Research Paper. PSW-RP-241. 1999.

1

Introduction

Forest land managers are currently experiencing a dilemma: on the one hand, the

human population is expanding and the wildland base is shrinking; on the other

hand, the need for wood products is increasing. Furthermore, society is

demanding that the inherent productivity of the land be maintained and that it

be productive in terms of “yields.” These yields take many forms and range from

the commodities of wood and water to the amenities of pleasing scenery and

viewing wildlife. Society also is advocating timber harvesting methods that are

perceived as more gentle on the land and that do not materially affect ecosystem

processes. Within the framework of sustaining ecosystem processes is a need for

information on silvicultural practices and their effect on species composition,

structure, and function over time (Aune and others 1993).

The silvicultural regeneration cutting system that has been suggested for

major implementation on Federal forest land in California is group selection.

Ecologically, it has special appeal because it creates scattered small openings like

those that develop when wildfires creep through the forest and occasionally flare

through groups of trees.

Fiske and others (1992) reported the broad effects of a group-selection

strategy for the Sierra Nevada mixed conifer forest type. However, information

on the density and development of conifer and hardwood seedlings, shrubs, and

herbaceous vegetation in group-selection openings is lacking (McDonald and

Fiddler 1991), and no information on plant species diversity or longer-term

successional trends is available. Concomitantly, Libby (1992) noted: “If we are

going to manage gaps [openings] to recruit vigorous sugar pines into the

overstory, we need to learn a lot more about the size and nature of the gaps that

will release sugar pine and not suppress it” (p. 216). Critical questions are

whether the desired species become established and develop satisfactorily in

group-selection openings (Guldin 1991) and how this development compares to

that achieved with other cutting methods.

The group-selection method, which is part of an uneven-aged silvicultural

regeneration system, involves the removal of groups of trees to create small

openings that range from 0.01 to 0.8 hectares (ha). The upper size limit of

openings is governed primarily by their environment. Openings should not be

large enough to lose the site protection of the surrounding trees (Daniel and

others 1979). Thus, slope, aspect, and height of surrounding trees influence

opening size. Several of these openings, scattered throughout a stand, usually

are harvested together on a cyclic basis. The cycle is often 10 to 20 years. In this

paper, the cycle was longer than 20 years, but the results are still pertinent

because second-cycle openings are often widely dispersed and usually have little

influence on previous openings.

Traditionally, in group selection there is no rotation and cutting continues in

perpetuity, usually removing clusters of mature trees. Initial and early entries

into the stand, however, often have a large element of “improvement” in them,

whereby trees of younger ages are removed (Hawley 1946). This provides the

opportunity to lower the proportion of less desirable species, trees with poor

growth, those that interfere with the growth of better trees, and poorly formed,

slow-growing, and diseased individuals (Smith 1962). This cyclic cutting creates

a stand of many age classes, often with several species, whose crowns and roots

fill nearly all available space.

Earlier studies (McDonald 1966, 1976) presented seedfall and regeneration

data for small openings cut to group-selection standards in northern California.

McDonald and Abbott (1994) reported seed crops for five conifer and three

hardwood species, quantified seedfall for four conifer species, and discussed

survival and density of conifer and hardwood seedlings during the 1965-1974

period. Seedling height was presented for trees and selected shrubs through

1973.
2 USDA Forest Service Research Paper. PSW-RP-241. 1999.

McDonald and Abbott (1994) found that each seedcrop contributed to

seedling numbers to the point that density in the small openings became very

high—more than 24,215 conifer and 3,580 hardwood seedlings per ha, at least 4

years old, in each opening. Height of seedlings after 9 years ranged from 0.2

meter (m) for ponderosa pine in 9-m diameter openings to 0.9 m for hardwoods

in 27-m openings. Ponderosa pine seedlings were significantly taller in 27-m

openings (0.4 m) than in 9-m openings (0.2 m), and hardwoods in 18- and 27-m

openings (0.8 and 0.9 m) were significantly taller than counterparts in 9-m

openings (0.5 m). Plants of all species were generally taller in the largest openings

because of better development near the center. Shrubs, however, were tall and

thin, with a much different form than when growing in sunlit environments.

This paper reports information after group-selection cutting in northern

California in which the plant community in 1991 is compared to surveys in 1973

and 1977; density and development of 10 conifer and hardwood species are

quantified and related to opening size and aspect; and average density, foliar

cover, and height of shrubs, forbs, graminoids, and bracken fern are also

quantified after 28 years.

Methods

Species and Site

The study was located on the Challenge Experimental Forest in northern

California (latitude 39o 30'; longitude 121o 13'). Here, site quality is high, and the

dominant species, ponderosa pine (Pinus ponderosa Dougl. ex Laws. var.

ponderosa), will average about 34 m in height in 50 years (Powers and Oliver

1978). Other tree species scattered over the Forest are coast Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco var. menziesii), sugar pine (Pinus lambertiana

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

incense-cedar (Libocedrus decurrens Torr.). Scientific and common names of trees

are from Little (1979) and scientific and common names of all other species are

from Hickman (1993). Hardwoods, principally California black oak (Quercus

kelloggii Newb.), tanoak (Lithocarpus densiflorus [Hook. & Arn.] Rehd.), and Pacific

madrone (Arbutus menziesii Pursh), are present throughout as individual trees,

clumps, or groves. Less common hardwoods are bigleaf maple (Acer macrophyllum

Pursh) and Pacific dogwood (Cornus nuttallii Audubon). These tree species

correspond to the montane and subalpine vegetation of the Sierra Nevada and

Cascade Ranges (Rundel and others 1977).

Altogether, trees larger than 8.9 cm in diameter at breast height (d.b.h.)

number more than 613 per ha and contain about 62 m

2

/ha of basal area. Dominant

trees were about 100 years old and 42 m tall when the study began. Trees in the

dominant and codominant crown classes averaged about 77 per ha, 70 percent of

which were ponderosa pines. Dormant but viable seeds of whiteleaf manzanita (Arctostaphylos viscida Parry), deerbrush (Ceanothus integerrimus H. & A.), and

several other shrub species are abundant in the soil on the Experimental Forest.

Apparently, these species were widespread in the past in many areas where not a

trace above ground remains today.

Summers on the Experimental Forest are hot and dry; winters cool and moist.

The average midsummer maximum temperature, based on 43 years of record, is

32

o

C; the midwinter minimum is -1

o

C. The growing season is about 200 days.

Precipitation averages 1,727 mm with 94 percent falling between October and

May. Moisture is the limiting factor and drought the primary cause of mortality

for conifer and hardwood seedlings. Aspects are mostly northeast and southwest,

and slopes vary from 3 to 30 percent. Soils are of clay loam-clay texture, deep,

moderately well-drained, and quite fertile.
USDA Forest Service Research Paper. PSW-RP-241. 1999. 3

Treatments, Measurements, and Analysis

Groups of large and small trees in the natural stand were harvested in the fall of

1963 to create openings of 9, 18, and 27 m in diameter (crown drip-line to crown

drip-line). Each opening size was replicated 16 times, and all openings were

located within 1.6 km of each other on relatively homogeneous ground having

similar soil and growth potential. Location of openings was random with the

restriction that they be within 60 m of skid roads. Opening size was randomly

assigned to the 48 chosen locations. In May 1964, unmerchantable conifers and

hardwoods were pushed over and the ground scarified by a bulldozer. The

scarification pattern resembled spokes radiating from a central hub with a small

flat pile of material located at the end of each spoke. In only a few openings was

the logging slash heavy enough to require piling in the adjacent skid road for

eventual burning. Consequently, the surface in all openings was mostly bare

mineral soil with virtually no competing vegetation (fig. 1).

All openings were visited in summer 1991 and their condition noted. A

number of openings were no longer representative of group selection because

the environment had been modified by logging in nearby compartments, edge

trees had fallen, or introduced blackberries had become extensive. Consequently,

the 1991 sample was comprised of 10 openings of each size. Twelve openings

occurred on north aspects and 18 openings on south aspects:

Opening size (m) Aspect Number

9 N6

S 4

18 N 3

S 7

27 N 3

S 7

All conifer and hardwood seedlings and saplings (referred to as saplings)

were sampled in 1-m wide transects that extended from the opening center to the

border. The transects were centered on the four cardinal directions (north, south,

east, and west) and varied in length with the radius of the three opening sizes.

This design allowed for a more intensive sample in the center of the openings.

All saplings in each transect were measured for height and diameter at the root

crown. To sample shrubs, forbs, and grasses, a 4-m2 subplot was randomly

Figure 1

After site preparation, each

opening was free of slash and

vegetation and constituted an ideal

medium for future colonization.
4 USDA Forest Service Research Paper. PSW-RP-241. 1999.

located near the center and in each quadrant of each opening. Density and

height were quantified.

Another sample took place in 1992. This was a destructive sample whereby

a total of 1,533 ponderosa pine, sugar pine, Douglas-fir, and California white fir

saplings were severed at groundline and aged to determine year of origin.

Sampling was similar to the 1991 sample, with random selection of seedlings

near the center and in each quadrant of each opening. The age of many saplings

was checked by small, colored (for species), and coded (for seed crop) plastic

sticks placed at the base of each seedling during the regeneration surveys of

1965-1974 (fig. 2).

The plant community in the small openings was that which invaded either

from seed or from below-ground structures. No root crowns of hardwood trees

or shrubs remained. All plant species were recorded in 1973, 1977, and 1991.

The experimental design was completely randomized. Statistical techniques

were analysis of variance (ANOVA) and multiple comparison tests. In general,

Tukey’s (HSD) equal N test was used for opening sizes, and the SpjotvollStoline analysis was applied for aspect and elsewhere where the sample size

was unequal. Significance in all tests was at α = 0.1.

Results

Plant Community Dynamics

In 1974 or 11 growing seasons after site preparation, the plant community in the

group-selection openings consisted of 40 species, including 10 trees, 9 shrubs,

16 forbs, 4 graminoids (grasses and sedges), and 1 species of fern (fig. 3; table 1).

Fourteen years after site preparation, the community had increased to 55 species,

with 1 additional shrub, 12 more species of forbs, and 2 more graminoids (table 1).

After 28 years, the plant community consisted of 55 species and included 10

species of trees, 16 shrubs, 24 forbs, 4 graminoids, and the ubiquitous bracken

fern (table 1). New additions to the shrubs included two introduced but

naturalized species of blackberries: Himalayan (Rubus discolor) and cut-leaved

(R. laciniatus) (table 2 ). Birds and other animals apparently disseminated seeds

of these species into the openings. Losses to the shrub category were a species of

Arctostaphylos and one of Baccharis.

Several successional trends were evident based on different numbers of

species present the 11th and 28th year. Number of species of conifer and

hardwood seedlings remained constant, shrub species doubled, forbs increased

Figure 2

Ten seasons after site preparation,

this small plot contained many

conifer seedlings including

ponderosa pine (white sticks) and

taller Douglas-fir (upper left) and

sugar pine (upper right).
USDA Forest Service Research Paper. PSW-RP-241. 1999. 5

Table 1—Plant species in small group-selection openings

various years after site preparation, Challenge Experimental

Forest, 1974-1991

Vegetation component Years after site preparation

11 14 28

----------------- Number of species --------------

Trees

Conifer 5 5 5

Hardwood 5 5 5

Shrubs 9 10 16

Forbs

Annual 6 8 5

Perennial 10 20 19

Graminoids 4 64

Ferns 1 11

Total 40 55 55

by 50 percent, and grass species increased and then leveled off at 11th-year

levels. The only annual species present were forbs. These increased slightly the

14th year but then decreased to 5 species after 28 years. Perennial forb species

increased 90 percent during this timespan.

Age Distribution of Conifer Seedlings

In the group-selection openings, the seedlings originated from many seedcrops

to the point that sapling density became excessive (McDonald and Abbott 1994).

But which seedcrops were effective? On the basis of the destructive sample of

1992, and for all openings taken together, most ponderosa and sugar pine

seedlings became established on both north and south aspects during the first 15

years after site preparation. Very few found the environment of the openings to

be conducive to survival after that. However, Douglas-fir and California white

Figure 3

Eleven seasons after site

preparation, this typical 27-m

opening contained numerous

conifer seedlings, graminoids,

shrubs, and forbs.
6 USDA Forest Service Research Paper. PSW-RP-241. 1999.

Table 2—Plant species in small group-selection openings, Challenge Experimental

Forest, 1991

Scientific name Common name

Trees

Abies concolor var. lowiana California white fir

Acer macrophyllum Bigleaf maple

Arbutus menziesii Pacific madrone

Cornus nuttallii Pacific dogwood

Libocedrus decurrens Incense-cedar

Lithocarpus densiflorus Tanoak

Pinus lambertiana Sugar pine

Pinus ponderosa Ponderosa pine

Pseudotsuga menziesii Coast Douglas-fir

Quercus kelloggii California black oak

Shrubs

Arctostaphylos viscida Whiteleaf manzanita

Ceanothus integerrimus Deerbrush

Ceanothus lemmonii Lemon ceanothus

Ceanothus prostratus Squawcarpet

Chamaebatia foliolosa Bearclover

Lonicera hispidula Hairy honeysuckle

Prunus virginiana var. demissa Western choke-cherry

Symphoricarpos mollis Creeping snowberry

Rhamnus rubra Sierra coffeeberry

Ribes roezlii Sierra gooseberry

Rosa gymnocarpa Wood rose

Rubus discolor Himalayan blackberry

Rubus laciniatus Cut-leaved blackberry

Rubus leucodermis Blackcap raspberry

Rubus parviflorus Thimbleberry

Toxicodendron diversilobum Western poison oak

Forbs

Adenocaulon bicolor Trail plant

Aster radulinus

Apocynum androsaemifolium Dogbane

Campanula prenanthoides California harebell

Chimaphila umbellata Prince’s pine

Clarkia rhomboidea

Collomia heterophylla

Dichelostemma capitatum Blue dicks

Fragaria vesca Wood strawberry

Galium bolanderi Bedstraw

Goodyera oblongifolia Rattlesnake plantain

Hieracium albiflorum White-flower hawkweed

Horkelia tridentata Three-tooth horkelia

Hypericum concinnum Gold-wire

Iris hartwegii

Lupinus sp.

Madia gracilis

Osmorhiza chilensis

Polygala cornuta Milkwort

Sidalcea malvaeflora

Solanum americanum

Trientalis latifolia Western starflower

Vicia americana

Viola lobata

Graminoids

Bromus sp.

Carex sp.

Elymus glaucus Blue wildrye

Juncus sp.

Ferns

Pteridium aquilinum var. pubescens Bracken fern
USDA Forest Service Research Paper. PSW-RP-241. 1999. 7

fir seedlings continued to become established for an additional 10 years, also on

both aspects. Apparently, adjacent trees and vegetation in the openings

ameliorated the environment on south aspects so that the shade-tolerant Douglasfir and California white fir seedlings could become established.

Conifer and Hardwood Saplings

Density

After 28 years, density of all conifer and hardwood saplings within all openings

combined ranged from 24,230 per ha in 9-m diameter openings to 26,580 per ha

in 18-m openings (table 3). Total density for conifers after 28 years was 10,710 per

ha in 9-m diameter openings, 18,750 per ha in 18-m openings, and 15,060 per ha

in 27-m openings. Total hardwood densities for similar opening sizes were

13,520, 7,830, and 9,840 per ha, respectively. Neither total conifers or total

hardwoods or the total of both differed significantly among opening sizes.

Because the analysis of conifer ages indicated differences between aspects,

all conifer and hardwood saplings present in all openings in 1991 were quantified

by north and south aspects. The total number of saplings per ha (hardwoods and

conifers combined) on north aspects was slightly more than 31,000; on south

aspects more than 21,000—a statistically significant difference (table 4). The total

number of hardwoods was significantly larger on north slopes than on south

slopes, but the total number of conifers did not differ significantly among aspects.

When analyses were expanded to include individual species in each of the

three opening sizes, saplings of Douglas-fir and California white fir were the

most numerous conifers in 9-m openings with 3,820 and 2,260 saplings per ha,

respectively; tanoak saplings were the most numerous of the hardwoods (11,200

per ha) in 9-m openings (table 3). In 18-m openings, ponderosa pine saplings

were the most numerous (7,050 per ha), followed by California white fir (5,540

per ha) and Douglas-fir (2,560 per ha). Tanoak, with 4,250 saplings per ha,

remained the most numerous of the hardwoods in this opening size. In 27-m

openings, ponderosa pine saplings (7,450 per ha) were most numerous followed

by Douglas-fir (3,960 per ha). Tanoak (5,040 per ha) continued to be the most

Table 3—Density of conifer and hardwood species on all aspects in three sizes

of group-selection openings, Challenge Experimental Forest, 1991

Opening size (m)

Species 9 18 27 SE1

------------------------- Density (no./ha) --------------------------

Conifers

Ponderosa pine 2,210 a2 7,050 b 7,450 b 1,020

Sugar pine 1,400 a 1,290 a 740 a 1,370

Douglas-fir 3,820 a 2,560 a 3,960 a 1,110

California white fir 2,260 a 5,540 a 2,390 a 760

Incense-cedar 1,020 a 2,310 a 520 a 1,300

Total 10,710 18,750 15,060

Hardwoods

Tanoak 11,200 a 4,250 b 5,040 b 510

California black oak 590 a 1,160 a 1,150 a 1,210

Pacific madrone 810 a 1,860 a 1,210 a 880

Bigleaf maple 270 a 0 a 1,290 a 780

Pacific dogwood 650 a 540 a 1,150 a 1,290

Total 13,520 7,830 9,840

1SE = Standard error.

2For each species, means followed by the same letter do not differ at the 0.1 level.
8 USDA Forest Service Research Paper. PSW-RP-241. 1999.

numerous hardwood. Statistical differences were limited to ponderosa pine and

tanoak. Ponderosa pine saplings were significantly more numerous in 18- and

27-m openings than in 9-m openings. Tanoak saplings were significantly more

numerous in 9-m openings than in larger openings.

When individual species were analyzed by aspect, several significant

differences were noted. Ponderosa pine and California black oak saplings were

significantly more numerous on south aspects. Ponderosa pine saplings

numbered 7,010 per ha on the south aspect versus 3,410 saplings per ha on the

north. Sapling density for California black oak was 1,280 per ha on the south

aspect and 500 per ha on the north (table 4). Three additional conifer and one

hardwood species were significantly more numerous on the north aspect. These

were sugar pine (1,860 saplings per ha on the north versus 660 on the south),

Douglas-fir (4,400 versus 2,810), California white fir (5,780 versus 1,810), and

tanoak (11,870 versus 3,470).

Development

When analyzed by opening size, ponderosa pines were significantly taller in 27-

m openings (215 cm) than in 9-m openings (84 cm), and California white fir

saplings were significantly taller in 18-m openings (256 cm) than in 9-m openings

(104 cm) (table 5). For hardwoods, California black oak saplings were significantly

taller in 18-m openings (214 cm) and 27-m openings (260 cm) than in 9-m

openings (45 cm). Pacific madrone saplings were significantly taller in 27-m

openings (470 cm) than in 9-m openings (209 cm), whereas saplings in 18-m

openings (352 cm) were intermediate.

When analyzed by aspect, several conifer and hardwood species were taller

on the south aspect than on the north (table 6). California black oak was the

exception. Sugar pine (444 cm on south versus 107 cm on north), Douglas-fir (224

cm versus 75 cm), California white fir (214 cm versus 135 cm), and tanoak (242

cm versus 179 cm) were the only species that were significantly taller.

Analysis of root collar diameters by species showed that the smallest average

diameter occurred in the 9-m openings without exception (table 7). For species

Table 4—Density of conifer and hardwood species for all opening sizes

on north and south aspects, group-selection cutting, Challenge

Experimental Forest, 1991

Aspect

Species North South SE1

------------------- Density (no./ha) ------------------

Conifers

Ponderosa pine 3,410 a2 7,010 b 1,040

Sugar pine 1,860 a 660 b 240

Douglas-fir 4,400 a 2,810 b 420

California white fir 5,780 a 1,810 b 730

Incense-cedar 690 a 1,680 a 640

Total 16,140 13,970

Hardwoods

Tanoak 11,870 a 3,470 b 1,180

California black oak 500 a 1,280 b 190

Pacific madrone 1,120 a 1,410 a 250

Bigleaf maple 220 a 720 a 310

Pacific dogwood 1,180 a 510 a 220

Total 14,890 7,390

1SE = Standard error.

2For each species, means followed by the same letter do not differ at the 0.1 level.
USDA Forest Service Research Paper. PSW-RP-241. 1999. 9

Table 5—Average height of conifer and hardwood saplings on all aspects in

three sizes of group-selection openings, Challenge Experimental Forest, 1991

Opening size (m)

Species 9 18 27 SE1

--------------------------- Height (cm) --------------------------

Conifers

Ponderosa pine 84.1 a2 145.7 ab 214.9 b 22.3

Sugar pine 86.4 a 217.2 a 406.8 a 92.4

Douglas-fir 86.4 a 173.8 a 233.1 a 34.1

California white fir 103.9 a 255.9 b 173.5 ab 20.8

Incense-cedar 58.1 a 102.8 a 92.2 a 20.1

Hardwoods

Tanoak 179.1 a 226.9 a 244.2 a 18.5

Californiablack oak 45.0 a 214.1 b 259.9 b 33.8

Pacific madrone 209.2 a 352.1 ab 469.6 b 40.5

Bigleaf maple 371.2 a - 427.0 a 208.0

Pacific dogwood 118.1 a 399.0 a 115.5 a 56.8

1SE = Standard error.

2For each species, means followed by the same letter do not differ at the 0.1 level.

Table 6—Average height of conifer and hardwood saplings for all opening

sizes on north and south aspects, group-selection cutting, Challenge

Experimental Forest, 1991

Aspect

Species North South SE1

---------------------- Height (cm) ---------------------------

Conifers

Ponderosa pine 107.0 a2 183.8 a 23.1

Sugar pine 106.7 a 444.1 b 85.2

Douglas-fir 74.7 a 224.3 b 32.6

California white fir 134.6 a 214.1 b 22.3

Incense-cedar 62.5 a 101.1 a 19.4

Hardwoods

Tanoak 179.3 a 241.5 b 18.0

California black oak 227.3 a 181.3 a 37.2

Pacific madrone 303.2 a 409.7 a 43.9

Bigleaf maple 371.2 a 427.0 a 208.0

Pacific dogwood 147.0 a 265.8 a 63.8

1SE = Standard error.

2For each species, means followed by the same letter do not differ at the 0.1 level.

with statistically significant differences in root collar diameter, that of ponderosa

pine was largest in 27-m openings (23.3 mm) versus 9-m openings (8.4 mm);

California white fir was largest in 18-m openings (33.1 mm) versus 9-m openings

(15.8 mm); California black oak was largest in 18- and 27-m openings (21.0 and

25.5 mm respectively) versus 9-m openings (5.1 mm); and Pacific dogwood was

largest in 18-m openings (41.3 mm) versus 9- and 27-m openings (10.7 and 12.9

mm, respectively).

When all openings sizes were combined and results presented by aspect,

average root collar diameter was largest on the south aspect for almost all

species of conifers and hardwoods (table 8). Ponderosa pine, sugar pine, Douglasfir, California white fir, and tanoak all had statistically larger diameters when

growing on a south aspect. No species had a statistically larger mean diameter

on a north aspect.
10 USDA Forest Service Research Paper. PSW-RP-241. 1999.

Table 8—Average root collar diameter of saplings for all opening sizes on

north and south aspects, group-selection cutting, Challenge Experimental

Forest, 1991

Aspect

Species North South SE1

-------------------- Diameter (mm) ---------------------

Conifers

Ponderosa pine 10.4 a2 20.8 b 2.5

Sugar pine 14.6 a 77.2 b 16.4

Douglas-fir 9.2 a 30.3 b 4.2

California white fir 16.6 a 30.4 b 2.7

Incense-cedar 9.5 a 18.7 a 3.9

Hardwoods

Tanoak 22.9 a 43.2 b 3.4

California black oak 19.8 a 19.0 a 3.2

Pacific madrone 38.9 a 60.4 a 7.5

Bigleaf maple 28.2 a 37.0 a 18.3

Pacific dogwood 16.1 a 27.3 a 6.1

1SE = Standard error.

2For each species, means followed by the same letter do not differ at the 0.1 level.

Shrubs, Forbs, Graminoids, and Ferns

Density

Twenty-eight years after site preparation, shrubs in the small openings were

characterized by those that tolerate shade. The most abundant shrub was western

poison oak (Toxicodendron diversilobum [Torrey and A. Gray] Greene) followed in

decreasing order by honeysuckle (Lonicera hispidula Douglas var. vacillans A.

Gray) and wood rose (Rosa gymnocarpa Nutt.). These and the other 13 shrub

species numbered 15,750 per ha in 9-m openings, 37,250 in 18-m openings, and

more than 37,800 per ha in 27-m openings (table 9). The two larger opening sizes

had a significantly higher shrub density than that in the smallest opening size.

The three most abundant forbs, all perennials, were a species of iris (Iris

hartwegii Baker), western starflower (Trientalis latifolia Hook.), and a milkwort

(Polygala cornuta Kellogg). Total forb density was 122,480 per ha in 9-m openings,

Table 7—Average root collar diameter of saplings on all aspects in three

sizes of group-selection openings, Challenge Experimental Forest, 1991

Opening size (m)

Species 9 18 27 SE1

------------------------- Diameter (mm) -----------------------

Conifers

Ponderosa pine 8.4 a2 16.4 ab 23.3 b 2.5

Sugar pine 12.0 a 33.5 a 71.0 a 17.7

Douglas-fir 12.4 a 22.0 a 31.1 a 4.5

California white fir 15.8 a 33.1 b 23.4 ab 2.8

Incense-cedar 9.4 a 19.4 a 15.9 a 4.0

Hardwoods

Tanoak 29.0 a 37.1 a 38.8 a 3.9

California black oak 5.1 a 21.0 b 25.5 b 2.8

Pacific madrone 25.0 a 46.1 ab 71.5 b 6.9

Bigleaf maple 28.2 a - 37.0 a 18.3

Pacific dogwood 10.7 a 41.3 b 12.9 a 5.2

1SE = Standard error.

2For each species, means followed by the same letter do not differ at the 0.1 level.
USDA Forest Service Research Paper. PSW-RP-241. 1999. 11

Table 9—Average density of shrubs, forbs, graminoids, and ferns on

all aspects in three sizes of group-selection openings, Challenge

Experimental Forest, 1991

Opening size (m)

Species 9 18 27 SE1

--------------------- Density (no./ha) -------------------

Shrubs 15,750 a2 37,250 b 37,840 b 4,440

Forbs 122,480 a 115,310 a 161,050 a 16,440

Graminoids 23,500 a 15,020 a 15,600 a 5,320

Bracken fern 8,380 a 12,740 ab 21,510 b 2,270

Total 170,110 180,320 236,000

1SE = Standard error.

2For each species, means followed by the same letter do not differ at the 0.1 level.

Table 10—Density of shrubs, forbs, graminoids, and ferns over all

opening sizes on north and south aspects, group-selection cutting,

Challenge Experimental Forest, 1991

Aspect

Species North South SE1

--------------------- Density (no./ha) -------------------

Shrubs 20,990 a2 36,470 b 4,560

Forbs 106,620 a 150,490 a 16,080

Graminoids 3,670 a 27,620 b 4,790

Bracken fern 9,120 a 17,600 b 2,320

Total 140,400 232,180

1SE = Standard error.

2For each species, means followed by the same letter do not differ at the 0.1 level.

115,310 in 18-m openings, and more than 161,000 in 27-m openings (table 9). Forb

density did not differ statistically among opening sizes.

Graminoids, chiefly species of brome (Bromus spp.) and sedge (Carex spp.),

had densities of 23,500 per ha in 9-m openings and over 15,000 per ha in 18- and

27-m openings (table 9). Graminoids did not differ statistically among opening

sizes.

Bracken fern, which typically is found in more open environments on the

Experimental Forest, increased steadily in density as opening size increased:

8,380 per ha in 9-m openings, 12,740 in 18-m openings, and 21,510 in 27-m

openings (table 9). Fern density differed significantly between the 9- and 27-m

opening, but not with the 18-m opening.

When shrubs, forbs, graminoids, and fern were analyzed by aspect, density

was consistently greater on the south aspect. Statistical differences in number of

plants per ha on north versus south aspects occurred for shrubs (20,990 versus

36,470), graminoids (3,670 versus 27,620), and bracken fern (9,120 versus 17,600)

(table 10). Forbs numbered 106,620 per ha on north slopes and 150,490 on south

slopes, but did not differ statistically.

Development

Height of shrubs, forbs, graminoids, and ferns on all aspects varied among

opening sizes, but no trend was discernible (table 11). For those classes of

vegetation where statistical differences occurred, shrubs were significantly taller

in 18-m openings than in 9-m openings and intermediate in 27-m openings.
12 USDA Forest Service Research Paper. PSW-RP-241. 1999.

Table 12—Average height of shrubs, forbs, graminoids, and ferns

over all opening sizes on north and south aspects, group-selection

cutting, Challenge Experimental Forest, 1991

Aspect

Species North South SE1

---------------- Height (cm) ---------------

Shrubs 53.1 a2 57.1 a 8.0

Forbs 13.2 a 18.0 a 0.8

Graminoids 22.8 a 40.2 a 3.8

Bracken fern 52.1 a 51.3 a 3.0

_______________________________________________________________________________

1SE = Standard error.

2For each species, means followed by the same letter do not differ at the 0.1 level.

Bracken fern was significantly taller in 27-m openings than in 18-m openings,

whereas 9-m openings were intermediate. Height of shrubs, forbs, graminoids,

and bracken fern did not differ significantly between aspects (table 12).

Discussion and Conclusions

In this study on the Challenge Experimental Forest in northern California, 48

openings, 9-, 18-, and 27-m in diameter, were created in 1963. The openings were

located such that groups of mostly mature trees were harvested along with many

individuals of poor form, slow growth, and low development potential.

After site preparation, the mineral soil seedbed provided an excellent

medium for seeds of conifers and hardwoods, shrubs, forbs, and graminoids to

germinate, and for seedlings to become established. Twenty-four seedcrops of

ponderosa pine, sugar pine, Douglas-fir, and California white fir were quantified

from 1964 to 1973 (McDonald and Abbott 1994). An additional 13 crops occurred

from 1974 to 1981 (McDonald 1992) with even more observed from 1982 through

1991. The large amount of seed, receptive seedbed, and sheltered environment

led to the establishment of an excessive number of conifer and hardwood

seedlings (27,795 per ha in 1973). Extensive age analysis of seedling stems

indicated that most ponderosa and sugar pines became established during the

first 15 years after site preparation, with the more tolerant California white fir

and Douglas-fir contributing new seedlings to the recruitment pool for an

additional 10 years. Of interest, was that tolerant conifer seedlings could become

established for 25 years after site preparation in the group selection environment.

Table 11—Average height of shrubs, forbs, graminoids, and ferns on

all aspects in three sizes of group-selection openings, Challenge

Experimental Forest, 1991

Opening size (m)

Species 9 18 27 SE1

------------------- Height (cm) ---------------------

Shrubs 38.7 a2 77.6 b 50.2 ab 7.5

Forbs 14.4 a 15.8 a 18.0 a 0.9

Graminoids 37.3 a 32.4 a 33.3 a 4.2

Bracken fern 47.0 ab 45.2 a 59.1 b 2.7

1SE = Standard error.

2For each species, means followed by the same letter do not differ at the 0.1 level.
USDA Forest Service Research Paper. PSW-RP-241. 1999. 13

Although seeds were plentiful, quality seedbeds were scarce. We noted

numerous month-old seedlings of all conifer species, especially ponderosa pine,

after each seedcrop. Apparently, recruitment was difficult because favorable

microsites already were occupied by established vegetation. At the end of the

study in 1991, conifer and hardwood saplings averaged more than 25,230 per ha,

and shrubs, forbs, graminoids, and ferns averaged more than 220,700 per ha.

Not only was the vegetation dense, it also was made up of many species. The

number of species in the small shady openings increased in general for the first

14 years after site preparation and then leveled off at about 55 species for the rest

of the study. Their origin reflected several classical regeneration strategies (Grime

1979). Most species originated from buried seeds in the soil, from seeds blown in

by the wind, and from rhizomes beneath the soil surface. Together, they formed

a community dominated by conifer and hardwood saplings with a large

component of shrubs and mostly perennial forbs. Most of the shrubs were low in

stature and tolerant of shade. Bracken fern and graminoids were present in

almost all openings. Bracken fern tended to be more abundant in larger openings

on south aspects, and the graminoids had more plants in the smallest openings

on south aspects.

The environment in which the various plant species had to become

established and survive was characterized in general by shade and the use of site

resources by trees adjacent to the openings. High plant density within openings

was another influence. Opening size and aspect, in general, also influenced plant

species density and development. Larger openings apparently provided more

area free of edge effects and hence more available site resources. Higher density

and better development tended to occur in the central portion of the larger

openings. Aspect seemed to correlate to the shade tolerance of some species.

However, for many species, density and development did not differ among

opening sizes or between aspects.

Development of almost all vegetation was poorest in the 9-m diameter

openings. This opening size probably is too small to be considered for operational

application. Roots of adjacent trees probably extend throughout openings of this

size and deny site resources (soil moisture and light) to new conifer and

hardwood seedlings (McDonald and Abbott 1994). Shade-tolerant plant species,

however, especially those with no particular need to grow rapidly, found this

environment quite suitable. Tanoak seedlings and seedling-sprouts (small

seedlings that die back to the root crown and resprout again and again

[McDonald 1978]) are a case in point. In this study, the 11,200 tanoaks per ha in

the 9-m diameter openings were using a particular regeneration strategy called

“seedling bank” (Grime 1979): the bank of tanoak persists; grows slowly, at least

above ground; and awaits a major disturbance that will create a more favorable

environment.

On the basis of the density and development information in this study, we

can project the likely composition of the future plant community. In the shortterm, most species are adapted to the environment of the small openings; thus,

the number of species, which already has leveled off, probably will remain

stable. The current high density of plants, especially the large number of

perennial shrubs and forbs, probably will decline because of the ever-increasing

size of the conifers and hardwoods, the shade they cast, and their increasing

demand for site resources. However, the number of conifer and hardwood

saplings also is excessive, and the shorter and weaker members will die.

Ponderosa pine saplings, many of which are more than 25 years old and less than

1 meter tall, are particularly vulnerable (fig. 4). Their numbers have already

declined significantly. In 1973 ponderosa pine amounted to 82 percent of total

conifer reproduction; in 1991, it constituted 37 percent of the total.
14 USDA Forest Service Research Paper. PSW-RP-241. 1999.

The relative growth rate of the saplings also is a major influence on the

future plant community. In many of the 18- and 27-m diameter openings,

saplings of both conifers and hardwoods are expressing dominance and

increasing in growth rate. Average height in meters for conifer species and

combined hardwoods after 10 years (1973) (McDonald and Abbott 1994) and 18

years later (1991) was:

Species 1973 1991

Ponderosa pine 0.32 2.15

Sugar pine 0.40 4.07

Douglas-fir 0.40 2.33

California white fir 0.45 1.74

Incense-cedar 0.27 0.92

Hardwoods 0.69 3.03

All species grew at least twice as fast in height the last 18 years as they did

the first 10 years. Sugar pine grew more than five times as fast, followed by

ponderosa pine and Douglas-fir, which grew more than three times as fast.

Because the development data are an average of a large number of saplings

of many ages, they tend to mask individual species development. For example,

the tallest tree, in meters, by species were:

Ponderosa pine 11.1

Sugar pine 15.7

Douglas-fir 15.1

California white fir 9.1

Bigleaf maple 11.5

Figure 4

Growing near the edge of a 27-m

opening, this 27-year-old

ponderosa pine seedling is less

than 1 meter tall.
USDA Forest Service Research Paper. PSW-RP-241. 1999. 15

Douglas-fir had by far the largest number of tall saplings. Although the other

hardwoods had one or two tall members, most were much shorter. But regardless

of species, all saplings had a tall slender form and less taper to the stem than

counterparts in more sunlit environments (fig. 5).

Long-term, the tree component in the group-selection openings is converting

from a primarily ponderosa pine stand to a mixed conifer and hardwood stand

dominated by the more shade-tolerant species. Ponderosa pine will continue to

be present but generally limited to the centers of the larger openings. Overall, the

vegetative component of the small openings will continue to be robust. And the

protection to the soil furnished by all the plants, plus the thick carpet of needles,

leaves, and other organic material that is developing, suggest that the inherent

productivity of the site will be maintained.

Earlier, McDonald and Fiddler (1993) suggested that the field of vegetation

management be expanded to include indirect vegetation manipulation

techniques. In indirect vegetation management, the environment manipulates

vegetation, not human-caused treatments such as manual grubbing, grazing, or

applying herbicides. Key natural elements in the environment that can be used

by vegetation managers are organic matter and shade. In southeastern Arkansas,

for example, Shelton (1995) found that increasing amounts of organic matter

decreased both the number of natural loblolly pine (Pinus taeda L.) seedlings and

the amount of competing vegetation. In the group-selection openings of this

study, shade caused aggressive sunlight-adapted species in the genera

Arctostaphylos, Ceanothus , and Rhamnus to develop poorly. More specifically,

they grew tall and slender—unlike their traditional bushy form in areas with

more sunlight. The weakened shrubs eventually die—a trend we noted in this

study and one that intensified with time (McDonald and Abbott 1994). Thus, the

normally aggressive shrub species were never really competitive, and the few

that remained at the end of the study were moribund.

Figure 5

In 1991, or 28 years after site

preparation, the openings are full of

slender conifer and hardwood

saplings such as California white fir

and tanoak.
16 USDA Forest Service Research Paper. PSW-RP-241. 1999.

Although the opening sizes studied here are at the lower end of the size

range associated with group selection, findings from them contribute to the

application of this regeneration cutting method. Stands can be regenerated with

a diversity of species while maintaining high forest cover; the reproduction,

although still too numerous, should continue to grow and even accelerate in

growth in the future—forming a spatially distinct age class.

Certainly, the plant community of the openings in this study is distinct from

the plant community in the uncut forest surrounding them. This uncut area is

characterized by conifers and an understory of tanoak and suppressed incensecedar saplings and trees. The ground is covered with a thick carpet of leaves and

needles and scattered tanoak seedlings and seedling-sprouts. A few incensecedar and Douglas-fir seedlings also are present, but most are so suppressed that

growth is limited and future mortality is virtually assured.

Silviculturists traditionally apply a controlled disturbance to a forested

ecosystem to create a desired species composition, number of plants, and stand

structure that will yield the amenities and commodities needed by society.

Inherent in this disturbance is a goal to guide the course and rate of secondary

plant succession toward a mature forest. This is accomplished by enhancing the

environment for desired species and making it unsuitable for undesirable species.

After 28 years the small openings in this study that were created by groupselection cutting provide the silviculturist with a method to naturally convert

essentially a one-species stand to that of several desired species, and to naturally

exclude undesirable species of aggressive shrubs.

References

Aune, Phil; Diaz, Nancy; Fiske, John; Meisenheimer, Ernie; Shepard, Ed; Bergsvik, Karl. 1993.

Silvicultural practices in the Pacific Northwest and Northern California. Internal Report.

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

8 p.

Daniel, Theodore W.; Helms, John A.; Baker, Frederick S. 1979. Principles of silviculture. 2nd ed.

New York: McGraw-Hill Book Company; 500 p.

Fiske, John N.; Husari, Susan J.; Ratcliff, Tom: Rogers, Robert R.; Smith, Mark T. 1992. Effects of a

group selection strategy for the Sierra Nevada mixed conifer. Internal Report. San Francisco,

CA: Pacific Southwest Region, USDA Forest Service; 29 p.

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

Guldin, James M. 1991. Uneven-aged BDq regulation of Sierra Nevada mixed conifers. Western

Journal of Applied Forestry 6(2): 27-32.

Hawley, Ralph C. 1946. The practice of silviculture. 5th edition. New York: John Wiley and Sons;

354 p.

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

California Press; 1400 p.

Libby, William J. 1992. Reflections on the symposium. In: Kinloch, Bohun B., Jr.; Marosy, Melissa;

Huddleston, May E., eds. Proceedings of a symposium on sugar pine: status, values, and roles in

ecosystems. Division of Agriculture and Natural Resources Publ. 3362. Davis: University of

California; 216-217.

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

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

McDonald, Philip M. 1966. Seed fall and regeneration from a group selection cut...first year

results. Res. Note PSW-113. Berkeley, CA: Pacific Southwest Forest and Range Experiment

Station, Forest Service, U.S. Department of Agriculture; 6 p.

McDonald, Philip M. 1976. Forest regeneration and seedling growth from five major cutting

methods in north-central California. Res. Paper PSW-115. Berkeley, CA: Pacific Southwest

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

McDonald, Philip M. 1978. Silviculture-ecology of three native California hardwoods on high

sites in north-central California. Corvallis, OR: Oregon State University; 309 p. Ph.D.

dissertation.

McDonald, Philip M. 1992. Estimating seed crops of conifer and hardwood species. Canadian

Journal of Forest Research 22(6): 832-838.
USDA Forest Service Research Paper. PSW-RP-241. 1999. 17

McDonald, Philip M.; Abbott, Celeste S. 1994. Seedfall, regeneration, and seedling development in

group-selection openings. Res. Paper PSW-RP-220. Albany, CA: Pacific Southwest Research

Station, Forest Service, U.S. Department of Agriculture; 13 p.

McDonald, Philip M.; Fiddler, Gary O. 1991. Vegetation in group selection openings: ecology and

manipulation. In: Proceedings 12th annual forest vegetation management conference; May 14-

16; Redding, CA. Redding, CA: Forest Vegetation Management Conference; 97-106.

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

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

Powers, Robert F.; Oliver, William W. 1978. Site classification of ponderosa pine stands under

stocking control in California. Res. Paper. PSW-128. Berkeley, CA: Pacific Southwest Forest and

Range Experiment Station, Forest Service, U.S. Department of Agriculture; 9 p.

Rundel, Philip W.; Parsons, David J.; Gordon, Donald T. 1977. Chapter 17. Montane and subalpine

vegetation of the Sierra Nevada and Cascade Ranges. In: Barbour, Michael G.; Major, Jack, eds.

Terrestrial vegetation of California. New York: John Wiley and Sons; 559-599.

Shelton, Michael G. 1995. Effects of the amount and composition of the forest floor on emergence

and early establishment of loblolly pine seedlings. Canadian Journal of Forest Research 25:

480-486.

Smith, David Martyn. 1962. The practice of silviculture. 7th edition. New York: John Wiley and

Sons; 578 p.