United States 

Department 

of Agriculture 

Forest Service 

Pacific Southwest 

Research Station 

General Technical Report 

PSW-GTR-185 

California’s Hardwood Resource: 

Seeds, Seedlings, and Sprouts of 

Three Important Forest-Zone Species 

Philip M. McDonald John C. Tappeiner, II 
Publisher 

Albany, California


Mailing address:


PO Box 245, Berkeley CA


94701-0245


(510) 559-6300 

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

February 2002 

Pacific Southwest Research Station 

Forest Service


U.S. Department of Agriculture


Abstract


McDonald, Philip M.; Tappeiner, John C., II. 2002. California’s hardwood


resource: seeds, seedlings, and sprouts of three important forest-zone 

species. Gen. Tech. Rep. PSW-GTR-185. Albany, CA: Pacific Southwest 

Research Station, Forest Service, U.S. Department of Agriculture; 39 p. 

Although California black oak, tanoak, and Pacific madrone are the principal 

hardwood species in the forest zone of California and Oregon and are key 

components of many plant communities, their seed production, regeneration, 

and early growth requirements have received little study. Information is 

presented on seed production, storage, and germination, and on the density, 

survival, and growth of three types of hardwood reproduction: seedlings, 

seedling-sprouts, and root-crown sprouts. Many trials showed that establishing 

planted seedlings in conventional sunlit plantations is difficult. Although initial 

stocking levels were high, height growth was poor. Dieback and death were 

common. Application of fertilizer and water and concomitant foliar analysis 

and tests of xylem sap tension indicated that internal moisture levels were 

inadequate to sustain seedling height growth. Thus, manipulating seedlingsprouts and root-crown sprouts currently are the silviculturist’s best techniques 

for establishing new stands. On a good site, root-crown sprouts of California 

black oak and tanoak were 20 feet tall in 10 years and those of Pacific madrone 

were 22 feet tall in the same time span. However, more information is needed on 

overstory-understory relationships for promoting the growth of seedlingsprouts and more knowledge is needed on clump density and thinning regimes 

for root-crown sprouts. 

Retrieval Terms: California black oak, ecology, growth, Pacific madrone,


regeneration, tanoak, vegetative propagation


The Author


Philip M. McDonald was, until his retirement, a research forester with the


Station’s Western Forest Management Research Unit, 2400 Washington Ave.,


Redding, CA 96001; e-mail: pmcdonald@fs.fed.us.


John C. Tappeiner II is a research forester in the Forest Resources Department,


Oregon State University, Corvallis, OR 97331; e-mail: John.Tappeiner@orst.edu


USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 
California’s Hardwood Resource: 

Seeds, Seedlings, and Sprouts of 

Three Important Forest-Zone Species 

Philip M. McDonald John C. Tappeiner, II


In Brief ...................................................................................................................... iii


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


Species, Occurrence, and Physical Environment ............................................... 2


Adaptation and Ecology ......................................................................................... 4


Seeds ........................................................................................................................... 6


Seed Production ............................................................................................... 7


Storage and Germination ............................................................................... 9


Direct Seeding................................................................................................. 11


Reproduction .......................................................................................................... 14


Natural Regeneration .................................................................................... 14


Seedling-sprouts ............................................................................................. 16


Artificial Regeneration .................................................................................. 21


Provenance Trial .................................................................................................... 27


Root-crown Sprouts ............................................................................................... 28


Summary and Recommendations ....................................................................... 32


References ................................................................................................................ 36


USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002.
 i 
In Brief . . .


McDonald, Philip M.; Tappeiner, John C., II. 2002. California’s hardwood.

resource: seeds, seedlings, and sprouts of three important forest-zone 

species. Gen. Tech. Rep. PSW-GTR-185. Albany, CA: Pacific Southwest 

Research Station, Forest Service, U.S. Department of Agriculture; 39 p. 

Retrieval Terms: California black oak, ecology, growth, Pacific madrone, 

regeneration, tanoak, vegetative propagation 

California black oak, tanoak, and Pacific madrone are California’s most 

widespread and most valuable forest-zone hardwoods. They are found 

throughout California and in part of Oregon and grow from near sea level to the 

7,500-foot elevation. They occur as pure hardwood stands, as components of 

mixed hardwood and conifer stands, and as occasional trees, clumps, and groves 

within the conifer forest. Their ecosystems are both numerous and complex. 

More than 300 species of wildlife use these hardwood-dominated habitats for 

reproduction, many people enjoy the contrast and beauty of these hardwoods in 

spring and fall, and many acre-feet of water originate in the hardwood forest. 

In spite of their recognized value as habitats and important components of 

ecosystems, these hardwood species are scarcely utilized and virtually 

unmanaged. Currently, the best “management” they receive is not cutting them. 

In some areas, these species have been eliminated in favor of other species or 

uses, and managers now want to reestablish them. In other areas, the old trees 

that are present have lost their ability to sprout, and seedlings are not present to 

replace them. In still other areas, small seedlings are plentiful, but never seem to 

grow larger. Plainly, silviculturists need to know how to successfully regenerate 

the hardwood forest. More specifically, they need to be able to secure 

regeneration, however initiated, that will be reliable and consistent and that will 

rapidly grow and become trees. This paper presents what is known on the 

reproductive silviculture of California black oak, tanoak, and Pacific madrone in 

the forest-zone of California and southwest Oregon. 

California black oak, tanoak, and Pacific madrone regenerate via three 

reproductive modes to form seedlings, seedling-sprouts, and root-crown sprouts. 

Seedlings, like their name suggests, originate from seed and their tops have 

never died back to the root crown (burl); seedling-sprouts also originate from 

seed, but their tops have died back and sprouted from small burls at least once; 

root-crown sprouts originate from larger burls on top-killed trees, and although 

they die, they seldom die back. Each reproductive type is unique, and the 

individual seedlings, single sprout stems, or multiple sprout stems develop 

differently and have different growth potentials. 

Although we present information on seed production, storage, germination, 

and direct seeding, we collected even more information on the three types of 

reproduction. In general, where a seed source is present, the seedlings of each of 

these three species can number 1,000 or more per acre. Some remain as single 

stems, but many die back one or more times, depending on the amount of light 

and other factors, to become seedling-sprouts. Populations of seedling-sprouts 

beneath tree crowns constitute an in-place resource that can be managed to form 

new stands. Research is needed on manipulating the overstory and in thinning 

the number of seedling-sprouts to provide adequate site resources for enhanced 

growth. Root-crown sprouts, which benefit from existing portions of parent-tree 

root systems, are another established resource that can be manipulated to form 

stands of these hardwood species. Much is known on root-crown sprout density, 

number per stump, and growth rates in various environments. Equations are 

available for projecting this information. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. iii 
Artificial regeneration with planted seedlings is a reproduction mode that 

needs more work. Although some research has been done in conventional sunlit 

plantations, and results from trials with fertilizer, water, and shading are 

available, knowledge on seedling growth in partially shaded plantations is 

needed. 

iv USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 
of Agriculture 

Department 

United States California’s Hardwood Resource: Seeds, Seedlings, and 

Forest Service Sprouts of Three Important Forest-Zone Species 

PSW-GTR-185 

General Technical Report 

Research Station 

Pacific Southwest 

iii

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Introduction 

In 1992, a series of publications was initiated on California’s hardwood resource 

in the forest zone. In the first publication, Huber and McDonald (1992) began 

by detailing the history of use for three species of economically important 

hardwoods, especially for wood and wood products, and presented 22 reasons 

why the industry had not been sustained. In a second publication, they followed 

the progress of the industry and cautiously suggested that a viable wood 

processing industry was possible in the near future (McDonald and Huber 

1994). By developing this industry, demand for products from the hardwood 

forest would be created, which would lead to active management of the 

resource. McDonald and Huber (1994) also recognized that wood products 

were just one of four major “yields” from the land and that wildlife, water, and 

pleasing scenery were currently more valuable than wood products. This led to 

an ecosystem management perspective that was followed a year later by a 

philosophy and guidelines for managing for these four yields in the general 

forest zone, as well as in an agroforestry and urban interface setting (McDonald 

and Huber 1995). These three publications (Huber and McDonald 1992; 

McDonald and Huber 1994, 1995) provided an overview and framework for 

managing California hardwoods, but lacked specifics on the reproductive 

biology and silvicultural practices necessary for regenerating the stands. This 

paper addresses these specifics and as such constitutes the fourth volume of the 

series on hardwoods. 

Native hardwoods in the forest zone of California’s mountains constitute a 

major resource that currently has great potential, but about which critical 

information is absent or fragmented. In old-growth stands, the hardwoods are 

decadent and dying, but little regeneration is present to replace them. In some 

locales, acorns and berries fall by the thousands, but seedlings do not result. In 

other areas, small hardwoods seem to always be present, but they never grow 

larger. In still other areas, planted hardwood seedlings either die outright or 

die back again and again and never become trees. Plainly, more information is 

needed on the establishment and development of early hardwood stands. 

Unfortunately, research on the reproduction of forest-zone hardwoods in 

the mountains of California is scant. When knowledge from research in the 

foothill-woodland zone of California and the Cascade Mountains of 

southwestern Oregon is included, several gaps are filled, but the overall 

research base remains small. Most of the work has been concentrated at a few 

locations where trials have been mostly case histories. While most of the major 

components of hardwood reproduction have been studied, they have not been 

examined in depth. However, studies in both California and Oregon, where 

replicated, have shown similar trends. Furthermore, findings on western 

species of Quercus show similarity in several areas to findings on related 

species of Quercus in the northern and central United States. Thus, the 

silvicultural concepts and principles examined in this paper are supported by 

previous studies, but the data are unreplicated and site-specific in many 

instances. 

The objectives of this paper are to bring together available information on 

the full spectrum for regenerating selected native California hardwoods, 

including information on seed production, the gathering and storing of acorns 

and berries, natural seedlings and seedling-sprouts, the survival and growth of 

artificially reproduced seedlings, and the density and development of rootcrown sprouts. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 1 
Species, Occur

rence, and Physical Environment 

The indigenous hardwoods of California can be divided into two major groups: 

those that grow in the forest-zone at higher elevations, and those that grow in 

the foothills and woodlands at lower elevations. Red alder (Alnus rubra Bong.), 

which grows best at low elevations along California’s north coast, is a separate, 

but relatively minor group. Although data from hardwood species at lower 

elevations in California or from other States are included to support a point or 

illustrate a technique, only those species that grow in the forest zone, primarily 

on upland sites, are discussed in this paper. In addition, only the three species 

that are the best studied, most abundant, and have a fairly large natural range, 

are presented. These are California black oak (Quercus kelloggii Newb.), which 

is a member of the red oak subsection of Quercus; tanoak (Lithocarpus densiflorus 

[Hook. & Arn.] Rehd.), which is not a true oak, but considered to be 

intermediate between the chestnuts (Castanea) and the oaks (Quercus) (McMinn 

1939); and Pacific madrone (Arbutus menziesii Pursh) (fig. 1). Black oak is 

deciduous and tanoak and Pacific madrone are evergreen. All three species 

have an established history of utilization for wood products and other yields 

(Economic Development Administration 1968) and as food and raw material 

for people (Wolf 1945), especially Native-Americans (Baumhoff 1963). 

Other forest-zone hardwood species that have a wide distribution or are 

locally abundant are canyon live oak (Quercus chrysolepis Liebm.), bigleaf maple (Acer macrophyllum Pursh), and giant chinkapin (Castanopsis chrysophylla 

[Dougl.] A. DC.). Although potentially important, little is known about their 

reproduction, and they are not covered in depth in this paper. 

The north-south range of California black oak is about 780 miles (McDonald 

1990). In Oregon it is found directly north of Eugene and southward along the 

lower slopes of the Klamath and Cascade Mountains. In California, black oak is 

present in the northern Coast Range from the Oregon State line to Marin 

County and then intermittently to the Santa Cruz and Santa Lucia Mountains. 

In southern California, the species becomes more common in the San 

Bernardino, San Jacinto, and Agua Tibia Mountains, extending a little south of 

Mt. Laguna. At least one small stand has been found in Baja California 

(Rodriguez 1987). In California’s Sierra Nevada, this oak grows abundantly 

along the west side from south of Lassen Peak to near Kings Canyon. California 

black oak then becomes intermittent southward to the Tehachapi Mountains, 

where it again increases in abundance. A few stands also are found along the 

east side of the Sierra Nevada range. 

Other than a disjunct stand north of the Umpqua River in southwestern 

Oregon, the general northern limit of tanoak is farther south in the Coquille 

River drainage (Tappeiner and others 1990). This species then extends 

southward to the California State line. Its eastern limit in Oregon extends from 

west of Roseburg to Grants Pass and then southwesterly into the Applegate 

River drainage. In California, tanoak extends southward in the Coast Ranges to 

the Santa Ynez Mountains northeast of Santa Barbara. Its range also extends 

northeastward from the Humboldt Bay region to the lower slopes of Mount 

Shasta, then intermittently southward along the western slopes of the Sierra 

Nevada as far as Mariposa County. 

Pacific madrone ranges from the east coast of Vancouver Island and the 

immediate mainland of British Columbia southward to near Palomar Mountain 

in San Diego County, California—a north-south distance of about 1,170 miles 

(McDonald and Tappeiner 1990). The species is common along the western 

slopes of the Coast Ranges in Washington, Oregon, and California, southward 

to San Luis Obispo County, California. It is abundant throughout much of the 

Klamath Mountains of Oregon and California, and from Yuba County, 

California southward through Calaveras County in the Sierra Nevada. 

2 USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 
Figure 1—Well developed trees of 

California black oak (A), tanoak (B), 

and Pacific madrone (C) in northern 

and central California. 

A	

B 

C 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 3 
The physical environment where California black oak, tanoak, and Pacific 

madrone reside is best described as moderate and variable. Within their natural 

ranges, all three species are found in a fairly broad range of slopes, aspects, 

elevations, soils, temperatures, and amounts of precipitation. Growth is best in 

areas having deep, well drained soils, moderate slopes, and a growing season 

of 200 days or more. Rarely are these species found in areas having less than 15 

inches of annual precipitation, poorly drained soils, or a growing season of less 

than 100 days. Tanoak has more restrictive site requirements than California 

black oak or Pacific madrone. In general, it is found in more moist environments 

such as areas of frequent fog, high relative humidity, and high annual 

precipitation. Tanoak foliage also is damaged from sudden exposure to bright 

sunlight, and the crowns of recently exposed trees will steadily die back to a 

point on the bole where they receive shade. Of the three species, California 

black oak has the widest elevational range (200 to 8,000 feet), Pacific madrone 

the narrowest (0 to 4,700 feet), and tanoak intermediate (0 to 6,500 feet). 

These hardwood species, either alone or together, seldom occupy entire 

mountain sides. Most often they are found as single trees, in clumps or groves, 

or occupying a given aspect in areas of up to 100 acres. Exceptions can occur, 

however, where extensive cutting and burning of conifer associates has allowed 

hardwood species to dominate over much larger areas. Each of these species 

seldom grows in pure stands, and rarely are the three species found growing 

together. Tanoak, Pacific madrone, and California black oak are most commonly 

found as associates in the northern Sierra Nevada. Black oak and canyon live 

oak sometimes intermingle on poorer sites throughout their range. Both 

California black oak and tanoak have a shrub form that grows on poorer sites 

and extends the species natural range to higher elevations. Shrub tanoak (Lithocarpus densiflorus var. echinoides), whose form is stunted and upright, is 

found in this environment. However, another form, which is not upright and 

sprawls along the ground, is found on above-average sites in the northern 

Sierra Nevada (McDonald [In press]). Although it never becomes a tree, it is not 

recognized as a variety. 

The three hardwoods in this paper are rarely found without conifer 

associates. In the Coast Ranges, the most common associates are Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco), redwood (Sequoia sempervirens [D. Don] 

Endl.), and western hemlock (Tsuga heterophylla [Raf.] Sarg.). In the Klamath 

Mountains and northern Sierra Nevada, Douglas-fir is an important species. In 

the Sierra Nevada and southern California ranges, ponderosa pine (Pinus 

ponderosa Dougl. ex Laws var. ponderosa), is most common, with California 

white fir (Abies concolor var. lowiana [Gord.] Lemm.), incense-cedar (Libocedrus 

decurrens Torr.), and sugar pine (Pinus lambertiana Dougl.) less abundant. 

Shrub species that associate with these hardwoods tend to be few and to 

vary inversely in species richness, density, and cover with overstory tree 

density. Some common shrub genera include Adenostoma, Arctostaphylos, 

Castanopsis, Ceanothus, Chamaebatia, Corylus, Prunus, Rhamnus, and 

Toxicodendron. Forbs and grasses, like the shrubs, vary tremendously beneath 

the hardwoods. They can be almost totally absent in the shade beneath dense 

stands or quite diverse and abundant in more open stands. 

Adaption and Ecology 

Through natural selection (Chaney 1925), California black oak, tanoak, and 

Pacific madrone have been adjusting to major and minor changes in their 

environment for millions of years. The fossil record reveals that they have 

lineage to the Mascall flora of the Miocene epoch of 12 to 26 million years ago. 

Consequently, they have survived such major geologic events as glaciation, 

volcanism, upthrusting, and subsidence. 

4 USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 
Figure 2—Rapidly growing rootcrown sprouts of tanoak give the 

species a strong presence after a 

forest fire, northern California. 

Specifically, they are well adapted to a broad range of biotic agents and 

abiotic events (Cooper 1922, Keeley 1977, Kummerow 1973, Mooney and Dunn 

1970). The adaptations are both morphological and physiological. Morphological 

features include special structures and coatings on leaves and stems to inhibit 

moisture loss, smooth upper-stem bark to facilitate the transport of water to the 

base of the tree via stem flow, a deep and extensive root system, capability to form 

a burl at an early age, and capacity to produce both an enormous amount of seed 

and large numbers of rapidly-growing root-crown sprouts (fig. 2). Physiological 

processes involve photosynthesis, transpiration, and respiration, which govern 

plant metabolism, energy intake, water losses, and eventually dominance potential 

(McDonald 1982). Photosynthesis can take place at low internal moisture levels 

and may provide an energy input. It also can happen quickly after the onset of 

favorable conditions. For example, positive net photosynthesis can occur early in 

the morning of a hot summer day and, even if for an hour, contributes to the plant’s 

well being at an opportune time. 

In a study on the internal water relationships of young tanoaks, Hanson 

(1977) noted the presence of “an internal controlling mechanism” that 

responded to environmental factors and served to “make tensions less negative 

to maintain the survival of the seedling.” Mooney and Dunn (1970) called this 

mechanism a “fail-safe” for lowering respiration when internal moisture levels 

are low and internal temperatures are high. Being able to internally monitor 

and control respiration keeps the plant from using all its energy reserves 

during the hot, dry, windy days of summer. A major limitation to the 

dominance of these forest-zone hardwood species, however, is tree height. 

None of these hardwoods grow as tall as their conifer associates. Because of 

their shorter stature, the hardwoods need periodic disturbance to retain their 

place in the stand. As Atzet and Martin (1992) noted: “Disturbance brings 

change that helps maintain compositional, structural, and functional diversity, 

helps to select adapted, resilient individuals, and helps to dampen the effects of 

minor environmental oscillations and extremes. Change is an essential 

ingredient of healthy ecosystems” (p. 40). These hardwoods depend primarily 

on fire, logging, blow-down, insect devastation, or mass soil movement to 

provide the disturbed and temporarily vegetation-free ground needed for 

establishment and growth (McDonald and others 1983). 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 5 
The size and intensity of the disturbance affects the amount and growth of 

the ensuing reproduction. Natural mortality of California black oak, tanoak, 

and Pacific madrone most often consists of the death of single trees or perhaps 

the death of a clump of trees, rather than the death of a stand. With a low level 

of disturbance, many seedlings of all three species die and others die back and 

sprout. Growth tends to be slow. With moderate disturbance like that from a 

ground fire, which typically involves a larger area and a more intense form of 

damage, some trees suffer topkill and sprout from the root crown. Most of the 

seedlings on the forest floor either are killed or put forth a few sprouts from a 

rudimentary burl. Many of these will die because the growth rate of sprouts 

from the topkilled trees is much greater than that of the sprouted seedlings. 

With heavy disturbance over larger areas, like that from a crown fire, the 

primary reproduction mode is sprouting from the top-killed trees. These rootcrown sprouts grow vigorously and deny site resources to the seedlings that 

originated from rudimentary burls. 

From the standpoint of reproduction, fire can be a blessing for black oak, 

tanoak, and Pacific madrone. It creates the necessary growing space and site 

resources by killing competing conifers, shrubs, and other vegetation. 

Capability to sprout and sprout vigor are valuable attributes in this regard. 

Although disturbance is necessary for the establishment of reproduction, 

hardwood stands generally are resistant to further disturbance, particularly 

from fire. The green leaves of hardwoods do not burn readily, and crown fires 

have been noted again and again to drop to the ground beneath hardwood 

canopies. Characteristically dense shade and low humidity then keep the fire 

on the ground. Even ground fires are of low intensity in California black oak 

stands, because the leaves decompose rapidly and little debris is present to 

carry fire. 

Animals also are more of a blessing than a curse for young hardwoods, 

although at times browsing and seed consumption can be severe. The two 

reproductive modes (sprouts and seeds) of California black oak, tanoak, and 

Pacific madrone serve the species well. Sprouts keep the species in place; seeds, 

through the action of disseminators, allow the species to expand to new areas. 

Birds, bears, rodents, deer, and a host of other animals both consume and 

distribute the acorns and berries of these hardwoods. Grinnell (1936) noted “It 

is not extravagance, but good investment for the oaks to provide subsistence 

for a continuing population of animal associates.” 

Insects and diseases, although almost always present, rarely have a major 

impact on the seedlings and sprouts of these hardwoods. For example, total 

defoliation of black oaks in northern California by the fruit-tree leaf roller 

occurred in April to May 1968, but evidence of the attack could scarcely be 

found by mid-July (McDonald 1969). Shoestring root disease (Armillaria spp.) is 

endemic on the roots of California black oak trees, but kills them only when 

they are old or weak. The length of root-crown sprouts of California black 

oak did not differ significantly among trees with or without heartrot 

(Garrison and others 2000). However, an unknown species of Phytophthora 

termed “sudden oak death phytophthora” has recently been killing mature, 

healthy trees in six coastal counties in northern California (Kliejunas 2000). 

To date, the species affected are tanoak, California black oak, and coast live 

oak (Quercus agrifolia Neé). 

Seeds 

In this part of the paper, we present information not only on the traditional 

categories of seed production, storage, and germination, but also on direct 

seeding and, more specifically, on the fate of acorns and berries and the effect of 

acorn position on germination and number of surviving seedlings. The seedlings 

6 USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 
that result from direct seeding are discussed in terms of early survival and cause 

of mortality. Growth and subsequent survival are presented in the section on 

artificial regeneration. 

Seed Production 

California black oak and tanoak acorns mature the second year (figs. 3, 4); 

Pacific madrone, berries mature at the end of a single growing season (fig. 5). 

Acorns are borne singly, or in clusters of two to four, rarely five or more. 

Madrone berries are borne on racemes having up to 60 berries on each. 

Figure 3—Reproductive anatomy 

of California black oak in early 

spring (A) pollen flowers, (B) young 

leaves, (C) small 1-year-old acorns, 

and (D) cup of mature acorn that 

fell a few months earlier. 

Figure 4—Branches of tanoak 

showing leaves, cups, and mature 

acorns. 

Figure 5—Twig of Pacific 

madrone showing leaves and 

cluster of berries. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 7 
The size of seed crops and the factors governing seed production are not 

well understood. Site quality, tree size and vigor, position in the stand, abortion, 

and weather, all play a role. In general, the better the site quality, the more 

resources will be available for tree functions, including the production of seed. 

Concomitantly, larger and more vigorous trees will have more branches, more 

loci on which acorns and berries can be produced, and more energy to commit 

to reproductive material. The position of the tree in the stand and the exposure 

of the crown to light have also been observed to affect the amount of 

reproductive material. Several observers have noted that weather at the time of 

flowering is important, probably because of its effect on pollinators. Warm, dry 

weather encourages pollinators and eventually the production of acorns and 

berries, and cold, wet weather discourages them. 

Abortion of tiny black oak and tanoak acorns the first year is a common 

observation, and has been noted as being more severe during drought years 

than in years of plentiful moisture—suggesting that balancing the trees’ 

resources with the acorn crop is probably necessary. Obviously, fewer fully 

developed acorns are better than many substandard acorns. For Pacific 

madrone, the number of racemes and the number of berries per raceme have 

been noted to vary, but the variables and processes that govern development, 

and ultimately the number of mature berries, are unknown. 

Age at the onset of seed production for California black oak and tanoak has 

been reported as early as 5 years on vigorous root-crown sprouts in clearcuttings. 

However, acorn production is generally lacking until age 30 or 40 (Tappeiner and 

others 1990). After age 40, acorn production for tanoak increases rapidly, but it is 

not until age 80 to 100 that acorns are produced in large quantities on California 

black oaks (McDonald 1990). The age at which Pacific madrone first produces 

berries is reported as 3 to 5 years (Roy 1974). Sixty-two berries were counted on a 

vigorous 4-year-old root-crown sprout on a productive site (McDonald 1978). 

Number of seed per madrone berry ranged from 2 to 37, averaging 20 in one test 

(McDonald 1978) and from 7 to 44 in another test (Harrington and others 1998). The 

production of seeds is highly variable for all three species. Some trees produce 

seeds almost every year, although others of similar size and crown nearby rarely 

produce any. Genetics obviously is a factor that governs the periodicity and 

magnitude of acorn and berry crops. In general, large, vigorous trees of all three 

species, 100 to 200 years old, with well developed crowns, consistently produce the 

most acorns and berries. 

The periodicity of seed crops is quite variable and depends more on local 

conditions than on regional ones. For example, one study reported that 

abundant seed crops of California black oak were produced at 2- to 3-year 

intervals (Roy 1962). At the 2,500-foot elevation on the Challenge Experimental 

Forest in the northern Sierra Nevada, medium to heavy black oak seed crops 

were produced in 4 of 20 years. At the 2,800-foot elevation in south-central 

Shasta County, medium to heavy seed crops were borne on large trees in 4 of 8 

years. At the 560-foot elevation in Shasta County, black oaks yielded sound 

acorns in 6 of 7 years. Of these, two each rated as heavy, medium, and light 

(McDonald 1990). In central-coastal California above the 2,500 foot elevation, 

Koenig and Knops (1995) recorded five above-average acorn crops for 

California black oak during the 1980-1994 period. 

Guides for estimating acorn crops by visual surveys are available (Garrison 

and others 1998b, Graves 1980, Koenig and others 1994). A general age-tree 

size-acorn yield relationship for a medium seed crop of California black oak on 

an above-average site is available (table 1) (McDonald 1969, U.S. Forest Service 

1973). 

Tanoak on the Challenge Experimental Forest in northern California, 

produced four medium-heavy and nine light to very light seed crops from 

1958-1981. During the same period, Pacific madrone yielded 2 medium-heavy 

8 USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 
Table 1—Seed production of California black oak by age and size of tree for a medium seed crop 

on a high-quality site, northern California. 

Age Breast-height Crown Acorn 

diameter diameter yield 

yrs inches ft lbs 

30 5 15 0 

50 9 20 5 

80 13 26 20 

100 17 32 60 

150 24 41 100 

200 32 52 140 

and 10 light to very light seed crops (McDonald 1992). The fecundity of the 

hardwood species, as indicated by individual trees, is amazing. In Trinity 

County, California, Roy (1957) recorded the number of tanoak acorns under 

18- to 24-inch diameter (dbh) tanoak trees during a good seed year. More than 

78,000 to almost 83,000 acorns per acre were produced; 49 percent were sound. 

A 16-inch dbh tanoak tree on the Challenge Experimental Forest had 1.1 

million acorns per acre beneath it in a bumper seed year. The acorns were 79 

percent sound (McDonald 1978). On the same site in a light seed year, a 

15.7-inch d.b.h. Pacific madrone tree produced 107,640 berries or about 2.1 

million seeds (McDonald 1978). 

Storage and Germination 

When gathering acorns for future propagation, it is important that they be ripe and 

sound. Mature acorns of both black oak and tanoak vary from dark tan to a rich 

chocolate brown. Warm, dry weather, usually with a north wind and low relative 

humidity, stimulates acorn fall. Under such conditions and a bumper crop, the 

forest fairly rains with fully ripe acorns. This is the time that they should be 

gathered, not before. Acorns that fall early tend to be unsound because of insects, 

immaturity, or internal problems, chiefly with the embryo. Insects, especially the 

filberworm (Melissopus latiferreanus) and the filbert weevil (Curculio uniformis) are 

particularly destructive. Relatively new evidence on an old technique may lessen 

their depredations. Many Native-American tribes “frequently burned under the 

black oaks to decrease this pest” (weevils) (Anderson 1992). Skinner (1981) noted 

that a prescribed burn in northern California in March resulted in a bumper crop of 

sound California black oak acorns while trees on unburned ground nearby bore 

only unsound acorns. Apparently, destructive insects in the duff and soil were 

reduced greatly by the burn. 

Fully ripe acorns should be gathered from shady locations soon after they 

fall. Because moisture content is critical to acorn viability and they may have 

dried too much before they fell, rinsing or soaking acorns in water soon after 

gathering is recommended. Exposure often is deadly to acorns on the ground, 

and only a few hours of sunlight slanting beneath a tree crown can overheat 

and kill the embryos. Once the moisture content of acorns falls below 25 to 30 

percent, the cotyledons, which comprise the bulk of the acorn and provide 

energy for the embryo, no longer are crisp, firm, and cream-colored. Instead, 

they become limp and dull with a tan-colored tinge. Later, the embryo becomes 

hard and the cotyledons spongy with a brownish hue. In one study, cotyledons 

of exposed California black oak acorns had withered to about one-half normal 

size nine days after falling (McDonald 1978). Freezing also kills the embryos in 

acorns that are not covered by leaves or other organic material. McDonald 

(1978) found that the cotyledons of frozen tanoak acorns were gray-black in the 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 9 
center with bright yellow, dry, and hard embryos. Although leaves often shield 

the acorn from freezing, they can create an environment where mold becomes a 

problem. A blue-gray mold often forms in the circular scar of the absent cup, 

penetrates the acorn, and destroys its contents. Jaeger (1920) reported that 

Native-Americans would gather only newly fallen acorns to avoid the mold. 

Determining the soundness of newly-fallen black oak and tanoak acorns at 

the time of gathering is fairly easy. Because both species produce large, heavy 

acorns, and damaged and unsound acorns are much lighter, the latter can be 

discarded on the basis of weight. Interestingly, acorn weight and exit holes 

were the best indicators of insect damage to Native-Americans (Anderson 

1992). An alternative technique for determining soundness is to place the 

acorns in a vat filled with water and discard those that float. Both tests eliminate 

most of the unsound acorns, but not all. 

At least nine short-term storage trials (3 to 4 months) with acorns of black 

oak and tanoak in northern California produced variable results; some were 

fatal (McDonald 1978). Another trial in southern California attempted to store 

about 3,000 California black oak and canyon live oak acorns for about 6 months 

(Anonymous 1980). They were stored first in a cool shed and then in a 

refrigerator. Upon removal, the cotyledons were found to be severely 

dehydated, and all were discarded. Storage was more successful for both black 

oak and tanoak acorns if they were immediately placed in bags in a 

temperature-controlled refrigerator at 34 to 38

°

F. 

Low temperatures and moderate moisture contents are best for acorn 

storage and near-perfect for stratification. The breaking of dormancy, or afterripening as it often is called, is not really necessary for the two species because 

some acorns will germinate without it. However, most propagators prefer to 

retard germination until spring and to compress it into as short a timespan as 

possible. Thus, in practice, both storage and stratification take place 

simultaneously. 

Although some acorns of the red-oak subgenus, which includes California 

black oak, retain viability for 5 years in storage, storage for not longer than 2 to 

3 years is recommended (Bonner and Vozzo 1987). The best storage method is 

one that maintains acorn moisture content above 30 percent, allows some gas 

exchange with the atmosphere, and keeps the temperature just above freezing. 

Because moisture content is critical, it should be monitored and a damp tissue 

or sponge placed in the bag if needed. Long-term storage trials for California 

black oak and tanoak are not known. 

Probably the most reliable short-term storage and stratification technique 

for California black oak and tanoak acorns is burial on-site. After gathering, 

California black oak and tanoak acorns are put in wire baskets or similar 

containers and placed in shallow holes in the ground near the outplanting site. 

The containers are then covered with a layer of soil and 2 to 3 inches of duff and 

leaves and allowed to overwinter in the natural environment. They can easily 

be opened in early spring and the acorns checked for soundness. This is 

accomplished by observing the opening of the acorn at the pointed end and the 

presence of the radicle (tiny white root). This radicle, if allowed to extend 

beyond 1 inch, makes outplanting difficult; thus, acorns should be sown before 

this happens. These acorns, which have essentially germinated, almost always 

lead to seedlings and result in high stocking levels after planting. 

Gathering madrone berries from the ground is rarely feasible. Most berries 

never reach the ground because they are consumed in the tree, or once on the 

ground, soon are devoured by a host of animals and insects. Colorful accounts 

of gorging by birds abound. Smith (1968) tells of a band-tailed pigeon (Columba 

fasciata) that ingested 111 berries—so many that it could not fly. Peattie (1953) 

noticed band-tailed pigeons devouring Pacific madrone berries, and remarked 

“... the madrone groves ring with the shots of their persecutors.” Consequently, 

10 USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 
berries are collected from the tree either by knocking bunches off it with a long 

pole, pruning branches, or by falling the tree. 

Several investigators have shown that the seed of Pacific madrone must be 

separated from the berry to facilitate storage and eventual germination 

(McDonald, 1978, Roy 1974). The berry can inhibit germination of the seed 

within, retard the emergence of the seedling, and aid the colonization of 

damping-off fungi. However, the berry may indirectly facilitate storage and 

germination of the seed. After passing through the digestive system of birds 

and other animals, the now-naked seed is in a better position to eventually 

produce a seedling. Harrington and others (1998) found that storing seed dried 

to 5.6 percent moisture content for 3 years in a sealed polypropylene jar at 3 to 

5 

°

C did not appreciably decrease seed germination. Longer-term storage has 

not been documented. 

Seed of Pacific madrone need stratification in order to germinate. Early 

investigators (Emery 1964, Mirov and Kraebel 1937) recommended stratification 

in cool, moist conditions for 3 months. An extensive trial—involving four 

treatments: cool-moist, acid and cool-moist, heat and cool-moist, and heat, 

acid, and cool-moist stratification for 30, 60, 90, and 120 days—showed that a 

short time period was desirable for both completeness and timing (McDonald 

1978). Should the plant propagator desire at least 90 percent of seed to 

germinate, cool-moist stratification for only 40 days is recommended. 

Once the stratification requirement has been met, germination is prompt. 

Most seed germinate in a few days; most within a week if placed in a warm, 

moist environment (Harrington and others 1998). 

Direct Seeding 

Trials with directly seeded California black oak acorns took place on the 

Challenge Experimental Forest in northern California in 1966 and 1969. In both 

instances, the acorns were placed in conventional plantations characterized by 

full sunlight, bare mineral soil, and freedom from almost all understory plants, 

especially shrubs. The exposure was south on gently sloping ground. Acorns, 

sorted for soundness, were seeded in the fall, buried 1 to 2 inches deep in soil 

loosened by hand tools, and protected by wire-mesh screens. 

Emergence began April 8 for the 146 seed spots in the 1966 trial and 

extended through July 8. Seventy-nine percent of acorns produced a seedling. 

Some were recorded as dead from drought by the end of summer, but most 

remained alive belowground and sprouted in the spring, usually with one 

stem. Survival in spring 1967 was 70 percent. A hard freeze in mid-April 1968 

damaged recently emerged leaves and terminal buds, and killed some seedlings 

back to the root crown. These also sprouted, generally with one stem. 

Emergence began April 18 in the 1969 trial, and involved 996 seed spots in 

eight blocks. It continued through October 9. Early emergers were frozen to 

groundline by heavy frosts on April 20 and April 30, but most subsequently 

sprouted with one stem. The long (174 days) emergence period was atypical. It 

was caused by severe winter storms that buried some acorns up to 4 inches 

deep and formed a hard crust on the soil surface. Thus, some seedlings emerged 

in the spring, some broke through in the summer, some finally emerged after 

the fall rains had softened the crust, and some held-over until the following 

spring. The hold-over “seedlings” were examined closely. In many, a small, 

irregular, knobby protrusion formed just below the soil crust and the seedling 

overwintered in this form. Most emerged by mid-May 1970. The hold-over 

seedlings were visually weaker and had skinny stems and small leaves. They 

also did not have the robust taproot development of their first-spring 

counterparts. Many died from drought. Peak stocking (number of spots having 

a living seedling) was 72 percent in summer 1970 and 67 percent at the end of 

the growing season. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 11 
For the early trials with direct-seeded tanoak acorns on the Challenge 

Experimental Forest, acorn position was of interest. From a monitoring and 

economic viewpoint, the ideal plantation is one where all outplanted spots 

have a seedling, and the time it takes for all the seedlings to emerge is as short 

as possible. The factor that governs this best is acorn position. An early 

definitive study on this subject was conducted by Molotkovskii (1955) in Russia. 

He found that reversing polarity resulted in higher germinative capacity (more 

seedlings per number sown), greater germinative energy (shorter time to peak 

germination), a decrease in time between planting and germination, increased 

seedling vigor, and straighter seedling stems. Reversing polarity is where the 

pointed end of the acorn is oriented pointed up, instead of down. Thus, the 

emerging radicle has to grow up and then curve downward. Molotkovskii 

speculated that the point-up position increased certain chemicals in the acorn 

that stimulated and speeded germination to overcome this obstacle. 

The various positions serve to lengthen the germination period. In nature, 

acorns reside in all positions: some orient point up, some point down, but most 

rest on their sides or at a slight angle. This increases the odds that weather will 

be favorable and that consumers will be absent or miss some acorns during this 

period. To test the effect of acorn position on germination capacity and speed, 

255 stratified black oak acorns were divided into equal lots of 85 and placed 

point-up, point-down, and on their sides (McDonald 1978). They were buried 

0.5 inch in moist peat moss in deep flats in a controlled environment (water and 

temperature) in a greenhouse. Although total germination was rather poor, 

trends could be ascertained: 

Variable Point up Side Point down 

Germinative capacity (percent by peak day) 95 46 62 

Germinative energy (days) 34 34 47 

On the basis of these results, a much larger test was performed. It involved 

844 tanoak acorns seeded point up and 772 placed point down in a field test in 

northern California. Seeding took place from January 6 through February 11. 

New seedlings were recorded at 2-week intervals after emergence, which was 

first observed on April 17. A sharp freeze with a temperature minimum of 21

°

F 

occurred on April 20 followed by four successive days of below-freezing 

temperatures. All seedling with stems and leaves aboveground during this 

period turned black and died. Because no seedlings from point-down acorns 

had emerged, these were all from point-up acorns. Of those blackened, about 

70 percent eventually sprouted from belowground with two to four stems. 

Acorns seeded point up germinated much faster than those placed point down. 

By April 29, 316 seedlings from point-up acorns were present before the first 

seedlings from point-down acorns began to emerge from the soil. Maximum 

germination was achieved by July 18 for acorns placed point up, but not until 

September 18 for those placed point down. Almost three times as many 

seedlings originated from acorns placed point up (McDonald 1978). Exhuming 

plantless seed spots where acorns had been placed point down revealed acorn 

after acorn to have germinated and put forth a short radicle that died before the 

epicotyl (tiny new shoot) reached the surface. Late germination almost always 

resulted in death from drought. By fall 1971 or after two growing seasons, 

seedlings from point-up acorns numbered 275 (31 percent); from point-down 

acorns, 65 seedlings (8 percent). 

In an extensive study in southwestern Oregon, Tappeiner and others (1986) 

found that second-year survival of tanoak seedlings from sown and protected 

acorns in exposed clearcuttings and in young and old conifer stands ranged 

from 58 to 70 percent, and after 4 years to between 44 and 49 percent. Rodents 

were the primary cause of mortality followed by drought and root disease. 

12 USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 
The only direct seeding trial with Pacific madrone that we could find took 

place in southwestern Oregon (Tappeiner and others 1986). It was an extensive 

trial involving 43,200 seeds, 90 percent sound, sown in lots of 200 seeds in 

exposed clearcuttings and in young and old conifer stands. Mortality began 

immediately after emergence, and on most plots was 100 percent after 1 year. 

Average survival at the end of the first summer was significantly lower (p = 

0.05) in old stands (5 to 14 percent) and young stands (8 to 12 percent) than in 

clearcuttings (32 to 34 percent). At the end of the second year, survival ranged 

from less than 1 to 3 percent in the young and old stands, and in the 

clearcuttings after 2 and 3 years, it ranged from 5 to 12 percent. First-year 

survival in clearcuttings increased significantly if microsites were shaded. In 

all stands, mortality in order of significance was caused by drought, litterfall, 

damping-off fungi, invertebrates, and frost. 

Whether in the bright sunlight of conventional plantations or as 

outplantings in partially shaded openings, acorns are at risk from consumers. 

Even acorns protected by pinned-down wire screens (fig. 6) are vulnerable to 

rodents. In a trial with black oak acorns on the Tahoe National Forest in 

northern California, Duer (1989) lost 287 seedlings out of 300 to western gray 

squirrels (Scirus grisius). He excavated the dead seedlings and found that the 

squirrels had dug under the seedlings, clipped the acorns, and consumed them. 

Obviously, the acorn still had some food value to the squirrels, even though a 

seedling had been produced. Clipping the acorns apparently deprived the 

seedlings of needed energy, and they died soon after. McDonald (1978) noticed 

that western gray squirrels would dig under wire screens to extract germinating 

tanoak acorns. Unsound acorns or those that germinated later were not touched. 

Apparently, a germinating acorn can be sensed by the squirrels. In four 

clearcuttings in southwestern Oregon, Tappeiner and others (1986) found that 

99 percent of sown, but unprotected, tanoak acorns were lost to predation in 

three annual sowings. 

Germinated acorns of California black oak and tanoak should be buried at 

least 2 inches deep to avoid consumption by herbivores, to avoid embryo 

death, and to give the radicle time to elongate before the epicotyl emerges 

aboveground. But even buried acorns need protection. Screens usually are 

cone- or pyramid-shaped and of 1/4-inch-mesh hardware cloth. They should 

extend into the soil at least 4 inches, more if pocket gophers (Thomomys bottae) 

are present, and be of equal height aboveground. 

Figure 6—A typical wire screen and 

pin used to protect buried acorns. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 13 
Reproduction 

Natural seedlings are those that originate directly from seed and have not died 

back and sprouted. Seedling-sprouts are defined as seedlings whose tops have 

died back and sprouted at least once. They are defined in this paper as 

originating from seedlings that are less than 2 inches in diameter at ground line 

when top-killed. Root-crown sprouts arise from stumps or trees larger than 2 

inches in diameter at ground line whose tops have been killed. All three types 

of reproduction are often collectively termed “advance reproduction” in the 

literature. Because the three reproductive types have different silvical 

requirements and growth trajectories, they are considered to be unique and 

presented separately in this paper. 

Natural Regeneration 

The amount of energy available to seedlings from the seeds of black oak, 

tanoak, and Pacific madrone is a study in contrast. The large energy-rich acorn 

is sufficient to produce a seedling with a thick stem and well developed root 

system, whereas the tiny seed of Pacific madrone can produce only a small, 

tender-stemmed seedling with a much weaker root system. 

The seed/seedling ratio of California black oak, tanoak, and Pacific 

madrone is best described as “many acorns and berries, but few seedlings.” 

The proportion of seedlings to sound seed almost always is less than 1 

percent. For example, the number of tanoak seedlings beneath five seed 

trees in Trinity County California averaged 264 per acre with an average 

acorn/seedling efficiency of 0.64 percent (Roy 1957). In southwest Oregon, 

only one tanoak seedling resulted from 156 sound acorns present after the 

Douglas-fir overstory had been removed (Tappeiner and others 1986). In 

central-coastal California, only one Pacific madrone seedling out of 100 was 

alive after 4 months (Pelton 1962). 

Germination of California black oak acorns in the field is best described as 

being highly variable, scanty (Sudworth 1908), and high (95 percent) (Mirov 

and Kraebel 1937). The radicle, which is the first structure to emerge from the 

acorn, grows downward for 10 to 20 days before the epicotyl emerges from the 

soil. This strategy benefits the seedling in getting to and staying in available 

soil moisture and in minimizing transpirational loss. It also temporarily avoids 

damage or death from above-ground herbivores. During the first growing 

season, seedlings only 2- to 6-inches tall, may extend their taproots as deep as 

30 inches (McDonald 1969). On the Sierra National Forest, the most vigorous of 

black oak seedlings had a taproot of 36 inches, many lateral roots (but none 

longer than 1 inch), and a shoot of about 12 inches after one growing season 

(Anonymous 1909). For tanoak, root length after one growing season is 

conservatively estimated to be several times that of shoot length (McDonald 

and Tappeiner 1987). Two-month-old Pacific madrone seedlings in a shaded, 

bare soil environment on a good site in northern California had a 1-inch shoot 

and a 2-inch root.1 

A comprehensive study on the fate of emerging Pacific madrone seedlings 

in the Santa Cruz Mountains of central coastal California involved 276 seedlings 

in a shade environment and an equal number in a sun environment (Pelton 

1962). Plots in the shade environment were described as densely shaded with 

heavy litter and moist mineral soil; sun plots were characterized as moderately 

open with thin litter, if any, and dry soil. By August 2, no seedlings in shade 

plots survived, and only 2 percent were alive in sun plots. Invertebrates, chiefly 

slugs, accounted for 29 percent of mortality. Drought associated with drying of 

the root tip while trying to penetrate the deep litter layer was 10 percent. Fungi, 

especially post-emergence damping-off and root decay types, accounted for 28 1 Unpublished data on file, Pacific Southwest Research Station, Redding, Calif. 

14 USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 
percent of mortality and was more important in sun than in shade plots. 

Combinations of factors (root decay plus drought, for example) killed 23 

percent. Rodents and litterfall constituted the remaining 9 percent of mortality. 

Natural regeneration of California black oak and tanoak occurs most often 

and in larger numbers beneath the crowns of parent trees, with only scattered 

individuals found elsewhere. The typically deep litter and organic material 

found beneath large trees is not an impediment to the new seedling root, and 

the moisture held in the organic matter probably is an asset. For Pacific 

madrone, bare mineral soil in shade, and the almost complete absence of 

organic matter, is the preferred seedbed for seedling establishment. In northern 

California and to a lesser degree in southwestern Oregon, most natural 

seedlings of Pacific madrone are found in recently disturbed areas along road 

cuts or on bare mineral soil at the base of uprooted trees. Occasionally, they 

become established beneath woody shrubs or small trees in clearcuttings where 

shade is plentiful (McDonald and Tappeiner 1990). Partially cut areas that have 

been burned or bulldozed often provide the necessary shade and loose bare soil 

needed by Pacific madrone seedlings. Black oak and tanoak seedlings become 

established in this environment as well. In general, seedlings of all three species 

tend to have a clumpy distribution over the landscape resulting from gaps 

brought about by disturbance. 

On the Challenge Experimental Forest in northern California, natural 

regeneration of hardwoods was evaluated from 1958 to 1968 in 15 

compartments that were cut to shelterwood, seed-tree, and single-tree selection 

standards. Compartment size ranged from 6 to 38 acres. Soil disturbance, 

created by site preparation, ranged from heavy to slight. Although conifers 

predominated, 3 to 17 relatively small trees (less than 12 inches in breast-height 

diameter) of each hardwood species on each acre, were present. Seeds from 

these hardwoods, plus that disseminated by birds and rodents from other 

hardwood trees, comprised the seed source. The number of new California 

black oak seedlings ranged from 0 to 700 per acre per year during the 11-year 

period. In many cutting methods and for several years, seedlings were not 

found. Survival after 4 years ranged from 15 to 44 percent with the highest 

occurring in the single-tree selection compartments and the lowest in the seedtree compartments (McDonald 1978). In these same blocks and for the same 

time span, the number of new tanoak seedlings ranged from 4 to 347 per acre 

each year in every cutting method. Survival after 4 years did not differ among 

cutting methods and averaged about 50 percent. 

For Pacific madrone, new seedlings in these compartments and for roughly 

the same time span, except for 1961, numbered 0 to 550 per acre per year with 

many absences in years and cutting methods. Only a few seedlings became 

established. One huge seed crop in 1960 resulted in 4,083 new seedlings per 

acre in the shelterwood compartments, 3,917 per acre in the seed-tree areas, 

and 866 per acre in the single-tree selection compartments in 1961. Survival 

after 4 years ranged from 41 percent in the seed-tree and shelterwood cuttings 

to 3 percent in the single-tree selection compartments. 

To augment these results, natural regeneration of the three hardwood 

species in this study was evaluated in a pure hardwood stand on the 

Challenge Experimental Forest. The stand was characterized by being 

undisturbed, having 3 to 4 inches of organic matter on the forest floor, and 

containing a good seed source for each species. The number of California 

black oak seedlings numbered 40 per acre; tanoak, 4,600; and Pacific 

madrone, 0 seedlings per acre (McDonald 1978). 

Height growth of natural seedlings of all three species is slow. Except 

where deep shade forces a long skinny stem, shoot growth probably does not 

begin to accelerate until root capacity is extensive enough to obtain adequate 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 15 
moisture. This may take 6 or 7 years or longer. After initial shoot growth (2 to 6 

inches for black oak, 2 to 8 inches for tanoak, and 1 to 2 inches for madrone), 

seedling growth is variable, but seldom exceeds 8 inches per year. Partial shade 

is the environment most conducive to growth. Growth of some seedlings, 

particularly those stressed by competition, never accelerates and these seedlings 

eventually die. 

Seedling-sprouts 

The strategy of becoming a seedling-sprout is to keep the species present until a 

better environment for growth occurs. An individual seedling may die back 

several times and produce one to seven new stems with the largest stem being 

the oldest. On the basis of scores of samples, Tappeiner and McDonald (1984) 

found no reliable relationship between the age and size of the above-ground 

stem and the total age of tanoak seedling-sprouts. However, the total age of 

seedling-sprouts can be ascertained quite accurately by counting the xylem 

rings in the stem below the burl. 

Seedling-sprouts may persist for scores of years until fire or logging 

removes the overstory—freeing them to grow. California black oak, tanoak, 

and Pacific madrone all have seedling-sprout capability, but the use of this 

ability differs among species and between sun and shade environments. In 

order to sprout, dormant buds must be present, and to be present, a structure is 

necessary. This structure is the burl, which takes the form of a thickened 

rootstock in young seedling-sprouts, and becomes present just below 

groundline at a young age. In tanoak for example, seedlings that had emerged 

only 7 days before a heavy frost died back to groundline and sprouted with 

three to seven members per seedling (McDonald 1978). Two months later, 80 

percent of frozen seedlings had become seedling-sprouts. None sprouted with 

a single stem. The conversion from seedlings to seedling-sprouts generally is a 

slow, steady process except when a fire or climatic event causes a pulse of them 

to occur. The build-up of seedling-sprouts, usually in the shade of the overstory, 

is the classic seedling-bank reproductive strategy (Grime 1979). 

Because at least some food reserves are stored in the burl, seedling-sprouts 

have a better-than-average chance of outgrowing competing vegetation. They 

also can become saplings and eventually trees. In western Oregon, Fried and 

others (1988) studied the density and growth of bigleaf maple (Acer 

macrophyllum Pursh) seedlings in a range of ages and overstory canopy classes. 

The seedlings of this maple are similar to those of tanoak, which are found in 

aggregations, and form seedling banks. A major finding was that the maple 

seedlings eventually became trees, especially when the canopy was more open. 

Of the three forest zone hardwoods in this paper, California black oak is 

intermediate in terms of frequency of becoming a seedling-sprout. A 

rudimentary burl develops on young seedlings, but precisely at what age is 

unknown. Observation suggests that it forms earlier and more frequently on 

poor sites and in shady environments. It is not nearly as likely to become a 

seedling-sprout in a sun environment as in a shade environment. In either 

environment, however, when it sprouts or resprouts, it almost always is 

with only one stem. In the shade environment, growth is very slow (fig. 7), 

and 30- to 50-year-old seedling-sprouts may be only 2 to 12 inches tall. Their 

tenacity for life, however, is strong. Repeated regeneration surveys on 

permanent plots with marked seedlings showed that a few black oak 

seedling-sprouts in deep shade would die back to the root crown; put forth 

a shoot in some years, but not in others; and still be alive after 10 years of 

examination. As early as 1912, Lyons described the seedlings as being 

“persistent,” (p. 2), especially after burning. 

California black oak seedling-sprouts in the three conifer cutting methods 

on the Challenge Experimental Forest ranged from 342 to 910 per acre and 

16 USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 
Figure 7—Above- and belowground development of California 

black oak seedling-sprouts in deep 

shade. Height of tallest seedlingsprout is about 1 foot.

Number per acre 

Figure 8—Increase and decline of 

California black oak seedling-sprouts 900

� � �

�

� �

�

�

� � � �

�

�

� � � �

�

�

�

� in three silvicultural regeneration 

cutting methods, Challenge 

Experimental Forest, 1959-1966. 

600

300

0

1958 1960 1962 1964 1966

Year 

Seed Tree 

Single Tree Selection 

� Shelterwood

�

�

Figure 9—Density and development of California black oak seedlingsprouts in a small opening with partial 

shade, Challenge Experimental 

Forest, California. 

indicated a pattern of both mortality and recruitment (fig. 8) (McDonald 1978). 

These data and observations elsewhere suggest that a slow but steady buildup 

of seedling-sprouts takes place. Height growth and form tend to be best in 

small openings in partial shade, particularly if density is high and the seedlingsprouts have to grow straight and tall to keep their tops in sunlight (fig. 9). The 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 17 
Figure 10—Average height 

development of California black oak 

seedling-sprouts in small openings 

in a shelterwood, Challenge Experimental Forest, California. 

6 

5 

4 

3 

2 

1 

0 

0 2 4 6 8 10 12 14 

Age (years) 

average height of black oak seedling-sprouts in openings among shelterwood 

trees was 5 feet in 13 years (fig. 10). 

As noted earlier, the distribution of California black oak seedlings often is 

dense beneath the crown of large trees and widely scattered elsewhere. 

Consequently, when the large trees die, the typical distribution is clumpy with 

most of the seedlings and seedling-sprouts present in small openings. If the 

trees are numerous and good acorn producers, the number of seedlings can be 

large over a much larger area. The number of seedling-sprouts can be large as 

well, particularly if a disturbance impacts the area. This happened in Placer 

County, California, on about 52 acres of a productive site covered with large 

California black oaks and ponderosa pines (Garrison and others 1998a). The 

pines were harvested and the slash scattered and broadcast burned in 1985. 

This combination killed the black oak seedlings to groundline and provided a 

partial-shade environment. In 1994 to 1995, the number of seedling-sprouts 

numbered 23,769 per acre (Garrison and others 1998a). In 1999, they were 1.5 to 

6.0 feet tall (Garrison 1999). The new stand is not stagnating, and some stems 

are beginning to dominate. Although atypical in size of area and density of 

seedling-sprouts, these data show the potential reproductive capability of black 

oak seedling-sprouts under ideal conditions. In nearby compartments of equal 

size, black oak seedling-sprouts ranged from 4,506 to 5,828 per acre. Angress 

(1985) noted that more than 70 percent of black oak seedlings in an underburn 

in Yosemite National Park had resprouted 5 months later. 

Of the three forest-zone hardwoods in this paper, tanoak has the greatest 

tendency to become a seedling-sprout. The burl on tanoak seedlings develops 

slowly and is strongly related to age and site quality (Tappeiner and McDonald 

1984). It is just as likely to produce sprouts in a sun environment as in a shade 

environment; however, the number of stems tends to be less in shade (fig. 11). 

Barring injury, each natural tanoak seedling consists of a single stem for the 

first 5 to 12 years. After that, dieback occurs not only for the obvious reasons of 

frost, drought, or browsing, but also for unknown reasons. Perhaps, the need 

for shade is a factor, and the outer stems of clumps provide shade to the inner 

stems and leaves. At any rate, the stems die back to the burl at least three to five 

times by age 60. Growth is slow and tanoak seedling-sprouts may be only 2.7 to 

5.3 feet tall after 50 years. 

In southwest Oregon, tanoak seedling-sprouts were studied beneath old 

(135-250 years) and young (50-75 years) conifer and hardwood stands, and the 

density-age-height relationship determined (Tappeiner and McDonald 1984). 

Together, these data portray the density and growth dynamics of young tanoaks 

over time in the understory (fig. 12). Height (feet) 

18 USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 
Figure 11—Root-shoot development of young tanoak seedlingsprouts in deep shade. Height of tallest 

seedling-sprout is about 4 inches. 

Figure 12—Density-age-height 

relationships of tanoak seedlingsprouts in two representative old and 

two representative young stands in 

southwest Oregon. Vertical bars are 

standard errors; numbers above bars 

are the average ages in each height 

class; numbers in parentheses are the 

ages of the oldest small tanoak. 

Under ideal conditions, the number of seedling-sprouts can be enormous. 

One almost pure tanoak stand on the Challenge Experimental Forest was 

thinned from 231 ft2 per acre to 153 ft2 per acre in 1972, and the trees responded 

by producing acorns almost every year. This led to new seedlings being 

produced almost every year as well. In spite of the thinning, the environment 

was still shady with 3 to 4 inches of organic matter on the soil surface. Annual 

observations showed that the seedlings would become seedling-sprouts 

sometime in the next 4 years for no apparent reason. By spring 1989, young 

tanoaks averaged 95,000 per acre, most of which were seedling-sprouts. The 

tallest was 30 inches and most had two stems per clump. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 19 
Tanoak seedling-sprouts in the three conifer cutting methods on the 

Challenge Experimental Forest ranged from 267 to 822 per acre with both 

mortality and recruitment taking place (fig. 13) (McDonald 1978). In the pure, 

but dense and shady hardwood stand, tanoaks numbered 5,680 per acre. 

Overall, their pattern was one of increasing numbers. Height growth and form 

were best in small openings under tree crowns having flecks of sunlight. An 

average seedling-sprout at age 10 would have a 0.5-inch diameter burl, four 

sprouts, and a height of 20 inches. By age 40, the burl will have at least doubled 

in size, the number of sprouts will be slightly larger or the same, and their 

height will have doubled. 

Compared to California black oak and tanoak, Pacific madrone ranks last 

in terms of tendency to become a seedling-sprout. A burl develops on young 

seedlings, but precisely at what age is unknown. Madrone rarely becomes a 

seedling-sprout in a shade environment, but if it does, only one stem usually 

results (fig. 14). In a sun environment, multiple stems are common. Injury is 

usually the only reason for sprouting in the shade environment, but injury, 

drought, too much sunlight, and other reasons can result in dieback and 

sprouting in sunny locations. Growth of the few seedling-sprouts in the shade 

environment is unknown, but probably better than that of the seedlings. Growth 

of madrone seedling-sprouts in the sun environment is variable and depends 

on intra-clump shading and the amount of dieback. 

Figure 13—Pattern of tanoak


seedling-sprout accumulation by 900/ cutting method, Challenge


�

� � �

�

�

�

� �

�

� �

� � �

�

�

�

�

Experimental Forest, 1959-1966. 

Number per acre 

600 

300 

0 

1958 1960 1962 1964 1966 

Year 

Seed Tree 

Single Tree Selection 

� Shelterwood

�

�

Figure 14—Root-shoot development of young Pacific madrone 

seedling-sprouts in deep shade. Height 

of tallest seedling-sprout is about 4 

inches. 

20 USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 
The largest number of madrone seedling-sprouts in the conifer cutting 

methods on the Challenge Experimental Forest were found in those that were 

the most disturbed—seed-tree and shelterwood (fig. 15) (McDonald 1978). 

Slightly more madrones were present in the seed-tree method but fewer died in 

the shelterwood. In the pure hardwood stand on the Forest, about 80 seedlingsprouts per acre were present. These relationships reflect the mineral soil and 

partial shade requirements of the species. 

Artificial Regeneration 

In this paper, seedlings from two artificial regeneration techniques are reported: 

direct seeding and the outplanting of containerized seedlings. Both techniques 

were applied on the Challenge Experimental Forest and elsewhere. Specific 

information on the plantation site, germination, emergence, and early survival 

(first 2 years) for California black oak, tanoak, and Pacific madrone were 

presented in the section on direct seeding. Material in this section covers the 

response of the hardwood seedlings to the plantation environment, generally 

through ages 3 to 10. 

For the direct seeding trial in the 1966 black oak plantation on the 

Challenge Experimental Forest, seedling survival after one growing season 

was 70 percent. Another hard freeze in 1968, deer browsing in 1970, drought 

in 1971, pocket gophers in 1973, and drought again in 1974 either damaged 

or killed seedlings. After the tenth growing season in 1975, survival was 54 

� �

� � � �

�

�

�

� � � �

� � � �

� �

�

Figure 15—Cumulative density of 

Pacific madrone seedling-sprouts by 

cutting method, Challenge 

2,000 Experimental Forest, 1959-1966.

Number per acre 

1,500 

1,000 

500 

0 

1958 1960 1962 1964 1966 

Year 

Seed Tree 

Single Tree Selection 

� Shelterwood

�

�

USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 21 
percent. Average height was 1.1 feet with a standard deviation of 1.0 foot 

and a range of 0.1 to 7.0 feet (McDonald 1978). Technically, many seedlings 

had become seedling-sprouts. 

For the 1969 black oak plantation, survival after two growing seasons was 

67 percent. Interplanting of acorns in unstocked spots took place in 1971 and 

increased total stocking to 82 percent at years end. By 1975, stocking had fallen 

to 64 percent; 44 percent in 1976. Drought and pocket gophers were the primary 

causes of mortality. In 1978 or after 10 growing seasons, stocking was 41 

percent. Average height after 3 growing seasons was 0.4 foot; after 7 seasons, 

0.7 foot; and after 10 seasons, 3.8 feet (fig. 16). 

Because seedling height growth was slow, a fertilizer trial with 16-20-0 (16 

percent nitrogen, 9 percent phosphorous, 0 percent potassium) was installed in 

February 1970 with 100 seed spots in two blocks of the plantation. Every other 

row was fertilized and compared to counterparts in alternate rows. A handful 

of fertilizer was placed about 4 inches above each seedling with the intent that 

rainfall would put it in the rooting zone when growth began. 

Fertilizer stimulated height growth of California black oak seedlings from 

the beginning (fig. 17). After five growing seasons, fertilized seedlings were 

more than three times taller than unfertilized seedlings. Stems of fertilized 

seedlings were more robust and thick, leaves were more numerous and larger, 

and leaf color was darker than for unfertilized plants. The amount of minerals 

Figure 16—At 1.2 feet, this 3-yearold, artificially seeded California black 

oak seedling is three times taller than 

average, Challenge Experimental 

Forest, California. 

3.0 

Figure 17—Height development of 

artificially seeded California black oak 2.5 seedlings with and without fertilizer, 

Challenge Experimental Forest, 

California. 2.0 

1.5 

1.0

0.5 

0 

0 1 2 3 4 5 

Fertilized 

Unfertilized 

Seed Height (feet) 

Growing Season 

22 USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 
in the leaves of fertilized and unfertilized seedlings was determined by foliar 

analysis in the laboratory in late June 1970. Analysis of variance indicated that 

nitrogen and phosphorous were significantly higher (p = 0.05) in fertilized 

seedlings (table 2). 

Because both foliar analysis and actual stem measurements indicated 

significant gains, fertilizer was applied to each spot in the entire plantation 

from 1976 through 1978, using the same fertilizer, amount, and technique of 

the first trial. The 10th-year survey in 1978 provided a perplexing observation: 

only 50 percent of black oak seedlings had responded to fertilization. 

Internal moisture stress (xylem sap tension) of black oak seedlings was 

evaluated to help explain the poor growth rates noted earlier. Twigs from five 

typical seedlings were placed in a pressure chamber using the technique 

prescribed by Scholander and others (1965). The sampling date was a clear, hot 

day in early September 1975. At this time of year, the seedlings were under 

maximum physiological stress because of high moisture deficits. For fertilized 

seedlings, the mean predawn xylem sap tension was -0.7 MPa (megapascals) 

(range of -0.45 to -0.8 MPa); for unfertilized seedlings it was much higher 

(mean of -1.l MPa, range of -0.6 to -1.8 MPa) (McDonald 1978). This relationship 

indicated that fertilized seedlings had a lower level of internal moisture stress 

and that the root system of fertilized seedlings probably was better developed 

and hence better able to capture scarce soil moisture. 

In the large field trial of tanoak at the Challenge Experimental Forest with 

point-up and point-down acorns, seedling survival after two growing seasons 

(1971) was 21 percent (McDonald 1978). Because this was unsatisfactory, all 

blank spots were again seeded in early 1972. The soil was loosened and the 

acorns placed point up and point down as before, and just as before, the early 

emergers were killed to groundline by frost and sprouted with multiple stems. 

Seedlings from this interplanting did not survive much better than earlier 

counterparts. However, they did increase the stocking of the tanoak plantation 

to 66 percent. In subsequent summers, drought and dieback were rampant. 

Seedlings would repeatedly die back and resprout and eventually die. After 

six growing seasons (1975), stocking was 33 percent. Mean height of tanoak 

seedlings was 1.1 feet in the range of 0.2 to 10.2 feet. After another interplanting 

in spring 1976, overall survival at the end of the study in 1979 was 41 percent. 

Many, but not all, seedlings had multiple stems, and average height had 

scarcely changed from the 1975 values. 

Because tanoak survival and height growth were poor, fertilizer and water 

were applied in each of 4 years (1972 to 1975) in an effort to increase 

establishment (McDonald 1978). The same fertilizer (16-20-0) and application 

technique as in the black oak plantation was used. A generous handful of 

fertilizer was placed just above selected seedlings in February of each year. 

Table 2—Mean foliar nutrient concentrations of fertilized and unfertilized California black oak 

seedlings, Challenge Experimental Forest, 1970. 

Nutrient Fertilizer No fertilizer 

------ percent of foliar dry weight -------

Nitrogen 2.59 a1 2.26 b 

Phosphorous 0.20 a 0.14 b 

Potassium 0.46 a 0.58 a 

Calcium 0.53 a 0.58 a 

Magnesium 0.18 a 0.18 

1For each nutrient, dry weight percentages in each row followed by the same letter do not 

differstatistically at the 0.05 level. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 23 
-----------------------------------------

Table 3—Average tanoak seedling height with and without fertilizer and water, Challenge Experimental Forest, 1970. 

Year Fertilizer and water Water Fertilizer Control 

----------------------------------------------- ft 

1972 0.49 a1 0.43 a 0.43 a 0.34 a 

1974 1.15 a 0.78 ab 0.90 ab 0.65 b 

1975 1.68 a 1.05 b 0.93 b 0.75 c 

1For each year, mean height in each row followed by the same letter does not differ statistically at 

the 0.05 level. 

Irrigation amounted to about one-half gallon of water per spot from a hose. It 

collected in a shallow earthen basin constructed around each seedling. 

Irrigation began about mid-June each year and took place at about 2-week 

intervals. Sampling intensity was 808 randomly selected seed spots, with 

approximately equal representation of original and interplanted seedlings and 

plants from point-up and point-down acorns. 

The effect of fertilizer and water on tanoak seedling height first showed up 

in 1974 and was more pronounced in 1975. Analysis of variance and a Tukey 

test showed significantly better height growth for each treatment relative to 

the control, and especially from fertilizer and water combined (table 3). Water 

apparently was an aid in getting the fertilizer into solution and making it 

available to tanoak seedling roots. The amount of minerals in the leaves of 

seedlings in the various treatments was determined by foliar analysis in the 

laboratory in late June 1975. The higher amounts of nitrogen and phosphorous 

in the leaves of watered and fertilized plants conformed with the height 

relationships of the measured seedlings. 

Internal moisture stress (xylem sap tension) of tanoak seedlings was 

evaluated to help explain the poor survival and growth rates noted earlier. As 

for California black oak, twigs from five typical seedlings were placed in a 

pressure chamber (Scholander and others 1965) on a clear, hot day in early 

September 1975. Seedlings had not received any water for 15 days and the soil 

around them was as dry as that elsewhere. 

Average predawn minimum moisture stress of the tanoak seedlings by 

treatment was: 

Treatment Stress (MPa) 

Fertilizer and water -0.50 

Water -0.49 

Fertilizer -0.68 

Control -0.62 

This relationship showed that the tanoak seedlings were able to recharge 

their systems over night and that internal moisture stress was less in seedlings 

that had been receiving water for three consecutive summers (implying a 

better developed root system). In a complementary study, moisture stress of 

24 USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 
two 6-year-old seedlings was monitored continuously for 24 hours to determine 

the diurnal trend in moisture stress. Average values during the day were: 

Pacific Standard Time MPa 

4 a.m. -0.4 

6 a.m. -0.8 

8 a.m. -1.5 

10 a.m. -1.8 

1 p.m. -2.3 

4 p.m. -2.2 

6 p.m. -1.3 

Internal moisture stress in one of the seedlings reached -0.2 MPa at 

midnight. This value is similar to that of trees with roots in running water and 

again shows tanoak’s capability to recharge its system. These data also show 

that internal moisture stress increased rapidly after first light in the morning, 

leveled off about 8 a.m., peaked at 1 p.m., and then rapidly declined. 

Additional moisture stress values were determined for six very young (6-

month-old) seedlings in the plantation area. These were so small that they had 

no branches (twigs) and the entire seedling had to be inserted in the pressure 

chamber. Two seedlings reached -2.0 MPa at first light in the morning, but 

before sunrise. An obviously stressed seedling in full sunlight with dead and 

partially dead leaves had a value of -3.4 MPa at 11:40 in the morning. Another 

robust-looking seeding in full sunlight endured a stress of -3.5 MPa in late 

afternoon. Two other seedlings that had been in full sunlight most of the day 

but were in shade at 6:10 p.m. indicated a stress of -2.2 MPa. 

Together, the internal moisture stress data suggest the reason for the death 

and dieback of the tanoak seedlings. At the first hint of light in the morning, the 

stomates in the leaves open widely and transpiration rapidly drains moisture 

from the plant’s system. Transpiration apparently exceeds the daylight recharge 

capability and the plant eventually dies. Efficient recharge ability at night only 

prolongs the process. 

Because too much light, too much heat, and too much transpiration could 

be mitigated by shade, 175 tanoak acorns with newly-emerged radicles were 

seeded point up in early March in another trial on the Challenge Experimental 

Forest (McDonald 1978). Some seedlings also were irrigated and fertilized as in 

earlier trials. Large wooden shingles were placed southwest of each seedling 

shortly after emergence. Although first-season mortality was slightly lower 

than for unshaded seedlings nearby, second-season survival was no better, and 

the trial was abandoned. Time and again, the tanoak seedlings would grow tall 

and skinny behind the shingle, lean away from it out into the sunlight, promptly 

die back, and eventually die. 

In the extensive direct seeding study with tanoak and Pacific madrone in 

southwestern Oregon (Tappeiner and others 1986), the height of tanoak 

seedlings ranged from 2 to 5 inches and for madrone from 1 to 2 inches after 

three growing seasons. 

Some seedlings were raised in containers in the greenhouse and then 

outplanted in prepared areas on the Challenge Experimental Forest (McDonald 

1978). For all three species, the plantation environment was essentially bare 

mineral soil in full sunlight. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 25 
One-hundred California black oak seedlings were grown in 6-inch deep 

containers filled with potting soil in a greenhouse, transferred to a lathhouse to 

harden off, and outplanted on the Challenge Experimental Forest in midMarch. Seedlings had been watered and fertilized and were robust with short, 

thick stems and root systems that extended beyond the containers. The roots 

were pruned just before outplanting. The soil at each planting spot had been 

loosened to about 12 inches with hand tools. Survival after one growing season 

was 66 percent. However, subsequent surveys indicated that survival was no 

better than that from direct-seeded acorns, and the effort was discontinued. 

The growing and outplanting procedures for tanoak were similar to those 

used for black oak, except that the containers were 8-inch deep, half-gallon 

milk cartons. The bottom of each carton was removed just before outplanting. 

And similar to black oak, the root:shoot ratio after pruning was 2 to 1. After one 

growing season, survival was 81 percent, but after two seasons survival had 

fallen to 46 percent. Height growth after outplanting was essentially nil. 

Examination of dead tanoaks showed that the seedling roots had grown 

through the loosened soil, but no farther. Root elongation was inadequate and 

the seedlings died from drought. 

One-year-old Pacific madrone seedlings in 13 half-gallon milk cartons were 

outplanted as plugs (bottom of carton removed), one to a spot. After three 

growing seasons, only 6 of the 13 spots had a living madrone seedling. Dieback, 

sprouting, poor form, and death were common. Plainly, the environment was 

too bright and too hot. After six growing seasons, five spots contained seedlings. 

Average height was 4.5 feet, and stems were crooked and forked. 

Additional trials of containerized hardwood seedlings, other than on 

the Challenge Experimental Forest, took place in California and Washington. 

Some trials were with stock grown in commercial nurseries and some took 

place in small greenhouses on National Forest land. Most involved starting 

the seedlings in the nursery and then transplanting them to the field as 

container seedlings or plugs. 

An intensive trial with California black oak seedlings took place in 1989 in 

Yosemite National Park, California, under an open overstory of mature trees. 

Five-hundred 2-year-old seedlings, grown from local acorns, were transplanted 

into D-pots (4 x 4 x 12 inches) and then into pre-drilled holes (Fritzke 1997). The 

holes were lined with steel mesh bottomless cylinders to protect the roots 

from rodents. Solid and open-mesh tree shelters were installed to protect 

seedlings from browsing. A time-release fertilizer tablet was dropped into 

half of the holes. After seven growing seasons, survival was 22 percent with 

mortality from drought and other causes. Average survival and height of 

fertilized seedlings was somewhat better than unfertilized seedlings, but 

not significantly. Average height of seedlings in solid plastic tree shelters 

(23 inches) was significantly better than for those in open mesh shelters (15 

inches); however, an average difference of only 8 inches may not be 

practicably important. 

McCreary (2001) also grew black oak seedlings in tree shelters at the 

Sierra Field Station in Yuba County, California, and found that they did not 

promote accelerated height growth. Furthermore, he noted: “it is unclear 

why this oak species seems to initially grow so slowly, both with and 

without treeshelters” (p. 49). 

Several regeneration trials with California black oak from both commercial 

and USDA Forest Service stock have been installed in southern California 

National Forests. Various combinations of germinated and nongerminated 

acorns, 12- to 18-inch open bottom pots, irrigation, fertilizer, and screens made 

of various materials were evaluated (Anonymous 1980, Blankenbaker 1986, 

Roberts and Smith 1982). The screens extended about 12 inches belowground 

26 USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 
and up to 36 inches aboveground. Values of 59 and 82 percent survival after 1 

year, and 40 percent after 9 years were recorded. Pocket gophers, drought, and 

browsing were the principal causes of mortality. The 9-year old seedlings 

averaged 3 to 4 feet in height. 

Artificial regeneration of Pacific madrone is difficult because the seeds are 

so small and the fate of the seedlings so uncertain, that scores, if not hundreds 

of seeds, are often used per container. Excess seedlings, if present, need to be 

removed. To lessen this burden, a trial with germinated seeds was performed 

in the laboratory. The goal was to have one virtually assured seedling per 

container. Stratified seeds were placed on a moist medium in petri dishes and, 

after a tiny white radicle was visible, were carefully placed in containers at a 

depth of 1/8 inch. Damping-off fungi ruined the experiment, but the technique 

showed promise.1 

In the Puget Sound area of coastal western Washington, Gonzalez (1999) 

grew 250 to 400 containerized Pacific madrone seedlings by using 

“standardized nursery practices.” He stressed the importance of placing the 

seedlings into containers at a very young age so that further transplanting 

maintained the fine root system. Winters and Hummel (1999) noted that 

nurseries did not grow many madrone seedlings because of “transplant 

failure.” To combat this lack, they transplanted madrone seedlings into three 

successively larger containers in the nursery, provided optimum levels of 

moisture and nutrients, and then transplanted them into the landscape. After 

one growing season, survival was high and some trees were about 3-feet tall. 

Unfortunately, a hard December freeze killed almost all the seedlings and 

terminated the study. Shoffner (1999) grew 168 madrone seedlings with seed 

from a single tree and outplanted them in sun and partial shade environments. 

After 1 year, he found that plants grown in full sunlight with weekly irrigation 

accumulated the most biomass and maintained the highest rate of 

photosynthesis despite moderate water stress. 

Provenance Trial 

Because early emergence was critical for California black oak seedling survival 

and point-up acorns resulted in early emergence, this technique seemed 

promising. However, late spring frosts consistently damaged seedlings. If 

seedlings could be found that withstood frost damage either directly or 

indirectly by emerging later, but with more rapid early height growth, the 

problem could be circumvented. Consequently, seed from eight sources that 

ranged from 3,200 to 5,625 feet were tested. Two of these locations were not 

only higher but drier, and the possibility existed that such seedlings would be 

more drought resistant than seedlings from the Challenge Experimental Forest. 

Acorns from each location were gathered, stored, and outplanted on 

prepared ground free of competing vegetation on the Challenge Experimental 

Forest as in previous studies (McDonald 1978). Survival, height and diameter 

growth, leaf-flush, and leaf-fall data were sampled both annually and 

periodically for seven growing seasons. Leaf-flush data were evaluated in five 

categories and leaf-fall data were differentiated by six different colors. The 

results were disappointing. Little difference among provenances and high 

variation within each provenance characterized all measured variables. 

However, some worthwhile adjunct information was gathered during the 

eighth growing season. About 82 percent of all seedlings began to elongate in 

height on April 26 with diameter growth beginning 7 to 21 days later. Diameter 

and height growth ceased after 43 days. Taller seedlings grew for a longer time 

span than shorter seedlings, but did not grow as fast. Thus, average height was 

the same at the end of the season. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 27 
Root-cr

own Sprouts 

The three forest-zone hardwoods in this paper produce both sprouts and seed. 

Obviously, species that have both reproductive modes have an advantage over 

those that have only one. When the above-ground portion of the tree is killed by 

fire or the tree is cut in logging, these species sprout from the burl, or root crown 

as it often is called. The root-crown sprouts are often thought of as being “instant 

reproduction” because of their abundance and rapid growth. Continuous 

vegetative reproduction may have a long-term disadvantage—the species may 

eventually become out-of-tune with the ever-changing environment and decline. 

Reproduction with seedlings, via the sexual process, helps the species adapt to 

the environment. 

Dormant buds are almost always present on the root crown of the tree, 

which is located at or just below groundline. When the top of the tree is alive, 

they are kept dormant by hormones produced in buds in the uppermost 

whorls. After the top is cut or killed, the hormones disappear, and the dormant 

buds become free to produce sprouts. Not all buds sprout in a given 

disturbance, however, and many are kept in reserve. Each sprouting bud has a 

direct vascular connection to a piece of the parent tree root system and a vast 

amount of resources are available to the sprout. A few quickly dominate and 

rapid growth is the result. Then, like the parent tree, hormones develop in the 

top of the dominant sprouts and inhibit the sprouting of dormant buds on the 

burl. This inhibition is effective for California black oak and Pacific madrone 

and sprouting occurs only in the first year after cutting. The inhibition is not as 

restrictive for tanoak, and new sprouts are formed for up to 3 years after the 

tree is killed aboveground. 

Root-crown sprouts are the primary reproductive mode of the forestzone hardwoods in this paper. The attributes of being both numerous and 

fast-growing allows them to outgrow most competing species and, if the 

disturbed area is small, to be in position to receive sunlight before the 

canopy closes. 

After cutting, burning, or other damage, sprouting is assured except for 

very old, moribund trees whose buds are occluded by thick bark. In fact, it is 

almost impossible to keep stumps of these hardwood species from sprouting. 

After the tree is killed aboveground, the number of sprouts in the initial flush 

varies tremendously, ranging from as high as 1,400 on one large tanoak stump 

(Tappeiner and others 1990) to more than 300 on one 10-inch Pacific madrone 

stump (McDonald and Tappeiner 1990). Other sprouts originate from the top of 

the stump or on the vertical part of the stump between the top and the ground. 

These are called stool sprouts and are undesirable for several reasons. They are 

weakly attached to the stump, are peeled off by wind and snow, and are prone 

to heart rot at an early age. Leaving a low stump less than 8 inches tall promotes 

numerous, healthy, rot-free sprouts. 

The size and vigor of the parent tree largely determines the number of 

sprouts and their height and crown spread (McDonald 1978, Roy 1955, 

Tappeiner and others 1990). In general, stumps from larger trees produce a 

larger number of sprouts and more vigorous ones. This proved true in both the 

northern Sierra Nevada and in southwest Oregon. In a clearcutting in the 

northern Sierra Nevada, number of California black oak sprouts and the width 

of their crowns were statistically correlated to stump diameter at sprout ages 4 

and 10 (McDonald 1978). For tanoak and Pacific madrone in southwest Oregon, 

sprout height, clump width, clump area, leaf area, total aboveground biomass, 

and number of stems per clump 1 to 16 years after cutting, were statistically 

correlated with parent tree diameter at breast height before cutting or burning 

(Harrington and others 1984, 1991, 1992, Tappeiner and others 1984). For 

example, tanoak and Pacific madrone trees whose parent stems were 8.7 inches 

in diameter were predicted to have sprout clumps 217 inches wide and 236 

28 USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 
inches tall 16 years after cutting; trees with 4-inch parent diameters would 

produce clumps about 158 inches wide and 177 inches tall over the same period 

(Harrington and others 1992). Thus, sprout clump size and total cover of sprout 

clumps can be predicted on a per-acre basis and used to estimate competition, 

biomass, and other useful determinations. 

Season of cutting and amount of shade can also affect the number of rootcrown sprouts. In southeastern Mendocino County, in the inner Coast Range of 

California, Longhurst (1956) cut five black oaks each month from December 

through November. For those cut in the December through May period, 92 

percent sprouted; for those cut in the June through November period, only 45 

percent sprouted. In a similar environment in Trinity County California, 

Wilkinson and others (1997) noted that sprouts from tanoak clumps in deep 

shade were about one-fourth as tall as those reported for a sunlit environment 

in southwest Oregon and northern California. Furthermore, sprouting in deep 

shade was delayed for several months after cutting of the parent tree, probably 

because the hormonal and metabolic processes in the stump were not 

sufficiently stimulated to produce sprouts. Light, of course, is a strong 

stimulant. Many sprouts were negatively impacted by mold and browsing by 

deer. In shade, the sprouts grow more slowly and have greener, more palatable 

leaves longer than counterparts in the sun. Mold rarely, if ever, occurs on sun 

sprouts, but is fairly common on those in the shade. Both factors decrease 

sprout height. 

Smith (1962) noted that “vegetative reproduction obtained after clearcutting 

is usually superior to that resulting from partial cutting.” In a study on the 

Challenge Experimental Forest with California black oak, tanoak, and Pacific 

madrone, sprout clump dynamics were quantified in both a clearcutting and in 

a hardwood shelterwood where 50 percent of the stand basal area was removed 

(McDonald 1978). Diameters ranged from 6 to 17 inches at breast height. For all 

three species, more sprouts per stump were found in the clearcutting (table 4). 

Even shade-tolerant tanoak grew best in the clearcutting, probably because no 

roots of parent trees were utilizing site resources, particularly water. After 10 

years, sprout clumps of California black oak and tanoak in the clearcutting 

averaged 20 feet tall and about 10 feet wide (table 5). Clumps of Pacific madrone 

Table 4—Number of sprouts per stump at various years after cutting for California black oak, tanoak, and 

Pacific madrone, Challenge Experimental Forest, California. 

California black oak Tanoak Pacific madrone 

Year clearcut shelterwood clearcut shelterwood clearcut shelterwood 

(29)1 (20) —2 (7) (6) (5) 

0 63 28 — 28 100 60 

2 50 23 — 31 85 30 

4 35 17 — 34 50 18 

6 23 15 — 33 30 12 

8 18 13 — 26 18 8 

10 15 12 — 24 15 7 

1 Number of stumps. 

2 Too many and too difficult to count. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 29 
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Table 5—Average height and crown width of California black oak, tanoak, and Pacific madrone sprouts at 

various ages after cutting, Challenge Experimental Forest, California. 

California black oak Tanoak Pacific madrone 

Age clearcut shelterwood clearcut shelterwood clearcut shelterwood 

Height 

ft 

4 8 4 8 4 8 5 

6 12 5 12 5 15 7 

8 16 6 15 7 19 8 

10 20 7 19 8 22 9 

Crown width 

ft 

4 6 3 8 3 5 4 

6 8 4 8 3 7 4 

8 9 5 9 5 9 5 

10 10 7 10 7 10 7 

were slightly taller (22 feet) after 10 years, but they also were 10 feet wide. The 

black oak sprouts in the shelterwood averaged as much in width as in height (7 

feet). This was caused in part by a cynipid gall wasp (Callirhytis perdens Kinsey) 

that damaged the terminal shoots of the black oak sprouts in the shelterwood 

(fig. 18), but not of those in the clearcutting. The more shady environment 

typical of the shelterwood apparently was more favorable to the wasp than 

that of the clearcutting. 

Harrington and others (1994) found that 6-year-old tanaok sprouts in 

southwest Oregon were better able to minimize the effect of water stress than 

Pacific madrone sprouts or planted Douglas-fir seedlings. Predawn plant water 

potential throughout the year never fell below about -0.5 MPa (megapascals) 

for tanoak, but it reached -1.2 MPa for Pacific madrone and nearly -2.0 for 

Douglas-fir. Madrone was able to photosynthesize longer than the other species 

when deficits in soil and atmospheric water were high. Both tanoak and Pacific 

madrone were able to photosynthesize in the spring and fall when soil moisture 

was available and the air temperature was warm. They were even able to 

photosynthesize during periods of mild winter temperatures. 

Internal plant moisture stress of 7-year-old root-crown sprouts on the 

Challenge Experimental Forest was determined by pressure chamber for the 

three species, following the sampling procedures described earlier for the 

seedlings (McDonald 1978). Likewise, the date was a clear, hot day early in 

September. Predawn minimum stress varied from -0.5 to -0.8 MPa, and peak 

stress, which took place about 10 a.m., ranged from -2.3 MPa in Pacific madrone 

to -3.0 MPa in tanoak. Immediate ill effects from this stress were not observed. 

In addition, Hanson (1977) studied internal moisture stress of young 

tanoaks—at least 5-years-old—in both a sun and a shade environment on the 

Challenge Experimental Forest. Full grown leaves in the sun were about half as 

long and wide as those in the shade. They averaged almost 346,000 stomata per 

whole leaf in the sun and almost 821,000 stomata in the shade. Having less 

evaporative surface with more stomata per unit area, and fewer total stomata 

than shade leaves could increase heat loss with less evaporative loss and 

enhance survival potential in the sun. This factor and possibly others caused a 

30 USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 
Figure 18—Typical damage to shoots 

of California black oak in partial shade 

by a cynipid gall wasp, northern 

California. 

peak and decline relationship of internal moisture stress during the season for 

plants in both the sun and shade environments, and internal moisture stress 

was actually less during the season in sun plants than for those in shade. One 

would expect internal stress to increase steadily throughout the summer and to 

be greater in sun plants than in shade plants. Apparently, the fail-safe 

mechanism operates seasonally as well as diurinally, and the use of soil 

moisture by roots of overstory trees in the shade increases internal moisture 

stress of seedlings more than does evaporative demand for those in the sun. 

Other investigators have quantified the growth of tanoak and Pacific 

madrone sprouts. In Trinity County California, Roy (1955) measured 50 clumps 

of each species and after the third growing season noted: 

Species Average height Average clump Sprouts per 

of tallest sprout diameter clump 

ft ft number 

Tanoak 6.8 7.0 12 

Madrone 0.1 7.6 13 

Minore (1986) found similar relationships for 4- through 7-year-old 

hardwood clumps in the western Siskiyou Mountains of southwestern Oregon: 

Species Average height Average clump 

of tallest sprout diameter 

ft ft 

Tanoak 5.1 11.5 

Madrone 7.4 15.1 

Additional data on the development of Pacific madrone root-crown sprouts 

was provided by Hughes and others (1990) in the Cascade Mountains of 

southwestern Oregon. Seven years after cutting and burning, dense clumps of 

madrone, spaced 9 feet apart, were about 10 feet tall and had a basal area of 96 

ft2 per acre, 84 percent cover, and an aboveground biomass of 22,500 pounds 

per acre. Clumps at the 18-foot spacing were about the same height with 40 

percent cover, 57 ft2 of basal area, and 14,800 pounds of biomass per acre. There 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 31 
were three to four times more cover of shrubs, forbs, and grasses at the 18-foot 

spacing than at the 9-foot spacing. 

Given that the number of sprouts per clump are numerous and that natural 

thinning is rapid, artificial thinning at an early age seemed a likely technique to 

stimulate growth of selected stems. This was done on the Challenge 

Experimental Forest for California black oak, tanoak, and Pacific madrone, 

always leaving three or four sprouts well distributed around the stump. 

Thinning was performed at ages 1 and 4. Thinning at age 1 was difficult and 

ineffective, and many selected stems were inadvertently removed. Thinning at 

age 4 was much easier because sprouts were more firmly attached, and 

dominant individuals could be identified and saved (McDonald 1978). These 

were quantified for the next 6 years and compared to sprouts in unthinned 

clumps. An advantage in average height, crown width, or crown volume of 

thinned over unthinned sprouts was not found for any species. 

Many observers over scores of years have noted the remarkable lack of 

mortality of clumps of root-crown sprouts from all three hardwood species 

discussed here. Individual stems may die, but the clump lives. For instance, 

mortality was recorded on 1,200 tanoak clumps in southwestern Oregon and 

none had died after 6 years (McDonald and Tappeiner 1987). 

Only one example of the whole clump dying was found. On the Challenge 

Experimental Forest, McDonald and others (1988) sampled 19 tanoak sprout 

clumps that were characterized by chlorotic leaf color, an abnormally large 

number of sprouts, a vastly different height-width relationship than healthy 

sprout clumps nearby, and a peculiar flat top with no exhibition of dominance 

by any sprout. All clumps were from at least two generations of sprouting. No 

pathogens or viruses that could account for the abnormal development were 

found in field or laboratory, and the reason for the decline and eventual death 

is unknown. 

Summary and Recommendations 

Because native hardwoods like California black oak, tanoak, and Pacific 

madrone need to be replaced in many locales in the California landscape, and 

because some managers would like those seedlings and sprouts that are already 

present to grow faster, the need for knowledge on reproductive mechanisms 

and growth potentials is obvious and pressing. The many habitats where these 

hardwoods are present need to be sustained. To be sustained, they need to be 

managed, and to be managed, they need to be propagated. More specifically, 

all three reproductive modes need to be maintained and enhanced. Although 

much remains to be learned, the following recommendations summarize what 

is known about propagating California black oak, tanoak, and Pacific madrone 

in the forest zone of California and southwest Oregon. 

• Because reliable techniques for multiple-year storage of acorns have not 

been determined, short-term, on-site storage in buried wire baskets is 

suggested. This type of storage avoids predation, is in-tune with the 

local environment, ensures a high degree of acorn soundness, and results 

in full or nearly full early stocking of the plantation with seedlings. 

• The typically long, hot, dry summers in California and southwestern 

Oregon make soil moisture the limiting environmental factor for the 

establishment of California black oak, tanoak, and Pacific madrone. This 

has caused them to develop various strategies to enhance early seedling 

development. For example, California black oak and tanoak concentrate 

energy from the acorn into a long, slender, deep-thrusting taproot with 

very little lateral root development. They also tend to delay emergence 

32 USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 
of the epicotyl aboveground until the taproot is extended, and to limit 

first-year shoot growth. 

• Deep, moist duff and litter are ideal for germination and downward 

penetration by the relatively stout taproots of new California black oak 

and tanoak seedlings. Loose mineral soil is equally advantageous. 

However, almost any amount of organic matter on the forest floor is 

deadly to tender madrone stems and roots, and sunlight and frost are 

undesirable, at least in California and southwestern Oregon. Hard, 

compacted soil is anathema for establishment of black oak, tanoak, and 

Pacific madrone seedlings. 

• Natural regeneration of all three species tends to be clumpy and to occur 

in gaps of various sizes brought about by disturbance. For California 

black oak and tanoak, disturbance is not necessary for seedling 

establishment, but is necessary for growth; for Pacific madrone, 

disturbance is necessary for both establishment and growth. The 

environment beneath seed trees is ideal for seedling establishment from 

acorns, but not for seedlings from tiny Pacific madrone seed. 

Consequently, animal disseminators that carry seeds to disturbed 

mineral soil environments are critical for madrone, but less so for the 

other species. Partial cutting and site preparation (broadcast burning, 

bulldozing) that provide mineral soil and shade enhance establishment 

and growth of black oak, tanoak, and madrone. 

• Natural regeneration of California black oak, tanoak, and Pacific 

madrone in an undisturbed setting is characterized more by a slow, 

steady accumulation of seedlings, than by large pulses of them. 

• California black oak, tanoak, and Pacific madrone all have capability to 

convert from seedlings to seedling-sprouts. Shoot dieback is the 

seedling’s way of alleviating environmental stress. Sprouting 

compensates for it. However, even on the best of sites, shoot growth is 

slow and does not increase until root biomass is large enough to capture 

adequate soil moisture. Consequently, the recurrent dieback and 

sprouting of seedling-sprouts probably is an adaptive strategy for 

becoming established in the Mediterranean climate of California. The 

tendency to become a seedling-sprout differs among species and between 

sun and shade environments. Unless damaged, black oak rarely becomes 

a seedling-sprout in the sun and Pacific madrone rarely becomes a 

seedling-sprout in the shade. On the basis of our data and observations 

in California and Oregon, the relationship is: 

Species Environment Number of stems 

California black oak Sun 1 

Shade 1 

Tanoak Sun 3-7 

Shade 1-3 

Pacific madrone Sun 3-5 

Shade 1 

• Seedling-sprouts, which occur irregularly over the landscape, usually 

form small aggregations of high density that are long-lasting and often 

regarded as seedling banks. They are worthy of future management. 

Being established, with root systems in place, is a big advantage. Their 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 33 
low growth rate is a drawback, but it probably can be increased through 

thinning and overstory manipulation. 

• Because seedling-sprouts die back repeatedly and their age may exceed 

50 years before they reach breast height, total age is difficult to determine. 

Conclusions about age-class distribution need to be made cautiously. 

• Similar to conifers, hardwood seedlings in plantations need to be from 

local seed sources, particularly at similar elevations, and to be 

maintained weed-free or nearly so until established. 

• Artificial regeneration of California black oak, tanoak, and Pacific 

madrone is characterized by many trials, but few successes. Almost all 

trials have been installed in conventional sunlit plantations with seed 

from local sources and good control of competing vegetation. The trend 

is for high initial seedling stocking, early mortality, seedling dieback, 

poor overall growth, increasing seedling death, and a failed plantation. 

Few saplings usually result from many seedlings. Consequently, 

silviculturists do not know how to achieve a reliable and consistent 

seedling growth rate, even when fertilizer and water are provided during 

the first few years. 

• Trials with fertilizer and water and concomitant foliar analysis and 

determination of internal moisture stress suggest that inadequate 

internal moisture is the primary reason for the poor growth of California 

black oak and tanoak seedlings. Although fertilizer provided 

significantly better seedling growth than not fertilizing, the magnitude 

of the increase was not enough to enhance the overall growth rate of the 

planted seedlings. Virtually all seedlings of these species are stressed for 

moisture in sunlit plantations. Those that were the most stressed 

apparently could not respond to fertilizer, and those that were less 

stressed could not respond adequately. 

One possibility for enhancing the early growth rate of oak seedlings in 

plantations involves seedling root mass and morphology. It is based on 

northern red oak (Quercus rubra L.), which grows in the northern and central 

United States. On prepared ground free of competing vegetation in a moderate 

shelterwood, 2-0 seedlings with clipped roots and tops and at least a 1/

4-inch 

diameter stem measured 1 inch above the root collar developed well (Johnson 

and others 1986). The tops were clipped 8 inches above the root collar and the 

taproot and laterals were trimmed 10 inches below it. This prescription 

produced a thick-stemmed seedling with a dense, fibrous root system that 

apparently absorbed enough soil moisture for rapid growth. The shelterwood 

was removed after three growing seasons. 

• Manipulating root-crown sprouts is the principal regeneration method 

currently available to silviculturists, and until artificial regeneration 

techniques are perfected, vegetative propagation is the most reliable 

means for renewing hardwood stands and for attaining an acceptable 

growth rate. 

• Root-crown sprouts of Pacific madrone grow faster than tanoak and 

black oak counterparts and occupy more space. However, clump density 

has a major effect on the height/width ratio of individual clumps. If 

close together, clump height exceeds clump width, but with increasing 

space between clumps, width exceeds height. Growth differs with local 

conditions but in general is rapid for the first 10 years. 

• Thinning of root-crown sprouts is impractical through age 10, but after 

age 10 it should stimulate growth of remaining sprouts. Retaining three 

to four of the most healthy sprouts evenly spaced around the 

circumference of the stump is necessary to maintain clump health. 

34 USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 
• By assigning comparative ratings to seed production, regeneration, and 

growth, future researchers can more accurately compare the potential of 

the various modes of natural regeneration and artificial regeneration for 

California black oak, tanoak, and Pacific madrone (table 6). 

More specific knowledge for enhancing the establishment and growth of 

black oak, tanoak, and Pacific madrone in each of their three reproductive 

modes needs to be developed. For seedlings and seedling-sprouts, information 

on optimum spacing, degree of shading, and amount of soil moisture and 

nutrients are needed. For root-crown sprouts, the number of sprouts per stump 

and the number of sprouting stumps per acre at a given age needs to be 

determined to maximize growth. 

For artificial regeneration of all three species, the plantation environment 

has not been fitted to the seedling, or the seedling fitted to the plantation 

environment. The environment where the seedlings of these species will 

establish consistently and grow reliably is yet to be determined. Much work on 

overstory manipulation with monitoring of light, internal moisture, and 

nutrients is needed. Because soil moisture is the limiting environmental factor 

in the Mediterranean climate of California, the key to successful artificial 

regeneration could be to develop a seedling that captures more soil moisture. 

Table 6—Comparative rating of California black oak, tanoak, and Pacific madrone seed production, regeneration, and growth both quantitatively (many, some, few) and qualitatively (good, fair, poor). 

Variable California black oak Tanoak Pacific madrone 

Biennial seed production Poor Fair Good 

Dissemination Good Good Good 

Natural Seedlings 

Number Few Some Few 

Survival Fair Fair Poor 

Growth Poor Poor Poor 

Seedling-sprouts 

Number Few Many Few 

Survival Fair Good Poor 

Growth Poor Poor Fair 

Root-crown sprouts 

Number Many Many Many 

Survival Good Good Good 

Growth Good Good Good 

Artificial Regeneration 

Survival Fair Poor Poor 

Growth Fair Fair Fair 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-185. 2002. 35 
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