Diversity, Density, and Development of

Early Vegetation in a Small Clear-cut

Environment

Philip M. McDonald

United States

Department

of Agriculture

Forest Service

Pacific Southwest

Research Station

Research Paper

PSW-RP-239

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

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

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

U.S. Department of Agriculture; 22 p.

On a high quality site in northern California, frequency, density, foliar cover, and height were measured on

every plant species present in an 8-acre clear-cut opening each year from 1976 through 1980. Plant species

numbered 71, although no more than 62 were present during a given year. Categories of vegetation with the

most plants per acre initially were shrubs, annuals and biennials, and ferns; at the end of the study the

categories were annuals and biennials, graminoids, and shrubs. At the beginning of the study, bracken fern

provided the highest amount of foliar cover, whereas 5 years later shrubs and annuals and biennials provided

the most cover. Hardwoods and graminoids were the tallest categories of vegetation. At the study’s end

density was 112,408 plants per acre, foliar cover was 17,433 ft2

 per acre and the tallest plants were 3.5 to 4.9

feet tall. Implications for future species development, plant succession, and community composition are

presented.

Retrieval Terms: natural vegetation, northern California, plant community, plant species development, small

forest opening

The Author

Philip M. McDonald is a research forester assigned to the Pacific Southwest Research Station’s Forest Growth

and Development Research Unit at the Silviculture Laboratory, 2400 Washington Ave., Redding, CA 96001.

Publisher:

Albany, California

Mailing address:

PO Box 245, Berkeley CA

94701-0245

510 559-6300

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

Pacific Southwest Research Station

Forest Service

U.S. Department of Agriculture

September 1999
Philip M. McDonald

Contents

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

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

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

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

Treatment, Measurement, and Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

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

Individual Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Categories of Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

The Plant Community . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Discussion and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Pacific Southwest

Research Station

USDA Forest Service

Research Paper

PSW-RP-239

September 1999

Diversity, Density, and Development of

Early Vegetation in a Small Clear-cut

Environment
ii

In Brief...

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

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

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

Retrieval Terms: natural vegetation, northern California, plant community dynamics, plant species

development, small forest opening The forest ecosystem manager of the near future will need a tremendous amount of data. An

inescapable fact is that an ecosystem cannot be managed without inventory data on as many

plants, animals, insects, and genes as possible. Disturbance, either from nature or humans, is

inevitable, and key questions include: how do ecosystems change and develop after a disturbance, and

what are the long-term implications of such changes? Unfortunately, data to answer these questions

are lacking or fragmented.

The primary focus of this 5-year (1976-1980) study was to record every plant species that was

present in a small composite clearing on a high quality site in northern California and to measure the

height and width of each over time. In addition, the five major regeneration strategies were examined

to determine which were operative and to link species presence and development to them. Change was

a major interest. The presence or absence of a species, the gain or loss in density, an elongation or

decline in height—all were observed with interest. Further, the ascendence or decline of various

categories of vegetation (conifers, hardwoods, shrubs, annuals and biennials, perennials, graminoids

[grasses and sedges], and bracken fern) were monitored with vigor.

The fact that this was a high quality site is important. To the vegetation, this means plentiful

rainfall, warm temperatures, and a long growing season. It also means deep soil, with inherent

capability to catch and hold critical moisture. Further, it suggests that the nutrient pool is large and

that critical nutrients are available as long as soil moisture is adequate. More specifically, it means that

the land can support many plants of many species with a potential for rapid growth. However, the long,

hot, rainless summers of the Mediterranean climate guarantee that when the soil moisture is gone,

there is no more. Soil moisture is the limiting factor to establishment, growth, and survival. Plants

must adapt a strategy of growing as fast as they can as soon as they can. Then they either die or find a

way to endure months of high temperatures, searing winds, and minimum amounts of soil moisture.

 Seventy-one species were present during this study. The number of plant species present after

one growing season was 47 and after five seasons was 62. Nine species had disappeared by the study’s

end, only to be replaced by many new species, mostly perennials. Plant density reflected the high

quality site with 24,860 plants per acre present initially and 112,408 per acre after five growing

seasons. Foliar cover increased from 950 to 17,433 ft

2

 per acre during the study, and the tallest plants

were 3.5 to 4.9 feet in height. In general, the annuals and biennials were major contributors to density,

shrubs to foliar cover, and the graminoids to height. For a given descriptor (density, cover, height),

and specific year, many species excelled at least once. The most consistent ratings, however, were

achieved by bracken fern, which ranked among the top four species each year in terms of density and

foliar cover, and tanoak, which was present among the top four species in terms of height for 4 of the 5

years in the study.

All five regeneration strategies were used: rapid growth above ground was characterized by the

root crown sprouts of the hardwoods and shrubs, rapid growth below ground by bracken fern, the

seedling bank by tanoak and at least one perennial, windblown seeds by many annuals and biennials as

well as graminoids and some perennials, and finally the seedbank in the soil by many shrubs and some

annuals and perennials.

Some early trends in the composition of the future plant community can be deciphered. Chief

among them were that initial species with tall life forms and either established root systems or

capability to rapidly develop downward thrusting systems probably will do well. Hardwoods and

shrubs have this capability and will dominate in the future plant community. The conifers, chiefly

ponderosa pine, will also be present in the future community, but scattered as individual trees and in

small aggregations. Shade-enduring perennials and bracken fern will be present in the understory of

the future plant community; they also tend to develop deep and extensive root systems. The more

shallow-rooted annuals and graminoids are likely to be represented only by small numbers in small

openings where site resources are more readily available.

USDA Forest Service Res. Paper PSW-RP-239. 1999.
USDA Forest Service Res. Paper PSW-RP-239. 1999.

1

Introduction As ecosystem management and the enhancement of forest health become applied to Federal forest

land (Dombeck 1997, Salwasser 1992, Thomas 1994), information on the past, present, and

future plant community will be invaluable. Small openings in the landscape that are created by

wildfire, insect outbreak, or logging are commonplace, and knowledge is especially needed about

them. Merchantable stems in these areas often are harvested, the slash disposed of, and the ground

prepared for natural seeding or planting of desirable species.

Soil surfaces in these areas often are bare and temporarily devoid of most plants and animals.

Available site resources, however, are high because large quantities of organic material are incorporated

into the soil through harvesting and site preparation, and large amounts of moisture are absorbed by

this organic matter. Warm temperatures and added moisture cause a rapid buildup of microorganisms

that decompose organic material and liberate nutrients. Such nutrients, particularly nitrogen, increase

on productive sites during the first year or two after site preparation and then decline precipitously

(Smethhurst and Nambiar 1990).

In this fertile, but unstable and rapidly changing environment, the early plant community is

dynamic—increasing rapidly in number of species and number of plants, but changing as plants of

some species become numerous and those of other species decline. In productive environments,

vegetative regrowth originates from five regeneration strategies: rapid growth above ground (as from

sprouting hardwoods), rapid growth below ground (as from rhizomatous species), buried seedbanks

in the soil (many shrub species), seedling banks (shade tolerant species), and windblown seeds (many

annual species) (Grime 1979). In addition to the regeneration strategies, with their inherent

considerations of plant morphology, structure, and propagule dispersion, many other factors influence

plant location, density, and development in small openings on productive sites. These include slope

and aspect, past community makeup, and dominance potential of the various species.

Secondary plant succession, which is concerned with the development of vegetation on

temporarily-bare soil, was once thought of as primarily an orderly process (Clements 1916, Odum

1969). The first category of plants to become established after the soil was bared were the annuals,

followed by the herbaceous perennials, then the shrubs, and eventually the trees. This sequence or set

of stages was based on the precept that each category of vegetation prepared the way for the next stage

through environmental modification. However, Egler (1954) suggested that succession was not

necessarily an orderly or predictable process. Rather, the ensuing plant community developed from

the propagules (seeds, rhizomes) initially present in the area. Margalef (1963) noted that the

composition of early (pioneer) communities was determined by chance arrival during the initial period

when competition was low. In this study, plants from buried seeds, rhizomes, and sprouts were already

present and composition was hardly random. The impasse of orderly or random processes could be

resolved by assuming that the future composition of many forest plant communities derives from a

combination of both.

What is the process of plant succession in small openings surrounded by trees? How can it be

determined when the very species in these openings are largely unknown? McDonald and others

(1996) noted a major weakness when beginning ecosystem management on forested or formerly

forested land: “very little is known about the shrubs, forbs, and grasses in the community” (p. 1).

Gordon (1979) recommended that foresters begin to build a database for vegetation that is expected in

specific areas. Wagner and Zasada (1991) stated that forest managers across North America need to

consider the potential effect of noncrop vegetation on nearly every acre of newly forested land. These,

of course, are the currently uneconomic (noncrop) species as opposed to the “valuable” (economic)

conifers. O’Hara and others (1994) suggested that future forestry must embrace a mix of commercially

valuable and nonvaluable species, and Rietveld (1992) noted an increased demand for diverse tree and

shrub nursery stock, especially for species that provide food and shelter for wildlife.

The major objectives of this study were to ascertain the species composition of an early plant

community in a small clear-cutting in the northern Sierra Nevada and to gain knowledge on early

successional trends. More specific objectives were to list every species that was present in the clearing

each year for 5 years after site preparation, and to determine each species’ density and development,

both alone and in such categories as conifers, hardwoods, shrubs, annuals and biennials, perennials,

graminoids, and bracken fern. A second objective was to determine density and developmental trends

in each of these categories.
2 USDA Forest Service Res. Paper PSW-RP-239. 1999.

Table 1—Scientific names, symbols, and common names of plant species in a composite clearcutting, Challenge Experimental Forest Table 1 ,

1976-1980

Vegetation Scientific Plant Common

 category name symbol name

Conifers Libocedrus decurrens Lide Incense-cedar

Pseudotuga menziesii

var. menziesii PsmeM Coast Douglas-fir

Pinus ponderosa

var. ponderosa PipoP Ponderosa pine

Hardwoods Arbutus menziesii Arme Pacific madrone

Lithocarpus densiflorus Lide3 Tanoak

Quercus chrysolepis Quch2 Canyon live oak

Quercus kelloggii Quke California black oak

Shrubs Arctostaphylos mewukka Arme3 Indian manzanita

Arctostaphylos viscida Arvi4 Whiteleaf manzanita

Baccharis pilularis Bapi Coyote brush

Ceanothus lemmonii Cele Lemmon’s ceanothus

Ceanothus prostratus Cepr Squawcarpet

Chamaebatia foliolosa Chfo Sierran mountain misery

Garrya fremontii Gafr Bearbrush

Haplopappus linearifolius Hali5 Ericameria linearifolia

Ribes roezlii Riro Sierran gooseberry

Rosa gymnocarpa Rogy Dwarf rose

Rubus glaucifolius Rugl Smoothleaf raspberry

Toxicodendron diversilobum Todi Pacific poison oak

Vitis californica Vica5 California wild grape

Cirsium vulgare Civu Bull thistle

Clarkia rhomboidea Clrh Diamond fairyfan

Conyza canadensis Coca5 Canadian horseweed

Collomia heterophylla Cohe2 Variableleaf mtn. trumpet

Epilobium paniculatum Eppa2

Eremocarpus setigerus Erse3 Turkey mullein

Galium aparine Gaap2 Stickywilly

Gnaphalium luteo-album Gnlu Jersey cudweed

Hypochaeris glabra Hygl2 Smooth catsear

Lactuca serriola Lase Prickly lettuce

Lotus denticulatus Lode Riverbar birdfoot trefoil

Lotus humistratus Lohu2 Foothill deervetch

Lotus purshianus Lopu3

Madia gracilis Magr3 Grassy tarweed

Mimulus torreyi Mito Torrey’s monkeyflower

Methods

Species and Site Characteristics

The study was located on the Challenge Experimental Forest in north central California (Yuba County,

T19N, R7E MDM, Section 29). Site quality is high and the dominant species, ponderosa pine (Pinus

ponderosa Dougl. ex Laws. var. ponderosa), will average about 95 feet in height in 50 years (Powers

and Oliver 1978). Other tree species scattered over the Forest are coast Douglas-fir (Pseudotsuga

menziesii [Mirb.] Franco), sugar pine (Pinus lambertiana Dougl.), California white fir (Abies concolor

var. lowiana [Gord.] Lemm.), and incense-cedar (Libocedrus decurrens Torr.). Scientific and common

names of trees are from Little (1979), scientific names of all vegetation other than trees is from

Hickman (1993), and common names and plant symbols are from the U.S. Department of Agriculture

(1994). Hardwoods, principally California black oak (Quercus kelloggii Newb.), (plant symbol Quke),

tanoak (Lithocarpus densiflorus [Hook. & Arn.] Rehd.), (plant symbol Lide3), and Pacific madrone

(Arbutus menziesii Pursh) (Arme) (table 1), are present throughout as individual trees, clumps, or

groves. In terms of ecological subregions of California, the area corresponds to section M261E Sierra

Nevada and the granitic and metamorphic hills subsection (U.S. Department of Agriculture 1997).

continues

Annuals and

biennials
USDA Forest Service Res. Paper PSW-RP-239. 1999. 3

Table 1, continued Table 1

Vegetation Scientific Plant Common

 category name symbol name

Annuals Sonchus asper Soas Spiny sowthistle

and Stephanomeria virgata Stvi2 Rod wirelettuce

biennials Tragopogon dubius Trdu Yellow salsify

Trifolium ciliolatum Trci Foothill clover

Vicia americana Viam American vetch

Viola lobata Vilo2 Moosehorn violet

Perennials Agoseris grandiflora Aggr Bigflower agoseris

Apocynum pumilum Appu

Aster radulinus Asra Roughleaf aster

Campanula prenanthoides Capr15

Convolvulus aridus Coar11

Dichelostemma capitatum Dica14 Bluedicks

Eriophyllum lanatum Erla6 Woolly eriophyllum

Fragaria vesca Frve Woodland strawberry

Galium bolanderi Gabo Bolander’s bedstraw

Horkelia tridentata Hotr Threetooth honeydew

Hypericum concinnum Hyco3 Goldwire

Hypochaeris radicata Hyra3 Hairy catsear

Iris hartwegii Irha Rainbow iris

Osmorhiza chilensis Osch

Polygala cornuta Poco4 Sierran milkwort

Potentilla glandulosa Pogl9 Gland cinquefoil

Sanicula graveolens Sagr5 Northern sanicle

Sidalcea malvaeflora Sima2 Dwarf checkermallow

Tauschia kelloggii Take Kellogg’s umbrellawort

Trientalis latifolia Trla6

Unknown rosette Unkn

Graminoids Bromus (unknown) Brsp

Bromus orcuttianus Bror2 Orcutt’s brome

Carex (unknown) Casp

Elymus glaucus Elgl Blue wildrye

Festuca myuros Femy2

Festuca occidentalis Feoc Western fescue

Sitanion hystrix Sihy

Bracken fern Pteridium aquilinum

var. pubescens Ptaq Western bracken fern

Trees on the Experimental Forest larger than 3.5 inches in diameter at breast height (d.b.h.)

number more than 245 per acre and the average acre contains about 270 ft2/acre of basal area. The

previous forest was logged (at least for the largest and best trees) from about 1860 through 1890

(McDonald and Lahore 1984). Thus, logging and inevitable fire caused the current forest to be a mosaic

of even-aged, second-growth stands, with the oldest dominant and codominant trees being more than

100 years and averaging about 140 feet tall. Trees 170 feet and taller at the same age are not unusual.

Trees in the dominant and codominant crown classes on the Experimental Forest average about

35 per acre, 70 percent of which are ponderosa pines. In general, many trees of the more shade-tolerant

species (Douglas-fir, California white fir, incense-cedar, sugar pine, and tanoak) are younger, reflecting

a decreasing incidence of fire in the area. Greenleaf manzanita (Arvi4), deerbrush (Cein3), and western

bracken fern (Ptaq) are common on the Forest and often become abundant (table 1). Poison oak (Todi)

is ubiquitous and abundant, and grows equally well in sun and shade environments.

Herbivores, chiefly deer (Odocoileus spp.), woodrats (Neotoma spp.), and deer mice (Peromyscus

maniculatus), are plentiful throughout the Experimental Forest.

Summers on the Forest are hot and dry; winters cool and moist. The average midsummer

maximum temperature, based on 43 years of record, is 90 °F; the midwinter minimum is 30 °F. The
4 USDA Forest Service Res. Paper PSW-RP-239. 1999.

growing season is about 200 days. Average annual precipitation is 68 inches with 94 percent falling

between October and May. Soil moisture is the limiting factor and drought the primary cause of

mortality for most plants. The Aiken soil grades from loam to clay-loam texture with depth, and is

deep, moderately well drained, and quite fertile. The study area, located at the 2,750-foot elevation,

faces southwest and has a 20 percent slope.

Treatment, Measurement, and Analysis

Merchantable trees were harvested in two small clear-cuttings in 1975, and slash and unmerchantable

trees were piled with a bulldozer in windrows and burned in the fall (fig. 1). Very little soil was placed

in the windrows. The clear-cuttings were 8.0 and 7.75 acres in size and about one-fourth of a mile

apart. Their soil, slope, aspect, and vegetation were representative of much of the Experimental Forest.

The two clear-cuttings were similar in every respect with one exception—most abundant shrub species.

In spring 1976, large numbers of whiteleaf manzanita (Arvi4) seedlings were present in one opening;

deerbrush (Cein3) seedlings in the other. Although not a trace of either species remained above

ground, large numbers of both species from dormant, but viable, seeds in the soil were expected in

each opening. The difference between openings was not anticipated. However, as noted by Sousa

(1984) and others, the environment within a patch cleared by disturbance is seldom, if ever,

homogeneous. Different microsites are inevitable and slightly different plant communities will become

present in each because of the adaptation of particular colonists to each. Because the overall

geographical features, soil, and vegetation were similar, data from the two openings were combined as

a composite to more closely represent this environment on the Experimental Forest.

Sampling

Sampling took place in the fall along three randomly selected diagonal transects in each opening that

roughly represented the top, middle, and bottom of each. Because the opening boundaries were

irregular, the length of the transects varied. Beginning and ending points of each transect were clearly

marked. Ten sampling locations were evenly distributed along each and determined by pacing. Sample

locations included the edge environment within 10 feet of the forest, but not burned windrows or

riparian vegetation in ephemeral stream channels near the bottom of the openings. Each location

became the center of a circular milacre (0.001 acre) plot. These were not permanently marked, and

thus the location of the plots varied slightly each year.

All vegetation was measured on each plot each year from 1976 through 1980. Years of extreme

drought were 1976 and 1977; 1978 was extremely wet, and 1979 and 1980 were about normal. Each

plant species was sampled for density, foliar cover, and height. Density was defined as the number of

Figure 1—A portion of the study

area on the Challenge Experimental

Forest in 1976. Close examination

shows a few small plants scattered

throughout the opening.

F P O

(for position only)
USDA Forest Service Res. Paper PSW-RP-239. 1999. 5

plants on each milacre plot expanded to a per-acre basis. Foliar cover was an estimate of the sum of

shadows that would be cast by leaves and stems of individual species expressed as a percentage of the

land surface (Daubenmire 1968). It is an expression of horizontal development. For each species,

amounts greater than 0.5 ft2 were recorded to the nearest 1.0 ft2 and less than this value as a trace (T). If

a plant leaned into the milacre and had at least a square foot of foliar cover in it, it was given a density

value of one plant. Plant height was denoted as “average dominant” and defined as the average of the

three tallest stems measured from mean groundline to bud. The height of an outward leaning plant was

recorded where it crossed the plot boundary. Frequency also was determined to provide an estimate of

species distribution within the opening. It was defined as the number of plots having one or more

plants of a given species divided by the total number of plots and expressed as a percent.

Results

Plant Diversity

A total of 71 plant species was found during the 5-year study (table 1), although no more than 62 species

were present during a given year (table 2). At the beginning of the study, the 45 species in the plant

community consisted of 0 conifer seedlings; 3 hardwoods from both root-crowns and seeds, 11 shrubs,

mostly from buried seeds; 15 annuals and biennials, all from seeds; 15 perennials, almost all from seeds;

2 graminoids (grasses and sedges), from seeds; and bracken fern, from rhizomes. At the end of the

study, the 62 species in the plant community consisted of 3 conifers, 2 hardwoods, 12 shrubs, 20

annuals and biennials, 18 perennials, 6 graminoids, and bracken fern (table 2; fig. 2). All categories of

vegetation increased, except hardwoods and fern, for an overall gain in diversity of 32 percent.

Table 2—Plant species diversity by vegetation category in a composite clearcutting, Challenge Experimental Forest, 1976-1980 Table 2

Year Conifers Hardwoods Shrubs Annuals Perennials Graminoids Fern Total

Number of species

1976 0 3 11 15 15 2 1 47

1977 3 2 12 16 12 7 1 53

1978 3 3 11 18 14 7 1 57

1979 3 2 12 16 15 6 1 55

1980 3 2 12 20 18 6 1 62

Figure 2—At the end of the study

in 1980, the land was rapidly becoming

clothed with many plants from several

categories of vegetation, Challenge

Experimental Forest, 1980.

F P O

(for position only)
6 USDA Forest Service Res. Paper PSW-RP-239. 1999.

continues

Individual Species

The vast majority of species became established early and persisted throughout the study period.

Several species, however, invaded early, were present for 1 to 3 years, and then disappeared. These

included Pacific madrone (Arme), bearbrush (Gafr), turkey mullein (Erse3), threetooth honeydew

(Hotr), canyon live oak (Quch2), northern sanicle (Sagr5), and Sitanian hystrix (Sihy) (table 3). They

represented almost all the vegetation categories in the study. Other species invaded later in the study.

Notable were coyote brush (Bapi), Convolvulus aridus (Coar11), woolly eriophyllum (Erla6), Bolander’s

bedstraw (Gabo), Jersey cudweed (Gnlu), goldwire (Hyco3), Osmorhiza chilensis (Osch), and yellow

salsify (Trdu), which, with one exception, were perennials.

Descriptive characteristics such as frequency, density, foliar cover, and height of the 71 plant

species portray the distribution, density, and development trends of individual species over the 5-year

study (table 3). Together, they encompass a wide variety of density and developmental trends, reactions

to competition, and adaptations to micro-environments. Strategies to dominate in some way at key

times also were observed. When the top four species in each descriptive characteristics class (density,

cover, height) were ranked, their regeneration and development strategies became more clear (table 4).

The first year after site preparation (1976), species like tanoak (Lide3), western bracken fern (Ptaq),

and Pacific poison oak (Todi), which derived energy from parent root systems, dominated in terms of

density and horizontal development (foliar cover). The second year (1977) was characterized by the

addition of annuals like bull thistle (Civu) and American vetch (Viam) and shrubs like whiteleaf

manzanita (Arvi4) and deerbrush (Cein3) that originated mostly from windblown seeds or from

dormant seeds in the soil. Year 3 (1978) was characterized by annuals like Civu, prickly lettuce (Lase),

and American vetch that originated mostly from newly produced seeds, and shrubs such as deerbrush

and whiteleaf manzanita that were developing rapidly. Species of note in year 4 (1979) were additional

annuals like smooth catsear (Hygl2) and riverbar birdfoot trefoil (Lode) along with the above shrubs

and western bracken fern (Ptaq). In year 5 (1980), density and cover were divided among most of the

species in year 4 plus blue wildrye (Elgl) and tanoak (Lide3). Of particular note was western bracken

fern, which was present among the top four species in both density and cover every year of the study.

This was the only species to do this.

Table 3—Characteristics of individual species as they regenerated and developed during the study period, Challenge Experimenta Table 3— l Forest,

1976-1980

Vegetation Species Year Freq. Density Cover Height

 category abbrev.

Pct Plants/acre Ft2/acre Ft

Value SE Value SE Value SE

Conifers Cade 1976 -------

1977 5 67 33 T 0 0.2 0.1

1978 2 17 0 T 0 0.5 .0

1979 3 33 0 T 0 0.5 0.4

1980 2 17 0 T 0 0.6 .0

PsmeM 1976 -------

1977 2 17 0 T 0 0.2 .0

1978 3 33 0 T 0 0.6 .0

1979 3 33 0 T 0 0.4 0.2

1980 5 50 0 T 0 0.6 0.4

PipoP 1976 -------

1977 25 467 29 T 0 0.2 0.1

1978 33 483 15 17 0 0.3 0.1

1979 35 433 10 67 0 0.7 0.2

1980 22 350 21 33 0 1.0 0.3

Hardwoods Arme 1976 -------

1977 2 33 0 T 0 0.3 0

1978 2 17 0 T 0 1.4 0

1979 -------

1980 -------
USDA Forest Service Res. Paper PSW-RP-239. 1999. 7

Hardwoods Lide3 1976 1 210 10 90 2 1.4 0.2

1977 22 233 6 217 2 2.6 0.3

1978 17 183 10 217 6 2.0 0.4

1979 17 217 15 783 145 4.8 0.5

1980 25 350 16 900 117 4.9 0.6

Quch2 1976 1 10 0 10 0 0.4 .0

1977 -------

1978 -------

1979 -------

1980 -------

Quke 1976 4 40 0 T 0 0.4 0.1

1977 10 150 22 100 100 1.5 0.4

1978 3 83 150 T 0 0.5 0.1

1979 5 100 100 17 0 0.7 0.3

1980 10 100 0 168 233 2.2 1.0

Shrubs Arme1 1976 2 17 0 T 0 0.1 .0

1977 3 17 0 T 0 0.1 .0

1978 2 17 0 T 0 0.1 .0

1979 5 33 0 33 0 1.8 0.1

1980 3 33 0 T 0 0.3 0.1

Arvi4 1976 41 1,680 100 70 0 0.3 0.1

1977 50 3,517 243 617 51 0.7 0.1

1978 58 2,917 142 1,383 73 1.2 0.1

1979 70 3,533 142 2,083 16 1.3 0.2

1980 65 4,467 146 4,183 153 2.4 0.2

Bapi 1976 -------

1977 -------

1978 -------

1979 -------

1980 2 17 0 T 0 3.2 .0

Cein3 1976 60 2,960 550 T 0 0.2 0.1

1977 63 3,150 580 717 20 1.2 0.1

1978 63 3,783 125 1,850 68 1.4 0.1

1979 72 3,000 46 4,100 114 2.3 0.2

1980 67 2,617 47 4,033 106 3.4 0.4

Cele 1976 9 360 138 10 0 0.2 0.1

1977 10 533 219 100 58 0.5 0.1

1978 7 417 214 150 100 0.7 0.1

1979 17 1,250 225 800 134 0.9 0.1

1980 8 683 553 583 585 1.2 0.4

Cepr 1976 15 180 14 T 0 0.1 0.1

1977 17 300 33 50 0 0.2 0.1

1978 23 400 18 150 13 0.2 0.1

1979 15 183 15 100 20 0.2 0.1

1980 22 467 44 283 51 0.2 0.1

Chfo 1976 16 630 73 80 14 0.5 0.1

1977 13 800 243 167 87 0.5 0.1

1978 18 750 118 117 24 0.5 0.1

1979 27 2,517 215 550 68 0.8 0.1

1980 22 2,267 301 283 48 0.7 0.1

Gafr 1976 9 140 29 T 0 0.2 0.1

1977 13 200 38 17 0 0.4 0.1

1978 -------

1979 -------

1980 -------

continues

Table 3, continued Table 3

Vegetation Species Year Freq. Density Cover Height

 category abbrev.

Pct Plants/acre Ft2/acre Ft

Value SE Value SE Value SE
8 USDA Forest Service Res. Paper PSW-RP-239. 1999.

Hali5 1976 -------

1977 -------

1978 3 33 0 17 0 1.3 0.7

1979 2 17 0 T 0 0.7 .0

1980 5 67 33 33 0 1.7 0.4

Riro 1976 7 80 14 T 0 0.4 0.1

1977 2 17 0 T 0 0.3 .0

1978 5 50 0 T 0 0.7 0.1

1979 3 33 0 T 0 0.4 0.4

1980 5 67 33 100 0 2.7 0.4

Rogy 1976 14 430 60 30 0 0.4 0.1

1977 10 417 91 83 67 0.6 0.1

1978 17 1,133 255 67 100 0.5 0.1

1979 12 367 116 33 T 0.7 0.1

1980 13 350 56 T 0 0.6 0.1

Rugl 1976 29 430 38 30 0 0.3 0.1

1977 20 483 61 117 48 0.6 0.3

1978 32 817 82 167 11 0.6 0.1

1979 27 500 39 217 75 0.4 0.1

1980 30 583 22 200 24 0.8 0.1

Todi 1976 65 2,810 440 90 18 0.4 0.2

1977 63 3,083 86 500 16 0.8 0.1

1978 48 1,767 48 100 0 0.7 0.1

1979 65 2,567 54 500 22 0.8 0.1

1980 63 2,733 72 483 22 1.5 0.2

Vica5 1976 -------

1977 2 17 0 T 0 0.5 .0

1978 -------

1979 2 17 0 T 0 0.4 .0

1980 -------

Annuals Civu 1976 49 1,860 67 110 43 0.6 0.2

and 1977 88 20,367 367 1,833 41 1.5 0.1

biennials 1978 95 13,583 216 2,467 66 1.7 0.2

1979 70 3,467 73 467 21 1.6 0.1

1980 62 4,017 55 267 27 1.6 0.1

Clrh 1976 2 0 0 T 0 1.0 0.4

1977 -------

1978 -------

1979 3 933 999 33 0 1.5 0.5

1980 3 750 250 100 200 2.5 0.5

Coca5 1976 -------

1977 3 50 50 17 0 2.8 1.0

1978 7 67 0 T 0 1.9 0.6

1979 3 50 50 T 0 1.1 0.2

1980 7 1,083 441 17 0 0.7 0.4

Cohe2 1976 1 90 0 T 0 0.3 .0

1977 8 950 229 T 0 0.3 0.1

1978 17 2,183 244 83 67 0.4 0.1

1979 -------

1980 10 817 539 T 0 0.3 0.1

Eppa2 1976 -------

1977 3 100 0 T 0 1.8 0.7

1978 13 717 266 50 50 2.1 0.3

1979 20 600 81 T 0 1.4 0.1

1980 42 3,500 244 67 0 1.7 0.2

Shrubs

continues

Table 3, continued Table 3

Vegetation Species Year Freq. Density Cover Height

 category abbrev.

Pct Plants/acre Ft2/acre Ft

Value SE Value SE Value SE
USDA Forest Service Res. Paper PSW-RP-239. 1999. 9

Erse3 1976 3 30 0 T 0 0.1 0.1

1977 2 183 0 T 0 0.3 .0

1978 2 183 0 T 0 0.1 .0

1979 -------

1980 -------

Gaap2 1976 -------

1977 2 17 0 T 0 0.5 .0

1978 -------

1979 -------

1980 2 17 0 T 0 3.1 .0

Gnlu 1976 -------

1977 -------

1978 12 133 14 17 0 0.3 0.2

1979 17 533 118 67 33 1.6 0.3

1980 15 317 75 67 33 1.8 0.4

Hygl2 1976 11 180 28 T 0 0.1 0.1

1977 13 183 38 17 0 0.9 0.1

1978 53 2,833 106 183 31 0.9 0.1

1979 38 4,600 281 250 24 0.7 0.1

1980 47 17,367 912 783 72 0.8 0.1

Lase 1976 4 60 50 T 0 1.4 0.4

1977 37 2,350 205 133 100 1.3 0.1

1978 62 10,050 386 533 76 1.6 0.2

1979 60 9,717 536 367 114 1.4 1.4

1980 7 11,517 311 267 22 1.4 0.1

Lode 1976 4 580 998 T 0 0.7 0.3

1977 2 1,167 0 167 0 1.0 .0

1978 18 8,033 999 467 242 0.9 0.1

1979 5 4,100 999 283 650 0.7 0.1

1980 7 3,467 999 250 550 0.8 0.1

Lohu2 1976 1 10 0 T 0 0.1 0.1

1977 -------

1978 8 483 114 T 0 0.3 0.1

1979 -------

1980 5 567 684 T 0 0.3 0.1

Lopu3 1976 9 540 251 T 0 0.2 0.1

1977 7 250 48 T 0 0.3 0.1

1978 10 1,700 900 17 0 0.4 0.1

1979 20 3,200 644 100 20 0.3 0.1

1980 3 667 0 T 0 0.3 .0

Magr3 1976 2 50 50 T 0 0.9 0.7

1977 5 67 33 T 0 1.1 0.5

1978 10 883 539 83 0 2.1 0.1

1979 12 833 338 33 0 1.6 0.2

1980 38 4,500 387 250 47 2.1 0.1

Mito 1976 12 480 246 T 0 0.1 0.1

1977 8 283 166 T 0 0.3 0.1

1978 12 1,433 525 17 0 0.3 0.1

1979 7 833 617 T 0 0.5 0.1

1980 15 817 172 T 0 0.5 0.1

Soas 1976 10 130 21 T 0 0.1 0.1

1977 3 50 50 17 0 1.7 1.6

1978 8 367 163 33 0 1.6 0.4

1979 5 50 0 T 0 0.8 0.3

1980 8 167 77 T 0 1.0 0.3

continues

Annuals

and

biennials

Table 3, continued Table 3

Vegetation Species Year Freq. Density Cover Height

 category abbrev.

Pct Plants/acre Ft2/acre Ft

Value SE Value SE Value SE
10 USDA Forest Service Res. Paper PSW-RP-239. 1999.

Stvi2 1976 -------

1977 7 850 762 133 100 1.6 0.7

1978 18 500 100 50 50 1.5 0.2

1979 12 250 55 T 0 1.7 0.2

1980 23 3,533 999 200 0 2.4 0.4

Trdu 1976 -------

1977 -------

1978 3 33 0 T 0 1.4 0.1

1979 2 17 0 T 0 1.0 .0

1980 2 17 0 T 0 2.2 .0

Trci 1976 1 10 0 T 0 0.2 .0

1977 -------

1978 -------

1979 -------

1980 3 217 350 T 0 0.3 .0

Viam 1976 44 2,610 104 10 0 0.2 0.1

1977 48 5,183 262 317 46 0.4 0.1

1978 53 10,000 408 233 29 0.3 0.1

1979 48 3,467 217 117 24 0.6 0.1

1980 47 7,450 433 400 99 0.7 0.1

Vilo2 1976 11 170 31 T 0 0.1 0.1

1977 10 117 17 T 0 0.2 0.1

1978 17 500 86 T 0 0.4 0.1

1979 7 183 55 T 0 0.2 0.1

1980 7 233 65 T 0 0.4 0.1

Perennials Aggr 1976 6 60 0 T 0 0.7 0.6

1977 7 67 33 T 0 0.8 0.1

1978 8 233 71 17 0 1.3 0.2

1979 12 200 57 33 0 1.3 0.1

1980 38 1,800 80 133 14 1.3 0.1

Appu 1976 2 20 0 10 0 0.2 .0

1977 2 67 0 17 0 0.5 .0

1978 3 83 150 T 0 0.6 0.1

1979 2 17 0 T 0 0.3 .0

1980 3 83 150 17 0 0.8 0.4

Asra 1976 8 220 105 10 0 0.6 0.1

1977 7 133 100 T 0 0.8 0.2

1978 12 417 157 67 33 1.4 0.3

1979 12 800 443 33 0 0.8 0.1

1980 13 317 38 33 0 1.1 0.3

Capr5 1976 -------

1977 -------

1978 5 33 0 T 0 0.6 0.3

1979 -------

1980 7 100 50 T 0 1.6 0.2

Coar11 1976 -------

1977 -------

1978 2 150 350 T 0 0.4 .0

1979 -------

1980 5 167 0 T 0 0.6 0.2

Annuals

and

biennials

continues

Table 3, continued Table 3

Vegetation Species Year Freq. Density Cover Height

 category abbrev.

Pct Plants/acre Ft2/acre Ft

Value SE Value SE Value SE
USDA Forest Service Res. Paper PSW-RP-239. 1999. 11

Dica14 1976 2 30 50 T 0 0.2 0.1

1977 2 17 0 T 0 0.9 .0

1978 -------

1979 5 50 0 T 0 1.6 0.1

1980 5 67 33 T 0 1.2 0.1

Erla6 1976 -------

1977 -------

1978 -------

1979 2 17 0 T 0 0.5 .0

1980 2 50 0 T 0 1.3 .0

Frve 1976 6 180 97 T 0 0.2 0.1

1977 2 117 0 T 0 0.2 .0

1978 7 100 29 T 0 0.3 0.1

1979 -------

1980 2 117 0 T 0 0.2 .0

Gabo 1976 -------

1977 -------

1978 10 200 37 30 0 0.5 0.1

1979 20 417 47 67 0 0.4 0.1

1980 23 450 34 117 17 0.7 0.1

Hotr 1976 2 40 100 T 0 0.1 0.1

1977 3 33 0 T 0 1.0 .0

1978 -------

1979 -------

1980 -------

Hyco3 1976 -------

1977 -------

1978 -------

1979 2 167 0 33 0 2.3 .0

1980 -------

Hyra3 1976 3 260 717 T 0 0.1 0.1

1977 -------

1978 7 67 0 17 0 0.9 0.1

1979 15 400 107 17 0 0.9 0.1

1980 22 1,400 124 T 0 0.7 0.1

Irha 1976 18 280 180 T 0 0.3 0.1

1977 5 67 33 T 0 0.5 0.1

1978 8 133 40 T 0 0.5 0.1

1979 25 300 11 83 0 0.7 0.1

1980 12 167 30 17 0 0.4 0.1

Osch 1976 -------

1977 -------

1978 -------

1979 -------

1980 2 17 0 T 0 0.5 0.1

Poco4 1976 4 90 48 T 0 0.2 0.1

1977 3 67 100 T 0 0.4 0.1

1978 7 83 25 T 0 0.5 0.1

1979 7 200 200 17 0 0.5 0.1

1980 2 17 0 T 0 0 .0

continues

Perennials

Table 3, continued Table 3

Vegetation Species Year Freq. Density Cover Height

 category abbrev.

Pct Plants/acre Ft2/acre Ft

Value SE Value SE Value SE
12 USDA Forest Service Res. Paper PSW-RP-239. 1999.

Pogl9 1976 5 80 40 T 0 0.2 0.1

1977 10 283 48 33 0 0.9 0.2

1978 10 467 102 33 0 0.5 0.1

1979 12 550 111 67 0 1.0 0.2

1980 13 450 169 83 25 0.9 0.2

Sagr5 1976 1 40 0 T 0 1.5 0.2

1977 2 17 0 T 0 0.2 .0

1978 2 17 0 T 0 0.6 .0

1979 -------

1980 -------

Sima2 1976 30 980 75 20 0 0.1 0.1

1977 20 900 125 183 15 1.1 0.1

1978 33 1,067 55 233 24 0.8 0.1

1979 23 867 113 150 58 0.7 0.1

1980 23 517 41 83 25 0.9 0.2

Take 1976 4 70 48 T 0 0.4 0.2

1977 -------

1978 -------

1979 3 33 0 T 0 0.7 0.2

1980 3 50 50 T 0 0.8 0.2

Trla6 1976 14 770 241 T 0 0.1 0.1

1977 20 783 115 T 0 0.2 0.1

1978 30 2,967 156 50 0 0.2 0.1

1979 23 2,133 277 50 0 0.2 0.1

1980 47 6,467 268 67 0 0.3 0.1

Unkn 1976 1 10 0 T 0 0.2 0.1

1977 -------

1978 -------

1979 2 17 0 T 0 0.4 .0

1980 2 17 0 T 0 0.3 .0

Graminoids Brsp 1976 -------

1977 17 1,100 327 217 98 2.7 0.1

1978 20 1,983 290 150 18 1.8 0.3

1979 7 2,383 999 500 409 3.1 0.1

1980 7 900 999 250 650 2.9 0.4

Bror2 1976 8 170 99 10 0 0.8 0.1

1977 5 267 233 33 0 2.5 0.1

1978 13 1,167 458 83 67 2.1 0.4

1979 23 2,467 285 300 69 2.6 0.2

1980 1 1,167 446 133 41 3.5 0.2

Casp 1976 23 1,000 112 20 0 0.5 0.1

1977 23 1,100 145 83 33 1.0 0.2

1978 28 583 41 100 29 1.1 0.1

1979 17 350 47 117 24 1.2 0.1

1980 22 333 27 100 0 1.1 0.2

Elgl 1976 -------

1977 3 33 0 T 0 1.6 1.3

1978 15 3,817 999 267 260 2.1 0.5

1979 12 1,950 541 150 0 3.1 0.4

1980 57 8,400 319 800 77 2.8 0.3

Perennials

continues

Table 3, continued Table 3

Vegetation Species Year Freq. Density Cover Height

 category abbrev.

Pct Plants/acre Ft2/acre Ft

Value SE Value SE Value SE
USDA Forest Service Res. Paper PSW-RP-239. 1999. 13

Femy2 1976 -------

1977 2 17 0 T 0 0.4 .0

1978 2 750 0 17 0 1.2 .0

1979 7 500 307 17 0 1.0 0.2

1980 8 317 73 T 0 0.9 0.1

Feoc 1976 -------

1977 5 500 379 100 58 2.5 0.4

1978 5 300 451 17 0 2.9 0.4

1979 5 1,550 999 267 219 2.6 0.2

1980 12 4,917 999 583 369 2.5 0.3

Sihy 1976 -------

1977 2 17 0 T 0 0.5 .0

1978 2 100 0 T 0 1.0 .0

1979 -------

1980 -------

Bracken Ptaq 1976 47 3,760 73 350 12 0.8 0.1

fern 1977 57 10,233 173 1,367 34 1.0 0.2

1978 65 10,333 265 1,517 107 1.0 0.3

1979 47 8,133 248 1,283 39 1 0 0.1

1980 52 7,883 229 1,067 49 1.1 0.1

Graminoids

Table 3, continued Table 3

Vegetation Species Year Freq. Density Cover Height

 category abbrev.

Pct Plants/acre Ft2/acre Ft

Value SE Value SE Value SE

Table 4—Top four plant species having largest number (density), best horizontal development (foliar cover), and best vertical d Table 4— evelopment

(height), Challenge Experimental Forest, 1976-1980

Year Rank Density Cover Height

1976 1 Ptaq Ptaq Sagr5

2 Cein3 Civu Lide3

3 Viam Lide3 Lase

4 Todi Todi Clrh

1977 1 Civu Civu Coca5

2 Ptaq Ptaq Brsp

3 Viam Cein3 Lide3

4 Arvi4 Arvi4 Feoc

1978 1 Civu Civu Feoc

2 Ptaq Cein3 Bror2

3 Lase Ptaq Elgl

4 Viam Arvi4 Magr3

1979 1 Lase Cein3 Lide3

2 Ptaq Arvi4 Elgl

3 Hygl2 Ptaq Brsp

4 Lode Cele Feoc

1980 1 Hygl Arvi4 Lide3

2 Lase Cein3 Bror2

3 Elgl Ptaq Cein3

4 Ptaq Lide3 Bapi
14 USDA Forest Service Res. Paper PSW-RP-239. 1999.

Average dominant height, which is a measure of vertical development, was expressed best by

tanoak (Lide3) in 1976 and a few plants of annual species that grew tall in the absence of competition.

Height development from 1977 through 1979 was notable for a species of brome (Brsp), western fescue

(Feoc), Orcutt’s brome (Bror2), and blue wildrye (Elgl)—all perennial grasses—whose strategy was to

grow tall at an early age. The tallest species in 1980 were a mixture of hardwood (Lide3), graminoid

(Bror2), and such shrubs as deerbrush (Cein3) and coyote brush (Bapi). Of particular note was tanoak,

which ranked among the four tallest species in 4 of the 5 years in the study.

One factor that can influence the density and horizontal development of plant species in newly

developed openings is damage from biotic and abiotic agents. The only agent in this study that had a

noticeable effect was deer. Browsing damage in fall 1976 to the young plants was severe. Species like

deerbrush (Cein3) and California black oak (Quke) were browsed to nubs of naked stems, and larger

perennials like dwarf checkermallow (Sima2) and gland cinquefoil (Pogl9) were virtually stripped of all

green material. Most remarkable was that species like western bracken fern (Ptaq), Sierran mountain

misery (Chfo), whiteleaf manzanita (Arvi4), Pacific poison oak (Todi), rainbow iris (Irha), and

smoothleaf raspberry (Rugl), which are scarcely touched when older, were severely browsed. Even they

became palatable, probably because of their high nutrient content—a response to the large amount of

soil nitrogen available just after site preparation. Many plants of American vetch (Viam) were pulled

out of the ground. Browsing declined rapidly in 1977 and rated only as occasional thereafter.

Categories of Species

Conifers

Conifer seedlings originated from seeds blown in from nearby trees in fall 1976. The most abundant

species was ponderosa pine (PipoP). Mean conifer seedling density decreased from 551 to 417 per acre

during the study (fig. 3). Horizontal and vertical development were slow, with values of 33 ft2 per acre

(fig. 4) and 0.7 foot (fig. 5), respectively, at the end of the study.

Figure 3—Density of hardwoods and conifers, Challenge Experimental Forest, 1976-1980. Standard errors for

hardwoods ranged from 48 to 125 plants per acre in a given year; for conifers, from 80 to 153 plants per acre.

600

500

400

300

200

100

0

Plants/acre

1976 1977 1978 1979 1980

_

_

_

_

Year

Hardwoods Conifers
USDA Forest Service Res. Paper PSW-RP-239. 1999. 15

Figure 4—Foliar cover of hardwoods and conifers, Challenge Experimental Forest, 1976-1980. Standard errors for

hardwoods ranged from 28 to 383 ft2 per acre in a given year; for conifers, from 5 to 22 ft2 per acre.

Figure 5—Height of hardwoods and conifers, Challenge Experimental Forest, 1976-1980. Standard errors for

hardwoods ranged from 0.3 to 2.0 feet in a given year; for conifers, from 0 to 0.1 foot.

4

3

2

1

0

Height (ft)

1976 1977 1978 1979 1980

_

_

_

_

Year

Hardwoods Conifers

1,200

1,000

800

600

400

200

0

Cover (ft2/acre)

1976 1977 1978 1979 1980

_

_

_

_

Year

Hardwoods Conifers
16 USDA Forest Service Res. Paper PSW-RP-239. 1999.

Hardwoods

Hardwoods initially were from two kinds of sprouts: root-crown sprouts that originated from dormant

buds on the burl and seedling-sprouts. Seedling-sprouts, most of which were tanoak (Lide3), are

resprouts of seedlings in the seedling bank that survived the harvest and site preparation, died back to

groundline, and resprouted. Additional recruits to the hardwood category were by seedlings from

acorns and berries. The few Pacific madrone (Arme) plants present in 1977-1978 were all from seed.

The major contributor to the hardwood category was tanoak, which at the end of the study, was

developing rapidly and forming tall, wide clumps of stems. During the study, hardwood density

increased 73 percent (fig. 3), foliar cover expanded more than ten times (fig. 4), and height increased

more than five times (fig. 5).

Shrubs

Plants from almost all species in this category were from seed. The one exception was Pacific poison

oak (Todi), which originated from plants that escaped harvest and site preparation. Mean shrub

density was characterized by a relatively high initial density (9,710 plants per acre) and a steady

increase to 14,351 plants per acre at the end of the study (fig. 6), for a 48 percent gain. Foliar cover of

shrubs expanded from 310 ft2 per acre at the beginning to 10,181 ft2 per acre at the end of the study for

over a thirtyfold increase (fig. 7). Mean shrub height increased from 0.3 feet in 1976 to 1.6 feet in 1980

for more than a fivefold increase (fig. 8). Major contributors to these gains were whiteleaf manzanita

(Arvi4), deerbrush (Cein3), Sierran mountain misery (Chfo), and Pacific poison oak (Todi). Deerbrush

in particular was developing rapidly and forming large clumps of tall stems.

Annuals and Biennials

Plants in this category originated mostly from windblown seeds or from dormant seeds in the soil.

Some species, notably bull thistle (Civu), developed first from windblown seed and then from seed of

the ensuing plants. In contrast, plants of American vetch (Viam) originated from buried seed with

subsequent recruitment from buried seed and seed produced by the plants. In terms of huge numbers

of plants present soon after disturbance, both species were equally successful.

The classical buildup and decline of a biennial invader was illustrated by bull thistle (Civu),

whose seeds blow in on the wind, germinate in the fall, result in plants that overwinter as a rosette,

Figure 6—Density of five categories of vegetation, Challenge Experimental Forest, 1976-1980. Standard errors for

shrubs ranged from 350 to 421 plants per acre in a given year; for annuals, from 197 to 1,268; perennials, from 74 to

360; for graminoids, from 92 to 489 plants per acre.

70,000

60,000

50,000

40,000

30,000

20,000

10,000

0

Plants/acre

1976 1977 1978 1979 1980

_

_

_

_

Year

Shrubs Annuals Perennials Graminolds Fern
USDA Forest Service Res. Paper PSW-RP-239. 1999. 17

Figure 8—Height of five categories of vegetation, Challenge Experimental Forest, 1976-1980. Standard errors for

shrubs ranged from 0.1 to 0.3 foot in a given year; for annuals, from 0.1 to 0.2; perennials, from 0.1 to 0.2; and for

graminoids, from 0.2 to 0.4 foot.

Figure 7—Foliar cover of five categories of vegetation, Challenge Experimental Forest, 1976-1980. Standard errors

for shrubs ranged from 11 to 443 ft2 per acre in a given year; for annuals, from 7 to 144; perennials, from 2 to 17; and

for graminoids, from 5 to 128 ft2

 per acre.

12,000

10,000

8,000

6,000

4,000

2,000

0

Cover (ft2/acre)

1976 1977 1978 1979 1980

Year

Shrubs Annuals Perennials Graminolds Fern

2.5

2

1.5

1

0.5

0

Height (ft)

1976 1977 1978 1979 1980

_

_

_

_

Year

Shrubs Annuals Perennials Graminolds Fern
18 USDA Forest Service Res. Paper PSW-RP-239. 1999.

bolt in early spring, grow tall, produce thousands of seeds, and die. The population peaked in 1977

and 1978, and then typically collapsed (table 3) (McDonald and Tappeiner 1986, Randall 1990).

Plants of other species from all but the hardiest of propagules had a difficult time becoming established

in these years (fig. 9).

The density of annuals and biennials began with fairly high numbers, increased almost fivefold by

the end of 1977, and again increased (67 percent) in 1978 (fig. 6). Almost a 39 percent decrease

characterized 1979 as the mean density of bull thistle (Civu), riverbar birdfoot trefoil (Lode), and

American vetch (Viam) fell dramatically. Over 60,000 plants per acre were present in this category in

1980 due largely to increases in density by many species, including Epilobium paniculatum (Eppa2),

smooth catsear (Hygl2), prickly lettuce (Lase), grassy tarweed (Magr3), rod wirelettuce (Stvi2), and

American vetch (Viam). Foliar cover peaked in 1978 at 4,233 ft2 per acre and declined to 2,668 ft2 per

acre in 1980 (fig. 7). Mean height of annuals and perennials ranged from 0.4 feet to 1.2 feet during the

study (fig. 8).

Perennials

Most perennial species in this study originated from both seeds blown in on the wind or those from the

seedbank in the soil. For the first 4 years, density was dominated by dwarf checkermallow (Sima2) and

Trientalis latifolia (Trla6) and then in 1980 by Trla6, bigflower agoseris (Aggr), and hairy catsear

(Hyra3) (fig. 6). Dwarf checkermallow also was a major contributor to foliar cover during the first 4

years, with bigflower agoseris and Bolander’s bedstraw (Gabo) contributing most in 1980 (fig. 7). The

tallest perennials were composed of different species almost every year and ranged from 0.1 to 1.5 feet

tall in year 1 to 0.3 to 1.6 feet in 1980 (fig. 8).

Graminoids

When the study began, the graminoids consisted of one grass (Orcutt’s brome [Bror2]) and one sedge

(Casp). Together, their density was 1,170 plants per acre. This value increased steadily, so that by the

end of the study the density of the six graminoids was more than 16,000 per acre (fig. 6). Foliar cover

likewise increased steadily from 30 ft2 per acre to 1,866 ft2 per acre at the study’s end (fig. 7). Mean

height increased from 0.6 to 2.3 feet during the study (fig. 8).

Bracken Fern

Western bracken fern (Ptaq) is found from the Arctic Circle to the Equator and is common on every

continent (Minore 1966). It is particularly adapted to disturbed areas, but retains a presence in all

stages of succession. The density of this species began fairly high (3,760 stems per acre), increased

dramatically to more than 10,200 stems per acre in 1977, flattened out in 1978 (10,333 per acre), and

then declined the next 2 years (fig. 6). At the end of the study, bracken fern density was 7,883 stems per

acre. Foliar cover began at 350 ft2 per acre, increased through three growing seasons to 1,517 ft2 per

acre, and then declined to 1,067 ft2 per acre at the end of the study (fig. 7). Mean height began at 0.8

foot and increased slowly to 1.1 feet at the study’s end (fig. 8).

The Plant Community

Density of all plant species was 24,860 plants per acre after one growing season, increased through the

third growing season to 91,631 plants per acre, declined the fourth season to 71,167 per acre, and then

increased to 112,408 plants per acre at the end of the study. Foliar cover increased each year from 950

ft2 per acre to 17,433 ft2 per acre at the study’s end.

When each category of species is presented for each descriptive characteristic and illustrated as a

proportion of the total of that characteristic each year, the changing nature of the plant community is

more apparent (figs. 10, 11).

On the virtually bare ground representative of the study area in fall 1976, the shrubs, annuals and

biennials, and ferns dominated in terms of number of plants (fig. 10). By 1977, more than half of all the

plants in the total community were annuals and biennials—a condition that continued throughout the

study. Another category whose members increased in density throughout the study was the graminoids.

Density of the conifers and hardwoods was very low compared to the other categories of vegetation.

Density of shrubs and bracken fern declined proportionally as components of the plant community.

In terms of foliar cover (fig. 11), the initial values were largest for bracken fern, shrubs, and

annuals and perennials, and continued as such for the next 2 years. In 1979, foliar cover of the
USDA Forest Service Res. Paper PSW-RP-239. 1999. 19

F P O

Figure 9—With over 20,000 thistles

per acre using available resources,

most other plant species would find

it difficult to become established.

Challenge Experimental Forest, 1977.

graminoids became larger than that of the fern. The large increase in shrub cover was also notable in

1979 when it amounted to more than 59 percent of that in the total plant community—a proportion

that continued in 1980. In the last 2 years of the study, foliar cover of the hardwoods and graminoids

was increasing, and that of the perennials was low and virtually stable. Foliar cover of the annuals and

biennials was characterized by a buildup in 1977 and 1978, followed by a major decline in 1979, and a

slight increase in 1980. The proportion of foliar cover contributed by the conifers was very low.

Of the species present during the study, 31 percent never had more than 0.5 ft2 of cover.

Conversely, after the first year, less than 25 percent of the species present contributed over 90 percent

of foliar cover.

In terms of height, and by definition “average dominant height,” all categories of vegetation were

increasing over time except the perennials (fig. 8). Average dominant height, of course, is lowered by

shorter new recruits, especially in instances where only one or two plants are present. Although many

species indicated a propensity to grow tall during the study (table 3), only one category of vegetation,

the graminoids, consistently dominated over all others in terms of vertical development (fig. 8). The

graminoids were also among the four tallest species present in 1977 through 1980 (table 4, fig. 8).

Indeed, in 1978 and 1979, three of the four tallest species in the study were graminoids. Although the

graminoids were taller, their height was leveling off (fig. 8). In contrast, the trend of shrub height not

only was increasing, but at an increasing rate (fig. 8).

Discussion and Conclusions

Before harvest, the study area was covered with a dense mixture of conifer and hardwood trees of many

sizes and age classes, including seedlings and saplings of shade tolerant species. The soil surface was

mostly a dense carpet of needles and leaves with western bracken fern (Ptaq) and Pacific poison oak

(Todi) scattered throughout. Sierran mountain misery (Chfo) also was present in scattered patches.

After harvest and site preparation, the study area consisted of mostly bare ground with small tanoak

(Lide3) and California black oak (Quke) stumps and residual plants of Pacific poison oak and Sierran

mountain misery above ground and western bracken fern (Ptaq) below ground, along with thousands

of dormant seeds in the soil.

These species, plus many more with plants from buried seeds and seeds that blew in on the wind,

quickly invaded the study area. By the end of the first growing season, several categories of vegetation,

including shrubs, annuals, ferns, and grasses, were well represented. None of these categories contained

less than 7,800 plants per acre or a cover of less than 1,000 ft2

 per acre at the end of the study. The

hardwoods also had a foliar cover of over 1,000 ft2

 per acre.
20 USDA Forest Service Res. Paper PSW-RP-239. 1999.

Figure 11—Proportional changes in

foliar cover for the various categories

of vegetation. Challenge Experimental

Forest, 1976-1980.

Figure 10—Proportional changes in

plant density for the various

categories of vegetation. Challenge

Experimental Forest, 1976-1980.

FERN

GRAMINOIDS

PERENNIALS

ANNUALS & BIENNIALS

CONIFERS

HARDWOODS

SHRUBS

1976 1977 FERN

GRAMINOIDS

PERENNIALS

ANNUALS & BIENNIALS

CONIFERS

HARDWOODS

SHRUBS

1978 FERN

GRAMINOIDS

PERENNIALS

ANNUALS & BIENNIALS

CONIFERS

HARDWOODS

SHRUBS

1979 FERN

GRAMINOIDS

PERENNIALS

ANNUALS & BIENNIALS

CONIFERS

HARDWOODS

SHRUBS

1980 FERN

GRAMINOIDS

PERENNIALS

ANNUALS & BIENNIALS

CONIFERS

HARDWOODS

SHRUBS

FERN

GRAMINOIDS

PERENNIALS ANNUALS & BIENNIALS

CONIFERS

HARDWOODS

SHRUBS

1976 1977

FERN

GRAMINOIDS

PERENNIALS

ANNUALS & BIENNIALS

CONIFERS

HARDWOODS

SHRUBS

1978 FERN

GRAMINOIDS

PERENNIALS

CONIFERS

HARDWOODS

SHRUBS

ANNUALS & BIENNIALS

1979 FERN

GRAMINOIDS

PERENNIALS

ANNUALS & BIENNIALS

CONIFERS

HARDWOODS

SHRUBS

1980 FERN

GRAMINOIDS

PERENNIALS

ANNUALS & BIENNIALS

CONIFERS HARDWOODS

SHRUBS
USDA Forest Service Res. Paper PSW-RP-239. 1999. 21

The categories of vegetation that were poorly represented at the end of the study were the conifers

and the perennials. The conifers, which were represented almost entirely by ponderosa pine (PipoP),

had a frequency value that indicated a clumpy distribution (table 3). They also got a late start with none

present until 1977 (table 3). Thus, they began life with heavy competition in many of the most

favorable microsites. Many died. Ponderosa pine seedlings that were alive at the end of the study were

those that occupied small areas free of shrubs, clumps of hardwoods, or high densities of annuals and

graminoids. The short height of the pines also suggests that some were overtopped and growing

slowly. More will die, but those that remain will eventually dominate.

The severe browsing of some shrubs by deer early in the study may actually have aided their

development and dominance potential. Deerbrush and whiteleaf manzanita (Cein3 and Arvi4) seemed

to have benefited by damage to the main stem, which led to the development of multiple stems at an

early age, and increased their potential for higher foliar cover.

 The diversity and development of the perennials in this plant community was puzzling. With 21

species present during the study, and a trend of increasing number of species, this category of plants

was well represented. However, their contribution to the community in terms of density and cover was

relatively small. Not only was their density value at the end of the study only 11 percent of the

community and their cover value only 4 percent, but the trend in density was that of a slow increase,

and cover was flat. Mean height was actually declining. Perhaps the strategy of the perennials is to first

establish a presence, and then await a more suitable environment. Perhaps a condition of being

perennial in the environment of this study is to develop better later. Antos and Halpern (1997) found that

perennials in a recent clear-cutting in western Oregon had greater root development than annuals, suggesting

that this condition probably contributed to their ascendency later in the successional sequence. Previous

work on the Challenge Experimental Forest has shown a high proportion of perennials becoming established

over a longer timespan in a more shady environment (McDonald and Reynolds 1999).

Although the total number of species increased at the end of the study, this gain was limited to the

annuals and perennials. Future increases may be tempered, however, by several factors. The resident

species already are numerous and of many categories, plant density is high, and the height of tanoak

(Lide3) and the shrubs is exploding. Certainly the supply of available resources such as light, nutrients,

and water is diminishing. The resident species probably are inhibiting invasion and establishment by

preempting available space or more specifically by occupying the habitable microsites. This was

readily seen in this study in areas of differing microrelief. Depressions often were occupied by many

plants of several species, while nearby mounds were barren. Resident species also modified the

environment (more shade for example), which in turn inhibited the germination of seeds and the

development of plants that became present.

Sousa (1984) noted that the resources made available by a disturbance are soon exhausted by new

colonists and regrowth of survivors. Further growth often is curtailed. At the end of the study, total

foliar cover was 17,433 ft2 per acre or 40 percent. Plainly, space was available for additional horizontal

development. But, although increasing, the rate of increase decreased each year from 1977 through

1980. Thus, on a site of high quality, such as this, growth may be more slowed than curtailed, at least

during the first 5 years.

 Although it is impossible to establish a definitive successional progression in only 5 years, some

early trends are noteworthy. Tanoak (Lide3) and ponderosa pine (PipoP) will be the most abundant

trees, and whiteleaf manzanita (Arvi4) and deerbrush (Cein3) will be the most abundant and dominant

shrubs. Tanoak and the shrubs will continue to expand rapidly in foliar cover and height and dominate

the plant community for years to come. Ponderosa pine will be scattered in small groups and as single

trees. The annuals and graminoids will be increasingly relegated to small openings among the trees and

shrubs, and the shade-tolerant perennials likely will increase in numbers and density and reside in both sun

and shade environments. Western bracken fern will be present in various amounts almost everywhere.

Consequently, the mode or process of succession is best characterized as “modified”

environmental succession. The dominant species of the near future will be those whose regeneration

strategies result in early dominance. Sprouting shrubs and hardwoods with burgeoning foliar cover

and height are good examples. As the crowns of trees and shrubs close, and the high density of the

annuals and graminoids decrease, more shade-tolerant conifers such as Coast Douglas-fir (PsmeM)

and incense-cedar (Lide) and other tolerant perennials and graminoids will become established. Thus,

succession will occur through environmental modification. It is not classical replacement of one stage

of species by another stage, however, because the first stage will be present for many years. Species of

random origin, especially those from windblown seeds, will not be a major part of the understory plant
22 USDA Forest Service Res. Paper PSW-RP-239. 1999.

community. Plants from the seedbank in the soil will not be a major part of this community either.

However, they will have accomplished their mission because the storehouse in the soil will have been

replenished, and they once again will be poised to take advantage of another disturbance.

As ecology becomes more important in forestry, knowledge about plant species and plant

communities that develop naturally or after a deliberate manipulation is increasingly needed.

Manipulation could be for a variety of reasons: to create a future forest, to provide an economic crop, to

grow plants whose seeds or browse would be critical to wildlife, or simply to have present a broad base

of species and age classes and thus be able to provide amenities and commodities that will be needed in

the future. Data from studies such as this will be invaluable for accomplishing such goals.

References

Antos, Joseph A.; Halpern, Charles B. 1997. Root system differences among species: Root system differences among species: Root system differences among species: implications for early successional changes

in forests of western Oregon. in forests of western Oregon. American Midland Naturalist 138: 97-108. in forests of western Oregon.

Clements, F.E. 1916. Plant succession: an analysis of the development of vegetation. Plant succession: an analysis of the development of vegetation. Carnegie Institute Washington Publication Plant succession: an analysis of the development of vegetation.

242; 512 p.

Daubenmire, R.F. 1968. Plant communities: a textbook on plant synecology. New York: Harper and Row; 300 p. Plant communities: a textbook on plant synecology

Dombeck, Mike. 1997. Concerning criteria for managing healthy forests. Presented before the subcommittee on forests and Concerning criteria for managing healthy forests

forest health, U.S. House of Representatives. March 18, 1997; 13 p.

Egler, F.E. 1954. Vegetation science concepts: I. Initial floristic composition, a factor in old-field vegetation development. Vegetation science concepts: I. Initial floristic composition, a factor in old-field vegetation development.

Vegetatio 4: 412-417.

Gordon, Donald T. 1979. Successful natural regeneration cutting in California true firs. Successful natural regeneration cutting in California true firs. Res. Paper PSW-140. Berkeley, CA: Successful natural regeneration cutting in California true firs.

Pacific Southwest Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture; 14 p.

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

Hickman, James C. 1993. The Jepson manual, higher plants of California. Berkeley: University of California Press; 1400 p. The Jepson manual, higher plants of California

Little, Elbert L., Jr. 1979. Checklist of United States trees (native and naturalized). Checklist of United States trees (native and naturalized). Agric. Handb. 541. Washington, DC: Forest Checklist of United States trees (native and naturalized). 

Service, U.S. Department of Agriculture; 375 p.

Margalef, R. 1963. On certain unifying principles in ecology. American Naturalist 97: 357-374. On certain unifying principles in ecology

McDonald, Philip M.; Fiddler, Gary O.; Meyer, Peter W. 1996. Vegetation trends in a young Vegetation trends in a young conifer plantation after grazing, conifer plantation after grazing,

grubbing, and chemical release. grubbing, and chemical release. Res. Paper PSW-RP-228. Albany, CA: Pacific Southwest Research Station, Forest Service, grubbing, and chemical release. 

U.S. Department of Agriculture; 17 p.

McDonald, Philip M.; Lahore, Lona F. 1984. Lumbering in the Northern Sierra Nevada: Lumbering in the Northern Sierra Nevada: Lumbering in the Northern Sierra Nevada: Andrew Martin Leach of Challenge

Mills. The Pacific Historian 28(2): 18-31. Mills.

McDonald, Philip M.; Reynolds, Phillip E. 1999. Plant community development after 28 years in small group-selection

openings; openings; 30 p. Manuscript on file at the Pacific Southwest Research Station, Redding, CA. openings; 

McDonald, Philip M.; Tappeiner, John C., Jr. 1986. Weeds: life cycles suggest controls. Weeds: life cycles suggest controls. Journal of Forestry 84(10): 33-37. Weeds: life cycles suggest controls. 

Minore, Don. 1966. The growth of The growth of Pteridium aquilinum (L.) Kuhn var. (L.) Kuhn var. pubescens pubescens in relation in relation to geographic source, soil to geographic source, soil

nutrients, and forest site. nutrients, and forest site. Corvallis: Oregon State Univ.; 96 p. Ph.D. Dissertation. nutrients, and forest site.

Odom, Eugene P. 1969. The strategy of ecosystem development. Science 164:262-270. The strategy of ecosystem development

O’Hara, Kevin L.; Seymour, Robert S.; Tesch, Steven D.; Guldin, James M. 1994. Silviculture and our changing profession. Silviculture and our changing profession.

Journal of Forestry 92(1): 8-13.

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

Res. Paper PSW-128. Berkeley, CA: Pacific Southwest Forest and Range Experiment Station, Forest Service, U.S.

Department of Agriculture; 9 p.

Randall, John M. 1990. Establishment and control of bull thistle (Cirsium vulgare) in Yosemite Valley. ) in Yosemite Valley. In: van Riper, C. III; ) in Yosemite Valley. 

Stohlgren, T.J.; Veirs, S.D. Jr; Hillyer, S.C., editors. Examples of resource inventory and monitoring in National Parks of

California. Proceedings of the 3rd biennial conference on research in California’s National Parks; 1988 September 13-15;

Davis, CA; 177-193.

Rietveld, W.J. 1992. Conservation forestry: an idea whose time has come, again. Tree Planter’s Notes 43(3): summer Conservation forestry: an idea whose time has come, again

(unpaginated).

Salwasser, Hal. 1992. An ecosystem perspective for managing the National Forests and Grasslands. An ecosystem perspective for managing the National Forests and Grasslands. Presented at the Blue An ecosystem perspective for managing the National Forests and Grasslands.

Mountains Biodiversity Conference, Walla Walla, WA, 1992, May 29; 16 p.

Smethurst, P.J.; Nambiar, E.K.S. 1990. Effects of contrasting silvicultural practices on nitrogen supply to young radiata pine. Effects of contrasting silvicultural practices on nitrogen supply to young radiata pine.

In: Dyck, W.J.; Mees, C.A., editors. Impact of intensive harvesting on forest site productivity. IEA/BE T6/A6 Rep. 2. Forest

Research Institute, Rotorua, New Zealand; 85-96.

Sousa, Wayne P. 1984. The role of disturbance in natural communities. Annual Review Ecological Systems 15: 353-391. The role of disturbance in natural communities

Thomas, Jack Ward. 1994. New directions for the Forest Service. Statement to members of several committees in the U.S. New directions for the Forest Service

House of Representatives; 14 p.

U.S. Department of Agriculture. 1994. Plants of California—alphabetical listing. Report 5. Plants of California—alphabetical listing. Report 5. USDA Soil Conservation Plants of California—alphabetical listing. Report 5.

Service; 274 p.

U.S. Department of Agriculture. 1997. Ecological subregions of California, section and subsection descriptions. Ecological subregions of California, section and subsection descriptions. Chapter 9. R5- Ecological subregions of California, section and subsection descriptions.

EM-TP-005. San Francisco, CA: Pacific Southwest Region, USDA Forest Service; p 6.

Wagner, Robert G.; Zasada, John C. 1991. Integrating plant autecology and silvicultural activities to prevent forest vegetation

management problems. management problems. The Forest Chronicle 67(5): 506-513. management problems. 
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EnvironmentEarly Vegetation in a Small Clear-cutDiversity, Density, and Development of