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Composition, Function, and Structure of

Old-Growth Douglas-Fir Forests

Jerry F. Franklin and Thomas A. Spies

Authors

JERRY F. FRANKLIN is chief plant ecologist, U.S. Department of Agriculture, Forest Service, Pacific Northwest

Research Station, and Bloedel Professor of Ecosystem

Analysis, College of Forest Resources AR-IO, University of

Washington, Seattle, Washington 98195. THOMAS A. SPIES

is a research forester, U.S. Department of Agriculture, Forest

Service, Pacific Northwest Research Station, Corvallis,

Oregon 9733 1.

Abstract

Ecological characteristics of old-growth Douglas-fir forests

are examined in terms of compositional, functional, and

structural features. Old-growth forests typically include distinctive animal and plant species-that is, organisms that are

most abundant in such forests. Functional behavior of oldgrowth forests differs from functional behavior under other

forest conditions. Productivity is typically high, but most

energy is used to maintain the large mass of living material;

growth and mortality are in approximate balance over long

periods. Nutrient and sediment yields from old-growth

forests are typically very low. Old-growth forests also differ

from younger forests in their effects on hydrologic cycles in

areas where cloud or fog precipitation, rain-on-snow events,

or both are important. The structural characteristics of oldgrowth forests are the basis for most of their unique compositional and functional attributes. Specifically, important

structural components are large individual old treeswhether live, dead and standing (snags), or dead and fallen

(logs)-in both terrestrial and associated aquatic environments. Old-growth forests also have stand attributes that are

very different from younger and, especially, from managed

forests. The distinctive communities of microbes, invertebrates, higher plants, and animals that occur in old-growth

forests are integrally related to the collective structural

attributes.

Introduction

In the Pacific Northwest, the term “old-growth forests”

typically connotes stands 200 to over 1000 years of age that

contain large, coniferous trees, especially Douglas-fir. Such

forests once covered millions of acres, but have been drastically reduced by logging and other forest clearing (Marcott

and others, this volume; Morrison 1988). The remaining

acreage is in high demand for a variety of conflicting uses,

such as a source of merchantable logs and as habitat for

animals and plants. As a result, the disposition of unreserved

old-growth Douglas-fir has recently become very

controversial.

A clearer understanding of the major ecological characteristics of old-growth Douglas-fir forests is relevent to the

ultimate resolution of this controversy. Until about 20 years

ago, little was known about the ecological nature of these

forests. For example, foresters and wildlife managers have

sometimes referred to old-growth stands as “cellulose

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cemeteries” and ‘biological deserts.” Research over the last

two decades has dispelled such notions, however, and provided insights into the distinctive ecological qualities of

old-growth forests. Scientific studies, sponsored largely by

the National Science Foundation (for example, Edmonds

1982, Franklin and others 1981) and, more recently, the

USDA Forest Service’s Old-Growth Forest Wildlife Habitat

Program (this volume), have documented many important

differences between younger and older forests and, especially,

between managed and unmanaged forest ecosystems.

In this paper, we provide an overview of the key ecological

features of old-growth Douglas-fir forests. Our paper is divided into three sections: composition, function, and structure. Composition receives relatively little attention here,

however, because it is the primary focus of many of the

papers in this volume. We emphasize the structural characteristics of old-growth Douglas-fir forests because they

determine many of the distinctive compositional and

functional features of these forests. Structure is also the

element that foresters manipulate to achieve specific

functional or compositional goals.

Composition

Old-growth Douglas-fir forests are now known to have high

biological diversity in groups as varied as plants (see Franklin

and others 198 1; Spies, this volume), vertebrates (see this

volume), invertebrates (see Moldenke and Lattin, this volume;

Schowalter 1989), and aquatic organisms (see Gregory and

others, in press).

Alpha (species) diversity of both plants and animals is often

highest early in succession before tree-canopy closure occurs,

lowest in the heavily shaded young forest, and recovers to

intermediate as the forest matures and evolves into old

growth (fig. 1). High diversity of plant species early in

succession is a combined result of the survival of forest

species and the addition of weedy generalist species (Halpern

1988, Schoonmaker and McKee 1988); this combination may

also occur with other classes of organisms. Habitats and

environmental resources appear to be relatively limited in a

fully stocked young forest (Spies and Franklin, this volume).

As a result, species diversity, as well as structural and functional diversity, is probably lowest in this stage of forest

development. Old-growth forests contain many highly specialized species, and several of these organisms appear to

have clear preferences for old-growth habitats, based on their

patterns of abundance. Ruggiero and others (1988) have

argued that such preference should be interpreted to reflect a

dependence on that habitat for survival over the long term.

Mammal diversity by forest stage

Herb/brush Young Mature Old growth

Figure I-Generalized relationship of mammal species diversity to

successional stage in Douglas-fir forests.

The major point here is that old-growth forests are biologically diverse ecosystems with several constituent species

that appear to be closely associated with these forests. From

a biological standpoint, such a conclusion is not surprising.

Many species would be expected to become adapted to a

habitat (old-growth forest) that has occupied large areas for

long periods. That some of these species would become

sufficiently specialized to require old-growth conditions for

their survival also seems reasonable.

Function

Function refers to the work that an ecosystem does and the

rate at which it is carried out. Examples of forest ecosystem

functions are production, the capture of the sun’s energy

through photosynthesis and its conversion to organic substances; regulation of nutrient cycling, including accumulation and conservation of nutrients: regulation of hydrologic

cycles; and provision of habitat for organisms. We will

briefly consider production and nutrient and water cycling;

the habitat function of old-growth forests is covered in the

section on old-growth structure.

Production

Old-growth forests are productive ecosystems, fixing and

processing large amounts of solar energy. The huge foliar

surfaces-the greenness-of typical old-growth Douglas-fir

stands makes this evident; trees do not retain leaves that are

respiring more energy than they are fixing through photosynthesis. Stand leaf areas are often very high in old-growth

stands, commonly with 9 to 15 m

2

of leaf surface per square

meter of ground surface. Young stands are typically in the

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range of 6 to 8 m2

 (Franklin and Waring 1980). Individual

old-growth trees may have 60 to 70 million needles with

4000 m2 of leaf surface (Pike and others 1977). Obviously,

such large photosynthetic factories could not be maintained

I if they were failing to support themselves.

Distinguishing between productivity as measured by biologists and that measured by foresters is important. Gross

production in ecological terms is equivalent to the amount of

energy fixed photosynthetically per unit area per unit time.

Ecologists define net primary production as the biomass

increment plus mortality, including litterfall and materials

removed by grazing. Foresters define productivity as wood

biomass increment, which describes only a portion of the

ecosystem’s total net productivity. Comments on the low

productivity of old-growth forests therefore refer only to the

relatively low rates of new wood production. Available data

indicate that productivity of old and young forests is typically

comparable but that the vast majority of production in

old-growth forests is used in respiration and maintenance

(Grier and Logan 1977).

Despite high respiration rates, most old-growth forests appear

to maintain or increase their amounts of wood. Only one

long-term study of timber growth and yield in an old-growth

Douglas-fir forest is available (DeBell and Franklin 1987).

Over 36 years, wood volumes remained constant even though

the stand was subjected to serious attacks by several pests.

Live-tree volume losses were high because of mortality, but

this loss was offset by substantial stand growth. A high

annual wood increment [15.8 m /ha (1582 bd ft/acre)] was

measured in a IO-year study of growth and mortality in a

250-year-old Douglas-fir stand on the Mount Hood National

Forest (Bemtsen 1960). Even an extraordinarily high annual

mortality of 14.1 m3/ha (1156 bd ft/acre) resulting from a

major windstorm and bark beetle outbreak that occurred

during this period failed to completely offset growth.

The conclusion that old-growth forests are generally stable

in biomass or board foot accumulations is logical. That

foresters have long recognized the basic stability of wood

accumulations in old-growth forests is evident in their

expression of “storing wood on the stump.” We have also

begun to realize that significant tree and forest growth occurs

well beyond culmination of mean annual increment (for

example, Williamson and Price 1971). Indeed, by cutting

forests before or at culmination, we are cutting them at the

transition from ecologically young to mature forests; growth

and biomass accumulation are very far from complete at this

Nutrient and Water Cycling

More data are available on the protective functions of oldgrowth forests-their effects on nutrient and water cycling

and on soil erosion-than on any other functional aspect.

Old-growth forest systems are highly retentive of nutrients.

Large amounts are tied up in both living and dead organic

material. Although the release of energy and nutrients from

dead organic materials is often slow, it makes old-growth

forests extremely conservative-nutrients are tightly retained

within the ecosystem. Typically, only small amounts of nutrients leach into the ground water and subsequently appear in

streams (for example, Fredriksen 1972, Sollins and others

1980). Soil erosion is also low in old-growth forests relative

to rates typical of early stages in forest succession (Swanson

and others 1982). The combination of low losses of dissolved

nutrients and of particulate matter results in the high water

quality of old-growth watersheds.

We are learning that old-growth forests have distinctive and

often unexpected effects on hydrologic cycles. At the time of

an earlier synthesis of old-growth characteristics (Franklin

and others 1981), old and young forests were assumed to

have similar net effects on water cycles, but this assumption

has not proved true. One example is in effects on condensation of cloud or fog moisture, In a study at mid-elevations

in the northern Oregon Cascade Range, fog drip from oldgrowth foliage was found to contribute up to 30 percent

(89 cm or 35 in) of measurable precipitation per year (Harr

1982). This discovery came after clearcutting of some experimental watersheds reduced, rather than increased, water

yields. Because old-growth forests typically have deep,

multilayered canopies and comparatively high leaf areas, we

can expect them to be more effective than young forests at

condensing and precipitating moisture and atmospheric

particulates The differences between age-classes will

probably be most profound where low clouds or fog are an

important part of the microclimatic environment.

The snow hydrology of old-growth forests is also distinct

from that of younger stands and, especially, clearcits.

Differences result mainly from a reduction in the potential

for rain-on-snow flood events (Harr 1986). Several factors

are responsible, including reduced snow accumulation in

old-growth stands because of canopy interception, and

protection of accumulated snow from the direct impacts of

warm air masses and rain.

stage.

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Structure

Structural characteristics of old-growth forests are extremely

important whether the concern is with the ecology of these

forests or their management. Many, and probably most, of

the distinctive compositional and functional characteristics of

old-growth forests are a direct consequence of their structural

features (fig. 2). Hence, structure is the key to understanding

the ecosystem dynamics of old-growth forests. Also, structure is what the forest manager can manipulate to achieve

various objectives; this structural manipulation is what

silviculture is about.

Old-growth forests, and unmanaged forests in general, tend

to exhibit high structural diversity. In fact, structural diversity offers some of the strongest contrasts between unmanaged forests and intensively managed, commercial timber

stands. Some key structural elements of old-growth forests

are obvious: wide ranges in tree sizes, including trees of

large diameter and height; deep, dense tree canopies; and

abundant dead wood (Franklin and others 1981, Spies and

others 1988) (fig. 3). Some of these attributes consist of

individual structures (for example, large live trees, large

snags, and large logs) and others are stand attributes (for

example, multiple canopy layers and understory

heterogeneity).

Individual Structural Features

Large live trees, large snags, and large logs are individual

structural features that have been identified as key elements

of old-growth Douglas-fir forests (for example, Franklin and

Spies, this volume; Franklin and others 1981; Maser and

others 1988; Old-Growth Definition Task Group 1986; Spies

and others 1988). We will consider each briefly.

Large old-growth trees-The most conspicuous of the

individual structural components of old growth are the large,

and very old, live trees. These old trees are typically Douglasfir, although many other species-such as western redcedar,

Sitka spruce, and noble fir-may play similar roles depending on site conditions and stand history. Although size varies

with site conditions and age, old-growth Douglas-fir trees are

very large, with diameters of 1 to 2 meters and heights of

50 to 90 meters. Because individual trees are often 350 to

750 years old, their long and unique histories give them

highly individual forms, in contrast to the uniformity of

trees in young (40-80 yr) or mature (80-250 yr) stands.

The large, deep, irregular crown, that is characteristic of

many old-growth Douglas-fir trees, is as ecologically important as the massive trunk. Branches are typically irregularly

distributed and include large, multiple, fan-shaped arrays.

Surfaces of these large branches or branch arrays are covered

by thick organic accumulations, which play important roles

as habitat for both plants and animals.

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I Compositional role Functional role

I 1 [ Large down, dead

Figure 2-Relationship of some structural components of old-growth forest

to distinctive habitat and ecosystem functions (from Franklin and others

1981).

The large, old, live trees are important contributors to the

distinctive functions of old-growth forests. Canopies are sites

for nitrogen-fixing foliose lichens, such as Lobaria oregana

(Franklin and others 1981). They are also locales for condensation of moisture, precipitation of other atmospheric

materials, and interception of snow. Large trees provide

diverse habitats for a myriad of organisms, including

epiphytic plants, birds, and mammals. Invertebrate communities are especially rich-an old-growth stand may

contain more than 1500 species. A comparative study of

canopy arthropods in an old-growth forest and in an adjacent

plantation illustrates this richness (Schowalter 1989). Sixtyone species occurred in the old-growth canopy and one

arthropod in four (individuals, not species) was a predator

or parasite on another arthropod. In contrast, the plantation

canopy supported only 16 species and only one in a thousand

individuals was a predator or parasite; most individuals were

herbivores, mainly aphids. Large trees also serve the important function of providing a source for the large snags and

logs that are two other important forest structures.

Large snags-Most old-growth forests contain significant

numbers of tall, large-diameter snags >50 cm d.b.h. and

>20 m tall) (Franklin and Spies, this volume; Franklin and

others 1981; Spies and others 1988). Snags have a variety of

functional roles in forests but are probably best known as

essential habitat for many species of vertebrate and invertebrate animals (this volume, Brown 1985, Maser and others

1988, Thomas 1979). Large snags are particularly important

for primary cavity excavators, such as the pileated woodpecker (see Part IV, this volume).

Large logs-Logs are nearly as conspicuous in old-growth

forest stands as are large live trees. In numbers, as well as in

volume and weight of organic matter, they are an important

structural component of natural stands (Spies and others

1988). Large logs typically persist for very long periods-up

to several centuries for some species, such as Douglas-fir and

western redcedar. Logs gradually decompose, undergoing a

variety of physical and chemical changes. For these reasons,

logs are present in a variety of decay states in most natural

stands (Harmon and others 1986).

Large logs are important contributors to the distinctive

compositional and functional features of old-growth stands

(Harmon and others 1986). Logs represent major long-term

sources of energy and nutrients as well as sites for nitrogen

fixation. Logs may also provide physical stability by protecting sites from erosion and other geomorphic processes.

Large woody debris is a dominant element in aquatic ecosystems associated with unmanaged Douglas-fir forests,

controlling the distribution of habitats, providing substrate,

and helping to retain materials within stream reaches.

Large logs provide essential habitat for many plant and

animal species (see Parts V and VI, this volume). In addition

to microbial and fungal species, many vascular plants use

logs as habitat. A classic example is the reproduction of tree

species on rotting logs (“nurse logs”), which is particularly

well represented in the coastal rainforests (Harmon and

Franklin 1988). Invertebrate communities are currently not

well known but certainly include hundreds of species in a

typical old-growth stand. And, as this volume documents,

many vertebrate species use logs as habitat to a considerable

extent.

Stand Structural Features

Old-growth forests also have important stand-scale structural

features. Unfortunately, our emphasis on individual structures

has tended to obscure the existence and importance of such

stand features. We emphasize, however, that the character of

old-growth forests is not reducible to a few individual structures or characteristics.

Tree size-class distributions provide a simple example of

stand-scale structure. Because of the large number of small

trees found in old-growth forests, average diameters and

heights in old-growth stands may be similar to those in

young stands. The range of values, however, is much greater

in old growth, and size-class distributions tend strongly

towards much larger numbers of the smaller trees.

Multiple canopy layers or, more specifically, the continuous

distribution of foliar surfaces from the top of the crown to

the ground, is another stand-scale structural feature. Such

canopy distributions are significant in creating greater

quantities and greater diversity of animal habitat.

Understory heterogeneity is another stand-scale characteristic

that is highly variable in old-growth stands. Understories in

old-growth stands tend to be much patchier than in younger

forest stands. This variability is partially a response to varied

overstory conditions. Gaps are important structural features

of old-growth stands and typically persist for long periods

(Spies and others 1990). Well-developed understories of

herbs, shrubs, and small trees characterize such open habitats,

Heavily shaded sites (“antigaps”), also characteristic of

old-growth forests, produce areas of bare litter from which

green plants may be almost totally absent. Interestingly,

except on dry sites, the distribution of gaps and antigaps in

old-growth stands appears to be controlled primarily by the

canopy density of western hemlock and other shade-tolerant

codominants and not by the canopy distribution of dominant

Douglas-firs.

Any consideration of old-growth forest structure must include

both individual and stand structural features. Better understanding and quantification of the roles of known structural

elements are needed along with basic research designed to

identify additional stand-scale attributes.

Conclusions and Management Implications

Old-growth forests in the Douglas-fir region appear to provide specialized habitat for a unique array of species. These

forests are also very productive in an ecological sense. Major

contrasts in compositional, functional, and structural features

exist between old-growth and managed young-growth stands.

Differences between old-growth and unmanaged younggrowth stands are less pronounced, however, because many

structural features-such as large snags and logs-are carried

over from the old stand to the new under natural disturbance

regimes (Spies and others 1988).

76
Several management strategies can be used to accommodate

plant and animal species associated with old-growth forests

and to sustain old-growth forests as ecosystems. Retaining

existing old-growth forests is, in many respects, the safest

strategy. Much is still unknown about the composition,

structure, and function of these ecosystems. How can we

propose to recreate replicas of existing old-growth forests if

we are still ignorant of many of the parts and how they are

related? Furthermore, the existing old-growth forests are, at

least to some degree, unique products of historical events;

they are thus not completely reproducible. Any approach that

emphasizes preservation of existing old growth must also

include some strategy for replacing the stands that will

inevitably be lost to natural catastrophes, such as fire,

windstorm, and volcanic eruption.

Managing forest stands on long rotations is a second strategy

for maintaining old-growth-like habitats. Natural developmental sequences (Franklin and Spies, this volume) show

that old-growth conditions typically begin to emerge at 175

to 225 years (fig. 4). Silvicultural treatments could accelerate

the development of old-growth structural and compositional

features, such as the presence of large trees and intermediate

canopy layers.

Partial cutting (sometimes referred to as partial or green-tree

retention) is another approach to recreating old-growth-like

forest structures in managed stands (fig. 4c). Cuttings of this

type typically retain 10 to 40 percent of the living trees

(fig. 5), as well as snags and logs. Proposals for this type of

cutting practice have been reinforced by observations of

mixed-age-structure stands (see sere illustrated in fig. 4b),

such as Douglas-fir forests originating after the 1902 wildfires in southwestern Washington and a 1921 blowdown on

the Olympic Peninsula. These naturally developed forests

show that many of the structural elements of old growth can

develop in less than 100 years if large structural “legacies”

remain from the previous stand. Partial cutting can be used

as either a substitute for or supplement to long rotations; that

is, the strategies are not mutually exclusive.

Providing a low density of individual structures, such as

large live trees, large snags, and large logs on clearcut areas

is another strategy. This approach can be used to provide

habitat for animal species that depend on specific types of

structures, such as snags, but are otherwise tolerant of

cutover habitats. Such approaches, which are designed to

provide for a continuing supply of large snags and logs, are

currently being widely applied on State and Federal forest

lands (fig. 6).

Developing sound management strategies obviously requires

dramatically expanded knowledge of natural forest ecosystems and how they work, including but not confined to

old growth. The relationships of forest structure and function

to various plant and animal species are critical and must

include considerations of “lesser” organisms, such as

invertebrates and fungi, as well as the vertebrates. 

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Annual Changes in Seasonal Production of

Hypogeous Sporocarps in Oregon Douglas-Fir

Forests

Daniel L. Luoma

Author

DANIEL L. LUOMA is a research associate, Department of

Forest Science, Oregon State University, Corvallis, Oregon

97331.

Abstract

Sporocarps of hypogeous ectomycorrhizal fungi were harvested from 10 Douglas-fir stands representing a variety of

natural habitats. Results are presented in a landscape context

by assuming that the reported sporocarp production is representative of Western Hemlock Zone forests in the central

western Cascade Range of Oregon. Over all stands, sporocarps were harvested from 5400 m2

 and yielded a total dry

standing biomass equivalent to 1.3 kg per ha. The maximum

single-stand sample biomass equaled 9.9 kg per ha. Fortyseven species of hypogeous fungi were recorded. Elaphomyces granulatus, Gautieria monticola, Hysterangium

coriaceum, Leucogaster rubescens, and Rhizopogon parksii

accounted for 73 percent of the biomass.

In contrast to epigeous species in the study area, hypogeous

sporocarp production was higher in spring than in fall, Individual fungal species showed strong seasonal trends; most had

spring production peaks. Year-to-year variation in relative

biomass for individual species was greater in spring than in

fall. The major species in this study were also major species

in studies from young Douglasfir stands in the Oregon Coast

Range. Gautieria monticola, in particular, seems to be a

widespread dominant species in Western Hemlock Zone

forests of western Oregon.

Introduction

Cooke (1972) defines mycocoenologists as “mycologists

with ecological orientation, [or] ecologists with mycological

interests.” Arnolds (1981) considers a mycocoenological

approach to ecological research as one that usually uses

sample plots (quadrats) to inventory macrofungi in stands of

well-defined plant communities or selected habitats. The

goals of such research are to describe the fungal composition

of a particular plant community and to draw conclusions

about relationships between fungi and vegetation on a

quantitative and qualitative basis.

Vegetation has long been used to assess site quality and to

help identify the importance of various environmental factors

(Cajander 1949). In the Pacific Northwest, quantification and

classification of vegetation in combination with autecological

observations has furthered development of the plant association and habitat type concepts (Daubenmire 1968, Hemstrom

and others 1987, Zobel and others 1976). The prevailing

regional system of plant community classification in the

83
Pacific Northwest greatly facilitated the execution of mycocoenological research by freeing the investigator of the need

to conduct elaborate vegetation studies to classify sample

stands. This study was part of a regional characterization of

Douglas-fir forests from which Spies and others (1988)

provided the habitat classification.

Studies of the community ecology of macrofungi have lagged

far behind those of vascular plants. Several daunting challenges face the would-be mycocoenologist. Arnolds (198 1)

provides a summary of some of these difficulties: fungal

species concepts are often poorly understood and defined;

collections are difficult to identify morphologically and often

require considerable research to reach independent taxonomic

decisions; research is limited to the study of sporocarps (fruiting bodies), which are strongly seasonal (Hueck1953), are

subject to yearly variation caused by variable weather patterns, and exhibit varying, largely unknown, rates of decay

and predation; sporocarp production is not necessarily related

to the abundance or activity of the mycelial colony; and,

autecological research is lacking both in the field, where it is

hampered by the concealed nature of the fungal colonies and

in the laboratory where it is constrained by the investigators’

inability to relate the conclusions to field situations with

confidence.

Fungi that produce hypogeous (belowground) sporocarps

(broadly referred to as truffles) pose additional challenges.

The sporocarps are not only hidden from view, but are also

often preferentially sought and consumed by small animals

(Ure and Maser 1982). Although quantitative community

studies of epigeous (fruiting above the ground) fungi have

been reported since at least 1933 (Haas), Fogel (1976) was

the first to provide a quantitative assessment of hypogeous

sporocarp production. Most of the fungal species producing

hypogeous sporocarps are thought to be ectomycorrhizal

(fungi which develop mutually beneficial associations in the

exterior layers of the roots of certain plants) (Castellano and

others 1989; Trappe 1962, 1971). Mycorrhizal fungi act as

extensions of the root system in forest trees and are thus

important to their nutrition (Tmppe and Fogel1978).

Currently, the only practical way to compare the relative

functional importance of species of ectomycorrhizal fungi in

an ecosystem is by estimating sporocarp production. Potential

functional roles of hypogeous species range from essential

symbiosis with the roots of over-story trees (Harley and

Smith 1983) to provision of sporocarps as food for animals

(Vogel and Trappe 1978).

Several recent studies focused on sporocarp production by

hypogeous fungal species in the Coast Range of western

Oregon. Fogel (1976) was the first to quantitatively analyze

the seasonal distribution of hypogeous sporocarps; he used

sporocarp dry weight and number to calculate mid-dates of

fruiting for individual species and populations.

In a 13-month study including the end of a severe winter

drought, Fogel and Hunt (1979) observed a strong fall peak

in total sporocarp dry weight. Fogel (1981) reviews techniques for quantifying hypogeous sporocarps and correlates

sporocarp production with temperature and moisture. Hunt

and Trappe (1987) point out that documenting all species of

hypogeous fungi in a forest stand requires longterm collecting over several years. Underestimation of species richness

due to small stand samples and infrequent fruiting of some

species was noted by Hunt and Trappe (1987). After 32

months of collection with a total sample area of 1536 m2

,

their species-area curve still had not stabilized.

The cited studies were confined to single, similar, secondgrowth Douglas-fir stands on Marys Peak in the Oregon

Coast Range, which had all developed over 35 to 65 years

after clearcut logging and burning. An obvious need existed

to characterize the occurrence of hypogeous sporocarps in a

landscape context from a variety of natural habitats over a

wider forest area.

This research aims at broadening the data on year-to-year

changes in the seasonal distribution of sporocarp production

and reports the sporocarp abundance of major species

(Hering 1966) of hypogeous fungi found in 10 forest stands

in the H. J. Andrews Experimental Forest (Oregon Cascade

Range physiographic province). Standing crop sporocarp

biomass was measured within five Douglas-fir forest habitats

covering a range of moisture- and age-classes. To obtain a

representative sample of the major species and to document

the differences in sporocarp production that are largely induced by yeartoyear changes in weather patterns, the study

spanned a 4-year period. Seasonal variation in fruiting

pattern was anticipated through intensive spring and fall

sampling. The following specific objectives were addressed:

identification of the major fungal species that produce

hypogeous sporocarps in Douglas-fir stands typical of the

central Oregon Cascades; characterization of the seasonal

fruiting aspect as determined by the major species; and

determination of yeartoyear changes in the seasonal distribution of each major species as measured by sporocarp

biomass.

Materials and Methods

Study Area

The H. J. Andrews Experimental Forest occupies the 6400-ha

drainage of Lookout Creek, a tributary of the McKenzie

River (see frontispiece). Elevations range from 420 to

1630 m. The area is typical of the western slopes of the

central Cascade Range in Oregon. The experimental forest

84
has been administered by the USDA Forest Service as part of

the Willamette National Forest for scientific, educational,

and management purposes since its establishment in 1948.

A cool-summer Mediterranean climate prevails in the study

area. Average annual precipitation ranges from about 2300 to

2800 mm, depending on topography. About 90 percent of the

precipitation occurs from October through April; summers

are dry. Above 900-m elevation, winter snowpacks accumulate to a depth of 1 m or more. Temperatures are moderate

and range from -2 (mean January minima) to 28 oC (mean

July maxima). Potential evapotranspiration exceeds

precipitation from mid-May to September (Bierlmaier and

McKee 1989, Franklin and Dyrness 1971).

Inceptosols dominate the three general soil types that are

characteristic of the experimental forest (Bemtsen and

Rothacher 1959, Brown and Parsons 1973, Dymess and

others 1974, Franklin and Dymess 1973). Steeper slopes and

ridgetops often support a residual Brown Podzolic gravelly

clay loam formed from andesite or basalt. Residual Reddish

Brown and Yellowish Brown Lateritic silty clay loams associated with breccia and tuff parent material are commonly

found on midslopes. Gentle slopes and benches are often

occupied by a colluvial clay loam.

The study area lies generally within the Western Hemlock

Zone of Franklin and Dymess (1973). Studies of forest communities within the Western Hemlock Zone reveal a generalized pattern of occurrence along a moisture stress gradient

(Zobel and others 1976). Characteristic understory vascular

plant species are used to describe the community types. For

example, abundant sword fern and Oregon oxalis typify moist

sites. Mesic sites may be occupied by Oregongrape and Pacific rhododendron. Towards the dry end of the scale, salal

increases in dominance. The driest sites capable of supporting forest vegetation are occupied by plant communities of

the Douglas-fir series. In these communities, Douglas-fir is

often considered climax and oceanspray is an important

shrub (Hemstrom and others 1987). A temperature gradient

reflecting elevation is also noted (Zobel and others 1976).

The coolest extreme is represented by the Western HemlockPacific Silver Fir/Twinflower association, transitional to associations in the Pacific Silver Fir Zone.

Sampling

Ten Douglas-fir forest stands were selected for sampling by

age and moisture status. Age-classes were <80,80 to 199,

and 2200 years of age and are referred to in this paper,

respectively, as young, mature, and old-growth. Relative

moisture-classes prevailing at these sites were identified by

generalized vascular plant habitat or community types by

Spies and others (1988).

Five habitat combinations were selected (wet old-growth,

mesic old-growth, dry old-growth, mesic mature, and mesic

young); two stands of each were sampled. Each stand, occupying about 5 ha of relatively homogeneous forest, represented a subset of typical stands originally located by other

researchers as part of a regional forest characterization (Spies

and others 1988). Stand locations (see frontispiece) and

selected descriptive characteristics of each stand (table 1) are

presented.

Stands were sampled in each season over 6 to 7 weeks. In

spring, stands on lower elevation south slopes were sampled

first, those on higher elevation north slopes last. We thereby

condensed the sample period relative to temperature and

moisture conditions that strongly influence fruiting. The fall

sampling strategy was reversed with stands on higher, northerly slopes sampled first. Field work was initiated in the

spring of 1983 and continued through spring of 1986.

Hunt and Trappe (1987) note the difficulty in determining

adequate sampling size and sampling procedures for hypogeous sporocarps because fruiting differs so much by species

and abundance in time and space. Additionally, Fogel(1976,

1981) and States (1985) report the clustered distribution of

fruit bodies. Accordingly, welldistributed small plots were

used in the conduct of this study.

For each stand sample, sporocarps were harvested from 25

circular 4-m2 plots for a total sample area of 100 m2. Plots

were placed systematically about every 25 m along three

transects running parallel to the slope contour and spaced

about 75 m apart. New transects were established for each

stand sample; no plots were resampled. In western Oregon

conifer forests, most hypogeous sporocarps are produced at

or above the mineralorganic soil interface (M. Castellano,

G. Hunt, D. Luoma, J. Trappe, pers. obs.). In each plot, the

forest floor was raked back to a 5- to IO-cm depth, thereby

exposing sporocarps in the upper soil layers. The number of

sporocarps from each collection in a plot was recorded. In

the laboratory, sporocarps were identified to species, dried in

a dehumidifier cabinet set to maintain <l5 percent relative

humidity, and weighed to the nearest 0.01 g to determine

biomass. Major species are those with 25 percent of the total

biomass in the study (Hering 1966).

The terms “dominant” and “subdominant” within categories

refers to sporocarp biomass as an indicator of a species’ importance relative to other species. Cooke (1955) measured

the dominance of epigeous sporocarp by estimating fruiting

body volume, and concluded his measure had “physiognomic

rather than competitive significance.” Cain and Castro (1959)

note that the term “dominance” is applied to different phenomena but argue against restrictive meanings because the

85
Table 1Selected characteristics by habitat of 10 Douglas& stands, II. J. Andrews Experimental 

Forest. Oreeon 

WOG 2 450 81 280 41 

3 450 101 526 19 

MOG 15 450 146 392 8 

17 450 108 670 13 

DOG 25 200 49 443 55 

29 200 47 163 52 

MUM 36 130 71 408 33 

90 84 38 433 25 

MY 48 69 58 1410 48 

86 79 52 1535 59 

differences are clear enough in co&?xt. Dominance (also coand subdominance) of a species indicates predominance as 

expressed by some measure that may or may not reflect 

ecological influence in the dynamics of the community. 

The term “stand sample” refers to the total 100-m’ collection 

area (Cram 25 plots) for a given stand at a give” seasonal harvest in a given year. This report uses data collected from 54 

stand samples over 4 years, 28 stand samples in spring and 

26 in fall. Seasons were defined by equinox and solstice calendar dates. Twelve stand samples were taken in wet old 

growth, 10 in mesic old growth, 12 in dry old growth, 8 in 

mesic mature, and 12 in mesic young habitats. 

Analysis 

Because of the unequal number of stand samples in the 

various seasonal categories, sporocarp biomass values were 

standardized to equivalent biomass, expressed in grams per 

hectare, and used to report seasonal results and relative 

values. The total biomass for a species in a category was 

divided by the appmpriate fraction of a hectare sampled in 

that category to obtain equivalent biomass. Relative annual 

biomass of each species by season was calculated as a 

percentage of a species’ total seasonal biomass (equivalent 

g/ha within each year). 

Results 

Total sporocarp production 

Sporocarps were harvested from 5400 m* and yielded a dry 

weight biomass of 697 g, equivalent to a standing biomass of 

1.3 kg per ha. The maximum single-stand-sample total biomass was 99 g dry weight or 9.9 kg per ha. Forty-seven 

species of hypogeous fungi were recorded during the study. 

Fourteen species accounted for 94 percent of the total biomass. Five major speciesE@homyces granulates Fr., 

Gautieria monficola Harkn., Hysterangium co&cum Hesse, 

Leucogmer rubescens Zeller & Dodge, and Rhiropogon 

pa&ii SmitLaccounted for 73 percent of the biomass. 

Year-to-year variation 

Spring fruiting was dominated by a different fungus each 

year: Hysrerangium coriaceum in year one, Gautieria 

vwnticola in year two, and Elaphomyces granulatus in 

year three (table 2). Eighty percent of the spring biomass 

of Elaphomyces granulatus in year three was attributable to 

one extreme stand sample of 99 g. This value represents a 

particularly Qxeresting outlier because it was obtained from 

a single 4-m plot containing 54 sporocafp~ If a more 

“reasonable” (for this sample size, 1000 m ) stand-sample 

value of 35 g for E. granulatus were assumed, then 

Gautieria would have been the spring biomass dominant in 

year three also. Elaphomyces granularus was a subdominant 

in year two. Rhiropogon parksii was not found in spring. 

Fall sporocarp production was dominated by Rhizopogon 

parkrii with >50 percent of the total biomass (table 2) in all 

years. I” each year, one stand sample contributed a large 

proportion of R. parksii’s fall biomass (29, 36, and 70 

percent in years 1, 2, and 3, respectively). EIaphomyces 

granularus was a fall subdominant in years one and two. 

Leucogawr rubescens was a fall subdominant in year three. 

Hysterangium coriaceum was not found in fall. Year one, 

with the least biomass, had relatively equal distribution of 

fall and spring biomass (table 2). 

86 
Table Z-Annual sporocarp biomass (equivalent g per ha) of maJor species by season in a 5400-m’ 

total sample from 10 Douglas-fir stands, HJ. Andrew Experimental Forest, Oregon 

YEAR 1 YEAR 2 YEAR 3 

SpIiIlg Fall SP+? Fail spring Fall 

(n=S) (n = 8) (n = 10y (n=9) (n = 10) (II = 9) 

65 109 231 82 1234 87 

4 30 790 19 525 19 

293 142 80 

10 u 84 43 13 131 

170 672 491 

372 330 1247 917 1852 728 

351 1091 1319 

The yearly proportion of each species seasonal sporccarp biomass is shown (figs. 1, 2). Variation in relative biomass from 

studies of hypogeous sporocarp production were confined to 

ywtoyear for individual species was greater in spring than 

single stands (Fog4 1976, Fogel and Hunt 1979, Hunt and 

in fall. Three spring species had one year with >60 percent 

Trappe 1987). Their major goals were to quantitatively 

of their total seasonal biomass. In fall, only Rhiropogon 

estimate sporocarp production, to determine phenology of 

parksii had such a strong single-year dominance. 

production, and to characterize the hypogeous fungal-species 

community composition. 

Discussion 

This paper seeks to put the results in a landscape perspective 

by generalizing seasonal sporccarp production as being representative of Western Hemlock Zone forests in the central 

Cascade Range of Oregon. The most extensive previous 

Fogel(1976) and Hunt and Trappe (1987) show that sporocarp biomass production of single species differs from year 

to year. In a 3.year study with small (50-m’) monthly samples, Fog4 (1976) had four major species in common with 

this study. The species and biomass ranges of the annual 

x7 
standing crop were as follows: Elaphomyces granulatus,

0 to 90 g per ha; Gautieria monticola, 13 to 432 g per ha;

Hysterangium coriaceum (as H. separabile Zeller), 294 to

572 g per ha; and Rhizopogon parksii, 89 to 252 g per ha.

Other major species of Fogel’s (1976) study include:

ffymenogasterparksii Zeller & Dodge, 76 to 435 g per ha;

Hysterangium setchellii Fischer (as H. crassum [Tul. & Tul.]

Fischer), 517 to 1206 g per ha; Truncocolumella citrina

Zeller, 30 to 2336 g per ha; and Tuber spp., 0 to 380 g per

ha. Hysterangium setchellii and Truncocolumella citrina

were moderately important, while Hymenogaster parksii and

Tuber spp. were minor species in Luoma (1988).

Fogel (1976) provides seasonal information on Hysterangium

coriaceum by reporting fruiting period (monthly range) and

mean calender day of fruiting with number of days standard

deviation. Hysterangium taxonomy was not well known at

the time of his study so that H. separabile is the species reported and may not entirely equate with what is now accepted as H. coriaceum. Fogel(1976) made collections of

H. separabile throughout the year and lists it as an “opportunistic” species. The mean fruiting date, however, in each of

3 years was in April with a standard deviation of 11 daysthe smallest of the eight species reported. Fogel(1976) lists

Rhizopogon parksii as a characteristic fall species.

Data from Dinner Creek, Oregon (Fogel and Hunt 1979, Hunt

and Trappe 1987), gathered over 2 years, revealed five major

species. Three-Gautieria monticola, 8 to 85 g per ha;

Leucogaster rubescens, 316 to 338 g per ha: and Rhizopogon

parksii, 116 to 463 g per ha-were also major species in the

current study. Two-Leucophleps magnata Harkn., 21 to

189 g per ha; and Truncocolumella citrina, 0 to 749 g per

ha-had moderate importance in Luoma (1988).

Hunt and Trappe (1987) sampled sporocarp production in a

1.5-ha stand for 21 months. Monthly production was estimated from twelve 4-m2 plots. Major species in common

with the present study were Gautieria monticola, 769 to

1527 g per ha and Hysterangium coriaceum, 106 to 204 g

per ha. Other major species were Hysterangium setchellii,

746 to 842 g per ha and Melanogaster sp. nov., 108 to 225 g

per ha.

Hunt and Trappe (1987) also report fruiting middate mean,

and standard deviation for selected species. Over 2 years,

Hysterangium coriaceum was collected from February to

December but its middate was in April with a standard

deviation of 8 days. Rhizopogon parksii was found only

from September to December.

In this study, total spring equivalent biomass ranged from 0.4

to 1.8 kg per ha. These values were consistently greater than

or equal to the fall range of 0.3 to 0.9 kg per ha (table 2) and

contrast with Fogel and Hunt’s (1979) marked fall biomass

peak in the 1st year of sampling at Dinner Creek. Hunt and

Trappe (1987) found comparable biomass between spring

and fall during the 2d year of sampling at Dinner Creek.

Fogel(1976) reports that spring and fall biomass were comparable but data in Hunt and Trappe (1987) show that Fogel

had a marked spring biomass peak in each of 3 years. The

single-sample maximum biomass of 9.9 kg per ha reported

here supplants the unpublished values (1.4, 1.7 kg per ha) of

Luoma and Hunt cited in table 6 of Hunt and Trappe (1987).

Total sporocarp biomass was substantially less in both spring

and fall of year one compared to the other years. The low

spring values may have been influenced by record high temperatures in May 1983. A 14-day period with only a trace

of rain encompassed 12 days in which high temperatures

reached more than 25 oC (mean monthly high = 18.7 oC) and

included the highest May temperature (40oC) recorded at the

H. J. Andrews station. Low sporocarp production in fall was

coincidental with well below average September and October

precipitation in 1983 (Bierlmaier and McKee 1989; F.

Bierlmaier, unpubl. data).

Year one had the maximum production for one species in

spring and another species in fall (figs. 1.2). Year two

showed highest relative sporocarp biomass for two species

in spring and two species in fall. One species had maximum

spring biomass and one species had maximum fall biomass

in year three. Hysterangium coriaceum was not found in the

fall and Rhizopogonparksii was not found in spring; otherwise, no strong trends were in these data. In this data set, a

single year with maximum relative biomass of two species

occurring in the same season is the nominal distribution.

Year two had both such species maximums for spring and

fall.

Weather patterns (particularly the timing and duration of

drought periods) likely account for much of the yeartoyear

seasonal variation observed in this and other studies (Fogel

1981). Although it is ecologically meaningful for a given

year, such variation detracts from attempts to characterize

general trends in importance or dominance (as measured by

sporocarp biomass) by season and habitat. Such a characterization will be presented elsewhere in the scientific literature

(Luoma and others, in press).

88
Conclusions

Relatively few species (five) of hypogeous fungi accounted

for most of the total biomass (73 percent). Many species

showed strong seasonal variation in relative biomass production. For the major species, spring had greater year-to-year

variation in sporocarp production and higher total biomass

production than did fall. The range of standing biomass

values for the species reported in this study is similar to

the values reported for hypogeous sporocarps by other

researchers. All of the major species in this study were

also major species in one or more of the studies from

young Douglas-fir stands in the Oregon Coast Range

(Fogel 1976, Fogel and Hunt 1979, Hunt and Trappe

1987). In Western Hemlock Zone forests of western Oregon,

Gautieria monticola seems to be a widespread sporocarp

dominant, Hysterangium coriaceum a predominantly spring

species, and Rhizopogon parksii characterizes the fall fruiting

aspect. In contrast to epigeous mycorrhizal fungi, hypogeous

sporocarp production is generally higher in spring than in fall

(Fogel 1976; Hunt, unpubl. data).

Acknowledgments

The research was supported by and done in cooperation with

the Pacific Northwest Research Station, Forestry Sciences

Laboratories in Corvallis, Oregon, and Olympia, Washington.

R. Molina provided assistance, guidance, and use of facilities;

his help is greatly appreciated. This project was initiated by

G. Hunt in spring 1983. I would especially like to thank J.

Eberhart, J. Chamard, and M. Seidl for providing technical

assistance. R. Frenkel, J. Trappe, and B. G. Smith generously

provided direction in many ways. M. Castellano shared his

knowledge of the genus Hyszerangium and provided helpful

comments.

This paper represents a contribution (IIIe) of the project,

“The Fallen Tree-an Extension of the Live Tree.” This

project is cooperative among the U.S. Department of the

Interior, Bureau of Land Management; U.S. Department of

Agriculture, Forest Service, Pacific Northwest Research

Station; Oregon State University, Department of Forest

Science; U.S. Department of Agriculture, Agricultural

Research Service; and Oregon Department of Fish and

Wildlife. 

89
y., WASHINGTON 

0 a” 

&j Crater Lake 

Siskiyou 

Mountains 

OREGON 

‘-=====. 

-4 CALIFORNIA 
The Structure of Natural Young, Mature, and

Old-Growth Douglas-Fir Forests in Oregon and

Washington

Thomas A. Spies and Jerry F. Franklin

Authors

THOMAS A. SPIES is a research forester, USDA Forest

Service, Pacific Northwest Research Station, Corvallis,

Oregon 97331. JERRY F. FRANKLIN is a research forester,

USDA Forest Service, Pacific Northwest Research Station,

and Bloedel Professor of Ecosystem Analysis, College of

Forest Resources, University of Washington, Seattle,

Washington 98195.

Abstract

Structural characteristics of forest overstories, understories,

and forest floor and coarse woody litter accumulations were

related to stand age, geography, and relative site moisture in

196 Douglas-fir stands in western Oregon and Washington.

Stands ranged in age from 40 to 900 years and typically originated after wildfire. A series of multivariate analyses was

used to identify structural attributes that distinguished oldgrowth (>195 years old) from mature (80-195 years old) and

young (40-80 years old) age-classes. Separate analyses of

four attribute sets-overstory, stand condition (degree of

damage and disease), understory vegetation, and forest floor

and coarse woody litter indicated that the age-classes differed

in numerous attributes. Discriminant models that used overstory characteristics, such as tree density, density of large

Douglas-firs, and variation in tree diameter, and models combining variables from the four different attribute sets were

most successful in distinguishing the age-classes. Age-classes

represent portions of a continuous gradient of structural

variation associated with age, based on ordinations with canonical discriminant analysis. Old-growth stands from different geographic provinces and relative site moisture-classes

differ considerably in structure. Much of this variation in oldgrowth structure was associated with variation in densities of

shade-tolerant trees and characteristics of the understory

vegetation. Variation in old-growth-forest structure strongly

suggests that low to moderate disturbance during the life of

the stands has had an important influence on stand structure.

The study provides a basis for defining and taking inventory

of old-growth conditions as well as for managing the natural

diversity of old-growth and earlier successional Douglas-fir

forests in western Oregon and Washington.

Introduction

Douglas-fir forms dense, long-lived coniferous forests that

dominate the mountainous landscapes of western Oregon and

Washington. The structure and habitat quality of these forests

varies greatly as a consequence of forest succession, disturbance, and plant community and environmental factors. The

loss of the habitat structure associated with natural and oldgrowth Douglas-fir forests is a matter of intense public

debate. The range of variability in the ecological structure

of these forests is becoming more and more limited as the

majority of forest lands are committed to short rotations for

wood products. Information about natural Douglas-fir forest

structure, its variability, and the processes that determine it

are needed to identify wildlife habitat relationships, to

91
inventory critical habitat conditions, and to provide management targets for silvicultural manipulations, habitat reserve

areas, and the maintenance of biological diversity.

Little quantitative information has been available on variation

in natural Douglas-fir forests over a wide range of ages.

Franklin and others (198 1) describe the general ecological

characteristics of old-growth Douglas-fir forests. They identify large live trees, large snags, and large logs as major distinctive features of these old ecosystems. Juday (1976) examines the species composition and some structural attributes

in old-growth forests in the Oregon Coast Range. Alaback

(1984) compares the structure of old-growth and secondgrowth western hemlock-Sitka spruce forests in southeastern

Alaska. Most quantitative studies in Douglas-fir forests have

focused on woody-debris components (Agee and Huff 1987,

Graham and Cromack 1982, Sollins 1982, Spies and others

1988) or live tree components (Grier and Logan 1977;

Franklin and DeBell 1988; Spies and others, unpubl. manuscript) in detailed studies of relatively few stands.

The major objectives of this study were to identify distinctive attributes and contrast the ecological structures of oldgrowth, mature, and young Douglas-fir forests; and to contrast the old-growth forest structure of different physiographic

provinces and relative site moisture-classes in western Oregon

and Washington. Several general questions were addressed:

Are overstory, understory, and debris components equally

distinctive among age-classes? Do different structural components change at the same rate and in the same manner

with stand development and succession? How similar is oldgrowth forest structure among site moisture-classes from

different physiographic provinces?

Study Area

Douglas-fir-dominated forests were studied in Washington

and Oregon in three physiographic provinces: the southern

Washington Cascade Range, the Oregon Cascade Range, and

the southern half of the Coast Ranges of Oregon (Franklin

and Dymess 1973). These provinces are characterized by

steep, deeply dissected terrain with well-developed soil.

Parent materials are Tertiary basalts and andesites in the

Cascade Range, and early Tertiary sedimentary rocks in the

Coast Range. The climate is wet in winter and dry in summer. Annual precipitation is heavy, ranging from 800 to over

3000 mm. Highest amounts of precipitation occur near the

upper western slopes of the Coast Range and in the Cascade

Range in Washington and northern Oregon (Franklin and

Dymess 1973). Lowest precipitation occurs on the eastern

slopes of the Coast Range and in the southern Oregon

Cascades.

The study area encompasses two major vegetation zones: the

Western Hemlock Zone and the lower elevational portion

of the Pacific Silver Fir Zone (Franklin and Dyrness 1973).

Western hemlock and Pacific silver fir are the climax species

on most sites in these zones; on dry sites, Douglas-fir may be

climax. In southern Oregon, the northern margin of the Mixed

Conifer Zone was sampled. In the Coast Range, the eastern

margin of the Sitka Spruce Zone was sampled.

Most Douglas-fir stands in the region originated after catastrophic wildfire (Franklin and Hemstrom 1981); see Franklin

and Dymess (1973) for a generalized, natural successional

sequence. Young stands originating from wildfires are typically dominated by Douglas-fir, although western hemlock or

red alder may dominate in some areas. By 200 years, many

stands exhibit old-growth characteristics (Franklin and others

1981, Spies and Franklin 1988), such as codominance of

western hemlock in the overstory, diverse vertical distribution of foliage, and large accumulations of woody debris

(Spies and others 1988). True climax forests are rare because

pioneer Douglas-fir can persist in stands for over 1000 years

(Franklin and DeBell 1988; Franklin and others 1988; Spies

and others, unpubl. manuscript), and wildfires occur more

frequently than 1000 years on most sites.

Methods

General Design

A total of 196 Douglas-fir stands in Washington and Oregon

representing different ages (40 to 900 years) and site conditions were sampled during 1983 and 1984 (see frontispiece).

All stands originated after wildfires, which killed all or nearly

all the overstory trees. We sampled along two gradients: a

chronosequence of Douglas-fir stands on sites with moderate

moisture, and a full range of site-moisture conditions for oldgrowth Douglas-fir stands (>200 years old). Resources were

not available to sample extremes of site moisture for stands

<200 years old. Consequently, the results of the Chronosequence analyses are based only on moderate or mesic sites

(from young through old growth), and site-moisture analyses

are based only on old-growth stands. To maintain a similar

geographic distribution among ages of sampled stands, sampling was concentrated in areas in each province that contained all three of the following broad age-classes: young

(<80 years), mature (80-195 years), and old growth (2195

Ye=N.

Site Moisture Classification

Stands >200 years were tentatively assigned during field

reconnaissance into three broad moisture-classes-dry, moderate, and moist-based on observations of vegetation composition (Franklin 1979, Zobel and others 1976), physiography,

and soils. Dry sites occur on steep upper slopes of southerly

aspects, commonly with skeletal soils. Plant communities of

92