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OCR for page 44
3
OLD GROWTH FORESTS
/NTRODUCT/ON
Issues surrounding old-growth forests are at the very center of discus-
sions about forest management in the Pacific Northwest. Terms such as
"overmature," "late successional," "ancient forest," "forest primeval,"
as well as "old growth," often are used interchangeably, adding to the
confusion of these discussions. Furthermore, public perceptions of what
an old-growth forest is might not jibe with quantitative definitions of
forest scientists and managers (Ribe 1989~.
This chapter describes the attributes that characterize old-growth
forests. Variations among forest types are described with respect to
those attributes, as wed as variations in the age at which forests acquire
particular characteristics after disturbance. The characteristics impart
several unique ecological features of old-growth forests, such as
complexity and high biodiversity, low susceptibility to disturbance, and
mesic microclimate.
WHAT /S VEGETATIVE SUCCESS/ON?
Succession implies structural and compositional change in the species
that dominate a plant community (and frequently an animal community
as well). Fire, wind, disease, and other disturbance processes of varying
intensity and frequency select for adaptions in a landscape's biota,
making some species more resistant to and other species more resilient
to effects of disturbance; some species have evolved to become depend-
44
OCR for page 45
Old-Growth Forests
45
enton disturbance. A landscape can tee viewed as a collection of patches
of varying size and undergoing changes influenced by disturbance, as
well as by the patches that surround it, and at any time, different parts
of a forested lancEscape will be at different successional stages. A Pacific
Northwest forest could comprise an evenly aged stand of red alder that
eventually is replaced by Douglas-fir, which might then be replaced by
hemlock or cedar.
WHAT IS AN 0! D-GROWTH FOREST?
Late-successionai, or late-seral, has commonly referred to forests in
which shade-tolerant tree species, such as western hemlock and grand
fir, begin to attain dominance (Spurr and Barnes 1973~. FEMAT (1993)
defined late-successional quite differently, as the period from first
merchantibility to culmination of mean annual increment. As traclition-
ally defined (e.g., by Spurr and Barnes), late-successional conditions in
Pacific Northwest forests occurred rarely, only after many years in the
old-growth condition and in the absence of significant disturbances that
maintained dominance of less shade-tolerant species (most commonly
Douglas-fir or ponderosa pine). Under FEMAT's definition, however,
late-successional has nothing to do with dominance by shade-tolerant
species, but rather is a stage of development of all forests that occurs
well before, rather than in the later stages of, old-growth conditions.
Unless noted otherwise, our use of late-successional will follow Spurr
and Barnes (1973~.
in the absence of fire or other disturbance, Douglas-fir ~ moderately
moist Westside forests is gradually replaced over many centuries by
shade-tolerant species, most commonly western hemlock. However,
because of intermittent fires, shade-tolerant species rarely replace
Douglas-fir altogether (Agee 1993~. Similarly, frequent fires maintained
dominance by ponderosa pine throughout most of the low- and micl-
elevation forests in the interior of the Pacific Northwest; hence, forests
dominated by shade-tolerant species were a minor component of the
region. Late-successional forests have been more common at higher
elevations in interior Oregon and Washington.
Old-growth forests are forests that have accumulated specific
characteristics related to tree size, canopy structure, snags and woolly
OCR for page 46
46
Pacific Northwest Forests
debris, and plant associations. Ecological characteristics of old-growth
forests emerge through the processes of succession. Certain fea-
tures presence of large, old trees, multilayered canopies, forest gaps,
snags, woody debris, and a particular set of species that occur primarily
In old-growth forests—clo not appear simultaneously, nor at a fixed time
in stand development. Old-growth forests support assemblages of
plants and animals, environmental conditions, and ecological processes
that are not found in younger forests (younger than 150-250 years) or
in small patches of large, old trees. Specific attributes of old-growth
forests develop through forest succession until the collective properties
of an older forest are evident.
The U.S. Forest Service (USES) Old-Growth Definition Task Group
(1986) defined old-growth forests as the third of three basic stages in
forest development. These forest stages are young, mature, and old; or,
as sometimes distinguished by foresters, immature, mature, and
overmature. In
Douglas-fir forests of
the Pacific Northwest,
maturation typically
occurs at 80 to 110
years. The mature
-
torest represents a
relatively stable stage with substantial continued growth and biomass
accumulation, albeit at a slower rate than in the young forest. Transition
from the mature to the oid-growth stage is gradual. Douglas-fir stands
do not begin to show the characteristics usually associated with old-
growth until hey are 175 to 200 years old.
Ecological characteristics of old-growth forests vary from one forest
type to another (Tables 3-1 and 3-2) (Franklin and Spies, 199Ja; Spies
and Franklin, 1991), and therefore, no single definition of old growth is
appropriate. Increasingly, definitions rely on indexes of successional
development based on multiple forest characteristics (e.g., Spies 1991~.
USES interim definitions for all types involve specific values or states for
five criteria—number of large, old trees; variation In tree diameter;
degree of tree decadence; amount of large, dead wood; and characteris-
tics of the canopy architecture (USFS 1993b; Williams 1992~.
· Number of large, old trees. The minimum density of large, old trees
necessary for a stand to qualify as old growth varies from 16 to 50 per
O/~-growth forests are forests that
have accumu/ated specific
characteristics re/atec/ to tree size,
canopy structure, snags ant/ Woody
debris, and plant associations.
OCR for page 47
OCR for page 48
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OCR for page 51
O/~-Growth Forests
51
ha, depending on forest type, with minimum sizes ranging from 52 cm
diameter et breast height (dbh) on less-productive sites (generally in the
interior) to 92 cm dbh on more-productive sites west of the Cascade
crest. Old-growth forest might have 2 to 3 times that density of large,
old trees. Minimum ages for these large dominant trees range from 150
years for the major interior forest types to 200 years for forests in
western Oregon and Washington.
Old-growth Douglas-fir and ponderosa pine stands typically contain
trees some 700 years old, and in some cases, more than 1,000 years. Old-
growth Douglas-fir in western Oregon and Washington most commonly
range from 350 to 700 years of age (Franklin et al. 1981~. Under some
circumstances, forests younger than 150-200 years produce trees that
meet minimum size requirements, but those trees do not have character-
istics of old-growth trees, such as thick, deeply incised bark and various
manifestations of decadence as discussed below (Spies and Franklin
1991~.
· Variation in tree diameter. Variation in tree diameters is greater in
old-growth forests than in younger forests. For example, in the western
hemlock zone of western Oregon and Washington, the standard
deviation of tree diameters in stands 200 years or older is 2 to 3 times
that of younger stands. In many forest types, that difference in diameter
reflects the increasing abundance of shade-tolerant tree species in the
understory as forests age. In other cases, such as ponderosa pine, it is
due to small patches of young pine regenerating within the old-growth
matrix.
· Tree decadence. In western Oregon and Washington, stands of
Douglas-fir that are considered old growth have greater numbers of
trees with broken tops, excavated bole cavities, root collar cavities, and
bark resinosis than either young or mature stands (Spies and Franklin
1991~. Those characteristics are typical of old trees throughout the
region; old grand fir trees, for example, are commonly infected with a
heart rot called Indian Paint fungus (Echinodontium tinctorium).
· Presence of large dead! wood. Large, standing snags and fallen tree
boles typify all types of old-growth forests. On average, 25-35% of the
standing boles in old-growth Douglas-fir stands are snags comparable
in size to living trees, with more than half of the snags larger than 50 cm
diameter (Franklin and Spies 1991 b). Large logs are also common on the
forest floor (termed "down wood") in Douglas-fir old growth forests, as
OCR for page 52
52
Pacific Northwest Forests
well as in high-elevation forest types. Down wood occurs in dry forest
types, such as ponderosa pine, but less commonly than in more mesic
forests. Snags and logs are important structural features of old-growth
forests in providing wildlife habitat (Maser et al. 1979; Thomas et al.
1979; Harmon et al. 1986~. In the Blue Mountains, for example, 39 bird
and 23 mammal species use snags, and 179 vertebrate species make at
least some use of down wood (Thomas et al. 1979; Maser et al. 1979~.
Young, naturally established stands also can have large dead wood
as legacies from the previous stand. Hence, presence of large, dead
wood does not distinguish an old-growth forest as reliably among
natural stands of different ages as does the number of large trees
(Franklin and Spies 199Ib; Spies and Franklin 1991~.
· Cano By architecture. Large variation in tree diameters in old-growth
forests is accompanied by a high degree of structural complexity in the
forest canopy. Old-growth forests contain multiple tree-canopy layers
(in addition to herb and shrub layers), a feature common to all types
except ponderosa pine, lodgepole pine, and Eastside Douglas-fir. That
layering reflects the growth of saplings (mostly shade-tolerant trees) into
midcanopy strata as stands age. O1~-growth forests in western Oregon
and Washington also tend to have greater shrub and herb cover than
younger stands (Spies and Franklin 1991~. That is largely a function of
overstory canopy density, inasmuch as open-grown younger stands
generally have abundant shrub cover. Frequent ground fires retard
understory growth in ponderosa pine and Eastside Douglas-fir forests.
A typical old-growth forest also has areas with little or no understory,
resulting in a patchy spatial structure. Patchiness is a distinguishing
characteristic of old-growth ponderosa pine, in which small islands
(roughly 0.25-0.5 ha) of regenerating pine occur scattered through a
matrix of oilier trees. Viewed from above, the pattern of canopy cover
in old-growth stands is distinct from younger stands. Cohen et al. (1990)
used {ow-altitude remote images from the central Oregon Cascades to
calculate semivariance, a geostatistical technique that quantifies average
patterns of variance. Different age classes of forests were easily
distinguished visually using the red bands of the spectrum. Nel et al.
(1994) assessed the value of remote imagery of canopy reflection to
identify old growthin spruce-fir forests of the interior West. They found
the same general patterns as Cohen et al. (1990) but concluded that
although remote imagery was a useful guide to old-growth stands, it
was not sufficient to identify old-growth stands with certainty.
OCR for page 53
Outgrowth Forests
Time Required for
O/~-Growth Development
53
Development of old-growth characteristics forests is progressive and
varies among forest types. Some characteristics first appear about a
century after a disturbance that destroys a forest stand (Table 3-3~.
Across the region, many old-growth characteristics develop during the
second century of stand development, but forests do not typically
display all of the properties described above before they are 200 years
old.
Rates of succession differ from site to site depending on environmen-
tal conditions, nutrient and moisture availability, and residual forest
components from the previous stand. To deal with the spatial and
temporal variability in succession, Franklin and Spies (1991 b) developed
a continuously varying index of old growth based on the following five
criteria for naturally established stands in the Oregon coast range,
Cascades, and the southern Washington Cascades:
· density of large trees (e.g., more than SOcm Dbh)
· density of shade-tolerant trees
· amount of crown decadence (e.g., broken tops and multiple tops)
· density of large snags
· log biomass (using 60 Mg per ha as the base value)
On the Westside, Douglas-fir stands younger than 200 years generally
have a low old-growth index (Franklin and Spies 1 99Jb). Forests in that
region have been classified as old growth at ages ranging from 150-250
years (Franklin and Spies 1991b; Johnson et al. 1991; Bonnicksen 1993;
FEMAT 1993; Bolsinger and Waddell 1993~. There is, however, consider-
able change in old-growth features across that age span. In the Franklin
and Spies (199lb) study region, the old-growth index averaged a little
more than 2.0 for stands younger than 100 years (range, 0-6.0), 3.0 for
stands between 100 and 300 years (range, 0.3-5.0), and 6.0 for stands
older than 300 years (range, I.0-10.0) (Spies and Franklin 1991~.
O/~-Growth Landscapes
Ideas about how forests developed following major natural disturbances
OCR for page 54
54
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OCR for page 62
62
Pacific Northwest Forests
increased presence of coarse wood) and a higher amount of woody
debris in streams and terrestrial areas. Old-growth forests are also less
susceptible to large-scale disturbances and pest outbreaks, and they
have a Tower incidence of root-rot problems. Old-growth forests have
unique microclimates and might have an effect on regional climate as
wed.
Species Diversity
The Scientific Analysis Team (SAT 1993) listed 80 terrestrial vertebrate
species (16 amphibians, 38 birds, and 26 mammals) that were "closely
associated" with old-growth stands in the range of the northern spotted
owl, along with 99 invertebrate species and Ill vascular plant species.
In his analysis of forests in western Oregon and Washington, Harris
(1984) estimated that I18 terrestrial vertebrate species used old growth
as primary habitat, 135 species used young forests (before canopy
closure), and 90 species used mature forests. He also noted that "all of
the species that meet their primary habitat requirements in...early stage
forests find abundant habitat throughout the western Cascades and are
generally common. Forty of the species finding primary habitat...in old-
growth or mature forest cannot meet their habitat requirements outside
this forest type."
Thomas et al. (1979) found somewhat different patterns in the Blue
Mountains of eastern Oregon and Washington. In all forest types in the
Blue Mountains, more terrestrial vertebrate species reproduced in
mature and old-growth stands than in early-successional stands, but
little difference was seen between old-growth and mature stands. The
Blue Mountains and the Cascades have significantly different environ-
ments and hence, different patterns of forest development.
Arthropods and other small or inconspicuous organisms account for
the bulk of diversity but have been largely overlooked until recently
(Parsons et al. 1991), despite their importance in terms of numbers,
species diversity, and functional importance. Lattin (1990) estimated that
8,000 arthropod species are found in the H.~. Andrews Experimental
Forest in the central Cascades, compared with 143 vertebrate species and
460 vascular plant species. Many of those arthropods live either in
OCR for page 63
Outgrowth Forests
63
canopies or soils, the least studied subsystems in forests. Schowalter
(2000) compiled data from 9 forest, grassland, desert, and marsh
ecosystems where extensive species inventories are available to show
that arthropods commonly account for at least 70-90% of all species
present.
The few studies that have been completed found striking differences
between old-growth and younger forests in epiphyte, arthropod, and
lichen communities. For example, one of the distinguishingcharacteris-
tics of old-growth Douglas-fir forests is the abundance of epiphytic
plants (mosses and lichens), especially the nitrogen-fixing lichen Lobana
oregona. J obaria occurs in younger stands but not nearly as abundantly
as In o1~-growth forests (Franklin et al. 1981~.
Arthropod communities in old-growth canopies are significantly
more diverse than in young plantations. Schowalter (1989, 1995)
measured more than 70 species of arthropods associated with Douglas-
fir and western hemlock foliage in old-growth forests in the central
Cascades and only 15 species associated with Douglas-fir in 7- to 11-
year-old stands. Diversity was 5-6 times greater in old-growth stands
than in younger stands, with some of the most striking differences
occurring in the diversity of predatory arthropods, such as spiders
(Schowalter 1995~. Moreover, the structure of arthropod communities
differed significantly between young and old forests. In the former, the
biomass of phytophages (largely aphids) was 800% greater than that of
predators (e.g., ants, wasps, and spiders), while in the latter, the biomass
of plant eaters (largely defoliators) was only 20% greater than that of
predators. That pattern suggests more effective internal controls over
plant eaters in old-growth stands than in younger stands.
The dominance of hardwoods and shrubs in young forests in part
reflects the suppression of conifers by insects and pathogens at this
stage. Conifers become re-established after populations of insects and
pathogens have been reduced because they have so few conifer hosts
(Goheen and Hansen 1 993~. The pines, western larch, western red cedar,
Engelmann spruce, and western hemlock have higher tree mortality
associated with root disease in early stages of stand development
(younger than 30 years), but mortality decreases thereafter (Hagle and
Goheen 1988~.
Indigenous insects and diseases might have important roles in stand
OCR for page 64
64
Pacific Northwest Forests
development by mitigating the effects of biomass accumulation and
competitive stress Trough natural pruning, thinning, and cycling
nutrients. Old-growth forests generally have higher populations of
predatory insects than younger forests; those insects might help
maintain populations of herbivorous insects at lower levels than in
young stands (Schowalter 1989, 1995~. Management practices that focus
on short rotations or plantations of single species result in an overall loss
of predators. Pests also are better able to find their hosts in such
managed forests, and the systems become more susceptible to insect
outbreaks (Hagle and Schmaltz 1993, Schowalter 1995~.
togs and Woocly Debris
Much of the influence of old-growth forests on environmental condi-
tions is conferred by their large persistent structures. Whereas younger
or smaller trees decompose relatively quickly (Harmon et al. 1986), large
boles of old trees contain terpenoid and phenolic compounds in the
heartwood that inhibit decay and provide structure and resources for
soil and aquatic systems for centuries after tree death and fall (Harmon
et al. 1986; Schowalter et al. 1992; Schowalter et al. 1998; Progar 2000~.
Logs decomposing on slopes stabilize soils, retain moisture during
dry periods (often more than 200% of wood dry weight, especially after
a period of decay has increased porosity), and provide organic matter
and nutrients that are tapped by mycorrhizae and roots penetrating
wood from surrounding plants (Harmon et al. 1986; Schowalter et
al.1992~. Logs falling into streams create the pool-and-riffle structure
that contributes to aquatic biodiversity. Logs are essential components
of salmon habitat, slowing erosion from upsIope and minimizing
scouring of streambeds that degrade salmon habitat.
Although amounts of woody debris that can function in conserving
mycorrhizal inoculi are highest in late-successional forests (Vogt et al.
1995), the actual diversity and biomass of mycorrhizai fungi may peak
in the early stages of stand development. Only limited data exist on the
pattern of mycorrhizal development with stand age (Vogt et al. 1992),
but existing information suggests that the number of mycorrhizal
species and the associated sporocarp biomass peak at canopy closure.
Thus, total diversity of mycorrhizal fungi may be more closely tied to
OCR for page 65
Outgrowth Forests
65
the net prunary production of a forest than to structural components
such as coarse wood. In contrast, the diversity of certain groups, such as
the truffle farmers, is higher in old-growth stands than in young stands
(Amaranthus et al. 1994~.
The number of sites for mycorrhizal fungal colonization of root tips
is maximal at canopy closure (Vogt et al. 1983~. The peaking of
mycorrhizal fungi in early states of stand development might indicate
a carbon cost to plants to maintain mycorrhizal associations (Vogt et al.
1991~; hence, less carbon might be available to sustain all plant parts
after that stage (Grier and Logan 1977~. All Pacific Northwest forest tree
species have a good complement of different mycorrhizal species that
are capable of colonizing tree-root systems (e.g., almost 1,000 species of
mycorrhizal associates have been reported for Douglas-fir (Perry et al.
1992~. Many of the trees share similar species of mycorrhizal
associations.
Insects and pathogens
are instrumental in
directing succession
Outgrowth forests are more
resistant to crown fires than are
through their selection of younger forests....
plant species. Although
tree characteristics have been emphasized in most studies of succession,
insects, pathogens, and other taxa influence seed production and
dispersal, tree growth and survival, nutrient cycling, and soil-fertility
patterns, and therefore affect the rate and direction of successional
transformation. For example, several insects and root pathogens that
kill Dougias-fir trees are instrumental in accelerating the transition to
hemlock or cedar forest but also might provide litter accumulation
sufficient to fuel a stand replacement fire (Goheen and Hansen 1993~.
Insects and root diseases responsible for stand replacement also can
retard germination and growth of young conifers after disturbances.
Suscepribi/ity to Disturbance
Old-growth forests are more resistant to crown fires than are younger
forests, perhaps because of high humidity and litter moisture (Perry
98Sa; Franklin et al. 1989; Chen et al. 1993~. The hardwood and shrub
species in the old-growth understory also appear to inhibit fire spread
OCR for page 66
66
Pacific Northwest Forests
and to protect interspersed conifers. Young, evenly aged conifer forests
are the most flammable ancE are particularly vulnerable to reburns (Agee
1993~. Old-growth forests might be most vulnerable to fire where
adjacent younger, drier, and more flammable forests provide the
necessary heat and fuels to carry flames into the forest canopy.
However, the heterogeneous structure of old-growth forests and the
water-saturatecl logs provide barriers to fire spread, allow trees to
survive, and provide open spaces for growth of understory (Perry 198Sa;
Paiazzi et al. 1992~.
AQUATIC ECOSYSTEMS
Streamsicle disturbance and flooding have important impacts on
virtually all components of aquatic ecosystems (Reiter and Beschta
1995~; however, no component has received more attention than salmon
and trout. Seven species of salmon exist in the Pacific Ocean, and five
occur on the North American continent: chinook (Oncorhynchus
tschawylscha), coho (O. kisutch), chum (O. keta), pink (O. gorbuscha), and
sockeye salmon (O. nerka). in addition, there are anadromous trout,
steelhead or rainbow trout (O. mykiss), coastal cutthroat trout (O. cZarki),
and DoEy Varden trout (SaZveZinus maZma). Those salmonid species cto
not obligately require old-growth forests for survival, but they dicI
evolve across a geographic range that closely overlaps that of the
Northwestern coniferous forests.
Anadromous salmon and trout spawn in freshwater streams. Fry and
juveniles rear in streams and rivers (sockeye in lakes), migrate to the
ocean, spend varying amounts of time (depending on species and
stocks), return as adults to their natal streams, spawn, and die. All
Pacific salmon die after spawning, but a small fraction of anadromous
trout are capable of repeated ocean migration and spawning. All eight
species of the anadromous salmon and trout spend a portion of their
lives in freshwater habitats in forested areas of the Pacific Northwest.
As a result, their survival and production are closely linked to the forest
ecosystem and are influenced by changes caused by forest practices
(NRC 1996~.
Disturbance, which is a critical feature of streams and rivers, strongly
influences the survival of salmon and trout. Floods are a natural and
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Outgrowth Forests
67
essential component of rivers. Streams are shaped by floods, and rivers
are more productive after flooding. Although productivity might
decline immediately after flooding, flooding in streams creates pools,
cleans gravels, and delivers dissolved and particulate nutrients.
Refuges, such as deep pools, boulders and logs, off-channelL habitats on
flooclplains, and stems and roots of streamside forests, are required for
aquatic organisms to survive frequent disturbances. Over short- and
long-term scales, old-growth forests along streams and floodplains
create sizes and amounts of woody debris Mat cannot be provided by
younger forests. Floodplain habitats' large woody debris, and pool
habitats have declined substantially in recent years, and conversion of
old-growth forests to younger stands is one of the causes of habitat
losses related to the decline of Pacific salmon (NRC 1996~. Many
processes mediated by old-growth trees can be provided in riparian
reserves or stream-management zones, but riparian management must
be integrated with watershed conditions and land-use practices.
EXTENTAND STATUS OF OLD-GROWTH FORESTS
Differences in estimates of the past and present extent of old-growth
forest in the Pacific Northwest reflect differences in the definitions used
in each study: the time frame (e.g., presettlement, early settlement, pre-
World War IT, or current), the geographic area (e.g., states, Eastside
forests, or Westside forests), land-use types (e.g., forest lands only or
combinations of forest, agricultural, residential, and urban lands), and
type of ownership (e.g., public, private, or national park). Eight studies
have attempted to evaluate the current extent of old-growth forest in the
Pacific Northwest, and eight studies have attempted to reconstruct the
past distribution (Table 3-4~. When allowances are made for the factors
above, the study results are much the same.
Regional patterns of forest age classes and structure before logging
resulted from the frequency and severity of natural disturbances,
primarily fire, and to a lesser degree, wind, insects, and pathogens. The
natural fire regime is closely linked to climate and, as a result, historic
patterns of forest succession have varied within the region.
Estimates of the extent of oid-growth before logging in the Douglas-fir
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Pacific Northwest Forests
TABLE 34. Comparison of Studies of the Historical Extent of 015-
Growth Forests in the Pacific Northwest
. . .
Study Timeframe Region Landbase Extent
Bonnicksen Pre-1850 W OR, Public and private 42%
1993 W WA forest land 77%
Boothl991 Pre-1850 W OR, Public and private 62%
W WA forest land
Teensmaet 1890 CoastalOR Public end private 46%
al. 1991 forest land
Morrison Pre-1850 WOR,WWA Public end private 66%
1991 forest land
Morrison 1200-1990 Central Public forest land 25%-
and Swanson Cascades, OR only 49%
1990
Andrews Mid-1930s WOR,W WA, Public end private 44%
and Cowlin NW CA forest land
1940
Cowlin et al. 1936 E OR, E WA Public and private 73%
1942 (excludes 2 forest land
counties)
Lehmkuhl et 1932-1959 E OR, E WA Public forest only Mean-
al. 1994 (6 national 8.8%
forests)
Bolsinger mid-1950 E OR Public land only 44%
and Berger (Ochoco National
1975 Forest)
Hemsbom 1980 Mt. Rainer Public forest land 65%
and Franklin (represents National Park only
1982 historical)
region west of the Cascades crest, inferred largely from fire histories,
range from 5.6 million ha to nearly ~ million ha, or 54-70% of the
commercial forest area (Andrews and Cowlin 1940; Franklin and Spies
1984; Norse 1990; Booth 1994~. The first inventory of Pacific Northwest
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Outgrowth Forests
69
forests on the west side of the Cascades, conducted in the m~-1930s
after a period of heavy logging in the lowlands and severe logging-
related fires, recorded old-growth forests covering 4 million ha, or 44%
of the commercial forest (Andrews and Cowlin 1940~. In southwestern
Oregon, where little logging had occurred by the 1930s, old-growth
trees of various species accounted for 73% of the commercial forest
(Cowlin et al. 1942~. In the Oregon Cascades and eastern coast range,
only S% of forests had been cut by the m~-1930s, and 57% remained in
old-growth stands. In western Washington, 18% of the commercial
forest had been logged by the 1930s, leaving 45% in old-growth stands.
Most reconstructions of presettlement conditions estimate that oIc[-
growth forests covered 54-70% of the forest area in western Washington
and Oregon. Timber harvest and development have reduced this to 13-
18% (Table 3-5~.
Using a landscape simulation mode} driven by climate change and its
coupling to fire, Wimberly et al. (2000) estimated that old-growth forest
coverage in the Oregon Coast Range varied from25-75% curing the past
3000 years. The earliest quantitative estimate for the Oregon coast range
was that old-growth trees covered 33% of the commercial forest in the
mid-1930s (Andrews ancE Cowlin 1940~. By that time, a significant
amount had been logged, and large areas of old-growth trees had been
destroyed by rampant wildfires. If logged areas and the TilIamook burn
are added to the 1930s inventory, estimates of old-growth stands in
presettlement coast range forests rises to 47%, which is consistent with
the Teensma et al. (1991) estimate of 46% in 1890. Slightly more than
one-third of coast range forests were between 90 and 200 years old in the
1930s survey. Because of logging-related fires, estimates of fire patterns
based on wildfires during the past century are likely to overestimate
presettlement fire frequency and, thus, underestimate the original extent
of old-growth forests.
At the time of the 1930s survey, an additional 2.5 million ha in
western Oregon and Washington were 90- to 160-year-old stands that
had been established by fire. About 50% of those stands had trees
averaging 50 cm dbh or more and were beginning to take on old-growth
characteristics. Thus, by the 1930s, despite extensive logging, 68% of
commercial forest land in western Oregon and Washington remained in
what FEMAT (1993) classified as "late-successional/old-growth" (stands
80 years of age or older). Based on that figure, when Euro-Americans
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Pacific Northwest Forests
TABLE 3-5. Comparison of Studies of the Existing Extent of Old-Growth
Forests in the Pacific Northwest
Study Timeframe Region Landbase Extent
. .
Morrison Mid 1980s W OR, W Public and 13%
1991 WA private forest
land
Lehmkuhl et 1985-1990 E OR, E WA Public forest Mean-
al. 1994 only
FEMAT 1993 1990 W OR, W Public forest <20%
WA, NW CA only
Hann et al. 1992 W MT Public forest 3%-21%
1994 only
(Beaverhead
N.F.)
Bolsinger and 1992 W OR, W Public and 18%
Waddell 1993 WA, NW CA private forest
lands
arrived in the area in the 1800s, as much as 80% of the forests in western
Oregon and Washington were older than 80 years and about two-thirds
were older than 200 years.
Forests of interior Oregon and Washington were also dominated by
old-growth stands. The first comprehensive survey of forest resources
in eastern Oregon and Washington (excluding northeastern
Washington) was completed in 1936, at which time "the area of
commercial forest land twas] characterized by a high proportion of old-
growth" (Cowlin et al. 1942~. The 1936 survey found that old-growth
forests of ah types made up 89% of the sawTog-sized stands and 73% of
all commercial forest in eastern Oregon and Washington. Nearly two-
thirds of Eastside forest lands covered by the 1936 survey were
dominated by ponderosa pine, which, even after a period of heavy
cubing that began in the early 1920s, was still mostly old-growth. If
adjustments are made for logging before 1936, the original low-and
midelevation ponderosa pine forests were nearly 90% old growth.
Those stands typically contained trees up to 60-70 in dbh with most of
the stand volume concentrated in trees 20-44 in dish (Cowlin et al. 1942~.
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O/~-Growth Forests
71
In the late 1800s on what is now the Ochoco National Forest, surveyors
recorded ponderosa pine at 93% of the section corners in all but the
wettest forest lopes (north slopes above 5,000 feet in elevation).
Various tree species other than ponderosa pine dominated forests at
higher elevations and on moist sites at m~delevations in the interior. In
the 1936 survey, those species were classified as either large or small
rather than as old-growth or second-growth, which was the case with
ponderosa pine and Douglas-fir. In 1936, 71-96% of species other than
ponderosa pine were classified as large, which almost certainly would
fit within current definitions of old-growth for these types. In 1936, 11%
of Eastside forest lands were lodgepole pine, a pioneer tree species that
colonizes sites after wildfire. Most of those stands were classified as
medium-sized and probably were not old-growth.
No comprehensive early surveys exist for Idaho, western Montana,
and extreme northeastern Washington. Forest types of central Idaho are
quite similar to those in the Blue Mountains of Oregon and Washington,
and historic patterns are unlikely to have differed substantially between
the two areas. In contrast, forest types in northeastern Washington and
northern Idaho are unlike other Eastside forests, having higher
proportions of Douglas-fir and a representation of species such as
western hemlock and western red cedar that are more typical of
Westside forests.
Historically, northeastern Washington and northern Idaho had
extensive stands of western white pine that were probably mostly old
growth. These have either been logged or killed by white pine blister
rust (an introduced pathogen). The moist western red cedar stands,
common in northeastern Washington and northern Idaho, probably had
a relatively large proportion of old growth, because fires were
infrequent and of a low intensity that seldom killed large overstory
trees.
The most extensive and recent analysis of the current extent of old-
growth forest included all federal, state, and private forest lands in
western Washington, western Oregon, and northern California
(Bolsinger and Waddell 1993~. Old-growth forests were estimated to
occupy IS% of the existing forest lands in the area. That analysis was
based on recent maps and interpretations by the array of institutions
and ownerships that have been responding to the debate over old-
growth stands during the past 2 decades.
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72
Pacific Northwest Forests
Conditions of Eastside forests were reviewed by the Eastside Forests
Scientific Pane} (Henjum et al. 1994), which concluded that
approximately 25% of the land on eight national forests in eastern
Washington and Oregon was old-growth forest. When public and
private lands are considered, that proportion decreases to less than 20 %,
which is consistent with the distribution of old growth estimated for
Westside forests (Bolsinger and Wadded 1993~.
The composition of Pacific Northwest forests has changed
dramatically over the past 10,000 years since the last ice age. Thus, the
distribution and amount of old-growth forests before settlement
represents only one point along a continuum of natural forest change.
in some prehistoric periods, old-growth coniferous forests made up less
than Me 60-70% of the forest that settlers encountered when they first
came to the Northwest (Brubaker et al. 1992; Whitiock 1992~. Regardless
of the extent that old-growth forest might have increased and decreased
naturally over thousands of years, the reduction of old-growth over the
past century is a more abrupt change than the forests have undergone
since the last ice age.
SUMMARY
Because the ecological characteristics of old-growth forests vary from
one forest to another, no single definition of old growth is appropriate.
However, as knowledge has progressed, various indexes of successional
development have been developed to characterize forests. Old-growth
forests are bioticaDy complex, win some species depending on unique
features of old growth to survive, and the biological functioning of old-
growth and late-successional forests is important to management of
terrestrial and aquatic ecosystems.
Fifty percent of Pacific Northwest land is forested. Depending on
locality, late-successional and old-growth forests originally made up
from54-70% of the forests, but now they are only 10-~%. Harvest since
1850 has removed more than 80% of the late-successional and old-
growth forests of the Pacific Northwest; nonetheless, more than 80% of
the remaining old-growth forests occur in national forests.
Representative terms from entire chapter:
ponderosa pine
