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Old Growth on the Middle Fork Ranger District
Introduction
The persistence of old growth forest has been a matter of strong public
interest over the last several decades. There is a common perception
these days that there is little old growth forest left in our public forests.
While old growth was preferentially harvested on the Middle Fork Ranger
District from the mid 1920s to the early 1980s, there is still
considerable acreage of this important, interesting, and beautiful forest
type existing on the our District. Before we discuss how much and
where these forests exist, we should explain exactly what the term old
growth means to us. Well also discuss what kinds of processes
allow for the persistence of old growth forests, as well as its destruction
and renewal.
There are four basic forest types on the Middle Fork district, Douglas-fir
dominated (with some western hemlock and western redcedar), mixed conifer
(which contains Douglas-fir, grand fir, sugar pine, incense cedar, and
ponderosa pine), Pacific silver fir, and mountain hemlock. These
are general categories; all tree species often occur as minor components
in other types. A group of Forest Service and university researchers
developed a very specific definition for Douglas- fir dominated old growth
in 1986 with a publication entitled Interim Definitions for Old Growth
Douglas-fir and Mixed Conifer Forests in the Pacific Northwest and California.
This publication indicates that an old- growth forest has at last eight
trees per acre larger than 32 inches in diameter, at least 12 trees per
acre greater than 16 inches in diameter of species such as western hemlock
and western redcedar which are tolerant of the shade produced by the larger
trees, more than four dead standing trees per acre greater than 20 inches
in diameter and 15 feet tall, and more than four dead trees per acre greater
than 24 inches in diameter and 50 feet long lying on the ground.
On the Middle Fork District, stands with these characteristics may take
as long as 250 + years to develop.
No such complete definitions exist for old growth characteristics of
other forest types in our area. We can generally consider the higher
elevation Pacific silver fir and mountain hemlock stands to be old growth
if they are more than 200 years old and/or have trees greater than 21 inches
in diameter. These typically higher elevation forests are often not
as diverse as Douglas-fir old growth stands, structurally or in terms of
species composition. The species that occur in these higher elevation
forests do not live as long nor get as large as Douglas-fir, and the dead
trees decompose faster. These forest types occur in areas with deep
winter snow packs and not as many understory species are adapted to live
in such harsh environments.
Forest Succession
Douglas-fir is an especially long lived tree; it can grow to be as old
as 1000 years. If a Douglas-fir forest is not disturbed by fire,
windthrow, or insects and diseases over its life, Douglas-fir trees will
eventually be replaced by species such as western hemlock and western redcedar
since the seedlings of these species are tolerant of the shade produced
by mature trees. This forest of shade tolerant species is called a climax
forest, since these species can theoretically regenerate themselves in
perpetuity. Douglas-fir seedlings and saplings cannot survive
to maturity underneath an intact canopy of their parent trees; they need
a rather large opening in the forest, typically as wide as the dominant
trees are tall, to get enough sun to grow vigorously in height.
While theoretically one could have an old growth stand composed entirely
of western hemlock and redcedar, this is rare to the point that we have
never had more than a few relatively small climax forest stands on the
Middle Fork district. The fire history on this southern portion of
the Willamette National Forest is such that stands are nearly always killed
naturally by a wildfire before all the Douglas-fir die of old-age or windthrow.
While there are occasional trees and small clumps of trees on the Middle
Fork district that are 500 to 700 years old, the vast majority of the old
growth forests in this area are around 300 to 400 years old.
After fires burn, a diverse set of plant species quickly re-vegetate
the sites. Many of those species are shrubs and herbs that require
the high amounts of sunlight found away from the deep shade of tall trees.
At the same time young Douglas-fir trees begin to grow from seeds produced
the year before the fire by the now dead large trees, or by adjacent survivors
of the fire. These young Douglas-fir and usually a few other minor
tree species may eventually grow into an old growth forest, depending upon
the density of tree seedlings and what disturbances they may be subject
to over their potentially long life.
Development of Old Growth
In the scale of a human lifespan, forests, and in particular old growth
forests, may seem to be eternal and unchanging, but this is not true on
the time scale of the trees themselves. The development of any forest
is a constant process that usually has a beginning and end point, in the
Northwest both closely associated with wildfire as discussed later, and
slowly changing at all times.
Many may think that old growth forest contain trees of all ages, from
venerable giants in excess of 1000 years old to seedlings several years
old. This sort of stand structure is not common in the fire-prone
Douglas-fir forests of the Cascade Mountains. In a typical 400 year
old Douglas-fir forest there may be many small understory tree seedlings
such as western hemlock which may be relatively young, and there may be
some larger western hemlock and redcedar from one to several hundred years
old which came into canopy openings created by past windthrow. The
occasional ground fires that may occur typically would remove this understory
tree component. The overstory Douglas-fir are typically all nearly
the same age, or if the area reforested gradually due to a severe disturbance
or lack of adequate seed sources, may vary in age by about 50 years.
Due to the relatively frequent occurrence of fire in the Douglas-fir ecosystem
on the Middle Fork district, stands of trees seldom get to be more than
500 years of age. As these forests age, individual trees die or are
blown over, and large amounts of fuel accumulate on the forest floor.
At some point when wildfire comes to that particular forest stand, it burns
so hot that the whole stand of trees is killed.
The development of old growth
from a young stand created by fire or harvest requires some amount of low
level disturbance, especially if the young trees are very densely established.
To become large, trees need room to grow, and a very dense stand of young
trees can be quite spindly and subject to wind and snow damage. A
given area of forest may never develop old growth characteristics if the
natural disturbance regime is frequent, or those characteristics may take
a very long time to develop without any disturbance. Small disturbance
events in younger stands, such as individual or small group tree mortality
from windthrow or insects and disease occurrence, may hasten the development
of old growth by providing gaps in the forest which allow understory conifers,
shrubs and herbs to proliferate. This opening in the forest canopy also
allows the adjacent overstory trees to expand the width and depth of their
crowns, and allows for development of a complex branching structure.
A very dense stand of young trees that is not disturbed may never provide
for the development of large tree stems since many small trees complete
with each other for water, nutrients and light, and there is not enough
to provide for growth of large diameter stems before the next stand replacing
fire.
Function of Old Growth
In addition to the aesthetic and spiritual values it holds for us humans,
Douglas-fir old growth forests in particular provide habitat for a number
of plant and animal species that either tend not occur in younger forest,
or occur less abundantly elsewhere. These habitats are provided by
the protection from sunshine and wind that the deep and dense tree canopies
provide, as well as the physical structures for nesting, hiding, and plant
growth provided by standing and down dead trees, thick bark, complex crown
structures and heavy branches, and undisturbed duff and litter layers.
Old growth trees also may provide a record of past climate and fire occurrence
in their many annual growth rings. Older forests also provide for
stream protection and input of large down wood to the stream system that
creates more complex aquatic habitat, shading of stream waters to keep
them cool, and filters for sediments.
Old growth Douglas-fir forests also contain some of the highest amounts
of stored biomass of any ecosystem on earth. This stored biomass
contains large amounts of carbon that would be released into the atmosphere
as carbon dioxide if these forests burned in a wildfire. As you can
see from the following discussion of fire occurrence, these forests can
only serve as relatively temporary carbon storage sites, as they will eventually
burn.
Fire
Old growth forests do not last forever and the most common event that
ends their life is wildfire. On the average, over the last 400 years, about
one quarter of the forests on the Middle Fork Ranger District (some
180,000 acres) has been mostly or completely killed by wildfire each century.
While many consider the western Cascade Mountains to be quite wet, the
climate in the Pacific Northwest can be very dry during the late summer
and early fall. This climate regime and the flammable nature of coniferous
tree needles and branches combine to produce an ecosystem that is subject
to and adapted to wildfire. Depending upon forest conditions, the
time of year, and the local weather, these fires can be slow creeping ground
fires that reduce the amount of flammable fuel on the forest floor, (while
killing most of the understory vegetation), or they can be raging crown
fires that may kill tens of thousands of acres of trees. From examination
of young stands that contain signs of past severe wildfire, it is apparent
that however devastating wildfire may appear to be in the short-term, the
forests destroyed by them almost always regenerate from seeds of the fire
killed trees in one to ten years.
It has not been uncommon on the Middle Fork district to have a young
forest get killed early in its life from another fire, as the dead trees
from the first fires eventually fall to the ground and become large amounts
of fuel which carries the second fire. This double burning,
defined here as two fires occurring on the same piece of land less than
30 years apart, can result in stands with little residual structural material,
such as snags and down logs, from the previous stand as this material typically
is consumed by the second fire. We do not know the full extent of
this type of fire regime on the Middle Fork district, but there are entire
drainages exceeding three to four thousand acres in area which appear to
have burned in this manner over the last 200 years.
Timber Harvest
Most of the early harvesting on the Willamette National Forest was concentrated
in old growth forests. This was because old growth typically has
more net lumber per acre and that lumber is of higher quality since it
is finer grained and has fewer knots. And forest managers at that
time thought that younger stands which had been regenerated by wildfires
around the turn of the century needed to grow more before they were harvested.
Though considerable old growth was harvested between the 1920s and
early 1980s, nearly one third of the Middle Fork District contains
old growth forests today (see Table 2). There are also many younger
stands, typically from 100 to 200 years old (late-successional forest),
which are in the process of developing old growth characteristics.
Old Growth Amounts and Locations
In response to the interest in old growth forests, the 1990 Willamette
National Forest Land and Resource Management Plan designated a number of
old growth groves (see Table 1). These stands are representative
examples of old growth forest types which are especially scenic and easily
assessable to the public, either by being adjacent to main roads, or accessed
by a short and easy hiking trail. Fourteen old growth groves have
been designated on the Middle Fork district, totaling about 2000 acres.
These stands were designated to provide for educational, aesthetic, and
recreational experiences.
Table 1 ~ Designated Old Growth Groves on the Middle Fork District
Grove Name |
Dominant species |
Significant attribute |
Big Swamp |
Douglas-fir, W. redcedar |
Tree diameter |
Cayuse Creek |
Douglas-fir, True fir |
Tree diameter |
Elk Camp |
Douglas-fir, True fir |
Outstanding example |
Fall Creek |
Douglas-fir |
Tree diameter |
Fisher Creek |
Douglas-fir |
Tree diameter |
Gold Lake |
Douglas-fir, Mt. Hemlock |
Outstanding example |
Kelsey Creek |
Douglas-fir |
Tree diameter, Age |
Little Fall Creek I |
Douglas-fir |
Tree diameter, Height |
Little Fall Creek II |
Douglas-fir |
Tree diameter, Height |
Sardine Butte |
Douglas-fir, True fir |
Tree diameter, Age |
Upper Furnish Creek |
Douglas-fir, True fir |
Stage diversity |
Upper Salmon Creek |
Douglas-fir |
Park-like stand |
Wall Creek |
Douglas-fir, W. redcedar |
Accessibility |
The 1990 Willamette Forest Plan also provided a number of much larger
Wildlife Habitats Areas, Special Interest Areas, Research Natural Areas,
Designated Wild and Scenic Rivers Areas, Dispersed Recreation Areas,
and Wildernesses that protect many more acres of old growth forest for
the purpose of maintaining ecosystem functions. The 1994 Northwest
Forest Plan amended the Willamette Forest Plan and increased the amount
of reserved older forests. The Northwest Forest Plan added large
Late-Successional Reserves and a network of wider Riparian Reserves.
On the Middle Fork district, the combined reserved areas established
in the Willamette Forest Plan and Northwest Forest Plan contain over
144,000 acres of old growth forest. The Middle Fork district currently
contains a total of about 205,000 acres of old growth forest (29 percent
of the districts total area) in all land allocations. And
when the old growth stands are combined with the mature forest stands
from 80 to 200 years of age which could develop old growth characteristics
over the next 50 to 100 years, the district contains about 340,000 acres
of late-successional forest (47 percent of the district, of which two
thirds is reserved from harvest).
While the Forest Plan old growth groves provide some beautiful
and relatively accessible forest for your enjoyment, there are numerous
other areas to visit in order to see majestic Douglas-fir old growth
forests. In particular, check out the upper portion of Aufderheide
Drive (Forest Road 19, paralleling the North Fork river between mile
posts 14 and 30), the Black Creek area (Forest Road 2421) , the Larison
Rock and Larison Creek trails just south of Oakridge, the Sourgrass Mountain
area along the Alpine Ridge Trail, and the Fall Creek National
Recreation Trail. Also, the road leading to Waldo Lake traverses
some beautiful examples of mountain hemlock old growth.
For more information on how to locate these old growth
stands, stop in at the Middle Fork District offices in either Lowell
or Oakridge for directions and maps and discuss with the receptionist
or District personnel the best way to find these old growth stands.
Table 2: Middle Fork Ranger District
Late Successional & Old Growth Forest Types by Watershed
Watershed |
Total
Acreage |
Total Acres
Late Successional*
forest |
Reserved* Acres
Late Successional
forest |
Total acres
Old Growth*
forest |
Reserved Acres
Old Growth
forest |
Hills Creek |
38,443 |
18,253 |
12,987 |
13,687 |
9,253 |
Downstream
Tributaries |
109,895 |
48,279 |
32,228 |
45,242 |
30,654 |
Upper
Middle Fork |
113,433 |
51,460 |
30,665 |
36,920 |
21,200 |
Salt Creek |
71,440 |
33,099 |
20,299 |
10,612 |
6,651 |
Salmon Creek |
82,442 |
40,738 |
32,208 |
17,878 |
14,641 |
Lower
North Fork |
81,618 |
32,295 |
16,694 |
21,776 |
11,814 |
Upper
North Fork |
69,841 |
31,676 |
29,537 |
8,011 |
7,464 |
Little Fall Creek |
6,286 |
2,723 |
2,718 |
2,595 |
2,991 |
Fall Creek |
72,398 |
39,141 |
33,328 |
27,704 |
24,064 |
Winberry Creek |
22,643 |
12,297 |
5,720 |
6,447 |
3,384 |
Lookout Point
Reservoir |
46,520 |
30,475 |
25,370 |
14,102 |
12,191 |
TOTALS |
714,959 |
340,435
(47%) |
241,754
(34%) |
204,974
(29%) |
144,307
(20%) |
Reserved: designated in the 1990 Willamette Forest
Plan or 1994 Northwest Forest Plan as land allocations with no scheduled
timber harvest.
Late-Successional: forest stands with average
tree stem diameters greater than 21 inches and a minimum of 81 years
old. Acreage includes old growth stands as well.
Old growth: Douglas-fir forest stands with average
tree stem diameters greater than 32 inches with and age greater then
200 years, or greater than 21 inches in diameter and greater than 250
years old for other forest types.
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