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Historic Disturbance Agents - A day of huckleberry picking at Buck Lake around 1905 (photo courtesy of the Anderson...


Historic Disturbance Agents



The disturbance agent that had the most

historic influence on ecosystems within the

mixed conifer and ponderosa pine zone was

fire (Agee 1993). Within the Spencer Creek

watershed, historic insect epidemics from

bark beetles (Dendroctunus spp., Ips spp.,

and Scolytus ventralis) moderately influ-

enced the forests within this zone (Miller and

Keen 1960). Root rots and diseases

(Heterobasidion annosum, Armillaria

ostoyae, and Leptographium wageneri;

blackstain) likely caused small-scale distur-

bances within the watershed in this zone

(Scharpf 1993). Indian paint fungus

(Echinodontium tinctorium) was also an

important small-scale disturbance within this

zone.

No significant windthrow events are known

to have occurred within the watershed

except for minor events involving a small

number of trees.

McNeil and Zobel (1980, cited in Agee 1 993)

found an average fire-return interval of 9 to

42 years along an elevational gradient from

about 1,350 m (4,500 feet) to 1,550 m

(5,170 feet) elevation in Crater Lake Na-

tional Park (see Map 1). This same study

found few fires that burned the entire area (it

left patches unburned) and there was

variation based upon a number of factors,

including extent and intensity of previous

fires, aspect, slopes, and vegetation. At

Oregon Caves, several fires appeared to

stop at the lower elevation boundary of the

white fir/herb plant community possibly in

response to high cover of green herbage

with high fuel moisture (Agee 1991 a, cited

by Agee 1993). Based upon this study, as

well as others by Weaver (1985), Bork

(1985), and Agee (1991, cited in Agee

1993), the fire-return interval for the mixed

conifer zone within the Spencer Creek

watershed probably ranged from 10 to 60

years.

Both Native American and lightning ignitions

were important sources of fire in white fir

forests (Agee 1993). Native Americans

burned these forests regularly and some-

what altered the successional development

of the vegetative communities (Gruell 1985,

cited by Covington 1994b). Within both the

mixed conifer and ponderosa pine zone the

intensity of these historic fires was usually

low because the frequent fires repeatedly

removed understory ladder fuels and

consumed the forest floor fuels (Kilgore and

Taylor 1979, cited in Agee 1993).

Within the Spencer Creek watershed, USDA

Forest Service records from 1961 to 1992

and Oregon Department of Forestry records

from 1979 to 1994 show a combined total of

142 fires (see Table 14). Of the 142 re-

corded fires (including 40 human caused

fires), 41 lightning fires (29 percent) oc-

curred in the mixed conifer zone. Most of

the fires were less than one acre. A few

fires were 1 to 3 acres in size. The largest

fire within the zone occurred in 1992, the Big

Buck fire, which was 67 acres in size.

Almost all lightning fires have been immedi-

ately extinguished so that fires in the last 60

to 80 years have had little to no role in

shaping the present day vegetation.

In regards to Dendroctonus spp., investiga-

tions into the biology and control of western

pine beetle (Dendroctonus brevicomis)

began in the early 1900s (Miller and Keen

1960). Miller and Keen (1960) began

monitoring bark beetle problems within the

Klamath Basin during the 1920s and 1930s,

inferring that there were concerns even then

about tree mortality within ponderosa pine

forests. In 1940 and 1941 Weyerhaeuser

Company implemented tests of a sanitation-

salvage type prescription designed by Keen

and others to help reduce losses from bark

beetles (Miller and Keen 1960).

Historic Seral Stages



Table 15 displays the 1945 estimate of seral

stages for the mixed conifer and ponderosa

pine zone within the watershed. Approxi-

mately 55 percent of the mixed conifer zone

4-22

7118195

was either mid or late seral in 1945. Prior to

1945, the amount of mid and late seral

forest was probably slightly higher because

much of the lower part of the watershed had

been harvested to some degree in the

1930s and 1940s. Leiberg's (1899) data

(Figure 1) for just township T.38S. R6E.,

which lies almost entirely within the water-

shed and much of it in the mixed conifer

zone, indicate that forested areas (classified

as mid or late seral in this analysis) com-

posed about 69 percent of the township.

Based on historical disturbance agents that

occurred in these forests, early seral stands

within the Spencer Creek watershed and

within the mixed conifer and ponderosa pine

zones probably composed about 5 to 25

percent of the area at any one time. This

was likely due mostly to historic fire patterns.

Many fires occurred that were low intensity

and the seral stage present prior to the fire

remained after the fire

Historic Structure



The lower elevation mixed conifer forests,

with a large component of ponderosa pine,

were open and parklike in the mid-nine-

teenth century (Agee 1993; Leiberg 1899;

Beale 1858, cited by Covington and Moore

1994a). The typical fire in ponderosa pine

forests had little effect on the herbaceous

components of the ecosystem other than

removing the cured material (dry, combus-

tible) above ground. Removing the accumu-

lated needles and above ground portions of

the shrubs generally aided (increased) the

grasses and forbs (Weaver 1951 b and

Biswell 1973, cited in Agee 1993). Periodic,

low intensity fire maintained a cyclic stability

in fuel loads (van Wagtendonk 1985, cited

by Agee 1993) and understory plant biom-

ass, and maintained a dominance of pines in

the overstory (Agee 1993). Ponderosa pine

has a competitive advantage in the pres-

ence of fire that it loses in a fire-free environ-

ment (Agee 1993). The lower part of

Spencer Creek watershed was likely domi-

nated by large open growth ponderosa pine

with canopy closure in many areas probably

less than 50 percent. Historically, as

elevation increased in the mixed conifer

zone, the ponderosa pine stand component

was reduced, while the white fir and under-

story brush component increased (Agee

1993). The cooler, moister conditions found

at the higher elevations of Spencer Creek's

mixed conifer zone resulted in longer fire

intervals. Longer fire intervals favor less fire

tolerant species which out compete the pine

in cooler environments. At the upper

elevations of the mixed conifer zone in

Spencer Creek, the average canopy closure

likely exceeded 50 percent (aerial photo

interpretation).

Historic fuel loads and snag levels were

likely different in the lower versus higher

elevations of the mixed conifer zone in

Spencer Creek due to different fire regimes.

Leiberg (1 899), Langille et. al. (1903), and

Munger (1917), all cited by Hopkins et al.

1993, indicate that large woody material in

ponderosa pine stands was essentially

absent. This was likely the case in the lower

part of the Spencer Creek watershed.

Leiberg (1899) talks about "a mere thin

sprinkling of pine needles" on the forest floor

of historic ponderosa pine forests. Photo

series for quantifying natural forest residues

(Blonski and Schramel 1981, and Maxwell

and Ward 1980) are excellent guides, but

can be somewhat misleading because of the

past fire suppression policies in the "natural

stands" that were monitored, particularly the

ponderosa pine stands. The duff depths

reported in these "natural stands" likely

exceeded the historic levels reported by

Leiberg. Foran (pers. comm. 1995) specu-

lates that historic ponderosa pine forests

residue levels probably contained less than

20 tons per acre of duff and litter combined.

Foran (pers. comm. 1995) also stated that

ground fires generally remain on the forest

floor with very limited mortality of the re-

sidual trees when tonnage levels are below

20 tons per acre of duff and litter combined.

He further stated that when tonnage levels

exceed 20 tons per acre, mortality from a

fire substantially increases in the trees. In

summary, Foran speculated that ponderosa

pine dominated forests in the lower parts of

Spencer Creek watershed probably con-

tained less than 20 tons per acre of duff and

litter combined.

In regards to snags in the lower part of the

watershed, Munger (1917, cited in Hopkins

et al. 1993) indicated that fires killed about

three percent of the 30 plus trees per acre

over 12 inches diameter at breast height per

acre in the "Yellow Pine" (Ponderosa Pine)

7/18/95



4-23

Spencer Creek Watershed Analysis

country. Munger further indicated that

insects killed about one tree per acre and

that root pathogens also added to the snags

in a stand. Spire tops (top killing of trees),

although less common today, were quite

common in the historic stands at the turn of

the century (Munger 1917, cited by Hopkins

et al. 1993). Munger (1917, cited in Hopkins

et al. 1993) indicated that 10 to 15 percent

of the "yellow pine" (Ponderosa pine) trees

had spire tops. Hopkins et al. (1993) old

growth definition for ponderosa pine forests

indicates a snag level of 3 snags per acre

greater than 14 inches diameter at breast

height. Miller and Keen (1960), in a

1,250,000 acre study within the Klamath

Basin, found during a 31 year period (1921

to 1952) that losses (potential snags) from

western pine beetle ranged from 0.4 percent

of the stand up to 3.5 percent of the stand

per year.

In the upper elevations of the mixed conifer

zone in the Spencer Creek watershed, fuel

loads and the number of snags were prob-

ably higher because of longer fire return

intervals, cooler environments, and more

productive soils. Hopkins et al. (1993) in

their old growth definition for grand fir/white

fir forests indicate a large woody debris

component of 3 to 6 eight foot pieces at

least twelve inches in diameter per acre.

Blonski and Schramel (1981), in "natural

stands" where fires have likely been sup-

pressed, showed that total residue levels

(excluding duff) in mixed conifer forests

commonly contained 10 to 30 tons per acre

with some areas containing as much as 40

to 50 tons per acre.

In regards to snag levels in the upper mixed

conifer zone, Hopkins et al. (1993) esti-

mated 2 to 12 snags per acre greater than

14 inches diameter at breast height.

Historic Composition



Much has been written about the historic

composition of mixed conifer and ponderosa

pine forests. Agee (1993) states that white

fir forests have a gradient of community

development patterns associated with the

fire regime gradient. As fire-return intervals

lengthen (likely due to a cooler, wetter

climate) there is a tendency to have higher

proportions of white fir in the overstory. The

mixed-conifer successional model of

Kercher and Axelrod (1984, cited in Agee

1993) predict that as elevation increases

from 1,500 to 1,800 meters (5,000 to 6,000

feet), ponderosa pine is reduced from 60

percent to 5 percent of the basal area; while

white fir, which covers only 5 percent of the

basal area at 1,500 meters (5,000 feet),

increases to over 60 percent at 1,800

meters (6,000 feet). This pattern of develop-

ment was likely the case for the mixed

conifer forests in Spencer Creek and is

supported by Leiberg's (1899) observations.

Leiberg's (1899) data (See Figure 2) give

some idea of what the species composition

was historically within the townships sur-

rounding Spencer Creek. For example,

Leigberg's data for townships 39S.,

R.5,6,&7E (the southern most townships

and lowest elevations) indicated approxi-

mately 55 percent of the standing trees over

4 inches in diameter were ponderosa pine.

One township to the north and slightly higher

in elevation, in the same 3 ranges, the

average ponderosa pine composition

decreased to 38 percent. Finally, the two

northern most townships and highest

elevations in the watershed, that include

some portions of Spencer Creek, had a

ponderosa pine composition of 5.5 percent.

The white fir composition within these same

townships is pretty much inversely related to

the ponderosa pine composition according

to Leiberg's data. In the same order and

township and ranges listed for ponderosa

pine, white fir composition went from 4.3

percent to 6 percent, to 42 percent.

Most of the shrubs in the mixed conifer and

ponderosa pine zone have adapted to

periodic burning either through an endurer

or evader strategy (Agee 1993). Endurer

are those plants with a life-history strategy of

resprouting following a fire (manzanita) or

survive the effects of a fire (mature, thick-

bark ponderosa pine). Evaders are those

plants with a life-strategy in which long-lived

propagules (seeds) are stored in the soil

(such as snowbrush) or canopy (lodgepole

pine) and germinate after fire.

7/18/95



4-24

Changes in Historic

Disturbance Regimes-

Changes in Seral Stages/

Vegetative Structure!

Composition
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