PEST RISK ASSESSMENT FOR STANDS MANAGED FOR THE NORTHERN SPOTTED OWL
BUREAU OF LAND MANAGEMENT – LAKEVIEW DISTRICT
KLAMATH FALLS RESOURCE AREA
Helen M. Maffei, Plant Pathologist
Andris Eglitis, Entomologist
Michael L. Simpson, Plant Ecologist
USDA Forest Service
Central Oregon Service Center for Insects and Diseases
Bend, OR
INTRODUCTION
The purpose of this report is to provide a written assessment of the risk posed by forest insects and
pathogens to existing and future northern spotted owl (Strix occidentalis) habitat features in the
Spencer Creek area under the Northwest Forest Plan at the request of Klamath Resource Area (BLM
Lakeview District). This assessment will include a process for determining stands at risk. For the at-risk
stands, we will also suggest a potentially successful silvicultural treatment strategy that is currently
being used by the Deschutes NF, as well as describe a general process for assigning and prioritizing
silvicultural treatments.
Field Visit and Overall Questions and Issues. On October 26, 2011, accompanied by Klamath Resource
Area personnel, we visited field sites both north and south of Highway 66, southwest of Klamath Falls
and examined the forested conditions around numerous spotted owl nest sites. These sites, according
to Resource Personnel, were representative of the conditions they were particularly concerned with in
the Spencer Creek LSR.
We were asked to address the following questions:
1) Which types of stands in the area are currently at high risk to significant mortality; primarily
from insects and diseases?
2) Based on this risk, are we trying to grow northern spotted owl habitat on sites that were not
habitat historically, because they are not sustainable?
3) Are existing large-diameter trees, and the late old structure they provide, at significant risk
to insects and disease given the present “hands off” management scenario?
4) How can we integrate the habitat needs of northern spotted owl within the high-risk
stands?
5) How aggressive should active management be?
1) General risk assessment of stands most vulnerable to disturbance, primarily to insects
and diseases
Determining Stand Risk. Northern spotted owl habitat is generally characterized by high densities,
complex species composition dominated by true fir species, multiple canopy layers and very large, old
trees. East of the Cascade crest, these stand characteristics occur together almost exclusively in white
fir/grand fir series stands. To function as spotted owl habitat over the long term, an area must be
relatively “stable” that is, able to sustain all of these desirable features at once over a relatively long
period of time, at least in sufficient amounts and spatial arrangement over the landscape to maintain
viable habitat. Unfortunately, much of the East Cascade habitat is not stable. In fact, significant areas
that were suitable spotted owl habitat 20 years ago are now no longer suitable as a result of the
combined effects of defoliator and bark beetle outbreaks, root disease mortality and wildfire. Mortality
from root disease pathogens can cause a surprisingly rapid decline in habitat suitability stands where
they occur by dramatically reducing the canopy cover provided by mid- and understory trees. We have
attempted to identify the parameters associated with stand vulnerability and to describe management
options for integrating habitat needs for NSO within these high-hazard environments.
We recommend that any vegetation analysis begin with identifying and mapping currently stable and
unstable stands across the analysis area. Two key factors collectively are used to determine the stability
of stands: 1) site capacity or productivity (as indicated by plant associations) and 2) the relationships
between tree species and their disturbance agents.
Site capacity: For the eastern slopes of the Cascade Mountains, available moisture is the most limiting
factor for determining site capacity. As available moisture increases, the potential for maintaining a
mixture of species, complex forest structure, and high canopy density also increases. The carrying
capacity of a site can be described by the “growth basal area” (GBA), which is the density at which
codominant 100-year old trees would grow at the rate of one inch in diameter in a decade. Typically,
plant association guides will provide these GBA numbers as measures of site productivity or carrying
capacity. Even though the site productivity values imply that a certain stand density can be carried on a
site, we have found that susceptibility to bark beetles occurs at densities below that carrying capacity
threshold. In order to identify susceptible stands we rely on the metrics provided by P. H. Cochran
(1992, 1994) who describes an “Upper Management Zone” (UMZ), a density threshold beyond which
mortality starts to occur. This threshold density for susceptibility varies according to site productivity,
and can be determined on site by determining the recent growth rate of a typical codominant
ponderosa pine tree around 100 years old. In this case, a growth rate of 15/20ths (13 rings in the last
inch of radial growth, or GBA15) is the threshold that corresponds to Cochran’s Upper Management
Zone. The UMZ can also be described in relation to Stand Density Index (SDI), and is about 55% of
Maximum Stand Density Index or 70% of Normal SDI.
We know that in eastside forests, there is the delicate balance between growing and sustaining forest
biomass, given the temporal fluctuations in available moisture that characterize those ecosystems.
During the times of abundant moisture, stands on dry sites can attain high densities and complex
structure that suddenly becomes vulnerable and rapidly deteriorates during the drier periods. In
between those dry periods, the disturbance agents operate at low levels, creating an illusion as to the
stability of these vulnerable stand conditions. In addition, these unstable stands are functioning as
valuable habitat during the “good times” and thus carrying an expectation that they be maintained
indefinitely. Experience from the recent past also suggests that the drier sites are affected more
dramatically during drought periods. The forests of southern Oregon experienced four distinct drought
periods during the 1900s, each of which produced significant tree mortality within the drier forested
types.
As stated earlier, we recommend any analysis begin with identifying and mapping stands on the
landscape that are above the long-term carrying capacity. Identifying stands that are substantially
above carrying capacity would also be useful to know. Not all vulnerable stand conditions can or should
be treated at the same time to reduce their vulnerability to disturbance; instead, the objective should be
to manage the vegetation so that disturbances will only affect a portion of an area at any one time.
Tree species and disturbance agents: Virtually all of the conifer species have significant insect and/or
disease agents associated with them. Some species such as white fir (Abies concolor) are particularly
susceptible to a wide variety of insects and fungi, while others such as western juniper (Juniperus
occidentalis) and incense cedar (Calocedrus decurrens) have relatively few. Some key disturbance agents
associated with the tree species occurring in the Klamath Resource Area are listed below:
Tree species
Ponderosa pine
Lodgepole pine
Douglas-fir
Insects
Mountain pine beetle
Western pine beetle
Pine engraver
Mountain pine beetle
Douglas-fir beetle
Western spruce budworm
Sugar pine
Mountain pine beetle
Western white pine
White fir
Mountain pine beetle
Fir engraver
Western spruce budworm
Modoc budworm
Shasta red fir
Fir engraver
Diseases
Western dwarf mistletoe
Annosus root disease
Lodgepole pine dwarf mistletoe
Quinine fungus
Laminated root rot
Armillaria root disease
Velvet-top fungus
Douglas-fir dwarf mistletoe
White pine blister rust
Annosus root disease
White pine blister rust
Armillaria root disease
Indian paint fungus
Laminated root rot
Annosus root disease
White fir dwarf mistletoe
Indian paint fungus
Annosus root disease
Laminated root rot
Armillaria root disease
Mountain hemlock
None of importance
Incense cedar
Cedar bark beetles
Laminated root rot
Hemlock dwarf mistletoe
Indian paint fungus
None of importance
In addition to these key disturbance agents, there are others that periodically affect their hosts and
make them more vulnerable to damage by the primary agents. Some examples include the pandora
moth and comandra rust on ponderosa pine and white fir dwarf mistletoe on white fir.
Some of these disturbance agents are found throughout the array of habitat types in which their hosts
occur, while others are clearly more important in some settings than in others. For example, in
ponderosa pine systems, both annosus root disease and pine engraver are significantly more important
on drier sites, and laminated root rot is typically more severe on wetter Douglas-fir sites.
Within the Spencer Creek area, the most significant disturbance agents that would be most likely to
exert a deleterious effect on present spotted owl habitat are the fir engraver, mountain pine beetle,
laminated root disease and annosus root disease. All of the bark beetles can be expected to be most
important during drought periods and when stand densities exceed the carrying capacity of the site. As
such, mortality events involving bark beetles will be episodic with high mortality coming in pulses shortly
after each drought period begins, and falling to “background levels” between the dry periods.
Where significant root diseases occur they tend to be steady contributors to tree mortality, with a few
trees dying each year, but accumulating to represent significant losses over time. The graph below
(Figure 1) shows an example of this significant accretion of mortality (measured in a 100 acre
unmanaged administrative study that falls within the Northwest Forest Plan, 25 miles NW of Klamath
Falls, OR) as a result of Armillaria root disease (Armillaria ostoyae). Over a relatively short time period
a 25% average loss of basal area was recorded over an 11-year period in unmanaged stands of Shasta
red fir and white containing Armillaria root disease (Maffei et al 2008).
% Decrease in Stand BA
% Observed Decrease in Stand Basal Area Over
11 years (1991-2002) in Unmanaged Armillaria
Root Disease Infested Mixed Conifer Stands
50
40
30
20
10
0
821 826 823 827 822 824 825 816 817 819 818 820
Stand ID
Figure 1. Loss of basal area to Armillaria root disease in unmanaged stands,
primarily composed of white fir and Shasta red fir in the OPUS Study Area
near Lake of the Woods, SW Oregon.
Within the recent history of the Spencer Creek area, there are several things that suggest the potential
for instability in the stands that constitute critical habitat for spotted owls. There is ample evidence of
root disease that preferentially affects the true fir component. We found decayed wood associated with
the S-strain of annosus root disease. More importantly we found some areas with significant root
disease centers attributed to laminated root rot which also affects true fir, as well as Douglas-fir (Figure
2). These agents will continue to affect host trees, both large and small, and the rates of loss over time
could be comparable to those shown in Figure 1. During the decade of the 1990s, there was
considerable salvage throughout the area, focusing on the true firs (white and Shasta red) that had
either been killed by the fir engraver or had sustained top-kill and were projected to die soon (M.
Bechdolt, 2012, personal communication). The abundance of tree mortality and top-kill are suggestive
of root disease within these moist sites where the salvage harvest was concentrated. This same time
period was one of extreme fir mortality in southern Oregon due to a severe drought. The Spencer Creek
area showed some fir mortality during that time, but substantially less than that seen in the drier sites of
the Fremont National Forest.
Figure 2. Owl circles with laminated root rot centers provided
by Klamath Falls BLM (red), from CVS plots (yellow) and
digitized by Paul Deignan – FHP from Google Earth (white
hand-drawn polygons near top of figure)
2) Are we trying to grow northern spotted owl habitat on sites that were not habitat
historically?
Yes and no. The critical habitat/nest sites near the Klamath River south of Highway 66 (shown as “Xeric
Mixed Conifer”) are all within a moisture band of 26-30 inches of annual precipitation, where it would
be considered difficult to sustain the existing species mixture and high density during drought periods.
During the drought of the 1990s, we found that mixed conifer stands in that precipitation zone on the
Fremont NF sustained heavy losses of white fir and legacy ponderosa pine. In some cases, well over 50%
of the basal area was lost within in some stands. Because white fir can grow rapidly within this
precipitation zone, the overall attributes of critical owl habitat can be reached during the times of
adequate moisture, but cannot be sustained through the recurring droughts. All of the owl circles
north of Highway 66 are within bands of higher moisture, ranging from at least 31 inches of annual
precipitation to over 40” (Figure 3). The vulnerability of white fir to fir engraver drops substantially in
areas where moisture exceeds 35” annually and these stands are less likely to experience the same high
levels of tree mortality during drought periods.
Figure 3. Annual precipitation bands for the Surveyor Mountain area,
derived from PRISM data summarized to 2-acre pixels. Yellow circles represent
nest sites for northern spotted owl
The most significant disturbance agents in those wetter settings will be the root diseases, with “slow but
steady” mortality that adds up over time. Typically, stands in these moister settings can be expected to
be more stable than the dry-site stands, unless root disease is extensive. Lacking root disease, these
stands in high-moisture settings would certainly be capable of providing suitable habitat for the spotted
owl. However, at least six of these owl nest areas have laminated root rot present (Figure 2) which will
be an issue over time for Douglas-fir and true firs of all sizes.
3) Are the large-diameter trees, and the structure they provide, at risk under the present no
management scenario?
The answer depends on the plant association group. In the dry white fire series plant associations (with
ponderosa pine or sugar pine as early seral species), legacy ponderosa pines and sugar pines do not
compete well with white fir. In the absence of management that removes this competing fir (e.g. fire or
mechanical treatment), they are gradually replaced by the rapidly growing shade fir tolerant species.
The western pine beetle (in ponderosa pine) and mountain pine beetle (in sugar pine) respond to high
stand densities and kill these trees during drought periods. Even when disturbance agents such as the fir
engraver or root diseases are selectively acting on the white fir, the loss of pines still occurs in these dry
systems, and no natural disturbance in fir (short of a high-severity wildfire) seems sufficient to lead to
regeneration or recruitment of ponderosa or sugar pine. In the moister plant associations (Shasta Red
Fir Series, or White Fir Series with Douglas-fir and western white pine as seral species), the key agents
operating on large trees are typically the root diseases, and mortality will be slow and steady,
accumulating to significant levels over time. Lack of active management in the moister associations will
not have the same damaging repercussions to large trees that are seen in the drier systems.
4) How can we integrate the habitat needs of northern spotted owl within the high-risk stands?
The stands of highest hazard to bark beetle (and greatest instability) will be those growing on the dry
sites, where ponderosa and sugar pines (and possibly Douglas-fir) are the seral species. We recommend
an overall strategy that accepts the concept that individual stands are not reliable long term providers of
spotted owl habitat and that a strategy of cycling these stands over time is probably necessary. Within
this overall strategy, there is a described process for value ranking, risk rating, and prioritizing these
stands for treatment. The process for assessing and prioritizing these stands that has been used on the
Deschutes NF for the past decade and is described by Maffei and Tandy 2002. We suggest that the
general process might be a useful model in this case when evaluating how to incorporate high risk
stands into the management of the LSR:
1) Rank the stand in terms of its present structural stage relative (temporally) to the structural
elements needed for suitable owl habitat. In the dry mixed conifer PAGs, we assume that the
large tree structure has to be developed first; that it will not develop under dense stand
conditions because it arises from the early seral species. For example, stands that have
insufficient large trees, are predominantly composed of white fir and contain no mid-sized early
seral species, will have a lower “value” ranking than stands with mid-sized early serals. These
mid-sized trees could be cultured to accelerate their growth to the larger size.
2) Identify and rank current threats to each of these stands progressing on to become habitat both
in terms of bark beetles (carrying capacity as discussed), root disease and fire.
3) For each habitat stage develop a list of treatment objectives and prescriptions including no
action.
4) Prioritize by likelihood of success. An assessment of how likely the proposed the treatments will
do what they are supposed to do should be made at this time. For example, is the presence of
root disease in the true fir and heavy mistletoe in the legacy pine going to make the success of
the thinning treatment unlikely, or less likely to succeed than a similar stand without the
mistletoe?
Once the high-risk stands have been identified and ranked, their distribution across the landscape
should be considered. If the greatest threat is to fire, then a thinning to increase height to live crown
and reduce ground fuels might be chosen, whereas if the threat is from bark beetles due to heavy
stocking, an aggressive understory treatment would be appropriate. Stands that currently provide highquality habitat would also require buffering to increase their chances of avoiding a stand-replacing fire
event.
Not all high-hazard stands need to be treated at the same time, especially if they currently have value as
quality habitat. However, because they ARE of high hazard, plans need to be made to recruit their
replacements for that time when the disturbances have occurred and their value has eroded. With this
in mind, we recommend that those stand conditions that eventually take their place as critical habitat
be managed in a way that stimulates growth of the early seral species and protects them from
disturbance until such time as they are on line as quality habitat. Basically, we are proposing a “cycling
through time” of the unstable stand conditions, and providing for replacement conditions that are close
to being suitable habitat, but still need time to develop either in terms of complexity, or tree size, or
other important habitat attributes. We recognize that the most critical piece of suitable habitat is the
large tree component, typically NOT the climax species, and as such, management should focus
primarily on providing for that attribute. Cover, as provided by rapidly growing shade-tolerant species, is
much easier to get, and can be done more quickly than growing the large early seral trees.
Those high-risk stands that are no longer functioning as critical habitat could be treated to address
recruitment of seral species or to retain whatever value they currently provide.
5) How aggressive should active management be?
We believe that the most compelling case for “aggressive management” can be made in those situations
where the ecosystem has undergone the most drastic alteration from the condition it would be in if all
ecological processes were operating naturally. The degree of departure from the “Natural Range of
Variation” (NRV) could be a driving force in determining how aggressive to be. The aggressive
management in the departed systems would have the focus of creating those conditions that are the
most under-represented on the landscape, by treating those conditions that are most over-represented.
The best example is the case where open park-like ponderosa pine stands have had ingrowth of white fir
on virtually all untreated acres and the park-like condition has become rare on the landscape. The drier
the system, the more likely it is to be departed from the NRV, and the more easily aggressive
management can be justified in order to restore the “lost” or under-represented condition. A strong
case can be made for aggressive management within stands containing legacy sugar pine or
ponderosa pine where the dense fir component threatens the remaining legacy trees, and where
stocking levels are so high as to invite uncharacteristic wildfire events.
Aggressive management is more difficult to justify in the wetter ecosystems where the current forest
structure and species composition may not be significantly departed from the NRV due to the longer
intervals in the disturbance cycle. The most compelling argument for aggressive management in those
systems could be made where root disease pockets are identified and where spotted owl habitat
deterioration will occur as the diseases progress and infection centers expand. (Root disease centers do
not improve spotted owl habitat, except to create openings for foraging). Local administrative field
studies (Filip et al 2010, southeast Cascades spotted owl habitat) have been unable to demonstrate a
significant improvement in the vigor (as measured by growth) or survival of the host trees when stands
were treated by thinning when compared to the untreated stands. In some of the wetter systems that
have not experienced significant disturbance for a long time, a case could be made for recruiting early
seral species and aggressive management might be appropriate in those situations to address that need.
There may be opportunities to recruit western white pine or Douglas-fir by creating gaps or openings in
the stands are dominated by red fir. Similar gains in recruiting early seral species could be obtained by
expanding the openings created by root diseases and then planting them with the desired non-host
species.
SUMMARY OF KEY POINTS
1) The relationship between the present stocking level of a stand and the carrying capacity of the
site is a good indicator of the stability of that stand. Stands on dry sites are sometimes stocked
at twice the long term carrying capacity and thus are seriously affected during drought periods
when available moisture becomes limiting.
2) When root diseases are present, there will be a “slow and steady” loss of vulnerable host trees
that, over time, can represent a very significant reduction in basal area and cover.
3) Habitat for the northern spotted owl is ephemeral and cannot be sustained on the drier sites
east of the Cascades, especially in the zones with less than 30” of annual precipitation.
4) Legacy ponderosa and sugar pines on dry sites cannot successfully compete with encroaching
white fir and require management intervention in order to persist.
5) The greater the departure from natural disturbance cycles, the more justifiable is aggressive
management for a particular stand.
6) Spotted owl habitat in unstable environments can be “cycled through time” in order to account
for losses and allow for recruitment of new habitat.