8 Spring 2017 Applegater
Increased tree mortality
in the Applegate AMA
BY BILL SCHAUPP
In t h e Ap p l e g a t e Ad a p t i v e
Management Area (AMA), which
encompasses the entire Applegate River
watershed, the 2015 aerial detection
survey results showed large increases
in acres with conifer mortality and
killed trees, as compared with the three
previous years (Figure 1).
These increases were likely due
to heightened tree stress and lowered
tree defense initiated by dry weather,
especially the severe drought of 2013
and smaller and less persistent snow
amounts in 2014 and 2015. Heightened
temperatures added additional stress
and likely exacerbated the impact of
reduced precipitation. Conifer mortality
was concentrated in crowded stands on
lower-quality growing sites.
In our report on the 2015
mortality increase, in the Spring
2016 Applegater, we described the aerial
detection surveys. That article began with
a lengthy quote from our previous article
on “all those dead trees” in the June 2003
Applegater. The quote ends with “But
even after decades of close observation,
we can sometimes be a bit surprised by
how quickly things change and how large
the scale of impacts can be.” In certain
areas of the AMA, there was indeed a bit
of surprise in 2016.
Aerial detection surveys show increases in
conifer mortality and killed trees. Photo: USFS.
Compared with 2015, the aerial
survey results for 2016 indicate a
doubling of acres with current mortality
and nearly six times more killed trees, an
amount that is literally “off the chart”
(Figure 1). This averages overall to about
four killed trees per mapped acre in 2016,
as compared with a bit over one tree
per mapped acre in 2015, indicating an
intensification as well as an expansion of
conifer mortality last year.
Ninety percent of the conifer
mortality mapped in 2016 in the AMA
affected Douglas fir and was attributed
to the flatheaded fir borer, Phaenops
drummondi, a beetle species in the family
Buprestidae, the metallic woodborers
(Figure 2).
As in previous years, fieldwork
found that the flatheaded fir borer
(FFB) was the only agent consistently
associated with such mortality of
Douglas fir in the Applegate drainage.
This woodborer-caused Douglas fir
mortality is a characteristic situation
primarily occurring in the Klamath-
Siskiyou ecoregion of southwest Oregon,
although it occurs elsewhere in the West
associated with drought. At Ferris Gulch,
for example, smaller amounts of Douglas
fir mortality occurred occasionally in
previous years, becoming epidemic in
2015 and 2016. Other locations in the
AMA that were heavily impacted by FFB
in 2016 include lower Thompson Creek
and Armstrong Gulch near Buncom,
although FFB-caused mortality was
widespread at lower elevations, especially
in the Jackson County part of the AMA.
In addition to large losses of
Douglas fir, pine mortality remained
at an elevated level in 2016, due almost
entirely to the western pine beetle
(Dendroctonus brevicomis) killing large
and medium-sized ponderosa pines
(Figure 2). The mountain pine beetle
killed an estimated 150 sugar pines
in 2016, more than two to four times
the total in each of the previous six
years. Beetle-killed sugar pines are
often among the larger pines in a stand,
survivors of previous selective logging
and the introduced pathogen Cronartium
ribicola, the cause of white pine blister
rust disease. In 2016, fewer than half as
many true firs were killed by fir engravers,
Scolytus ventralis, as compared with 2015.
Although still at an elevated level, the
reduction in true-fir mortality may result
from improved moisture conditions at
the higher elevations of the AMA.
It is unknown if this level of
mortality will persist in 2017. A
relatively large amount of precipitation
has fallen thus far in fall and winter,
which, if continued, should reduce tree
stress in 2017 and favor tree defense over
beetle attack. However, a large adult
beetle generation emerged in 2016 from
the many infested and killed trees, and
this may have successfully overcome
additional host trees that will die in 2017.
The relatively crowded condition of
many forest stands in the AMA indicates
a potentially significant degree of
background stress caused by competition
for limited resources, especially around
pines, which need space and light to
thrive and which succumb to bark beetles
when crowded and stressed. Douglas fir
growing on sites in the AMA that are
marginally suited for them are already
stressed; unfavorable weather adds more
stress, providing opportunistic insects
an improved chance to reproduce at the
expense of more trees. Unfortunately,
the surprisingly large recent mortality
increase in the AMA in 2016 prevents
reasoned predictions for 2017.
Bill Schaupp • 541-858-6125
Entomologist, USDA Forest Service
Southwest Oregon Forest Insect and
Disease Service Center
bschaupp@fs.fed.us
Note: Oregon Department of Forestry’s
forest health fact sheet on the flatheaded
fir borer can be found online at oregon.
gov/ODF/Documents/ForestBenefits/
flatheadedfirborer_2016.pdf.
Figure 1 (left). Aerial Detection Survey from 2005 to 2016
for all lands within the Applegate Adaptive Management Area
and Medford airport annual and average annual precipitation.
Figure 2 (below). Mortality by major insect agent: Aerial detection survey
from 2005 to 2016 in the Applegate AMA.
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