EFFECTS OF WESTERN JUNIPER (Juniperus occidentalis

EFFECTS OF WESTERN JUNIPER (Juniperusoccidentalis) REMOVAL ON
AVIAN SPECES COMPOSITION IN SHRUB-STEPPE HABITAT IN SOUTHCENTRAL OREGON
By
Thomas David Sabol
A thesis submitted to the Department of Biology of Southern Oregon University in
partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE
in
ENVIRONMENTAL EDUCATION
Southern Oregon University, Ashland, OR
2005
APPROVAL PAGE
Approved:
Date
Date
Dr. Steven Jessup, Associate Professor
Biology
2sIv
-7
Date
/, h ., /
Date
If
Dr.re/ones, Associate Professor of Geography
o
Dr. J ep Graf; Deao f Sciences
To my wife Karey... for everything.
ii
ACKNOWLEDGEMENTS
The author wishes to acknowledge Nat Seavy for his patience and guidance in the
endeavor of the creation of this thesis. Thanks to Matt Broyles from the Bureau of Land
Management for fielding many questions. Thanks go to Doctors Greg Jones, Stewart
Janes and Steven Jessup for their help whenever called upon and for their guidance and
editing. Thanks also to Dr. Frank Lang for his input and suggestions. Thanks to John
Alexander for his support and editing. Thanks also go to Marsha Hunter for her editing
abilities and willingness to use them.
iii
ABSTRACT OF THESIS
EFFECTS OF WESTERN JUNIPER (Juniperusoccidentalis) REMOVAL ON
AVIAN SPECIES COMPOSITION IN SHRUB-STEPPE HABITAT IN SOUTHCENTRAL OREGON
By Thomas Sabol
Western juniper (Juniperus occidentalis) is a native component of the shrub-steppe
and ponderosa pine (Pinusponderosa)habitats in south-central Oregon and has been
expanding its range in the western United States during the twentieth century. In
response to juniper expansion, the Bureau of Land Management implemented habitat
restoration projects from 2001 to 2003 on large areas of BLM land in south-central
Oregon. The purpose of this study was to document the avian community response to
those removals. Juniper treatments were shown to have decreased the coverage of
juniper in large areas. Different indicator bird species were shown to be associated with
juniper covered areas, historical shrub-steppe areas and juniper treatment areas after
treatment. These bird associations can be used to assess future juniper treatment
effectiveness in south-central Oregon.
iv
TABLE OF CONTENTS
CHAPTER
PAGE
I.
INTRODUCTION
1
II.
METHODS .........................................................
6
III.
RESULTS..............................................................
19
IV.
DISCUSSION.........................................................
25
WORKS CITED .......................................................
36
PERSONAL COMMUNICATIONS CITED.....................
50
v
LIST OF FIGURES AND TABLES
PAGE
Figure 1. Study site
7
.......................................
Figure 2. Mechanical shear for cutting juniper ..
................ ..... 9
Figure 3. Piled and cut juniper left to dry
........................
10
Figure 4. Revegetation of treatment areas
........................
11
Figure 5. Juniper Index
20
....................................
Figure 6. Herbaceous cover at treated stations
....................
...........................
Table 1. Species counts on all stations
Table 2. Indicator values showing species association
vi
..............
21
22
24
CHAPTER I
INTRODUCTION
Western juniper (Juniperus occidentals) is a native component of the shrub-steppe
and ponderosa pine (Pinusponderosa) habitats in south-central Oregon (Hickman 1993,
Gedney et al. 1999). Western juniper favors semi-arid habitats and has increased greatly
in the intermountain region of the western United States during the twentieth century
(Belsky 1996, Soul6 et al. 2003).
Historically, western juniper was often restricted to rocky outcrops (Miller et al.
1992) and was not a major component of these habitats (Burkhardt and Tisdale 1976,
Agee 1993) though see Hansen (1956). Increasingly, western juniper has moved into
new habitats (Miller and Wigand 1994) where it is becoming dominant (Burkhardt and
Tisdale 1976, Agee 1993). That western juniper is increasing is not a matter of
contention among researchers, but the reasons for this increase are debated (Belsky
1996). Many in the debate attribute the increase of juniper to human activities (Soul6 et
al. 2003).
Because many believe that juniper increases are due to humans, the Bureau of Land
Management (BLM) has implemented habitat restoration projects on large areas of land
in south-central Oregon to restore the shrub-steppe characteristics that are believed to
have existed prior to European settlement. There are, however, many ranchers,
1
2
rangeland managers and range scientists that question the rationale ofjuniper removal
and reject assumptions that juniper has deleterious effects on streamflows, aquatic
organisms, soil properties or wildlife habitat (Belsky 1996). In spite of these doubts,
juniper cutting, removal, and burning projects, as well as native shrub and grass
plantings, are being implemented on large areas of land. These treatments are designed
to decrease the cover ofjuniper, and increase native shrub and grass cover which is
hoped to promote the movement of the flora and fauna to a more historic condition
(Broyles personal communication).
Sagebrush shrub-steppe habitats are imperiled because of extensive degradation
across much of their range (Knick et al. 2003). As a result, conservation of sagebrush
habitats and their associated birds is a primary management concern in the shrub-steppe
ecosystem (Paige and Ritter 1999). Some bird populations in sagebrush (Artemisia
spp.) ecosystems decline with increasing juniper abundance (Knick et al. 2005). This
may be due to changing habitat structure (Knick et al. 2005), or it may be related to
Brown-headed cowbirds (Molothrus ater), which increase in bird communities in
juniper woodlands (Rienkensmeyer 2000, Noson 2002).
Several species of birds such as the Sage Sparrow (Amphispiza belli) depend on
sagebrush habitat (Martin and Carlson 1998). Bird species whose distribution is closely
tied to sagebrush during at least part of the year are considered sagebrush obligates
(Braun et al. 1976, Paige and Ritter 1999). Sagebrush provides cover for many small
non-game birds (Dittbemer 1983). Other species such as the Vesper Sparrow
(Pooecetes gramineus)prefer a mixture of shrub-steppe grass and shrub species (Jones
3
and Comely 2002, Altman and Holmes 2000). Birds like the Grasshopper Sparrow
(Ammodramus savannarum) are closely dependant on grassland (Vickery 1996). Both
of these groups of birds may be found in parts or all of a native mosaic of shrub-steppe.
The name "shrub-steppe" itself means mosaic of shrub and steppe (grassland) habitats.
Other bird species like the Juniper Titmouse (Baeolophus ridgwayi) are associated
with juniper (Altman and Holmes 2000) and may have increased in recent times in
correlation with juniper expansion (Knick et al. 2005). Some bird species such as the
Gray Flycatcher (Empidonax wrightfi) require both sage and juniper (Wiens and
Rotenberry 1985, Sterling 1999, Miller 2001).
When trees, like juniper, form a portion of the landscape mosaic, avian diversity
increases (Medin et al. 2000). However, there is an unidentified point where the shrub
and herbaceous layers start to decrease as dominance of junipers increases (Miller et al.
2000), resulting in a decrease in avian abundance and diversity (Medin et al. 2000).
When junipers increase beyond a certain level, the bird species that depend on grass
and sage decline (Ehrlich 1988). For example in the central and eastern United States
the decline in the Vesper Sparrow species was caused by shrub-steppe/grassland
destruction (Askins 1993). Shrub-steppe bird species have been shown to attain their
highest numbers on plots with higher shrub coverage while grassland bird species are
more abundant where grass cover is higher (Rotenberry and Wiens 1980).
Many shrub-steppe species are correlated with physiognomic features of their
habitat. Shrub-steppe species with similar ecologies tend to be found in similar habitats
and are drawn together by their common response to similar features of the habitat
4
(Rotenberry and Wiens 1980). Within-habitat shrub-steppe bird community response is
strongly associated with details of floristics; however, these responses may vary at
different scales of spatial resolution (Wiens and Rotenberry 1981).
Relating the findings of Wiens and Rotenberry (1981) to this study, cutting 20
percent of the juniper on a 100 ha plot may affect local bird populations more than
cutting 20 percent of the juniper on a I ha plot. The effects of habitat alterations in an
area on the bird community are dependant on the spatial resolution of the changes.
Additionally, it is important to consider the size of the area to look at and the movement
of animal species within the area, when determining how large of an area to use to
analyze the effects of alterations. The reason for this is that more passerine bird home
ranges are completely encompassed by a 100 ha plot than a I ha plot. The same I ha
plot may have similar impacts on small rodents living within it with relatively small
home ranges, as on the birds in a 100 ha plot. So it is important to know the natural
history of the animals being used to assess effects of habitat modifications.
I hypothesized that birds associated with shrub-steppe and grassland would increase
after juniper removal, while birds associated with junipers would decrease. This study
was conducted to discover what bird species are indicative of the current juniper forests
of south-central Oregon and what bird species are indicative of the desired shrub-steppe
habitat in south-central Oregon. Further, it was conducted to discover what bird species
are indicative of the juniper forest sites before BLM removal treatments and which are
indicative of sites after the treatments in order to assess the effect and impact of future
treatments.
5
The purpose of this study is to investigate changes in the avian community
associated with western juniper removal in south-central Oregon. The results will
provide a measure of ecological response to restoration efforts.
CHAPTER II
METHODS
Study Site
This study was conducted east of Klamath Falls (42.130 N, 121.49° W), in the
Gerber Reservoir and Upper Lost River watersheds of south-central Oregon (Fig. 1).
This area is characterized by low, rolling foothills and mountains, 1280 m to 1890 m in
elevation, with loam and clay soils and intrusions of Dehlinger complex rock outcrops
(USDA 2005). The climate of the area is characterized by hot, dry summers and cool to
cold winters with an average annual precipitation of 38 to 51 cm (NOAA 2005). Prior to
settlement by Europeans, vegetation in the area was sagebrush-dominated shrub-steppe,
open pine forest and sporadic grasslands (SouI6 2003). The shrub-steppe community in
south-central Oregon is dominated by sagebrush (Artemisia tridentata)and ponderosa
pine (Pinuspondersosa) with western juniper (Juniperusoccidentalis). Other shrub
species that characterize this shrub-steppe community include bitterbrush or antelope
bush (Purshiatridentata), gray rabbitbrush (Ericamerianauseosa)and curl-leaf
mountain-mahogany (Cercocarpus ledifolius, Hickman 1996).
Prior to 150 years ago western juniper was present in south-central Oregon but did
not occur in as many elevation, aspect and climate zones and was not as dominant as
today (Soul et al. 2003). Similar historic states ofjuniper coverage have been recorded
6
7
for other parts of Oregon and the intermountain region (Burkhardt and Tisdale 1976,
Eddleman 1987). Since the arrival of European settlers there has been an increasing
amount of western juniper present in south-central Oregon and the intermountain region
(Souls 2003). An inventory of eastern Oregon woodland reported that the land coverage
of western juniper forests quadrupled from the mid-1930's to the late 1980's (Gedney
et al. 1999). Returning the shrub-steppe to its natural vegetation state is the focus of a
juniper removal project that is being implemented by the BLM, Lakeview District,
Klamath Falls Resource Area (Broyles personal communication).
Figure 1. Study site. Location of units and sampling stations.
Study Design
Juniper Removal Treatments
The BLM implemented a patchwork ofjuniper removal treatment areas up to 580
ha with some adjacent treatment areas bordering to form treatment units up to 1780 ha
8
in size across the landscape of the study area (Fig. 1). Juniper treatment patches were
chosen by the BLM's range/botany, wildlife and hydrology staff (Broyles Personal
Communication 2005). Biologists from each discipline independently identified areas
that they wanted to treat based on what was beneficial for their resource program (i.e.
the wildlife department wanted to treat habitat historically occupied by Greater SageGrouse [Centrocercusurophasianus]). These three lists of proposed areas were entered
into a Geographic Information System (GIS) system and a map was produced
indicating three resulting types of treatment areas. There were areas that all three
disciplines wanted to treat (high priority), areas where 2 of the 3 disciplines wanted to
treat (medium priority) and areas that only one discipline wanted to treat (low priority).
In accordance to BLM protocol, juniper cutting by machines on these areas takes
place from June to November, whenever the soil moisture is below 20% at 15 cm
below the surface, to reduce soil compaction. Juniper cutting by hand takes place when
there are no fire restrictions preventing it. Within the treatment units, any juniper
individual with a diameter at breast height (1.5 m) of > 61 cm was left standing.
Smaller junipers were cut either with chainsaws or large machinery that used
mechanical clippers to shear each juniper tree individually (Fig. 2). Any tree or branch
> 15 cm in diameter was left where it fell after being cut, and all trees and branches <
15 cm in diameter were piled. Piles were left to dry for at least one year and were
burned within two years of being cut (Fig. 3).
9
Photo: BEIJ. Slid.: Broyles 2X220.
Figure 2. Mechanical shear for cutting juniper.
Some sites were replanted with shrubs and grasses due to site disturbance and low
natural revegetation (Fig. 4). Not all sites were replanted because there was good
residual cover of native shrubs and grasses. If a site calls for it, shrub planting takes
place in the spring (March and April and sometimes into May in wet/cool years) when
the soil is thawed, but still cool, to put dormant plants in the ground. The BLM plants
native shrubs (curl-leaf mountain-mahogany, bitterbrush and sage in burn holes, skid
trails and landings.
10
Photo: OIM. Slie: Broes 2MA6.
Figure 3. Piled and cut juniper left to dry. These piles were left to dry for up
to two years before being burned.
Grass seed is distributed after the removal ofjunipers where the soil has been
disturbed. This is done in the fall, before fall and winter precipitation occurs so seeds
go into loose soil and germinate with the moisture. Grass species used in planting vary
depending on availability and typically include Sandberg's bluegrass (Poa secunda),
blue wild rye (Elymus glaucus), bottlebrush squirrel tail (Elymus elymoides), and Idaho
fescue (Festuca idahoensis) in decreasing order of percentages used.
11
FireIdlled
Scorched
juniper, not
dead yet,
mavivem\
Machine pile that did
not bum completely
\
junipe
Ve"'r
tubes
protecting
recently
planted
shrubs in
bum pile
scars.
Tubes
z
reduIe
browsing
Phdoi RLM. Ghdc
roon22
.
Figure 4. Revegetation of treatment areas. This is an area that had recently
had juniper removal treatment, burning of cut juniper piles and planting of
bitterbrush and curl-leaf mountain-mahogany.
Sampling Routes
The Klamath Bird Observatory (KBO) received GIS data from the BLM containing
polygons identifying location and planned dates for juniper treatments. Using the GIS
polygons, the BLM and KBO established 272 bird and vegetation monitoring stations
along 27 routes. Routes were established to include areas both to be treated and areas
left as controls. Universal Transverse Mercater (UTM) coordinates for each station
were recorded using a Trimble backpack-style Global Positioning System (GPS)
receiver. In 1998 and continuing annually through 2004, bird and vegetation surveys
were conducted at the survey stations by KBO biologists. These surveys took place
before, during and after juniper treatments. The pre- and post- data treatment count data
12
provide an opportunity to use bird presence, species diversity and species richness to
assess the effects of the habitat restoration efforts implemented by the BLM on bird
populations.
Bird Surveys
I conducted a literature search to establish habitat type preferences of species
observed in the study. I grouped birds into preferring shrub-steppe/grassland and those
preferring juniper-forest/forest. Bird surveys were conducted following bird census
methodologies found in Ralph et al. (1993). Survey stations were placed a minimum of
150 m apart to ensure independence, and bird surveys were conducted at each station
between sunrise and 1100 Pacific Daylight Time. During 5-min counts, all individuals
seen and heard were recorded, and it was noted whether individuals were detected
within or beyond 50 m from the station. Each station was surveyed between 21 May
and 16 July each year of the study.
Vegetation Surveys
Vegetation data were collected at each station using the relevd method (Radeloff
2003, Ralph 2004). A variable-radius plot was established at each station that varied
from 25 to 50 m depending on the homogeneity and density of the surrounding
vegetation. Each plot's variable-radius was increased or decreased and then fixed to
include all vegetative species that made up the major structural components of the
vegetative habitat around the station.
Once the plot radius had been established, the number of major layers of vegetation
(tree, shrub, and herb) was recorded. The tree layer was defined as trees > 5 m in
13
height. The shrub layer was defined as shrubs or small trees > 0.5 m, but < 5 m. The
herb layer was defined as low growing plants (< 0.5 in), typically non-woody, although
seedlings and small trees and shrubs were sometimes present. For each layer the
average height, percent cover and diameter at breast height of dominant species was
recorded. The species of vegetation most common in the upper and lower limits of each
layer was also recorded. Each species found in each layer and its percent cover was also
recorded. Cover was recorded in the field using categories (5, 4, 3, 2, 1 or 0). A "5" was
indicating >75% cover and 50-75%, 25-50%, 5-25%, <5% cover, respectively, and 0
for absent.
For the purposes of this study, trees, shrubs and some herbs were identified and
recorded to the species level. Some grasses and mosses, bryophytes and lichens were
not identified to the species level. At each location the observers also recorded the
geographical coordinates (northing and easting) and burn status of the site.
Data Analysis
Juniper Index
Vegetation Data from each survey was used to derive a juniper cover index for each
station. I converted the recorded cover class percentages (0, <5, 5-25, 25-50, 50-75, 75100%) to proportions and then converted each class into its midpoint (i.e. 0, 0.025,
0. 15, 0.375, 0.625, 0.875) for analysis. For each station I calculated a Juniper Index
value by adding its midpoint value for junipers in its tree layer with its midpoint value
for junipers in its shrub layer. I then calculated the mean Juniper Index for each unit by
averaging the indices from each of the stations in each unit.
14
Point Selection
Because juniper removal by the BLM in actuality did not always correspond exactly
with the prescribed timeline or treatment areas (GIS polygons) that had been used to
plan the bird station placement, I excluded stations that 1) were outside of treatment
areas, but whose field reports showed they had actually been burned, 2) had no
vegetation data collected, or 3) were treated before bird and vegetation surveys were
conducted.
Stations were grouped into units based on their proximity to each other, and each
unit was identified as treated or untreated. Units with only a single survey station were
also excluded from the analysis. All units whose survey points had a collective mean of
> 15% ponderosa pine canopy coverage were excluded. Ponderosa pine dominant sites
were not considered representative of the shrub-steppe or grassland habitat and
therefore were not considered appropriate for use as control units.
I used the "select features by location" tool in ArcGIS 9.0 (GIS; ESRI) to group
stations into treated and untreated units. These were then separated into three types of
units: 1) treated units 2) desired control units and 3) current control units. The treatment
units had high initial densities of juniper that were reduced to low densities. Units
(groups of stations) in untreated areas with high juniper densities served as currentcondition control units (current controls). Units (groups of stations) in relatively
juniper-free untreated areas, that had the type of vegetation that the BLM is trying to
replicate by implementing juniper removal, were labeled desired-vegetative-condition
controls (desired controls). The controls were compared to the treatments before and
15
after treatment to determine if treatments were successful in creating the desired
vegetative condition.
There were 36 stations in 7 treatment units chosen as treatments. Treatments had
pre-treatment juniper indices of > 0.30. All treatments occurred between 2001 and
2003, and each treated unit had at least one year of pre-treatment and one year of posttreatment data.
All stations defined as being in control units were > 250 m outside of any treatment
polygon to reduce the effects of the treatment clearings on the activity of the birds
recorded at untreated stations. Control units were located in extensive areas of
vegetation with no defined boundaries. I chose 250 m away from any treatment area to
maximize the distance from any treatment while still allowing enough control stations
for the study. Because the treatment areas were more limited in area coverage I
employed a 50 m buffer and not the 250 m buffer used in the controls. This is
acceptable because the vegetation Relev6 plots and bird recordings at each station were
limited to 50 m so all birds recorded from the station was determined to be using the
recorded vegetation.
There were 9 units of 70 stations chosen as controls. I identified two types of
control. Five units of 28 stations were selected as "current controls" to represent the
pre-treatment (i.e. high juniper cover) conditions. These current controls were control
units that had a juniper cover index of > 0.30 which is a level similar to the treated units
before treatment. Four units of 42 stations were selected as "desired controls" and were
selected to represent post-treatment conditions (areas with low juniper cover), which
16
the treatments are designed to create in the treated units. I assigned all control units
with a collective Juniper Index < 0.20 as "desired."
The goal of having current condition control units is to have units that represent
pre-treatment conditions as a baseline (Moore and McCabe 1993). Similarly, desired
condition controls were used to represent post treatment conditions. The control is any
treatment against which one or more other treatments are to be compared (Hurlbert
1984). The level of vegetation variation within the control units in this study is similar
to the vegetation variation of the treatment units; therefore the controls are appropriate.
Vegetation Statistics
I calculated the mean juniper cover indices for control units (current controls and
desired controls) using vegetation data collected in 2002. I then calculated pretreatment juniper indices for treatment units using data from the first year before
treatments occurred. I also calculated post-treatment juniper indices for these units
using data collected during the last year of the study after treatments.
I compared the current condition control unit jumiper indices to the desired
condition control unit juniper indices using a Wilcoxon's one-tailed test (Gould and
Gould 2001). For the treatment units I used this test to compare the pre-treatment
juniper indices with the post-treatment indices.
I used the same methods to analyze shrub cover. To evaluate potential changes in
shrub cover on the treated sites, I compared the shrub cover value on treated sites in the
initial year before treatment to the shrub cover value on the treated sites in the final
year of the study using a Wilcoxon's two-tailed test (Gould and Gould 2001).
17
To analyze the herbaceous vegetation response to treatment, a mean yearly
herbaceous cover value since treatment was calculated for each station. These values
were averaged to calculate each treatment unit's mean yearly herbaceous value since
treatment. The average unit values from all treatment units were averaged to calculate a
yearly mean herbaceous cover since treatment for all units.
Bird Data Analysis
I limited the analysis to birds detected < 50 m from point count stations to insure
accurate identification and independence of observations between stations (Ralph et al.
1993). The analysis was also limited to woodpeckers and passerines. I conducted an
indicator species analysis in PC-ORD version 4, as outlined by Dufrene and Legendre
(1997) and McCune and Grace (2002), to evaluate if bird species were representative of
the current or desired controls in 2002. I then used the indicator species analysis to see
if bird species were representative of treatment units before and after treatments
occurred.
These analyses generated Indicator Values (Dufrene and Legendre 1997) for each
species based on a synthesis of relative abundance and frequency among the different
clusters of units (current controls, desired controls, treated sites before, treated sites
after):
IV j1 = Aj * Bo * 100,
where IVy,is the indicator value for species i in groupj, A4 is the relative abundance of
species i in groupj, and Bo,is the relative frequency of species i in groupj.
18
Indicator values range from 0 (a species does not occur in a cluster) to 100 (a
species always occurs with greatest relative abundance and frequency in a cluster). The
IV is a metric that can be used to rank species within clusters and examine variation
among clusters. Statistical significance of IV values was evaluated by using a Monte
Carlo randomization procedure in which surveys were randomly reassigned to clusters
10,000 times, and the IV of the randomized data was recorded each time. With this
procedure, the probability of Type I error is the proportion of randomized indicator
values that exceeds the observed value (Dufrene and Legendre 1997, McCune and
Grace 2002). Birds were considered significantly associated with a category of units if
their p-value was < 0.05, but I recognized that species close to the critical value may
still be ecologically important.
This process generated lists of bird species associated with high levels of juniper
(current controls), low levels of juniper (desired controls), and treatment units before
treatment and after treatment. I predicted that ifjuniper removal treatments had
achieved their desired ecological effects, then the list of indicator species associated
with pre-and post-treatment surveys should be similar to those associated with current
and desired controls.
CHAPTER III
RESULTS
Vegetation Census Results
The mean Juniper Index on desired condition control stations (0.07) was less than
the juniper index on current condition control stations (0.89; T = 10.00, p = 0.0242; Fig.
5). The Juniper Index on treated stations after treatment (0.06) was less than on treated
stations before treatment (0.94; T = 77.00, p = 0.0045). Shrub cover on treated stations
after treatment (0.14) was less than on treated stations before treatment (0.44; T
=
74.00, p = 0.0 186).
The herbaceous cover appeared to change slightly on the treated sites following
treatment (Fig. 6). There was an initial drop in herbaceous cover followed by an
increase to a level similar to the pretreatment level.
Bird Census Results
A total of 13,308 birds were seen at all stations including 10,765 woodpeckers and
passerines from 92 different species were seen during the study. A total of 299
individual birds comprising 38 different species were observed within 50 m of the
selected control and treated units between 2000 and 2004 (Table 1).
19
20
1.4 -
12
08
0.6
0.4
0.2-
0
Current
Desired
Control Units
Before
After
Treated Units
Figure 5. Juniper Index (Juniper tree cover + Juniper shrub cover) on
current condition and desired condition controls as compared to Juniper
Index on treated sites before and after treatment. This graph depicts that
the treatments moved the juniper cover on treated sites from the current
condition to the desired condition. Standard Error bars are included.
There were 81 individual birds from 12 species observed from the current junipercovered control stations. On desired shrub-steppe control stations, 52 individual birds
from 21 species were recorded. Before any juniper removal took place, 91 individual
birds from 19 species were observed from the treatment stations. After juniper removal
on the treatment areas, 75 individual birds from 24 species were observed from the
treated units' stations.
21
0.8
8
o 0.6
C.)
04
0. -2
0
0
1
2
3
4
Years since treatment
Figure 6. Herbaceous cover at treated stations. All treated sites graphed by
the number of years since treatment. The number of treated units included is
labeled above each point with standard error bars. The graph shows the
immediate decrease in herbaceous cover after juniper treatments and the
later increase.
Four species of birds were significantly associated with the current controls (Table
2). These included American Robin (Turdus migratorius), Mountain Chickadee
(Poecile gambeli), Dark-eyed Junco (Junco hyemalis) and Gray Flycatcher. Two
species, the Chipping Sparrow (Spizellapasserina)and Bewick's Wren (Thryomanes
bewickii) were not significantly associated with the current control but were close (p '
0.060) and appear to be biologically relevant (Table 2).
22
Table 1. Species counts on all stations. Number of birds detected < 50 mn from
control stations in 2002 and from treatment stations the first year before and
last year after juniper treatment.
UnIt Ty
Control
Treatment
Species
current Idesired Ibefore Iafter
Red-breasted Sapsucker (Sphyrapicus ruber)
1
1
Hairy Woodpecker (Picoides villosus)
1
Western Wood-Pewee (Contopus sordidulus)
1
1
Dusky Flycatcher (Empidonax oberholseri)
7
Gray Flycatcher (Empidonax wrightii)
12
1
6
2
Ash-throated Flycatcher (Myiarchus
cinerascens)
I
1
Western Kingbird (Tyrannus verticalis)
1
Horned Lark (Eremophi/a alpestris)
2
Tree Swallow (Tachycineta bicolor)
1
Steller's Jay (Cyanocitta ste/leri)
I
2
Western Scrub-Jay (Aphelocoma californica)
1
Pinyon Jay (Gymnorhinus cyanocephalus)
10
Clark's Nutcracker (Nucifiraga columbiana)
1
Black-billed Magpie (Pica hudsonia)
1
Mountain Chickadee (Poecile gambeli)
14
1
6
4
Pygmy Nuthatch (Sittapygmaea)
8
5
Rock Wren (Salpinctes obsoletus)
4
3
7
8
Bewick's Wren (Thryomanes bewickii)
9
1
House Wren (Troglodytes aedon)
I
Blue-gray Gnatcatcher (Polioptilacaerulea)
1
Mountain Bluebird (Sialia currucoides)
2
5
American Robin (Turdus migratorius)
13
2
15
12
Western Tanager (Pirangaludoviciana)
2
I
Lazuli Bunting (Passerinaamoena)
9
Green-tailed Towhee (Pipilo chiorurus)
2
3
Spotted Towhee (Pipilo maculat~us)
9
11
2
1
Black-throated Sparrow (Amphispiza
bilineata)
1
Chipping Sparrow (Spizellapasserina)
11
2
10
7
Brewer's Sparrow (Spizella breweri)
7
2
3
Vesper Sparrow (Pooecetes gramineus)
2
1
Lark Sparrow (Chondestes grammacus)
1
Dark-eyed Junco (Junco hyemalis)
6
1
23
Unit Type
Control
Treatment
Species
Western Meadowlark (Sturnella neglecta)
Brewer's Blackbird (Euphagus
cyanocephalus)
Brown-headed Cowbird (Molothrus ater)
Cassin's Finch (Carpodacuscassinii)
Lesser Goldfinch (Carduelispsaltria)
Evening Grosbeak (Coccothraustes
vespertinus)
Total Birds Seen
current I desired | before I after
4
1
4
3
1
1
I
1
5
3
3
1
81
1
52
91
75
The indicator values showed one bird species, Lazuli Bunting (Passerinaamoena),
to be significantly associated (p < 0.01) with the desired controls (Table 2). The
Brewer's Sparrow (Spizella breweri) was not significantly associated with the desired
controls but, again, the outcome was close (p ' 0.056) and appeared to be biologically
meaningful.
No bird species were significantly associated with the treatment sites before
treatment; however, the Dusky Flycatcher (Empidonax oberholseri) was significantly
associated (p < 0.01) with the treatment sites after treatment. The Dusky Flycatcher
was not one of the 6 current condition control indicators.
24
Table 2. Indicator values showing species association. The values were figured by
multiplying the relative frequency by the relative abundance. The p-values resulting
from the Monte-Carlo tests of significance of observed maximum indicator values
are included. Species with significant indicator values (p ' 0.05) and biological
significance (p < 0.06) are shown.
Indicator Value Based on Cluster Type
Treatment
Current
Desired
Cluster
Condition
Condition
After
Species
Control
Control
Treatment
p
American Robin
27.9
0.025
Chipping Sparrow
21.2
0.060
0.011
25
Dark-eyed Junco
0.014
26.7
Mountain Chickadee
0.035
23.1
Gray Flycatcher
0.055
Bewick's Wren
17.9
0.006
28.6
Lazuli Bunting
Brewer's Sparrow
17.9
0.056
19.4
0.013
Dusky Flycatcher
CHAPTER IV
DISCUSSION
The BLM conducted juniper removal in large areas of south-central Oregon to
transition the vegetation in these areas toward a more historical shrub-steppe state. The
vegetation had an average of two years to recover, and the bird populations in these
areas have changed slightly toward a complement of shrub-steppe associated species.
Different birds species were significantly associated with juniper-covered control,
shrub-steppe control and treatment stations after treatment. Four bird species were
significantly associated with untreated juniper-covered areas that are representative of a
large percentage of the current habitat in south-central Oregon. This juniper-covered
habitat is the focus ofjuniper removal by the BLM. One bird species was significantly
associated with untreated, currently existing, shrub-steppe areas that are representative
of the vegetative habitat that BLM juniper removal is seeking to create. On the juniper
covered areas that were to be treated there were no bird species significantly associated
with the sites. After the juniper was removed from the treated areas, there was one
species significantly associated with them.
Vegetation monitoring demonstrated that the BLM juniper removal treatments have
achieved the goal of reducing juniper cover in the treated units (Fig. 5) and indicate that
the BLM juniper treatments are moving the vegetative condition of the treated areas
25
26
toward the desired shrub/steppe vegetative condition. This study was conducted to
discover what bird species are indicative of the current juniper forests of south-central
Oregon that are being reduced, and what bird species are indicative of the existing
shrub-steppe habitat in south-central Oregon that is the goal of BLM treatments.
Further, it was conducted to discover what bird species were indicative of the juniper
forest sites before BLM removal treatments and after the treatments.
Vegetation communities are dynamic and are probably still responding to the
treatments. The herbaceous cover on treatment polygons was shown to drop
substantially in the first year after treatments and then gradually increased. By the third
and fourth year after treatment, herbaceous cover was similar to the initial pretreatment
herbaceous cover value (Fig. 6). Because at the end of the study most of the units were
only 2-years post treatment the herbaceous vegetation on the units had probably not
fully recovered; therefore, long term impact of treatments on the shrub-steppe
community is still unknown.
A literature review identified many passerines that are dependent on areas
dominated by shrub-steppe vegetation including Brewer's Sparrow (Rotenberry et al.
1999), Sage Sparrow (Martin and Carlson 1998), Grasshopper Sparrow (Vickery 1996),
Sage Thrasher (Oreoscoptes montanus; Reyonlds et al. 1999), Western Meadowlark
(Sturnella neglecta; Lanyon 1994), Black-throated Sparrow (Amphispiza bilineata;
Johnson et al. 2002), Loggerhead Shrike (Lanius ludovicianus; Yosef 1996), Lark
Sparrow (Chondestes grammacus;Martin and Parrish 2000) and Vesper Sparrow (Jones
and Comely 2002). All of these species depend on a mosaic of shrub and steppe habitat
27
in some combination of coverage density (Rotenberry and Wiens 1980, Wiens and
Rotenberry 1981, Knick et. al. 2005, Janes pers. com. 2004).
Many species depend on forest habitat or juniper forest specifically for their
survival. The seed cones ofjuniper are an important food source for many birds, such
as, the Townsend Solitaire, which in winter may form and defend a territory to ensure
an adequate supply (Eastman 1960, Ehrlich et al. 1988, Bowen 1997). Several other
birds that depend on both the seed cones of juniper and use juniper for nesting, or other
life history aspects, include the American Robin (Eddleman 1984), Lewis' woodpeckers
(Melanerpes lewis, Koehler 1981), Western Scrub-jays (Aphelocoma californica)and
Steller's Jays (Cyanocitta stelleri, Eddleman 1994, Curry et al. 2002). The Northern
Flicker (Colaptes auratus)nests and feeds in western juniper communities of the Blue
Mountains of Oregon (Thomas et al. 1976, Moore 1995) and other juniper related
species of the area include Juniper Titmouse (Cicero 2000) and Green-tailed Towhee
(Pipilo chlorurus;Dobbs et al. 1998, Janes personal communication 2005). Other
forest related species in the area include Chipping Sparrows (Middleton 1998), Darkeyed Juncos (Nolan et al. 2002) and Mountain Chickadees (McCallum et al. 1999).
These juniper and forest-related species may have increased in recent times as a result
of juniper expansion and were predicted to decrease after the juniper treatments reduce
the amount ofjuniper and forest in the study area (Marshall et al. 2003, Knick et al.
2003, USDA 2004, Knick et al. 2005).
28
Some bird species require open areas, shrub-steppe and forest mix, and juniper
forest for their survival. The Gray Flycatcher is dependent upon both sagebrush shrubsteppe and on juniper (Sterling 1999, Miller 2001).
Before the analysis I hypothesized that the bird species that would be significantly
associated with the juniper covered controls would be the same as those on the juniper
covered treatment areas. Similarly, it was hypothesized that the indicator bird species on
the shrub-steppe covered juniper-free controls would be the same as those on the
treatment sites after their juniper trees were removed.
No indicator bird species were the same on both controls and treatments before or
after treatment. However, the avian species that were on all of the sites (control and
treatment) did correspond with the individual bird species' published habitat
associations. This was demonstrated by the presence of forest bird species in forest
habitat juniper-covered sites and shrub-steppe/sagebrush birds on the shrub-steppe sites.
Results also suggest that the bird communities in the treated units may only be
beginning to respond to the juniper treatments.
Four bird species were significantly associated with the juniper forest covered
controls. These four species, American Robin, Chipping Sparrow, Dark-eyed Junco and
Mountain Chickadee are all forest or juniper-associated species. Three of these species
use trees for nesting, one, the Mountain Chickadee, nests in cavities (Ehrlich 1988,
McCallum et al. 1999), and two use limbs as nesting substrate (American Robin and
Chipping Sparrow; Ehrlich et al. 1988, Middleton 1998, Janes personal communication
2005). The Dark-eyed Junco lives and nests in scrub, trees, open woodland and forest
29
(Ehrlich 1988, Nolan et al. 2002). Having been shown to be indicative ofjuniper forests
of south-central Oregon, these species are useful in assessing if juniper removal is
successful at changing the habitat at a level that is being reflected in the bird population.
If these species continue to be present after juniper removal, the extent, or size of
treatment areas may need to be increased.
Indicator values for two species, the Gray Flycatcher and Bewick's Wren, suggest
that they were associated with the juniper covered controls (Table 2). Considering that
the Bewick's Wren is a cavity nesting species (Ehrlich 1988, Janes personal
communication, 2005) and has been recorded as dependant on scrub or woodland
(Kennedy and White 1997, Marshall et al. 2003) it could have been predicted that this
species might be present in the juniper covered controls.
The presence of the Gray Flycatcher on the juniper covered controls was not
anticipated. It is associated with both juniper and sage, and the effect ofijuniper
treatments on its populations was not predicted (Wiens and Rotenberry 1985, Sterling
1999, Miller 2001).
The Brewer's Sparrow was not significantly associated with the treatment created
shrub-steppe but the values were close suggesting a possible association. This possible
association is supported by the literature. The Brewer's Sparrow is primarily found in,
and associated with, shrublands dominated by sagebrush (Rotenberry et al. 1999,
Hutchings 2000) and breeds primarily in shrublands where the average canopy height is
less than 1.5 m. (Wiens and Rotenberry 1981). The Brewer's Sparrow is listed by some
to be a shrub-steppe obligate (Altman and Holmes 2000).
30
The Lazuli Bunting was significantly associated with the juniper-absent controls.
This association is confirmed by other studies. In central and eastern Oregon, the Lazuli
Bunting is found in arid, montane bushy hillsides, wooded valleys, sagebrush, open
scrub and recent post fire habitats and regenerating clearcuts (Ridgway 1901, Erickson
1968, Greene et al. 1996). East of the Cascade Mountains it is found to breed in
montane brush fields and regenerating clearcuts (Evanich 1990, Summers 1993). The
Lazuli Bunting is also found in riparian and pine-oak stands east of the Cascades
Mountains (Evanich 1990).
The Dusky Flycatcher was the one bird that was a significant indicator of the posttreatment sites. Its breeding habitat in the nearby Klamath Mountains is typically opencanopied brushy areas (often clearcuts), typically with scattered small trees (Fix 1989).
East of the Cascade Mountains its breeding habitat includes juniper woodlands
(Littlefield 1990) and other open mountain areas with scattered trees (Huff and Brown
1998, Sedgwick 1993). Additionally, east of the Oregon Cascade Mountains, Dusky
Flycatchers are associated with both juniper and sagebrush (Fix 1989).
The Dusky Flycatcher's presence in the treated areas after treatment can be
explained by the fact that the large diameter juniper trees were left standing on site to
mimic the pre-European settlement vegetation condition. Dusky Flycatchers often
occupy habitat with scattered large trees (Huff and Brown 1998).
Although only one bird species was associated with the treated sites after treatment,
this may change. As vegetation continues to respond to the reduction in juniper density,
bird communities may also continue to change.
31
The reason there were no tree-dependant species (e.g. American Robin) associated
with the pre-treatment sites is less apparent. The fact that they do not have significant
indicator values means that they were equally abundant in post-treatment sites. One
reason for this may be that the tree-associated birds were using piles of drying cut
juniper trees, left on sites to dry, as they would use standing juniper trees (Fig. 3). The
forest-associated bird species are likely to decline on the treated sites after the piles of
cut juniper are burned and herbaceous and shrub vegetation has time to return.
The continued presence of bird species that use forest habitat in the treated areas
after treatment may also be due to a time lag. Individual birds may continue to exhibit
site fidelity by continuing to use the site even after the site's condition is degraded as
observed in other species (Wiens and Rotenberry 1985, Beheler et al. 2003, Sedgwick
2004). It may be only a matter of time until the bird community responds to the changes
in vegetation. Sedgwick (2004) found that degraded site quality appeared to influence
philopatry in juvenile Willow Flycatchers (Empidonax trailiji), and birds reared in lowquality sites did not return to breed, even if their parents did. Some birds do appear to
assess the current and potential future quality of a location and then respond
accordingly by returning or not returning to a site and to concentrate in areas where
nesting success was high (Hoover 2003). Thus, shrub-steppe birds may not "fine tune"
their responses to local habitat variation, but may respond to larger landscape variation
(Rotenberry and Wiens 1980).
Many of the treatment sites were only one to two years post treatment at the
conclusion of the study and vegetation had not fully recovered from treatment and
32
burning. Herbaceous cover, and especially the shrub cover, may involve longer
response times to respond to treatments than the time of this study has covered. The
herbaceous layer of the treated sites however, already shows some signs of responding
to the treatments and is at a coverage level corresponding to where it was before
treatments occurred (Fig. 6). The shrub layer was significantly decreased by the juniper
treatments and it remains to be seen how the shrub layer will respond to the treatments
with the help of the BLM's shrub replanting (Fig. 4). An important question here is
whether the sagebrush, and other desirable shrub-steppe species, will recolonize the
treated areas faster than the juniper. With environmental, grazing and fire conditions
remaining the same on the sites as before the treatments, the juniper may return to
dominance of the vegetation.
To replace lost shrub cover after treatment burnings, the treatment areas will depend
on the BLM shrub replanting, reproduction from the existing seed bank and shrubs that
survive the burning. Sagebrush do not regenerate from root crowns (West and Young
2000), and sagebrush seed dispersal is limited to the immediate area surrounding the
mother plant (Young and Evans 1989, Meyer 1994). Additionally, seeds in the soil
longer than 6-months to a year rarely germinate (Young and Evans 1978, Hassan and
West 1986) and recovery of large expanses devoid of sagebrush following bums,
without replantings, may require >100 years (U.S. Dep. Inter. 1996, Hemstrom et al.
2002).
In the treatment areas, piles of cut juniper trees were left to dry for a year before
they were burned. This is important to note because it means that many of these sites
33
had either recently been burned, or were only one year post-fire, at the last time of bird
and vegetation censusing. Given these two facts, many of the study treatment sites had
not sufficiently responded from treatment to support a change in bird species that were
using those sites. The number of forest bird species present in the juniper treated areas
will likely decrease over time as shrub and herbaceous growth continue to respond to
the treatment. Time lags complicate attempts to formulate management plans based on
short-term before and after studies (Wiens and Rotenberry (1985). A longer term of
study is needed in large scale habitat alteration studies to assess the response of the bird
community.
The effects of treatment scale must also be factored in when considering the effects
of habitat rehabilitation on the avian community. A bird with a territory that is
completely enclosed in a juniper treatment unit will likely be affected more than a bird
whose territory is only partially treated. Similarly, individual birds or species with
larger territories may have only part of their territory affected by the juniper treatments,
whereas, individuals or species with smaller territories, have a greater chance of all of
their territory being treated if any of it is treated. Thus, the larger the scale of the
treatments the more chance that a functioning community of birds will be affected.
The juniper treatments in this study were large in size and consisted of adjacent
patches combining to form patches up to 1780 ha in size. Many passerine bird breeding
territories, or home ranges, can fit completely into treatment units of the size used in
this study (Howell 1942, Odum 1955, Albrecht and Oring 1995). As an example, the
Chipping Sparrow has an average home range of 3.1 ha during nest building and
34
incubation (Odum 1955) and a defended territory size of 0.2-1.0 ha (Albrecht and Oring
1995, McKernan and Hartvigsen 2001). Further, the American Robin has an average
territory of 0.11-0.30 ha (Howell 1942, McKernan and Hartvigsen 2001). The size of
the passerine bird territories and home ranges discussed in this paper are small relative
to the size of the treatments used in this study.
Several steps were taken to limit temporal pseudoreplication issues in the study
(Hurlbert 1984). To assure that treatments were temporally replicated, stations were
placed in juniper treatments occurring in more than a single year. To further limit the
possibility of temporal pseudoreplication, only one station visit per year was randomly
chosen and then used, even though many of the stations had been visited multiple times
in a year.
To limit spatial pseudoreplication, the point count stations were planned and
conducted so the distance between them was sufficient to suggest independence (Ralph
et al. 1993). Though some of the initial units (groups of stations) were relatively near
one another, the limiting of units for inclusion in the study for other reasons, as outlined
in the methods section, resulted in increased spatial dispersion of units. Further, points
included in this study were up to 54 km from each other (Fig. 1). Having stated these
efforts to limit pseudoreplication, I recognize the dangers of it and interpret my results
with caution.
With decreased juniper cover, returning herbaceous cover and the limited number of
years of data after treatment in this study taken into consideration, it is likely that the
sites will change increasingly toward higher densities of grass and shrubs. These
35
changes will likely favor shrub-steppe bird species. This assumes that juniper will
continue to remain at lower levels into the future.
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