EFFECTS OF EVEN-AGED FOREST MANAGEMENT ON EARLY SUCCESSIONAL
BIRD SPECIES IN MISSOURI OZARK FOREST
A Thesis
Presented to
the Faculty of the Graduate School
University of Missouri-Columbia
In Partial Fulfillment
of the Requirements for the Degree of
Master of Science
by
RAFAEL BRITO-AGUILAR
Dr. John Faaborg, Thesis Supervisor
MAY 2005
To:
Xochitl…
Gracias por estar a mi lado
Michelle y Samantha…
Con todo mi amor
Papá y Mamá…
Gracias por lo que soy
Ulises, Mélida y Homero…
Mis queridos hermanos
ACKNOWLEDGEMENTS
Funding and assistance were provided by the Missouri Department of Conservation
and the Department of Biological Sciences. The people at the office of the Missouri
Department of Conservation in Ellington, MO, provided valuable help during the field
seasons, especially Randy Jensen.
I am grateful to many people. I would like to thank Wendy Gram, for the big push
into the ornithology field, she started it all. I would like to thank my advisor, Dr. John
Faaborg, for providing me with the enormous opportunity to get into graduate school, and for
sharing his knowledge and passion for the birds. I would like to thank my committee
members, Dr. Mark Ryan and Dr. James Carrel, for their helpful comments. Special thanks to
Rick Clawson from the Missouri Department of Conservation, for the opportunity to be part
of MOFEP.
I would like to thank to my field assistants, Rafael German, Carlos, Salvador and
Vinicio, for all the hard work they did collecting field data on the clearcuts, and for the great
moments at Ellington.
Thanks to all my friends at the avian ecology lab, Marissa, Jennifer, Stacy, Mike,
Ernesto, Dana, Sue, Kelly and Chris.
I would like to thank Paul Porneluzi, for his friendship, helpful comments, and for
sharing his knowledge with me.
I want to thank Dr. Abelardo Saldivar, from the Universidad Autónoma de
Tamaulipas, for all his support while getting ready everything for coming to MU.
Funding for school was provided through the scholarship CONACYT-160761 by the
Consejo Nacional de Ciencia y Tecnologia of Mexico.
ii
TABLE OF CONTENTS
ACKNOWLEDGMENTS………………………………………………………………...ii
LIST OF TABLES…………………………………………………………………….......iv
LIST OF FIGURES………………………………………………………………………..v
EFFECTS OF EVEN-AGED FOREST MANAGEMENT ON EARLY
SUCCESSIONAL BIRD SPECIES IN MISSOURI OZARK FOREST………….1
ABSTRACT……………………………………………………………………….1
INTRODUCTION………………………………………………………………...2
STUDY AREA……………………………………………………………………8
METHODS………………………………………………………………………10
Bird Sampling……………………………………………………………10
Data Analysis…………………………………………………………….12
RESULTS………………………………………………………………………..13
Species Richness…………………………………………………………13
Relative Abundance……………………………………………………...14
Effect of Clearcut Size on Relative Abundance…………………………15
Reproductive Success……………………………………………………15
DISCUSSION……………………………………………………………………16
Species Richness…………………………………………………………16
Relative Species Abundance……………………………………………..18
Reproductive Success……………………………………………………19
Conservation Implications…………………………………………….…20
LITERATURE CITED…………………………………………………………..22
iii
LIST OF TABLES
Table 1.
Bird species detected in the clearcut stands in the Missouri
Ozarks (2001-2003). Species in bold represent early successional
birds………………………………………………………………………29
Table 2.
Mean number of species (early successional and mature forest birds) by
clearcut stand size in the Missouri Ozarks, during 2001-2003………….30
Table 3.
Mean number of territories by clearcut size for five focal early successional
species in the Missouri Ozarks (2001-2003)………………....................31
Table 4.
Nest success for four focal early successional bird species in clearcut stands in
the Missouri Ozarks (2001-2003)…………………………….................32
iv
LIST OF FIGURES
Figure 1.
Study area in the Ozark region in southeastern Missouri. The sites are part of
the Missouri Ozark Forest Ecosystem Project (MOFEP), managed by the
Missouri Department of Conservation (Brookshire and Shifley
1997)……………………………………………………………………33
Figure 2.
Arrangement of clearcut stands within the sites Cardareva, Paint rock and
Peck Ranch. The size of the 10 clearcuts range from 0.95 to 11.38 ha, they
had similar vegetation characteristics, and were surrounded by mature oakhickory forest. Bird paths were created to have better abundance estimates of
early successional birds………………………………….…..................34
Figure 3.
Species richness response to different clearcut sizes in southeastern Missouri
(2001-2003). A total of 41 bird species were recorded, including early
successional species and mature forest species…………………......…35
Figure 4.
Relative abundance response to different clearcut sizes in southeastern
Missouri (2001-2003). Number of bird territories has a positive relationship
with stand size, except for Hooded Warbler……………..…...............36
Figure 5.
Total number of nests found by year on the clearcut stands (2001-2003). This
includes both early successional birds and mature forest birds……...38
Figure 6.
Effect of clearcut size in the mean number of nests found (2001-2003) for all
species combined. No relationship was found between the number of nests
found and clearcut size……………………………………………....39
Figure 7.
Comparison of two protocols for monitoring early successional birds in
clearcut stands in southern Missouri. One protocol was conducted by
monitoring birds around the clearcut perimeter and the other one used bird
paths inside the clearcut stands……………………………………….….40
v
EFFECTS OF EVEN-AGED FOREST MANAGEMENT ON EARLY
SUCCESSIONAL BIRD SPECIES IN MISSOURI OZARK FOREST.
ABSTRACT
I examined the effect of different clearcut sizes on species richness, abundance, and
reproductive success of five early successional birds: Yellow-breasted Chat (Icteria virens),
Indigo Bunting (Passerina cyanea), White-eyed Vireo (Vireo griseus), Hooded Warbler
(Wilsonia citrina), and Prairie Warbler (Dendroica discolor) in the Missouri Ozarks. Ten
clearcut stands were surveyed. The stands ranged in size from 0.95 to 11.38 ha and were 5-7
years old post-cut at the time of the survey (2001-2003). A total of 41 bird species were
recorded; of these, 12 were considered early successional specialists. A positive relationship
between clearcut size and avian species richness was found (r2= 0.6975, P<0.05), indicating
that the number of species was higher in larger clearcuts than in smaller openings. Clearcut
size had a significant effect on the relative abundance on four of the five early successional
species; Hooded Warbler abundance was not affected by clearcut size. Statistical analysis of
reproductive success was difficult to achieve because of the low number of nests found (n=
51). My results suggest that even-aged treatments of different size in a large forest matrix had
a positive effect on early successional birds. Implementation of even-aged practices in a
forest-dominated landscape create habitat for early successional birds. Larger clearcuts,
between 3 and 10 ha in size, sustained greater abundance of early successional birds and did
not affected significantly mature forest bird species.
1
INTRODUCTION
The effects of forest management on mature forest birds have been widely studied
(Franzreb and Ohmart 1978, Keller and Anderson 1992, Thompson 1993, King et al. 1996,
Yahner 1997, Germaine et al. 1997, Annand and Thompson 1997, Merrill et al. 1998, Hagan
and Grove 1999, Kilgo et al. 1999, Lambert and Hannon 2000, Hutto and Young 2000,
Bayne and Hobson 2001, Manolis et al. 2002, Gram et al. 2003), and conservation efforts
have focused largely on this group (Askins 2001, Faaborg 2002). Early successional bird
species have been largely ignored by conservationists and wildlife managers (Conner and
Adkisson 1975, Askins 1998) despite the fact that in recent years concerns about the
population status of this group of birds have been raised (Brawn et al. 2001, Hunter et al.
2001, Askins 2000, DeGraaf and Yamasaki 2003).
In eastern North America, populations of early successional bird species or shrubland
bird have declined primarily because of habitat loss as a result of forest maturation and
growth of forest on abandoned farmlands (LeGrand and Schneider 1992, Confer 1992,
Litvaitis et al. 1999, Askins 2000, Askins 2001, Trani et al. 2001, Hunter et al. 2001,
Thompson and DeGraaf 2001, Murphy 2003). Breeding Bird Survey (BBS) data show that
many early successional bird species have declining population trends (Smith et al. 1993,
Hunter et al.2001). For example, Askins (1993) examined the evidence for population
declines in three groups of passerines: forest migrants, grassland species and shrubland
species. He found that of 16 species of shrubland birds studied in Eastern North America, 12
tended to decline between 1966 and 1991 (six significantly), while four species tended to
increase (one significantly). In the Midwest, BBS data indicated that for 23 species of
shrubland birds for which significant trends have been estimated, 12 have declining
2
population trends, while 11 have increasing trends (Sauer et al. 2004). The Midwest working
group of Partners in Flight listed 10 shrubland birds as species of concern (Thompson et al.
1992).
Proposals for the conservation of shrubland bird species have focused on
reestablishment of early successional habitat by increasing managed disturbances, either by
natural phenomena (fire, windstorms, floods) or human activities (silvicultural methods), but
this must be accomplished with efforts to reduce forest fragmentation effects (Hunter at al.
2001, Askins 2001). Natural disturbances must have a high frequency of occurrence and
must have an influence on large areas in order to provide sufficient habitat for all the species
that depend on this type of vegetation. Brawn et al. (2001) stated that restoring natural
disturbance regimes to protect shrubland bird species can only be done on fairly large areas,
such as those in the western United States; in other regions, shrubland birds will likely
depend on artificially-created habitats made by human activities, such as timber harvest.
Clearcutting is a common silvicultural practice used to manage early successional
bird species (Thompson and Fritzell 1990, Thompson and Dessecker 1997, Hunter et al.
2001, Gram et al. 2001). This is a method to harvest and regenerate trees by removing
essentially all trees to create a rather uniform habitat patch for the development of a new
even-aged stand of timber. The practice of large-sale clearcutting has been highly criticized
since at least the mid-1960s, creating much controversy among conservationists, forest
managers and the general public (Askins 1998, King et al. 2001). Clearcutting is generally
viewed by environmentalists and the public as a destructive practice to the forest lands and
its resources. In addition, clearcutting represents a negative visual impact on forest aesthetics
(Gobster 2001). Clearcutting can change the composition of the bird community of a forest in
3
complex ways, in part by reducing habitat quality for bird species that require mature trees
but create suitable habitat for early-successional bird species (Gram et al. 2003). However,
some studies of the impact of clearcutting on forest songbirds indicate that densities of most
forest species are not substantially reduced as a result of moderate clearcutting in extensively
forested landscapes (Derleth et al. 1989, Thompson et al. 1992, Welsh and Healy 1993).
Because of negative aspects associated with clearcutting (even-aged management),
alternative forms of timber harvest that do not involve clearcuts have been developed. These
uneven-aged techniques involve smaller cuts over a larger area of forest. Several studies have
examined the impacts of different forest regeneration methods on the density of early
successional birds. Annand and Thompson (1997) studied breeding songbird populations in a
managed forested landscape in southern Missouri to determine differences in the relative
abundance of breeding birds in four forest regeneration methods (clearcut, shelterwood,
group selection, and single tree selection) as well as in mature even-aged stands. They
reported that species numbers varied greatly among the five treatments and concluded that
habitat requirements of birds in managed forests can be best met by a mixture of even- and
uneven-aged forest management that creates a range of disturbance sizes. In southern Illinois,
Robinson and Robinson (1999) evaluated the effects of small gaps created by group and
single-tree selection logging within a mature deciduous forest on abundances of breeding
birds. They report that selective logging had a minor effect on the forest bird community
composition. Selective logging also created a short-lived availability of habitat for gap
species such as Hooded Warbler (Wilsonia citrina), Indigo Bunting (Passerina cyanea), and
White-eyed Vireo (Vireo griseus). Species that depend on larger gaps, such as Yellowbreasted Chat (Icteria virens), Blue-winged Warbler (Vermivora pinus), and Prairie Warbler
4
(Dendroica discolor), were absent. In a New Hampshire northern hardwood forest, Costello
et al. (2000) determined if avian species richness and composition differed between clearcut
and group selection openings. They reported that species richness per stand was significantly
higher in clearcut openings than in group selection openings. Hence, they suggested that the
group selection system does not provide habitat similar to that created by clearcutting in
extensive northern hardwood stands, and gradual replacement of clearcutting with group
selection harvests could result in reduced avian diversity across large forested tracts.
Clawson et al. (2002) and Gram et al. (2003) reported that changes in density of early
successional birds in southern Missouri forest were positive in response to both even-aged
and uneven-aged treatments, but the response to even-aged management was greater than for
uneven-aged management.
Evaluating the value of clearcut stands must control for the dynamic nature of these
cuts, which can go from bare ground to closed canopy forest in 10-20 years. In southwestern
Virginia, Conner and Adkisson (1975) compared density of breeding birds in clearcuts of
different age (1, 3, 7 and 12 years old), finding that species diversity was low on 1-year-old
clearcuts and reached its highest level in the 7-year-old clearcuts. In addition, clearcutting
provided nesting habitat for a greater diversity of birds compared to areas with no cutting. In
a similar way, also in southwestern Virginia, Conner et al. (1979) determined diversity of
birds on 3-year-old and 10-year-old clearcut stands, and 30-year-old and 80-year-old forest
stands. The analysis revealed that the 3-year-old clearcuts had a higher density of birds
during the breeding season than the other areas. In central Missouri, Thompson and Fritzell
(1990) compared bird densities and diversity in clearcut and mature oak-hickory forest. They
determined breeding bird densities and diversity in small stands 1 year before and 3 years
5
after clearcutting and in adjacent mature, undisturbed stands of forest, finding that bird
density was greater in clearcuts than in mature forest. Thompson et al. (1992) studied
breeding bird populations in an extensively forested region of southern Missouri to determine
if the number of breeding birds differed between areas managed by the clearcutting method
and areas of mature forest with no recent disturbances. They concluded that clearcutting
reduced numbers of forest interior birds that were dependent on mature forest, but also there
were forest interior bird species that made extensive use of early and mid-successional evenaged stands and occurred in greater number on clearcut sites.
Few studies have looked at the effects of even-aged management on reproductive
success of early successional birds. Yahner (1991) examined abundance, location, and
success of avian nests in small, even-aged aspen (Populus deltoids) stands in central
Pennsylvania. He found that the total number of nests differed among stands of 3 age classes
and nesting success was independent of stand age and distance from an edge, but was
inversely related to height of nest. In a different study, King et al. (2001) compared the
effects of group selection (uneven-aged) vs. clearcutting (even-aged) on nest survival rates of
early successional shrubland birds in New Hampshire. They found no difference in daily nest
survival rates between clearcuts (0.990) and group cuts (0.987) for 16 bird species combined
(n=290 nests), suggesting that clearcuts and group cuts provided similar habitat for early
successional bird species that inhabit both clearcuts and group cuts. In a more extensive
study, Barber et al. (2001) studied the nesting success and levels of nest predation and
cowbird parasitism among five different silvicultural methods: regeneration (3-6 years old),
mid-rotation (12-15 years), thinned (17-23 years), single tree selection, and late-rotation, on
pine-hardwood stands in Arkansas. Their findings showed differences in daily mortality and
6
daily predation rates among two or more treatments for 4 and 3 of 12 bird species,
respectively. On the other hand, relative abundance of cowbirds differed among treatments,
with the highest densities in regenerating, thinned, and single-tree selection stands.
Few researchers have examined the effects of clearcut size on species richness,
abundance and reproductive success of early successional birds. Rudnicky and Hunter (1993)
determined the effects of clearcut size on bird species richness in a forest-dominated
landscape in Maine. They found no species were restricted to any clearcut size. They
concluded that species richness increased with clearcut size and that there was some evidence
of increased richness in clearcuts up to 20 ha. In contrast, Christie (1997) examined the
effects of clearcut size (2.8 to 25.9 ha) on shrub-scrub bird community dynamics at the
Savannah River Site, South Carolina. Christie found that species richness declined as clearcut
size increased. Alternatively, Krementz and Christie (2000) also found no differences across
clearcut stand sizes (2 to 57 ha) on bird species richness, reproductive effort, and relative
abundance at the same Savannah River Site in South Carolina, concluding that clearcut size
does not appear to be an important management issue for the bird community variables that
they considered.
Here, I examined the effects of clearcut size on early successional bird species in a
forest-dominated landscape. My goal was to determine how clearcut size affects community
structure of early successional bird species. Specifically I focused on species richness and
relative abundance, as well as reproductive success. I also looked at differences of species
richness, relative abundance and reproductive success among breeding seasons. The results
presented here supplement the more general survey of avian response to even-aged
management as shown in Gram et al. (2003), in particular because here I report data gathered
7
using more intensive survey methods developed to better evaluate clearcut use by bird
species.
STUDY AREA
I conducted my research in the neighboring counties of Shannon, Carter, and
Reynolds counties (lat. 91 011’ – 91 13’ W, long. 37 00’ – 37 12’ N; Fig. 1) in the Ozark
Forest region of southeastern Missouri, USA. This is one of the most heavily forested regions
in the state, with 84% forest cover (Giessman et al. 1986, Sheriff 2000).
My research was part of the Missouri Ozark Forest Ecosystem Project (MOFEP),
managed by the Missouri Department of Conservation (MDC). MOFEP is a long-term
manipulative experiment designed to determine the impacts of forest management practices,
such as even-aged, uneven-aged, and no-harvest methods on multiple ecosystem
characteristics, such as Neotropical migrant birds, litter and canopy invertebrates, small
mammals, reptiles and amphibians, the physical environment, genetics, and overstory and
understory vegetation. For a more detailed description of the MOFEP experimental design
see Brookshire and Shifley (1997), Shifley and Brookshire (2000), and Shifley and Kabrick
(2002).
Nine study sites were selected to develop the MOFEP experimental design. These
sites were divided into areas of common slope and aspect. The forest management treatments
(even-aged, uneven-aged and no harvest) were each randomly assigned within three blocks,
each containing three of the nine MOFEP sites (Sheriff and He 1997). The stand boundaries
were used to apply the experimental treatments (Brookshire et al. 1997). The sites assigned
with the even-aged treatment were identified by MDC as Cardareva (site 3), Paint Rock (site
8
5) and Peck Ranch (site 9). The MOFEP sites were located in oak-hickory-forest-dominated
landscape, where the dominant tree species were oak trees, such as white oak (Quercus alba),
post oak (Q. stellata), black oak (Q. velutina), and scarlet oak (Q. coccinea). Hickory tree
species like mockernut hickory (Carya tomentosa) and short leaf pine (Pinus echinata) also
were abundant (Shifley et al. 2000, Brookshire and Dey 2000). The forest management
treatments were applied by MDC foresters, beginning commercial timber harvest in early
May 1996 and concluded by November of that year.
A field crew and I surveyed birds in 10 clearcut stands distributed among the sites 3,
5 and 9 (Fig. 2) during two consecutive breeding seasons (2001 and 2002). Additionally, data
were gathered by a different field crew in 2003. The clearcut stands were 5 years old post-cut
at the time of the first breeding season surveyed (2001). The size of the 10 clearcut stands
surveyed ranged from 0.95 to 11.38 ha; they were of irregular shape, had similar vegetation
characteristics, and were surrounded by mature oak-hickory forest. Vegetation height ranged
between 0.5 and 1.95 m at the start of the study, but was between 2 to 3.8 m at the end of the
2003 breeding season. The dominant plant species were summer grape (Vitis aestivalis),
Bosc’s panic grass (Panicum boscii), whip nutrush (Scleria triglomerata), Pennsylvannia
blackberry (Rubus pennsylvanicus), oldfield cinquefoil (Potentilla simplex), Virgina-creeper
(Parthenocissus quinquefolius), winged elm (Ulmus alata), heliopsis (Heliopsis
helianthoides), black edge sedge (Carex nigromarginata), black gum (Nyssa sylvatica),
bracken fern (Pteridium aquilinum), and a very few trees (oaks and pines), which became a
more pronounced portion of the vegetation by 2003. Some oak trees were left uncut to
provide wildlife shelter and shortleaf pines were left to provide seeds for pine regeneration
(Grabner and Zenner 2000).
9
METHODS
Bird Sampling
All early succession bird species found in the clearcuts were recorded during the
surveys. Relative abundance and reproductive success data were gathered for five focal early
successional bird species: Yellow-breasted Chat, Indigo Bunting, White-eyed Vireo, Hooded
Warbler, and Prairie Warbler. These species were selected because they are easy to detect
and record because they are territorial and vocal, they are common on the study area (based
on data from prior and concurrent studies), and we had relatively easy access to their nests
for monitoring reproductive success.
Following cutting in 1996, MOFEP personnel continued to monitor bird populations
as they had before treatments were applied. This involved spot-mapping on fairly large plots
(45 ha) that were visited 8 to 10 times per season (Clawson et al. 2002). Some of these plots
had clearcuts on them and some did not. The clearcuts were impenetrable thickets of dead
wood in 1997 and dead wood covered with vines in 1998 and 1999. Counts of birds on the
clearcuts through the year 2000 were done by walking the edge of the clearcut and detecting
birds within the cuts as best one could. Published results that presented second-growth bird
data used these counting techniques (Gram et al. 2003)
As the clearcuts grew and the bird populations increased, MOFEP personnel knew
they would not be able to detect many individuals living in the interior of the clearcuts.
Underestimating the numbers of breeding bird territories on the clearcuts would cause them
to misjudge the importance of even-aged treatments to early-successional birds, especially in
larger cuts. To avoid this, it was decided to create narrow paths through the clearcuts (Figure
10
2) to better survey the entire clearcut area. These bird paths were trails made especially for
walking in the interior of the clearcuts. Trails were cleared of shrubs and fallen woody
material just enough to facilitate walking by observers and were no more than one meter
wide. The bird paths did not open at the edges of the clearcut stands to avoid negative effects
on the study that would occur if deer or other animals started using these trails on a regular
basis.
I used spot-mapping to estimate species richness and relative abundance. Spotmapping was performed from mid-May to the end of June in 2001, 2002, and 2003. Each
clearcut was surveyed by my field assistants and me10 times in the first field season, 12
times in the second season, and 9 times in the third season. Each clearcut was surveyed by a
single field assistant each morning at first light for a period of 3 to 4 hours. All field
assistants received training in both bird vocalizations and the spot-mapping method. Starting
points and directions were chosen randomly in advance. Field assistants monitored a
different clearcut each morning to avoid observer biases. Censuses were not conducted
during periods of extreme weather conditions (heavy rain or strong winds). We used enlarged
topographic maps (1:3330 mm) of the clearcuts to record all detections of birds heard and
seen in the clearcuts, using alpha-code names to record each bird species detected (Ralph et
al. 1993).
Reproductive success data were collected by locating bird nests while conducting
spot-mapping and by deliberate searching from mid-May through July in 2001, 2002 and
2003. Every nest found was recorded on a topographic map of the corresponding clearcut
stand and nest location was also marked on-site by placing a piece of pink flagging 3-5 m
away from the nest to facilitate consecutive visits to monitor nest progress. Each nest was
11
monitored every 3-4 days until nest fate could be determined, following BBIRD protocol
(Martin et al. 1997). Additionally, I recorded any evidence of predation and brood parasitism.
A nest was considered a failure when the nest was empty and/or damaged before the
predicted fledging date and we were not able to see either any bird activity near the nest or
did not find adults feeding fledglings nearby. I classified a failed nest as: depredated when
nest, eggs, or nestlings disappeared; abandoned when eggs or nestlings were left unattended
in the nest; failed because of stochastic events (weather or other casual event); or parasitized
by cowbirds (no host young fledged although cowbirds may have fledged successfully).
Conversely, if the nest had nestlings up to the predicted date of fledging and we were able to
find adults feeding fledglings, the nest was considered successful. For each nest, we recorded
the date found, the number of host and cowbird eggs, the number of nestlings, and the
number of fledglings.
Data Analysis
Once the bird data had been collected, I estimated species richness as the total
number of bird species found on each clearcut stand. To test for differences in species
richness among the three years I use a general linear model (PROC GLM, SAS 1995). To
determine whether or not clearcut size had any effect on species richness I used a linear
regression model (PROC REG, SAS 1995).
Relative abundance was estimated for each focal early successional bird species and
represented as number of territories/stand (Robbins 1970, Ralph et al. 1993, and Bibby et al.
2000). Relative abundance was estimated by generating composite maps for each focal
species by year by clearcut stand. I used a color-coded system to separate detections by date.
12
To define bird territories I considered clusters of three or more observations from three or
more different census dates to constitute a territory. To analyze for differences among years
I used a general linear model (PROC GLM, SAS 1995). The effect of clearcut size on
relative abundance was analyzed by using linear regression models (PROC REG, SAS 1995).
I determined reproductive success by the Mayfield method (Mayfield 1961, 1975). I
calculated daily nest mortality and nesting success (probability that a nest survived the entire
nesting cycle). Nesting success is defined as daily survival raised to the exponent of the
number of days in the nesting cycle for each species. I calculated nesting success for each of
the five focal early successional bird species.
In all the statistical analyses, a significant level of alpha of 0.10 was used because
sample size was small (n= 10 clearcuts). All analyses were performed with SAS (version
8.02).
RESULTS
Species Richness
A total of 41 bird species were recorded in the clearcut stands during 2001-2003
(Table 1). In 2001, 36 species were recorded, with 37 species in 2002, and 41 species in
2003. Most species were detected during all three years except for American Crow (Corvus
brachyrhynchos), American Goldfinch (Carduelis tristis), American Redstart (Setophaga
ruticilla), Carolina Chickadee (Poecile carolinensis), Carolina Wren (Thryothorus
ludovicianus), Common Yellowthroat (Geothlypis trichas), Hairy Woodpecker (Picoides
villosus) and Ruby-throated Hummingbird (Archilochus colubris), which were recorded only
on one or two of the three field seasons. Of the 41 species, 12 were considered early
13
successional specialists because they were never recorded during the pre-treatment period
(1991-1995, Gram et al. 2003) and the rest were primarily forest bird species. The 12 early
successional species were detected in all years except for Common Yellowthroat and
American Goldfinch which were absent in 2001 and 2002 respectively. The five early
successional bird species were detected on all of the 10 clearcuts surveyed during the three
consecutives years. Over all years, the total mean number of species by clearcut stand size
(Table 2) ranged from 22.3 (+ 2.3 SE) in the smallest stand (0.95 ha) to 33 (+ 1.52 SE) in the
largest clearcut (11.38 ha). Species richness did not differ significantly by year (F=1.62,
df=2, P=0.2261). Therefore, I pooled data for the three years and used a linear regression
model (PROC REG, SAS 1995) to examine the effect of stand size on species richness. A
positive relationship between clearcut size and species richness was found (P= 0.0026, r2=
0.6975), indicating that the number of species was higher in larger clearcuts than in smaller
stands (Fig. 3).
Relative Abundance
Relative abundance estimates were calculated for the five focal early successional
bird species (Yellow-breasted Chat, Indigo Bunting, White-eyed Vireo, Hooded Warbler, and
Prairie Warbler), which also represented the five most abundant species on all of the 10
clearcut stands. Over all years, Yellow-breasted Chat was the most abundant species found
on the clearcut stands combined with a mean number of 27 (+ 4.54 SE) territories, followed
by Indigo Bunting with 14.9 (+ 2.54 SE), White-eyed Vireo with 11.6 (+ 1.62 SE), Hooded
Warbler with 7.6 (+ 1.36 SE), and Prairie Warbler with 5.6 (+1.49 SE) territories (Table 3).
14
Effect of Clearcut Size on Relative Abundance
Over all, clearcut size had a significant effect on the number of territories on four of
the five focal early successional species. Abundance of Hooded Warbler seemingly, was not
affected by clearcut size. I combined the three year abundance data for each focal early
successional species to test for the effect of clearcut size on relative abundance. A positive
relationship between clearcut size and the number of territories/stand was detected for
Yellow-breasted Chat (r2= 0.5664, P= 0.0120), Indigo Bunting (r2= 0.3192, P= 0.0888),
White-eyed Vireo (r2= 0.3969, P= 0.0509), and Prairie Warbler (r2= 0.7340, P= 0.0015),
indicating that the number of territories/stand increased when increasing the size of the
clearcut stand (Fig. 4). On the other hand, regression analysis revealed no effect of clearcut
size on the number of territories/stand on Hooded Warbler (r2= 0.0008, P= 0.9379).
Reproductive Success
I recorded 64 nests from 11 different species for the three breeding seasons surveyed.
I found and monitored 51 nests of the focal early successional birds, excluding the Prairie
Warbler for which no nest could be found. I found nests of early successional species in all
years except for the Hooded Warbler. Statistical significance was difficult to achieve due to
the low number of nests found and monitored during the three breeding seasons. Analysis of
variance revealed that number of early successional species nests found varied among years
(F= 4.32, df= 2, P= 0.0293), showing a decrease from 2001 throughout 2003 mainly because
during the last breeding season the number of nests found was very low compared with the
previous years (Figure 5). Linear regression showed no effect of clearcut size on the mean
number of nests found (r2= 0.0022, P= 0.8978). The number of nests found showed a random
15
distribution among the different clearcut sizes (Figure 6). Because of the low number of nests
found, I was unable to test for the effect of clearcut size on nest success and daily survival
rate. Instead, I pooled nest data from all years for each early successional species and present
nesting success data and daily survival rates for four focal early successional species (Table
4). Indigo Bunting and Yellow-breasted Chat were the species with the most nests found.
Nesting success averaged 59% for Yellow-breasted Chat and 64% for Indigo Bunting based
on Mayfield calculations. The rate of brood parasitism for nests of early successional birds
altogether was 7.8 % (n= 51 nests).
DISCUSSION
Overall, my results suggest that even-aged forest management treatments have a
positive effect on early successional breeding birds. Species richness as well as relative
abundance of early successional birds increased proportionally with clearcut size. Despite the
low number of nest found, reproductive success appeared to be relatively high and was not
influenced by different clearcut size treatments.
Species Richness
My results showed that clearcut stands supported both, early successional bird species
and forest species. The total number of species detected in all the clearcut stands combined
did not show a significant difference during the three-year study. The number of early
successional bird species did not change considerably from one breeding season to another,
remaining in 11 species in 2001 and 2002, and 12 species in 2003. In addition, forest birds
also showed practically no difference on the number of species from one breeding season to
16
another, going from 25 species in 2001 to 26 in 2002, and 29 in 2003. Early successional
species used clearcut for breeding and foraging, while forest bird species might use clearcuts
mainly for foraging and cover, by taking advantage of the dense understory (Thompson and
Fritzell 1990, Thompson et al. 1992, Annand and Thompson 1997).
When species richness was analyzed on a per stand-size basis, there was a significant
relationship between the number of bird species and clearcut size, meaning that larger stands
contained more species than smaller stands. This species-area relationship, which is one of
the widest generalizations in ecology, can be explained from different viewpoints. The
“habitat-diversity” hypothesis (Williams 1964) proposes that as an area becomes larger, new
habitats or microhabitats are encountered, and thus species richness increases with area.
Although the clearcut stands in this study were selected to be as homogeneous as possible, it
likely there were differences in micro and macro habitat scales between larger and smaller
clearcuts, influencing perhaps the number of species that occurred on the different stand
sizes.
A second aspect that may explain the positive species-area relationship has to do with
the sampling hypothesis proposed by Connor and McCoy (1979) which it says that the
number of species increases with area because sampling intensity is greater in large areas that
in smaller ones. Although I attempted to standardize sampling methodology in this survey it
is clear that sampling larger clearcuts would take longer observer effort that in smaller
clearcuts, and then record of individuals could be greater.
My results on species richness are similar to the patterns observed by Rudnicky and
Hunter (1993), who found a relationship between clearcut size and avian species richness in a
forest-dominated landscape in Maine. Also my findings are comparable to those obtained by
17
Welsh and Healy (1993), who found that even-aged treatment had a positive effect on bird
species diversity in New Hampshire. In contrast, my results differ from the pattern observed
by Krementz and Christie (2000), who found that species richness did not increase with
increasing clearcut size at the Savannah River Site in South Carolina, arguing that they
controlled for sampling effort, by sampling in a constant basis, both in terms of area sampled
per stand and net hours sampled per plot.
Relative Species Abundance
Overall, clearcut size affected relative abundance of Yellow-breasted Chat, Indigo
Bunting, White-eyed Vireo, and Prairie Warbler as expected, but not Hooded Warbler.
Relative abundances for Yellow-breasted Chat, Indigo Bunting, White-eyed Vireo and
Prairie Warbler were consistent throughout the three breeding seasons, indicating that despite
the size of the stand, these 5-7 years old clearcuts are suitable habitat for the focal early
successional bird species. The number of territories for these species increased with
increasing clearcut size, so larger clearcuts had more bird territories. It is obvious that larger
clearcuts provide more space where birds can establish breeding territories.
Hooded Warbler was the fourth most abundant species in the study and its relative
abundance did not seem to be affected by clearcut size. This may be to the fact that Hooded
Warblers were found mainly in the edges of the clearcuts because it has been found that this
species prefers smaller openings created by uneven-aged treatments because of the small
canopy gaps (Annand and Thompson 1997). Therefore, clearcut edges may have been
preferred by this species because of their closeness to the canopy forest.
18
Relative abundances for the four focal species were greater in clearcuts that ranged
between 7 and 10 ha in size, and lower abundances were in clearcuts between 0.95-1.13 ha.
Despite the small size of some clearcuts, they still support early successional birds perhaps
because these smaller stands were adjacent to larger clearcuts.
Reproductive Success
The number of early successional bird nests decreased gradually from one breeding
season to another, because on 2003 the number of nests recorded was very low compared
with the 2001 and 2002 breeding seasons. Clearcut size did not affect the number of nests
found; no nest distribution pattern was evident.
Because of the low number of early successional bird nests found (n=51), I was
unable to test for the effect of clearcut size on nest success and daily survival rates. The
causes of finding a low number of nests can be attributed to the difficulty to enter the
clearcuts despite the bird paths created, because of the snags and woody debris that were not
removed during the timber harvest. Nest predation or brood parasitism might not be a
determinant factor that leads to finding few nests because little evidence of predators was
detected on any of the clearcuts surveyed and rates of brood parasitism were low as those
found for Clawson et al. (2002) and Gram et al. (2003). In addition, landscape characteristics
also may be an important factor that can affect reproductive success of both early
successional and forest birds. In the scenario where patches of early successional habitat are
embedded in heavily forested landscapes, as in the Ozark region in southern Missouri, it has
been considered that the openings are more viable for early successional birds than habitats
in agricultural landscapes, and seem to have a less negative effect on forest birds as well
(Annand and Thompson 1997, Thompson and Dessecker 1997).
19
Conservation Implications
The results presented here provide valuable implications for the conservation and
management of early successional bird species in southeastern Missouri. Implementation of
even-aged practices in a forest-dominated landscape create new habitat for early successional
bird species that were absent or in low numbers, providing cover, food and nesting sites.
Previous data from the same area (Clawson et al. 2002, Gram et al. 2003) showed that forest
management practices have an adverse effect on forest bird abundances in and around the
openings; however, the number of forest birds detected in the clearcuts can be an indication
of the use that these species make of some resources such as food and cover, especially for
adult birds raising fledglings, which were encountered very often during nest monitoring.
Also, post-fledgling juvenile birds can use clearcut habitat as a source of food and cover
while dispersing to another areas (Anders et al. 1997; Vega Rivera et al. 1998), and in
general, birds can use clearcuts to fatten up before starting the annual migration cycle.
After implementation of the even-aged treatments in 1996, abundance of the five
focal early successional bird species increased significantly (Gram et al. 2003), and at the
time the stands were between 5 and 7 years old it seemed that abundances for these species
were still high. All of the five focal species were recorded in all of the different clearcut
sizes, although nesting of Hooded Warbler was not recorded during the 2001 breeding season
and no Prairie Warbler nests were found during the three breeding seasons. Although some
of the early successional bird species are considered to have “minimum-area” requirements,
it seems that space availability contributed more to abundances for this species. Early
successional birds seem to take advantage of the clearcuts regardless of the size, species like
20
Yellow-breasted chat, considered with minimum-area requirements, were making use of even
the smaller clearcuts (0.95 and 1.13 ha).
It is clear that uneven-aged treatments would have a less severe effect on forest bird
abundances, but the openings created by this method are preferred by a few species such as
Indigo Bunting and Hooded Warbler and are less suitable for the majority of the early
successional birds. My results for even-aged stands are similar to those reported by studies
comparing the effect of uneven-aged and even-aged harvest methods on bird abundances in
the Ozark region in southern Missouri, where clearcuts created by the even-aged method had
greater abundances of early successional birds and also revealed that a number of mature
forest birds made use of these regeneration stands (Thompson et al. 1992, Gram et al. 2003).
Creating bird paths inside the clearcuts resulted in better bird abundance estimations (Fig. 7).
My study showed that abundances of early successional birds are higher compared with those
data reported for the same sites with no bird paths (Clawson et al. 2002).
Even-aged treatments seem to be a feasible strategy to create suitable habitat for early
successional bird species without significantly affect mature forest bird species. This timber
harvest method creates sufficient undersory to provide foraging and nesting cover for early
successional birds. Implementation of even-aged treatments in largely forested areas, such
the Missouri Ozark forest, have a les significant effect on mature forest bird species and will
provide suitable habitat for early successional birds. To achieve conservation and
management goals for early successional birds, it is necessary to generate an array of
different clearcut sizes, 3 and 10 ha.
21
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28
Table 1. Bird species detected in the clearcut stands in the Missouri Ozarks (2001-2003).
Species in bold represent early successional birds.
Common Name
Scientific Name
Alpha
Code
Mourning Dove
Yellow-billed Cuckoo
Ruby-throated Hummingbird
Downy Woodpecker
Hairy Woodpecker
Pileated Woodpecker
Eastern Wood-Pewee
Acadian Flycatcher
Great Crested Flycatcher
Red-eyed Vireo
White-eyed Vireo
Yellow-throated Vireo
Blue Jay
American Crow
Tufted Titmouse
Carolina Chickadee
White-breasted Nuthatch
Carolina Wren
Blue-gray Gnatcatcher
Wood Thrush
Northern Parula
Blue-winged Warbler
Cerulean Warbler
Prairie Warbler
Pine Warbler
Yellow-throated Warbler
Worm-eating Warbler
Black-and-white Warbler
American Redstart
Ovenbird
Kentucky Warbler
Common Yellowthroat
Hooded Warbler
Yellow-breasted Chat
Summer Tanager
Scarlet Tanager
Northern Cardinal
Indigo Bunting
Eastern Towhee
Brown Headed Cowbird
American Goldfinch
Zenaida macroura
Coccyzus americanus
Archilocus colubris
Picoides pubescens
Picoides villosus
Dryocopus pileatus
Contopus virens
Empidonax virescens
Myiarchus crinitus
Vireo olivaceus
Vireo griseus
Vireo flavifrons
Cyanocitta cristata
Corvus brachyrhynchos
Baeolophus bicolor
Poecile carolinensis
Sitta carolinensis
Thryothorus ludovicianus
Polioptila caerulea
Hylocichla mustelina
Parula americana
Vermivora pinus
Dendroica cerulea
Dendroica discolor
Dendroica pinus
Dendroica dominica
Helmitheros vermivorus
Mniotilta varia
Setophaga ruticilla
Seiurus aurocapillus
Oporornis formosus
Geothlypis trichas
Wilsonia citrina
Icteria virens
Piranga rubra
Piranga olivacea
Cardinalis cardinalis
Passerina cyanea
Pipilo erythrophtalmus
Molothrus ater
Carduelis tristis
MODO
YBCU
RTHU
DOWO
HAWO
PIWO
EAWP
ACFL
GCFL
REVI
WEVI
YTVI
BLJA
AMCR
TUTI
CACH
WBNU
CARW
BGGN
WOTH
NOPA
BWWA
CERW
PRAW
PIWA
YTWA
WEWA
BAWW
AMRE
OVEN
KEWA
COYE
HOWA
YBCH
SUTA
SCTA
NOCA
INBU
EATO
BHCO
AMGO
29
Table 2. Mean number of avian species (early successional and mature forest birds) by
clearcut stand size in the Missouri Ozarks, during 2001-2003.
Stand Size (ha)
Mean
N
Standard Error (+)
0.95
1.13
3.04
3.68
3.77
4.9
7.65
7.73
10
11.38
22.3
23.3
28.6
28.6
27
30.6
31.3
29.6
33
30.6
3
3
3
3
3
3
3
3
3
3
2.33
0.66
1.33
0.33
0
2.18
0.88
1.76
1.52
0.88
N= breeding seasons (2001, 2002, 2003)
30
Table 3. Mean number of territories by clearcut size for five focal early successional species
in the Missouri Ozarks (2001-2003).
Clearcut size (ha)
Species
Yellow-breasted Chat
0.95 1.13 3.04 3.68
3.77
4.90
7.65
7.73
10.00 11.38
Mean 2.33 3.33 6.67 6.33 10.00 8.67 13.33 13.67 17.67
SE
0.33 0.88 1.20 1.86 2.52 2.33 2.85 4.70 3.18
8.00
1.15
Indigo Bunting
Mean 1.67 1.33 5.00 3.67
SE
0.88 0.33 0.00 0.88
8.67
1.20
4.67
1.86
5.00
0.58
4.67
0.67
10.00
1.53
5.00
1.53
White-eyed Vireo
Mean 1.33 1.33 4.00 3.66
SE
0.33 0.33 1.53 1.20
4.00
1.53
3.66
1.20
5.66
2.33
6.33
0.88
5.66
2.19
3.00
1.00
Hooded Warbler
Mean 2.00 1.66 3.66 4.00
SE
0.58 0.67 2.33 1.15
1.00
0.58
3.00
1.53
1.00
0.58
4.66
2.19
3.66
2.19
0.66
0.33
Prairie Warbler
Mean 0.00 0.33 0.66 0.33
SE
0.00 0.33 0.66 0.33
2.33
0.66
1.66
0.88
3.66
0.66
2.00
0.57
4.66
0.88
3.00
0.57
SE = standard error
N=3 (years 2001, 2002, 2003)
31
Table 4. Nest success for four focal early successional bird species in clearcut stands in the
Missouri Ozarks (2001-2003).
Species
YBCH
No.
successful/Total
nests
10/19
Observation
days
252
Daily survival
rate
0.9543
Nest
Success (%)*
0.59
INBU
11/19
219.5
0.9636
0.64
WEVI
5/9
97
0.9588
0.60
HOWA
3/3
45.5
1
1
*Nest success calculated using Mayfield method
32
Figure 1. Study area in the Ozark region in southeastern Missouri. The sites are part of the
Missouri Ozark Forest Ecosystem Project (MOFEP), managed by the Missouri Department
of Conservation (Brookshire and Shifley 1997).
Ellington
106
21
Site 5
Even-aged management sites
Clearcuts
Site 3
N
Site 9
33
Figure 2. Arrangement of clearcut stands within the sites Cardareva, Paint Rock and Peck
Ranch. The size of the 10 clearcuts range from 0.95 to 11.38, they had similar vegetation
characteristics, and were surrounded by mature oak-hickory forest. Bird paths were created to
have better abundance estimates of early successional birds.
Bird paths within clearcut stands
Site 5
Paint Rock
Site 3
Cardareva
N
Site 9
Peck Ranch
34
Figure 3. Species richness response to different clearcut sizes in southeastern Missouri
(2001-2003). A total of 41 bird were recorded, both early successional species and mature
forest species.
35
Num. of species
30
25
20
15
y = 0.7949x + 24.179
2
10
R = 0.6975
5
0
0
2
4
6
8
stand size (Ha)
35
10
12
Figure 4. Relative abundance response to different clearcut sizes in southeastern Missouri
(2001-2003). Numbers of bird territories have a positive relationship with stand size, except
for Hooded Warbler.
36
20
12
Yellow-breasted Chat
Indigo Bunting
10
15
8
10
6
y = 1.0011x + 3.5671
2
5
R = 0.5664
0
4
y = 0.4215x + 2.6774
2
R = 0.3192
2
0
0
2
4
6
8
10
12
0
2
4
6
N u m b e r o f b ir d t e r r it o r ie s
Hooded Warbler
10
12
y = -0.0114x + 2.5916
5
White-eyed Vireo
7
6
5
4
3
2
1
0
8
2
R = 0.0008
4
3
2
y = 0.2985x + 2.2442
1
2
R = 0.3969
0
0
2
4
6
8
10
12
0
2
Prairie Warbler
5
4
3
2
y = 0.3737x - 0.1637
1
R = 0.734
2
0
0
2
4
6
8
10
12
Clearcut stand size (ha)
37
4
6
8
10
12
Figure 5. Total number of nests found by year on the clearcut stands (2001-2003). This
includes both early successional birds and mature forest birds.
35
30
N u m b er o f N ests
30
26
25
20
15
8
10
5
0
2001
2002
2003
Year
38
Figure 6. Effect of clearcut size on the mean number of nests found (2001-2003) for all
species combined. No relationship was found between the number of nests found and
clearcut size.
y = -0.001x + 2.1342
5
2
R = 6E-06
4.5
Number of Nests
4
3.5
3
2.5
2
1.5
1
0.5
0
0
2
4
6
8
Stand size
39
10
12
Figure 7. Comparison of two protocols for monitoring early successional birds in clearcut
stands in southern Missouri. One protocol was conducted by monitoring birds around the
clearcut perimeter and the other one used bird paths inside the clearcut stands.
180
Average Density
Estimate w/Bird Path
Average Within Stand Density Estima
(# Territories/100ha)
160
140
Average Density
Estimate w/o Bird
Path
120
100
80
60
40
20
0
INBU
HOWA
YBCH
40
WEVI