1.0 T T T T T T

0.8 - 4

0.6 4

Plot Suitability Index, PV4

ae ee ee oe |
o 1 2 3 4 5 67 8 i

Microhabitat diversity l

Figure 6. The relationship between the average number of elements of
microhabitat diversity per 0.1 ha and the suitability index (Ele-
ments of microhabitat diversity include: seeps or springs, shore- i
line (stream or pond), depression for temporary water, sandy
areas, logs, piles of debris or brush, tree cavities, leaf litter over !
>25 percent of area}

Table 4
Area Categories for Forested Wetland Tracts

Effective Area, ha Documentation

0-16 0-0.29 Blake and Karr (1984) - tracts <16 ha
contain virtually no interior birds.

> 16-100 0.29-0.45 Blake and Karr (1984) - tracts > 16 ha
regularly contain interior bird species.

> 100-600 0.45-0.69 At 100 ha, Temple (1986) found
87-percent frequency of occurrence of
interior bird species.

>600-3,000 0.69-1.0 At 600 ha, Blake and Karr (1984) had
100-percent frequency of occurrence
of 12 interior bird species.

>3,000 1.0 Robbins et al. (1989) suggested a

minimum of 3,000 ha are needed to
retain all breeding forest birds in :
Atlantic reg i

14

Chapter 2. Habitat Model



Appendix A

Table A1
Forest Interior Birds, Reptiles, and Amphibians Occurring in Decid-
uous Palustrine Forested Wetlands in Maryland

Scientific Name
Forest Interior Birds’

Cooper’s hawk Accipiter cooperii
Sharp-shinned hawk Accipiter striatus
Broad-winged hawk Buteo platypterus
Barred owl Strix varia
Pileated woodpecker Dryocopus pileatus
Hairy woodpecker Picoides villosus
Acadian flycatcher Empidonax virescens
Wood thrush Hylocichla mustelina
Cerulean warbler Dendroica cerulea
Worm-eating warbler Hetmitheros vermivorus
Black-and-white warbler Mniotilta varia
Prothonotary warbler Protonotaria citrea
Northern parula warbler Parula americana
Kentucky warbler Oporornis formosus
Ovenbird Seiurus aurocapillus
Louisiana waterthrush Sejurus motacilla
American redstart Setophaga ruticilla
Hooded warbler Wilsonia citrina
Scarlet tanager Piranga olivacea

Note: All forest interior birds and those reptiles and amphibians marked with an asterisk
are considered to be sensitive to habitat fragmentation.

1 From Butcher et al. (1981), Whitcomb et al. (1981), Hamel et al. (1982), Blake and Karr
(1984}, Hayden, Faaborg, and Clawson (1985), and Small and Hunter (1989), with review
comments provided by C. Robbins and M. E. Keller.

2 From Harris (1975) and Behler and King (1979), with review comments provided by

K. BuhImann, S. Gotte, J. Jacobs, J. Mitchell, and R. Reynolds.

Appendix A Al

>


example, assume a tract with a perimeter of 1,000 m had 600 m adjacent to
cropland and 400 m adjacent to upland forest. The permeability factor would
be computed as a weighted average, as follows:

Perimeter Relative Permeability Weighted
Cover Type _Length Proportion _Factor__ + Average __
Cropland 600 m 0.6 xX 1.40 = 0.84
Deciduous 400 m 0.4 x 2.55 = 102
Forest r=1.0 overall = 1.86

The second measure of isolation used in the model is the proximity of
other deciduous forested wetlands. The assumption is that the effective area
of deciduous palustrine forested wetlands should be increased if the tract is
within 2 km of other deciduous forested wetland tracts. This factor ranges
from 1 to 2.55 and is quantified as follows:

Factor for percent forested wetland habitat within 2 km of tract boundary
= 1.0 + (percent deciduous forested wetland within 2 km of tract bound-
ary (decimal form) x 1.55)

The overall isolation factor (a value ranging from 1 to 6.5) used in the
model is determined by multiplying the two separate measures:

Isolation factor (TV2) = (permeability factor x percent deciduous forested
wetland factor)

It should be noted that although corridors are not treated as a separate
tract-level variable, their influence is a component in defining a tract and
determining the permeability factor. The definition of a tract includes all
contiguous deciduous palustrine forested wetland. A narrow corridor of
deciduous palustrine forested wetland habitat connecting two larger forested
wetlands would serve to make one contiguous and larger total tract. Thus, the
model treats corridors as a part of the tract and their effect in the model is to
increase the total area of the tract. I agree with Wilcove, McLellan, and
Dobson (1986) that land-use practices which allow populations of target spe-
cies to exist at least marginally in the surrounding habitat and allow popula-
tions to diffuse, as indicated by the permeability factor, are more useful than
corridors.

Tract suitability index (TS!)

The tract suitability index (TSI) is derived from a modified species-area
curve (Figure 2). The input value (x-axis) is effective tract area and the out-
put (y-axis) is scaled from 0 to 1. Tracts with effective areas >3,000 ha

receive a TSI of 1.0.

Chapter 2 Habitat Model



other hand, very large tracts of bottomland forest will generally have native
richness indices >0.3, even with plot variables in their worst-case condition.

The model is most sensitive to changes in the area of the bottomland tract.
A change in tract area in smaller size tracts will have the most significant
impact on the native richness index. Changes in area of larger tracts have a
less significant impact but still more impact than changes in other model
variables. Changes in any one plot or tract variable result in relatively small
changes in the richness index.

A sample worksheet to determine plot and tract suitability index values and
the overall HSI is provided in Table 5.

Table 5
Sample Worksheet for Plot and Tract SI and Overall HSI
Determination

_

Tract Identification

Plot Number and Raw Data

Plot Variables 1 le Is la [s 6 |7 |8_ [9 [10 [Average |si
Average height tree canopy, m PVI =
Foliage height diversity pV2 =
Soil moisture regime PV3 =
Microhabitat diversity PV4 =

Plot St = 20PV1_X Per + PV3 + PV4
'
i

Tract Variables

Tract area, ha =

Core area factor =

Permeability factor =

Product of permeability factor and percent deciduous forested wetland factor = Isolation

{

i

i

{

Percent deciduous forested wetland factor = |
factor =

Effective area, ha = tract area x core area factor x isolation factor =

2.227 x (effective area)?” }
19.8

Tract SI =

Habitat Suit

ity Index

|
HSI = Plot SI x Tract SI |

18

Chapter 2. Habitat Model



Preface

The work described in this report was authorized by Headquarters,
U.S. Army Corps of Engineers (HQUSACE), as part of the Delineation and
Evaluation Task Area of the Wetlands Research Program (WRP). The work
was performed under Work Unit 32756, for which Mr. Ellis J. Clairain, Jr.,
Wetlands Branch, Environmental Laboratory (EL), U.S. Army Engineer
Waterways Experiment Station (WES), was Technical Manager. Mr. John
Bellinger (CECW-PO) was the WRP Technical Monitor for this work.

Mr. Dave Mathis, Jr. (CERD-C), was the WRP Coordinator at the Direc-
torate of Research and Development, HQUSACE; Mr. William L. Klesch
(CECW-PO) served as the WRP Technical Monitor’s Representative;

Dr. Russeli F. Theriot, EL, was the Wetlands Program Manager.
Mr. Clairain was the Task Area Manager.

This work was performed by Mr. Richard L. Schroeder, National Biologi-
cal Service, Midcontinent Ecological Science Center, Fort Collins, Colorado.
Mr. R. Daniel Smith, Wetlands Branch, EL, was the Project Manager under
the general supervision of Mr. Clairain, Chief, Wetlands Branch, EL;

Dr. Conrad Kirby, Chief, Ecological Research Division, EL; Dr. Edwin
Theriot, Assistant Director, EL; and Dr. John Keeley, Director, EL.

Ms, M. E. Keller and Mr. C. Robbins assisted in compiling the list of
Maryland forest interior birds, and Messrs. K. Buhlmann, S. Gotte, J. Jacobs,
J. Mitchell, and R. Reynolds assisted with compiling the list and cover type
use of Maryland reptiles and amphibians. Ms. S. L. Haire provided assis-
tance with the compilation of habitat requirements for the reptiles and amphi-
bians, and conducted the Geographic Information System applications of the
model. Ms. N. Sexton provided assistance with compiling habitat information
for forest interior birds. Mr. R. Bruleigh assisted with the requisition of maps
and data for the Breeding Bird Census (BBC) plots used to test portions of the
model hypotheses. The compilers of the 18 BBC plots are commended for
their assistance in identifying the bird census plot locations and providing
additional information on plot and habitat conditions.

Individual reviewers assisting with their thoughtful and constructive com-
ments were: Ms. Keller and Messrs. A. W. Allen, R. H. Jones, S. Martin,

and R. B. Stiehl.

vii



Mader, H. J. (1984). “Animal habitat isolation by roads and agricultural
fields,” Biological Conservation 29, 81-96.

Minton, S. A., Jr. (1968). “The fate of amphibians and reptiles in a subur-
ban area,” Journal of Herpetology 2(3-4), 113-116.

Pague, C. A., and Mitchell, J. C. (1991). “The amphibians and reptiles of
Back Bay, Virginia.” Proceedings of the Back Bay Ecological Symposium.
H. G. Marshall and M. D. Norman, ed., Old Dominion University, Nor-
folk, VA, 159-166.

Pechmann, J. H. K., Scott, D. E., Gibbons, J. W., and Semlitsch, R. D.
(1989). “Influence of wetland hydroperiod on diversity and abundance of
metamorphosing juvenile amphibians,” Wetlands Ecology and Management
1(1), 3-11.

Robbins, C. S. (1979). “Effect of forest fragmentation on bird populations.”
Workshop proceedings: Management of north central and northeastern
forests for nongame birds, January 23-25, 1979, Minneapolis, Minnesota.
R. M. DeGraaf and K. E. Evans, ed., U.S. Forest Service, North Central
Forest Experiment Station, General Technical Report NC-51, St. Paul,
MN, 198-212.

Robbins, C. S., Dawson, D. K., and Dowell, B. A. (1989). “Habitat area
requirements of breeding forest birds of the Middle Atlantic states,” Wild-
life Monographs 103, 1-34.

Robinson, S. K. (1992). “Population dynamics of breeding neotropical
migrants in a fragmented Illinois landscape,” Ecology and conservation of
neotropical birds, 408-418.

Sauer, J. R., and Droege, S. (1992). “Geographic patterns in population
trends of neotropical migrants in North America.” Ecology and conserva-
tion of neotropical land birds. J. M. Hagen and D. W. Johnston, ed.,
Smithsonian Institution Press, Washington, DC, 26-42.

Schroeder, R. L., Cable, T. T., and Haire, S. L. (1992). “Wildlife species
richness in shelterbelts: Test of a habitat model,” Wildlife Society Bulletin
20, 264-273.

Small, M. F., and Hunter, M. L., Jr. (1989). “Response of passerines to
abrupt forest-river and forest-powerline edges in Maine,” Wilson Bulletin
101(1), 77-83.

Stamps, J. A., Buechner, M., and Krishnan, V. V. (1987). “The effects of
edge permeability and habitat geometry on emigration from patches of
habitat,” American Naturalist 129, 533-552.

Tate, J., Jr. (1986). “The Blue List for 1986,” American Birds 40, 227-236.

29

References

eS


assess average conditions for the wildlife community of the entire tract.
Compute a single SI value for each plot-level variable for the entire
tract, and combine these into the overall plot SI for each tract or sub-
sample of tracts.

c. Use remotely sensed data to assess the tract-level variables. Classify
habitats adjacent to the forested wetland tracts and determine the core
area and isolation factors. Determination of the isolation and core area
factors may he facilitated through the use of a Geographic Information
System (GIS), although measures with such tools as a planimeter and
dot-grid overlay would also be appropriate. Determine the effective
area of each tract, as follows:

Effective area = measured area X core area factor x isolation factor

Enter the effective area into the tract SI graph formula (Figure 2), and
determine an SI value.

d. Compute an overall native richness index for each tract by multiplying
the tract SI by the average plot SI for that tract.

e. For between-tract comparisons, such as in a HEP application or other
management action, assign the tract to a specific size category
(Table 4), based on the effective area. Management or mitigation
recommendations should not allow tradeoffs such that actions in
smaller tract-size categories are allowed to compensate for losses in
larger tract-size categories.

Applying the model to portions of a tract

Situations may arise where the model is to be applied to some portion of
an entire tract, for example, when a 15-ha corner of a 700-ha tract is to be
impacted. The basic procedure to be followed in determining the native rich-
ness index is similar to the steps outlined above, with the following
differences:

a. Determine the size of the evaluation area, based on the nature and
extent of the potential impact. For example, if a road is cut through
the corner of a large tract, the evaluation area might be the area of the
actual impact, and any necessary buffer for secondary impacts. Com-
pute the plot variable SI’s only within the evaluation area within the
tract.

b. Computation of Habitat Units (HUs) (area x native richness index) for
use in HEP should be based on the size of the evaluation area, not the
entire tract.

15

Chapter 2 Habitat Model



Table 7
Occurrence of Forest Interior Birds in Relation to Extensive Forests
(from Whitcomb et al. 1981)

Number of Points

Recorded from Number of Points
Sites With Exten- | Recorded in all
Species sive Forest Other Habitats Sign., P

i

Black and white warbler 14 0 0.001
Prothonotary warbler 4 i} 0.01

Northern parula warbler 25 2 0.001
Ovenbird 30 3 0.001
Louisiana waterthrush 5 i 0.01

Kentucky warbler 14 2 0.001
Hooded warbler 12 4 0.001

American redstart 13 i} 0.001
DI

Brown 1993). Robinson (1992) found very high rates (75 percent) of parasit-
ism by brown-headed cowbirds on the nests of neotropical migratory birds in
Illinois forest fragments. Only one young was fledged from 15 wood thrush
nests. Robinson concluded that these small, isolated woodlots function as
population sinks and may be receiving immigrants from source populations
from as far as 200 km.

Several studies have estimated minimum areas needed by forest birds
(Galli, Leck, and Forman 1976; Robbins 1979; Hayden, Faaborg, and
Clawson 1985). Patches larger than estimated minimum areas may be needed
to support viable populations of certain bird species (Gibbs and Faaborg
1990). Increasing the effective size of forest areas is necessary to counter the
negative side effects of forest insularization (Lynch 1987). This can be
accomplished by: (a) increasing contiguous size, (b) promoting compatible
land uses in adjacent lands, and (c) increasing the amount of forest area within
the region.

Pague and Mitchell (1991) recommend that efforts to conserve the reptile
and amphibian community in Back Bay, Virginia, should focus on the protec-
tion and restoration of wetlands in large areas.

Isolation

Whitcomb et al. (1981) found that decreasing forest isolation was positively
correlated with species richness of forest interior birds. Extensive deforesta-
tion in areas surrounding a forest tract may cause populations of forest interior
birds to decline and result in their local extinction (Askins and Philbrick

21

Chapter 3. Habitat Use Information



size categories of forested wetland tracts (Table 4). HUs should be calculated
for the total area within each area category, and any tradeoffs among catego-
ties for purposes such as mitigation must occur in an equal or larger area
category than the HUs of concern. This is basically the same as treating each
size category as a separate cover type. In impact assessment applications, this
will ensure that losses in larger tracts will only be mitigated with actions in
large tracts. Without such a system, it is possible for HU losses in large
tracts to be made up by gains in the combined total of HUs from several
smaller tracts. Habitat units should not be summed across all tracts because
certain species found in larger tracts will not occur in any number of smaller
tracts.

Sample data sets

A more complete understanding of the logic and behavior of quantitative
models can be obtained through assessment of sample data sets. The follow-
ing sample data sets are intended to show the effects of the plot and tract
variables on the overall native richness index. Verbal descriptions of these
hypothetical situations should aid in visualizing the habitat conditions being
portrayed.

i The relative importance of the tract and plot variables in the model can be
assessed by setting one at very low levels of suitability and the other at maxi-
mum levels. The following two scenarios demonstrate the effects on the
native richness index from these two extreme conditions.

Scenario 1, This data set depicts a very small forested wetland tract that
is highly isolated from other tracts and surrounded by croplands. The internal
! (plot) habitat represents a mature forest with ideal conditions for the plot
variables. The factor for percent forested wetland within 2 km is 1.08, and
the permeability factor is 1.4, yielding an isolation factor of 1.51. The core
factor is 0.15. The original area is 1.0 ha, and the resultant effective area is
0.23 ha. The tract SI is 0.075 and the plot SI is 1.0, resulting in a native
richness index of 0.075.

Scenario 2. This data set depicts a very large forested wetland tract that is
not isolated and has a large amount of core area. The internal (plot) habitat
represents a very young forest, with small trees, low amounts of understory
and ground cover, moderate soil moisture conditions, and low levels of micro-
| habitat diversity. The plot SI for such conditions is 0.3. If the tract condi-
| tions are a 1.0 SI, the resultant overall native richness index is equal to 0.3.

Based on these two scenarios, the tract portion of the model exerts the
greatest influence on the final native richness index. It is not unreasonable to
expect to encounter very small tracts that have high values for the plot
variables. The small size of the tract alone will cause the native richness
index to be very low and approach zero in cases of very small tracts. On the

17
Chapter 2 Habitat Model

a



Temple, S. A. (1986). “Predicting impacts of habitat fragmentation on forest
birds: A comparison of two models.” Wildlife 2000: Modeling habitat
relationships of terrestrial vertebrates. J. Verner, M. L. Morrison, and
C. J. Ralph, ed., University of Wisconsin Press, Madison, 301-304.

Temple, S. A., and Cary, J. R. (1988). “Modeling dynamics of habitat-
interior bird populations in fragmented landscapes,” Conservation Biology
2, 340-347.

Tiner, R. W., Jr. (1985a). “Wetlands of Delaware,” U.S. Fish and Wildlife
Service, National Wetland Inventory, Newton Corner, MA, and Delaware
Departmetn of Natural Resources and Environmental Control, Wetlands
Section, Dover, DE, cooperative publication.

- (1985b). Wetlands of New Jersey. U.S. Fish and Wildlife
Service, National Wetlands Inventory, Newton Corner, MA.

U.S. Fish and Wildlife Service. (1980). Habitat evaluation procedures
(HEP). Division of Ecological Services ESM 102.

Whitcomb, R. F., Lynch, J. F., Klimkiewicz, M. K., Robbins, C. S., Whit-
comb, B. L., and Bystrak, D. (1981). “Effects of forest fragmentation on
avifauna of the eastern deciduous forest.” Forest island dynamics in man-
dominated landscapes. R. L. Burgess and D. M. Sharpe, ed., Springer-
Verlag, New York, Heidelberg, Berlin, 125-206.

Wiens, J. A., Crawford, C. S., and Gosz, J. R. (1985). “Boundary dynam-
ics: A conceptual framework for studying landscape ecosystems,” Oikos
45(3), 421-427.

Wilcove, D. S. (1988). “Forest fragmentation as a wildlife management
issue in the eastern United States. Is forest fragmentation a management
issue in the northeast?” U.S. Forest Service, Northeastern Forest Experi-
ment Station, General Technical Report NE-140. Wilderness Society,
Washington, DC, 1-5.

Wilcove, D. S., McLellan, C. H., and Dobson, A. P. (1986). “Habitat
fragmentation in the temperate zone.” Conservation biology: The science
of scarcity and diversity. M. E. Soule, ed., Sinauer Associates, Inc.,
Sunderland, MA, 237-256.

Wilkerson, L. (1988). “SYSTAT: The system for statistics.” SYSTAT,
Inc. Evanston, IL.

Wyman, R. L. (1990). “What’s happening to amphibians?” Conservation
Biology 4, 350-352.

30

References

ee



1.0 T T

0.8F 4

0.6 - |

0.47 4

0.2F 7

Plot Suitability Index, PV2

0 1 1
0 1 2 3

Foliage height diversity

Figure 4. The relationship between foliage height diversity and the suitabil-
ity index

Plot suitability index (PSI)

The plot suitability index (PSI) is determined with the following formula:

PSI = 2(PV1_ x PV2)!? + PV3 + PV4
4

Determination of Index of Native Richness

The overall index of native richness is a function of the suitability of the
tract, directly modified by the conditions of the plot variables, as follows:

Native richness index = tract SI x plot SI

Application

Sampling effort may vary because of practical or statistical constraints.
Therefore, the level of sampling required to apply the model must be

Chapter 2. Habitat Model



Y = 2.227 * A072

where
Y = bird species richness

A = area in hectares.

Table 1
Minimum Tract Sizes for Forest Interior Birds

| sees | Minimum Tat Size, a | source
Kentucky warbler 2.3 Blake (1991)
Wood thrush 5.1 Blake (1991)
Scarlet tanager 16.2 Blake (1991)
Worm-eating warbler 23 Askins et al. (1987)
Acadian flycatcher 24 Blake (1991)
Ovenbird 24 Blake (1991)
Louisiana waterthrush 42 Hayden et al. (1985)
Northern parula warbler 54 Hayden et al. (1985)
Cerulean warbler 65 Blake (1991)
American redstart 118 Blake (1991) i
Hooded warbler 600 Blake (1991)

Comparable data for all forest interior birds, reptiles, and amphibians
occupying deciduous palustrine forested wetlands were not found in the litera-
ture. It is assumed that this species-area curve can be used to reflect the
changes in native richness in different sizes of forested wetland tracts. In
theory, the number of species will continually increase with increases in area.
For purposes of this model, however, a maximum size area must be selected
to represent the highest output of the model, a suitability index of 1.0. This
area is assumed to be 3,000 ha. Using the species-area equation presented
above, a 3,000-ha forested wetland tract would yield a prediction of 19.8
forest interior bird species, approximating the 19 species used in this model.

Based on the small home ranges of most reptiles and amphibians, 3,000 ha
should be adequate to retain a full complement of these animals. Users of this
model should be aware that to support black bears or other large mammalian
carnivores, total areas of available (accessible to the animal) and suitable
(forested wetlands, upland forest, etc.) habitat would need to be larger than
3,000 ha. ‘

Chapter 2. Habitat Model



Blake, J. G., and Karr, J. R. (1984). “Species composition of bird commu-
nities and the conservation benefit of large versus small forests,” Biologi-
cal Conservation 30, 173-187.

. (1987). “Breeding birds of isolated woodlots: Area and habitat
telationships,” Ecology 68(6), 1724-1734.

Blymyer, M. J., and McGinnes, B. S. (1977). “Observations of possible
detrimental effects of clearcutting on terrestrial amphibians,” Bulletin of the
Maryland Herpetological Society 13(2), 79-83.

Béhning-Gaese, K., Taper, M. L., and Brown, J. H. (1993). “Are declines
in North American songbirds due to causes on the breeding range?” Con-
servation Biology 7(1), 76-85.

Buhlmann, K. A., Mitchell, J. C., and Pague, C. A. (1992). “Amphibian
and small mammal abundance and diversity in saturated forested wetlands
and adjacent uplands of southeastern Virginia.” Proceedings of a work-
shop on saturated forested wetlands in the mid-Atlantic region: The state
of the science. January 29-31, 1992, Annapolis, MD, 1-7.

Burton, T. M., and Likens, G. E. (1975). “Salamander populations and
biomass in the Hubbard Brook Experimental Forest, New Hampshire,”
Copeia 3, 541-546.

Bushman, E. S., and Therres, G. D. (1988). “Habitat management guide-
lines for forest interior breeding birds of coastal Maryland,” Wildlife
Technical Publication 88-1, Maryland Department of Natural Resources.

Butcher, G. S., Niering, W. A., Barry, W. J., and Goodwin, R. H. (1981).
“Equilibrium biogeography and the size of nature preserves: An avian
case study,” Oecologia 49, 29-37.

Environmental Systems Research Institute. (1989). Arc/Info computer soft-
ware. ESRI, Redlands, CA.

Freemark, K., and Collins, B. (1992). “Landscape ecology of birds breeding
in temperate forest fragments,” Ecology and conservation of neotropical
birds, 443-454.

Galli, A. E., Leck, C. F., and Forman, R. T. T. (1976). “Avian distribu-
tion patterns in forest islands of different sizes in central New Jersey,” Auk
93, 356-364.

Gibbons, J. W. (1988). “The management of amphibians, reptiles and small
mammals in North America: The need for an environmental attitude
adjustment, Management of amphibians, reptiles and small mammals in
North America.” R. C. Szaro, K. E. Severson, and D. R. Patton, ed.,
U.S. Forest Service General Technical Report RM-166, Fort Collins, CO.

27

References



24

aquatic habitats by draining, dredging, pollution, or vegetation removal has
serious negative effects on most amphibians. To benefit reptile and amphibian
populations, Jones (1988) recommended maintaining or enhancing surface
litter and vegetation structure, because they help to moderate temperatures,
increase moisture, and provide food and cover.

Based on a literature review of the 51 species of reptiles and amphibians
noted to use deciduous palustrine forested wetlands, key habitat features
needed to support high numbers of herpetofauna were summarized. The
majority of reptiles and amphibians would find suitable habitat in forested
wetlands with high amounts of soil moisture, as well as herbaceous and other
ground cover and underbrush. The presence of a diversity of microhabitats
would be highly desirable. Key features include seeps, springs, shorelines,
sandy areas, logs, leaf litter, debris, and tree cavities.

Chapter 3 Habitat Use information



1. Introduction

This document provides habitat information and a model for evaluating the
quality of wildlife habitat in deciduous palustrine forested wetlands in Mary-
land. The primary intended use of the model is to assist biologists involved in
evaluating these wetlands, both from an impact assessment and management
perspective. The U.S. Army Corps of Engineers and the National Biological
Service have a common interest in providing improved tools for community-
based wildlife habitat assessment.

The Habitat Model section provides documentation of the logic and perti-
nent assumptions used to develop the model. The model presents testable
hypotheses, based on a comprehensive review of pertinent literature, and use
of existing data. The Habitat Use Information section provides a summary of
the information used as the foundation for the model. The Model Test section
describes the current status of tests of model hypotheses.

Chapter 1 Introduction


At the time of publication of this report, Director of WES was
Dr. Robert W. Whalin. Commander was COL Bruce K. Howard, EN.

This report should be cited as follows:

Schroeder, R. L. (1996). “Wildlife community habitat evalua-
tion: A model for deciduous palustrine forested wetlands in
Maryland,” Technical Report WRP-DE-14, U.S. Army Engineer
Waterways Experiment Station, Vicksburg, MS.

The contents of this report are not to be used for advertising, publication,
or promotional purposes. Citation of trade names does not constitute an
official endorsement or approval of the use of such commercial products.

viii



1.0

0.6 - 4

Plot Suitability Index, PV3

A B c D
Soil moisture regime

Figure 5. The relationship between the soil moisture regime during the
growing season and the suitability index ((A) Seasonally inun-
dated (15 to more than 30 consecutive days); (B) Seasonally

1 saturated (15 to more than 30 consecutive days); (C) Temporar-

i ily flooded or saturated (7 to 15 consecutive days); (D) Typically

dry (inundated or saturated for less than 7 consecutive days))

determined by each user. The following guidance is provided to assist in
applying the model in various situations and at varying intensities.

| Applying the model to entire tracts

The basic procedure for applying the model to entire forested wetland
tracts is outlined below.

a. Identify and define the boundaries of individual forested wetland tracts
and compute the area of each tract.

b. Develop a sampling design to measure the plot-level variables in each
tract or in a suitable subsample of tracts stratified by the size categories
shown in Table 4. Determine the habitat conditions for each plot-level
habitat variable on each selected sampling plot. The actual habitat
measurements should be averaged for all plots in the entire tract or
subsample of tracts, even though there will likely be variation in some
of the habitat measurements across plots. Computation of an SI value
for each plot is not recommended because the model is intended to

. 13
Chapter 2 Habitat Model



The model may be suitable for application in other areas of the eastern
United States with deciduous palustrine forested wetlands or other structurally
similar wetlands. Application in other areas should be conducted only after a
thorough review of the model to determine if the assumptions and model
structure appear to be reasonable for the habitat and species of concern.

Model Description

Overview

The richness of forest interior birds and reptiles and amphibians in decidu-
ous palustrine forested wetlands is related to the size and shape of the wet-
land, its internal habitat features, and the landscape context in which it exists.
Internal habitat features are referred to as plot-level variables and include
measures of vegetative structure, such as tree canopy cover. Landscape fea-
tures are referred to as tract-level variables and include measures of size,
shape, and isolation. Tract and plot definitions are as follows:

a. Tract. A contiguous unit of deciduous palustrine forested wetland,
including the combined habitat of forested wetlands joined by corri-
dors, bounded by an area > 10 m wide (Lynch and Whigham 1984;
Askins, Philbrick, and Sugeno 1987) and consisting of either nondecid-
uous palustrine forested wetland habitat or a barrier to species
movement.

b. Barrier. A physical feature that restricts movement at the boundary of
atract. Barriers include roads, rivers, lakes, railroad tracks, and
similar large exposed areas.

c. Plot. A sampling area within a tract for the purposes of estimating
values for internal habitat variables.

Description of tract variables and relations

This section describes the variables and methods that are used to assess the
suitability of individual tracts of deciduous palustrine forested wetlands.
Documentation of the sources of literature used to develop these variables and
hypotheses is provided in the Habitat Use Information section.

The species-area relation forms the basis of the model because the number
and types of species that occupy forested wetland tracts are strongly influ-
enced by tract size. A species-area curve was developed from data on mini-
mum tract sizes used by forest interior birds. These data were found for 11
of the 19 interior birds used in this model (Table 1). The formula for the
species-area curve to fit these data was developed with the “Nonlin” program
from SYSTAT (Wilkerson 1988). The equation to fit this curve (Figure 1) is:

Chapter 2 Habitat Model



3 Habitat Use Information

General

A wide variety of wildlife species occupy deciduous palustrine forested
wetlands in Maryland and surrounding states. This model focuses on two
species groups of special concern in this area: (a) reptiles and amphibians,
and (b) forest interior birds (Appendix A).

Amphibians and reptiles are a significant and important wildlife component
of North American ecosystems and need special consideration in management
and conservation decisions (Gibbons 1988). Anuran amphibians are important
in resource evaluations because they serve as indicator species that integrate
changes in both terrestrial and aquatic portions of their habitat (Beiswenger
1988). Many amphibians require specialized habitats in wetlands and may
serve as indicators of the overall health of wetland ecosystems. The impor-
tance of amphibians in eastern forest ecosystems is indicated by the fact that
salamander biomass at the Hubbard Brook Forest in New Hampshire is about
twice that of birds during the breeding season, and about equal to that of small
mammals (Burton and Likens 1975). Declines in amphibian populations are
of worldwide concern (Wyman 1990; Bishop and Pettit 1992).

Forest interior bird species are important components of forested ecosys-
tems in Maryland (Bushman and Therres 1988), and regionally throughout the
eastern United States (Whitcomb et al. 1981). Of the 19 species identified as
forest interior birds in Maryland deciduous palustrine forested wetlands, 13
have declining populations over some portion of their range (Table 6).

Area and Configuration

The species richness of forest interior birds is positively correlated with the
size of forest tracts (Whitcomb et al. 1981; Askins, Philbrick, and Sugeno
1987; Freemark and Collins 1992). Bird species requiring forest interior
habitat occurred in a highly nested distribution in isolated forest tracts of
different sizes in Illinois (Blake 1991). Most species that occurred in smaller
woodlots also occurred in larger woodlots, whereas the opposite was not true.
Small woodlots were dominated by generalist species that breed and forage in

19

Chapter 3 Habitat Use Information

|



Corps of Engineers Research Report Summary, September 1996

Wildlife Habitat Evaluation

K.

Wildlife Community Habitat Evaluation: A Model for Deciduous Palustrine
Forested Wetlands in Maryland (TR WRP-DE-14)

ISSUE:

Wildlife habitat models have typically focused
on one species. Models are needed to evaluate
habitat for wildlife communities and groups of
key wildlife species.

RESEARCH OBJECTIVE:

This wetland community model meets the needs
of Corps field biologists by providing them with
a well documented, straightforward approach to
evaluating the habitat functions and values of
deciduous palustrine forested wetlands. This
information is necessary to aid the Corps in its
role under Section 404 of the Clean Water Act
to protect existing wetlands or to provide ade-
quate mitigation for unavoidable wetlands
losses. The model is structured to allow rapid
(general) or time-consuming (more detailed)
applications.

SUMMARY:

The model was developed with several levels
of detail and can be applied using a Geo-
graphic Information System (GIS) approach.

The model output is a measure of the expected
level of species richness of forest interior birds,
reptiles, and amphibians. Model inputs include
typical habitat variables such as tree height as
well as spatial variables such as permeability of
tract boundaries and tract isolation. The test of
the model indicated significant positive correla-
tions between the output and interior bird spe-
cies richness from 18 Breeding Bird Census
locations.

AVAILABILITY OF REPORT:

This report is available on Interlibrary Loan
Service from the U.S. Army Engineer Water-
ways Experiment Station (WES) Library, 3909
Halls Ferry Road, Vicksburg, MS 39180-
6199, telephone (601) 634-2355.

To purchase a copy, call the National Technical
Information Service (NTIS) at (703) 487-4650.
For help in identifying a title for sale, call (703)
487-4780.

NTIS report numbers may also be requested
from the WES librarians.

Please reproduce this page locally, as needed.



richness. The effective area of a tract is a function of: (a) the actual-area;
(b) the amount of core area in each tract; and (c) the degree of isolation of
each tract, as follows:

Effective tract area = (measured area X core area factor X
isolation factor)

Core area factor (TV1). The definition of core area is:

The area of a tract that is 100 m or more from a tract boundary that is bor-
dered by nonforested habitat.

The percent of a tract in core area is determined by dividing the amount of
area 100 m or more from a nonforested tract boundary by the total tract area.
Many forested wetlands occur in larger areas of upland forest. A forested
wetland entirely surrounded by upland forest can have 100-percent core
habitat.

A tract with 0 percent of its area in core habitat (either a very small tract
or one that is highly linear or convoluted, and surrounded by nonupland for-
est) is assumed to support 40 percent fewer species over a long time period on
a regional scale. The 40-percent reduction was estimated from an assessment
of the 70 species of birds and herps. It is assumed that all 19 forest interior
birds are sensitive to fragmentation, and based on comments received from
eastern herpetologists, it is assumed that nine of the herps are sensitive (all
sensitive species are noted in the list of species in Appendix A).

The amount of core area can be factored into this model by modifying the
actual tract area to yield a lower effective area of suitable habitat. The core
area factor is computed as follows:

0.15 + (0.85 X percent core area (decimal form))

The 0.15 constant is necessary to modify tract area in such a manner that
predicted species richness levels will be 40 percent lower than predicted using
the original total area, for worst-case conditions. The 0.85 constant scales the
core area factor to a maximum value of 1.0, as core area approaches
100 percent.

Isolation factor (TV2). The definition of the isolation factor is:

A function of two variables: permeability of the edge of a tract and the
amount of deciduous palustrine forested wetland habitat within a 2-km
buffer of the tract.

It is assumed that tracts that are highly isolated will support approximately
40 percent less species than those that are not isolated, specifically, those
species assumed to be sensitive to fragmentation. For the model to reflect

Chapter 2 Habitat Model


13.0

10.4

NN
0%

o
io

Forest interior bird richness
o

1 L 1 1 4

0
0 100 200 300 400 500 600

Area (ha)

Figure 1. | Species-area curve developed from forest interior bird data

Most palustrine forested wetlands in Maryland are much smaller than
3,000 ha (81 percent of individual palustrine forested wetlands are less than
4ha in size).! Thus, most palustrine forested wetlands will score fairly low
for this part of the model, reflecting the fact that they are not expected to have
high species richness of forest interior birds, reptiles, and amphibians.
Regardless of where the maximum size area is set for the model, the output
will yield the same relative differences in suitability between two different
sized areas. The 3,000-ha standard is chosen because it appears to be biologi-
cally reasonable and because it is likely that all of the palustrine forested
wetlands in Maryland will fall within this range, allowing effective application
of the model without revisions.

The species-area curve alone is insufficient for an evaluation. Habitat
fragmentation can modify the effective size of a forest tract as it relates to the
ability of the tract to contribute to native richness. An individual forest tract
is functionally linked to the habitats that surround it. The area of a tract may
be effectively enlarged with permeable boundaries (similar cover types at the
tract’s perimeter) or an abundance of other nearby forested wetland tracts.
Further, tracts with low amounts of interior or core habitat have less effective

i area for interior species, which are an important component of native

' ©. E, Keller, personal communication, U.S. Fish and Wildlife Service, Annapolis, MD.

Chapter 2 Habitat Model



References

Allen, A. W., and Corn, J. G. (1990). “Relationships between live tree
diameter and cavity abundance in a Missouri oak-hickory forest,” Northern
Journal of Applied Forestry 7, 179-183.

Ambuel, B., and Temple, S. A. (1983). “Area-dependent changes in the
bird communities and vegetation of southern Wisconsin forests,” Ecology
64, 1057-1068.

American Ornithological Union. (1983). “Checklist of North American
birds. American Ornithological Union.” Allen Press, Lawrence, KS.

Askins, R. A., and Philbrick, M. J. (1987). “Effect of changes in regional
forest abundance on the decline and recovery of a forest bird community,”
Wilson Bulletin 99, 7-21.

Askins, R. A., Philbrick, M. J., and Sugeno, D. S. (1987). “Relationship
between the regional abundance of forest and the composition of forest bird
communities,” Biological Conservation 39, 129-152.

Behler, J.-L., and King, F. W. (1979). The Audubon Society guide to North
American reptiles and amphibians. Alfred A. Knopf, Inc., New York,
NY.

Beiswenger, R. E. (1988). “Integrating anuran amphibian species into envi-
Tonmental assessment programs, Management of amphibians, reptiles, and
small mammals in North America.” R. C. Szaro, K. E. Severson, and
D. R. Patton, ed., U.S. Forest Service General Technical Report RM-166,
Fort Collins, CO.

Bishop, C. A., and Pettit, K. E. (1992). “Declines in Canadian amphibian
populations: Designing a national monitoring strategy,” Occasional Paper
No. 76. Canadian Wildlife Service, Environment Canada, Ottawa,
Canada.

Blake, J. G. (1991). “Nested subsets and the distribution of birds on isolated
woodlots,” Conservation Biology 5, 58-66.

26

References

e


4 Test of Tract Hypotheses

Literature covering a wide geographic area was used to develop the model
hypotheses related to interior birds. The sensitivity of forest interior bird
richness to area, core habitat, and isolation appears to apply across their range
in the eastern deciduous forest, including forested wetlands. Therefore, a
study of the relation of the tract variables to the richness of forest interior
birds in 18 Breeding Bird Census (BBC) plots in eastern deciduous forests was
initiated to provide an independent test of several important model hypotheses.
The BBC plots included both upland and wetland deciduous forest types and
were mostly in states along the eastern seaboard, from South Carolina to
Rhode Island.

An Index of Avian Integrity (IAI) was used as the dependent variable in
this test and was defined as the proportion of forest interior birds occurring on
a BBC plot compared to the number expected. The expected number was
determined from the geographic distribution of the forest interior birds, as
indicated in the American Ornithological Union checklist (American Ornitho-
logical Union 1983). Only birds listed in Appendix A were included in the
analysis. Landscape data for the 18 BBC plots were obtained by working with
the plot compilers to identify the plot location on a topographic map. Aerial
photographs of these areas were acquired and the forest tract and surrounding
2.5-km buffer were photointerpreted and digitized. Spatial analyses of the
model tract variables were conducted using an automated program written for
the Arc/Info GIS software.

The IAI was significantly correlated with both the core area factor (TV1)
(r = 0.498, P = 0.035) and the isolation factor (TV2) (r = 0.572, P =
0.013). Regression of the IAI on the TSI yielded a highly significant (R=
0.503, P = 0.001) result:

IAI = 0.097 + 0.516 (TSA)

This initial test of tract-level hypotheses corroborates the relation between
forest interior bird richness and the tract portion of the model. Additional
tests are needed to analyze the plot variables and to assess the relationship
between model variables and the richness of reptiles and amphibians.

25
Chapter 4 Test of Tract Hypotheses

re


2 Habitat Model

Model Output

This model provides a rapid method to evaluate the quality of wildlife
habitat in deciduous palustrine forested wetlands. The model does not attempt
to evaluate all aspects of the wildlife community, but focuses on two species
groups of special concern in the area: (a) forest interior birds, and (b) reptiles
and amphibians (see Appendix A). These two groups are of special concern
because of their sensitivity to forest fragmentation and changes in wetland
hydrology and because of their declining populations.

The output of the model is ‘an index of native richness defined as the com-
bined richness of birds sensitive to fragmentation and reptiles and amphibians.
The index is scaled from 0 to 1, where 1.0 represents a deciduous palustrine
forested wetland that has the habitat and landscape conditions necessary to
support maximum native richness over time. The model is scaled from 0 to 1
to be used with the Habitat Evaluation Procedures (HEP) developed by the
U.S. Fish and Wildlife Service (1980).

Model Applicability

The model is intended for application in deciduous palustrine forested
wetlands in Maryland. The following description of deciduous palustrine
forested wetlands was taken from publications describing wetlands in Dela-
ware and New Jersey (Tiner 1985a, 1985b). Comparable descriptions of
wetlands in Maryland were not found.

Red maple (Acer rubrum) is a widespread tree in these forested wetlands
and is generally dominant in seasonally flooded swamps and very abundant in
temporarily flooded areas. Although red maple dominates most of these
forested wetlands, specific plant community structure varies between individ-
ual wetlands based on soil type, water regime, and historical land use
practices.

Chapter 2 Habitat Model


16

c. Regardless of the size of the evaluation area, it is recommended that
mitigation or tradeoffs between tracts consider the size categories
(Table 4) and not allow inappropriate tradeoffs between large and small
tracts. Thus, a loss of 15 HUs from an impact to a corner of a 700-ha
tract should be mitigated in a tract > 600 ha in size.

Simplified applications of the model

Detailed measurements of all plot- and tract-level variables may not be
needed for some applications. The size of forested wetland tracts is the most
significant determinant of native richness. A reasonable, but very simple,
application of the model could consist of rating tracts using the measured area
as an input to the effective tract area SI graph. Such an analysis would pro-
vide a quick separation of higher versus lower value habitats.

It may be desirable to conduct a rapid evaluation with a GIS for the entire
tract portion of the model but without gathering the plot-level field data. A
further level of detail could be added by estimating plot-level conditions or
assigning general plot-level suitability values based on age classes of forested
wetland stands.

Applying the model using geographic information systems (GIS)

Geographic Information Systems (GIS) enable display and analysis of geo-
referenced data. A GIS database of landcover types can be digitized from
existing maps or aerial photos, or interpreted from satellite images. Analysis
of variables in this model can be greatly facilitated using a GIS database con-
structed for an area of interest.

Procedures were developed to compute the tract-level variables in this
model using pcArc/Info software (Environmental Systems Research Institute
1989). Automation of the analyses was accomplished using the Prime mini-
computer version of Arc/Info, and this program was later converted to run on
a Unix workstation. The program allows the user to run analyses on multiple
areas very quickly and consistently. Output of the variables is reported to the
screen and in an ASCII file for use in spreadsheet and statistical programs. A
digital database containing one or more forested wetland polygons of interest
and at least 2 km surrounding the areas of interest is required to run the auto-
mated analysis. More specific information or assistance in using GIS for a
model application can be obtained by contacting the author.

Habitat unit determination
If this model is to be used in a HEP analysis, it will be necessary to com-

pute HUs by multiplying area by the native richness index (HU = area x
richness index). Habitat units are to be determined for each of five specific

Chapter 2 Habitat Modet



Table A1 (Concluded)

Common Name Scientific Name
Reptiles and Amphibians?

Southeastern five-lined skink

Eumeces inexpectatus

Ground skink

Scincella lateralis

Black rat snake

Elaphe obsoleta obsoleta

Eastern kingsnake

Lampropeltis getulus getulus

Coastal plain milk snake

Lampropeltis triangulum temporalis

Northern water snake

Nerodia sipedon sipedon

Rough green snake

Opheodrys aestivus

Northern brown snake

Storeria dekayi dekayi

Eastern ribbon snake

Thamnophis sauritus sauritus

Eastern garter snake

Thamnophis sirtalis sirtalis

Copperhead Agkistrodon contortrix
Worm snake Carphophis amoenus
Racer Coluber constrictor
Corn snake Elaphe guttata

Queen snake

Regina septemvittata

Red-bellied snake

Appendix A

Storeria occipitomaculata

(Sheet 3 of 3}

A3

ee


1987). Robbins, Dawson, and Dowell (1989) noted the “proximity to other
forests appears to enhance the effective area of a forest for some area-sensitive
species.” For example, the abundance of long distance migratory forest birds
was positively related to the abundance of regional forest area (defined as the
total area of forest within 2 km of the center of a forest tract).

From 1953 to 1976, six of ten forest interior bird species declined, while
none increased or colonized, in a 23-ha Connecticut nature reserve (Butcher
et al. 1981). Extensive urban and suburban development occurred in the
immediate vicinity (2-km buffer) of the reserve, increasing the isolation of the
site from similar habitat, reducing the buffer of low-density human use, and
increasing disturbance from construction, noise, pets, and other human-related
activities.

Boundary permeability has been defined as the degree to which the bound-
ary of a habitat patch deflects the movements of a species (Wiens, Crawford,
and Gosz 1985). The degree of permeability is a function of characteristics of
the species and the boundary itself. The effect of the boundary on an animal
depends on features of the patch such as habitat structure, resource levels, and
the presence or absence of predators or competitors. In a study of insect
movement patterns, Stamps, Buechner, and Krishnan (1987) found that hard
edges (totally unsuitable adjacent habitat) inhibited dispersal, whereas even
modest increases in edge permeability dramatically increased emigration rates.
Land-use practices in adjacent lands that allow at least marginal existence of
target species, and thus dispersal between tracts, are thought to be more valu-
able than corridors (Wilcove, McLellan, and Dobson 1986). Bird species
occupying forest patches in Illinois expanded their territories into adjacent old-
field or second-growth areas (Blake and Karr 1987). Forest fragments sur-
rounded by urban development had lower forest interior bird richness than
fragments surrounded by agricultural land (Whitcomb et al. 1981).

Roads, railways, and canals produce a variety of biotic and abiotic discon-
tinuities that create barriers to animal movements (Mader 1984): Specific
effects of roads are: (a) changes in microclimatic conditions; (b) emissions
and disturbance, such as noise, headlights, and dust; (c) herbicide spraying
and mowing; (d) intensified competition along the edge; and (e) traffic or
hunting mortality. Lynch and Whigham (1984) and Askins, Philbrick, and
Sugeno (1987) used a 10-m width to define separate tracts in their bird habitat
studies, whereas Robbins, Dawson, and Dowell (1989) used 100 m. Any
such delineation is somewhat arbitrary (Lynch and Whigham 1984).

Species richness of herpetofaunal assemblages decreases with increasing
insularity (Heatwole 1982). Isolation of wetlands, without upland buffers and
corridors, may result in higher mortality for younger age classes of amphibi-
ans and reduce recruitment and gene flow (Buhlmann, Mitchell, and Payne
1992). Management and protection of wetland wildlife requires the protection
of the surrounding terrestrial habitat.

22

Chapter 3 Habitat Use Information

ee ae


vi

List of Figures

Figure 1.  Species-area curve developed from forest interior bird data... 5
Figure 2. Determination of TSI from effective area .............. 9
Figure 3. The relationship between the average height of the tree

canopy and the suitability index ..................-, 10
Figure 4. The relationship between foliage height diversity and the

suitability index 2.6... 00... 2 eee 11
Figure 5. The relationship between soil moisture regime during the

growing season and the suitability index .............. 12
Figure 6. The relationship between the average number of elements of

microhabitat diversity per 0.1 ha and the suitability index ... 13
List of Tables
Table 1. | Minimum Tract Sizes for Forest Interior Birds . . 24
Table 2. Permeability Factors for Each Cover Type ............ 7
Table 3. Percent of Species Using Cover Types Other Than

Deciduous Palustrine Forested Wetland .............. 7
Table 4. | Area Categories for Forested Wetland Tracts ........... 14
Table 5. | Sample Worksheet for Plot and Tract SI and Overall HSI

Determination .. 2.2.0.0... 0.00 cece ee eee eee 18
Table 6. | Maryland Deciduous Palustrine Forested Wetland Interior

Birds with Reported Population Declines ............. 20
Table 7. | Occurrence of Forest Interior Birds in Relation to

Extensive Forests 2.0... 0... eee eee 21



=
fo}

Tract Suitability Index (Ts1)

(0) 1 1
0 1000 2000 3000

| Effective area (ha)

i Figure 2. Determination of TSI from effective area (TSI = (2.227 x Effec-
i tive Area®?’*)/19.8)
i
\

Description of plot variables (PV) and relations

This section describes the variables and methods that are used to assess the
suitability of plot-level habitat of deciduous palustrine forested wetlands.
Documentation of the sources of literature used to develop these variables and
hypotheses is provided in Chapter 3. The habitat characteristics in each tract
strongly influence the level of native species richness. The individual life
history of each species of concern dictates the precise habitat features needed
for its survival and success. From a community perspective, however, the
goal is to describe a general set of conditions that will maximize richness of
forest interior birds and herps. It is assumed that maximum native richness
will exist in mature forests, with well-developed herb and shrub layers, high
levels of soil moisture, and high levels of microhabitat diversity. The specific
variables selected to assess these habitat needs are: average tree canopy
height, foliage height diversity, soil moisture regime, and microhabitat
diversity.

In a study of shelterbelts in Kansas, Schroeder, Cable, and Haire (1992)
found that shelterbelts containing forest interior birds had significantly higher
values for tree height and foliage height diversity than shelterbelts without
interior birds. Forest maturity can be assessed through measures of tree

Chapter 2 Habitat Model



It is assumed that habitats with the highest (score of 3) levels of FHD will
support the highest native richness and that richness will approach zero as
FHD approaches zero (PV2, Figure 4).

The FHD index is a measure of how equally distributed the vegetation is in
the three layers, not a direct measure of the absolute amount of vegetation in
the layers. The probability P is the number of hits in a given layer divided by
the number of total hits in all layers combined. The following examples
illustrate this measure:

Example 1:
Assume 30 = the total amount of hits in all three layers.

Assume the 30 total hits were equally distributed, 10 hits in each layer.
Thus, the FHD would be:

FHD = 1/[(10/30)? + (10/30)? + (10/30)"] = 1/0.33 =3
Example 2:

Assume 30 = total hits in all three layers, but unevenly distributed, with 5
in the bottom layer, 5 in the middle layer, and 20 in the top layer.

FHD = 1/{(5/30)? + (5/30)? + ($/30)"] = 1/0.5 =2

Given that the model applies to forested cover, there will often be many
hits on vegetation in the top layer. The best habitats occur where the
vegetation is equally distributed in all three layers.

Soil moisture is an important determinant of the richness of herpetofaunal
assemblages. Based on individual life history information, the 19 forest inter-
ior birds used in this model would find suitable habitat in forests with interme-
diate to wet soil moisture conditions. It is assumed that the highest levels of
native richness will be found in areas where the soils are typically seasonally
saturated or inundated during the growing season. Native richness is assumed
to decrease to moderate levels in areas that are temporarily flooded or satur-
ated, and to be low in areas with soils that are typically dry (PV3, Figure 5).

A diversity of microhabitat features is assumed to be necessary to support
the highest levels of native richness. Key microhabitat features include seeps,
springs, shorelines, sandy areas, logs, leaf litter, debris, and tree cavities. It
is assumed that the best habitats will contain six or more of these microhabitat
features, well distributed throughout the entire area (PV4, Figure 6).

Chapter 2. Habitat Model

11


Contents

Preface 2.6... ee
j—Introduction .......--..+---
2—Habitat Model ......-
Model Output ....
Model Applicability
Model Description . sees
Overview . 0... eee ee ee
Description of tract variables and relations .....-..-.-+++++> 3
Tract suitability index (TSI) 8
Description of plot variables (PV) and relations ........------ 9
Plot suitability index (PSI) 13
Determination of Index of Native Richness 13

Application... 6... eee ee eee bee see . 14
Applying the model to entire tracts
Applying the model to portions of a tract .....- secs
Simplified applications of the model ....--.-- 0 +++ +5 0-05 16
Applying the model using geographic information

systems (GIS) .....
Habitat unit determination
Sample data sets... 6. eee ees 17

3—Habitat Use Information

General 2.0... ee te
Area and Configuration
Isolation... 2.6... eee eee tee

Vegetation Structure 2.2... 61-22 eee ete

4—Test of Tract Hypotheses

References

Appendix A
SF 298



A2

Table A1 (Continued)

Common Name

Reptiles and Amphibians”

Spotted salamander*

Ambystoma maculatum

Marbled salamander*

Ambystoma opacum

Northern dusky salamander

Desmognathus fuscus fuscus

Northern two-lined salamander

Eurycea bislineata bislineata

Long-tailed salamander

Eurycea longicauda longicauda

Four-toed salamander*

Hemidactylium scutatum

Red-spotted newt

Notophthalmus viridescens viridescens

Red-backed salamander

Plethodon cinereus cinereus

Eastern mud salamander*

Pseudotriton montanus montanus

Northern red salamander

Pseudotriton ruber ruber

Jefferson's salamander*

Ambystoma jeffersonianum

Tiger salamander*

Ambystoma tigrinum

Slimy salamander

Plethodon glutinosus

Northern spring peeper

Hyla crucifer crucifer

Upland chorus frog

Pseudacris triseriata feriarum

Bullfrog

Rana catesbeiana

Green frog

Rana clamitans melanota

Pickerel frog

Rana palustris

Wood frog

Rana sylvatica sylvatica

Southern leopard frog

Rana utricularia utricularia

Northern cricket frog

Acris crepitans

American toad

Gufo americanus

Fowler's toad

Bufo woodhousii fowleri

Cope’s gray treefrog

Hyla chrysoscelis

Green treefrog

Hyla cineria

Gray treefrog

Hyla versicolor

Striped chorus frog

Pseudacris triseriata

Carpenter frog*

Rana virgatipes

Common snapping turtle

Chelydra serpentina serpentina

Eastern painted turtle

Chrysemys picta picta

Spotted turtle*

Clemmys guttata

Eastern mud turtle

Kinosternon subrubrum subrubrum

Eastern box turtle

Terrapene carolina carolina

Wood turtle*

Clemmys insculpta

Five-lined skink

Eumeces fasciatus

(Sheet 2 of 3)
|

Appendix A

ee



20

Table 6

Cooper’s hawk

Maryland Deciduous Palustrine Forested Wetland Interior Birds
With Reported Population Declines

Species Source

Tate (1986}

Sharp-shinned hawk

Tate (1986)

Acadian flycatcher

Robinson (1992}

Wood thrush

Sauer and Droege (1992)

Worm-eating warbler

Robinson {1992}, Sauer and Droege (1992)

Black and white warbler

Butcher et al. (1981), Hill and Hagan (1991)

Northern parula warbler

Hill and Hagan (1991}

Kentucky warbler

Robinson (1992), Sauer and Droege (1992)

Ovenbird

Butcher et al. (1981), Sauer and Droege (1992)

Louisiana waterthrush

Robinson (1992)

American redstart

Hill and Hagan (1991), Sauer and Droege (1992)

Hooded warbler

Butcher et al. (1981)

Scarlet tanager

Butcher et al. (1981)

many different habitats. Larger woodlots contained more species with special-
ized habitat requirements. The need for large forests to support forest interior
birds is also supported by an analysis of bird survey miniroute data conducted
by Whitcomb et al. (1981) (Table 7). Wilcove (1988) determined that popula-
tions of neotropical migratory birds did not decline in Great Smoky Mountains
National Park during the period from 1947-1948 to 1982-1983, when such
declines were in evidence throughout many other areas. These data support
the hypothesis that large areas are important for the preservation of neotrop-
ical migrants. Robbins, Dawson, and Dowell (1989) recommend that forests
be 23,000 ha to support all of the native breeding forest birds in the mid-
Atlantic region.

The configuration of forest fragments is important in determining the abun-
dance and productivity of forest interior birds. Temple (1986) found that inte-
tior bird species were more abundant in habitats with larger amounts of core
area (core habitat defined as being > 100 m from nonforest habitat). It is
recommended that riparian corridor width in Delaware and Maryland be at
least 100 m wide to provide habitat for forest interior birds (Keller, Robbins,
and Hatfield 1993). The impacts of predation, competition, and nest parasit-
ism by brown-headed cowbirds (Molothrus ater) are greater near edges
(Temple and Cary 1988). Analyses of the life history patterns of declining
songbirds supported the hypothesis that nest predation and parasitism are pri-
marily responsible for recent population declines (BOhning-Gaese, Taper, and

Chapter 3. Habitat Use Information



Wetlands Research Program Technical Report WRP-DE-14
September 1996

Wildlife Community Habitat Evaluation:
A Model for Deciduous Palustrine
Forested Wetlands in Maryland

by Richard L. Schroeder

Midcontinent Ecological Science Center
National Biological Service

4512 McMurry Avenue

Ft. Collins, CO 80525-3400

Final report
Approved for public release; distribution is unlimited

Prepared for U.S. Army Corps of Engineers
Washington, DC 20314-1000

Monitored by U.S. Army Engineer Waterways Experiment Station
3909 Halls Ferry Road, Vicksburg, MS 39180-6199



28

Gibbs, J. P., and Faaborg, J. (1990). “Estimating the viability of ovenbird
and Kentucky warbler populations in forest fragments,” Conservation
Biology 4, 193-196.

Hamel, P. B., LeGrand, H. E., Jr., Lennartz, M. R., and Gauthreaux,
S.A., Jr. (1982). “Bird-habitat relationships on southeastern forest
lands,” GTR SE-22, Southeast Forest Experiment Station, Asheville, NC.

Harris, H. S., Jr. (1975). “Distributional survey (amphibia/ reptilia): Mary-
land and the District of Columbia.” Bulletin of the Maryland Herpetologi-
cal Society 11(3), 73-167.

Hayden, T. J., Faaborg, J., and Clawson, R. L. (1985). “Estimates of
minimum area requirements for Missouri forest birds,” Transactions of the
Missouri Academy of Science 19, 11-22.

Heatwole, H. (1982). “A review of structuring in herpetofaunal assem-
blages.” Herpetological communities: A symposium of the Society for the
Study of Amphibians and Reptiles and the Herpetologists’ League, August,
1977. N. J. Scott, Jr., ed., Wildlife Research Report 13. Washington,
DC, 1-19.

Hill, N. P., and Hagan, J. M., III. (1991). “Population trends of some
northeastern North American land birds: A half-century of data,” Wilson
Bulletin 103(2), 165-182.

Jones, K. B. (1988). “Distribution and habitat associations of herpetofauna
in Arizona: Comparisons by habitat type, Management of amphibians,
reptiles, and small mammals in North America.” R. C. Szaro, K. E.
Severson, and D. R. Patton, ed., U.S. Forest Service General Technical
Report RM-166, Fort Collins, CO.

Keller, C. M. E., Robbins, C. S., and Hatfield, J. S. (1993). “Avian com-
munities in riparian forests of different widths in Maryland and Delaware.”
Wetlands 13(2), 137-144.

Laan, R., and Verboom, B. (1990). “Effects of pool size and isolation on
amphibian communities,” Biological Conservation 54, 251-262.

Lynch, J. F. (1987). “Responses of breeding bird communities to forest
fragmentation.” Nature conservation: The role of remnants of native
vegetation. D. A. Saunders, G. W. Arnold, A. A. Burbidge, and
A. J. M. Hopkins, ed., Beatty and Sons Pty., Surrey, 123-140.

Lynch, J. F., and Whigham, D. F, (1984). “Effects of forest fragmentation
on breeding bird communities in Maryland, USA,” Biological Conserva-
tion 28, 287-324.

References



L

Laan and Verboom (1990) studied the effects of pool size and isolation on
amphibian communities in the Netherlands. They found that the probability of
species’ occurrence in patches with suitable habitat increased with the proxim-
ity of a source population and increasing connectivity of the landscape. The
presence of wooded areas appeared to be the most important element in
increasing landscape connectivity.

Species use of cover types other than forested wetlands can be used as an
indicator of their ability to disperse through various surrounding landscapes.
Table 3 provides a summary of cover type use by the 70 bird and herp species
considered in this model. All of the herps and interior birds would make use
of deciduous forest habitat, and thus, would not find such habitat to be a
barrier to dispersal. Agricultural lands would pose a barrier to most species
and only 26 percent of the species are considered to be able to use agricultural
lands.

Vegetation Structure

Bushman and Therres (1988) provided a comprehensive review of the
literature on forest interior bird habitat requirements, and additional literature
was surveyed. Based on these reviews, a summary of the basic habitat needs
of the 19 forest interior birds in Maryland was compiled. The majority of
these birds would find suitable habitat in a closed canopy, mature forest, with
a mix of dense and open understory conditions. Special habitat needs include
the presence of snags, proximity to water, and areas with little or no human
disturbance.

Lynch and Whigham (1984) summarized the habitat requirements of
15 neotropical migratory birds (9 of which are included in the list of interior
birds used in this model). They noted that these birds tended to be more
abundant in mature forests with high plant species richness, tall canopies, and
well-developed herb and shrub layers. Foliage height diversity (along with
area) was a positive factor in a multiple regression predicting the density of
uncommon long distance migratory birds in Wisconsin (Ambuel and Temple
1983).

Species richness of herpetofaunal assemblages can be expected to decrease
with decreasing availability of moisture (Heatwole 1982). Species richness of
metamorphosing juvenile amphibians was positively correlated with hydro-
period in three South Carolina wetlands (Pechmann et al. 1989). Blymyer and
McGinnes (1977) studied the effects on amphibians of clearcuts in Virginia
forests. They found 7 species and 82 individuals in uncut forests, no amphibi-
ans in 6- to 7-year-old clearcuts, and three species and seven individuals in a
2-year-old clearcut. They note that the abiotic factors of low upper soil mois-
ture and higher temperatures in the clearcuts were the likely causes of the
lower numbers of amphibians. Removal of ground cover and underbrush,
associated with land clearing, affects all terrestrial species, but is particularly
severe for salamanders and certain snakes (Minton 1968). Modification of

Chapter 3. Habitat Use Information

23



this, the effective area of tracts that are not isolated should be increased by a
factor of 6.5. A factor of 6.5 indicates that a tract is not isolated and is sur-
rounded by similar habitat. When applied in the model, this factor will mod-
ify tract area to reflect the 40-percent difference in native richness levels
compared to the original tract area predictions. The two measures of isolation
used in this model are each scaled from 1.0 to 2.55, so their product yields a
value ranging from 1.0 to 6.5.

Edge permeability refers to the ability of the adjacent habitat to be tra-
versed by wildlife species to accommodate dispersal and movement. The
permeability factor (Table 2) is determined by assuming that upland deciduous
| forest represents the most permeable border, and thus should have the highest
| value. Specific values for the other cover types were determined by relative
i comparison to percent use of upland forest. Data used to support these
hypotheses are presented in the Habitat Use Information section (see Table 3).

; Table 2

: Permeability Factors for Each Cover Type
Deciduous forest 2.55
Coniferous forest 1.97
Shrub 1.89
Palustrine emergent wetland 1,89

i Grass/forb 1.60
Lakes/rivers 1.53
Pasture/hay/cropland 1.40
Urban 1.00

Table 3
Percent of Species Using Cover Types Other Than Deciduous
Palustrine Forested Wetland

Cover Type

Palustrine Pasture/

Deciduous | Coniferous Emergent Grass/ Hay/
Forest Forest Wetland Forb Cropland

A single overall permeability factor (ranging from 1 to 2.55) is determined
for each forested wetland forest tract by computing the total length of the tract
perimeter and the length of perimeter adjacent to each cover type. For

Chapter 2 Habitat Model



10

height. The average height of the tree canopy is readily measured in the field
and may be estimated from low-level aerial photographs. Tree height is cor-
related with tree diameter, and tree diameter is correlated with the availability
of cavities (Allen and Corn 1990). It is assumed that tree canopy heights of
20 m or greater are needed for highest native richness, and that richness will
decrease linearly as tree heights decline to zero (PV1, Figure 3).

1.0 T
S L 4
A 08
x
3
£ 0.6 +
=
8 04b 5
Ss
a
3 o2r 4
a
(0) L 1
0 10 20 30
Average height of tree canopy (m)

Figure 3. The relationship between the average height of the tree canopy
and the suitability index

High levels of foliage height diversity are important to forest interior bird
richness (Ambuel and Temple 1983). The literature review of individual
reptile and amphibian life histories indicates that habitats with high levels of
herbaceous cover and shrubs will support more species than habitats lacking
these characteristics. Foliage height diversity is a measure of the distribution
of vegetation in the herbaceous, shrub (<5 m), and tree (>5 m) layers, and
is highest when there is vegetation in all three layers. It is quantified as
follows:

Foliage height diversity (FHD) = Dy (Py

where
P, = probability of a “hit” in layer i

Chapter 2 Habitat Model