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Management Goals and Habitat Structure 1
Henry L. Short 2
Abstract. --Many management goa 1s can be deve 1oped for
riparian habitats. Each goa 1 may dictate different management policies, strategies, and tactics and result in different impacts on wildlife. Habitat structure, expressed in
terms of habitat layers, can pro vi de a useful framework for
developing effective strategies for a variety of management
goals because many different 1and uses can be associ a ted
with habitat layers. Well-developed goals are essential
both for purposeful habitat management and for monitoring
the impacts of different land uses on habitats.
INTRODUCTION
NEED FOR A MANAGEMENT GOAL
Habitat managers sometimes inadequately
estab 1ish management goa 1s for 1and units, 1ike
riparian habitats, which results in expensive
and ineffective management and an i nabi 1i ty to
monitor changes in habitat qua 1i ty. I demonstrate, in this paper, how different management
goals affect the management policies, strategies,
and activities developed for a land unit. I
also discuss how some management strategies for
achieving management goals can be modeled in
terms of layers of habitat.
The management goal for a riparian area
needs to be well-defined. Policies, strategies,
and tactics vary with different goals and result
in different impacts on the area. Consider the
two management options for the same ri pari an
habitat listed in figure 1. The goal in the
first example is to maximize plant and animal
richness. The management po 1icy, in this case,
is to implement a system that will result in a
diverse ecosystem. The management strategy is
to determine the habitat structure that will
best pro vi de the diverse ecosystem. The goa 1
for the same land unit in example two is to
maximize forage yield for domestic livestock
production. The management policy is to implement a grazing system that wi 11 maximize the
production and use of forage over time. The
management strategy is to produce a particular
habitat structure where forage production can be
maximized.
The tactics chosen to meet the ·
management goals obviously differ for these two
examples.
Management goals, policies, strategies, and
tactics provide a hierarchical series of plans
and actions. Management goals are a determination of the desired product from some land unit.
The development of goals requires an understand; ng of what can be reasonably produced on that
land unit. Goals may need to be developed in a
workshop setting with advocates of different
land uses as participants.
Policy, in the
examples below, is a commitment to achieve a
particular habitat structure to attain a management goal.
The management strategy in the
following examples is a description of the
particular habitat structure to be achieved in
management.
I describe species-habitat word
models, and simple optimization models as techniques for developing management strategies.
Tactics are those activities used to produce the
desired habitat structure required to attain the
management goal. A discussion of procedures to
evaluate the effects of management is beyond the
scope of this paper.
An impact to a land unit can be considered
positive or negative, depending on the management
goal for that land unit. This fact is illustrated in figure 2. Reductions in the structure
of habitat that reduce diversity in the riparian
ecosystem would have a negative impact in example
one but a positive impact in example two. On
the other hand, an increase in structural diversity would result in reduced light penetration to
the understory and 1ess forage production for
livestock. This change would have a positive
impact in example one but a negative impact in
example two.
1
Contributed paper, Symposium on Riparian
Ecosystems and Their Management, Apri 1 16-18,
1985, Tucson, AZ.
2
Terrestrial Ecologist, Western Energy and
Land Use Team, U.S. Fish and Wildlife Service,
Fort Collins, CO 80526-2899
MODELING HABITAT STRUCTURE FOR MANAGEMENT
Goal setting is the most important activity
in habitat management. The future appearance of
257
Example one
Example two
Goal
To restore or preserve
the integrity and diversity of wildlife and plant
communities.
To maximize forage yield within
the riparian zone for the production of domestic livestock.
Policy
Establish a management
system that will produce
a diverse ecological
system.
Establish a management system
that will maximize forage yield
and use over time.
Strategy
Determine the habitat structure that will favor plant
and wildlife diversity.
Determine a habitat structure
that will maximize forage
production.
Tactics
Modify habitat to provide
and maintain a structure
that favors plant and
animal diversity.
Modify the structure of vegetation within the riparian zone
to maximize light penetration to
the understory.
Develop an irrigation system to
maximize forage production.
Develop a fencing system to
regulate grazing at different
seasons to intensively harvest
forage over time without
destroying grazing habitat.
Figure 1. Different goals, policies, strategies, and tactics can be
developed by users of riparian zones.
many riparian habitats depends on the establishment of management goa 1s. In many instances,
the goa 1 wi 11 be formula ted in terms of some
product from that land, such as forage, fish and
wildlife habitat, scenery, recreation opportunity, or timber, and the strategy for attaining
the management goal will describe a vegetative
structure to be estab 1i shed or restored that
will yield the desired product.
The advantage of such a representation is that
many land uses can be considered in terms of how
they impact habitat layers. A variety of different land uses can be considered in the same
model of habitat structure. I indicate, in the
fo 11 owing section, how two different management
goals can be developed by considering habitat
structure in terms of layers of habitat. These
two goals are:
(1) to restore or preserve
breeding populations of selected wildlife species
within the riparian zone; and (2) to restore or
preserve a habitat structure that wi 11 a 11 ow
managers to maximize products from a variety of
Other
land uses within the riparian zone.
management goals also could be addressed, using
the concept of 1ayers of habitat as a common
denominator for expressing habitat structure.
The structure desired for riparian habitats
often can be represented in terms of habitat
layers, such as surface water, terrestrial
subsurface, understory, midstory, tree bole, and
overstory (Short and Burnham 1982; Short 1983).
Impacts
Example one
Example two
Develop multilayered vegetative cover
positive
negative
Limit grazing
positive
negative
Maximize understory vegetative
cover
negative
positive
Management for Wildlife Values
A riparian zone can be managed to maximize
wildlife diversity or to favor selected wildlife
species.
The following discussion describes
management efforts to favor selected wildlife
species. The goal, policy, strategy, and management tactics to favor this type of effort are
summarized in figure 3. The goal is to restore
or preserve breeding populations of selected
species within the riparian zone; the management
policy is to establish a management system that
wi 11 meet that goal. The strategy is to determine a habitat structure that will all ow the
Figure 2. An impact can be either positive or
negative, depending on the management goal
for a land unit.
258
goal to be attained. There are three intermediate steps between the policy and strategy
levels in this planning hierarchy. These can be
considered tools for determining the management
strategy. The first tool is to determine the
species to be favored in management. Species
may be considered for selection either because
they are listed in some legislative mandate or
because they have been selected by some logical
process, like the process for selecting species
of 11 hi gh concern 11 described by Short and
Williamson (in prep.).
Nesting habitat is in
the boles of cottonwoods or other
deciduous trees
along watercourses.
r--
No-
1---
No
~
No-
Yes
Cottonwoods or other
trees are at least
25 em dbh.
Yes
The second tool is to determine the habitat
requirements of species of 11 hi gh concern 11 • These
requirements can be summarized by developing
simple species-habitat word models, like the one
for the screech owl summarized in figure 4. The
word models describe the layer of habitat (tree
bole) where breeding occurs, the layer of habitat
(understory with limited cover) where foraging
occurs, and major habitat dependencies, such as
the size of habitat blocks necessary or, in the
case of the screech owl, a dependency on tree
holes excavated by cavity-making birds.
The
word model is a generalization of the specieshabitat information available in the literature.
Potential nesting
trees possess
woodpecker/flicker
holes suitable for
use as nest sites.
Yes
Understory layer in
woodland or nonwoodland sites provides
short or intermittent
vegetative cover where
successful foraging
can occur.
The third tool is to summarize the information in the word models to yield a description
of the habitat structure (layers) to be developed
or maintained within the riparian zone. The
summarization may be either descriptive or a
matrix (Short and Williamson in prep.), which
lists the structural conditions that occur
within each layer of habitat. A portion of a
matrix that lists habitat conditions in the
understory layer where the screech owl feeds is
reproduced in Table 1. The appropriate elements
of the matrix are notated for each species of
11
high concern 11 • The resulting pattern describes
the conditions within layers of habitat that are
to be restored or preserved by management
actions. This is the management strategy for
achieving the management goal.
Goal:
To restore or preserve breeding
populations of selected wildlife
species.
Policy:
Establish a management system that
will restore or preserve habitat for
the selected wildlife species.
Strategy:
Determine the habitat structure
required to achieve the management
goal.
Tactics:
Develop the habitat structure required
by selected wildlife species. Maintain required habitat structure
through time.
Habitat may be
-" of limited
potential as
nesting habitat for the
screech owl
Figure 4. Simple word model describing the
important characteristics of the nesting
and foraging habitat of the screech owl.
Management tactics for the example in
figure 3 are those that will produce and maintain
the habitat structure that seems most important
to the wildlife species of 11 hi gh concern 11 •
Multiple Use Management
The multiple use management goal listed in
figure 5 is to restore or preserve a habitat
structure that will optimize the products from a
variety of land use options in a riparian
habitat.
The management strategy in this example is
to describe the appropriate habitat structure to
meet the management goal. The models described
below are simple optimization models, similar to
those used in business planning (Wagner 1969).
The models occur at the same level in the planning hierarchy as did the word model and the
summary matrix in the previous section. The
optimization models are tools for determining
preferred -management strategies.
The major
difference between business planning and the
applications discussed in this paper is that the
value of the products of habitat management
usually are not expressed in monetary terms. It
is difficult to consider a multiple use model in
11
market value 11 terms because not all legitimate
land uses can be equally well represented in the
market place.
Figure 3. The goal, policy, strategy, and
tactics for managing a riparian zone for
its wildlife value.
The alternative is to give common scalar
values to products of land uses such as grazing,
259
timber management, and wi 1dl i fe management.
Product values for such land uses are given the
maximum value of 1.0 under some most favorable
habitat structure configuration and are given
the minimal value of 0.0 under some least favorab 1e habitat structure configuration. Habitat
structure configurations of intermediate quality
are given intermediate product values in the
models.
have considered only the understory,
mi dstory, and overs tory 1ayers of habitat in
this analysis of vegetative structure because
the tree bole layer is produced at the same
ecological cost as is the overstory layer and
the two layers are highly dependent variables.
Two alternative examples for multiple use
management are described below. The two alternatives exist because the riparian systems differ
in the two examples. Example A, in figure 6,
determines the desired habitat structure for a
large riparian area where wildlife species breed
and forage mostly within the riparian area.
Understory layer
sa lt. p1ay a s
bare ground (sand to rubble)
boulder-covered surface
talus, unvegetated
talus, vegetated
cliff-ledge or cavity near
valley floor
cliff-ledge or cavity near
mesa or mountain top
woody litter (includes shrub
branches, tree branches,
and stumps) < 50% cover
woody litter~ 50% cover
herbaceous vegetation - short
(< 0.5 m)
sparse ~ 33% cover
moderate 34 to 66% cover
dense ~ 67% cover
herbaceous vegetation - c~ 0.5 m)
sparse ~ 33% cover
moderate 34 to 66% cover
dense ~ 67% cover
supine or dwarf woody vegetation
sparse ~ 33% cover
moderate 34 to 66% cover
dense ~ 67% cover
cactus stems and pads
sparse ~ 33% cover
moderate 34 to 66% cover
dense ~ 67% cover
To restore or preserve habitat structure that will allow managers to maximize products from a variety of land
uses within the riparian zone.
Policy:
Establish a management system that
will optimize products of different
land uses from the riparian zone.
Strategy:
Determine the habitat structure that
will maximize values from the potential land uses.
Tactics:
Develop the habitat structure that
will optimize production from a
variety of land uses within the
riparian zone. Maintain that
habitat structure through time.
Figure 5. The goal, policy, strategy, and
tactics for managing a riparian zone to
optimize production from a variety of
1and uses.
Example B, in figure 6, determines the desired
habitat structure for a limited riparian habitat
in which species may breed but where many of the
species rely on cover types away from the riparian area for foraging activities.
The two
examples in figure 6 illustrate how different
strategies may exist for attaining the same goal
in two different habitats where the wi 1dl i fe
values are perceived differently.
Table 1.--A large variety of structural
conditions occurs within the understory
layer of habitat, and the use of particular conditions by the screech owl and
other species of 11 high concern 11 can be
summarized in a matrix format.
Structural condition
Goal:
Screech owl
requirements
Products from land uses like grazing,
timber management, and wildlife management can
be considered products of particular layers of
habitat. Grazing products are maximized in the
riparian area in both examples when the overstory
and mi dstory 1ayers are absent and there is
maximum sunlight penetration to the understory.
The value of the grazing product is 1.0 in both
examples when only the understory layer is
present; 0.3 in example A when the overstory,
midstory, and understory layers are equally
abundant because 1ess forage is avail ab 1e for
livestock; and 0.1 in both examples when the
only understory vegetation
is the early
regenerative stage of treelands.
X
Timber management products are maximized in
both examples when most of the riparian area is
in trees and tree boles are allowed to mature to
a stage useful for cutting. Some small portions
of the treeland should be in regenerative stages,
so that early successional (understory) and
mid-successional (midstory) stages also are
present. The value of the timber product is 1.0
when extensive portions of the riparian area are
in overstory vegetation; 0.4 in example A when
the areas of overstory, midstory, and understory
vegetation are similar and the forested area is
reduced; and 0 in both examples if only the
understory layer is present.
X
X
Wildlife species richness is favored in
example A and species richness is presumed to be
enhanced when the overstory, midstory, and
understory 1ayers each are present and equally
260
Example A
Matrix Summarizing Multiple Use Problem
Example B
Matrix Summarizing Multiple Use Problem
Portion of each
layer to maximize
Wildlife
Timber
Grazing
Overs tory
Mid story
Understory
0
0.34
0
0.33
1.0
0.33
Values of the 12roducts
Grazing
Wildlife
Timber
Total Values
1.0
0.2
0
1.2 (Pd
Objective function:
Constraints:
pl
p2
p3
pl
~
~
~
+
0.3
1.0
0.4
1.7 (P&2
1.2 P1
1. 00
1. 00
1. 00
p2 + PJ
Solution for variable value:
+
0.7
0.2
0.1
Overstory
Mid story
Understory
0.1
0.4
1.0
1.5 (P 3 2
Grazing
Wildlife
Timber
Total Values
1.7 P2 + 1.5 P3
pl
~
Portion of each
layer to maximize
Wildlife
Timber
Grazing
~
p2 ~
p3 ~
1. 00
= 0.10
= 0.80
p3
0. 10
Constraints:
0.1
1.0
1.0
2.1 (P 2 2
pl
p2
p3
~
~
~
1.00
1.00
1. 00
Solution for variable value:
0.1
1.0
1.0
2.1 (Pd
pl
p2
p3
~
~
~
pl
0.10
0.10
0.10
= 0.10
0.45
0.45
Solution to determine quantity of different
layers of habitat:
Overstory
1.0
0.2
0
1.2 {P 1 2
0.7
0.2
0.1
Objective fundtion:
0.10
0.10
0.10
pl
p2
0
0.7
0
0.2
1.0
0.1
Values of the 12roducts
Solution to determine quantity of different
layers of habitat:
(0 X 0.1) + (0.34 X 0.8) +
(0.7 X 0.1) = 0.34 = 34.3%
Overs tory
(0 X 0.10) + (0.7 X 0.45) +
(0.7 X 0.45) = 0.63 = 63%
Midstory
(0 X 0.1) + (0.33 X 0.8) +
(0.2 X 0.1)
0.28 = 28.3%
Mid story
(0 X 0.10) + (0.2 X 0.45)
(0.2 X 0.45) = 0.18 = 18%
+
Understory
(1.0 x 0.1) + (0.33 x 0.8) +
(0.1 X 0.1)
0.37 = 37.4%
Understory= (1 x 0.10) + (0.1 x 0.45)
(0.1 X 0.45) = 0.19 = 19%
+
Figure 6. Matrices, linear program algorithms, and solutions of two
alternatives for the multiple use management of riparian habitats.
distributed throughout the riparian zone. Data
in Short (1983) indicated that species richness
is maximum when the number of layers of habitat
on a land unit is maximum. The value of the
wildlife product in example A in figure 6 is 1.0
when the overst~ry, midstory, and understory
layers are present and equally abundant throughout the riparian zone, 0.2 when only the understory layer is present, and 0.4 when most of the
riparian zone is a mature treeland with only
limited quantities of understory and midstory
present. The value of the wildlife product in
example B is maximized when a large portion of
the land area is covered by overstory vegetation
that provides nest sites for species that forage
in non-riparian cover types. The value of the
wildlife product is 1. 0 in ex amp 1e B for the
same structural condition for which timber
values were maximized.
determined by max1m1z1ng the values present for
the three management options in examples A and
8. This was accomplished by using the LINDO
Computer Program (Schrage 1984) to solve the two
linear programming problems.
Multiple use
values in example A are maximized when overstory,
midstory, and understory are each dominant over
about equal portions of the riparian area.
Multiple use values in example B are maximized
when overstory conditions predominate on the
riparian area. The solutions for examples A and
B differ because wildlife values are different
in A and B. More explicit statements of the
desired habitat structure in example A and B
were obtained by using the values for P1 , P2 ,
and P3 to estimate the quantities of each layer
of habitat to be produced and rna i nta i ned in the
ri pari an habitats. These quantities represent
the management strategies required to attain the
management goal listed in figure 5. The quantity
of each layer of habitat desired was estimated
by summing, for each habitat layer (overs tory,
The structure to be favored in multiple use
management in these very simplified examples was
261
SUMMARY
midstory, and understory), the product of the
quantity of that layei' in each land use option
and the relative value contribution of each land
use option. This value is expressed as a percent
of the summed total of the products of the layer
quantity x relative value contributions.
In
example A, the products for the overstory layer
~ere (0 X 0.10) + (0.34 X 0.80) + (0.70 X 0.:0),
which equals 0.34 (fig. 6). This value is 34.3%
of the summed total of the products of che nine
individual
layer
quantity x relative
value
contribution combinations (0.99 in fig. 6). In
1ike manner, the desired quantity of mi dstory
vegetation was calculated as 28.3% of the land
area, and the desired quantity of understory
vegetation was calculated as 37.4% of the land
area. The strategy for attaining the multiple
use management goa 1 for the habitat conditions
listed in example A in figure 6 is to produce a
habitat where the overs tory is dominant on 34%
of the land arPa, the midstory is dominant on
28% of the land a rea, and the understory is
dominant on 37% of the land area.
The efficient management of ri pari an habitats requires the formulation of an explicit
management goal for a land unit and the development of the appropriate management policies,
strategies, and activities to achieve that goal.
Setting goals enhances the efficiency of habitat
management and helps managers evaluate the
impacts of potentia 1 land use changes. Vegetative structure of riparian areas, expressed in
terms of layers of habitat, is a habitat
criterion that can be used in modeling to help
develop management strategies and predict impacts
on habitats.
ACKNOWLEDGEMENTS
appreciate Adrian Farmer's help in formulating the linear programming models and helpful
reviews by Samuel C. Williamson, Carl Armour,
and Charles Segelquist. Cathy Short edited the
paper and Jennifer Shoemaker prepared the
manuscript for camera reproduction.
Carolyn
Gulzow and Dora Ibarra provided the word
processing.
The same type of so 1uti on for ex amp 1e 8
describes a very different habitat structure.
Based on the same type of calculations, the
management strategy in this example is to produce
a habitat where the overstory is dominant on 63%
of the land area, the midstory is dominant on
18% of the 1and area, and the understory is
dominant on 19% of the land area (figure 6).
LITERATURE CITED
Schrage, Linus. 1984. User's manual. Linear,
integer, and quadratic programming with
LINDO. 86 pp. The Scientific Press, Palo
Alto, CA.
Short, Henry L.
1983. Wildlife guilds in
Arizona desert habitats. USDI Bureau of
Land Management Tech. Note 362. 258 pp.
Short, Henry L. , and Kenneth P. Burnham. 1982.
Technique for. structuring wildlife guilds
to evaluate impacts on wildlife communities.
USDI Fish Wildlife Service, Special Scientific Report -Wildlife 244. 34 pp.
Short, Henry L., and Samuel C. Williamson. A
procedure for selecting cover types for
management. in prep.
Wagner,
Harvey M.
1969.
Principles
of
operations
research.
937 pp. + append.
Prentice-Hall, Inc., Englewood Cliffs, NJ.
The tactics to achieve the multiple use
management goals in both example A and example 8
include the application of grazing and timber
management practices that will obtain and maintain the desired habitat structures across time.
These two examples indicate that establishing different objectives for a wildlife resource
can influence the habitat structure required as
a management strategy to attain a multiple use
management goa 1 .
262