COMBINING ECONOMIC AND ECOLOGICAL
INDICATORS TO PRIORITIZE SALT MARSH
RESTORATION ACTIONS
ROBERT J. JOHNSTON, GISELE MAGNUSSON, MARISA J. MAZZOTTA,
AND JAMES J. OPALUCH
Restoration of damaged or degraded ecosystems often represents an important component of environmental management
(National Research Council). However, funds
are typically insufficient to restore all candidate sites. This paper summarizes an
ecological-economic model designed to assist
managers in prioritizing salt marsh restoration
actions. The model integrates information
concerning both the production (supply) and
value (demand) of wetland habitat functions.
Although the project focuses on salt marshes
in Narragansett Bay (RI), the approach is
more generally applicable to assessing habitat
restoration actions.
Ecological production relationships determine links between salt marsh attributes and
associated habitat functions. Although there is
an extensive ecological literature on these relationships, considerable judgment is needed
to interpret the literature in order to quantify
how restoration actions would contribute to
habitat for a range of species (e.g., Burdick
et al., Able and Hagan, Wigand et al.). For
this reason, we developed a survey of wetlands
professionals to identify a consensus of expert
opinion on production relationships among
physical marsh attributes and particular habitat or ecological functions.
While habitat functions are determined
by ecological (physical) relationships, social
values for these functions are determined by
Robert J. Johnston is assistant professor in the Department of
Agricultural and Resource Economics, University of Connecticut;
Gisele Magnusson, Marisa J. Mazzotta, and James J. Opaluch are,
respectively, graduate research assistant, adjunct professor, and
professor in the Department of Environmental and Natural Resource Economics, University of Rhode Island. Authors listed in
alphabetical order; senior authorship not assigned.
The research was funded by the National Science Foundation
STAR Grant Program and by the University of Rhode Island Agricultural Experiment Station, AES #3936.
This article was presented in a principal paper session at the
AAEA annual meeting (Long Beach, CA, July 2002). The articles in these sessions are not subjected to the journal’s standard
refereeing process.
public preferences. Rhode Island residents’
preferences for salt marsh functions were estimated through an application of stated preference (conjoint) analysis. The two models were
designed to integrate production with values of
wetland functions, thereby providing insights
into the set of restoration actions that would offer the greatest potential for welfare improvement, given a fixed restoration budget. This paper discusses the design, implementation and
estimation of the integrated model, and provides an example of how the model may be
used to prioritize multiattribute restoration
policies.
Estimating Production Relationships:
The Expert Survey
Consultation with wetlands experts revealed
that the provision of wildlife habitat was likely
the most significant function of Narragansett
Bay salt marshes; this also represents a primary
function for which sufficient information exists
to substantively differentiate among alternative restoration sites. The expert survey instrument was designed to determine the extent to
which physical attributes of salt marshes and
their surrounding landscapes contribute to the
provision of habitat for various species groups
of birds, fish, and shellfish.
Survey development required approximately two years, and involved extensive
background research, including interviews
and pretests with twenty-seven experts in salt
marsh ecology, and a literature review of existing assessment and evaluation methods (e.g.,
Shriver and Vickery, Bartoldus, King et al.).
The survey asked respondents to rate the
potential of coastal wetland complexes—
characterized by a range of physical
attributes—to provide habitat functions for
different species groups. The responses allow
estimation of the relationship between the
Amer. J. Agr. Econ. 84 (Number 5, 2002): 1362–1370
Copyright 2002 American Agricultural Economics Association
Johnston et al.
Prioritizing Salt Marsh Restorations
physical attributes of a wetland and resultant
potential for various habitat functions. These
results supplement findings from the existing
wetland ecology literature. Survey booklets
were printed in color and mailed to 102 experts in wetland ecology and biology, located
primarily in New Hampshire, Massachusetts,
Rhode Island, Connecticut, and New York.
Analysis presented here incorporates responses from forty-nine surveys (48% response rate).
Table 1.
Variable
Name
1363
Focused interviews and literature reviews
were used to select twenty-one primary
attributes for inclusion in the conjoint survey.
An example survey scenario—characterizing
a hypothetical coastal wetland—is shown in
figure 1. Coastal wetland attributes included
ten features internal to the wetland and
eleven features of the surrounding landscape
(table 1). Based on these attributes (cf.
figure 1), respondents rated the potential
for the site to provide habitat functions for
Expert Survey Model Variables: Definitions
Description
Units and
Measurement
Wetland Features
Size
Area of all contiguous, vegetated salt and brackish wetland
Acres (1, 5, 17, 65)
Water
Type of adjacent water body (coastal river, embayment, or
Dummy variables (0,1)
salt pond)
Fringe
Shape of the contiguous wetland area (fringe versus meadow)
Dummy variable (0,1)
Percentage of contiguous wetland area covered in Spartinia
spp.
SM M
– SM L (10–27% Spartinia, 69–83% Phragmites)
Dummy variables (0,1)
SM H
– SM M (50–62% Spartinia, 32–50% Phragmites)
– SM H (80–95% Spartinia, 4–9% Phragmites)
Low H
High% of low marsh (Spartinia alterniflora) (10% versus 4%)
Dummy variable (0,1)
Brack
Presence/absence of brackish marsh (3–6% of wetland area)
Dummy variable (0,1)
ESS
Presence/absence of estuarine scrub-shrub (3–6% of wetland
Dummy variable (0,1)
area)
Rest M
Tidal restriction: none, moderate, or severe restrictions
Dummy variables (0,1)
Rest S
Creeks
The presence/absence of creeks which drain at low tide
Dummy variable (0,1)
Channels
The presence of subtidal channels inundated during all
Dummy variable (0,1)
tidal stages
Pan
5%
% of marsh covered by pannes: 1%, 5%, or 15% of marsh
Dummy variables (0,1)
15%
area
Pool 10%
% of marsh covered by pools: 1%, 10%, and 20% of marsh
Dummy variables (0,1)
20%
area
Landscape Features
Buff shrub
Presence and type of 100 ft. vegetated buffer around wetland: none, shrub, or
Buff for
forested
Dev M
% of developed land in 500 ft. area around wetland. Includes residential,
Dev H
commercial and industrial. Levels include low (19–27%), medium (35–56%), and
high (72–83%)
Ag M
% of ag. and managed grass land within 500 feet. Includes crops, grazing, playing
fields, golf courses, and extensive lawns. Levels include low (8–18%) and
medium (29–62%)
For M
% forested land within 500 feet. Forested land including brushland, forested upland
and forested freshwater wetlands. Levels include low (8–16%) and medium
(29–65%)
Fresh w
Distance to the freshwater wetland: within 1/4 mile, or greater than 1/4 mile
Fresh f
Flats
Presence of tidal flats 25% of the size of the coastal wetland area (indicated in acres
on the survey)
Eelgrass
Presence of eelgrass in adjacent waters
OtherSM
Indicates the presence of another salt marsh within 1/2 mile
Access
Indicates that access to the coastal wetland is not limited, as compared to restricted
access
1364
Number 5, 2002
Amer. J. Agr. Econ.
Figure 1. Example: Expert survey salt marsh scenario
wading birds, waterfowl, shorebirds, marshdependent songbirds, other songbirds, resident fish, nonresident fish, and shellfish, as
well as for overall birds and fish. The five-
level scale ranged from “no significant potential” to “exceptional potential.” In addition,
for each species group, respondents had
the opportunity to indicate that there was
Johnston et al.
Prioritizing Salt Marsh Restorations
“Insufficient Information” provided by the
instrument, or that they were “Not Qualified
to Answer.” Data analysis incorporated eleven separate ordered logit models—one for
each species group.
Production Relationship
(Expert Survey) Results
Tables 2 and 3 list ordered logit results for
each species group. All models are significant
Table 2.
Preliminary Results of Expert Survey—Birds
Variable
Wading
Birds
Size (1 Acre)
5 Acres
17 Acres
65 Acres
Saltmarsh (Low)
Medium
High
Adjacent Water Type
(Salt Pond)
Coastal River
Coastal Embayment
Tidal Restrictions (None)
Medium
Severe
Percent Coverage by
Pools (1%)
10%
20%
Buffer Type (None)
Shrub
Percentage Land Development
(Low)
Medium
High
Freshwater Wetlands
(Immediately Adjacent)
Within 1/4 Mile
Over 1/4 Mile
Fringe Marsh (vs. Meadow)
Tidal flats (vs. not significant)
Adjacent Eelgrass (vs. no
eelgrass)
Creeks (vs. no creeks)
Channels (vs. no channels)
Other Saltmarsh w/i 1/2 mi.
(vs. none)
Cut point 1
Cut point 2
Cut point 3
Cut point 4
−2LnL 2
N
1365
MarshDependent
Other
Waterfowl Shorebirds Songbirds Songbirds
0.96∗∗∗
0.93∗∗∗
2.31∗∗∗
1.06∗∗∗
1.13∗∗∗
2.16∗∗∗
1.20∗∗∗
1.31∗∗∗
2.84∗∗∗
0.85∗∗∗
0.97∗∗∗
2.56∗∗∗
0.77∗∗∗
0.83∗∗∗
0.53∗
0.48∗
0.67∗∗
0.88∗∗∗
0.85∗∗∗
0.82∗∗∗
−0.89∗∗∗
−0.93∗∗∗
−0.84∗∗∗
−0.66∗∗∗
1.28∗∗∗
1.20∗∗∗
1.82∗∗∗
Overall
Birds
1.48∗∗∗
1.37∗∗∗
2.78∗∗∗
0.74∗∗
0.80∗∗∗
−0.52∗∗
−0.63∗∗
−0.91∗∗∗
−0.97∗∗∗
−0.55∗
−0.57∗∗
−0.79∗∗
−0.72∗∗
−0.86∗∗∗
−0.87∗∗∗
−0.49∗∗
∗
0.40
0.64∗∗∗
0.57∗∗
0.48∗∗
−0.81∗∗
−0.50∗
0.73∗∗∗
0.42∗∗
0.49∗∗
1.92∗∗∗
0.51∗∗
0.49∗∗
0.88∗∗∗
0.60∗∗
−1.12∗∗∗
1.16
2.93
5.39
333.94
318
−0.79∗∗
1.33
3.02
5.11
274.92
309
Note: ∗∗∗ significant at 99%; ∗∗ significant at 95%; ∗ significant at 90%.
−0.05
2.67
4.44
6.81
362.55
311
−0.53
1.26
2.78
5.02
203.06
262
−2.23∗∗∗
0.30
2.28
5.19
349.56
255
−0.88∗∗
1.77
3.85
6.59
363.49
286
1366
Number 5, 2002
Table 3.
Amer. J. Agr. Econ.
Results of Expert Survey—Fish and Shellfish
Variable
Size (1 Acre)
5 Acres
17 Acres
65 Acres
Saltmarsh (Low)
Medium
High
Adjacent Water Type (Salt Pond)
Coastal River
Coastal Embayment
Tidal Restrictions (None)
Medium
Severe
Percent Coverage by Pools (1%)
10%
20%
Buffer Type (None)
Shrub
Percentage Land Development (Low)
Medium
High
Freshwater Wetlands (Immediately Adjacent)
Within 1/4 Mile
Over 1/4 Mile
Fringe Marsh (vs. Meadow)
Tidal flats (vs. not significant)
Adjacent Eelgrass (vs. no eelgrass)
Creeks (vs. no creeks)
Channels (vs. no channels)
Other Saltmarsh w/i 1/2 mi. (vs. none)
Cut point 1
Cut point 2
Cut point 3
Cut point 4
−2LnL 2
N
Marsh
Resident
Fish
Marsh
Nonresident
Fish
Overall
Fish
Shellfish
1.17∗∗∗
1.39∗∗∗
2.06∗∗∗
0.82∗∗∗
1.08∗∗∗
1.41∗∗∗
1.11∗∗∗
1.45∗∗∗
1.92∗∗∗
0.60∗∗
0.57∗
1.25∗∗∗
0.37∗
0.61∗∗
0.53∗
0.67∗∗
0.59∗∗
0.41∗∗
−0.55∗∗
−0.69∗∗
−1.10∗∗∗
−0.56∗∗
−0.62∗∗
−1.14∗∗∗
0.47∗
0.55∗
−0.44
−2.03∗∗∗
1.05
2.55
5.50
423.05
318
−0.63∗∗
−0.58∗∗
−0.35∗
−0.38∗
∗∗
0.68∗∗∗
−0.40∗
0.40∗
∗∗
−0.43
0.40∗
−0.80∗∗∗
−1.03∗∗∗
∗∗
0.54
0.45∗∗
0.43∗∗
−0.37
1.26
2.66
5.30
182.82
296
0.46∗∗
0.52∗∗
0.58∗∗∗
0.88∗∗∗
0.36∗
0.51∗∗
0.36∗
−1.59∗∗∗
1.10
3.05
5.84
381.48
311
−0.52
1.32
2.56
4.96
216.60
294
Note: ∗∗∗ significant at 99%; ∗∗ significant at 95%; ∗ significant at 90%.
at p < 0.005. Signs of coefficients are consistent
with findings from the literature and expert interviews. While the results, as expected, differ across species group, there are some commonalities. For all species, parameter estimates
associated with the size of the wetland were
positive, relatively large and significant, while
the estimate for the severe tidal restriction
variable was negative and significant for all
species. Also significant for a number of species
groups are the relative quantity of salt marsh
(spartinia sp.) acreage, coverage by open water
pools, buffer type, presence of tidal flats, and
level and type of development in the surrounding landscape.
As expected, several attributes have a significant positive or negative impact on one
species group, but have either an opposite or
insignificant impact on other groups. Hence,
actions taken to increase habitat quality for
one species group may either decrease or leave
unchanged habitat quality for other species
groups. For example, for marsh-dependent
songbirds, moderate coverage of a wetland
with open water pools has a negative coefficient (i.e., negative impact on habitat potential), while for fish the coefficient is positive. Thus, restoration that affects open water
pools would require habitat trade-offs involving songbirds and fish.
Johnston et al.
Prioritizing Salt Marsh Restorations
Conjoint Analysis of Preferences
for Coastal Wetland Restoration
The stated preference survey instrument
Rhode Island Salt Marsh Restoration: 2001 Survey of Rhode Island Residents was designed
to assess the relationship between salt marsh
functions and public values. Survey development required over sixteen months and involved extensive background research, interviews with experts in salt marsh ecology and
restoration, and over sixteen focus groups with
more than 100 Rhode Island residents. Numerous pretests, including verbal protocol analysis (Schkade and Payne) were also conducted
to ensure that the survey language and format
could be easily understood by respondents,
and that respondents shared interpretations of
survey scenarios (cf. Johnston et al.).
Focus groups and pretests led to a selfadministered, in-person survey approach that
combined a printed survey booklet with
an eight-minute introductory computer-based
presentation. This presentation introduced
Table 4.
1367
respondents to information regarding salt
marshes and salt marsh restoration; reminded
respondents of the trade-offs involved in salt
marsh restoration; reminded respondents of
their budget constraint and the implications
of choosing to direct funds to restoration
programs; emphasized the importance of respondents’ choices; and provided basic survey
instructions. The presentation script and graphics were pretested extensively, and iteratively revised along with the survey booklet.
Following the general approach of Johnston,
Swallow, and Weaver, the conjoint survey presented respondents with four sets of discrete
choices, each involving two alternative, multiattribute restoration plans. Fractional factorial design was used to construct a range of
survey questions with an orthogonal array of
attribute levels, resulting in eighty contingent
choice questions divided among twenty unique
booklets. Attributes distinguishing plans were
selected based on background research, expert
interviews, and focus groups (table 4). Based
on these attributes, respondents chose one of
Model Variables: Definitions and Summary Statistics
Variable
Name
Description
Neither
Neither = 1 identifies “Neither Plan” selected
Environ
Membership in environmental organizations
Taxgrp
Membership in taxpayer associations
Loincome
Household income less than $35,000/yr
Hiedu
Greater than a four-year college degree
Birds
Improvement to bird populations (0–10 scale)
Fish
Improvement to fish populations (0–10 scale)
Shellfish
Improvement to shellfish populations (0–10 scale)
Mosquito
Control mosquito nuisance (0–10 scale)
Size
Size of restored salt marsh
Pro access
Indicated access should be “somewhat limited” or “unlimited”
Con access
Indicated that access should be “severely limited” or “prohibited”
Platform
Restoration provides “viewing platforms”
Both
Restoration provides both “viewing platforms” and “trails”
Cost
Annual cost of plan (increase in taxes)
Mean
(Std. Dev.)
0.3333
(0.4714)
0.1900
(0.3923)
0.0233
(0.1510)
0.2450
(0.4301)
0.1817
(0.3856)
2.7608
(2.6072)
2.9075
(2.6530)
2.9079
(2.6518)
2.9077
(2.6506)
4.8890
(4.3965)
0.8367
(0.3697)
0.1633
(0.3697)
0.2266
(0.4187)
0.2215
(0.4153)
63.1694
(70.7816)
1368
Number 5, 2002
Amer. J. Agr. Econ.
the two plans, or chose “Neither Plan.” In total, interviewers collected 661 completed surveys, providing complete and usable responses
to 2341 individual contingent choice questions
(89% of the potential 2644).
Preference Model Results
The conditional logit model was used for data
analysis (table 5). The model is statistically
significant at p < 0.0001. All individual parameter estimates are statistically significant
at p < 0.05, with most significant at p < 0.01.
Signs of parameter estimates correspond with
prior expectations derived from focus groups,
where prior expectations exist. Respondents
favor plans that restore larger salt marshes;
improve bird, fish, and shellfish habitat; control mosquitoes; provide public access; and result in lower household cost. The likelihood
of rejecting restoration (i.e., choosing neither
plan) was smaller for members of environmental organizations; and larger for members
of taxpayers organizations, lower income individuals, and highly educated individuals. All
these effects are significant at a minimum of
p < 0.05.
Comparing preferences for habitat improvements and mosquito control (all measured on a
ten-point scale), respondents placed the greatest weight on mosquito control, followed by
habitat improvements for shellfish, fish, and
birds, respectively. From a statistical perspec-
Table 5.
tive, parameter estimates for mosquito control, shellfish habitat, and fish habitat cannot be shown to differ at p < 0.10, based on
asymptotic Wald tests (Judge et al.). Parameter estimates for bird habitat improvements
may be shown to differ from those associated
with mosquito control and shellfish habitat at
p < 0.10 (Wald 2 = 3.61 and 3.28, df = 1).
Model results also indicate that the provision of public access facilities is a positive
attribute of salt marsh restoration plans, but
only for those who feel that salt marsh access
should be either “somewhat limited” or “unlimited” (pro access = 1; table 4). For these
respondents, viewing platforms (table 4; platforms) are preferred to the lack thereof, and
a combination of walking trails and viewing platforms (table 4; both) are preferred
to platforms alone. Both effects are significant at p < 0.05, as indicated by the parameter estimates and standard errors for the
interaction terms pro access × platforms and
pro access × both (table 5). However, preliminary models (not shown here) indicated that
neither effect was statistically significant at
p < 0.10 for those who oppose public access;
hence the interactions con access × platforms
and con access × both were dropped from
early versions of the model, and do not appear in table 5. These combined findings correspond with prior expectations—drawn from
focus groups—of preference heterogeneity associated with the provision of salt marsh access
facilities.
Conditional Logit Results
Neither Option
Neither × Environ
Neither × Taxgrp
Neither × Loincome
Neither × Hiedu
Birds Habitat
Fish Habitat
Shellfish Habitat
Mosquito Control
Size
Pro Access × Platform
Pro Access × Both
Cost
N
−2LnL 2
Pseudo R2
Parameter
Estimate
Std.
Error
Z
P > |z|
1.16
−1.18
0.87
0.31
0.41
0.12
0.15
0.16
0.16
0.05
0.17
0.43
−0.0072
7023
1157.56
0.2250
0.19
0.22
0.37
0.14
0.17
0.015
0.016
0.016
0.016
0.0098
0.0826
0.0844
0.0005
5.98
−5.30
2.38
2.16
2.46
7.78
9.36
9.78
9.95
5.22
2.03
5.11
−14.23
0.0001
0.0001
0.0170
0.0310
0.0140
0.0001
0.0001
0.0001
0.0001
0.0001
0.0420
0.0001
0.0001
Prob > 2
0.0001
Johnston et al.
Prioritizing Restoration Actions
The expert and public surveys were designed
in an integrated fashion, such that the models could be linked through respective habitat scales. Expert survey results indicate the
potential for habitat on a 0–4 scale, based
on professional, expert judgment. The public
preference model, in turn, estimates welfare
change as a function of habitat improvement,
“as judged by wetlands experts,” measured on
a 0–10 scale. Accordingly, results from the expert survey may be treated as attributes within
the public preference model, after adjustment
for differences in measurement scales.
The following example illustrates the integration of production and preference models to prioritize restoration projects. To simplify the exposition, we contrast two relatively
simple restoration programs; however, more
complex policies may be easily addressed.
Table 6 characterizes a degraded coastal wetland and two potential restoration alternatives.
The baseline (degraded) wetland consists of a
5-acre marsh dominated by Phragmites, with
severe tidal restriction. Both of the presented
restoration alternatives (table 6) reduce the
Table 6.
Prioritizing Salt Marsh Restorations
1369
tidal restriction, allowing for the development
of a medium level of Spartinia marsh. However, under restoration Alternative 1, additional funds are used to excavate open pools
(20% of marsh area), subtidal channels, and
intertidal creeks. Under Alternative 2, funds
would be used to create a 100 ft. buffer of
shrub vegetation. All other plan attributes are
assumed identical.
Both alternatives increase expected habitat
potential for birds, fish, and shellfish, relative
to the degraded baseline. However, while Alternative 1 provides a relatively greater improvement in expected habitat potential for
fish, Alternative 2 provides relatively greater
improvement habitat potential for bird species
(table 6). Public survey results (table 5) provide one means to resolve this potential tradeoff. After adjusting for differences in the
scale used to assess habitat improvements
(table 6), the associated changes in estimated habitat potential are substituted into
the restoration preference function, estimated
from public survey data (table 5).
Welfare results of the combined model are
summarized at the bottom of table 6. Incorporating the estimated habitat improvements
Example: Prioritization of Potential Restoration Programs
Restoration Optionsa
Degraded Marsh
Alternative 1
Attributes
Size
5 acres
NC
Salt marsh area
low
medium
Adjacent water
salt pond
NC
Tidal restriction
severe
moderate
Percent coverage by open pools
1%
20%
Vegetated buffer
none
NC
Percentage of surrounding upland developed
high
NC
Nearest freshwater wetland
within 1/4 mile
NC
Marsh shape/type
fringe
NC
Adjacent tidal flats
significant
NC
Eelgrass in adjacent waters
none
NC
Intertidal creeks
absent
present
Subtidal channels
absent
present
Nearest salt marsh
within 1/2 mile
NC
Expert survey results (implications for habitat potential)
Expected habitat potential rating
Birds
1.437
1.752
Fish
1.310
2.120
Shellfish
1.484
1.710
Public survey results (welfare implications of habitat potential differences)
Welfare Rating (Alternative 1 versus Alternative 2)b
dv
WTP (for Alternative 1 over Alternative 2)
a NC =
Alternative 2
NC
medium
NC
moderate
NC
shrub
NC
NC
NC
NC
NC
NC
NC
NC
1.959
1.686
1.710
0.1005
$13.96
No change relative to degraded wetland.
the expert survey is matched to the 0–10 habitat improvement scale in the public survey using a 10/4 adjustment factor.
b The 0–4 habitat potential scale in
1370
Number 5, 2002
into the preference model and comparing
restoration Alternative 1 to Alternative 2 illustrates that predicted welfare is higher under Alternative 1, as indicated by dv > 0.
Model results imply that Alternative 1 would
be favored in a referendum by 53% of residents (compared to 47% choosing Alternative 2), and the estimated willingness to pay
(Hanemann) for Alternative 1 over Alternative 2 is $13.92. Hence, the combined model
would prioritize Alternative 1 over Alternative 2 as a restoration option for the baseline
degraded site.
Future work will incorporate this combined prioritization model with a menu-driven
Geographic Information System interface, incorporating a database of salt marshes in
Narragansett Bay, Rhode Island and a range
of potential restoration actions that may be
undertaken to improve each site. This interface will be designed to allow resource managers and stakeholders to explore, visualize,
and prioritize different restoration alternative, in terms of both ecological and welfare
implications.
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