United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
Las Vegas, NV 89193-3478
Research and Development
EPA/620/SR-94/015 July 1994
EPA Project Summary
Environmental Monitoring and
Assessment Program—
Arid Ecosystems 1992 Pilot
Report
Susan E. Franson
The U.S. Environmental Protection
Agency (USEPA) and its collaborators
have initiated a long-term, policy-rel-
evant research project, the Environmen-
tal Monitoring and Assessment Pro-
gram (EMAP), focused on evaluating
ecological conditions on regional and
national scales. In 1992 the EMAP Arid
Ecosystems Resource Group (one of a
number of EMAP resource groups) con-
ducted a pilot study in the southeast-
ern Utah portion of the Colorado Pla-
teau. This report describes this first
field activity for arid ecosystems. The
1992 pilot study was developed to
evaluate sampling plot design and the
sensitivity of selected indicators. The
study focused on four objectives re-
lated to plot design, indicator develop-
ment, sampling frame material, quality
assurance, information management,
and logistics. The primary categories
of indicators selected for evaluation in
the 1992 pilot study were vegetation
composition, structure, and abundance;
spectral reflectance; soil properties;
and soil erosion. Data were collected
on 29 sites within two major resource
classes—desertscrub and conifer
woodland. Indicator measurement
methods and the study results for each
of the four objectives are explained in
this report. Each of these sections in-
cludes recommendations based on the
1992 study. The final section summa-
rizes the major conclusions and rec-
ommendations drawn from the 1992 pi-
lot study, draws implications from the
study results, and discusses planned
future studies.
Introduction
In 1992 the Arid Ecosystems Resource
Group conducted a pilot study in the south-
eastern Utah portion of the Colorado Pla-
teau. The purpose of this EMAP group is
to measure and report on the extent, con-
dition, and trends of several resource
classes in the biogeographical provinces
of nearctic and neotropical North America
within the United States.
The study focused on four objectives:
• Assessment of sampling variance—
Evaluation of the EMAP-Forests Re-
source Group sampling plot design
relative to the selected indicators.
• Indicator sensitivity—Evaluation of the
sensitivity of the indicator measures
to independent evaluations of site con-
dition as designated by various land
management.
• Sampling frame and extent—Evalua-
tion of the utility of using classified
TM imagery and other data acquired
from the U.S. Fish and Wildlife Ser-
vice (FWS) Gap Analysis Program
(GAP) to select frame materials for
the pilot study and future studies and
to provide data for extent estimation
of arid ecosystems.
• Quality assurance, information man-
agement, and logistics—Evaluation of
the quality assurance, information
management, data analysis, logisti-
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cal, and reporting requirements and
constraints based on the pilot study
area.
1992 Pilot Study Area
The Colorado Plateau is an arid and
semi-arid tableland in the southwestern
U.S. The entire 130,000-square mile re-
gion of the Colorado Plateau is much more
extensive than needed to fulfill the re-
quirements of the intended indicator evalu-
ation pilot; therefore, only a portion of the
plateau was chosen for data collection.
This region is predominantly managed as
federal lands, (i.e., Bureau of Land Man-
agement, National Park Service, and For-
est Service, and part of Navajo Nation,
state, and private lands). The diversity of
ownership and jurisdiction promoted inter-
agency participation in the pilot implemen-
tation. The area is bisected by the Colo-
rado River and includes many canyon
lands that allowed for evaluation of logisti-
cal requirements in some of the most diffi-
cult terrain that EMAP-Arid activities will
likely face. The area includes two resource
classes which are prevalent within the
Colorado Plateau (desertscrub and coni-
fer woodlands) that were chosen for indi-
cator evaluation.
Indicator Measurement
Methods
Vegetation Composition,
Structure, and Abundance
Vegetation composition and structure
have been evaluated for decades in arid
ecosystems and are well established as
important indicators of ecosystem condi-
tion. The difficult decision for the 1992
pilot was to determine what type of mea-
surement technique best fit within the
EMAP approach. Numerous vegetative
sampling techniques were evaluated in-
cluding plot sampling, belt transects, and
line intercept techniques. Most of the veg-
etative sampling techniques have been
developed for measuring forage supplies
for big game and other herbivores. The
literature was reviewed and the EMAP-
Arid researchers decided to use a modi-
fied Daubenmire (1968) approach because
it provides the ability not only to measure
vegetation attributes about species rich-
ness and diversity, but also to keep open
options for relating this information to wild-
life habitat in future pilots.
Spectral Reflectance
A remote sensing approach to collect
information about a site offers a number
of advantages for indicator development
such as producing spatially explicit esti-
mates of ecological condition over entire
regions in a cost-effective manner. A num-
ber of researchers have developed strong
relationships between measurements and
indices derived from remote sensing and
ecosystem variables. The Normalized Dif-
ference Vegetation Index (NDVI) is such
an index and researchers have shown
very high relationships between NDVI de-
veloped from satellite and ground mea-
surements and leaf area index. The leaf
area index correlates strongly with a num-
ber of other extremely important ecosys-
tem variables such as primary productivity
and biomass. The NDVI was selected as
a candidate indicator for the 1992 pilot
study because it has both a demonstrated
relationship to vegetation parameters and
a lack of sensitivity to atmospheric condi-
tions; in addition, it has been used to
monitor phenological (vegetation) variables
on regional, continental, and global scales.
The Landsat TM satellite data were used
to determine NDVI because the waveband
location for deriving information concern-
ing vegetation parameters is superior to
multispectral scanner (MSS) data and the
pixel size of 30 by 30 m correlates more
easily with field-based measurements than
does the 1.1 - by 1.1 -km pixels of the Ad-
vanced Very High Resolution Radiometer.
Soil Properties and Soil Erosion
Soil properties were selected because
they were determined to be critical in evalu-
ating ecosystem health and interpreting
vegetative information. The literature pro-
vided the rationale for looking at (physi-
cal, chemical, and biological crusts) soil
parameters and focusing on their implica-
tions to management options, plant growth
and the water balance. Soil erosion was
also included in the 1992 pilot because
most of the data required for estimating
erosion were collected in the soil profile.
These data could then be used as inputs
to the Revised Universal Soil Loss Equa-
tion (RUSLE) erosion models for evaluat-
ing the relationship between soil erosion
and site condition. Several researchers
have identified a positive correlation be-
tween increased runoff and erosion with a
decrease in the serai stage of arid eco-
systems and have evaluated the sensitiv-
ity of the models.
Assessment of Sampling
Variance
The process of collecting samples can
produce extraneous variability in the indi-
cator measurements in addition to the vari-
ability associated with the resource condi-
tion. The EMAP survey design protocols
include annual visits to sampling sites
throughout the region and will require mul-
tiple sampling crews to procure the mea-
surements within adequate time frames.
The utility of indicators of resource condi-
tion to some extent depends upon the
degree to which these extraneous sources
of variation inhibit the ability of the indica-
tor measurement to describe resource
characteristics. Knowledge of these vari-
ance values is necessary not only to con-
struct confidence intervals for the mea-
sured indicators but also to evaluate the
viability of the measurements as indica-
tors. The magnitude and influence of each
of these components of variability must
be evaluated by the EMAP-Arid program
as it progresses through the indicator de-
velopment process. Variance components
that continue to require a high level of
investigation include those associated with
the year, crew, measurement, and plot
design.
The evaluation of indicator measure-
ment variances associated with the sam-
pling units that potentially could be used
in a common plot design for monitoring
EMAP-Arid extensive resources was a pri-
mary objective of the 1992 pilot study.
Year and crew components of variance
were not considered for investigation in
the 1992 pilot study and will be deter-
mined from larger and long-term studies
in the future. Measurement variances are
discussed in Section 7 of the report.
Measurements considered most influ-
ential for the spectral, vegetation, and soils
indicator categories were selected as can-
didates for evaluation of their variance
properties. The variable selected for the
spectral measure was the NDVI; the vari-
ables selected for vegetation measure-
ments were total vascular plant cover,
shrub cover, and tree cover; and the soil
variables analyzed were the clay, silt, sand,
and very fine sand percentages; organic
matter; the soil erodibility factor (K); and
the length-slope (LS) steepness factor.
The variables for this analysis also were
selected to represent measurements ac-
quired from different components of the
plot design. The selected variables are
each representative of uniquely different
types of statistical variables which affect
how the indicator variables are used in
the analyses. Each category of indicator
measurements is discussed separately.
It is recommended that a study be con-
ducted to determine an optimal integrated
response design for EMAP-Arid monitor-
ing. Such a study should be conducted
using a uniform sampling grid that allows
a wide range of arrangements of the ba-
sic measurement units from linear
transects of varying lengths to varying
shapes and sizes of rectangular arrays of
the units. The relationships of the arrange-
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ments to their respective variances can
be used to craft efficient sampling designs
at a site. Also, this type of study would
result in data to estimate the level of spa-
tial correlation that can be expected from
the measurements. Knowledge of the spa-
tial correlation would indicate the need for
any spatial separation among the mea-
surement units to increase the amount of
independent information acquired from the
units.
Indicator Sensitivity
One of the primary aims of the indicator
evaluation process is to evaluate the de-
gree to which individual indicators repre-
sent a range of ecological condition. This
is often referred to as evaluation of indica-
tor sensitivity. Two general types of indi-
cator sensitivity are commonly evaluated:
the grouping or clustering of indicator val-
ues across an environmental gradient and
the degree to which an indicator varies
within a known range of conditions.
The first type of sensitivity analysis nor-
mally involves recognition of patterns or
clusters (pattern recognition or detection)
of values of indicators across an environ-
mental gradient. The study is designed to
determine if indicator values will separate
or cluster into one or more groups and
whether the groups correspond to the en-
vironmental gradient. This design allows
an evaluation of indicator sensitivity to a
range of environmental conditions, even if
standards (desired conditions) for evalu-
ating condition are not known.
The second type of sensitivity analysis
generally involves selecting sample sites
based on a range of "known" or "desired"
conditions and evaluating the degree to
which indicators vary across those condi-
tions. This type of sensitivity analysis re-
quires an a priori agreement on what con-
stitutes condition (nominal, marginal,
subnominal) and knowledge of the geo-
graphic range of the condition (so that
representative sites can be selected).
Initially, the EMAP-Arid researchers had
intended to evaluate indicator sensitivity
relative to known or desired conditions as
determined by existing information avail-
able from federal land management agen-
cies. The EMAP-Arid team decided to con-
duct this initial pilot study in the Colorado
Plateau due to the wealth of information
available from this area. Discussions were
held with a number of management agen-
cies and these discussions led to the un-
derstanding that EMAP-Arid could obtain
congruous determinations of site condi-
tion for the Colorado Plateau area. How-
ever, the EMAP team discovered signifi-
cant differences in agency descriptions of
the condition of a site. This difference was
substantial enough in several cases that
no consistent rating of a site could be
established. Recently, similar concerns
have also been reported by the NRC in
their review of rangeland health. As a
result of these factors, the 1992 pilot study
was not able to address the objective to
evaluate indicator sensitivity against sites
of "known" condition. Results presented in
this report are only indicative of patterns
in the Colorado Plateau and the actual
range condition, delineated in these pat-
terns, is not known. However, it is reason-
able to assume the sites were different
and represented at least a partial range in
condition.
Frame Materials
The EMAP-Arid group definitions of veg-
etation resource classes, as well as bio-
geographic provinces have been estab-
lished. A method, or set of methods, to
estimate extent of arid resources needs to
be developed, with the idea that an area
sampling technique will provide a better
estimate of extent.
An evaluation of the FWS GAP infor-
mation was conducted to determine how
well the satellite-derived data base identi-
fied plant communities found at the pilot
study sample points. It is important to
note that the GAP data used were consid-
ered "preliminary", and have been im-
proved since the initial comparison was
made.
The evaluation of the GAP data was
inconclusive partly because, for a com-
prehensive evaluation, more sites are
needed, and, some discrepancies ap-
peared to exist. If the EMAP-Arid group
wants to consider using GAP data in the
future to select frame materials and to
provide data for extent estimation of arid
ecosystems, then a further assessment of
the accuracy of the GAP data must be
performed. This assessment should be
done on the second generation (or the
most recent version) of the GAP data and
must include a sufficient sample number
for each land cover type.
Quality Assurance, Information
Management, and Logistics
Quality assurance (QA), information
management, and logistics are integral
components of EMAP field activities. In a
program of the magnitude of EMAP, over-
looking or ignoring even apparently minor
issues or details may eventually jeopar-
dize the success of the program. Planning
and documenting QA, information man-
agement, and logistics activities are es-
sential. The report documents these ac-
tivities for the 1992 pilot study.
Conclusions and
Recommendations
The 1992 pilot study was the first EMAP-
Arid field study, and addressing the objec-
tives developed for this study is essential
to full implementation of the program.
Questions related to these objectives will
continue to be important elements in plan-
ning for future pilot studies. During the
1992 pilot study, the EMAP-Arid team was
successful in partially addressing these
objectives but, more importantly, the plan-
ning and implementation of this study un-
covered issues that were not fully under-
stood or perceived in initial design efforts.
For example, the original assumptions that
the EMAP-Forest design would be appli-
cable to EMAP-Arid indicator measure-
ments or that independent site condition
assessments from land management
agencies could readily be used to evalu-
ate sensitivity of indicators were inaccu-
rate. Only as the 1992 field work pro-
gressed were these difficulties pinpointed.
The USEPA, through its Office of Re-
search and Development (ORD), funded
and collaborated in the research described
here. It has been peer-reviewed by the
Agency and approved as an EPA publica-
tion. Mention of trade names or commer-
cial products does not constitute endorse-
ment or recommendation for use.
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Susan E. Franson (also the EPA Project Officer, see below) is with the Environmental
Monitoring Systems Laboratory, Las Vegas, NV. 89193-3478.
The complete report, entitled "Environmental Monitoring and Assessment Program—
Arid Ecosystems 1992 Pilot Report," (Order No. PB94-176898/AS; Cost: $27.00;
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring Systems Laboratory
U. S. Environmental Protection Agency
Las Vegas, NV 89193-3478
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
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