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LESSONS FROM 5 YEARS OF
VEGETATION MONITORING ON
THE NEVADA TEST SITE
Richard Hunter
quality of the environment." DOE order 5400.1 references
many government orders, laws, and policies, and requires
environmental surveillance of "air, water, soil, foodstuffs,
biota and other media ...." The objectives of environmental surveillance under 5400.1 are listed in table 1.
The NTS currently consists of about 3,500 km2 (1,350
mi2), ranging in altitude from about 884 m (2,900 ft) in
Frenchman Flat to about 2,556 m (7 ,400 ft) on Rainier
Mesa. Vegetation at lower altitudes is Mojave Desert
shrubland dominated by creosote bush (Larrea tridentata), which gradually changes with altitude and latitude
to a transition desert dominated by blackbrush (Coleogyne
ramosissima), then to Great Basin Desert vegetation
dominated by big sagebrush (Artemisia tridentata) and
black sagebrush (A nova), and above about 1,800 m
(6,000 ft) to pinyon-juniper forest dominated by singleleaf
pinyon pine (Pinus monophylla) and Utah juniper
(Juniperus osteosperma) (fig. 1, Beatley 1976).
ABSTRACT
In 1987 the U.S. Department of Energy began continuous monitoring on the Nevada Test Site to understand
temporal changes in the distribution and abundance of
plants and animals. The need to detect changes, as opposed to mere characterization, required careful parameter
selection and permanent plots to distinguish spatial from
temporal variation. Repeated measurements revealed errors and imprecision in relocating plants, which required
changes in data collection and verifreation techniques.
After several years it is obviously important to monitor
not only changes, but causes of change. A requirement for
records to be available over long time periods also poses
problems of archiving and publication.
INTRODUCTION
In 1987 the U.S. Department of Energy (DOE) set up
a long-term monitoring program for the Nevada Test Site
(NTS) to monitor the flora and fauna. The stated goal
was to maintain and update an understanding of the spatial distribution and changes over time of the flora and
fauna on the NTS. That goal persisted until1991 when
"understanding" was changed to "record" in a belief that
future monitoring efforts should have an exact record of
procedures and results, in preference to interpretations
of results.
The basic usefulness of monitoring is to warn of any
changes that might have deleterious consequences. On
the NTS, the program follows influences relating to human health, NTS land management practices and decisions, and legal proceedings relating to nuclear weapons
testing and activities associated with testing. Flora and
fauna monitoring focuses primarily on land clearing, because radioactive contamination on the NTS is too lowintensity to significantly affect plants and animals.
Historical Vegetation Monitoring
Botanists have studied the NTS since the late 1950's,
when atmospheric nuclear weapons testing ceased. Goals
varied, though most interest was focused on effects of
testing (for example, Shields and others 1963). Beatley
set up permanent plots where she measured densities and
cover of annual and perennial plants from 1963 through
1975. In the 1970's the U.S. International Biological
Table 1-0bjectives of environmental surveillance on DOE sites
(DOE Order 5400.1)
a.
Verify compliance with applicable environmental laws and
regulations;
b.
Verify compliance with environmental commitments made in
Environmental Impact Statements, Environmental
Assessments. Safety Analysis Reports, or other official DOE
documents;
c.
Characterize and define trends In the physical. chemical, and
biological condition of environmental media;
d.
Establish guidelines of environmental quality;
Legal Requirement
Monitoring by government agencies is required by the
National Environmental Policy Act and the executive order implementing it: "... heads of Federal agencies shall:
(a) Monitor, evaluate, and control on a continuing basis
their agencies' activities so as to protect and enhance the
e. . Provide a continuing assessment of pollution abatement
programs;
Paper presented at the Symposium on Ecology, Management, and
Restoration oflntermountain Annual Rangelands, Boise, ID, May 18-21,
1992.
Richard Hunter is Principal Ecologist, Reynolds Electrical & Engineering Co., Inc., P.O. Box 98521, Las Vegas, NV 89193-8521.
f.
402
Identify and quantify new or existing environmental quality
problems.
PAHUTEMESA
SHOSHONE
MOUNTAIN
VEGETATION TYPES ON THE NEVADA TEST SITE
~~LARREA
ffiili} COLEOGYNE
D COLEOGYNE
EJ
~
LYCIUM PAW DUM
[W
ATRIPLEX
LARREA/
~ARTEMISIA
GRAYIA-LYCIUM
D
MOUNTAINS, HIU.S,
ANO MESAS
Figure 1- Vegetation types on the Nevada Test Site.
403
m
LYCIUM SHOCKLEY!
SCALE
0)~~1"'
~iHHi km
tN
Program's Desert Biome collected data on Mojave Desert
annual and perennial plants in Rock Valley. Many scientific papers have been published on the NTS biota by biologists working on these and several smaller projects
(O'Farrell and Emery 1976).
The work that most closely approached a monitoring
effort was the work by Janice Beatley on 68 plots. Her
raw data are stored at the Desert Laboratory, University
of Arizona, and can be used to determine annual plant
population parameters for periods of more than 10 years
at seven plots, and for 5 years at others. She published
1963-75 summary data for perennial population changes
on plots grouped by vegetation "type" (Beatley 1979).
My goal for this paper was to provide information on
potential problems in setting up programS for monitoring
plant and animal populations. It is based on experience
over the first 5 years (1987-92) of the NTS monitoring
program.
human exposure), locations of drill holes for test emplacement, outlines of subsidence craters (resulting from underground weapons tests), and roads. The extent of range
fires from 1978 to 1988 was estimated by the NTS fire
department. Widths of paved and dirt roads were measured, and lengths estimated from maps. The extent of
blast zones denuded by shock waves from aboveground
tests was estimated from a published map (Allred and
others 1963a). The extent of waste burial areas was reported by NTS' Low-Level-Waste-Management personnel.
Hunter and others (1992) reported surface areas for these
various disturbances (table 2).
The primary reasons for monitoring permanent plots
were that they could be located at points of previous studies, they remove spatial variability, they allow efficiencies
in work effort, and densities could be determined on plots,
whereas techniques based on lines or points only provide
relative values. Five permanent baseline plots (300 by
300 m) were set up in 1987 and 1988, and smaller plots
were set up in particular disturbances to monitor recovery
or changes associated with the disturbance. If possible,
plots were set up at sites studied by earlier researchers,
to provide historical continuity and to extend the time
span monitored. Plots were marked with metal stakes
covered by PVC pipe, with brass markers attached to the
PVC. Their locations were surveyed by global positioning
system equipment (GPS).
An attempt was made to monitor parameters that were
not technique dependent. Largely nondestructive measurements were attempted for species composition and
mean density, size, sex, or weight, but not for cover, frequency, diversity, or relative abundance. Confidence limits were calculated for each measurement. Estimates for
cover and biomass of plants and such parameters as
survivorship of animals were derived from primary data.
We harvested 0.025-m2 randomly placed quadrats for
annual plants, made dimensional measurements of perennial plants in permanent belt transects, and made
mark-recapture density estimates for lizards and small
mammals on permanent plots. Cover and biomass were
estimated assuming an ovate cylindrical shape for all
shrubs and an experimentally determined regression of
weight verses volume (Hunter and Medica 1989).
Certain species are too rare to sample on small plots,
and too important to be ignored. Examples include
desert tortoises (a threatened species since 1990), deer,
and horses, as well as certain larger plants, in particular
Joshua tree (Yucca brevifolia), Mojave yucca (Yucca
schidigera), Utahjuniper, and singleleafpinyon pine.
To monitor the status of those species we marked individuals and monitored growth, death, and health status
at intervals of one to several years. We did not attempt to
measure their densities, but did monitor their health status and threats to their health. Convenient, rather than
random, populations were selected (generally on or adjacent to permanent baseline plots), and no specific attempt
was made to study those species in relation to particular
disturbances.
Common names for plant species follow Scott and
Wasser (1980) and DeDecker (1984).
METHODS
The Basic Environmental Compliance and Monitoring
Program (BECAMP), set up by DOE in 1987, uses historical data and current measurements of plants and animals
at specific sites to assess effects of DOE operations. Historical data include published reports (see O'Farrell and
Emery 1976) and a considerable amount of raw data present when BECAMP monitoring began. Raw data were
collected, microfilmed, and stored, and reprints were collected from libraries. Attempts were made to compare results from the first years of BECAMP data with historical
measurements to detect significant changes in small
mammal and plant populations.
Examination oflocal high-resolution maps enabled us
to choose study sites where changes due to DOE activities
were likely. These maps included fences surrounding radiation exclusion zones (areas of potential significant
Table 2-Extent of various disturbances on the Nevada Test Site,
estimated from high-resolution maps
Disturbance
Burned, 1978-87
Blast zones, 1950's
Radiation exclusion
Drill pads
Paved roads
Subsidence craters
Pu contamination
Dirt roads
Facilities
Waste burial
Waste radex
Tunnel radex
Total
Percent of
total
area
Percent of
disturbed
area
4.33
1.59
.57
.36
.27
.25
<.18
>.11
.09
.08
.03
.02
55.0
20.2
7.2
4.6
3.4
3.2
<2.3
>1.4
1.1
1.0
.4
.2
7.88
100.0
404
RESULTS
line), and Beatley did not measure widths of sampled
plants, so cover could not be derived from her size data
as it is with belt transect data. Only carefully worded and
vague comparisons, and no firm conclusions as to change
in vegetation cover, density, or biomass could be drawn
from use of the two techniques.
Determining the extent of disturbance by human activities and natural forces from maps proved very useful in
siting study plots. Fires were a very significant disturbance (table 2), and were therefore given some priority in
sampling effort. Plots were set up to sample each of the
top six disturbances (table 2). Since the program started
we ceased sampling the one radioactive plot, primarily
because spatial variation in vegetative parameters surrounding the site prevented selection of a suitable comparison plot. We were, however, also unable to postulate
any measurable effects of the contamination on that site,
considering dose rates effects determined in previous NTS
studies (French and others 1974; Kaaz and others 1971;
Vollmer and Bamberg 1975). Sampling is still being carried out on burned areas, blast zones, drill pads, subsidence craters, and paved roads.
The value of separating spatial from temporal variability can be demonstrated with an analysis of variability
of population densities on five transects within two 9-ha
plots sampled in 1987. Not one of 10 common species'
mean densities could be determined to within 25 percent
by five transects (table 4). Numbers of randomly placed
transects needed to detect density differences of 25 percent varied from nine to 964. Transects take two to four
person-days each to measure, and considerably longer to
analyze, and it was therefore impractical to try to reach
even that level of precision by sampling random nearby
points. This means there was no effective way to measure
multiple random transects to monitor changes in plant
density.
Differences in technique of the various NTS researchers
were a significant hindrance to use of historical data. Only
Beatley's annual data for Rock Valley have been used
(Hunter 1990, 1991), and that was possible only for density. Sampling by Brigham Young University (BYU) at the
Sedan event site provided data that. could be used to calculate small mammal densities, although the authors refrained from doing so (Allred and others 1963b). Other researchers measured parameters like radionuclide content,
trap success, or species composition. There were no density
estimates of lizards in the historical record.
A comparison of Beatley's line intercept technique and
BECAMP's belt transect shows how technique dependence
can influence comparisons, and illustrates why technique
continuity is so important for monitoring. To make this
comparison, in 1989 we used both techniques to examine
plant populations within Beatley's plot 3. A total of 335 m
(1,100 ft) of line intercept (Beatley 1979) are compared to
100m2 of belt transect (following Hunter and Medica
1989). Summary statistics reveal sizable differences for
mean height, percentage of the population, and percent
cover (table 3). Mean heights (by species) were estimated
to be larger by line intercept than by belt transect (paired
t =4.52, 10 d.f., p =0.001). This occurs because plants are
intersected by a line only when their bases are within one
canopy radius of the line. Therefore, larger plants have a
greater probability of being selected. Belt transects select
all plants with bases within the area sampled, and are not
biased toward large plants. Cover by belt transect was inflated because of the inability to correct for overlap in plant
canopies. The "mean cover" for the line intercept technique
is easily calculated by ignoring species, while "total cover"
(table 3) includes overlap. One cannot calculate density for
line intercept data (Beatley reporte4 plants per 335 m of
Table 3-Comparison of Beatley's line intercept and BECAMP's belt transect techniques. Line intercept overestimated percent of population
(%n) and height (ht, em) for large plants, and belt transects overestimated cover (%c)
Line lnterceRI
Species
desert needlegrass
Indian ricegrass
desert globemallow
Shockley goldenhead
bursage
littleleaf krameria
Mojave aster
winterfat
spiny hopsage
Nevada ephedra
Anderson wolfberry
Fremont dalea
common blackbrush
pale wolfberry
creosote bush
Total population
Total cover
Cover, no overlap
o.kn
%c
0
0
0.4
1.3
39.3
1.7
1.7
.9
7.4
13.5
7.0
.9
2.6
6.1
10.0
0
0
0.0
.1
11.4
1.7
.2
.1
2.0
4.6
3.0
0.5
.6
2.4
6.8
229
36.2%
29.9%
405
ht
6
32
39
44
49
50
56
58
60
61
66
70
109
o.kn
0.6
.6
.6
0
48.3
1.2
5.2
3.5
5.8
15.7
7.6
0
1.7
2.6
5.8
Belt transect
%c
0.0
.0
.0
0
10.9
1.3
.3
.3
1.5
6.4
4.5
0
3.2
1.5
12.8
172
42.7%
ht
1
3
4
0
30
32
27
40
51
43
55
64
48
81
Table 4-Average plant numbers per transect from five-replicate,
randomly placed 1OO-m2 belt transects, and estimated
numbers of transects needed to detect a change in a
species' density of 25 percent at p =0.05 (Bonham 1989)
Species
Shockley
goldenhead
bursage
winterfat
Nevada ephedra
spiny hopsage
white burrobrush
creosotebush
Anderson wolfberry
Indian ricegrass
Frenchman Flat
Number Transects
20.4
35.2
7.8
.2
2.8
41.6
8.0
1.8
5.1
19
36
335
964
79
29
17
250
45
found they differed significantly by chi-square analysis
253, d.f. = 28, p << 0.001). For practical purposes,
therefore, measuring the status of an "association" was
not considered a goal when setting up the BECAMP monitoring program. Our intent was to measure the status of
individual species. We do, however, measure community
components (densities, sizes by species), which we presume will allow significant changes to be detected.
(;t2 =
Yucca Flat
Number Transects
54.1
9
63.8
24.8
34.8
23.6
20
102
22
123
7.8
14.1
185
77
DISCUSSION
Hard lessons are embodied in some of the foregoing experiences. The inability to make significant use of the
relatively extensive history of biological research on the
NTS was not expected, nor were the problems with precision in the perennial plant measurements. Spatial variability in plant species distributions was only guessed at
prior to the first analysis of replicate transects. The tentative solution of use of permanent plots or transects is
unsatisfying because by aiming at good temporal trends
we have eliminated the possibility of measuring spatial
distribution, except on a superficial level.
There are some obvious but nevertheless important conclusions to be drawn for others who might be in the initial
stages oflong-term monitoring programs. It is important
to carefully pick parameters to be measured. Some good
recommendations have already been made, such as monitoring all trophic levels in an ecosystem (Bruns and others
1991; Wiersma 1990), but such recommendations are divorced from fiscal concerns. I believe it is important to
measure absolute rather than relative parameters, because techniques continually change, hopefully improving.
We are currently considering changes in trap design, and
wider use of GPS for locations. Hopefully, changing traps
will not change mark-recapture density estimates, and
GPS locations will be accurate enough to compensate for
future loss of some plot boundary markers.
"Disturbances" (table 2) that were used to set priorities
for plot selection do not include general ones such as
air pollution, climate change, grazing, and introduced
Temporal variability in plant numbers on a single transect was much lower than the spatial variability in density. For example, on one belt transect in 1990, 412
shrubs were found. In 1991, 395 (91 percent), or their remains, were identified. Only 17 (4 percent) could not be
found. In addition, 35 more (8 percent) were found in
1991. Intrayear changes were largely due to difficulties
distinguishing separate plants in clumps of similar individuals (ambiguous numbers), to inexact locations (tape
placement), and ambiguous locations (inexact measurement). Of the 35 "new" plants, only three were considered
seedlings in 1991 (table 5). Thus, we can define a species'
density on one permanent transect to within a few percent, but with five transects density on randomly sampled
areas could be defined to within a factor of 2 only for the
most common species (Bonham 1989: 67 -69).
The better precision with permanent transects therefore allows us to follow temporal trends that could only
be guessed at with random sampling. Lacking random
samples, however, inferences about the broader community cannot be made from permanent transect data, although differences between measured points can be tested
with several statistical techniques.
When ambiguous locations were found to be a problem,
several changes were made. In 1988 and 1989 plant locations were recorded to ±25 em from a steel tape, and
within 1m along the tape. After 1989, distances from the
tape were recorded to ±1 em, and distances along the tape
to the nearest decimeter. The center of the 50-m tape
(25 m) was pinned by permanent lath stakes to prevent
wind displacement. Plants just outside the edge of the
belt were marked, and students measuring the plants
were given data sheets generated from the previous year's
data, forcing them to try to find each plant. Finally, data
from each transect were checked in the field by senior personnel before the data were analyzed. The increased precision is evident in table 5 for the 1990-91 period.
Beatley divided NTS vegetation into "plant associations" defined by the dominant species (for example
pinyon-juniper, Larrea-Ambrosia, Grayia-Lycium, flg. 1).
I examined the distribution of species abundances within
five transects located within 300 m of Beatley plot 46 and
Table 5-Reasons for inability to match plants from one transect
with the same plants in the previous year's data
Symptoms
Plants matched (live and dead)
Matched but ambiguously alive
Plants that disappeared
Tape placement-edge plants
not measured
Ambiguous number of individuals
Ambiguous locations
Plants missed year 1, present year 2
Plants missed year 2, present year 1
Mismeasured or misrecorded
Misidentified species, year 1
New small plants, probable seedlings
Totals
Percent successfully matched
406
1989·90
1990·91
177
39
8
396
13
5
26
66
18
55
15
10
19
15
20
0
446
441
48
93
0
2
0
0
3
3
species. Although baseline plots are being affected by
these influences, the absence of "controls" is another
source of discomfort. How can we isolate the effects of,
for example, a 2-degree temperature rise, from concurrent
fluctuations in precipitation or increased competition for
water due to new species introductions?
Over the first 5 years of monitoring there were changes
in all of the populations measured. Drought appeared to
cause most changes, but grass and shrub populations on
denuded areas were slowly recovering, north- and southfacing slopes of subsidence craters were changing, the
species mix of annual plants was changing, and small
mammals located near roadsides appeared to be reproducing better than controls. Monitoring was thus detecting
change, but one is then led to ask, what was causing these
changes? More important, are we collecting evidence that
can allow us to choose between, for example, predatorprey interactions and disturbance effects on lizard populations? Answers to those questions posed by the results of
monitoring will probably have to be based on shorter term
research projects. Thus, a monitoring program should
plan to include some mechanism for funding and performing research on ecosystem processes and responses
to disturbance.
Finally, the preservation of data and results is an
unsolved problem. We produce an annual summary report, which is published as a government document (for
example, Hunter and Medica 1989). Data from the NTS
will also be archived. Nevertheless, knowledge of the
data's existence is liable to depend on publication of
selected results in refereed journals.
transition of the Nevada Test Site, 1963-1975. U.S.
Department of Energy, DOE/NV/2307-15. 52 p. Available from National Technical Information Service, U.S.
Department of Commerce, 5285 Port Royal Road,
Springfield, VA 22161.
Bonham, Charles D. 1989. Measurements for terrestrial
vegetation. New York: John Wiley & Sons. 338 p.
Bruns, D. A.; Wiersma, G. B.; Rykiel, Edward J., Jr. 1991.
Ecosystem monitoring at global baseline sites. Environmental Monitoring and Assessment. 17(1): 3-31.
DeDecker, Mary. 1984. Flora of the northern Mojave
Desert, California. Spec. Publ. 7. Berkeley, CA: California Native Plant Society. 164 p.
French, N. R.; Maza, B. G.; Hill, H. 0.; Aschwanden, A. P.;
Kaaz, H. W. 1974. A population study of irradiated
desert rodents. Ecological Monographs. 44(1): 45-72.
Hunter, R. B. 1990. Recent increases in Bromus populations on the Nevada Test Site. In: McArthur, E. D.;
Romney, E. M.; Smith, S. D.; Tueller, P. T., comps.
Proceedings-symposium on cheatgrass invasion, shrub
die-off, and other aspects of shrub biology and management. Gen. Tech. Rep. INT-276. Ogden, UT: U.S.
Department of Agriculture, Forest Service, Intermountain Research Station: 22-25.
Hunter, R. B. 1991. Bromus invasions on the Nevada Test
Site: present status of B. rubens and B. tectorum with
notes on their relationship to disturbance and altitude.
Great Basin Naturalist. 51(2): 176-182.
Hunter, R. B.; Medica, P. A. 1989. Status of the flora and
fauna on the Nevada Test Site: results of continuing basic environmental research January through December
1987. U.S. Department of Energy, DOE/NV/10630-2.
103 p. Available from National Technical Information
Service, U.S. Department of Commerce, 5285 Port
Royal Road, Springfield, VA 22161.
Kaaz, H. W.; Wallace, A.; Romney, E. M. 1971. Effect of
a chronic exposure to gamma radiation on the shrub
Ephedra nevadensis in the northern Mojave Desert.
Radiation Botany. 11:33-37.
O'Farrell, Thomas P.; Emery, LaVerne A. 1976. Ecology
of the Nevada Test Site: a narrative summary and annotated bibliography. NV0-167. U.S. Energy Research
and Development Administration, Nevada Operations
Office. 249 p. Available from National Technical Information Service, U.S. Department of Commerce, 5285
Port Royal Road, Springfield, VA 22161.
Scott, Thomas G.; Wasser, Clinton H. 1980. Checklist
of North American plants for wildlife biologists.
Washington, DC: The Wildlife Society. 58 p.
Shields, Lora M.; Wells, Philip V.; Rickard, William H.
1963. Vegetational recovery on atomic target areas in
Nevada. Ecology. 44(4): 697-705.
Wiersma, G. B. 1990. Conceptual basis for environmental
monitoring programs. Journal of Toxicological and Environmental Chemistry. 27(4): 241-249.
Vollmer, A. T.; Bamberg, S. A. 1975. Response of the
desert shrub Krameria parvifolia after ten years of
chronic gamma radiation. Radiation Botany. 15:
405-409.
ACKNOWLEDGMENTS
This work was performed under contract DE-AC0889NV10630 with the U.S. Department of Energy. We
are grateful to the many officials who have supported '
ecological research on the Nevada Test Site over 40 years
of testing.
REFERENCES
Allred, Dorald M.; Beck, D Elden; Jorgensen, Clive D.
1963a. Biotic communities of the Nevada Test Site.
Brigham Young University Science Bulletin, Biological
Series. 2(2): 1-52.
Allred, Dorald M.; Beck, D Elden; Jorgensen, Clive D.
1963b. Close-in effects of an underground nuclear detonation on small mammals and selected invertebrates
(Project SEDAN). U.S. Atomic Energy Commission,
PNE-226 IV. 18 p.
Beatley, Janice C. 1976. Vascular plants of the Nevada
Test Site and Central-Southern Nevada: ecologic and
geographic distributions. Energy Research and Development Administration, TID-26881. 308 p. Available from
National Technical Information Service, U.S. Department of Commerce, 5285 Port Royal Road, Springfield,
VA22161.
Beatley, Janice C. 1979. Shrub and tree data for plant
associations across the Mojave/Great Basin Desert
407