LESSONS FROM 5 YEARS OF VEGETATION MONITORING ON THE NEVADA TEST SITE

Richard Hunter

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.

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

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.

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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).

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;

e. . Provide a continuing assessment of pollution abatement programs;

f. Identify and quantify new or existing environmental quality problems.

This file was created by scanning the printed publication.Errors identified by the software have been corrected;

however, some errors may remain.

PAHUTEMESA

SHOSHONE MOUNTAIN

VEGETATION TYPES ON THE NEVADA TEST SITE

~~LARREA ffiili} COLEOGYNE

D LARREA/ COLEOGYNE

EJ GRAYIA-LYCIUM

~ LYCIUM PAW DUM

[W ATRIPLEX

~ARTEMISIA

D MOUNTAINS, HIU.S, ANO MESAS

Figure 1- Vegetation types on the Nevada Test Site.

403

m LYCIUM SHOCKLEY!

SCALE 0)~~1"' ~iHHi km

t N

'

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.

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

Percent of Percent of total disturbed

Disturbance area area

Burned, 1978-87 4.33 55.0 Blast zones, 1950's 1.59 20.2 Radiation exclusion .57 7.2 Drill pads .36 4.6 Paved roads .27 3.4 Subsidence craters .25 3.2 Pu contamination <.18 <2.3 Dirt roads >.11 >1.4 Facilities .09 1.1 Waste burial .08 1.0 Waste radex .03 .4 Tunnel radex .02 .2

Total 7.88 100.0

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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).

RESULTS 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

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.

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 Belt transect Species o.kn %c ht o.kn %c ht

desert needlegrass 0 0 0.6 0.0 1 Indian ricegrass 0 0 .6 .0 3 desert globemallow 0.4 0.0 6 .6 .0 4 Shockley goldenhead 1.3 .1 32 0 0 0 bursage 39.3 11.4 39 48.3 10.9 30 littleleaf krameria 1.7 1.7 44 1.2 1.3 32 Mojave aster 1.7 .2 49 5.2 .3 27 winterfat .9 .1 50 3.5 .3 40 spiny hopsage 7.4 2.0 56 5.8 1.5 51 Nevada ephedra 13.5 4.6 58 15.7 6.4 43 Anderson wolfberry 7.0 3.0 60 7.6 4.5 55 Fremont dalea .9 0.5 61 0 0 common blackbrush 2.6 .6 66 1.7 3.2 64 pale wolfberry 6.1 2.4 70 2.6 1.5 48 creosote bush 10.0 6.8 109 5.8 12.8 81

Total population 229 172 Total cover 36.2% 42.7% Cover, no overlap 29.9%

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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)

Frenchman Flat Yucca Flat Species Number Transects Number Transects

Shockley goldenhead 20.4 19 54.1 9

bursage 35.2 36 winterfat 7.8 335 63.8 20 Nevada ephedra .2 964 24.8 102 spiny hopsage 2.8 79 34.8 22 white burrobrush 41.6 29 23.6 123 creosotebush 8.0 17 Anderson wolfberry 1.8 250 7.8 185 Indian ricegrass 5.1 45 14.1 77

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

406

found they differed significantly by chi-square analysis (;t2 = 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.

DISCUSSION Hard lessons are embodied in some of the foregoing ex­

periences. 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

Table 5-Reasons for inability to match plants from one transect with the same plants in the previous year's data

Symptoms 1989·90 1990·91

Plants matched (live and dead) 177 396 Matched but ambiguously alive 39 13 Plants that disappeared 8 5 Tape placement-edge plants not measured 26 0

Ambiguous number of individuals 66 2 Ambiguous locations 18 0 Plants missed year 1, present year 2 55 20 Plants missed year 2, present year 1 15 0 Mismeasured or misrecorded 10 0 Misidentified species, year 1 19 3 New small plants, probable seedlings 15 3

Totals 446 441

Percent successfully matched 48 93

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.

ACKNOWLEDGMENTS This work was performed under contract DE-AC08-

89NV10630 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

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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.

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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.

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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.

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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.