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Abstract-Acquiring an understanding of the pinyon-juniper ecosystem challenges our current research technologies. Extremely variable site conditions and protracted time considerations result in a complex research environment. Utah State University has established a long-term watershed scale research site in the Clover Creek
Management Unit near Tooele, UT. The objective is to perform mechanistic research in pinyon juniper ecosystem dynamics, for example, energy, water and nutrient cycling, organismal structure and function at relevant scales, sediment source/sink relationships, and so forth, while simultaneously addressing the more pragmatic concerns associated with management objectives, the effects of drastic disturbance and the results of custodial management. The project utilizes small watersheds and spatial nesting of tributary basins with uniform soils, slope, and aspect to provide integration of spatial and temporal variability and a more realistic scale for assessing the influence of land management activities.
Historically, land managers have associated canopy closure by pinyon and juniper with site degradation, measured by a reduction in desirable plant species and forage production for wildlife and livestock (Bedell 1987, Pieper
1990, West 1984). A lack of management (that is, custodial management) is often identified with accelerated soil erosion. Other researchers have found little evidence to support the idea of environmental degradation.
Once accepted as a sound rangeland rehabilitation program, the justification of pinyon-juniper type conversion is now raising concerns about disturbance of archaeological sites, conflicts with wilderness preservation, the recreational and economic importance of pinyon nuts, aesthetic values, wildlife ha.Jitat needs and the economics of brush management. Justification of active management by mechanical methods, chemical techniques and/or prescribed burning often demand answers that require a greater knowledge of the pinyon and juniper ecosystem than now exists in the available scientific literature. Soils of pinyonj uni per woodlands are typically shallow, well-drained, and have low fertility (see Lowe and Dobrowolski, this conference). As the trees mature, herbaceous cover declines. Due
In: Monsen, Stephen B.; Stevens, Richard, comps. 1999. Proceedings: ecology and management of pinyon-juniper communities within the Interior
West; 1997 September 15-18; Provo, UT. Proc. RMRS-P-9. Ogden, UT: U.S.
Department of Agriculture, Forest Service, Rocky Mountain Research
Station.
James P. Dobrowolski is Associate Professor in the Department of Rangeland Resources and Acting Director, Watershed Science Unit, Utah State
University, Logan, UT 84322-5230. to little soil cover coupled with typically erodible soils, many land managers have come to the conclusion that pinyon and juniper invasion results in poor watershed condition (Bedell 1987). However, Heede (1987) found the microtopography produced by tree coppices (mounds that decrease in elevation from the trunk outward) to absorb the energy of flowing water and to restrict sediment delivery downslope.
"Improvement" ofthe soil hydrologic condition by pinyonjuniper clearing is considered to be a fact in land management working documents and other publications (Johnsen and Raymond 1990). However, the concept's basis is rooted in an early U.S. Forest Service paper (Arnold and Schroeder
1955) describing differences in active erosion between cleared and untreated areas. This conclusion was reached with field observations not subject to the rigors of scientific experimentation.
Typically, many published studies focussed on different technologies to improve the forage resource and they only included ancillary observations of the treatment effects on soil hydrologic condition. Clary and others (1974) found no meaningful change in sediment yield after removing pinyon-juniper by cabling or the application of herbicides at
Beaver Creek, Arizona. Measured salt concentrations produced from surface soils of pinyon-juniper sites are not cri tical to deli very of sal t wi thin maj or ri ver basins (Hessary and Gifford 1979). Gifford (1987) in Utah and Wood and
Wood (1988) in New Mexico concluded that removal of pinyon-juniper by chaining does not reduce sediment production.
Many erosion plot studies (sensu Buckhouse and Gifford
1976, Busby and Gifford 1981) have relied on a limited number of rainfall events with the potential to produce overland flow. Standard erosion plots typically represent the spatial effects of only one tree and its associated intercanopy spaces. These plots often were installed prior to the collection of pretreatment data. When sample size is small, spatial interspersion is missing, and/or pretreatment data is lacking, the power of the statistical test can be substantially affected, risking the possibility of a Type II statistical error and the problems associated with it. An error of the second kind or Type II error is made when the experimenter accepts the null hypothesis and the alternative is true. The concept of a Type II error is particularly important in determining the sample size necessary to detect a difference of an a priori magnitude.
Williams and Buckhouse (1993) measured the amount of sediment exported and overland flow differences from 10 different ecosystems in eastern Oregon. Using runoff plots
(1 x 5 m) treated with simulated rainfall,juniper dominated systems were found to have greater overland flow and higher potential for sediment export. However, Williams
(personal communication) felt that efforts to distinguish
188 USDA Forest Service Proceedings RMRS-P-9. 1999

differences in sediment production from treated and undisturbed ponderosa pine ecosystems with the same runoff plot technology (Williams and Buckhouse 1993), was susceptible to a Type II error.
Researchers have postulated that successional trajectories currently in place and likely to carryon for future centuries due to tree longevity, result in a self-destructive system. Carrara and Carroll (1979) and others felt that a large portion of the pinyon-juniper type is exhibiting undesirable successional tree "superdominance" leading to site degradation due to loss of biodiversity, the threat ofa fire holocaust, in addition to accelerated soil loss. West and
Van Pelt (1987) expressed a need to know where and why this was occurring, and felt these disturbing trends to contradict the prevalent idea that succession always leads to more stable, more diverse, and more economically valuable communities. Pinyon-juniper woodlands at higher elevations tend to follow the usual concept of linear plant succession. On sites when the time between regeneration events is longer than the lifespan of established trees, alternative steady states occur (Jameson 1987). The successional trajectory of pinyon-juniper sites subjected to drastic disturbance appears to depend upon the density and size of trees before disturbance (Schott and Pieper
1987). Tausch (1977) found a steady reduction of understory cover and production beyond the fifth to eighth year after drastic disturbance, dependent upon site characteristics.
It is imperative that land managers have the knowledge to anticipate what will happen with successional change and be able to recognize problems associated with unimpeded succession (Schott and Pieper 1986).
In addition to their potential influence on water cycling, these ecosystems might influence global temperature change most directly by acting either as a sink for excess CO
2 or by giving up some of the CO
2 currently stored, that is, act as a carbon "source" (Perry and others 1991). Net primary production (NPP) can increase and thereby sequester carbon or the decay of organic matter may be greater than
NPP, or fire, insects and drought may reduce NPP leading to a release of CO
2 ,
Destruction of forests and drastic disturbance have been linked to a 30 percent increase in atmospheric CO
2 in this century. Little is known about the carbon cycling properties of a pinyon-juniper woodland.
Efforts to investigate nutrient accumulation in pinyonjuniper woodlands were traditionally restricted to the fate of plant macronutrients after application of some management technology (DeBano and others 1987). With the recent interest in global climatic change and the concentration of greenhouse gases in the atmosphere, knowledge of the temporal dynamics of carbon cycling and feedback interactions in the pinyon-juniper ecosystem is essential
(Perry and others 1991). Productivity of pinyon pines and junipers as indexed by carbon gain was found to be highly correlated to some abiotic factors, particularly soil moisture (Barnes and Cunningham 1987). Klopatek (1987) found organic carbon contents of the soil beneath canopies to be statistically greater for mature pinyon-juniper canopies than stands recovering from historic fire.
New plot data have sparked further debate over the relationship between soil hydrologic condition and the pinyonjuniper ecosystem. These data might have limited statistical inference simply because of small plot size (1 plots, including the standard erosion plot (3 x 3 m). Small x 10 m) often neglect the spatial mosaic of soil hydrologic conditions typical of the pinyon-juniper ecosystem. Plots may only encompass the influence of one or possibly two pinyon or juniper trees.
Heede (1987) determined that spatial variability imparted to the pinyon-juniper site by litter-produced hummocks reduced the slope gradients and diverted runoff. In this case Heede's experimental areas were 5 x 8 m "microwatersheds." Heede's microwatersheds, which add 10 square meters to the standard erosion plot, likely cannot escape the same criticism for a lack of spatial representation.
A watershed-scale study integrates spatial and temporal variability and provides a more realistic scale for assessing the influence of land management activities. In addition, modelling scale-dependent problems such as a changing global climate requires the procurement of data at a variety of scales. Standard experimental watershed methodologies, such as the paired-watershed approach, often require two like watersheds and the calibration of flow from each watershed. These experimental procedures have been criticized for their high cost and for the apparent difficulty in extrapolation. Proper design, cautious planning and careful site selection can augment statistical inference from results and address the criticisms of an experimental watershed approach (Bosch and Hewlett 1982).
The time scale for pinyon-juniper research is very difficult to realistically accommodate. Houghton (1969) states that it may take 30 years or more simply to determine average annual precipitation in the Great Basin. Pinyonjuniper, and other western woodlands tend to exhibit very low dynamism (Little 1987) and appear to be some of the most static of all western ecosystems (West and Van Pelt
1987). These attributes exceed the life expectancy and attention span of most research efforts. Past research was conducted over a few years period, often coinciding with the availability of graduate student assistance. The long lifespans and time to maturity ofthe trees means that they are subject to significant environmental fluctuations and disturbances requiring patient observation, hence the minim urn requirement of a 10-year experimental horizon planned for the study proposed here. Long-term watershed studies
USDA Forest Service Proceedings RMRS-P-9. 1999 189

are needed to provide a frame of reference for shorter-term plot research (Schmidt 1987).
Pinyon-juniper research by Utah State University will attempt to define and resolve these critical ecological questions at the watershed scale.
1. To establish a long-term, watershed-scale research site for applied and basic research into the dynamics of a
Great Basin pinyon-juniper ecosystem. This effort will involve investigators from across the USU campus and be coordinated with other regional studies at Los Alamos
National Laboratory, Oregon State University, and the
University of Nevada, Reno. Utah Agricultural Experiment Station funds will be used to delineate the site and to promote the acquisition of development funding from other sources. It is hoped that a study at a watershed scale will eventually be assisted by long-term ec-ological reserve funding (LTER, partially funded by the National Science Foundation), representing a pinyon-juniper ecosystem in the
Great Basin.
2. To perform mechanistic research of pinyon-juniper ecosystem dynamics, such as, energy, water and nutrient cycling, organismal structure and function at relevant scales, sediment source/sink relationships, and so forth, while simultaneously addressing the more pragmatic concerns associated with management by objectives, the effects of drastic disturbance, or the results of custodial management.
• Do sites that are dominated by mature, middle-aged, or young pinyon-juniper represent degraded or degrading sites?
Sediment source / sink relationships, soil profile / organic carbon dating
• Why might pinyon-juniper dominance influence biodiversity? How will understory plants respond to partial or complete removal of the pinyon-juniper overstory? How will the abundance of mammal and bird species change with shifting successional stage?
Mechanical manipulation under best management practices, simulated catastrophic wildfire, mosaic thinning
• How does the water balance of a pinyon-juniper ecosystem change when vegetation dominance shifts?
Mosaic thinning, tree removal with an undisturbed understory
• Does a pinyon-juniper ecosy..:;tem act as a source or sink for carbon?
Ecophysiological studies of drastically disturbed and / or relatively undisturbed stands at different age classes
• Why are pinyon and juniper trees considered to be invasive under some conditions? What are the dispersal mechanisms in the Great Basin?
Pinyon-juniper population dynamics in drastically
disturbed and / or relatively undisturbed environments
190
We propose to use an overall study design that was successfully applied to answer geomorphic and ecologic questions in Australia, Great Britain, and the U.S., a nested-watershed approach (sensu Jarvis 1976, Neary
1985). Spatial nesting of tributary basins with uniform soils, slope, and aspect is identified, and these tributary basins are instrumented as components of a larger watershed (fig. 1). Often the watershed measuring devices are located so that each drainage area monitored increases by an order of magnitude from one location to the next
(Amphlett and others 1987). Nested subareas (1.2 to
98.9 km 2
) of the Highland Water Catchment in Great
Britain were used to analyze the difference in runoff depth and peak discharge between heath and woodland covered areas at several spatial scales (Gurnell and others 1990).
Six nested watersheds provided the background for a study of the spatial and temporal variation in suspended sediment from different cropping systems in central Iowa
(Hamlett and others 1987). At the variable scales common
. ........ -
.........
----~'-.............
I ..... , .. , . , . ,
Figure 1-Nested tributaries within a larger watershed (redrawn from Jarvis 1976). Potential treatments are indicted for illustrative purposes.
CONTROL
\
\ to a nested watershed study, Dickinson and others (1990) were able to show dramatic variations between annual sediment yields, and suggested that the common procedure of applying sediment ratings to fill data gaps on noninstrumented watersheds is not recommended.
In our study, different land treatments will be applied to these small "nested" watersheds and the integrated effects assessed by the larger watershed (fig. 1). These studies of small watershed process, nested within a larger watershed require intensive efforts but can often make use of very simple techniques over short periods. A summary and review of 94 catchment experiments throughout the world revealed that paired, nested, or grouped catchment experi-
USDA Forest Service Proceedings RMRS-P-9. 1999

ments produced stronger evidence than less controlled studies (Bosch and Hewlett 1982). The nested approach will provide an opportunity to confirm or extrapolate smallscale findings (Nowson 1979).
The attributes that set this proposed research apart from earlier efforts to establish cause and effect include:
1. Physically and biologically meaningful spatial scales that are integrated.
2. A philosophy based upon the assumption that an understanding of processes (process-oriented research) provides greater power to predict system response to perturbation. Additionally, using a mechanistic approach, looking for mechanisms that can be explained in terms of physics and chemistry.
3. A reasonably long time scale to obtain relevant results.
4. A study design that is flexible enough to provide for statistical analyses and the application of deterministic modelling (Deschesnes and others 1985).
The Clover Creek Watershed is located in northeastern
Tooele County approximately 32 km (20 miles) south of
Tooele, Utah (St. John Quad, Sect. 35, T.6S, R.6E). The study area straddles the semidesert and upland climatic zones. Precipitation averages 32 cm (12.8 inches) each year with approximately 88 percent coming as snow and 12 percent as spring and summer thunderstorms. Temperatures can range from -7°C to 38 °C (-19 to 101°F) throughout the year. Soils were formed from alluvial deposits and they are presently classified as loamy-carbonatic, mesic, aridic Petrocalcic Palexerolls of the Borvant series.
The vegetation type is ajunipe-rwoodland thatinterdigitates with a shrub steppe. The overs tory is dominated by Utah juniper (Juniperus osteosperma) with an understory composed of microbiotic crusts and Indian ricegrass (Oryzopsis hymenoides), Sandberg's bluegrass (Poa secunda), bluebunch wheatgrass (Pseudorigneria spicata), and a mix of introduced grasses and forbs. Tree interspace dominants include Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) and gray rabbitbrush (Chrysothamnus nauseosus), understory composition is similar to the juniper understory.
As canopies close, herb species appear to dwindle to a fairly stable set exhibiting shade tolerance. In long-lived tree stands with shade-tolerant herbs, some researchers feel that partial removal of the canopy can negatively influence the herb biomass (Papp 1977) and their relative importance (Metzger and Shultz 1984). However, Reader and Bricker (1992) found partial canopy removal in a deciduous forest, to conserve the understory herbs. Herb species disappeared from undisturbed forest at about the same rate as partial canopy removal. These results suggest a "conserving function" that could be used to help preserve the forest understory. Manipulating the small watersheds at Clover Creek using a mosaic approach offers a unique opportunity to elucidate some of the processes producing these conflicting results. It will also add to a depauperate literature for selective removal of unmerchantable timber.
Canopy closure in the pinyon-juniper ecosystem appears to reduce the fine fuels available for surface fires, with the result that eventually, prescribed burning becomes an ineffective vegetation manipulation tool (Blackburn 1983).
At the same time, the threat oflarge-scale destruction by a crown fire increases. Evaluation of the consequences of a severe wildfire through tree crowns is important to the understanding of ecosystem dynamics and risk analysis under custodial management (Tausch and West 1989).
Application of a full-scale wildfire treatment with the in tensi ty necessary to reproduce the effects of a firestorm is not possible for obvious safety reasons. However, a portable propane plant burner, originally developed for use in evaluatingthe effects offire on individual plants, can be adapted to apply specific time-temperature heat treatments to the pinyon-juniper understory. Propane burners can be constructed in a variety of sizes, depending upon the species to be treated. According to Dr. Allen Rasmussen (personal communication), a burner unit capable of moving over the soil surface could be designed and used to simulate wildfire at a small watershed scale without the threats posed by na tural fire.
When pinyon-juniper is uninhibited either by fire or by full-scale plant competition, the trees, with their resistance to herbivory and decay and greater physiological efficiency, permits thickening of their cover. That correlates, in most previous studies, with a further decline in understory productivity as they mature (West 1984). Dragging an anchor chain between two bulldozers or "chaining" has been used throughout the U.S. since the 1950's to remove unwanted woody vegetation. Typically, chaining was carried out in the most level portion of a pinyon-juniper dominated watershed. This heavy treatment produced an expected canopy cover shift from trees to seeded grasses, potentially lasting for at least 56 years. Disturbance levels and recovery times depend upon a myriad offactors. Disturbance levels are altered by the number of passes of the chain (for example, one-way versus two-way chaining), whether angle iron is welded to the chain, application season, and composition of the seeded mix. The permutations are numerous. Best management practices (BMP's) exist, taking slightly different forms for each management agency. These experimental studies are not intended to evaluate the efficacy of BMP's per se, though knowledge
USDA Forest Service Proceedings RMRS-P-9. 1999 191

about the effects of this type of disturbance on pinyonjuniper at Clover Creek under the established environmental and experimental conditions will be greatly enhanced.
Carbon Sequestration-A recent workshop about the natural sinks of carbon dioxide (Wisniewski and Lugo
1992) proposed the hypothesis that temperate and tropical forests have the potential to sequester a part of the carbon emitted by the burning of fossil fuels not found in atmospheric and oceanic cycling. Terrestrial ecosystems supporting pinyon-juniper woodlands may be absorbing some of this misplaced carbon. As pinyon-juniper forests expand, increases in carbon storage may occur under similar circumstances as the increase in European forests since the industrial revolution. Glenn and others (1993) indicated that reversing the trend towards desertification by restoration and revegetation of degraded rangelands could, in part, result in net carbon sequestration. Annual biomass yields will need to be assessed that can produce values for net carbon uptake (sensu Sedjo 1989). Investigation of carbon residence times in soils supporting pinyon and juniper, likely significantly greater than forest soils, will require effort and coordination by cooperating scientists
(Rick Miller, USDA-ARS, Burns, OR; David Breshears, and others, USDOE, Los Alamos).
Seed Dispersal and Population Dynamics-Koniak and Everett (1982) assert that when closed canopies of pinyon-juniper are opened artificially, few native plants tend to recover, apparently because seed banks and seed sources have been lost. The proposed experimental manipulations may be too small to gain a reasonable understanding of how large-scale treatments affect patterns of seedfall and seed predation due to the proximity and influence of the surrounding matrix. However, since treatment manipulations may differentially affect shading, water availability, and competition, experimental studies can be designed to elicit how these factors influence the incorporation of seeds into the soil, germination and successful emergence, establishment, growth and survival of seedlings (Eugene Schupp 1997, personal communication).
HistoricallEcological Relationships-See Creque,
West, and Dobrowolski this proceedings.
Social Considerations-The relatively recent and vocal concern over land improvement practices in pinyonjuniper woodlands fosters a need to understand public attitudes toward such practices as chaining, prescribed burning, and seeding. The Clover Creek Study Area offers an opportunity for social science research that might link general attitudes toward rangeland improvement practices with photographs of actual sites over a period of years.
Lay persons can be asked to evaluate trade-offs among alternative management scenarios after viewing computersimulated photographs and hearing site-specific information about biodiversity, soil erosion, and other biophysical factors.
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