I. Results from Prior NSF Support *
II. Project Description *
A. Background and Context for the Shortgrass Steppe Managed Ecosystem Research and Education Center *

1. Scientific Opportunities *

2. Education and Outreach Opportunities *

3. Overview of the Planning Proposal *

B. Site Description *

1. Climate *

2. Vegetation *

C. Description of the Existing Facility and Its Capabilities *
D. Planning Steps for the Shortgrass Steppe Managed Ecosystem Research and Education Center *

1. Refinement of the Vision *

2. Travel to FSML's *

3. Interagency relationships *

4. Architectural and Engineering Planning *

5. Outcome of Planning Proposed Planning Project *

III. Utilization of Facility for Research and Education *
A. Research Utilization *
B. Educational Utilization *
C. Other Utilization *

IV. Significant Research Accomplishments 1993-1998 *
A. Introduction *
B. Populations and Processes *
C. Biogeochemical Dynamics *
D. Paleoecology/Paleopedology *
E. Water and Energy Dynamics *
F. Disturbances *

Natural disturbances *

Human-induced disturbances *

G. Synthesis *
V. Selected Bibliography *
A. Ten Significant Research Publications 1993-1998 *

I. Results from Prior NSF Support

No FSML awards have been made to this facility in the last five years.

2. Project Description

A. Background and Context for the Shortgrass Steppe Managed Ecosystem Research and Education Center

Ecologists at Colorado State University (CSU) and the Agricultural Research Service have been studying the shortgrass steppe ecosystem of eastern Colorado intensively for many years. The current strong focus on the shortgrass steppe represents the continuing development of a research tradition that began in 1937-8 with the establishment of the Central Plains Experimental Range (CPER), a 6,280 hectare research site owned by the
Agricultural Research Service (ARS), and the adjacent 78,100 ha Pawnee National Grasslands (PNG). Scientists associated with the Agricultural Research Service (ARS) initiated several long-term experiments on the CPER, including large experiments on grazing intensity, and the initiation of long-term datasets on primary productivity. During the late 1960's, the time at which ecosystem science was formally recognized as a sub-discipline in ecology, the CPER was the site of the Grassland Biome project of the International Biological Program, which focused on the issue of productivity of natural ecosystems. Many of the CSU researchers involved in this program have continued to work at the research site since that time, receiving numerous grants and contracts. In 1982, the Shortgrass Steppe Long Term Ecological Research Project (abbreviated SGS-LTER, originally called the Central Plains LTER) was funded to support a joint CSU-ARS
effort to study shortgrass steppe ecosystem structure and function. This project currently serves as the centerpiece of a very large amount of scientific activity occurring on the shortgrass steppe in eastern Colorado, providing opportunities for collaborative work to be conducted on ongoing long-term experiments for scientists of many disciplines, supplying long-term datasets on ecological communities and ecosystem structure, and providing logistical support for fieldwork and data analysis. The SGS LTER recently expanded the definition of its site to include the adjacent Pawnee National Grasslands (PNG), to capitalize on opportunities to study a broader and more representative array of populations and landscape types. There are currently 30 scientists working on the CPER-PNG site, representing 10 institutions and numerous research grants. Scientists working at the CPER-PNG have been important contributors and participants in some of the major changes in ecosystem science over the past 30 years, particularly in the areas of primary productivity, element cycling, soil organic matter dynamics, ecosystem simulation modeling, and landscape to regional scale ecology. Scientists working on the CPER-PNG have produced 639 journals, 181 chapters, 141 theses, and 336 abstracts.

Our objective in this proposal is to develop a master plan for the construction of a Shortgrass Steppe Managed Ecosystem Research and Education Center. The current vision for such a Center is to:

• facilitate, support, and attract excellent basic and applied science by the local, regional, national and international scientific communities;
• provide opportunities for undergraduate, graduate and K-12 education;
• provide opportunities for education and outreach to the Colorado/Wyoming public; and to
• develop and enhance existing partnerships with the U.S. Forest Service, the Agricultural Research Service and other institutions within the framework of the Shortgrass Steppe Managed Ecosystem Research and Education Center.

1. Scientific Opportunities

The major goal for the broad scientific community studying the shortgrass steppe ecosystems of northeastern Colorado is to understand the processes that account for the origin, maintenance and sustainability of shortgrass steppe ecosystems.

The CPER and PNG represent a broad range of the variability found in shortgrass steppe ecosystems and provide exceptional opportunities for a diverse array of scientists to address this goal. Below, we list several of the most important opportunities.

First, the shortgrass steppe is broadly representative of a large proportion of Earth's semiarid ecosystems, including major parts of Asia and South America, such that our work here on the controls over ecosystem structure and function may be reasonably extrapolated to a significant fraction of semiarid steppes of the world. Recent studies
demonstrate that the factors that explain net primary productivity, soil organic matter, and plant functional type distributions in the Great Plains of the U.S. are similar in Argentina (Paruelo et al. 1998).

Second, the system is biologically unique among North American grasslands for its long evolutionary history of intense selection by both drought and herbivory, leading to an ecosystem that is very well adapted to withstand grazing by large generalist herbivores, including domestic livestock (Milchunas et al. 1988, and Mack and Thompson 1982). Much of the tolerance is conferred by the drought and grazing tolerance of the dominant native plant species, Bouteloua gracilis, which contributes 60-80% of the plant cover, biomass, and net primary productivity of shortgrass ecosystems, in addition to representing the key forage species for livestock. Recent work (Milchunas et al. 1992) has indicated that the removal of grazing by livestock results in increased cover by exotic plant species. This grazing tolerance and perhaps even dependence is not only biologically unique, it also confers some interesting opportunities for relationships with the "customers" of our science. Managers with either a livestock production goal or a conservation goal have great interest in utilizing our results for maintaining the sustainability of the shortgrass steppe.

Third, the shortgrass steppe is likely to be very sensitive to changes in precipitation, temperature, and CO₂ concentrations. Prior research on the CPER demonstrates that the system is primarily water limited; in the north, the system shares an ecotone with the northern mixed prairie which is dominated by a mixture of plants with the C₃ and C₄ photosynthetic pathways (Lauenroth and Milchunas, 1992). In the south, the shortgrass
steppe interfaces with the Chihuahuan desert. Thus, plant community dynamics and ecosystem function may be very sensitive to increases in CO₂, climatic variability, and directional global climate change. Because of its short stature, the system lends itself to study of the potential effects of direct and indirect consequences of increasing greenhouse gases. Such experiments are already underway, providing opportunities for scientists of many disciplines to study the results of these treatments.

Fourth, a keystone species of the shortgrass steppe, the black-tailed prairie dog, is locally extinct over a large portion of the shortgrass steppe, but persists in small remnant populations on the PNG. Estimates of the presettlement numbers of black-tailed prairie dogs in North American grasslands range from hundreds of millions to billions, and it is thought that up to 170 other vertebrate species are dependent in whole or in part on the activities of prairie dogs (Miller et al. 1994). The Forest Service is committed to maintaining some populations on the PNG, which provides excellent opportunities for interdisciplinary study of the biology of this important species, and its effects on ecosystem structure and functioning.

Fifth and not least, the CPER-PNG has been an important and very active location of ecological science, resulting in over 200 sets of ecological data that are freely accessible over the web at http://sgs.cnr.colostate.edu/sgshome.html and numerous publications in the peer reviewed literature (bibliography available at http://sgs.cnr.colostate.edu/sgshome.html).

2. Education and Outreach Opportunities

The goal of the education and outreach components of the Shortgrass Steppe Managed Ecosystem Research and Education Center is to provide educational opportunities in ecology for a broad range of students. Our traditional educational activities have focused on undergraduate and graduate students. We plan to continue to place a large emphasis on these two important groups in the future. The new activities we begin over the next several years will add K-12, specific interest groups and the general public to our
list of clientele. We are planning, in conjunction with an effort by the LTER network, to begin working with school districts and educational specialists to develop a program that will fit into and complement the current K-12 curricula of the school districts in our region. Our Forest Service partners are particularly interested in a visitor center as a way to communicate with the both special interests such as environmental and outdoor recreation groups (Sierra Club, Audubon etc.) and the general public. We envision both indoor and outdoor displays and nature trails for the proposed facility. The visitor center would also serve as a classroom for both traditional as well as non traditional educational activities.

3. Overview of the Planning Proposal

The planning steps that we propose are:

1. to organize workshops to incorporate the vision and needs of the national and international scientific community and of the educational community into a site master plan;
2. to identify the interests and specific roles of our partner institutions, the Forest Service and the Agricultural Research Service;
3. to support travel to successful FSML facilities;
4. to develop architectural and engineering feasibility analyses and detailed blueprints for the facility;
   and
5. to develop a master site plan for the Center

We describe the planning process in more detail in a later section of the proposal.

B. Site Description

From 1982 until 1996, most of the CSU and ARS research on shortgrass ecosystems has been located on the Central Plains Experimental Range. The CPER is a 6280-ha tract of shortgrass steppe located in the piedmont of north central Colorado approximately 61 km northeast of Fort Collins and the campus of Colorado State University (lat. 40x49'N; long.104x46'W; elevation 1650 m). The CPER is administered by the Agricultural Research Service. In 1996, we increased the spatial extent of our LTER site to include both the CPER and the Pawnee National Grasslands. The PNG represents 78,100 ha of public lands
administered by the Forest Service adjacent to the CPER, and extending 90 km to the east. The PNG is discontinuously distributed across northeastern CO because these lands are the result of acquisitions of private land beginning in the Dust Bowl era. Site expansion substantially increased the range of variability in shortgrass steppe ecosystems we can investigate.

1. Climate

The climate of the SGS is typical of mid-continental semiarid regions in the temperate zone except for the strong influence of the Rocky Mountains approximately 60 km to the west (Lauenroth and Burke 1995). Mean annual temperature is 8.6 degrees C and monthly temperatures range from -4 to 22 degrees C seasonally. The daily average max-min range of 17 degrees C. Mean annual is 322 mm (51 years) with a standard deviation of 98 mm and a ranged of 107-588 mm. Approximately 70% of the mean annual precipitation occurs during the April to September growing season. (For further information please see http://lternet.edu/im/climate/climdes/sgs/sgsclim.htm)

2. Vegetation

The vegetation of the SGS is dominated by shortgrasses, forbs, succulents, and dwarf-shrubs. The key species of these groups are Bouteloua gracilis and Buchloe dactyloides; Sphaeralcea coccinea; Opuntia polyacantha; and Chrysothamnus nauseosus, Gutierrezia sarothrae, and Eriogonum effusum, respectively. Average aboveground net primary production is 125 g/m² and ranges from 60 to 180 g/m² depending on
available soil water (Lauenroth and Sala 1992). Major differences in vegetation structure occur in saltgrass meadows dominated by Distichlis stricta and Sporobolus asper, and on floodplains where the shrub Atriplex canescens is an important component.

C. Description of the Existing Facility and Its Capabilities

The CSU Headquarters was built at the CPER in the late 1960's, when it was the core of the NSF-funded International Biological Program (IBP) Grassland Biome Project. Hundreds of scientists, graduate students, and research technicians were on-site each day, collecting data, processing samples in the laboratories, having meetings in the classroom, being served from the large kitchen at that time, doing heavy work in the workshop/garage, and staying in the dormitories. The site manager lived in the on-site house to manage the bison and pronghorn herds, and to manage the huge logistics of the research program. This intensive field program lasted until 1974; from 1974 until 1982 the site was used in a slightly less intensive fashion by the large number of ecological research projects that followed the IBP. In 1982, the Shortgrass Steppe Long Term Ecological Research Program was funded by NSF. Since then, the site has continually increased
in use, with 18 CSU projects currently studying the shortgrass steppe and using the CSU facilities at the CPER. The research conducted by the CSU faculty at the CPER is recognized worldwide as one of the most important sources of new ideas and important results in grassland ecology in the world. Our research has also had major implications for range management in the region (Lauenroth et al. 1994).

The CSU field station consists of the headquarters area located on a 1.6 ha plot, a residence for the site manager, and a corral and pasture area of 53 ha. Three buildings are located in the headquarters area: a dormitory, a storage/workshed building, and an office/laboratory building.

The main headquarters building (214 m²) has offices, laboratories, a dining/meeting room, and a kitchen. This multi-purpose building serves as the focal point for all activities at the site including conferences, meetings, and classes. The laboratory has workbenches, a digital balance, a ph meter, a conductivity meter, and two grieve drying ovens which enable an investigator to process field samples to a finished or nearly-finished state. This laboratory space is used by researchers for weighing and sorting soil and vegetation
samples, national atmospheric deposition program sample processing, and preparing mammal traps. Adjacent to the headquarters is a storage/sample processing building (134 m²) with facilities for washing, drying, and storing samples. This building also serves as the workshop/garage for field station heavy equipment. The dormitory has six rooms; five capable of double occupancy and one with four beds.

The site manager’s home is located directly across from the headquarters. This 102m² serves as the year round residence for the manager and his family. The corral facilities adjacent to the house are constructed of heavy timber and are capable of holding up to 40 head of livestock. They consist of four pens (10.4 m x 14.6 m), a working chute and scales (1400 kg capacity), a head catch, and an adjustable loading ramp.

The CSU field station is very intensively used by the scientific community, and by graduate and undergraduate students. It hosts numerous visiting scientists each year, who may stay in residence for days up to months. These visitors commonly utilize the facilities for laboratory space, computer connectivity to their home institutions, sample processing and laboratory space, and access to site data, collections and the herbarium. Nonetheless, the current facility is severely lacking in capabilities to support many of these and other activities.

During the past several years, we have begun to realize that our current facilities may not be adequate to maintain the high quality of grassland research that has traditionally occurred at the CPER. The key limitations to supporting and attracting both local and visiting scientists, and to educational activities at this time are: 1) very limited space for sample processing and analysis, shop activities, and animal care; 2) limited room for reference collections and archived samples; 3) poor computer connections and
equipment; 4) inconvenient and poorly equipped dorms/kitchen; 5) limited space for conferences/meetings/ classrooms; 6) limited space for displays; 7) limited space and opportunities for outside demonstrations and nature trails; 8) general disrepair; 9) no vehicles for site travel; and 10) a site manager's house which is in very poor repair.

At this stage, it is unclear whether the best strategy is to develop our new facility at the current site, or to relocate and begin anew. This issue will be resolved during the planning process and workshops that we propose.

D. Planning Steps for the Shortgrass Steppe Managed Ecosystem Research and Education Center

Our overall goal for the planning project is to produce a master site plan. Many steps will be required to complete such a detailed plan, and we describe these below.

1. Refinement of the Vision

We propose to organize two workshops to incorporate input from the regional, national and international scientific community and from the educational community into a site master plan. These workshops represent the key budgetary request to NSF.

The first workshop will be held for the scientific community. We will invite approximately 50 members of the scientific community from two groups: those who already have an investment in the shortgrass steppe and a representation of those who might be future users.

The second workshop will focus on gathering input from the educational community. We will invite 20 representatives from the surrounding K-12 school districts, the local colleges and Universities as well as local and national educational specialists.

If it is possible, we will schedule the two workshops simultaneously, so that there can be interactions between the two, with respect to our scientific and education missions. Both workshops will culminate in a written set of recommendations.

The specific issues to be resolved at these workshops include the following:

• vision and goals for the facility
• physical needs to meet those goals
• agency roles
• funding sources
• recommendations for specific location

Candidates for the scientific workshop, not including current local CSU and ARS researchers, are: Edie Allen, University of California, Riverside, CA; Joy Bergelson, University of Chicago, Chicago, IL; David Briske, Texas A & M University, College Station, TX; Tom Crist, Miami University, Oxford, OH; Kay Gross, Kellogg Biological Station, MI; Kris Havstad, Research Leader, Agricultural Research Service, Las
Cruces, NM; Elizabeth Holland, National Center for Atmospheric Research, Boulder, CO; Dennis Knight, University of Wyoming, Laramie, WY; Jeff Loech, District Ranger, Pawnee National Grasslands, Greeley, CO; Imanuel Noy-Meir, Hebrew University, Jerusalem, Israel; John Moore, University of Northern Colorado, Greeley, CO; Bob Parmenter, University of New Mexico, NM; Osvaldo Sala, University of Buenos Aires,
Buenos Aires, Argentina; William Schlesinger, Duke University, NC; Jerry Schuman, Research Leader, Agricultural Research Service, Cheyenne, WY; Russell Monson, University of Colorado, Boulder, CO; Daniel Uresk, Forest Service Research, Rapid City, SD. The remaining invitees will be selected from local CSU and agency researchers currently working on the shortgrass steppe.

We do not currently have a list of invitees for the educational workshop but they will be selected from the local school districts, members of education and outreach committees for environmental groups and education specialists from Colorado State University and the University of Northern Colorado. In addition, we will invite persons with experience conducting education and outreach programs under similar circumstances such as Alan Berkowitz from the Institute of Ecosystem Studies and Diane Ebert-May from Northern Arizona University.

2. Travel to FSML's

We propose to visit 4 successful FSML's as part of our planning process. The goal is to visit sites that vary in their size, complexity, distance from home University, breadth of mission, and interagency relationships. At each of the sites, we will collect information on facility planning and implementation. Some of the specific items that we will address at each site include: 1)How did the FSML planning process project space needs, and how satisfied with them is the group now? 2)What computer facilities and internet connections were originally planned, how many purchased, and what is the actual intensity of use of the equipment? 3)How is space arranged for maximum usage and overlap among needs?
4)If sample reference collections and/or archives were built as part of the FSML, how are they arranged for maximum usefulness and minimum space requirements? How much space has been set aside for future collections and why? 5)How is kitchen space arranged for overnight and longer visitors, including both group/conference affairs and individual visitors, and how efficient is the arrangement? 6)What kinds of strategies were used to phase in the construction, given the maximum field station project budget? 7)What kinds of inter-relationships were forged with other institutions or agencies? What is the land ownership? 8)What kinds of agreements were made with the University regarding project
overhead for research projects using the site, site fees for researchers, site maintenance and security, and availability as a conference center? 9)Are there things that the FSML wishes it had planned for or done differently?

We (one PI for each trip) plan to visit 4 well-established biological field stations, one of which will be local and will not require travel support (Mountain Research Station, Niwot Ridge LTER, University of Colorado). We have already visited several research stations and have been speaking extensively with FSML managers across the country.

3. Interagency relationships

A major part of the vision for the Shortgrass Steppe Managed Ecosystem Research and Education Center is a strong interagency partnership; we are convinced that such interagency relationships will significantly enhance the scientific, education, and outreach missions of the Center. We have initiated several tiers of meetings with the Forest Service and the ARS, both of whom have shown strong interest in the facility. For instance, our current vision includes a partnership with the Forest Service Pawnee National Grasslands in which the FS would have space for a Visitor's Center for the PNG, a much-needed facility for the avid bird-watchers and other recreationists, and potentially house a
wildlife biologist and part time receptionist on the site. This partnership could provide terrific visibility for the research projects and scientists, and opportunities to connect to the public in ways that our research presently does not. We will seek other appropriate partners during the next year (e.g. NRCS, the Nature Conservancy, and local grazing associations). We plan to continue to interact closely with the ARS, FS, and other potential partners during the planning process, through workgroups and personal interactions, to develop the best possible facility.

4. Architectural and Engineering Planning

Feasibility studies and design planning will be an important stage in our planning project. We will work with engineers and architects with the ideas that arise from the workshops and interagency working groups, and assure that such professionals are part of the actual planning process to some extent (a lesson we learned from phone conversations with a current FSML director). We will need landscape architectural design planning, engineering and site analysis planning (features such as waste disposal for a wet chemistry lab will need special attention), and architectural designs for the actual buildings. Matching funds in the amount of $10,000 from Colorado State University will be used to fund these architectural planning efforts.

5. Outcome of Planning Proposed Planning Project

The ultimate product of our planning project will be a 25-year master site plan. The plan will consist of an extensive long-term research and education plan for the facility, a governance structure for the facility (e.g. Advisory Board, director positions, etc), a detailed description of the physical structure that will allow the facility to accomplish its research and educational objectives, detailed institutional/interagency relationships, roles and responsibilities, a long term maintenance plan for the site, the specific site location, and detailed architectural and engineering plans for the facility. We plan to submit this master plan to NSF as part of a construction grant in 1999.

III. Utilization of Facility for Research and Education

A. Research Utilization

There are currently 18 CSU projects utilizing the site (Table 1) with 2 submitted proposals focusing entirely on the CPER site (Table 2). The LTER project is only one of the currently funded projects, but it represents the core. The scientists of the SGS-LTER are currently conducting 46 long-term experiments, numerous short-term experiments and several simulation modeling projects (please visit our website for more information on these experiments - (Table 1.1). To a large extent, the other grants are only made possible because of the presence of the LTER project: the proposals justify the research to the agencies on the basis of the LTER experiments and long term datasets we maintain, the project reputation for high productivity, and the presence and security of an operating field headquarters. Because the LTER is the most consistent user of the site, we have assumed responsibility for managing the headquarters and building there.

Projects that utilize the site headquarters do so for many reasons. Many use the conference room facility as a place to work indoors between sampling times, and as a good field meeting room for interagency meetings. There is significant use of the laboratory, for sorting and weighing samples, and at times there has been considerable chemical work done there. The electricity is used by a number of projects to maintain data loggers and other experimental manipulations (timers, instruments, automatic shelters, and weather
stations). Water use at the site ranges from bathroom use to irrigation experiments and laboratory work such as washing plant material. The dormitories are used by intensive field crews, graduate students, Research Experience for Undergraduate participants, postdocs, and visiting scientists who are either visiting the field station or working long days or early mornings/nights. The garage is very heavily used for storing field equipment and archiving samples. The site manager’s house is of course used by the site manager
and his presence is important to all of the projects using the CPER in securing their experiments and helping with site logistics. At noon during the weekdays in summer, you are likely to see as many as 30 people at the site headquarters, representing numerous projects.

Table 1 shows only the CSU projects that utilize the site itself, and not those that utilize primarily the data and models generated by the LTER project, since the issue at hand is the field facility. At least 10 scientists at CSU have very large modeling and spatial analysis programs that utilize our data and models, and that are funded in large part because of their relationship with our LTER. Distinguished visiting scientists from the U.S. National Academy of Science, the French National Academy, the Mongolian National Academy, the Chinese National Academy, the Indian National Academy, and a delegation of
Argentinean scientists have visited the site in recent years. Visiting scientists conduct research at the site and live in our dormitories, including faculty from Duke University, University of Chicago, the University of California, the University of Michigan, Miami University, the University of Buenos Aires, the University of Toronto, the University of Nebraska – Lincoln, the University of Texas - Austin, the University of Dayton, the University of Budapest and many others. Most important of all, from our perspective, is that the collective effort to study shortgrass steppe systems is a world-recognized program because of the scientific quality, diversity, and productivity of our program.

Table 1. CSU projects utilizing the CSU Headquarters at the CPER during 1996 and 1997:
 

Table 2. Submitted Proposals Focusing on the Shortgrass Steppe LTER site
 

B. Educational Utilization

The site has long been used as an educational resource. Each year ten to fifteen classes in Range, Biology, Environmental Science, Soils, and Geomorphology representing three colleges use the site several times each year for instruction. In addition, classes from the University of Wyoming regularly visit the site. The federal government currently supports eight graduate and undergraduate research fellowships for work at the site.

Table 3. Current Grants Focusing on Research Education for Undergraduates and Graduates
 

C. Other Utilization

Professional groups have large field trips to the site, including just in the last several years the Ecological Society of America, the Soil Science Society of America, and the International Landscape Ecology Society. Other public groups visit the site frequently, including the Nature Conservancy, Sierra Club, and the Crow Valley Grazing Association. The Audubon Society has a special interest in the site, since it is part of the limited habitat of two rare birds. The Audubon Society runs public participation field trips and a Christmas bird count at the site, and all of their birding guides list the CPER as a major
birding site; many individual birders visit the site each week. Finally, we have initiated a new major research program into the biology of prairie dogs, which have been nearly exterminated from grasslands but are known to be key species. We hope that the site will become a focal area for the public interested in grasslands in general and in some of the particularly important species.

Because of the longstanding contribution of our research to the discipline and to natural resource management in the region, our work has had significant media attention in recent years. Both the New York Times and the Washington Post covered one of several key papers in 1991. We have been featured in the Coloradoan four times in the last several years, and a series of articles in the Denver Rocky Mountain News in winter 1995 featured our combined research and educational program as a highlight at CSU. More recently, in January 1998, the Denver Rocky Mountain News featured an article describing the
research we have completed on the impacts of grazing. This article was released to the Associated Press and distributed nationally. At the same time, Denver TV station 9NEWS covered the grazing story, with a resulting piece on the 5:00 news. There is recent interest in featuring the site in an article in Nature Conservancy magazine, and in a video being developed by the Denver Museum of Natural History on "The Disappearing Shortgrass Steppe."

IV. Significant Research Accomplishments 1993-1998

A. Introduction

The SGS LTER project focuses on the processes that account for the origin and maintenance of structure and function in shortgrass steppe (SGS) ecosystems. The key questions that continue to organize and guide our research are:

1. How are the distribution and abundance of biotic components of the SGS maintained through time and over space?

2. To what factors are the distribution and abundance of biotic components vulnerable?

3. How do changes brought about by these factors influence biological interactions and ecosystem structure and function?

We have made significant progress toward answering these questions through research efforts that include long­ and short­term experiments, monitoring, survey, simulation analyses, and spatial analyses.

In the past five years we have produced 135 papers in refereed journals, 38 book chapters, 16 dissertations and theses, and 81 abstracts from national and international meetings. We supported a large number of graduate (36) and undergraduate (~160) students and post doctoral fellows (5). Scientists at our site are involved in a number of LTER network activities, through comparative modeling studies, international collaborations, and development of new cross-site experiments. This section is organized by a modified
version of the LTER core areas. Because of space constraints, comprehensive and more detailed results from our experiments and monitoring can be found on our World Wide Web site (http://sgs.cnr.colostate.edu/sgshome.html).

B. Populations and Processes

Bouteloua gracilis (blue grama) is the most drought and grazing tolerant grass species and it is also the dominant plant species of the shortgrass steppe (SGS) (Milchunas et al. 1990, Lauenroth and Milchunas 1992). Similar to many other dominant perennial grasses in North American grasslands, blue grama recruits infrequently (Lauenroth et al. 1994) and has a long lifespan (Coffin and Lauenroth 1989, Lauenroth et al. 1996). Key processes for recruitment are seed production (Coffin and Lauenroth 1992), dispersal, establishment (Lauenroth et al. 1994), and competition from established individuals (Aguilera and Lauenroth 1993, 1995). Loss of this species results in more diverse but unstable systems.

Our research on consumer populations ranges from swift foxes to nematodes. Fifty-four of 68 captured swift foxes, a Category II species, have been radio-collared and ear tagged. Comparison with data from the late 1970's suggests a population increase over the past 20 years and that the (CPER) has a higher density of foxes than the surrounding area (Fitzgerald, in prep). Coyote predation is the most important source of fox mortality.

Diets of great horned owls are composed mostly of lagomorphs, although most individual prey items taken are rodents (Zimmerman et. al., submitted). Thirteen-lined ground squirrels and other rodents are most abundant in shrublands in association with high orthopteran density (Higgens and Stapp 1995). The spatial distributions of shrubs and orthopterans concomitantly increase along a soil texture gradient from grassland (sandy loam) to shrubland (loamy sand) (Stapp 1995a, Stapp 1995b, Stapp 1994, Stapp et al. 1994, Stapp and Van Horne 1995). The shrubby, sandy lowlands in SGS appear very important to landscape-level biodiversity, even though the area of this habitat is small. Preliminary work on landscape-level plant diversity suggests a conceptually similar relationship; most of the diversity is concentrated in habitat types that make up a small proportion of the total landscape (Kotanen, submitted).

Nematodes at the CPER occur within 6 orders, 23 families and 40 genera and fall into five trophic groups (i.e. bacterial feeders, fungivores, omnivores, predators, and plant parasites) (Wall et al. in press). Populations are approximately twice as large in soil under individuals of blue grama than in the interspaces between individuals and appear to be unaffected by grazing.

Our work on patterns in detrital food webs supports the "dynamics hypothesis" that food chain length is a function of the limitations that increased length places on the likelihood of the system recovering from a minor disturbance (Moore et al. 1993a, b, Moore and De Ruiter 1993, Moore et al. accepted, De Ruiter et al. submitted). A second important result is that the feasibility of food chains (ability to maintain positive population densities at steady state) is a function of productivity and detritus inputs. Higher levels of productivity sustain longer food chains. The conclusion of this work is that the energetic organization of communities forms the basis of ecosystem stability.

C. Biogeochemical Dynamics

In addition to long-term monitoring of net primary production, we have been very active in issues concerning patterns and controls on primary production, as well as in assessing methodological problems, developing new techniques, and spanning spatial scale issues (Biondini et al. 1991, Milchunas and Lauenroth 1992, Lauenroth and Sala 1992, Todd et. al 1993, McNaughton et al. 1996). Early modeling and analytical work showed that traditional means of estimating NPP could lead to serious errors (Singh et al. 1984, Lauenroth et al. 1986, Sala et al. 1988). A long-term 14C experiment substantiated these
findings, and provided realistic estimates of NPP and an alternative to error-prone methods (Milchunas and Lauenroth 1992).

Spatial patterns of aboveground net primary production (ANPP) at the CPER are controlled by location on catenas at a toposequence scale, and soil texture at the larger landscape scale (Liang et al. 1988). Soil texture is also an important control on plant functional types with different rooting distributions (Milchunas et al. 1992, Lee and Lauenroth 1994). Analyses of temporal patterns of ANPP showed a positive relationship
with precipitation, but that ANPP was more variable than precipitation (Lauenroth and Sala 1992). An important result from comparing these data to a regional data set was that spatial and temporal relationships between ANPP and precipitation are not interchangeable. Grazing has negative but small effects on ANPP and variability in cool-season precipitation has a large effect on ANPP (Milchunas et al. 1994).

The SGS is characterized by patchy plant cover and associated spatial heterogeneity of soil resources (Hook et al. 1991). Heterogeneity in soil organic matter (SOM) at this scale is as strong as that induced by topography, and is tightly associated with root biomass (Hook et al. 1994, Kelly et al. 1996). Enrichment of C and N under plants is associated with perennial bunchgrasses (Vinton and Burke 1995), and develops at a rate that corresponds with plant community successional dynamics (Burke et al. 1995). Death in individual
bunchgrasses results in rapid depletion (3 years) of the enriched zone with respect to mineralizable N and labile SOM pools, but heterogeneity of total C and N persists for decades (Kelly and Burke, 1997).

SOM and nutrient availability are also strongly influenced by both soil texture and topographic position (Hook and Burke, 1996). In two long-term 15N studies (Delgado et al. 1995 and Hook et al. in prep), we have found that toeslope areas tend to retain up to 90% of 15N added 10 years ago, while summits and midslopes retain half or less. Grazed pastures retain less 15N than ungrazed pastures.

Our trace gas flux studies (Mosier et al. 1991, 1993, 1994a,b, 1995, Bronson and Mosier 1994, Parton et al. 1994, Scholes et al. 1994) are confirming that aerobic SGS soils are important sinks for atmospheric CH⁴, and that gaseous N losses may be important to long-term N balance and productivity. Calculations using IPCC global warming potential indicate that the SGS has a net global warming capacity of -1100 (sink for greenhouse gases), and N gas loss rates are similar to atmospheric inputs. Fertilization has a large
effect on N2O emissions and CH4 uptake.

D. Paleoecology/Paleopedology

In our investigation of paleosol geochemistry at the CPER, we proposed a Holocene paleoclimatic scenario (Kelly et al, 1993). A number of factors indicated that the early Holocene was cooler than either the mid-Holocene or current soil forming intervals, and that temperature has not increased from the mid-Holocene to the present (Blecker et al., 1997). The 13C/12C ratios of paleosol SOM, phytoliths and CaCO3 established the dominance of C3 vegetation in the soil forming interval spanning 10,000-8,000
y.b.p., and the dominance of C4 vegetation in both the 5,000-3,000 y.b.p. and contemporary soil forming intervals (Kelly et al, 1993). Organic C and phytolith data suggest that both the early- and mid-Holocene climatic conditions were more favorable for plant productivity than the present climate (Kelly et al. submitted). This suggests cooler, moister conditions than presently occur. Pedon development in both the early and mid Holocene paleosols suggests wetter soil moisture regimes than in the present (Blecker,
1993).

E. Water and Energy Dynamics

Soil water monitoring data emphasize the interannual and seasonal variability in soil water as well as the critical role that soil texture plays in mediating storage and losses (Singh et al. in prep). Soil water availability is critical in controlling recruitment of blue grama (and probably other species) by influencing seed production, germination and establishment (Lauenroth et al. 1994). Soil water availability is closely related to ANPP (Singh et al. in prep). Relationships between ANPP and precipitation assume that precipitation is a good surrogate for soil water. At large temporal (growing season or larger) and spatial scales (km² or larger), this is a good assumption.

Water losses (evaporation and transpiration) in the shortgrass steppe are largely controlled by water availability. Energy to evaporate water is almost always far in excess of the supply as indicated by the annual or seasonal ratio of precipitation to potential evapotranspiration (Parton et al. 1981). Sala et al (1992) found that the probability of a ratio of precipitation to potential evapotranspiration >1 was only 0.1 at the daily scale and decreased exponentially to 0.01 at the monthly scale. Quantifying bare soil evaporation and understanding how it is affected by soil texture are critical issues in understanding
water loss. Results from an experiment with mini-lysimeters confirm a 2-stage water loss pattern with a short period of high water loss followed by a long period in which losses decrease exponentially (Wythers et al. submitted). By contrast, the mini-lysimeter results contradict the idea that the depth to which evaporation can remove water from a soil decreases as coarseness of soil texture increases. We found the greatest depth of loss for a coarse sand.

Many of our questions about structure and function of SGS ecosystems require an understanding of long-term patterns of soil water dynamics. We used a simulation model to generate 30 years of soil water data for the CPER to provide this long-term view (Sala et al. 1992). Several key results were identified by this work. First, the general temporal pattern in soil water at the daily scale is not identical to the pattern in precipitation because of an interacting pattern of atmospheric demand. The peak in average soil water precedes the peak in average precipitation by almost a month. Second, the layer that most frequently had available water was very shallow (4-15 cm). Layers above this were drier because of bare soil evaporation and layers below because most precipitation events are too small to move water that deep in the soil. Third, on average water penetrated to 100 cm. In wet years, it reached 135 cm but in dry years, it only reached 45 cm. These data provide important information for understanding vegetation structure in the SGS.

F. Disturbances

Our work in this area is extensive. We divide this section into natural and human-induced disturbances. Currently landcover in the SGS is 60% cropland and 40% native grassland grazed by cattle (Burke et al. 1993).

Natural disturbances

The majority of natural disturbances are small (<100 m2) and there is an inverse relationship between size and frequency (Coffin and Lauenroth 1988). The most frequent disturbances (cattle fecal pats, harvester ant nest sites, root feeding invertebrates, and burrows from small animals) produce patches that range in size from 5-40 cm diameter (Hook et al. 1994) and are important in shaping plant community structure and diversity across the landscape (Coffin and Lauenroth 1990). An important focus of our natural disturbance work has been the effect of disturbances on individuals of blue grama and its subsequent recolonization of disturbed patches. Previous studies had reported that blue grama can not recover after disturbance. In a study designed to look at the effects of patch size and neighbors on blue grama seedling growth and survival, we found that in openings <30 cm diameter, established neighbors could preempt resources and inhibit seedling establishment (Aguilera and Lauenroth 1993). Openings >30 cm were large enough to result in seedling establishment. Hook et al. (1994) reached a similar conclusion about the size of a regeneration gap based upon how the root systems of neighbors explored patches created by disturbances. Simulation analyses and assessments of recovery on abandoned
fields (see below) confirm that blue grama does reestablish following a disturbance although in some situations the rate may be quite slow (Coffin and Lauenroth 1990, Coffin et al. 1996, Lauenroth et al. 1994). Recovery rates are dependent upon the characteristics of the disturbance, and in particular size and soil texture (Coffin and Lauenroth 1994, Coffin et al. 1993).

Human-induced disturbances

We are continuing our research on the recovery of plants and soils on abandoned agricultural fields along precipitation and temperature gradients in Pawnee National Grasslands and soil texture gradients at the CPER (Burke et al. 1995, Coffin et al. 1996). We found a large variability in recovery of the vegetation that could not be explained by climatic factors. Recovery may be related to soil texture, since the ability of blue grama to recover through seedling establishment is affected by silt content of the soil (Lauenroth et al. 1994). Net N mineralization and other indicators of active SOM were lowest on cultivated fields, but were not significantly different between abandoned and native fields, suggesting slow recovery rates. Higher N mineralization and turnover in cultivated fields may make them more susceptible to N losses (Ihori et al. 1995a), and recovery of N cycling in abandoned fields appears to involve a return to slower N turnover and tighter N cycling similar to native SGS. Although variation in native soil C and N correlated with climate and soil texture (Ihori et al. 1995b), soil losses due to cultivation were not explained by these variables.

We are also assessing the long-term recovery on nutrient-enrichment treatments (Lauenroth et al. 1978). Invasions by exotic species and the development of characteristics of highly disturbed plant communities did not occur until several years after treatments were terminated (Milchunas and Lauenroth 1995). The tendency of existing plant populations to continue to occupy a site when conditions become unfavorable, can create time-lags in response that represent important challenges for environmental monitoring. The existence of time-lags means that an ecosystem can pass through a threshold to an alternate state before it is detectable in species composition. These results have important implications for such things as global climate change and atmospheric nitrogen deposition, which also have the potential to act as enrichment stressors.

The SGS has a long evolutionary history of grazing by large herbivores. The importance of this force in shaping current-day structure and function of this system, and the importance of cattle grazing on both public and private land, have been reasons for the emphasis in research at this site in plant-animal interactions and long-term effects of grazing. Research in this area spans all five major areas. Long-term ungrazed SGS plant communities are more similar to disturbed than were long-term grazed communities
(Milchunas et al. 1990). Ungrazed compared to heavily grazed communities were found to be more susceptible to invasion by "weed" species (Milchunas et al. 1992). Current-year defoliation does have important effects on individual plants and on nutrient uptake by plants (Milchunas et al. 1995, Varnamkhasti et al. 1995). Increased forage quality in response to defoliation suggests a positive feedback between plants and grazers.

Although plant population changes with grazing are minor, other populations display a wide range of responses to grazing (Milchunas et al. in prep.). Groups such as aboveground arthropods, birds, and lagomorphs show large changes in abundance, dominance, or diversity in response to grazing, whereas groups such as microarthropods and nematodes show very little change. Endemic birds associated with SGS prefer to nest in heavily rather than lightly grazed treatments. Changes in biodiversity do not relate to changes in other structural or functional characteristics of the ecosystem.

In a grazing experiment initiated in 1991, we are examining long-term grazed and protected and newly ungrazed and protected SGS at 6 sites at the CPER. Key results to date focus on C and N dynamics (Burke et al, in press). Total soil C and N pools were unaffected by moderate grazing or exclosure following both 2 and 53 years of treatment. Pools representing recent belowground litter inputs and substrate available for decomposition (particulate SOM and microbial biomass) were also unaffected by grazing treatments. However, mineralizable C and N, representing the most active pools of SOM,
were significantly higher under long-term exclosure than long-term grazing, but only in bare soil areas between plants. Small decreases in mineralization may reflect slight erosion due to reduced canopy and litter cover, but the overall small effects of grazing may be due to increased plant basal cover that ameliorates thermal effects of reduced litter.

G. Synthesis

We have produced many synthesis products including cross-site studies and simulation modeling over the past 5 years. We describe our current activities in detail in on World Wide Web site
(SGS LTER Homepage).

V. Selected Bibliography

A. Ten Significant Research Publications 1992-1997

Burke, I.C., E.T. Elliot, and C.V. Cole. 1995. Influence of macroclimate, landscape position, and management on nutrient conservation and nutrient supply in agroecosystems. Ecological Applications. 5 (1): 124 - 131.

Burke, I.C., W.K. Lauenroth, and D.P. Coffin. 1995. Recovery of soil organic matter and N mineralization in semiarid grasslands: Implications for the Conservation Reserve Program. Ecological Applications. 5 (3) : 793 - 801.

Coffin, D.P., W.K. Lauenroth, and I.C. Burke. 1996. Recovery of vegetation in a semiarid grassland 53 years after disturbance. Ecological Applications. 6 (2): 538-555.

Lauenroth, W. K. and O. E. Sala. 1992. Long-term forage production of North American shortgrass steppe. Ecological Applications. 2 : 397 - 403.

Milchunas, D.G. and W.K. Lauenroth. 1992. Carbon dynamics and estimates of primary production by harvest, C14 dilution, and C14 turnover. Ecology. 73 (2) : 593 - 607.

Moore, J.C., P.C. de Ruiter, and H.W. Hunt. 1993. Influence of ecosystem productivity on the stability of real and model ecosystems. Science. 261 : 906 - 908.

Sala, O.E., W.K. Lauenroth, and W.J. Parton. 1992. Long-term soil water dynamics in the shortgrass steppe. Ecology. 73 (4) : 1175 - 1181.

Vinton, M.A and I.C. Burke,. 1995. Interactions between individual plant species and soil nutrient status in shortgrass steppe. Ecology. 76 : 1116 - 1133.

Wiens, J.A., T.O. Crist, K.A. With, and B.T. Milne. 1995. Fractal patterns of insect movement in microlandscape mosiacs. Ecology. 76 (2) : 663 - 666.

With, K.A. 1994. Ontogenetic shifts in how grasshoppers interact with landscape structure: an analysis of movement patterns. Functional Ecology. 8 : 477 - 485.

                  

 

11/22/02

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