Introduction
Cedar Creek Ecosystem Science Reserve is a 2,200-hectare experimental ecological reserve operated by the University of Minnesota in cooperation with the Minnesota Academy of Science. It is located in Anoka and Isanti Counties about 50 km north of Minneapolis and St. Paul, just east of Bethel, Minnesota (east of U.S. Highway 65).
Cedar Creek Natural History Area, established in 1942, was designated a National Natural Landmark by the National Park Service in 1975. In 1977, it was included as an Experimental Ecology Reserve in a proposed national network, and in 1982 it was one of 11 sites in the United States selected by the National Science Foundation for funding of Long Term Ecological Research.
The first 500 acres of Cedar Creek were acquired in the early 1940s with the understanding that they would be kept in their natural condition and used for scientific and educational purposes. Funds for acquisition of additional land, development of permanent buildings and preparation of accurate maps became available from a variety of sources including personal contributions, the National Science Foundation, the Max Fleischmann Foundation, the Minnesota Natural Resources Commission and the US Land and Water Conservation Program.
Cedar Creek lies at the boundary between prairie and forest. It is a mosaic of uplands dominated by oak savanna, prairie, hardwood forest, pine forests, and abandoned agricultural fields and of lowlands comprised of ash and cedar swamps, acid bogs, marshes, and sedge meadows. Large tracts of the pre-agricultural ecosystems of the region are preserved within its boundaries as is a successional chronosequence of more than 80 old fields of known history. A program of prescribed burns, begun in 1964 in a large tract of native oak savanna, has 12 blocks with fire frequencies ranging from one per year, to one per seven years, to unburned controls.
These have diverged dramatically in their vegetation and soils in response to fire frequency and some areas are now exhibiting characteristics not seen in this region since settlement in the 1800s. The soils of CedarCreek, derived from a glacial outwash sandplain, span five of the ten soil orders. Upland soils are nitrogen poor: numerous nutrient addition experiments performed in both old fields and native savanna have shown that nitrogen is the major soil resource that limits plant growth. Cedar Creek has a continental climate with cold winters, hot summers, and precipitation (66 cm/yr) spread fairly evenly throughout the year. The mean July temperature is 22.2°C while the mean January temperature is -10°C.
Long-term Ecological Research Projects (LTER)
The Cedar Creek LTER combines long-term experimentation and observation to examine the controls of successional dynamics and spatial patterning in ecosystems at the prairie-forest boundary. The LTER project has established more than 1100 permanent, long-term experimental plots as well as 2300 permanent observational plots distributed across a chronosequence of 22 old fields. Our studies focus on hypotheses concerning the direct, indirect and feedback effects of various species and ecosystem elements on each other. Although we study whole ecosystem processes, a major goal of our project is to understand the underlying mechanisms that control these processes. Work focuses on:
- mechanisms of plant competition for nutrients and light;
- dynamics of carbon and nitrogen in the soil;
- controls of the primary productivity, species competition and species diversity of grasslands;
- herbivory, including feedback effect of herbivores on soils and plants;
- disturbance; and
- modeling and ecological theory.
Our studies of the mechanisms of plant competition, done by David Tilman and David Wedin, use results from over 900 plots in a long-term experimental garden in which we are growing many major grassland species in monocultures and in various pairwise combinations. These plots were established on an experimental soil nitrogen gradient. We routinely monitor soil nitrate and ammonium concentrations, as well as plant biomass and allocation patterns, in these plots.
Our studies of soil carbon and nitrogen dynamics include work on litter decomposition, species-specific litter feedback effects, N mineralization, nitrification and leaching, N fixation, microbial and mycorrhizal biomass, and dissolved organic carbon dynamics.
Studies of primary productivity and the controls of plant community: This research includes nutrient addition experiments in uplands and wetlands, water table manipulations in wetlands, detailed studies of the nutrient and light dependence of growth of major plant species, studies of the role of soil heterogeneity and of plant colonization, growth and competition in patchy habitat.
Herbivory research, led by Mark Ritchie and David Tilman, includes long-term observations on the population dynamics of the major herbivores (small mammals, deer, and grasshoppers), selective removal of herbivore guilds, deer exclosure experiments, gopher exclosure experiments, comparisons of fenced and unfenced nitrogen gradients, studies of the impact of herbivores on carbon and nitrogen dynamics and cycling, and studies of replicated monoculture and competition plots in our experimental garden that either do or do not have one or more grasshopper species.
Our studies of disturbance consist of comparisons of disturbed and undisturbed plots that receive different rates of nitrogen addition, our 29-year running set of prescribed burns in oak savanna, a six-year running set of prescribed burns in an old field, manipulations of depth to water table (as a mimic of effects of climatic change), and observations on the pattern and frequency of disturbances in old fields, savanna, forest, and wetlands.
We are also working on analytical and simulation models of various ecosystem attributes. These models, which address processes occurring on a range of spatial and temporal scales, are being developed and tested under the direction of David Tilman and others.
Applications + significance
Results of Cedar Creek research are contributions to our fundamental knowledge of the workings of nature and are being utilized by many organizations, including the Minnesota Department of Natural Resources, the Environmental Protection Agency, and The Nature Conservancy. In addition, Cedar Creek Ecosystem Science Reserve serves as a research and teaching facility for six colleges from the University (Biological Sciences, Agriculture, Forestry, Liberal Arts, Institute of Technology, and Veterinary Medicine) and for other colleges and universities both within and outside Minnesota.
In this time of increasing concern for the global environment in which humans live, it is important to recognize the value of past and future contributions of research facilities such as the Cedar Creek Ecosystem Science Reserve. Applications of research findings from Cedar Creek play an important role in sound management of our forests, farmlands, prairies, lakes, marshes and other natural resources.
The Cedar Creek LTER group and other researchers at Cedar Creek invite and encourage interested scientists to work at Cedar Creek Ecosystem Science Reserve or to expand their research to include Cedar Creek as a site. We encourage undergraduate students to become involved in ecological research, and we provide housing for students interested in serving as Ecological Research Assistants.
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