University of Minnesota
University of Minnesota
College of Biological Sciences
http://www.cbs.umn.edu/
Photosynthesis measurements in BioCON experiment e141

Research at Cedar Creek

Research at Cedar Creek focuses on understanding the fundamental processes and principals that govern the dynamics and functioning of communities and ecosystems. We explore topics of fundamental scientific interest, as well as those relevant to current environmental change.

Our work synthesizes the sometimes disparate approaches of ecophysiology and population, community and ecosystem ecology, and exploits the interplay between experimental results, observational data, and theoretical prediction.

 

Investigations at Cedar Creek pursue six major themes of research:

1) What underlying mechanisms and feedback effects determine the impacts of human-driven changes -- especially loss of biodiversity, climatic variation, N deposition, land cover and use change, changes in fire frequency, elevated CO2, and exotic species -- on invasion dynamics, biotic interactions, and community and ecosystem functioning?

2) How do the traits and evolutionary heritages of species and environmental conditions combine to determine the pattern and dynamics of community assembly and the species composition, ecosystem dynamics, biogeochemistry, and biodiversity of sites ranging across scales from square meters to landscapes?

3) How do changes in one level of a trophic web influence other levels, and how do these changes, in turn, feedback on the initial level? For example, how does climate change influence plant species abundances, and how does this influence soil microorganisms, decomposition and nutrient cycling, soil pathogens, and thus plant dynamics?

4) What traits of established species, communities and ecosystems and what traits of novel species (be they native or exotic) determine the establishment and abundances of exotic species, and their impacts on resident species?

5) Do the same constraints and tradeoffs that explain multispecies coexistence also explain effects of diversity and composition on ecosystem processes, and vice versa?

6) What general principles determine the quality and quantity of the services produced by ecosystems, and how can these services be valued, including economically?

Cedar Creek researchers address these questions through interrelated sets of long-term experiments and observational studies, and shorter-term, mechanistic, process-oriented research.

  • Human-Caused Environmental Change: Some of the largest and best-known experiments at Cedar Creek focus on the long-term consequences of human-driven environmental changes. This research includes comprehensive examinations of the effects of nitrogen deposition, biodiversity loss, alterations of species composition, climatic warming, and elevated carbon dioxide on grassland and savanna ecosytems.
  • Succession, Invasion and Trophic Webs: Over the past decades, abandoned pastures and croplands at Cedar Creek have been allowed to revert into the natural prairie and forest. By studying changes in the plants, insects, mammals, and soils, researchers have learned more about the process called succession, how living species replace one another over time. Experiments have examined the rapidity of plant migration, soil development, the differences between natural and agricultural lands, and the impact of various natural enemies and herbivores on plant communities.
  • Fire Frequency: In the 1960s, Cedar Creek scientists started one of the earliest and longest-running experiments on fire and fire suppression in forest ecosystems. The results have illuminated the way forests and prairies develop and have clarified the global carbon cycle. Using three on-going long-term experiments and multi-scale analyses, the influence of disturbance and resource variation on grassland and woodland dynamics continues to be explored.
  • Biofuels: With the biofuels’ potentials coming into the public forefront, researchers at Cedar Creek began considering what their findings implied about the industry and its impacts on the ecosystem. Using data from biodiversity experiments, Cedar Creek researchers have published seminal work comparing low-input high-diversity prairie-grasses to conventional biofuel feedstocks. Based on this work, Cedar Creek researchers have initiated a series of applied experiments that test the feasibility of prairie biofuel harvesting, and explore the possibility of using these prairies to protect wildlife habitat.
  • Human Dimensions : The area surrounding Cedar Creek is one of the most rapidly developing parts of the country, with housing and traffic increasing each year. Before long, Cedar Creek will be a large natural oasis in the midst of suburbia. Surveys of both urban and peri-urban households and their surrounding biophysical environment will be used to assess how social and ecological patterns affect the flow of ‘elements’ through residential landscapes.
  • Syntheses and Cross-Site Studies: Experiments at Cedar Creek are complemented by cross-site studies and syntheses that extend beyond the geographical boundaries of CCESR. These include development of a global plant physiological database, GLOPNET, the Ecophylogenetics work group that is developing a database and software to investigate links between evolutionary history, plant traits, community structure and ecosystem processes, and NutNet, a cross-site project testing the influence of herbivory and fertilization over herbaceous plant diversity and productivity.

Cedar Creek Transformational Science Bullets
  • We have discovered that elevated CO2 levels do not have the hoped-for effect of greatly increasing plant growth and thus helping decrease atmospheric levels of CO2.

In particular, 11-years of exposure to elevated CO2 increased net photosynthesis of 13 grassland species by just 10%. Results of this study - the longest-term with the most species - suggest that carbon cycle models that assume strong and sustained stimulation of photosynthesis (e.g. >25%) by rising CO2 for all of Earth`s terrestrial ecosystems should be viewed with caution. Moreover, the study has shown that nitrogen limitation constrains ecosystem responses to elevated CO2.

  • Through three long-term experiments, we have discovered that the number of species in an ecosystem - its biodiversity - has surprisingly strong impacts on ecosystem functioning.

1. In particular, a 15-year grassland experiment showed that ecosystem stability is strongly dependent on biodiversity.

2. Higher plant biodiversity leads to greater ecosystem productivity. All experiments found much greater plant productivity when many plant species were grown together than when these same species were grown in monocultures.

3. Plant diversity also greatly influenced the ability of these grassland ecosystems to capture atmospheric carbon dioxide and sequester it as soil organic carbon. High-diversity led to the annual storage of about 2 tons of CO2 per hectare, whereas monocultures had no detectable carbon storage.

4. Low plant diversity constrained ecosystem responses to elevated CO2 and nitrogen deposition.

5. High plant diversity ecosystems also had more diverse insect communities that were dominated by predatory and parasitoid insects, whereas the insect communities of monocultures were dominated by herbivorous insects.

6. All of these results suggest that society will receive more services from ecosystems that are managed to retain their naturally high diversity to restore high biodiversity to disturbed ecosystems

  • A 25-year grassland experiment showed that chronic atmospheric deposition of nitrogen led to the loss of plant diversity. Plant species numbers were reduced more per unit of added nitrogen at lower N addition rates, suggesting that chronic but low-level nitrogen deposition may have a greater impact on diversity than previously thought. A second experiment showed that a decade after cessation of nitrogen addition, relative plant species number, although not species abundances, had recovered, demonstrating that some effects of nitrogen addition are reversible. A third decade-long experiment showed that reductions in plant species richness due to nitrogen deposition were half as large under elevated as ambient atmospheric CO2 concentrations. This unanticipated interaction suggests that future trends in global biodiversity may be surprising and non-intuitive.
  • Flows of carbon, nitrogen, and phosphorus through urban and exurban households are highly variable and often skewed, with a small number of households contributing disproportionately to the total fluxes of these environmental pollutants. This was particularly true for air and vehicle travel, fertilizer use, and home energy use.
  • Savannas, forests, and grasslands each make up roughly one-third of the world`s terrestrial vegetation, yet our understanding of savanna ecology lags far behind that of the other biomes. Through the world`s longest-term, large-scale experimental fire experiment in woodlands, running since 1965, we have identified the way in which fire molds vegetation, and in turn how altered vegetation influences resource availability, ecological succession, and carbon and nitrogen cycling, with impacts at local to global scales.
  • We have found that high-diversity mixtures of perennial prairie plants can be a highly productive biofuel crop that offers many environmental advantages over the use of food crops for biofuels.