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Evidence for the sustainability movement can be found across the Midwest and Great Plains as widespread restoration initiatives have specifically targeted the rejuvenation of the tallgrass prairie. Much of this has evolved rapidly since the mid 1980s with the initiation of the federal Conservation Reserve Program (CRP). Since 1986, 14 million hectares of degraded agricultural land have been taken out of row crops and rehabilitated to native vegetation. Today, the fundamental benefits of such a program are reduced soil erosion and runoff from farms, enhanced aboveground biodiversity, improved water quality, and the potential for carbon sequestration. Concurrently, other non-governmental organizations and concerned citizens contribute to many hectares of prairie restoration each year for similar benefits, but in many cases landowners simply desire an aesthetically pleasing landscape. With so many resources contributing to the CRP and other prairie restoration projects across the cornbelt, an important question to ask is whether such restorations are meeting the ultimate goals of ecological restoration – are structure and function in these ecosystems mimicking undisturbed ecosystem counterparts? If we believe that these restoration activities are contributing to long-term sustainability, shouldn’t it be to our advantage for future planning to develop a means to verify that recovery is taking place or has resulted due to landuse change? It's been hypothesized that it may be easier to restore function rather than structure.
One model for assessing the success of such restoration goals is to compare species diversity and frequency in prairie remnants with prairie restorations. However, remnant prairies are not static entities and we do not have detailed catalogs of vegetation in remnant ecosystems from centuries ago when atmospheric conditions (e.g., CO2) were different than today. It is therefore difficult to make strong comparisons with restored counterparts. As Leach and Givnish (1996) discuss, prairies can lose up to 1.0% of species each year due to fire suppression and the fact that they are usually growing in small isolated patches (Allison, 2002). Moreover, extinction of species and changes in climate and atmospheric CO2 during the past few centuries can also make these comparisons difficult.
The few prairie restoration studies that do exist have generally failed to provide descriptions of soil conditions and response, which are highly influential to ecosystem structure and function, and obviously impact aboveground vegetation dynamics and succession of species. Studies of soil conditions in prairie restorations that do exist have been typically confined to soil quality indicators of recovery (Staben et al., 1997; Karlen et al., 1999; Baer et al., 2000), and lack quantification of aboveground productivity and phenology, fine root biomass, or temporal (e.g., seasonal, interannual) changes in soil and vegetation conditions. In general, soil organic matter (or soil carbon, C) is widely used as an indicator of soil recovery and paired sites or chronosequences consisting of restored prairies adjacent to cropping systems (e.g., business as usual) are used to quantify carbon accumulation (e.g., sequestration) due to land-use change (Knops and Tilman, 2000; Brye and Kucharik, 2003; Kucharik et al., 2003). Unfortunately, the young age of many of the prairie restorations that are part of the CRP make it difficult to assess whether changes have occurred (Brye et al., 2002; Kucharik et al., 2003), and the natural heterogeneity of soil conditions makes it necessary to study a large number of sites to make any defensible generalizations (Kucharik et al., 2003).
In response to the recent international focus on developing a better understanding of carbon and nitrogen cycling in both natural and managed ecosystems because of the importance to the global climate system, we suggest that studies of biogeochemical cycling within ecosystems that have been rehabilitated with varied ecological restoration methods would benefit multiple disciplines. In our research, we have targeted the University of Wisconsin-Madison Arboretum, site of the world’s oldest and arguably most meticulously restored tallgrass prairie. The site is unique because on the far eastern boundary lies a high-quality prairie remnant, estimated to be approximately 3000 years old. Concurrently, we are studying the impacts of a 15-year old prairie restoration as part of the CRP on an upland site near Blue Mounds, WI.
The overall objective of the current research is to better understand the impacts of longer-term prairie restorations on major components of the carbon cycle when compared to adjacent prairie remnants or agricultural land-use in southern Wisconsin. Specific goals were: 1) compare soil surface CO2 fluxes and estimate annual efflux, 2) quantify differences in plant phenology (e.g., leaf area index [LAI]), peak vegetation biomass and C and N content, and quantify aboveground net primary production (NPP), 2) assess differences in soil physical properties (e.g., soil pH, soil C and N, soil texture, surface bulk density, and soil temperature and moisture), 3) compare peak fine-root biomass, rooting depth profile information, and microbial communities, 4) correlate soil temperature and moisture to soil CO2 flux and microbial community structure.
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Curtis Prairie, the world’s oldest known prairie restoration (1941), after a 2002 controlled burn in April. The 28 hectare prairie is located within the UW-Madison Arboretum.
UW undergraduate Ryah Nabielski collects soil samples at Curtis Prairie in October, 2001 for future physical and chemical analysis.
A Campbell Scientific CR10X data logger collects hourly average soil temperature and moisture data in a prairie remnant in the UW Arboretum; this 1.2 hectare remnant is estimated to be 3000 years old.
SAGE student researchers collect soil samples at the UW Arboretum prairie remnant to assess soil carbon and nitrogen storage and bulk density.
Graduate student Kim Nicolas Cahill measures soil surface CO2 efflux on a Conservation Reserve Program (CRP) food plot in western Dane County, near Blue Mounds, WI.
Kim Nicolas Cahill samples aboveground vegetation to help quantify aboveground net primary productivity (ANPP) on a WI CRP land prairie restoration.
A CRP prairie restoration near Blue Mounds, WI outfitted with a Campbell Scientific CR10X data logger to monitor rapid changes in soil temperature and moisture. Note the abundance of goldenrod, an invasive species not originally planted as part of the prairie restoration.
A controlled burn taking place on CRP land and within a SAGE study plot in April 2003 near Blue Mounds, WI.
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This research was supported by the Barker Fund, a Holstrom Fellowship to Erica Grimm, SC Johnson, Inc. and Madison Gas & Electric.
Related Literature
Allison, S.K. 2002. When is a restoration successful? Results from a 45-year-old tallgrass prairie restoration. Ecological Restoration, 20:10-17.
Baer, S.G., C.W. Rice, and J.M. Blair. 2000. Assessment of soil quality in fields with short and long term enrollment in the CRP. J. Soil Water Cons., 55:142-146.
Brye, K.R., J.M. Norman, and S.T. Gower. 2002. Assessing the progress of a tallgrass prairie restoration in southern Wisconsin. Am. Midl. Nat., 148:218-235.
Brye, K.R., J.M. Norman, S.T. Gower, and L.G. Bundy. 2002. Carbon budgets for a prairie and agroecosystems: effects of land use and interannual variability. Ecol. Appl., 12:962-979.
Brye, K.R., and C.J. Kucharik (2003). Carbon sequestration in two prairie topochronosequences on contrasting soils in southern Wisconsin. American Midland Naturalist 149, 90-103.
Karlen, D.L., M.J. Rosek, J.C. Gardner, D.L. Allan, M.J. Alms, and et al. 1999. Conservation Reserve Program effects on soil quality indicators. J. Soil Water Cons., 54:439-444.
Knops, J.M.H., and D. Tilman. 2000. Dynamics of soil nitrogen and carbon accumulation for 61 years after agricultural abandonment. Ecology, 81:88-98.
Kucharik, C.J., K.R. Brye, J.M. Norman, J.A. Foley, S.T. Gower, and L.G. Bundy. 2001. Measurements and modeling of carbon and nitrogen cycling in agroecosystems of southern Wisconsin: Potential for SOC sequestration during the next 50 years. Ecosystems, 4:237-258.
Kucharik, C.J., J.A. Roth, and R.T. Nabielski (2003). Statistical assessment of a paired-site approach for verification of C and N sequestration on Wisconsin Conservation Reserve Program (CRP) land. Journal of Soil and Water Conservation, 58, 58-67.
Kucharik, C.J., and E.J. Grimm. Carbon budget differences between a prairie remnant and a 60-year old prairie restoration in southern Wisconsin. To be submitted to American Midland Naturalist.
Leach, M.K. and T.J. Givnish. 1996. Ecological determinants of species loss in remnant prairies. Science, 273: 1555-1558.
Staben, M.L., D.F. Bezdicek, J.L. Smith, and M.F. Fauci. 1997. Assessment of soil quality in Conservation Reserve Program and wheat fallow soils. Soil Science Society of America Journal, 61:124-130.
Soil surface CO2 fluxes measured at the UW Arboretum Curtis prairies during 2002.
Total root mass for July, 2002 as sampled at the UW Arboretum Curtis prairie.
Leaf area index measurements at the UW Arboretum remnant Curtis prairie and 60-year old prairie restoration (Curtis Prairie).
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