- Agronomic: general hay and forage crops, grass (misc. perennial), hay
- Animal Production: feed/forage
- Education and Training: on-farm/ranch research
- Natural Resources/Environment: biodiversity, carbon sequestration
- Production Systems: agroecosystems, holistic management
The tallgrass prairie ecosystem is one of the most endangered ecosystems in North America. Interest in restoring prairie is growing because of the potential for increasing soil organic carbon (SOC) sequestration when degraded soils and ecosystems are restored. Also, finding long-term C storage in terrestrial ecosystems is being promoted as a key part to climate stabilization as greenhouse gases (GHG) continue to accumulate in the atmosphere. Re-introducing warm-season grasses (C4) to cool-season (C3) pastures has the potential not only to increase forage production, but also improve wildlife habitat, soil organic matter, and resilience to drought. While much is known about C4 prairie grasses and C3 pastures, there is a paucity of information about mixed C4-C3 grasslands in the upper Midwest.
We conducted an experiment in two restored prairies in southern Wisconsin to assess their carbon sequestration potential under a gradient of C4-C3 grass ratios. We identified areas of naturally occurring C4-C3 gradients in two restorations (10- and 17-year-old) that have been recolonized by C3 grasses and quantified above- and below-ground net primary productivity (ANPP and BNPP) and soil respiration (Rs) for two years. Across both sites and years, we found a weak but positive relationship between net ecosystem production (NEP) and C4 grass cover. However, this relationship was driven by the abundance of a particular species, Andropogon gerardii. Also, the relationships between the major components of the C cycle (ANPP, BNPP, and Rs) and C4 grass cover and A. gerardii cover were modified primarily by site, indicating that aboveground dynamics were driving C balance at the high-productivity site and belowground processes controlled the site with lower productivity. These results have important implications for land managers and policymakers seeking to promote C sequestration.
The tallgrass prairie, which is dominated by warm-season (C4 photosynthesis) grasses such as Andropogon gerardii Vitman (big bluestem), Panicum virgatum L. (switchgrass), and Sorghastrum nutans (L.) Nash (indiangrass) has been transformed mainly into grassland/agricultural mosaics if not totally converted to annual crops (Rhemtulla et al., 2007). Interest in restoring the native prairie has increased at the same time that the potential for increasing soil organic carbon (SOC) sequestration when degraded soils and ecosystems are restored have been touted (Lal, 2003). Finding long-term C storage in terrestrial ecosystems is being promoted as a key part to climate stabilization as greenhouse gases (GHG) continue to accumulate in the atmosphere (Bruce et al., 1999; Smith, 2004). Much emphasis has been placed on the adoption of best management practices and restoration to perennial vegetation in agricultural systems (Smith et al., 2008; Johnson et al., 2005) because soil carbon increases the most after a carbon enhancing land-management change is adopted (Smith, 2004; McLauchlan et al., 2006; Matamala et al., 2008). Indeed, studies have reported that the restoration of tallgrass prairie has the potential to accumulate soil organic carbon (SOC) on the order of 40 to 60 g C m-2 yr-1 (Baer et al., 1992; McLauchlan et al., 2006; Mahaney et al., 2008). A successful example of unification of food production and conservation is the conservation reserve program (CRP), whose primary goal is to protect erodible land with the establishment of perennial grasslands, but it also has been adopted because of the reported potential to increase SOC levels decreasing atmospheric CO2 (Gebhart et al., 1994; Reeder et al., 1998; Follett et al., 2001; Baer et al., 2002; Post et al., 2004).
Working grasslands, such as sown pastures, tend to be dominated by European species that are highly productive in the spring and fall since they are mostly cool-season (C3 photosynthesis) grasses (Paine et al., 1999). These pastures sustain the profitable dairy (Taylor and Foltz, 2006) and beef industry (CIAS, 2008) in Wisconsin.
Combining the challenges of food production and the need for environmental conservation on such working lands have the potential to positively impact a large part of the landscape since in the U.S. alone over 50% of US is cropped or grazed (Robertson and Swinton, 2005). The reintroduction of C4 prairie grasses into working lands offers a compromise between the complete restoration and the complete eradication of the native prairie (Woodis, 2008; Nelson and Burns, 2006) and simultaneously promotes the multifunctional use of the rural landscape (Buttel, 2003; Western, 2001; Hilderbrand et al., 2005).
While much is known about C4 prairies and C3 dominated pastures ecosystems, there is a lack of information about mixed C3-C4 grasslands in the upper Midwest. Adding functional diversity to the C3 dominated pastures have the potential to increase ecosystem properties through positive interaction among functional groups by complementarity and facilitation (Spehn et al., 2000; Hooper et al., 2005). For instance, using CENTURY model to evaluate how plant communities (100% C3, 100% C4, and 50% C3 50% C4 mix of grasses) could affect NPP revealed that plant production was lowest for C3 grasses and highest for the mixed C3-C4 community (Seastedt et al., 1994). However, most of the recent studies evaluating the effects of photosynthetic pathway on ecosystem services focus on the effects of totally converting agricultural lands to prairie or to CRP (Camill et al., 2004; McLauchlan et al., 2006). Only a few studies have recognized the need to understand how ecosystems are affected by the reintroduction of C4 native grasses into C3 grassland (sensu Hooper et al., 2005); but even then, the comparisons are made between C4 dominated and C3 dominated communities (Mahaney et al., 2008), not mixed C3-C4 grasslands per se. Little is known about how the C3 dominated grasslands may change as C4 prairie grasses are reintroduced to working lands—this information will assist land managers in decision-making on issues such as: How much prairie grass is needed to boost productivity? Is the ecosystem storing carbon? How does the seasonality of production change with various rations of C3 and C4 grasses?
To address the above mentioned questions, we compared how net ecosystem production (NEP) and the major components of this metric, net primary production (NPP) and soil respiration (Rs), were influenced by the relative abundance of C3 and C4 grasses in restored tallgrass prairie of southern Wisconsin over two years. We expected that NEP would increase as C4 grass abundance increased because C3 and C4 grasses differ in important functional traits such as quantity and quality of below- and above-ground biomass that can directly and indirectly alter soil processes (Dijkstar et al., 2006).
The project seeks to improve understanding of ecosystem support, provisioning, and regulating services provided by pasture ecosystems in the Upper Midwest. This work intend to provide much needed understanding about C3 pastures and the benefits of re-storing native grasses to working lands.
Products include peer-reviewed publications, an Agroecology MS thesis, and presentations at field-days, conferences, and to interested conservation-research groups.