Prairie Ecosystem Conservation Project: Restoring native prairie environment
... three of which are factors contributing to increased soil erosion (Bissonnais 1996, Unger 1996). To decrease soil erosion, surface coverage and top soil disturbances must be maintained. Many approaches are available including; conservation tillage techniques, mulches and cover crops. Of these, PECP will utilize cover crops. Cover crops. Cover crops are grown on cultivated fields during the wintering season (October through April) to offer dormant-season protection against soil erosion via wind and water run-off (Bissonnais 1996, Unger 1996). Run-off erosion can be reduced by decreasing the amount of run-off or by decreasing the velocity of run-off allowing time for sediments to settle from the water before they exit the field (Bissonnais 1996, Unger 1996). By providing increased surface roughness and root stem density, cover crops help to increase soil porosity, water infiltration rates and reduce run-off velocity. Additionally, decomposing cover crops increase soil organic carbon content, an important factor in water retaining capabilities of soil aggregates. As a result cover crops facilitate reductions in soil erosion and water conservation. Common cover crops include grasses, legumes and small grains (Mullen et al., 1998, Unger 1996). Particularly effective are legumes which efficiently promote nitrogen (N) and organic carbon (C) availability in soil. Mullen et al. (1998) studied the effects of no-cover crop; hairy vetch (legume) and winter wheat cover crops on soil organic C, N and microbial activity in corn fields. Following a 2-year period, greatest increases in soil C and N were obtained with the use of hairy vetch as a cover crop. Increased C content translated into generally higher numbers of heterotrophic bacteria (those that require an outer source of organic C) and microbial activity. Also, fresh corn-plant biomass was measured highest on plots that received hairy vetch as a cover crop. By contributing significant amounts of organic matter to the soil, legumes not only act to minimize soil erosion but also increase soil productivity both biologically and biochemically (Mullen et al. 1998). A mixture of legume seedlings will be introduced onto previously cultivated property as a measure to decrease soil erosion and increase soil organic matter and water conservation. Since they more effectively add organic matter to soil than other cover crops and presumably grasses native to southern Alberta, use of legumes will continue for 2 years to establish nutrient rich soil. These 2 years will be followed by subsequent reintroduction of native grass seedlings (such as rough fescue) to land where legumes communities were formerly established. In contrast to conventional cover crop-cultivation systems PECP will not rotate between legumes and seasonal crop growing. Instead legumes will be kept on plots year-round. By increasing surface coverage year-round and decreasing unnatural soil disturbances (cultivation and tilling), soil erosion due to human input will be kept minimal. Fire Prior to intensive settlement and cultivation the prairies were vast, open systems composed of relatively flat, continuous land and abundant with grasses which served as fuel for prairie fires. Such conditions permitted the ignition and spread of prairie fires (Vogl 1974, 1979). Through building of infrastructure, heavily grazed ranchlands, inhabitation and establishment of native grounds for agricultural purposes humans have been instrumental in reducing the frequency of naturally lit fires (Brockway et al. 2002, Vogl 1974). While roads and towns cannot be removed to promote ignition and spreading of fires, PECP involves the discontinuation of fire prevention and control programs currently in use. Moreover, as plant biodiversity increases fine fuel will become more available thus increasing probability of ignition. Not only will PECP implement steps necessary for returning fire back to its natural states, but will utilize fire for its effect on other ecological processes. Grasslands can be characterized by their rapid growth and slow decomposition rates (Vogl 1974, 1979). Fire not only rapidly releases valuable nutrients such as N, P and K into the soil for availability to emerging plants, but promotes the expansion of grass growth at the expense of woody non-native plants that are mainly fire intolerant (Vogl 1974, 1979). As mentioned in previous sections the initial stage in reclaiming a native ecosystem is concerned directly with rehabilitating soil quality to its pre-disturbed state. Currently, soil quality on the project site is being determined by intense observation and measurement. Plots to be burned will be chosen upon these measurements. During the first year of PECP prescription burning will occur at the end of wintering season when soil is sufficiently moist to protect seeds and rootstocks from intense heat and heat-induced mortality (Vogl 1974) on plots determined to have highly degraded soil qualities (such as low organic matter and acidic pH) as a mechanism to recycle nutrients immobilized in the legume cover crops. Subsequent controlled burns will be kept at a minimum. Grazing In contrast to the natural grazing of bison and other ungulates prior to modern settlement, which was variable in both intensity and frequency, grazing presently occurs with low variation and high frequency on pastures and range lands. The grazing of ungulates contributes to soil disruption and their effects on certain processes have been well documented (Bakker et al. 2003, Burkhardt and Tisdale 1976, Dormaar and Willms 1990). Due to foraging on heavily stocked pastures, fine fire fuel has been substantially reduced thereby decreasing probability of ignition and occurrence of prairie fires (Brockway et al. 2002). The study of Bakker and colleagues (2003) revealed increases in native plant species richness due to continuous grazing over a short period of time at moderate intensities. Within an 8-year period of continuous grazing on moderately productive land, plant species richness increased by 25%. Data from this study suggests that grazers effect species richness by establishing areas of variable light availability and promoting events of species extinction and colonization. Results from other studies (Burkhardt and Tisdale 1976, Dormaar and Willms 1990) further suggest that not only does plant species richness increase at moderate stocking intensities, but grazing also prevents invasion of non-native, weedy plants by promoting native plant growth. Once native grasses have begun to establish new communities, which is projected to be approximately 4 years from introduction or 6 years from the beginning of the project, ungulates native to Southern Alberta such as white-tailed deer, mule deer and pronghorn (Stelfox 1993) will be released onto previously established plots of varying size and will be allowed to graze continuously. As a consequence of varying plot size intensity of grazing will vary comparable to varying intensities of natural conditions. Using the Bakker study as a template (Bakker et al. 2003), we anticipate similar increases in species richness over an 8-year period. By managing stocking rates and length of duration of grazing PECP will employ the positive effects grazing has been shown to have on plant productivity. In addition, by returning...