Extension column: Landscape conversion to grasslands
July 29, 2013
An obvious trend, for anyone who's watching the landscape, is the westward progress of cultivation. Since 2007, more than 23 million acres of grassland have been converted to cropland. The majority of this conversion is taking place in the Northern Great Plains.
One of the most valuable products of the Missouri River basin (the primary drainage of the northern plains) is an abundant and safe water supply. Additionally, the grasslands of the Northern Plains provide a rich habitat for wildlife and fish. Half of the duck production in North America occurs in the grasslands of the northern prairie. Grasslands also store large quantities of carbon. Cultivation returns this sequestered carbon to the atmosphere. The processes of cultivation and development and resulting fragmentation make the Northern Great Plains native grasslands on of the most endangered ecosystems globally.
Even when cultivated land in the region is replanted to grass, there has been an historical tendency to employ exotic grasses, primarily as monocultures of very simple mixtures. This tendency toward uniformity, amplified by grazing patterns which attempt to achieve uniform utilization reduces the diversity that is typical of natural grassland ecosystems.
A recent article in Rangelands magazine [Vol. 35(3):16 – 20] reports on a successful effort to restore cropland to grassland in southeastern Alberta, at the northern extent of the mixed grass prairie. Recognizing the expense of native grass seed, investigators took advantage of an adjacent tract of native prairie to examine what species could be reasonably expected to occur on the site being re-established. Inventory and compromise with seed cost (needle and thread was very costly) led to a decision to plant a mixture of five species, all of which were abundant in the adjoining native grassland. Glyphosate was broadcast applied to the entire area in early May followed by broadcasting the seed mixture. A light harrow was used to improve seed soil contact. Two primary weeds, kochia and Russian thistle, were mowed and baled in August of the seeding year. Herbicide was applied the following spring to target the same weeds. Vegetative plugs of silver sagebrush were planted the second spring, in low lying areas, to add a shrub component.
Beneficial precipitation, especially during the second year, favored establishment of the stand. Range health surveys made during the third growing season approached 70 percent and litter accumulation was comparable to what was expected for well managed native grassland. Bird surveys made prior to, and following re-establishment revealed a change from a very simple population dominated by a single species to a much more diverse population which included two grassland obligate species which are approaching threatened status. During the same three-year period, species richness on the planted stand increased so that it was comparable to the native stand.
Several items in this report are noteworthy. The care taken in selection of the seeding mixture, referencing local vegetation community, resulted in successful re-establishment. Vegetation control of undesirable plants undoubtedly contributed to success. While the seed mixture was expensive, the planting method, using a broadcast seeder, was lower cost than some alternatives and establishment was successful.
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Improvement in wildlife habitat, as indicated by the increased diversity of birds present, is a useful indicator of increasing ecosystem function. For livestock production, the greatest benefit of such an effort is the restoration of diversity to the plant community. Diverse vegetation offers livestock the opportunity to select a more nutritious diet for a longer duration of the growing season, potentially enhancing livestock performance.
If you're wondering about the possibility of re-establishing some prairie, this example demonstrates that it can be done successfully in a reasonable amount of time.