• Atrazine, Spring Burning, and Nitrogen for Improvement of Tallgrass Prairie

      Gillen, R. L.; Rollins, D.; Stritzke, J. F. (Society for Range Management, 1987-09-01)
      Spring application of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] (1.1 kg ha-1 a.i.), burning, and nitrogen (33 kg ha-1 as ammonium nitrate) were evaluated alone and in all combinations for improvement of mid-seral tallgrass prairie in northcentral Oklahoma. Studies were initiated in 1984 (Study I) and 1985 (Study II). Precipitation and successional status of the vegetation at treatment application were higher for Study II than for Study I. Atrazine effectively reduced forbs and annual grasses for 2 years after application. Atrazine stimulated warm-season perennial grasses but did not generally increase total herbage production. Burning was similar to atrazine for annual grass control in both studies. Burning was also similar to atrazine for forb control in Study I but had no impact on forb production in Study II. Burning increased perennial grass production only in the second year of Study I. Burning decreased total herbage production in the first year of Study I by reducing annual grasses and forbs but did not affect total herbage production on other dates. Nitrogen did not consistently increase perennial grass production but did increase forb production by 250-300% when applied alone. Both atrazine and burning rapidly shifted species composition in favor of desirable perennial grasses. Nitrogen was not as effective in changing species composition either alone or in combination with atrazine and burning. The number and complexity of treatment responses declined as successional status and/or precipitation improved.
    • The Effect of Agriculture on Ferruginous and Swainson's Hawks

      Schmutz, J. K. (Society for Range Management, 1987-09-01)
      Raptors are an important component of prairie ecosystems. I examined the effects of grassland conversion to agricultural fields on densities of nesting prairie hawks. Densities of Swainson's hawks were recorded for comparison. The 2 species of congeneric hawks responded differently to habitat loss despite considerable overlap in their use of resources. As cultivation on study plots increased, ferruginous hawks declined. Swainson's hawks were more abundant in areas of moderate cultivation than in grassland or in areas of extensive cultivation. Differences in the hawks' responses were attributed to differences in their ecology, primarily prey utilization. There was no evidence that soil quality affected hawk abundance.