IMPACT OF CLIMATE AND MANAGEMENT ON SPECIES COMPOSITION OF SOUTHERN TALLGRASS PRAIRIE IN OKLAHOMA

Authors: Northup, Brian; Daniel, John

Submitted to: Proceedings of the National Conference on Grazing Lands
Publication Type: Proceedings
Publication Acceptance Date: 8/15/2000
Publication Date: 10/1/2000
Citation: Northup, B.K., Daniel, J.A. 2000. Impact of climate and management on species composition of southern tallgrass prairie in Oklahoma. Proceedings of the National Conference on Grazing Lands, December 5-8, 2000, Las Vegas, NV. pp. 693-700.

Interpretive Summary: Composition of plant communities is important to sustainable use of tallgrass prairie, and producers must understand how management and climate will impact its condition. This study defined how pasture management and rainfall caused changes in species composition of a southern tallgrass prairie during 1985-95. In each year, the contribution of six functional groups of plants to community composition were defined on 4.0 ac pastures under four different forms of management. A pasture unmanaged for 25 years was different from managed pastures by 1995, with weedy forbs (annual sunflower and thistles) becoming dominant, and key warm-season grasses declining. Both light and heavy grazing caused the composition of grazed pastures to change beginning in 1990, with reductions in key warm-season grasses (big bluestem, little bluestem, switchgrass, and indiangrass) and increases in annual bromes and weedy warm-season grasses (foxtails, crab- grass and dropseeds). Annual application of fertilizer and herbicide in combination with grazing caused weedy warm-season grasses to become more common, and the key warm-season grasses did not respond. Changes in species composition were associated with the combination of dry conditions at key times during 1988 and 1989, and applied management; composition had not returned to pre-study conditions by 1995. Management of southern tallgrass prairie should balance rainfall and production potential of the plant community, and be flexible in response to growing conditions.

Technical Abstract: Human and abiotic factors can affect composition of tallgrass prairie, which can impact sustainable use. This study described how paddock management & rainfall effected species composition of a southern tallgrass prairie during 1985-95. The contribution of functional groups of herbaceous plants to species composition were defined on 1.6 ha paddocks under different management regimes. Plant groups were: 1)dominant warm-season grasses (4 species); 2)shortgrasses (4 species);3)other warm-season grasses (11 species); 4)annual bromes (2 species); 5)other cool-season grasses (5 species); and 6)forbs (17 species). Management regimes were: unmanaged for 25 years; heavily grazed by cattle (215 animal unit days [AUD] grazing/ha/ year); lightly grazed (115 AUD/ha/year); lightly grazed with annual applications of broadleaf herbicide & N fertilizer. Percent composition was analyzed by principal components & correspondance analyses to examine changes in plant communities. Composition of the unmanaged area was different from grazed units by 1995; weedy forbs & annual bromes were dominant. Both grazing pressures caused changes in species composition beginning in 1990. The dominant warm-season grasses declined while annual bromes and weedy warm-season grasses increased. Fertilizer and herbicide applications caused increases by weedy warm-season grasses and annual bromes, while the dominant grasses did not respond. Changes in composition were partly related to dry conditions that occurred at key periods during 1988-1989, and interacted with applied management. Paddock compositions had not returned to pre-study conditions by 1995. Sustainable use of southern tallgrass prairie must balance rainfall and production potential of the plant community, and be flexible in response to growing conditions.