Prescribed fire, soil nitrogen dynamics, and plant responses in a semiarid grassland

Authors: Augustine, David; BREWER, PAUL - Colorado State University; Blumenthal, Dana; Derner, Justin; VON FISCHER, J - Colorado State University

Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2014
Publication Date: 2/27/2014
Citation: Augustine, D.J., Brewer, P., Blumenthal, D.M., Derner, J.D., Von Fischer, J. 2014. Prescribed fire, soil nitrogen dynamics, and plant responses in a semiarid grassland. Journal of Arid Environments. 104:59-66.

Interpretive Summary: Fire occurs in most grasslands worldwide, and prescribed fires can be an important tool for managing grassland ecosystems. Fires can potentially affect ecosystems by removing litter, and therby increasing the temperature of the exposed soil and increased evaporation from the soil. Fires can also directly kill plants or plant parts, which limits the amount of regrowth after a fire. One common effect of fire in drylands is an increase in soil nitrogen (N) availability, why this occurs is poorly understood. We studied annual and triennial prescribed fires conducted in early spring in terms of the effect on soil moisture, temperature, and nitrogen, plant growth, and plant nitrogen content in a semiarid grassland in eastern Colorado. Annual burning increased soil temperature, increased soil nitrogen availability throughout the growing season, and reduced the amount of nitrogen taken up by cool-season plants such as sedges and western wheatgrass. However, because fire did not affect growth and N uptake by warm-season grasses such as blue grama, the increase in soil nitrogen was modest and did not increase success of weedy species. Our results show that prescribed burns conducted in early spring can be used in the management of this grassland without risking the invasion of weedy species, but excessively frequent burning can reduce production of cool-season plants.

Technical Abstract: Fire is a key driver of the structure and function of grassland ecosystems. In arid and semiarid ecosystems, where moisture limits plant production more than light, fire can potentially affect ecosystem dynamics through changes in soil moisture, temperature, and nitrogen cycling, as well as through direct effects on plant meristem mortality. One frequent response of semiarid ecosystems to fire is an increase in soil inorganic nitrogen (N) availability, but the mechanisms leading to this response and the consequences for plants are poorly understood. We examined effects of annual and triennial prescribed fires conducted in early spring on soil moisture, temperature, and nitrogen, plant growth, and plant nitrogen content in semiarid shortgrass steppe. Annual burning increased soil inorganic N availability throughout the growing season, which was associated with increased soil temperature and reduced N uptake by C3 plants. However, because fire did not affect growth and N uptake by C4 perennials, the increase in inorganic N availability was modest and did not increase success of ruderal species. Negative fire effects on C3 plant production could be due to increased soil temperature, reduced soil moisture, or direct negative effects on C3 plant meristems, although fuel loads and maximum fire temperatures were low relative to other grassland ecosystems. In contrast to annual burning, triennial burning had little effect on N availability or C3 plant production. Our results show that prescribed burns conducted in early spring can be used in the management of this semiarid grassland without facilitating annual plant invasion, but excessively frequent burning can reduce production of C3 plants.