C3/C4 production shift on seasonal burns: northern mixed prairie

  • Published source details Steuter A.A. (1987) C3/C4 production shift on seasonal burns: northern mixed prairie. Journal of Range Management, 40, 27-31.


Prairie grassland management may aim to enhance forage for grazing animals. One traditional method of attempting to achieve this is by prescribed burning. This study investigated the production of C3 (cool-season) and C4 (warm-season) herbage in response to burns in different seasons in two native northern Mixed Prairie communities on the Samuel H. Ordway, Jr. Memorial Prairie (3,076 ha), South Dakota (45º43’N, 99º06’W), central USA.

The study site comprised native grassland on a south-facing slope within a 97 ha pasture. This study evaluated fire effects on the xeric high (top of slope) and mesic low (bottom of slope) prairie communities.
A 0.4 ha area was divided into eight, 15 x 40 m units, each with a high and low prairie components. Units were randomly assigned a burn treatment: dormant spring burn (19 April 84), mid-summer burn (3 August), dormant autumn burn (17 Oct 1983), or an unburned control.
Vegetation was clipped in sample quadrats (0.10 m²) monthly from May to September 1984, and at peak cool season (7 June, based on green needlegrass Stipa viridula flowering) and warm season (31 July, based on big bluestem Andropogon gerardi flowering) standing crop (samples dried and weighed) in 1985. The relative contribution of C3 and C4 plants to live (green) material was determined through mass spectrometer analysis.

High prairie: The C3/C4 ratio during the cool-season growth period was generally unaffected by burning. During the second (drier than average) season following burns, there was no difference in the green C3/C4 percentages compared with controls.
The C3 green herbage component was highest during May and September and lowest during July and August for all treatments; the C3 fraction in all treatments remained above 50% throughout the growing season. In August, unburned plots had the highest C4 herbage in the green component (around 60%).
Low prairie - The C3/C4 ratio and herbage accumulation in low prairie was more responsive to burns than the high prairie community. Highest percentage of green C3 herbage on all treatments was recorded in May and September. The spring burn had the highest percentage of green C4 herbage (around 75%) throughout the warm-season growth period. Vegetation production (standing crop) was reduced on all plots during the second (dry) year.
Conclusions: All burn treatments increased the C3 herbage fraction relative to controls. Total production was unaffected by burns. High prairie communities appeared more resilient to fire or weather effects. Spring burning shifted low prairie towards C4 herbage (relative to other treatments) due to an increase in C4 herbage rather than to a decrease in C3 herbage.
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