The Effects of Prairie Burns

The effects of annual spring burns are displayed below. Significant results are marked with (*) and are bolded.

Table provided by Professor Jonathan Brown (Grinnell College, Biology 252). 

As predicted, fire significantly decreased necromass (litter), which resulted in significantly increased soil temperature. Soil moisture was not significantly decreased; it had rained prior to our sampling, which made measurements of soil moisture unreliable. Diversity also increased in burned plots as expected.

There were several unexpected results. First, shoot density and above ground biomass were both significantly lower, not higher as hypothesized, on burned plots. We sampled plots very soon after the spring burn. There had not been enough time after disturbance for the colonizers shoots to begin to grow and any early shoots had been killed in the fire. On tall grass prairies, C4 grasses usually colonize burned plots because such grasses are better able to withstand the drier soil which results from burning. These C4 plants usually begin to grow in summer. These analyses should be repeated in a few weeks to determine if these unexpected results were simply temporal effects.

Soil organic matter was not significantly changed through fire. Therefore, changes in soil organic matter are not a major fire effect. Finally, below-ground biomass was not significantly changed by fire and did not increase in burned blots as hypothesized. As discussed earlier, new shoots had not begun to colonize the burned plots and add their below-ground biomass to the soil. Until the new shoots begin to grow and are impacted by the drier soil, below-ground biomass will not likely change on burned plots.

We are still waiting for the results of soil respiration.