Burning down the house: A pyromaniacs guide to PRS™-probe use in fire ecology research

Background/Question/Methods

Semi-arid ecosystems evolved with fire as a periodic disturbance, and prescribed burning is commonly used as a tool to manage these ecosystems. The method, timing, and frequency of burning needs to be considered when using fire in areas used for livestock production or where there is a likelihood of invasive plant establishment or soil degradation following a burn event. One important aspect to monitor is how fire management affects soil nutrients. We compared three separate studies that utilized Plant Root Simulator (PRS™)-probes to aid in monitoring soil nutrients immediately following burning to 3.5 years after burn treatments. One study focused on the effects of slash pile burning on soil macronutrients along transects from pile centers to unburned areas in forested upland and grass-dominated meadow in Little Valley, Nevada. A second study examined the effects of prescribed fire and grazing on herbaceous plant production in shortgrass steppe, and the third study addressed whether fire affects the invasibility of big sagebrush (Artemisia tridentata) steppe by cheatgrass (Bromus tectorum).

Results/Conclusions

Soil phosphorus was affected by slash pile burning, with P levels at pile centers being lower in the newly burned upland sites (p=0.019) and higher in the old burn upland and meadow sites (p=0.014 and p=0.001, respectively). Sulfur and magnesium were elevated across all sites following burning. Slash pile burning significantly increased soil NO₃^- in the meadow piles, but not the upland piles. These results were quite different from results obtained from conventional soil tests, but were similar to NO₃^- and NH₄⁺ results from ceramic cup lysimeters. In shortgrass steppe, burning did not immediately affect bioavailable soil N, but resulted in higher bioavailable soil N three months after burning (p=0.04). Bioavailable soil N in big sagebrush steppe was 1.6 fold greater in control treatments than burn treatments (p=0.01), 3.5 years after burning. These studies indicate that the effect of fire on soil nutrients depends on both fire intensity and time period since burning. These factors had implications for soil health, aboveground herbaceous production, and invasibility.