I did my best to remove studies that cannot be correlated to The Driftless Area; ecosystems such as chaparral or longleaf pine. Yet, much of our fire studies are from Kansas and the tallgrass prairie region. Fire effects, nutrient cycling, and soil processes in these areas of dominant-C4 grasslands are vastly different from a diverse prairie. I have noted when a study from this region was listed.

Miscellaneous Comments:

• As of 1997, few studies quantify soil N dynamics in annual, infrequent, and unburned prairies. (Blair 1997)
• C4 grasses reduce N “below the level at which many other prairie plants can survive.” (Collins and Steinauer, 1998:147) This is a vicious cycle when burning annually.
• Wells et al. 1979 – varies a lot – soil heating is dependent on SOM – how moist and how thick it is.
• Studies of fire frequency and N cycling come from plant responses to added N and not real life examples (Blair 1997)
• Fire both volatilizes nitrogen, which is lost from the site, and returns inorganic nitrogen and other nutrients to the soil in ash, thus altering soil resource supply (Chapin et al. 2002). [Note: whether ash recycles nutrients isn’t proven. Read the link for more info on that topic.]

• Aldous 1934 – No decrease in N after 6 years of annual fire
• Blair et al. 1998:243 – Empirical studies from LTER “have not detected any decrease in soil C and N pools in annually burned relative to unburned prairie.”
• Daubenmire 1968 – in the short term, the fire-caused N losses were thought to be offset by increased rates of soil N mineralization
• Dell et al. 2005 – The immobilization of N in the soil offset volatilized N
• Fonturbel et al. 2021 – prescribed burning effects are “generally minor” or have “limited effect” on soil properties; no clear relationship to prescribed fire, fire frequency, and changes in soil properties
• Hough 1981 – N does not decrease with repeated burns. Prescribed burning doesn’t deplete nutrient levels but changes nutrient cycling
• Knapp et al. 1998 – Fire may increase leaf N concentration for a short time but in general leaf N concentrations similar in burned and unburned sites
• Ojima et al. 1994
• Reich et al. 2001 – the uncoupling of C and N is not happening because chronic N deposition is not yet occurring in this region (Minn)
• Risser et al. 1981 – in 1934 “no reduction of nitrogen after six years of annual burning” was found but humus was reduced. This was in the Kansas Flint Hills
• Unknown 2024 – Soil N was unaffected
• Wells 1971 – Burns over a 20 year period resulted in no detectable N losses when summed through 4” of mineral soil
• Wells et al. 1979 – forest floor burned at 4-5 year intervals except for the first year
• Zhou et al. 2021 – Fire generally has neutral to negative impacts on soil N availablity on long-term scales

• Alcaniz et al. 2021 – soil nitrogen content in mineral soils after prescribed fires can increase
• Christensen 1976 – Nitrogen content has been improved after a fire. Additionally, a portion of the nitrogen not volatilized is available as ammonium N near the soil surface
• DeBano 1991 – Some nutrients are volatilized; most are made more available
• Dell et al. 2005 – increased mineralization offsetting any loss of N to fire
• Dijkstra and Adams 2015 – losses to combustion happens but soil N is “markedly increased after fire”; increased N by 32%
• Fenn et al. 1998 – Low to moderate fire enhances N retention in the long term
• Fonturbel et al. 2021 – If the soil temperature is lower than 200C, as is common in prescribed fires, the N may be unaffected or may even increase due to the deposition of N-rich materials from partial combustion of vegetation and incorporation of ash into the soil.
• Grogan et al. 2000 – Ammonium (NH4+) levels are markedly increased; ash enhancings soil N availability
• Kicker 2007 – burning increases inorganic N, alters SOM structure with likely long-term consequences for N availability and primary production
• Knicker and Skjemstad 2000 – burning increases N
• Perry et al. 2010 – disturbance increase available N by removing vegetation, which reduces uptake and alters N cycle
• Raison 1979 – Heating accelerated the accumulation of NH4- because of increased biological activity
• Scharenbroch et al. 2012 – Burned plots had higher NO_3-, total N, and potential N mineralization.
• Vlamis and Gowans 1961 – brush burning increased the supply of N in soils already deficient in N; more N is fixed by nonsymbiotic microrganisms following burning
• Wan et al. 2001 – Frequent burning can enhance soil N. Fire increase NH4+ and NO3-.
• Wells 1971 – Two annually burned plots shows N increases of 500-900lbs per acre during the 2^nd 10 years of the study
• Wells et al. 1979 – N content has improved

Each of these talks about this as a negative to annual net production or emphasizes that it reduces diversity or other negative effects on soil, organic matter, microbial biomass, and soil processes. Some mention N reductions due to the volatilized aboveground plant material but the ecosystem is more than plants. When fire frequency increases substantially, however, the loss of carbon and nitrogen from the system can reduce soil fertility and water retention. Looking at the whole system and what is happening belowground would provide more thorough information.

• Anderson 2006 – fire reduces N 2x what annual rainfall will replace
• Arenz and Joern 1996 – frequent fire decreases N via the detrimental effects of N-fixing microbes 
• Blair 1997 – plants show signs of limited N and lower N mineralization – testing is on tall C4 in Kansas
• Blair et al. 1998 — Long term, the annual losses of N from annual burns results in reduced storage of N in the soil and decreased productivity. Testing is on tall C4 grasses in Kansas
• Callaham et al. 2003 — grass roots are of lower nutritional quality because of reduced N from annual and frequent burning
• Collins 1992 – Annual fires are said to reduce nitrogen by removing the aboveground biomass
• Collins and Steinauer 1998 – Extractable soil N (NH4 and NO3-) is generally lower in annually burned vs. unburned. There is no info on intermediate burned ecosystems.
• Coolan et al. 2013 – Studies show annual burning decreases nitrogen via volatilization of the aboveground biomass
• DeBano et al. 1998 – not without its caveats of other negatives
• Fonturbel et al. 2021 – N losses can occur when the soil temperature during fire exceeds 200 ◦C
• Perry et al. 2010 – Fire may lower N if desired species generate plant-soil feedback that maintains low N availability in response to fire. These species are the tall C4 grasses.
• Risser and Patton 1982 – Soil organic N is reduced with annual burns but could take up to 10-30 years and are 50% lower than these simulated values
• Seastedt and Ramundo 1990 – volatilized N in fire is the major pathway of N loss
• Soong et al. 2014 – Annual fires are said to reduce nitrogen by removing the aboveground biomass. There is more to the ecosystem than just plants; what is happening to the N belowground?
• Staver 2017 – Reduces C and N, slowing plant growth. This article isn’t viewing this as a positive thing.
• Towne and Knapp 1996 – annually burned prairie has N-deficient soil.
• Wan et al. 2001 – N replenishment after fire is usually less than fire-induced N loss