Dicksissel

Driftless Prairies: Native Ecosystems

Frequent Fire Decreases Biodiversity

Frequent or annual fire will reduce the biodiversity of your ecosystems. It does this because of how fire and the tall C4 grasses (e.g. Indian grass, big bluestem, switchgrass) interact.

Throughout my reading, I’ve maintained of list of studies with this outcome. This is not intended to be an exhuastive list. I have not seen any studies using frequent or annual fire that these results didn’t apply. Most of the research on fire frequency was in the initial beginning of ecological research; it was also on tall C4-dominated ecosystems in a different region than the Driftless Area. These type of ecosystems need more frequent fire than if you’re wanting a high-diversity one. Before accepting an old-school management plan that encourages the heavy use fire or recommends it as the main tool, know the outcome will be reduced biodiversity.

Cutting edge conservation emphasizes the need for using combinations of management techniques. Not only is it more effective at battling the invasives, it maintains our biodiversity.

How Fire and Grass Interacts

A good prairie management system to increase diversity utilizes techniques that vary by intensity, season, and location.

Daryl Smith

  1. Abrams et al. 1986 — Annual burns increase C4 grass at the expense of forbs and woodies.
  2. Ansley et al. 2010 – Annual spring and biennial summer fires increased C4 grass cover but C4 tallgrasses Andropogon gerardii, Sorghastrum nutans and Panicum virgatum increased to a greater degree
  3. Arenz and Joern 1996 – Frequent fire decreases diversity
  4. Bazzaz 1996 – fires homogenize an initially heterogeneous habitat
  5. Becker 1989 – Spring-flowering forbs were nearly absent on annually burned sites
  6. Biondini et al. 1989 – Fire cause the community structure to change such that grasses dominate while forbs decrease
  7. Bowles and Jones 2013 – richness decreases with increasing fire frequency; frequent fire increase C4 grass dominance
  8. Briggs and Knapp 2001 — After 14 years of study, “it appears that reduced growth rates of forbs per se do not limit their success in annually burned prairie.” Forbs are 9% in annually burned areas and 29% in unburned.
  9. Callaham et al. 2003 — Annual prescribed burning decreases prairie plant diversity because it favors warm-season grasses. When these grasses become more abundant because of frequent burns, their roots are also more abundant and they are lower quality because the burning reduces soil nitrogen
  10. Carbone et al. 2024 – graminoids will increase with fire due to abiotic factors
  11. Collins 1992 – The decrease in heterogeneity with burning results from increased cover of C4 grasses
  12. Collins et al. 1998 – the abundance of forbs is “reduced strongly” by burning. (See biodiversity)
  13. Collins and Callabrese 2011 – Species diversity was maximized in sites that were infrequently burned and grazed by bison with the strongest response on infrequently burned slope sites, while diversity was lowest on frequently burned ungrazed sites and on frequently burned slope sites. . Forb richness was highest in infrequently burned and grazed sites.
  14. Collins and Steinauer 1998:141-2 – Annually burned sites are dominated by C4 grasses. Species richness can be maintained with annual burns only by using an additional disturbance technique, such as mowing, that would reduce the competitiveness of the C4 grasses. On annually burned sites, flora is a “nested subset” of what is found on less frequently burned areas.
  15. Collins and Steinauer, 1998:147 – C4 grasses reduce N “below the level at which many other prairie plants can survive.” This is a vicious cycle when burning annually.
  16. Collins et al. 1998:308 – Forbs are keystone species for biodiversity. On annually burned prairies, the proportion of forb ANPP to total ANPP is 1-8% on unburned it’s 63-70%
  17. Collins et al. 1995 – With increasing fire frequency, there was a “significant decline in species richness with no evidence of an optimum.” Average species richness was always lower on annually burned sites than on sites burned at 4 year intervals.
  18. Copeland et al. 2002 – Management practices, such as frequent fires, strongly favor dominant C4 grasses have negative effects on subdominants and undermine the long-term maintenance of prairie biodiversity.
  19. DeBano et al. 1998 – Long term fire free intervals can increased densities and reproduction of “climax” communities, resulting in increased diversity.
  20. Engle et al. 1998 – Because of their growth habit and competitive ability, tallgrass-
    es are more tolerant of fire than are little bluestem and other
    bunchgrasses
  21. Gibson 1988 – C4 grasses increased and diversity, richness of forbs decreased
  22. Gibson and Hulbert 1987 – Annually burned sites homogenize between topographical locations (uplands vs lowlands) when normally these host more diversity.
  23. Hartnett and Fay 1998:91 – Increasing fire frequency results in an abundance of dominant C4 grasses. There is more homogeneity in frequently burned prairies.
  24. He et al. 2019 – shortened fire intervals often lead to decreased species richness and
    diversity
  25. Henderson 1990 – species diversity declined over 7 years when burned 8 of the 10 years of the study
  26. Hill and Platt 1975 – After a fire, the community shifts to C4 dominated
  27. Hobbs and Huenneke 1992 – When additional nutrients are provided, such as happens after a burn, grasses respond to the detriment of forbs.
  28. Howe 1995 – In the presence of spring fire, C4 grass species outcompete most forbs and C3 grass competitors
  29. Hulbert 1986 – Annual burning resulted in uniform grass cover. Burning favors tall warm season grasses.
  30. Johnson and Matchett 2001 – C4 grasses increase their root growth 25% in annually burned prairies because plants compensated for N limitations by increasing root allocations.
  31. Kitchen et al. 2009 – increases the dominance of perennial C4 grasses
  32. Kline 1997 — repeated spring burns favor tall grass over forbs
  33. Knapp 1985 — frequent fire increases C4 grasses
  34. Knops 2006 – In more productive prairie, fire can lead to a decrease in diversity due to an increase in C4 dominance
  35. Knops and Tilman 2000 – C4 grasses are able to produce more biomass under N-limited conditions and the litter decomposing more slowly.
  36. Kucera and Koelling 1964 – Annual burning after five years resulted in a uniform cover of prairie grass with a sharp decline in broadleaved species, particularly coarse composites. Annual burning favors grass species to the exclusion of other prairie compo- nents, whereas a less frequent schedule is desirable in maintaining a wider composition spectrum.
  37. Lack 2022 – Low growing plants are declining because tall grasses are shading them out
    Leitner et al. 1991 – fire increased homogeneity
  38. Li et al. 2013 – decreased species richness (aka diversity) occurred with increased fire frequency.
  39. Martin et al. 2005 – frequent spring burning increase dominance of dominance C4 grasses
  40. McAllister et al. 1998 – Frequent fire increases dominance by grasses; frequent fire in tallgrass prairie leads to lower species richness
  41. Milbauer and Leach 2007 – Annual burns decrease diversity
  42. Odum and Barrett 2005 – Increasing productivity increases dominnce and reduces biodiversity
  43. Packard and Mutel 2005 – Annual burns increase the dominance of prairie grasses to the detriment of forbs, and burning at regular intervals can favor certain weeds
  44. Pauly 1997 — Annual burns decrease divesity and increase tall C4 grasses
  45. Peterson and Reich 2008 – Many studies in North American tallgrass prairie have shown that fire can increase C4 grasses abundance
  46. Reich et al. 2010 – frequently burned communities were increasingly dominated by grasses
  47. Scott et al. 2014 — Diversity in grasslands increases where fires are suppressed.
  48. Shaw et al. 2015 – Burning is a “common management strategy” use to promoted growth of warm season grasses
  49. Spasojevic et al. 2010 – Fire tends to have a uniform impact spatially. Species richness decreases with fire.
  50. Steinauer and Collins 1996 – Frequent fire increases the tall C4 grasses, reduces forbs, and reduces diversity
  51. Swengel 1996 – Frequent fire shift plant cover from forbs to grasses
  52. Towne and Knapp 1996 – Annual fires decrease forb biomass production by about half. From 94g/m2 to 45g/m2. Stem mass being greater offsets any biomass production on burned and unburned
  53. Vogl 1974 — repeated burning tends to simplify species composition and stand structure.
  54. Wade et al. 2000: 92 – Annually burned areas had lower diversity than unburned areas or those burned every 4 years. (several authors) In annually burned areas, fewer species can become established.
  55. Whiles and Charlton 2006 – frequent fire reduces plant tissue quality and shifts community structure toward lower quality C4 grasses