“Burn, Prairie, Burn,” say KSU Researchers [1]

“Burn, Prairie, Burn” say KSU Researchers [1]
A Critique by Craig Volland and Ellie Skokan

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In a journal article[1] published in July, researchers at the Konza Prairie Biological Station (KPBS) warned that a large increase in burning of range land in the Kansas Flint Hills will be necessary to avoid wholesale loss of tall grass prairie from encroachment by woody plants “in the coming decades.”  KPBS is associated with Kansas State University (KSU).  Their projection combines data from experimental plots within some 8000 acres at KPBS and conclusions from other studies, with satellite imagery measurements of burn rates in the Flint Hills from 2000 to 2010.

The prospect of yet more burning in the Flint Hills got the attention of Kansas Chapter members concerned not only with air pollution exposures to downwind communities and rural residents but also with loss of biodiversity, including the destruction of wildlife habitat.  Except in occasional drought years, landowners in the Flint Hills burn between 2 and 3 million acres of grassland every year.[2]  The Flint Hills encompasses some 6.9 million acres.  This article is a detailed review of the KSU researchers’ claims.

Narrow Focus of the Study.
Several key studies[3-6] cited by the article, and the article itself, acknowledge that the spread of woody plants in the Flint Hills-type of grassland is dependent on several other important variables besides burn frequency, including grazing intensity, species of grazer, and topography (upland vs. lowland).  There is also conflicting evidence that temperature and precipitation are factors within the multi-decadal term covered by the various research groups working in this field.

Grazing intensity.  The authors qualitatively recognize that overgrazing is a major factor, and briefly allow that changes in grazing management may be necessary to build fuel loads.  But nowhere did the authors quantitatively assess this element in their analysis.  A significant number of acres in the Flint Hills are burned almost every year under the intensive early stocking technique (IES) which involves ranch-wide burning most years followed by maximum density of grazing by stocker cattle.  It’s also called double stocking.[7,8]  This takes place in a narrow window in early to mid-April.  This annual routine is related to scheduling-in yearling stocker cattle from points south (Texas) on their way to vast cattle feedlots in western Kansas by July.

The authors’ data does not address this issue. The KPBS research plots, when grazed, were grazed by bison not cattle. It can be argued that the intensive grazing associated with the IES regime requires annual burning to prevent woody plant encroachment.  The high stocking rate reduces the fuel load available for the next burn.  Before the advent of IES in the 1980s, a one in three year burn cycle with moderate grazing pressure was quite sufficient because the burn was intense enough to kill both shrubs and small trees.  In other words, IES is the problem, not the solution.

Topography.  The KPBS fire return estimates are primarily based on data obtained in their lowland experimental plots.  Much of the Flint Hills is upland.  This is important because lowlands contain much deeper soils with higher moisture than uplands soils.  Such conditions encourage the spread of woody plants.   Collins, et al,[9]  noted that “response of lowland areas to variable fire and grazing may differ from that of upland sites.”  Ratajzcak, et al,[3] noted that shrubs will not spread easily in thin upland soils.

Grazer species.  As anyone who passes through the flint Hills can attest, it’s cattle that do the grazing.  In contrast, the only cattle at KPBS are on plots being studied under a patch burn regime, not included in the present research.  Collins, et al[9] found that plant species richness and community stability were maximized in the system at KPBS with infrequent fire (every 4– 20 years) and bison grazing across a range of soil types.

How Typical is the KPBS?
Our discussion of these unexamined factors raises an even bigger issue.  Just how representative of the entire Flint Hills physiographic region is the 8000 acres of the KPBS observed for this study?  Previously we noted that the topography and grazing regimes were not typical.  In addition, these research plots comprise only about 0.1% of the region’s 6.9 million acres.  The KPBS in Riley County is near the northern extremity of the Flint Hills that stretches 250 miles north to south and features a substantial gradient in rainfall.  For example, normal rainfall in Riley County is 33.54 inches per year.  In the center, Chase County’s normal rainfall is 36.66 inches, and to the south, Elk County’s normal rainfall is 40.60 inches.[10]   There is also a temperature gradient.  This issue needs closer examination.

Shaky Estimate of Transition Threshold
The primary variable examined by the authors was the fire return interval, or burn frequency.  The authors’ selection of woody plant transition thresholds appears arbitrary and contradictory to statements they make elsewhere.  At several points in the text they say that fire return frequencies of 3 years or less will limit woody encroachment.  In an earlier paper[3] from KPBS some of the same authors say, “In tallgrass prairie, recurring fire intervals of > 3 years between fires can potentially result in transitions to shrublands or woodlands.”  In fact there is no 3-year experimental burn interval in the data set they use for their cited transition threshold research, ie. they skip from 1 year to 4 (they have some limited 2-year fire return data at KPBS used elsewhere).

But in Figure 3A of the present study they have selected the crucial threshold, a “mean fire return interval,” to be only 2.2 years.  No range around this mean is given.  Above 2.2 years they claim any particular area is “precarious” with respect to risk of transition to woody species.  Apparently unable to rely on KPBS data to support this number, they cited Bowles, et al[11] and Fuhlendorf, et al[12], instead.

The Bowles data came from ungrazed, prairie remnants of dissimilar topography near Chicago where the plant growth pattern was actually measured only at years 1 and 25 of the study.  The Fuhlendorf study used an average 3- 5 year fire return interval with bison, not cattle, grazing under a random, patch-burn regime, uncommon in the Flint Hills, and a variety of burn times (fall, late spring and during the growing season).  The authors said,   ” … composition of functional groups differed most between plant communities that had been burned and grazed in the past year and those that have not been burned or grazed in the past 3 or more years.”  They were most interested in whether the plant community had recovered without significant change after a three-year patch-burn interval.  Neither the Bowles nor the Fuhlendorf study supports the notion that a 3-year burn interval is insufficient to prevent woody encroachment in the Flint Hills landscape.  That is, they differ enough in technique and setting that they are not applicable to the present study.

As for transition to woodlands (mainly red cedar) the authors stated that “fire-free intervals >10 years can potentially lead to the formation of woodlands,” and areas not burned for 30−50 year almost always transition to woodland given enough time.”  They did not explain how they differentiated upland from lowland areas throughout the Flint Hills in their model. This would be crucial for differentially assessing the susceptibility of upland areas to encroachment by either shrubs or trees.  The near disappearance of grassland in their projection of the future end-state (Fig. 1) suggests they extrapolated a lowland shrub threshold assumption to the entire Flint Hills.

The authors’ satellite observations[2] were taken March 1 through May 10, with most observations between March 15 and April 15, and thus did not include any burns done at alternate times of the year.  Their observations, though innovative, also did not assess what, if any, woody encroachment actually occurred during the 2000 to 2010 period.  The satellite monitoring merely calculated the fire return interval spatially and does not add information to the estimation of plant community transition thresholds.  The author’s conclusions are only a projection forward.

The authors seem to acknowledge these uncertainties by stating, “We stress that the length of time needed to trigger state transitions is currently an estimate that requires significant refinement.”

What Really Happened After Settlement of the Flint Hills?
In the subject article, the authors estimate that the pre-settlement, fire return interval was within a range of 2 to 10 years with an average of ~2.5−4 years … ”   In their earlier paper[3], they estimated a range of 3 to 5 years, with an approximate 4 year average.  These intervals seemed to work fine prior to settlement, so what changed?  We submit that the major changes were the substitution of cattle for bison, which were slaughtered to near extinction in the second half of the nineteenth century, and the introduction of IES in the 1980’s, which greatly intensified the grazing pressure.

Indeed KPBS researchers said in their earlier paper[3] that “conventional cattle grazing generally favors greater tree establishment by reducing fuel loads, and thereby fire intensity,” and “In contrast, native grazers such as bison (Bos bison) can significantly restrict woodland development.”  While it is unrealistic to bring back the bison, any progress on the question of woody encroachment in the Flint Hills must address the damage wrought by IES, including its impact on wildlife.

Why are Parts of the Flint Hills Unburned?
The lowland areas most at risk for woody transition generally lie on the periphery of the Flint Hills region.  The authors say more than 2 million acres are unburned or burned less frequently than every ten years.  No detailed data or analysis is given as to why such a large area is not now being burned.  This prevents any kind of assessment of how realistic are the prospects for additional burning.  It would be foolhardy to proceed with enhanced burning without a detailed analysis of this question.

Socio-Economic Challenges
To their credit the authors recognize the complex socio-economic issues surrounding the management of the Flint Hills.  In Table 1, they point to changes that need to be considered. These include getting landowners to burn at times other than in April and the use of the innovative patch burn system where a different portion (typically one third) of a ranch is burned every year.  This protects wildlife habitat and creates a more natural, heterogeneous landscape.  This would be a crucial element in moving forward.  The authors did not elsewhere assess the impacts of more burning on wildlife or plant diversity.

Advocacy vs. Science
This paper can be perhaps best understood by its alignment with a paper published in 2013 by Twidwell, et al[6] of Oklahoma State University.  Both papers advocates for “burning cooperatives” that pool labor, equipment and expertise to achieve more range burning.  The OSU group, however, has also pioneered the patch burn technique to mitigate some of the negative effects.

KSU’s press release[1], “Burn, prairie, burn,” announcing the subject article says:

To find solutions for this problem, Briggs said land managers are working with fire cooperatives and the Kansas Flint Hills Smoke Management to find best practices and compromise.

It’s unclear from which stake holders, the authors are expecting a compromise.  The 2010 all-voluntary, Flint Hills Smoke Management Plan, which after six years has clearly failed to reduce the air quality problem, does not represent a compromise, not from the cattle industry anyway.  Actually the 2010 SMP called for less burning, not more.  Even if the authors’ recommendations were applied to only those areas currently unburned or burned only once every ten years, we are looking at burning, every other year or so, another 1.5 million acres.[2]  That’s a lot of new smoke.

Nonetheless, to the extent that this effort results in major changes to current range management practices, such as burning outside the usual April time window and much greater use of the patch burn technique, it could be a step in the right direction.  If it becomes a distraction from dealing with current intensive burning and grazing practices, with everybody burning at roughly the same time, we will continue to have a major public health problem.  All this smoke most directly afflicts citizens in small towns and rural areas.  Some of these people may not benefit when the cattle industry is able to maximize profits with excessive burning and stocking.

The authors’ projection of woody encroachment in the coming decades goes far beyond what is justified by the breadth and quality of their data.  In particular their claim that a three-year fire burn frequency is not sufficient to prevent woody encroachment is inadequately supported. Their model does not address several important variables in the Flint Hills including topography, grazing intensity and grazer species.  The authors acknowledge that their primary independent variable, the fire return interval that enables woody encroachment, needs significant refinement.

Author information:  Craig Volland, of KC, Ks. is Chair of Agriculture and Air Quality Committees of the Kansas Chapter, Sierra Club, and Ellie Skokan is a retired biologist and a member of the Conservation Committee of the Chapter’s Southwind group in Wichita.

1. News Release entitled, “Burn, prairie, burn . . .:  http://www.k-state.edu/media/newsreleases/may16/prairiefireresearch53116.html .  The article, Ratajczak, Z., Briggs, J. M.,  Goodin, D. G., Luo, L., Mohler, R. L., Nippert, J. B., Obermeyer,  B., “Assessing the Potential for Transitions from Tallgrass Prairie to Woodlands: Are We Operating Beyond Critical Fire Thresholds?”  Rangeland, Ecology & Management, 69(4):280-287 .
2. Mohler, R.R.L., Goodin, D.G., 2012. “Mapping burned area in the Flint Hills of Kansas and Oklahoma, 2000–2010.” Great Plains Res. 22, 15–25.  Also http://www.ksfire.org/
3. Ratajczak, Z., Nippert, J.B., Briggs, J.M., Blair, J.M., 2014a. “Fire dynamics distinguish grasslands, shrublands and woodlands as alternative attractors in the Central Great Plains of North America.” J. Ecol. 102, 1374–1385.
4. Ratajczak, Z., Nippert, J.B., Ocheltree, T.W., 2014b. “Abrupt transition of mesic grassland to shrubland: evidence for thresholds, alternative attractors, and regime shifts.” Ecology 95, 2633–2645.
5, Twidwell, D., Fuhlendorf, S.D., Taylor, C.A., Rogers, W.E., 2013a. “Refining thresholds in coupled fire-vegetation models to improve management of encroaching woody plants in grasslands.” J. Appl. Ecol. 50, 603–613.
6. Twidwell, D., Rogers, W.E., Fuhlendorf, S.D., Wonkka, C.L., Engle, D.M., Weir, J.R., Kreuter, U.P., Taylor, T.A., 2013b. “The rising Great Plains fire campaign: citizens’ response to woody plant encroachment.” Front. Ecol. Environ. 11, 64–71.
7. Robbins, M.B., A. T. Peterson, and M. Ortega-Huerta. 2002. “Major negative impacts of early early intensive cattle stocking on tallgrass prairie: The case of the Greater Prairie-Chicken (Tympanuchus cupido).” North American Birds 56:239-244.
8. Reinking, D.L., 2005, “Fire regimes and avian responses in the central tallgrass prairie,” Studies in Avian Biology No. 30:116–126.
9. Collins, S.L., Calabrese, L.B., 2012. “Effects of fire, grazing and topographic variation on vegetation structure in tallgrass prairie.” J. Veg. Sci. 23, 563–575.
10. http://mesonet.k-state.edu/data/20002016+Monthly+Precipitation+by+County.txt
11. Bowles, M.L., Jones, M.D., 2013. “Repeated burning of eastern tallgrass prairie increases richness and diversity, stabilizing late successional vegetation.” Ecol. Appl. 23, 464–478.
12. Fuhlendorf, S.D., Engle, D.E., Kerby, J., Hamilton, R., 2009. “Pyric herbivory: rewilding landscapes through the recoupling of fire and grazing,” Conserv. Biol. 23, 588–598.

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