Browsing by Author "Harr, Ryan N."

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Constraints to restoring fire and grazing ecological processes to optimize grassland vegetation structural diversity
(2016-10) Scasta, John D.; Duchardt, Courtney J.; Engle, David M.; Miller, James R.; Debinski, Diane M.; Harr, Ryan N.
Extirpation of the ecosystem engineer (bison) and its interaction with fire, coupled with the utilitarian concept of moderate grazing, have contributed to homogenization of grassland habitat in North America. Although cattle may serve as a proxy for bison, combining fire with cattle grazing has been uncommon and to date managers have not always successfully applied cattle and controlled burns as tools to manipulate grassland vegetation heterogeneity and increase habitat diversity. Using an information-theoretic approach, we assessed factors constraining the fire-grazing interaction ecological process to engineer habitat structure of grasslands via patch-burn grazing. We assessed how grazing, fire, and biotic and abiotic features in tallgrass prairie influenced establishment and maintenance of low vegetative structure in burned patches, the positive feedback driving the fire-grazing interaction, and subsequent structural heterogeneity across a pasture. Four pastures were divided into three patches with a different patch burned annually in March/April from 2007 to 2013. Cattle were stocked from light to heavy (1.1–4.4 AUM/ha) from May to October (∼150 days) with access to the entire pasture. We hypothesized that the exotic C3 grass tall fescue (Schedonorus arundinaceus), lag-time between burning date and the date cattle were put into experimental pastures, and burn date would be the constraining factors. However, the most informative model included stocking rate, date of burn completion, and precipitation. The lightest cattle stocking rate did not establish low vegetative structure in the burn patch, which resulted in the lowest heterogeneity among patches. The heaviest cattle stocking rate established but did not maintain low vegetative structure in the burn patch. The intermediate cattle stocking rate maintained the lowest vegetative structure in the burn patch and the greatest heterogeneity among patches, i.e., the best efficacy of patch-burn grazing to engineer habitat structural heterogeneity. The relationships of stocking rate to burn patch vegetative structure and to landscape heterogeneity were both quadratic and were both optimized at intermediate stocking rate.
Fire induced reproductive mechanisms of a Symphoricarpos (Caprifoliaceae) shrub after dormant season burning
(2005-07) Scasta, John D.; Engle, David M.; Harr, Ryan N.; Debinski, Diane M.
"Background Symphoricarpos, a genus of the Caprifoliaceae family, consists of about 15 species of clonal deciduous shrubs in North America and 1 species endemic to China. In North American tallgrass prairie, Symphoricarpos orbiculatus (buckbrush) is the dominant shrub often forming large colonies via sexual and asexual reproductive mechanisms. Symphoricarpos shrubs, in particular S. orbiculatus, use a unique sexual reproductive mechanism known as layering where vertical stems droop and the tips root upon contact with the soil. Because of conflicting societal values of S. orbiculatus for conservation and agriculture and the current attempt to restore historical fire regimes, there is a need for basic research on the biological response of S. orbiculatus to anthropogenic burning regimes. Results From 2007 through 2013 we applied prescribed fires in the late dormant season on grazed pastures in the Grand River Grasslands of Iowa. From 2011 to 2013, we measured how S. orbiculatus basal resprouting and layering stems were affected by patchy fires on grazed pastures, complete pasture fires on grazed pastures or fire exclusion without grazing for more than three years. We measured ramet height, ramet canopy diameter, stems per ramet, ramets per 100 m2, and probability of new layering stems 120 days after fire. Height in burned plots was lower than unburned plots but S. orbiculatus reached ~ 84% of pre-burn height 120 days after fire. Stems per ramet were 2x greater in the most recently burned plots due to basal re-sprouting. Canopy diameter and density of ramets was not affected by time since fire, but burned pastures had marginally lower densities than plots excluded from fire (P = 0.07). Fire triggered new layering stems and no new layering stems were found in plots excluded from fire. Conclusions The mechanisms of both basal sprouting and aerial layering after fire suggest S. orbiculatus is tolerant to dormant season fires. Furthermore, dormant season fires, regardless if they were patchy fires or complete pasture fires, did not result in mortality of S. orbiculatus. Dormant season fires can reduce S. orbiculatus structural dominance and maintain lower ramet densities but also trigger basal resprouting and layering."
Landowners' perceptions of risk in grassland management: woody plant encroachment and prescribed fire
(2005-07) Harr, Ryan N.; Morton, Lois W.; Rusk, Shannon R.; Engle, David M.; Miller, James R.; Debinski, Diane M.
Ecologists recognize that fire and herbivory are essential to maintaining habitat quality in grassland ecosystems. Prescribed fire and grazing are typically used on public reserves to increase biodiversity, improve grassland productivity, and control encroachment of woody plants. However, these tools, particularly prescribed fire, have not been widely adopted by private landowners. Fire suppression and prescribed fire are strategies that present competing risks to owners who make management decisions. We explore landowner perceptions of risk associated with (1) eastern redcedar (Juniperus virginiana) encroachment, and (2) the use of prescribed fire to control woody species in the Grand River Grasslands of Iowa and Missouri, USA. We found that although mapping data of eastern redcedar in this region showed substantial encroachment over the past three decades, concept mapping of landowner beliefs and in-person interviews of local community leaders revealed that perceived risks associated with prescribed fire often outweighed those associated with loss of forage and grassland habitats.