Effects of fire intensity on resprouting potential of woody groundcover vegetation in midwestern barrens

Background/Question/Methods

Fire intensity influences the resprouting dynamics of woody plant populations, primarily by damaging buds on underground organs and at the base of stems. In savannas, however, fire intensity can have negligible effects on resprouting potential of woody vegetation, especially in localized areas where fuels are composed of mostly flashy, herbaceous groundcover vegetation and flame residence times are short. We hypothesize that this is also the case in oak barrens of southern Ohio where fires are driven by similar fuel types. We examined fire intensity effects on resprouting responses of woody plant populations in oak barrens by comparing clipping, which simulated fires of no intensity, to prescribed dormant season fires. We randomly positioned seventy-five 1-m² quadrats in three oak barrens sites. At each site, one third of the quadrats were clipped at ground level, another third were burned during the dormant season, and remaining quadrats served as a reference condition. Quadrats were re-treated similarly two years later. We measured aerial cover of woody vegetation, as well as densities and lengths of woody plant stems in quadrats before and after treatments (from 2003-2007). Resprouting potential following biennially applied treatments was evaluated in the context of a randomized block design with repeated measures.
Results/Conclusions

Differences in woody plant resprouting responses were not detected following clipping and prescribed fire. Regardless of our treatments, aerial cover of woody vegetation decreased 35% over the course of the study, but stem densities increased 28% over the same time period. In addition, stems grew an average of 25 cm immediately following treatment. In non-manipulated quadrats, aerial cover at the end of the study was 44% greater than initial levels, but densities had not changed. Further, stems in non-manipulated quadrats grew an average of 2 cm each year. Fire and clipping stimulated sprouting in similar ways, suggesting that fire did not damage buds on root crowns of woody groundcover vegetation. On this basis, fire intensity has negligible effects on resprouting dynamics in oak barrens. Instead, such responses likely depend on plant physiological status and location of carbohydrate reserves at the time of fire. Thus, resprouting potential may be more influenced by fire season. Moreover, it recently has been suggested that lightning-initiated, growing season fires characterized oak barrens. We postulate that growing season fires, which remove aboveground carbohydrate reserves of physiologically active plants, will reduce resprouting potential and deter encroachment of woody groundcover vegetation in oak barrens.