Fire intensity influences the dynamics of herbaceous plant populations in savannas, primarily through variation in shrub damage. In contrast, fire intensity can have less pronounced effects on herbaceous plant abundance and richness in low productivity communities where fuel availability is low. We hypothesize that this is the case in oak barrens of southern Ohio where soils are typically shallow, rocky, and nutrient deficient. We examined fire intensity effects on herbaceous plant functional groups (forbs and graminoids) 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 all vegetation in quadrats before and after treatments (from 2003-2007). Aerial cover and richness following biennially applied treatments were evaluated in the context of a randomized block design with repeated measures.
Results/Conclusions
Differences in forb and graminoid aerial cover and richness were not detected following clipping and prescribed fire. Regardless of treatment, aerial cover of forbs and graminoids decreased by 13% and 20%, respectively, and richness remained unchanged by the end of the study. Similar results were found in non-manipulated quadrats. Overall, fire and fire intensity had negligible effects on herb dynamics in oak barrens despite a 35% decrease in woody plant aerial cover in treated plots and a 44% increase in woody plant cover in non-manipulated plots over the course of the study. Instead, herbaceous plant dynamics may have been more related to yearly variation in other environmental factors, including precipitation. Moreover, it has been recently suggested that lightning-initiated, growing season fires once characterized oak barrens. We postulate that growing season fires, which remove aboveground carbohydrate reserves of physiologically active plants, will deter encroachment of woody groundcover vegetation in oak barrens and foster herb abundance and diversity.
