Abstract:
The ground flora stratum affects stand structure, resource acquisition, nutrient cycling, and taxonomic richness in forest ecosystems. Disturbances, such as thinning and prescribed fire, alter understory growing conditions that generally increase ground flora cover and richness in stands across the U.S. However, few studies have quantified annual changes in ground flora after a prescribed fire in thinned stands to provide finer temporal resolution of ground flora recovery. I performed a space-for-time study that quantified changes in ground flora assemblages over three growing seasons post-fire in thinned and frequently burned Pinus-Quercus stands. My results corroborated trends from other forest types and regions that indicated greater ground flora richness and cover after thinning and burning compared to thin-only treatments. I also found that the stratum experienced relatively rapid succession between growing seasons. Forbs had annual reductions in cover and richness with increasingly difficult growing conditions after the first growing season, while woody plants and shrubs increased in richness over time. The transition from herbaceous to woody dominance in three years was indicative of changing competition dynamics that favored quick growth in the first growing season and long-term investment in vertical growth in the third growing season. Although beneficial for increased ground flora cover, forb taxonomic richness, and reduced fuel levels, the three-year fire return interval did not produce comparable Pinus and Quercus regeneration to overstory composition. Management of eastern U.S. Pinus-Quercus stands may need to account for potential mesophytic dominance in seedling and sapling size classes that occur in thinned and burned stands over time. If mesophytic dominance becomes an issue, managers could include growing season fires and a secondary thin to foster desired regeneration to recruit into the overstory, although general weather conditions during the growing season could make fires hard to routinely implement.
