Effects of thinning and prescribed fire frequency on ground flora in mixed Pinus-hardwood stands

Forest management is increasingly focused on enhancing native biodiversity. In temperate forests, a common goal is to increase native plant diversity of the ground flora and silvicultural treatments such as thinning and prescribed burning are often used alone or in combination to achieve this goal. These treatments often increase understory light availability, decrease litter depths, and increase nutrient availability. We examined the effects of thinning without fire and thinning with different fire frequencies (four burns on a three year return interval and two burns on a nine year return interval) to identify changes in community structure and species composition with a focus on taxonomic richness, diversity, and cover of ground flora in post-agricultural Pinus-hardwood stands on the Cumberland Plateau in Alabama, USA. This paper reports on one year of post-treatment data (two years post burn) within a longer-term study of thinning and repeated burns. Overstory basal area and density were lower with increased management intensity. Sapling density was substantially greater with increased management intensity; however, this did not affect ground flora richness, diversity, or cover. Ground flora richness, diversity, and cover were greatest in stands that were thinned and burned every three years, and these measures were negatively correlated with litter depth and positively correlated with exposed mineral soil in a non-metric multidimensional scaling (NMS) solution. Our results signify the need for a combination of thinning and burning in these systems. Forest managers that wish to promote native plant diversity in similar systems may consider thinning and frequent burning to increase light availability, decrease litter depth, and promote ground flora richness, diversity, and cover.