Effects of thinning and burning on ground flora in mixed pinus-hardwood stands
Commercial thinning and prescribed fire are tools used to accomplish forest management objectives such as increased timber revenue, fuel reductions, and increased biodiversity. Silvicultural treatments can alter forest structure and nutrient flow to increase resiliency by promoting regeneration of native species, especially in the ground layer, where the majority of plant diversity is stored. Management regimes that optimize ground layer attributes in mixed Pinus-hardwood stands following timber monoculture are less understood. I examined the effects of thinning without fire and thinning with different fire frequencies to identify changes in community structure and species composition with a focus on taxonomic richness, evenness, diversity, and percent cover of ground flora in Pinus-hardwood stands on the Cumberland Plateau in northern Alabama. Overstory (live woody individuals ≥ 5 cm dbh; diameter at breast height, 1.37 m above the root collar) basal area and density decreased with increased management intensity. Sapling (live woody individuals < 5 cm dbh and > 1 m in height) density substantially increased with increased management intensity in the second growing season post-fire. Sapling density did not negatively affect light reaching the ground layer, as light availability increased with management intensity. Ground flora richness, diversity, evenness and cover were greatest in stands that were thinned, and then burned every three years, negatively correlated with litter depth and positively correlated with exposed mineral soil based on a non-metric multidimensional scaling (NMS) solution. Ground flora diversity was greater in thinned stands with fire compared to stands that were thinned and never burned, emphasizing the need of the combination of thinning and burning in these systems for native biodiversity conservation. Forest managers who wish to promote biodiversity may consider frequent burning to promote ground flora richness, diversity, and cover.