Initial ground layer response to prescribed burning, thinning, and season on the southern Cumberland Plateau

Background/Question/Methods Ground layer vegetation (<1.4 m height) in temperate forest ecosystems is high in vascular plant diversity, especially herbaceous species. Silvicultural treatments influence patterns of cover and richness in the ground layer by altering seed-bed properties and light availability. We examined the ground layer community on plateau-tops of the southern Cumberland Plateau before and after prescribed burning and thinning in 22 mixed pine hardwood stands (>9 ha each) in the W.B. Bankhead National Forest, Alabama. The stands were mixed pine-hardwood dominated by planted loblolly pine (Pinus taeda L.). Vascular plants in each stand were sampled to obtain average cover, species richness, and diversity estimates and to obtain cover and richness of herbs, graminoids, and vine life forms. We also examined the ground layer in 18 of 22 stands 3 times (spring, summer, early fall) across the first post-treatment growing season following thinning and burning treatments. Thinning (residual basal areas 10-18 m²/ha) and dormant-season prescription burns were implemented during 2006 and 2007. The cover and richness of herbs, graminoids, and vines was calculated in each plot to determine how these groups performed across the growing season immediately after burn and thin treatments and if any seasonal changes varied with treatment type (i.e., interaction between treatment and season).
Results/Conclusions Significant burn and thin interaction effects were observed on the cover of all species (p=0.05), diversity (p=0.03), and herb cover (p=0.02), indicating that the effect of burning on cover is different depending on the thinning severity. Cover of all species combined was reduced in both thinned and burned stands compared to control stands. When considering life forms separately, vine and herb cover were reduced. Graminoid cover and richness increased significantly (p<0.01) in the first post-treatment growing season. Although vine richness did not change after treatments, vine cover decreased after burning (p=0.03) but not thinning. Ground layer cover and richness significantly changed across the first growing season following treatments while species diversity did not. The cover of herbs and graminoids increased significantly across the growing season and was greatest in those stands that were thinned and burned, suggesting that there may be an additive effect of these treatments on herb and graminoid cover. The results will be useful for forest managers at the Bankhead National Forest and other parts of the Cumberland Plateau, who are interested in ground-layer vegetation dynamics and in increasing the cover of graminoids in particular.