Understory community shifts in response to repeated fire and fire surrogate treatments in the southern Appalachian Mountains, USA

Abstract

Background Decades of fire exclusion in the southern Appalachian Mountains, USA, has led to changing forest structure and species composition over time. Forest managers and scientists recognize this and are implementing silvicultural treatments to restore forest communities. In this study, conducted at the southern Appalachian Fire and Fire Surrogate Study site in Green River Game Land, North Carolina, USA, we assessed the effects of four fuel-reduction methods (burned four times, B; mechanical treatment two times, M; mechanical treatment two times plus burned four times, MB; and control, C) on the changes in understory community from pre-treatment to post-treatment years (2001 to 2016). We used non-metric multidimensional scaling (NMDS) to determine overall understory community heterogeneity, agglomerative hierarchical cluster analyses (AHCA) to determine finer-scale changes in understory community structure, and indicator species analyses (ISA) to identify the species that were associated with the different fuel reduction treatments over time. Results The NMDS ordination showed little separation between treatment polygons. The AHCA resulted in two main categories of understory species responses based on how treatment plots clustered together: (1) species apparently unaffected by the treatments (i.e., no treatment pattern present within cluster); and (2) species that responded to B, M, or MB treatments (i.e., pattern of treatment plots present within cluster). Nearly half (49.2%) of tree-species plots clustered based on treatments; 60% of shrub-species plots clustered based on treatments; and 64% of herbaceous-species plots clustered based on treatments. Many plots clustered similarly in response to fire-related treatments (B and MB). The ISA identified 11 total tree species: three in B, one in M, and seven in MB; six total shrub species: two in M, and four in MB, and 17 total herbaceous species or genera: one in C, and 16 in MB. Conclusion Fire and fire surrogate treatments did not dramatically shift understory composition after 15 years. However, certain ruderal and early seral species responded positively to MB, which was the most intensive treatment. Modest understory community changes were also observed in B, suggestive of early signs of shifting composition toward a more open forest community after four burns.

Season of burn has minimal effect on groundlayer community structure and composition in an Appalachian mixed‐oak forest

“…Although eastern white pine and red maple remained indicators of CON and DSB post‐burn, yellow‐poplar was a new species indicative of post‐burn conditions in GSB. This finding corroborates findings by Oakman et al (2021) indicating that fire may promote the germination and subsequent establishment of yellow‐poplar seedlings, which are often abundant in the buried seed bank (Keyser et al 2012). Due to its shade intolerance, however, the yellow‐polar cohort that established after GSB is unlikely to recruit into larger size classes without subsequent overstory disturbance or additional burns (Hutchinson et al 2005 b ).…”

Changes in canopy cover and forest structure following dormant season and early growing season prescribed burns in the Southern Appalachians, USA

“…Diversity indices were highest in growing season burn treatment units, indicating that these res are more effective at not only closed canopy structure and creating early successional and open canopy forest conditions, but also at creating a more even distribution of closed, early, and open canopy throughout the burned stand. A single dormant season burn does not appear to be as effective at restoring forest structural and compositional diversity, which is consistent with other studies(Oakman et al 2019(Oakman et al , 2021. However, repeated dormant season burns may eventually meet management objectives in enhancing structural diversity in this region,…”