Understory Vegetation Responses to 15 Years of Repeated Fuel Reduction Treatments in the Southern Appalachian Mountains, USA

Abstract

Decades of fire exclusion in the Southern Appalachian Mountains led to fuel accumulation and conversion from open oak-pine woodlands to closed-canopy mesic forests dominated by shade-tolerant hardwoods and shrubs that often do not support a diverse understory. Southern Appalachian forest managers and scientists recognize this and are implementing silvicultural treatments such as prescribed burning, mechanical treatments or a combination of these to restore forest structure. In this study, conducted at the Southern Appalachian Fire and Fire Surrogate Study site in Green River Game Land, North Carolina, we assessed the effects of four fuel reduction methods: burned 4x (B), mechanical treatment 2x (M), mechanical treatment 2x + burned 4x (MB), and control (C) on the changes in understory vegetation guilds from pretreatment to post-treatment years (2001–2016). The MB treatment was most effective at meeting the restoration objectives, as it resulted in increases in oak (ΔMB = 23,400 stems/ha) and pine (ΔMB = 900 stems/ha) stem density, importance value - calculated as the sum of relative cover and frequency - for graminoids (ΔMB = 26.0), and density of oak stems >50 cm in height (ΔMB = 7133 stems/ha). The B and M treatments were generally less effective, but nonetheless met a subset of the restoration objectives. The B treatment reduced ericaceous shrub cover (ΔB = −1.2%) and increased oak stems 10–50 cm in height (ΔB = 10,017 stems/ha), while the M treatment resulted in only modest increases of mesic hardwoods, specifically for yellow-poplar (ΔM = 200 stems/ha) and blackgum (ΔM = 200 stems/ha) as compared with other treatments, but significantly increased mountain laurel and rhododendron cover (ΔM = 10.0%). Overall, these fire and fire surrogate treatments had some success in restoring understory structure, but our findings suggest a slow response in understory herbaceous vegetation.

Long-Term Effects of Repeated Prescribed Fire and Fire Surrogate Treatments on Forest Soil Chemistry in the Southern Appalachian Mountains (USA)

“…As of 2018, 4 dormant season prescribed burns had occurred in the burn-only and cut + burn units: February-March 2003, 2006, 2012, and 2015. These burns were ignited using aerial ignition (spot fire) or strip head fire techniques [14].…”

“…In order to accurately assess true, treatment-induced soil changes, pre-existing heterogeneity had to be addressed. Soil order (ultisols), species composition, landform, aspect, elevation, and disturbance history were similar for the forests selected as part of this study [12][13][14]. Despite this similarity, however, some soil chemical properties differed within the Green River Game Lands based upon spatial arrangement, independent of treatment-related effects.…”

“…Soils-related treatment effects vary not only as a result of time since treatment, but also as a result of treatment frequency [1,2]. In the case of wildland fire, they may also vary as a result of other fire behavior (i.e., fuels, weather, and topography) or fire regime (i.e., seasonality) factors [14][15][16]. This is particularly noteworthy when considering wildfire and prescribed fire impacts.…”

“…On the Green River Game Lands near Asheville, North Carolina, USA, in the southern Appalachian Mountains, fuel reduction and woodland restoration treatments consisting of prescribed fire only, mechanical cutting of mid-story and understory vegetation, and a combination of these two treatments were first implemented in 2001 as part of the National Fire and Fire Surrogate Study (FFSS) [12][13][14]. Historic forests of the Appalachian region, dominated by upland oaks (Quercus spp.…”

“…Since 2001-2002, additional treatments have been conducted on the Green River Game Lands: four total burns for the burn-only treatment; two total cuts for the cut-only treatment; and two total cuts + 4 burns for the cut + burn treatment [14]. Recent fuels and vegetation research following the repeated use of these treatments at this site suggested that: (1) all fuel reduction and restoration treatments reduced one or more fuel types, (2) the burn-only and cut + burn treatments reduced most fuels and most likely decreased wildfire hazard best, (3) desired upland oak and pine regeneration and graminoid density and cover increased following cut + burn treatments, and (4) cut + burn treatments induced forest structural changes most consistent with restoration goals, but no treatment regime had fully achieved the desired woodland structure [12,14]. No additional soils research from this site has been published, however.…”