Forest composition, fuel loading, and soil chemistry resulting from 50 years of forest management and natural disturbance in two southeastern Coastal Plain watersheds, USA

Abstract

Globally, prescribed fire, harvesting, and understory mastication, alone and in combination, are common forest management practices. Timber commodities, wildlife habitat, wildfire fuel reduction, soil conservation, and water quality are frequently targeted and assessed as these practices are utilized. In the 1960s, a study of paired, first-order watersheds was established in coastal South Carolina, USA, to evaluate the long-term impacts of forest management (i.e. prescribed fire, thinning, mastication of understory vegetation) on water quantity and quality. Following Hurricane Hugo in 1989, this included salvage logging on one watershed, but not the other. In 2015, these watersheds were comprehensively evaluated to determine differences in forest species composition, fuels, and soil chemistry. Softwood basal area was greater in the managed watershed than in the unmanaged watershed and hardwood basal area was greater in the unmanaged watershed than in the managed watershed. Total fuel mass did not differ between the two watersheds, but 1-hr and 1000-hr rotten fuel mass were greater on the unmanaged watershed. Ten-hr fuel mass was greater on the managed watershed. Calcium, nitrogen, magnesium, phosphorus, potassium, and pH differed between the litter (Oi horizon) and duff (Oe + Oa horizons) of both watersheds, but carbon only differed in the duff. Mineral soil (Ultisols, 0-10 and 10-20 cm depths) calcium and phosphorus differed between the watersheds, but pH and the other chemicals did not. Collectively, these results indicated that: (1) forest management and natural disturbance on these watersheds altered long-term forest structure; (2) different species compositions and the inclusion or exclusion of salvage logging after Hurricane Hugo produced different fuel compositions that may potentially impact potential wildfire hazard and fire behavior; (3) organisms as a primary soil-forming factor were impacted by long-term management, therefore, some soil chemical properties were affected. Collectively, these analyses highlighted the broad, long-term impacts to ecosystem properties and processes that might directly and indirectly result from active forest management and natural disturbance and the scale of site-specific assessment that might be considered when landowner objectives are targeted in forest management plans and practices.

Generating a Baseline Map of Surface Fuel Loading Using Stratified Random Sampling Inventory Data through Cokriging and Multiple Linear Regression Methods

“…This system is quite similar to the fuel types of coniferous, deciduous, mixed wood, slash, and open grassland, as defined in the Canadian Fire Behavior Prediction System (FBPS) [36]. Various research has demonstrated the feasibility of integrating ALS and optical images to map the fuel types (alternatively fuel models), such as the ones defined by the Northern Forest Fire Laboratory (NFFL) [36,41,49,50,60,61]. The proposed algorithm for mapping the surface fuel load is therefore most likely able to substitute the fuel types of the FBPS, NFFL, and NFDRS classification systems to moderately improve the mapping performance for forests with undulating terrain morphology in mountainous area.…”

“…Surface fuel loads and bulk density are primarily subject to forest structures related to species composition, phenology, and canopy height [41,[46][47][48][49][50]. Distribution of surface fuel loads is therefore a consequence of the interaction of multiple factors such as forest type or overstorey/understorey species, topographic relief, and climate.…”

Long-term impacts of silvicultural treatments on wildland fuels and modeled fire behavior in the Ridge and Valley Province, Virginia (USA)

“…Litter (Oi Horizon), duff (Oe + Oa Horizons), and woody fuel depth (defined as the length from the top of the Oi horizon to the top of a down and dead woody fuel particle lying along a planar transect) were measured at 3.7, 7.6, and 12 m along each linear transect. Additionally, litter and duff were destructively sampled within a 0.09 m 2 PVC plastic frame to determine the O Horizon load (Coates et al 2020). Along each transect, one sample was collected at the end of the 120 • and 240 • transects and one sample was collected within 1.5 m of the origin for the 0 • transect.…”

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

“…Some management objectives, such as wildlife habitat management and hazardous fuel reduction, for example, necessitate different forest structures and species compositions [15,27]. Altered fire regimes, that may include more frequent and persistent prescribed fire ignitions to achieve desired management goals, may directly affect organisms as a primary soil-forming factor [28,29]. Therefore, soil chemical properties may also be altered as a product of management intent [29].…”

“…Altered fire regimes, that may include more frequent and persistent prescribed fire ignitions to achieve desired management goals, may directly affect organisms as a primary soil-forming factor [28,29]. Therefore, soil chemical properties may also be altered as a product of management intent [29]. Furthermore, atmospheric N deposition and N saturation in some geographic locations may actually hamper management objectives because anthropogenic N enrichment may stifle any potential competitive advantages pyrophytic vegetation exhibit [15][16][17][18]25,26].…”