Post-fire bedload sediment delivery across spatial scales in the interior western United States

Post-fire sediment yields can be up to three orders of magnitude greater than sediment yields in unburned forests. Much of the research on post-fire erosion rates has been at small scales (100m2 or less), and post-fire sediment delivery rates across spatial scales have not been quantified in detail. We developed relationships for post-fire bedload sediment delivery rates for spatial scales up to 117ha using sediment yield data from six published studies and two recently established study sites. Sediment yields and sediment delivery ratios (SDRs; sediment delivered at the catchment scale divided by the sediment delivered from a plot nested within the catchment) were related to site factors including rainfall characteristics, area, length, and ground cover. Unit-area sediment yields significantly decreased with increasing area in five of the six sites. The annual SDRs ranged from 0.0089 to 1.15 and these were more closely related to the ratio of the plot lengths than the ratio of plot areas. The developed statistical relationships will help quantify post-fire sediment delivery rates across spatial scales in the interior western United States and develop process-based scaling relationships

Factors affecting connectivity and sediment yields following wildfire and post-fire salvage logging in California\u27s Sierra Nevada

Sediment delivery following post-fire logging is a concern relative to water quality. While studies have assessed the effect of post-fire logging on sediment yields at different spatial scales, none have explicitly identified sediment sources. Our goal was to quantify post-fire and post-salvage logging sediment yields and use rill patterns to identify sediment sources. We measured the extent and type of logging disturbance, length of rills per unit area or “rill density”, ground cover, and sediment yields in nine logged and five control small catchments or “swales”, 0.09 to 0.81 ha, for 5 years after the 2013 Rim Fire in California\u27s Sierra Nevada. The logged swales had a mean ground disturbance of 31%. After the first wet season following logging, there was no difference in either mean rill density (0.071 and 0.088 m m−2, respectively) or mean transformed, normalized sediment yields between the control and logged swales. Untransformed mean sediment yields across three sites ranged from 0.11–11.8 and 1.1–3.2 Mg ha−1 for the controls and salvage-logged swales, respectively. Rill density was strongly related to sediment yield and increased significantly with the amount of high-traffic skid trail disturbance in logged swales. Rill density was not significantly related to the amount of bare soil despite a significant relationship between sediment yields and bare soil. Rills usually initiated in bare soil and frequently connected high traffic skid trails to the drainage network after being diverted by waterbars. Rill connectivity and sediment yields decreased in control and logged swales where vegetation or other surface cover was high, suggesting this cover disconnected rills from the drainage network. Increasing ground cover on skid trails and between areas disturbed by post-fire logging and stream channels may reduce sediment yields as well as the hydrologic connectivity between hillslopes and the drainage network

Seasonal Trends of DOM Character in Soils and Stream Change With Snowmelt Timing

In many watersheds, runoff occurring with snowmelt brings the largest pulse of dissolved organic matter (DOM) from soils to streams. Yet, exactly how soil and stream DOM fractions are altered as snowmelt timing changes is not well understood. We studied the optical character of DOM as it moved through a first-order northern hardwood watershed through the snowmelt period. While stream dissolved organic carbon (DOC; mean = 4.6 mg C L−1) concentrations were not correlated with snowmelt flushing, stream DOM appeared humic-like throughout the study period (humification index, HIX; mean = 10.9). Within the stream, we measured seasonal increases in an inverse index of DOM molecular weight and processing (spectral slope, S275–295; range = 0.0102–0.0214) and in an index of recently derived DOM (Biological Index, BIX; range = 0.2–1.1). We measured a decrease in an inverse index of DOM oxidation (ratio of Peak C to Peak A, or C/A; range = 0.59–2.01) through the snowmelt period. Stream BIX and C/A tracked those measured in the north aspect soils throughout the study. C/A was unique as it decreased from source to stream, likely reflecting the diagenesis of DOM through soils. These data suggest that changes in the timing of snowmelt and hydrologic connectedness within a watershed affect seasonal changes in stream DOM character. We suggest that watersheds with deep glacial till parent materials have stream connectivity limited by subsurface flow paths, with stream DOM character being determined largely by slow melt and a longer period of infiltration

Continued evaluation of post-fire recovery and treatment effectiveness for validation of the ERMiT erosion model

The use and cost of post-fire emergency stabilization treatments continues to grow. To help maximize the impact of these treatments, many assessment teams use the Erosion Risk Management Tool (ERMiT) erosion model to predict postfire erosion and mitigation effects. However, despite several completed JFSP projects, the long-term effects of these treatments remain unknown, and the ERMiT model has not been validated. Long-term post-fire erosion and runoff data on a variety of mulches and erosion barriers were collected using 12 existing sites throughout the Western U.S. The agricultural straw and wood strand mulch treatments were very effective at reducing erosion and runoff. The contour-felled log treatment was effective at reducing runoff and erosion for small storms, but was not effective for larger events. The hydromulch formulations tested in this study were not effective at reducing runoff or sediment yields. Numerous presentations, field trips, and Burned Area Emergency Response (BAER) trainings were conducted. These activities provided much-needed information about the effectiveness of stabilization treatments

Evaluating Post-fire Salvage Logging Effects on Erosion

Legal challenges have delayed numerous post-fire salvage logging operations, which often results in lost economic value of the burned timber and unrecovered legal expenses. The scientific literature has shed little light on the additive effect of salvage logging operations on post-fire runoff, erosion, flooding, and sedimentation. Hence, there is an urgent need to better understand the impacts of post-fire salvage operations so that land managers can evaluate the relative and cumulative effects of different salvage logging practices. Intensive, multi-scale studies are needed because the effects of post-fire logging are superimposed on the effect of wildfires; rates and processes change according to the spatial and temporal scales of the investigation; and the studies to date indicate tremendous variability in the effects of post-fire salvage logging with the type and extent of the logging, site characteristics, and climatic conditions. To address this need, the current project was established in the Northern Rockies to integrate experiments at the hillslope and small watershed scale that focus on erosion processes. Replicated plots were used to measure sediment production rates from burned and unlogged plots, logged areas, tracked areas due to ground-based logging, and tracked areas with added slash as an erosion control treatment. Measured erosion rates were related to detailed measurements of site characteristics including ground cover, rilling, water repellency, amount of area disturbed due to salvage logging operations, number of passes of logging equipment, soil compaction, and the number and type of erosion mitigation practices (e.g., application of logging slash, mulch, and water bars). Runoff and sediment yield data were collected from two pairs of small watersheds to determine how salvage logging affects runoff, peak flow, and erosion rates, and whether the erosion estimates from the hillslope plots can be extrapolated to the small watershed scale. Rill simulation studies were conducted on three sites affected by ground-based salvage logging to evaluate the various types of equipment and identify site factors that affect runoff and erosion rates

Mid-term and scaling effects of forest residue mulching on post-fire runoff and soil erosion

© 2016 Elsevier B.V. Mulching is an effective post-fire soil erosion mitigation treatment. Experiments with forest residue mulch have demonstrated that it increased ground cover to 70% and reduced runoff and soil loss at small spatial scales and for short post-fire periods. However, no studies have systematically assessed the joint effects of scale, time since burning, and mulching on runoff, soil loss, and organic matter loss. The objective of this study was to evaluate the effects of scale and forest residue mulch using 0.25 m2 micro-plots and 100 m2 slope-scale plots in a burnt eucalypt plantation in central Portugal. We assessed the underlying processes involved in the post-fire hydrologic and erosive responses, particularly the effects of soil moisture and soil water repellency. Runoff amount in the micro-plots was more than ten-fold the runoff in the larger slope-scale plots in the first year and decreased to eight-fold in the third post-fire year. Soil losses in the micro-plots were initially about twice the values in the slope-scale plots and this ratio increased over time. The mulch greatly reduced the cumulative soil loss measured in the untreated slope-scale plots (616 g m− 2) by 91% during the five post-fire years. The implications are that applying forest residue mulch immediately after a wildfire can reduce soil losses at spatial scales of interest to land managers throughout the expected post-fire window of disturbance, and that mulching resulted in a substantial relative gain in soil organic matter

Hydrologic Implications of Post-Fire Mulching Across Different Spatial Scales

Besides direct damage, wildfires can produce striking direct and indirect impacts, including extreme runoff–erosion responses with serious negative consequences for land-use sustainability and downstream values at risk. The best way to reduce post-fire runoff is the rapid application of mulch: a protective cover of straw, needles, wood-based material, or other ground cover. In this study, we assessed the efficacy of forest residue mulching for reducing post-fire runoff across spatial scales on a logged and burnt eucalypt hillslope. Additionally, we assessed the underlying processes involved in the hydrologic responses of burnt areas in central Portugal during the first 2 years after a wildfire, with special focus on soil moisture, soil water repellency, and rainfall. Forest residue mulch reduced post-fire runoff by 50% in both micro-plots (0·25 m2) and hillslope scale silt fence plots (100 m2) during the first year after the wildfire. Runoff in the micro-plots was tenfold higher than the larger plots, regardless of mulching. The main controlling factors for the volume of runoff were rainfall amount (direct correlation) and soil moisture (inverse correlation). Soil water repellency and soil moisture were not affected by the mulch but played a role in the hydrologic response. In contrast, there was no decrease in runoff rate within the first two post-fire years. Forest residue mulching can be an effective post-fire treatment for reducing runoff rates, and the consistent decrease in runoff rates between the two spatial scales suggests that the scaling of runoff was not affected by the mulch. Copyright © 2015 John Wiley & Sons, Ltd

Effects of post-fire salvage logging and a skid trail treatment on ground cover, soils, and sediment production in the interior western United States

© 2014 Elsevier B.V. Post-fire salvage logging adds another set of environmental effects to recently burned areas, and previous studies have reported varying impacts on vegetation, soil disturbance, and sediment production with limited data on the underlying processes. Our objectives were to determine how: (1) ground-based post-fire logging affects surface cover, soil water repellency, soil compaction, and vegetative regrowth; (2) different types of logging disturbance affect sediment production at the plot and small catchment ( swale ) scales; and (3) applying logging slash to skid trails affects soil properties, vegetative regrowth, and sediment production. Four study areas were established in severely burned forests in the interior western USA. We installed plots at two study areas to compare burned but unlogged controls against skid trails, feller-buncher trails, and skid trails with added slash. Salvage logged and control swales were established at each study area, but only one study area had simultaneous measurements on replicated swales. Data were collected for 0-2 years prior to logging and from 2-8 years after logging.The skidder and feller-buncher plots generally had greater compaction, less soil water repellency, and slower vegetative regrowth than the controls. Sediment production from the skidder plots was 10-100 times the value from the controls. The slightly less compacted feller-buncher plots produced only 10-30% as much sediment as the skidder plots, but regrowth was similarly inhibited. The relative differences in sediment production between the disturbed plots and the controls tended to increase over time as the controls exhibited more rapid regrowth. Adding slash to skid trails increased total ground cover by 20-30% and reduced the sediment yields by 5-50 times compared to the untreated skidder plots.The replicated logged swales at one study area generally had higher sediment production rates than their controls but the absolute values per unit area were much lower than from the skidder and feller-buncher plots. Results from the swales at the other study areas indicated that logging did not increase runoff, peak flows, or sediment yields.Vegetative regrowth and sediment production rates varied widely among the four study areas. This variation was largely due to differences in rainfall and soil properties, with the more productive sites having more rapid regrowth and thereby a more rapid reduction in sediment production. The susceptibility to surface runoff and erosion after high severity fires suggests that areas disturbed by ground-based salvage logging need additional mitigation practices

Temperature responses of carbon dioxide fluxes from coarse dead wood in a black ash wetland

The invasive emerald ash borer (EAB, Agrilus planipennis Fairmaire) causes widespread ash tree mortality in North America, and the CO2 efflux (respiration, F) from coarse dead wood (CDW) following the EAB infestation is unknown. We examined seasonal variations in CO2 fluxes from various types of CDW (cut ash stumps, downed logs, and standing girdled dead stems) and the surfaces of soil and live stem in a black ash wetland in which EAB infestation was simulated. Responses of FCDW to seasonal changes in temperature were less sensitive than that of live stems. However, FCDW from the stump and log cross-section were significantly greater than the other component fluxes. The mean CO2 flux from girdled stems was similar to those from soil and live stems. The log and stump cross-sections may function as an unaccounted pathway of CO2 flux following pre-emptive or salvage harvests associated with EAB mitigation. The increases in the amount of CDW and temperature caused by canopy openness and subsequent increased insolation, and potential long-term increase in water level and CDW moisture might accelerate the respirational carbon loss from soil and CDW after black ash wetlands are infested by EAB. These results identify and quantify CO2 pathways in EAB affected wetlands, which can be used to improve respiration modeling and carbon accounting in black ash wetlands

Temperature responses of carbon dioxide fluxes from coarse dead wood in a black ash wetland

The invasive emerald ash borer (EAB, Agrilus planipennis Fairmaire) causes widespread ash tree mortality in North America, and the CO2 efflux (respiration, F) from coarse dead wood (CDW) following the EAB infestation is unknown. We examined seasonal variations in CO2fluxes from various types of CDW (cut ash stumps, downed logs, and standing girdled dead stems) and the surfaces of soil and live stem in a black ash wetland in which EAB infestation was simulated. Responses of FCDW to seasonal changes in temperature were less sensitive than that of live stems. However, FCDW from the stump and log cross-section were significantly greater than the other component fluxes. The mean CO2 flux from girdled stems was similar to those from soil and live stems. The log and stump cross-sections may function as an unaccounted pathway of CO2 flux following pre-emptive or salvage harvests associated with EAB mitigation. The increases in the amount of CDW and temperature caused by canopy openness and subsequent increased insolation, and potential long-term increase in water level and CDW moisture might accelerate the respirational carbon loss from soil and CDW after black ash wetlands are infested by EAB. These results identify and quantify CO2 pathways in EAB affected wetlands, which can be used to improve respiration modeling and carbon accounting in black ash wetlands