Pyrogenic carbon erosion after the Rim Fire, Yosemite National Park: The Role of Burn Severity and Slope

Abstract

Pyrogenic carbon (PyC) is an incomplete combustion by-product with longer soil residence times compared with nonpyrogenic components of the soil carbon (C) pool and can be preferentially eroded in fire-affected landscapes. To investigate geomorphic and fire-related controls on PyC erosion, sediment fences were established in three combinations of slope (high 13.9-37.3%; moderate 0-6.7%) and burn severity (high; moderate) plots within the perimeter of the Rim Fire in 2013, Yosemite National Park, California, USA. After each major precipitation event following the fire, we determined transport rates of total sediment, fine and coarse sediment fractions, and C and nitrogen (N). We measured stable isotope (δ 13 C and δ 15 N) compositions and 13 C-nuclear magnetic resonance spectra of soils and eroded sediments. The highest total and fine (<2 mm) sediment transport in high severity burned areas correlated with initial discharge peaks from an adjacent stream, while moderate burn severity sites had considerably more of the >2 mm fraction transported than high burn severity sites. The δ 13 C and δ 15 N values and 13 C-nuclear magnetic resonance analyses indicated that sediment eroded from moderate severity burn areas included fresh organic matter that was not as significantly affected by the fire, whereas sediments from high severity burn areas were preferentially enriched in PyC. Our results indicate that along a single hillslope after the Rim Fire, burn severity acted as a primary control on PyC transport postfire, with slope angle likely playing a secondary role. The preferential erosion of PyC has major implications for the long-term persistence of PyC within the soil system.

Pyrogenic Carbon Generation From Fire and Forest Restoration Treatments

“…There is increasing interest in the role that PyC plays in long term carbon (C) storage in terrestrial and aquatic ecosystems, yet there is only limited understanding of the rate at which PyC accumulates in forest ecosystems during natural and prescribed (Rx) fire events. Of the PyC formed during forest fire events, much remains onsite as stored C (Lynch et al, 2004), eventually lost to depositional areas due via surface erosion (Abney et al, 2019) and if incorporated into mineral surface soils, the PyC may remain in surface soils an indefinite length of time (Abiven and Santín, 2019). Given this longevity in soil ecosystems, PyC has been identified as being an important C storage medium (Lehmann et al, 2006;DeLuca and Aplet, 2008;Santín et al, 2015) and receives a great deal of attention across a variety of research fields (Carcaillet, 2001;Gavin, 2004;Gavin et al, 2006;Power et al, 2006).…”

Pyrogenic Carbon Increases Pitch Pine Seedling Growth, Soil Moisture Retention, and Photosynthetic Intrinsic Water Use Efficiency in the Field

“…Where forest fire is absent and prescribed fire is unavailable for use, mechanical thinning is an option which fosters open canopies and reduces forest floor or grassland fuel (Anderson, 2017). This bioturbation method (Abney et al, 2019) is akin to other types of disturbance (e.g., animal, human, or climate pressures). Thinning is found to generate temporary nutrient turnover following soil disturbance (Saursaunet et al, 2018) without the associated risks of fire close to human settlement.…”

Linking Mesoscale Meteorology With Extreme Landscape Response: Effects of Narrow Cold Frontal Rainbands (NCFR)

“…The canyon slopes are covered by conifer forest and dense chaparral woodlands on the south side, and grasses with sparse chaparral vegetation on the north side. The area was affected by wildfire in 2013; however, local burn severity was low on the hillslopes that underwent landsliding in 2018 (Abney et al, 2019; Staley, 2013). Hillslopes are underlain by mostly metamorphic assemblages of the Paleozoic Shoo Fly and Calaveras Complexes (Wagner et al, 1991).…”