Abstract
BackgroundStraw mulching is one of the most common treatments applied immediately post fire to reduce soil erosion potential and mitigate post-fire effects on water quality, downstream property, and infrastructure, but little is known about the long-term effects on vegetation response. We sampled six fires that were mulched between 9 and 13 years ago in western US dry conifer forests. We compared understory plant species diversity and abundance, tree seedling density and height by species, and fractional ground cover on mulched and unmulched paired plots.ResultsMulch did not influence understory plant diversity, species richness, or fractional ground cover. However, on mulched plots, tree seedlings grew taller faster, especially on north-facing aspects, and there was slightly more graminoid cover. Mulch did not affect overall tree seedling density, but there were fewer ponderosa pine (Pinus ponderosa Lawson & C. Lawson) and more Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) in mulched areas, especially on south-facing slopes.ConclusionsManagers will be able to weigh the long-term implications of mulching against the short-term reductions in soil erosion potential. While there are many concerns about vegetation suppression and exotic species introduction from using straw mulch, our study suggests that the long-term effects are subtle 9 to 13 years after post-fire mulching.
Highlights
Large wildfires have been increasing in both size and frequency in recent decades (Westerling et al 2006; Dennison et al 2014; Westerling 2016)
Study areas We focused on wildfires in the US Interior West where a minimum of 40 ha of agricultural straw mulch was aerially applied in steep areas burned with high severity (Fig. 1)
Mulch had minimal effects on long-term understory vegetation response Our results suggest that any initial effects of agricultural straw mulch on understory vegetation are not long-term, ecosystem-altering effects
Summary
Large wildfires have been increasing in both size and frequency in recent decades (Westerling et al 2006; Dennison et al 2014; Westerling 2016). Agricultural straw mulch greatly decreases soil movement (Wagenbrenner et al 2006) until vegetation can establish in abundance (Dodson and Peterson 2010; Robichaud et al 2013). Due to expense, mulching is used as a strategic treatment of areas of high soil erosion potential and risk of loss of downstream values (i.e., road infrastructure, aquatic habitats, etc.; Bautista et al 2009; Williams et al 2014). Straw mulching is one of the most common treatments applied immediately post fire to reduce soil erosion potential and mitigate post-fire effects on water quality, downstream property, and infrastructure, but little is known about the long-term effects on vegetation response. We compared understory plant species diversity and abundance, tree seedling density and height by species, and fractional ground cover on mulched and unmulched paired plots. While there are many concerns about vegetation suppression and exotic species introduction from using straw mulch, our study suggests that the long-term effects are subtle 9 to 13 years after post-fire mulching
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