Rill Connectivity and Erosion Following Logging on Burned Hillslopes in Central California.

After high severity wildfires, soil erosion is an important concern. Sometimes there is also an economic incentive to harvest burned trees, which can serve to meet management objectives such as potential fuel load reduction. Yet salvage logging can increase soil erosion and potentially reduce understory vegetation recovery rates. Rilling can occur in disturbed forest soils, and is a major source of erosion and sediment transport in burned forests. Our goal is to assess the impacts of post-fire salvage logging on rill erosion and sediment yields relative to unlogged burned hillslopes. We measured erosion in seven small catchments (~0.05-0.2 ha “swales”) in an area burned by the 2013 Rim Fire in central California, five of which were logged in fall 2014. Silt fences were installed at the outlet of each swale prior to substantial rainfall in winter 2015 to capture eroded sediment.  Mechanical disturbance was surveyed in the logged swales and ranged from 26-47%, with high use skid trails comprising 4-20% of each swale. After the first sediment producing rain event yields in logged swales ranged from 0.26 to 8.05 Mg ha^-1, while controls ranged from 2.3 to 5.7 Mg ha^-1. Rills formed in both unlogged and logged swales, and rill density increased with high use skid trails. A high proportion of rills were diverted out of skid trails by waterbars, but these often connected to ephemeral channels. Shorter rills were typically formed in unlogged swales, and these also frequently connected to ephemeral channels. Increased surface cover decreased sediment yields. Rill length increased in swales with more disturbed area, and increased rill length relative to swale area lead to higher sediment yields. Rills in burned and logged areas form more densely in areas of increased disturbance, and waterbars that drain into areas of sparse vegetation or soils of low infiltration form rills.