Jayne L. Jonas, Erin Berryman, Brett Wolk, Penelope Morgan, Peter R. Robichaud
Following high-severity wildfire, application of mulch on the soil surface is commonly used to stabilize slopes and limit soil erosion potential, protecting ecosystem values at risk. Despite the widespread use of mulch, relatively little is known about its effects on ecosystem recovery and soil processes important for plant re-establishment. Following a high-severity wildfire in a Colorado lodgepole pine forest, we studied the effects of both mulch material and application rate on plant recovery and the relative importance of soil abiotic conditions and microbial substrate availability as drivers of plant community development over the first four years of recovery. Mulches were applied to experimental plots in a randomized complete block design immediately following the High Park Fire in July 2012. Treatments included wheat straw, wood strands, and wood shreds applied at two coverage rates (standard and high). Two controls, non-mulched and a microbially-neutral synthetic mulch, were included in each block to assess the relative importance of mulch effects on abiotic versus biotic dynamics. Plant and soil monitoring occurred at least annually for four-years post fire. Understory plants increased in total cover and shifted in composition over time, but these trends were largely unaffected by mulch type or application rate. Non-native understory plant species were not abundant at the end of this experiment, but their cover was higher in plots treated with wheat straw and high-rate wood strands compared to non-mulched control. Lodgepole pine seedling densities were higher in wood shred and mulched control treatments than in wheat straw and non-mulched control treatments. Because there were few effects of mulch treatments on plant available nitrogen, it is likely that effects of mulch on soil abiotic conditions (moisture and temperature) drove ecosystem responses in this system. Our findings indicate wood mulches can provide soil protection for many years and accelerate lodgepole pine establishment following wildfire with few negative near-term effects on plant recovery. In systems such as this, post-fire application of wood mulch can help managers meet site protection goals with minimal impacts on plant recovery.