VEGETATION RESPONSE AFTER POST-FIRE MULCHING AND NATIVE GRASS SEEDING

Post-fire mulch and seeding treatments, often applied on steep, severely burned slopes immediately after large wildfires, are meant to reduce the potential of erosion and establishment of invasive plants, especially non-native plants, that could threaten values at risk. However, the effects of these treatments on native vegetation response post fire are little studied, especially beyond one to two years. We compared species richness, diversity, and percent canopy cover of understory plants one, two, three, four, and six years after immediate post-fire application of wood strand mulch, agricultural wheat straw mulch, hydromulch + seed with locally adapted native grasses, seed only with locally adapted native grasses with no mulch, and untreated (no mulch or grass seeding) after the 2005 School Fire in Washington, USA. For wood strand mulch treatments, mean canopy cover of grasses and forbs was low, varying from 3 % to 20 % in post-fire years two through six; whereas wheat straw mulch had the lowest mean cover of grasses, <1 %, and the highest canopy cover of both forbs and shrubs, each >29 % in post-fire years two through six. Plots hydromulched and seeded with grass, and those seeded with grass but not mulched, tended to have higher grass cover than other treatments and untreated plots over the six years. Species richness and diversity was highest for the hydromulch + seed treatment. Ten non-native species were found, but never with more than 2 % canopy cover, each. Although the inference of our small-plot work is limited, our results suggest that post-fire rehabilitation treatments apparently altered the abundance and diversity of native perennial understory plants for one to six years post fire-effects that could persist for decades.