Soil Nitrogen Availability After Mechanical Fuel Mulching Treatments In Colorado Conifer Forests.

New mechanical methods for reducing woody fuel loads are being implemented on millions of acres throughout western North America.  Redistribution of standing forest biomass to the soil surface by these treatments has no ecological analogue and may have important implications for long-term forest productivity.  We evaluated the initial effects of mulch addition on soil nitrogen availability at fifteen sites distributed across the southern Rocky Mountains and Colorado Plateau regions of Colorado.  Mulching added 29 Mg ha^-1 of woody residue on average, an amount 1.6-fold more than the mass and twice depth of the forest floor in untreated stands.  Mulch application decreased maximum summer soil temperatures and temperature fluctuations and increased volumetric soil moisture content compared to unmulched stands.  Overall, mulching had a slightly positive effect on soil N availability at the operational scale and significant positive increases in montane forests.  Based on the findings of this broadly replicated study, it seems unlikely that mulching treatments will have negative consequences on soil productivity in most conifer forests.