VEGATATION RESPONSES TO BIOSOLIDS APPLICATION FOLLOWING FOREST FIRE

The area included in the Buffalo Creek fire of May 1996 has been subjected to multiple, severe floods. The intense fire and subsequent flooding have caused degradation in the physical and chemical properties of the soil as well as loss of biological attributes of the forest ecosystem. In order to stabilize the soil, improve water and air quality, and restore the site, research was proposed to study the benefits of biosolids in accelerating ecosystem recovery. Special interest is on plant community recovery, soil water-holding capacity, and nutrient cycling.In 1997 a research site was established in order to test the effect of different rates of biosolids application on plant community development and soil characteristics. A total of 24 treatment plots received a single application of Metro Wastewater Reclamation District (Denver, CO) composted biosolids at six rates (0, 5, 10, 20, 40 and 80 Mg ha−1dry weight) with four replicates for each treatment. The materials were incorporated by discing in soil to a depth of 10-20 cm. The plots were seeded at a rate of 27 kg seed ha-1 with a standard grass mixture. Evaluation of the post-fire vegetation in the summers of 1997, 1998, 1999, and 2000 indicated that the seeded grasses are thriving in biosolids plots and that native grasses, forbs and shrubs are colonizing through natural succession.Data from 2001 shows increases in biomass, percent plant canopy cover, soil total N, C and NH4+-N, and plant tissue percent nitrogen with increased biosolids application rates. A decrease in soil pH and an increase in electrical conductivity were observed with increasing rates of biosolids application. Plant tissue concentration of metals did not significantly increase with increased application rates of biosolids however, several nutrient elements have. Results indicate that plots receiving higher rates of biosolids continue to have higher soil fertility and hence support greater biomass and cover of plants relative to control plots.