PARENT SESSION
Poster Session #16: Fire Ecology.
Tuesday, August 7, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

Fire has mixed effects on decomposition in boreal forests of interior Alaska.

Valentine, David¹, Boone, Richard¹, Sparrow, Emmalisa², ^{1 2}

ABSTRACT- In addition to direct losses of carbon, fires in boreal forests might enhance indirect soil carbon losses through accelerated decomposition because decreased albedo and transpiration may lead to warmer and moister soils. In the 1.5 growing seasons following the 1999 Frostfire burn, however, soil respiration has not recovered from its initial 20-50% decline. The loss of root respiration likely more than accounted for this decline, suggesting that a rapid increase in heterotrophic decomposition may have partially offset that loss. We sought evidence for such an increase by examining mass loss rates of a standard substrate in burned and unburned mixed hardwood (MH) and closed-canopy black spruce (CBS) forests. We placed replicate clusters of birch tongue depressors on the soil surface (FF) and at the organic/mineral soil interface (O/A), then retrieved them one year later. Fire increased mass-loss rates in FF by 30% in both CBS and MH plots, and by 50% in CBS plots at the O/A interface (p<0.05). Mass loss rates at the O/A interface in MH plots were more than twice as high as anywhere else, but burning decreased mass loss rates by 15% (p<0.05). Foliar litter decomposition rates at the O/A interface in the burned hardwood plots also were significantly lower than in unburned plots. Thus while fire usually enhanced decomposition rates, fire slowed overall decomposition rates in MH stands. These were the same stands where our previous results showed the greatest fire-caused decrease in soil respiration. From this we infer that fire can increase or decrease heterotrophic carbon losses depending on its overall effects on forest floor characteristics.

KEY WORDS: carbon balance, soil respiration