PARENT SESSION
Oral Session #6: Disturbance Ecology of Forests: Fire, Patterns. Presiding: R. DeFries.
Monday, August 6, 2001. 8:00 AM to 12:00 PM. Hall of Ideas F.
Impacts of forest floor disturbance on vegetation and nutrient dynamics in clearcut and partial-cut stands.
FREY, BRENT1, LIEFFERS, VICTOR1, MUNSON, ALISON2, 1 2
ABSTRACT- The interactive effects of harvest type and forest floor disturbance on vegetation and nutrient dynamics were evaluated in the boreal mixedwood of Alberta. The experiment used a split-plot design with harvest types of clearcut and partial-cut, and forest floor disturbances of burn, mix (organic matter mixed with mineral soil), scalp (forest floor removed), mound (inverted mineral-cap) and control. Ion exchange resins were used to assess availability of NO3-N, NH4-N, Ca, Mg and K in all disturbances. A general increase in nutrient availability was noted with increased tree removal, although this varied with forest floor disturbance. Overall, NH4-N, Ca, Mg and K were higher in clearcuts while NO3-N was higher in partial-cuts. Within forest floor disturbances, burns had the highest levels of NH4-N and NO3-N in both harvest types, while controls had the lowest NO3-N levels in both harvest types. Ca and Mg were highest, but K lowest, in the scalps in both harvest types. The ratio of NH4-N: NO3-N was greatest in clearcuts and lowest in burns suggesting lower relative rates of nitrification or higher NO3-N uptake in clearcuts, and relatively higher nitrification or reduced NO3-N uptake in burns. Vegetation response was evaluated by species, percent cover and height for all shrubs, Populus spp. and Epilobium angustifolium. Burns were dominated by E. angustifolium and scalps by Populus spp, while mix and mound disturbances suppressed vegetation significantly.
KEY WORDS: forest, nutrient, disturbance, understory vegetation