PARENT SESSION
Contributed Oral Session 24: Disturbance Ecology: Management; Response to Fire
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 516 D, Level 5, Palais des congrès de Montréal

Ecological Memory: Do pre-fire disturbances influence post-fire nitrogen cycling and regeneration?

Rumbaitis-del Rio, Cristina ^{*,1, 2}, Wessman, Carol ¹, ¹ University of Colorado, Boulder, CO² Columbia Univerisity Earth Institute, New York, NY

ABSTRACT- This study evaluates the hypothesis that prior disturbance conditions modify the initial effects of a stand-replacing wildfire on soil nitrogen (N) availability, net N mineralization rates, vegetation cover, and seedling density. The study area is a northern Colorado coniferous subalpine forest that was disturbed by catastrophic windthrow in 1997, salvage-logging in 1999, and wildfire in 2002. In the first two growing seasons after the wildfire, newly established conifer seedlings were found in previously undisturbed burned areas, but not in burned blowdown or burned salvage-logged areas, possibly reflecting the lack of seed trees as a result of pre-fire disturbances. A greater abundance of invasive species were found in previously disturbed burned areas relative to previously undisturbed burned areas. Fire increased inorganic N availability in the top 10 cm of soil by a factor of five, and decreased soil carbon and N concentrations by 75% and 60%, respectively. However, net N mineralization rates did not differ between burned and unburned areas, or between burned areas and measurements made in the two years preceding the wildfire. There were few differences in edaphic variables among burned areas as a result of pre-fire disturbance history. Only soil carbon concentrations were significantly lower in burned blowdown areas than in other burned areas, possibly as a result of greater fire intensity in burned blowdown areas. This study suggests that initially, the effects of a severe fire tend to erase the effects of previous disturbances on soil properties. However, conspicuous vegetation differences among burned sites suggest that, with time, the effects of disturbances that occurred prior to the wildfire may become even more pronounced.

Key words: large infrequent disturbance, nutrient cycling, regeneration, disturbance interactions