PARENT SESSION
Oral Session #7: Disturbance in Forests: Fire, wind, and other.
Presiding: G. Murray
Monday, August 5. 8:00 AM to 11:30 AM. Cochise Meeting Room, TCC.

Synergistic influences of fire and spruce beetle disturbances on a Colorado subalpine forest.

Kulakowski, Dominik^*,1, Veblen, Thomas¹, Bebi, Peter², ¹ Department of Geography, Boulder, CO² Swiss Federal Institute for Snow and Avalanche Research SLF, Davos, Switzerland

ABSTRACT- There is increasing research attention being given to the role of interactions among natural disturbances in ecosystem processes. We studied the interactions between fire and spruce beetle (Dendroctonus rufipennis) disturbances in a Colorado subalpine forest. The central questions of this research were: 1) How does fire history influence stand susceptibility to beetle outbreak? And conversely, 2) How does prior occurrence of a beetle outbreak influence stand susceptibility to subsequent fire? We reconstructed the spatial disturbance history in a c. 4,600 ha area by first identifying distinct patches in the landscape on aerial photographs, and then in the field by determining the disturbance history of each patch by dating ages of post-fire cohorts, fire scars, dates of mortality of dead trees, and releases on remnant trees. We used a geographic information system (GIS) to overlay disturbance by fire and spruce beetle. The fire regime was characterized by large, infrequent, severe fires. The study area was also affected by a severe spruce beetle outbreak in the 1940s and a subsequent low-severity fire. Stands affected by stand-initiating fire in the late 19th century were less affected by the beetle outbreak than older stands, but stands which initiated after fire in 1796 and c. 1700 and old-growth stands did not show differential susceptibility to beetle outbreak. This suggests that stand susceptibility to beetle outbreak does not increase linearly with stand age, but rather that there is a threshold, or relatively narrow span of years, in forest development during which stand susceptibility to Dendroctonus greatly increases. Following the beetle outbreak, stands less affected by the beetle outbreak were more affected by fire than stands more severely affected by the outbreak. The landscape mosaic of this subalpine forest was strongly influenced by the interactions between fire and insect disturbances.

KEY WORDS: dendrochronology, disturbance, interactions, legacies