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Fire history of a naturally fragmented landscape in central Oregon

Summary: Fire history of a naturally fragmented landscape in
central Oregon
Karen B. Arabas, Keith S. Hadley, and Evan R. Larson
Abstract: We examined the fire history of 11 forest isolates surrounded by lava flows (kipukas) in central Oregon to
determine historical differences in fire regimes between kipukas and the surrounding forest, and the role of spatial and
environmental variables in fire occurrence. Tree-ring analysis and statistical comparisons show that historical agency re-
cords underestimate the number of fires based on the incidence of fire scars. Fires occurred more frequently on
kipukas, were typically smaller, and were predominantly lightning-initiated. Except for three widespread fires, fires on
kipukas and in the surrounding forest were largely asynchronous. The mean fire-return interval (MFRI) in the surround-
ing forest decreased following Euro-American settlement and increased on the kipukas with spot-fire removal. This
suggests either that forest management and fire exclusion in the surrounding forest decreased fire spread to the
kipukas, or that most fires originated on the kipukas. MFRI correlates strongly with distance to the nearest kipuka and
a distance-weighted isolation index. The number of fires correlates with elevation change and distance to the nearest
kipuka. Fire in naturally fragmented landscapes is influenced by the spatial arrangement of patches, environmental con-
ditions, and human activities. Reconstructing fire histories from forest isolates in the context of their mainland counter-
parts may have methodological advantages and theoretical implications for forested landscapes characterized by human-
imposed insularity.
Résumé : Les auteurs ont étudié l'historique des feux dans 11 îlots de forêt entourés de coulées de lave (kipukas) dans
le centre de l'Oregon afin de déterminer les différences passées dans le régime des feux entre les kipukas et la forêt
environnante, ainsi que le rôle des variables spatiales et environnementales dans l'occurrence des feux. L'analyse den-


Source: Arabas, Karen - Environmental and Earth Sciences Department, Willamette University


Collections: Environmental Sciences and Ecology; Geosciences