PARENT SESSION
Symposium 19: Spatial nonlinearities and cross scale interactions: Cascading effects in the Earth System
Organized by: DC Peters and BT Bestelmeyer
Thursday, August 11, 1:30 PM - 5:00 PM, Meeting Room 517 A, Level 5, Palais des congrès de Montréal
Cross-scale patterns of forest fire synchrony in southwestern North America.
Falk, Donald*,, Swetnam, Thomas,
ABSTRACT- Spatial and temporal patterns of fire occurrence in the mountains of southwestern North America are governed by scale-dependent processes. Depending on local topography, weather, and fuels, fires can spread readily within forest stands and watersheds. However, climate is the only mechanism known to synchronize fire events among mountain ranges isolated by barriers to fire spread. The primary data for our study are derived from a network of 135 tree-ring based fire history chronologies throughout the Sky Island mountains of southwestern North America, in which we examine the relative influence of regional climate entrainment of natural fire regimes separate from local mechanisms of fire spread. Most of these chronologies extend several hundred years before present, offering a detailed record with long temporal extent, annual resolution and high spatial precision. We analyze fire scar chronologies composited across a range of spatial scales from forest stands and watersheds (101 - 103 ha) to whole mountain ranges (104 - 105 ha) and sub-regional and regional scales (105 - 106 ha). For each year in the period of common record (approximately AD 1600 to 1900), we plot fire occurrence at multiple spatial scales, and compute indices of similarity and parameters of the event-area function, a direct measure of spatio-temporal synchrony. Slopes of the event-area function are shallowest during periods when cross-scale fire synchrony is highest. Among mountain ranges, synchronous fire years reflect interactions of dominant regional climate factors, including the El Niño Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and the Atlantic Multidecadal Oscillation (AMO). Fire events can be locally widespread during years when the regional fire record is asynchronous, indicating conditions in which local processes dominate. At the regional scale, periods of maximal cross-scale synchrony tend to coincide with extreme, inverse climate phases of the PDO and AMO, a configuration that tends to enhance the effects of interannual ENSO variability. Our results demonstrate that multi-scale assessment of ecosystem processes can isolate mechanisms operating at various spatial and temporal scales.
Key words: fire regime, fire-climate relationship, multiscale analysis, dendroecology