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This study investigates the influence of climatic variability on subalpine forest fire occurrence in western Colorado during the AD 1600-2003 period. Interannual and multidecadal relationships between fire occurrence and the El Nino Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO) were examined, in addition to the effects of phase interactions among these oscillations. Fires occurred during short-term periods of significant drought and extreme cool (negative) phases of ENSO and PDO and during positive departures from mean AMO index. At longer time scales, fires exhibited 20-year periods of synchrony with the cool phase of the PDO, and 80-year periods of synchrony with extreme warm (positive) phases of the AMO. Years of combined positive AMO and negative ENSO and PDO phases represent 'triple whammies' that significantly increased the occurrence of drought-induced fires. Fires were synchronous with this phase combination over 0-30 year periods and distinctly asynchronous with the opposite phase combination. Overall, because fires are synchronous at supra-annual to multidecadal time scales with warm AMO events, particularly when combined with cool ENSO and PDO phases, this suggests that we may be entering a qualitatively different fire regime in the next few decades due to the recent shift in 1998 to a likely long-term warm AMO phase. Although uncertainty remains regarding the effects of C[O.sub.2]-induced warming at regional scales, given the multidecadal persistence of the AMO there is mounting evidence that the recent shift to the positive phase of the AMO will promote higher fire frequencies in the region. Key words: AMO; climate; ENSO; fire ecology; multidecadal; PDO; Rocky Mountains; subalpine forests.

Byline: A. J. Pitman (1), G. T. Narisma (2), J. McAneney (3) Abstract: We explore the impact of future climate change on the risk of forest and grassland fires over Australia in January using a high resolution regional climate model, driven at the boundaries by data from a transitory coupled climate model. Two future emission scenarios (relatively high and relatively low) are used for 2050 and 2100 and four realizations for each time period and each emission scenario are run. Results show a consistent increase in regional-scale fire risk over Australia driven principally by warming and reductions in relative humidity in all simulations, under all emission scenarios and at all time periods. We calculate the probability density function for the fire risk for a single point in New South Wales and show that the probability of extreme fire risk increases by around 25% compared to the present day in 2050 under both relatively low and relatively high emissions, and that this increases by a further 20% under the relatively low emission scenario by 2100. The increase in the probability of extreme fire risk increases dramatically under the high emission scenario by 2100. Our results are broadly in-line with earlier analyses despite our use of a significantly different methodology and we therefore conclude that the likelihood of a significant increase in fire risk over Australia resulting from climate change is very high. While there is already substantial investment in fire-related management in Australia, our results indicate that this investment is likely to have to increase to maintain the present fire-related losses in Australia. Author Affiliation: (1) Climate Change Research Centre, The University of New South Wales, Sydney, NSW, 2052, Australia (2) Center for Sustainability and the Global Environment, Nelson Institute for Env. Studies, University of Wisconsin, Madison, 1710 University Avenue, Madison, WI, 53726, USA (3) Risk Frontiers, Macquarie University, Sydney, NSW, 2109, Australia Article History: Registration Date: 29/01/2007 Received Date: 30/06/2005 Accepted Date: 15/11/2006 Online Date: 17/03/2007

Climate influences forest structure through effects on both species demography (recruitment and mortality) and disturbance regimes. Here, I compare multi-century chronologies of regional fire years and tree recruitment from ponderosa pine forests in the Black Hills of southwestern South Dakota and northeastern Wyoming to reconstructions of precipitation and global circulation indices. Regional fire years were affected by droughts and variations in both Pacific and Atlantic sea surface temperatures. Fires were synchronous with La Ninas, cool phases of the Pacific Decadal Oscillation (PDO), and warm phases of the Atlantic Multidecadal Oscillation (AMO). These quasi-periodic circulation features are associated with drought conditions over much of the western United States. The opposite pattern (El Nino, warm PDO, cool AMO) was associated with fewer fires than expected. Regional tree recruitment largely occurred during wet periods in precipitation reconstructions, with the most abundant recruitment coeval with an extended pluvial from the late 1700s to early 1800s. Widespread even-aged cohorts likely were not the result of large crown fires causing overstory mortality, but rather were caused by optimal climate conditions that contributed to synchronous regional recruitment and longer intervals between surface fires. Synchronous recruitment driven by climate is an example of the Moran effect. The presence of abundant fire-scarred trees in multi-aged stands supports a prevailing historical model for ponderosa pine forests in which recurrent surface fires affected heterogenous forest structure, although the Black Hills apparently had a greater range of fire behavior and resulting forest structure over multi-decadal time scales than ponderosa pine forests of the Southwest that burned more often. Key words: Atlantic Multidecadal Oscillation; crossdating; dendrochronology; El-Nino Southern Oscillation; fire history; fire regime; Pacific Decadal Oscillation; precipitation variation.

Spatial heterogeneity of vegetation types and the abiotic environment can influence the occurrence and spread of wildfires, but in some landscapes the importance of these effects varies under conditions of severe fire weather. In the northern Patagonian landscape of forests and shrublands we examined the effects of vegetation type (tall forest vs. tall shrubland) and abiotic factors (elevation, topography, and precipitation) on fire occurrence at a broad scale and on fire spread at a fine scale. We used satellite images (1985-1999) and aerial photography (1950-1999) to map fires in relation to pre-burn vegetation type and abiotic factors. Fire extent is greatest at intermediate elevations and locations of intermediate precipitation. Fire extent is limited by lack of fuel quantity at the lower end of the precipitation gradient and by infrequent or insufficient fuel desiccation at the upper end. Tall shrublands are proportionally more affected by fire than are adjacent mesic forests of Nothofagus dombeyi and N. pumilio. Patches of subalpine forests often tend to serve as natural fire breaks, except under the most severe fire weather. Tall shrublands are dominated by species that resprout vigorously so that fuels quickly recover. In contrast, forests are dominated by species dependent on seed reproduction that sometimes fails after severe fires so that shrublands tend to replace burned forests. The greater propensity of shrublands to burn is a positive feedback that is favorable to fire and that accelerates the replacement of forest by shrublands. Infrequently occurring severe weather is important in the burning of otherwise relatively fire-resistant subalpine forests. Past burning, associated both with drought and early forest clearing, expanded shrublands at the expense of forests so that in the modern landscape an increase in anthropogenic ignitions and the positive feedback of fire and shrublands are synergistically accelerating conversion from forest to shrubland. Key words: fire ecology; landscape ecology; logistic regression model; Nothofagus; Patagonia; shrub resprouting; spatial analysis.

A 21-yr gridded monthly fire-starts and acres-burned dataset from U.S. Forest Service, Bureau of Land Management, National Park Service, and Bureau of Indian Affairs fire reports recreates the seasonality and interannual variability of wildfire in the western United States. Despite pervasive human influence in western fire regimes, it is striking how strongly these data reveal a fire season responding to variations in climate. Correlating anomalous wildfire frequency and extent with the Palmer Drought Severity Index illustrates the importance of prior and accumulated precipitation anomalies for future wildfire season severity. This link to antecedent seasons' moisture conditions varies widely with differences in predominant fuel type. Furthermore, these data demonstrate that the relationship between wildfire season severity and observed moisture anomalies from antecedent seasons is strong enough to forecast fire season severity at lead times of one season to a year in advance.

Those of us who have lived long in southern California are no strangers to fire. 'Every 20 or 30 years, dating back to the early 1800s, large swaths of the [...]