Aim The historical variability of fire regimes must be understood in the context of drivers of the occurrence of fire operating at a range of spatial scales from local site conditions to broad-scale climatic variation. In the present study we examine fire history and variations in the fire regime at multiple spatial and temporal scales for subalpine forests of Engelmann spruce-subalpine fir (Picea engelmannii, Abies lasiocarpa) and lodgepole pine (Pinus contorta) of the southern Rocky Mountains.Location The study area is the subalpine zone of spruce-fir and lodgepole pine forests in the southern sector of Rocky Mountain National Park (ROMO), Colorado, USA, which straddles the continental divide of the northern Colorado Front Range (40°20¢ N and 105°40¢ W).Methods We used a combination of dendroecological and Geographic Information System methods to reconstruct fire history, including fire year, severity and extent at the forest patch level, for c. 30,000 ha of subalpine forest. We aggregated fire history information at appropriate spatial scales to test for drivers of the fire regime at local, meso, and regional scales. ResultsThe fire histories covered c. 30,000 ha of forest and were based on a total of 676 partial cross-sections of fire-scarred trees and 6152 tree-core age samples. The subalpine forest fire regime of ROMO is dominated by infrequent, extensive, stand-replacing fire events, whereas surface fires affected only 1-3% of the forested area.Main conclusions Local-scale influences on fire regimes are reflected by differences in the relative proportions of stands of different ages between the lodgepole pine and spruce-fir forest types. Lodgepole pine stands all originated following fires in the last 400 years; in contrast, large areas of spruce-fir forests consisted of stands not affected by fire in the past 400 years. Meso-scale influences on fire regimes are reflected by fewer but larger fires on the west vs. east side of the continental divide. These differences appear to be explained by less frequent and severe drought on the west side, and by the spread of fires from lower-elevation mixed-conifer montane forests on the east side. Regional-scale climatic variation is the primary driver of infrequent, large fire events, but its effects are modulated by local-and meso-scale abiotic and biotic factors. The low incidence of fire during the period of fire-suppression policy in the twentieth century is not unique in comparison with the previous 300 years of fire history. There is no evidence that fire suppression has resulted in either the fire regime or current forest conditions being outside their historic ranges of variability during the past 400 years. Furthermore, in the context of fuel treatments to reduce fire hazard, regardless of restoration goals, the association of extremely large and severe fires with infrequent and exceptional drought calls into question the future effectiveness of tree thinning to mitigate fire hazard in the subalpine zone.

Understanding the effect of variation in climate on large‐fire occurrence across broad geographic areas is central to effective fire hazard assessment. The El Niño– Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) affect winter temperature and precipitation regimes in western North America through mid‐latitude teleconnections. This study examines relationships of ENSO and the PDO to drought‐induced fire occurrence in subalpine forests of three study areas across the Rocky Mountains: Jasper National Park (JNP, northern Rockies), Yellowstone National Park (YNP, central Rockies) and Rocky Mountain National Park (RMNP, southern Rockies) over the 1700–1975 period. Large‐scale climatic anomalies captured by ENSO (NIÑO3) and PDO indices had differential effects on large‐fire occurrence across the study areas. Superposed epoch analysis (SEA) showed that large fires in RMNP occurred during extreme La Niña years, while the PDO, although predominantly negative during fire years, did not depart significantly from the mean. In YNP and JNP, neither ENSO nor PDO indices were significantly different from the mean during large‐fire years, although fires tended to occur during El Niño and positive PDO years. Constructive phases (years of combined warm [positive] or cool [negative] phases) of ENSO and the PDO were significantly associated with large‐fire occurrence across the Rockies, even though these large‐scale climatic anomalies were not significant when considered singly in SEAs. Combined warm phases (positive PDO during El Niño) co‐occurred with large fires in the central and northern Rockies, while the combined cool phases (negative PDO during La Niña) appeared to promote large fires in the southern Rockies. Almost 70% of large fires in RMNP burned during La Niña events that coincided with a negative PDO, although these phases co‐occurred during only 29% of the 1700– 1975 period. Spatial teleconnection patterns between drought, PDO and ENSO across western North America independently support the sign and strength of relationships between these climatic anomalies and subalpine fire occurrence along a broad north–south gradient of the Rockies. Forecasts of ENSO that are dependent on the expected PDO phase suggest promise for fire hazard prediction across the West.

Aim An understanding of past relationships between fire occurrence and climate variability will help to elucidate the implications of climate-change scenarios for future patterns of wildfire. In the present study we investigate the relationships between subalpine-zone fire occurrence and climate variability and broad-scale climate patterns in the Pacific and Atlantic Oceans at both interannual and multidecadal time-scales.Location The study area is the subalpine zone of Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa), and lodgepole pine (Pinus contorta) in the southern sector of the Rocky Mountain National Park, which straddles the continental divide of the northern Colorado Front Range.Methods We compared years of widespread fire from AD 1650 to 1978 for the subalpine zone of southern Rocky Mountain National Park, with climate variables such as measures of drought, and indices such as the El Niño-Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and the Atlantic Multidecadal Oscillation (AMO).Results Years of extensive subalpine-zone fires are significantly related to climate variability, phases of ENSO, the PDO, and the AMO, as well as to phase combinations of ENSO, the PDO, and the AMO at both interannual and centennial time-scales.Main conclusions Years of extensive fires are related to extreme drought conditions and are significantly related to the La Niña phase of ENSO, the negative (cool) phase of the PDO, and the positive (warm) phase of the AMO. The co-occurrence of the phase combination of La Niña-negative PDO-positive AMO is more important to fire occurrence than the individual influences of the climate patterns. Low-frequency trends in the occurrence of this combination of climate-pattern phases, resulting from trends in the AMO, are the primary climate pattern associated with periods of high fire occurrence (1700-89 and 1851-1919) and a fire-free period (1790-1850). The apparent controlling influence of the AMO on drought and years of large fires in the subalpine forests of the Colorado Front Range probably applies to an extensive area of western North America.

Abstract. The Andes span a length of 7000 km and are important for sustaining regional water supplies. Snow variability across this region has not been studied in detail due to sparse and unevenly distributed instrumental climate data. We calculated snow persistence (SP) as the fraction of time with snow cover for each year between 2000 and 2016 from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite sensors (500 m, 8-day maximum snow cover extent). This analysis is conducted between 8 and 36 • S due to high frequency of cloud (> 30 % of the time) south and north of this range. We ran Mann-Kendall and Theil-Sens analyses to identify areas with significant changes in SP and snowline (the line at lower elevation where SP = 20 %). We evaluated how these trends relate to temperature and precipitation from Modern-Era Retrospective Analysis for Research and Applications-2 (MERRA2) and University of Delaware datasets and climate indices as El Niño-Southern Oscillation (ENSO), Southern Annular Mode (SAM), and Pacific Decadal Oscillation (PDO). Areas north of 29 • S have limited snow cover, and few trends in snow persistence were detected. A large area (34 370 km 2 ) with persistent snow cover between 29 and 36 • S experienced a significant loss of snow cover (2-5 fewer days of snow year −1 ). Snow loss was more pronounced (62 % of the area with significant trends) on the east side of the Andes. We also found a significant increase in the elevation of the snowline at 10-30 m year −1 south of 29-30 • S. Decreasing SP correlates with decreasing precipitation and increasing temperature, and the magnitudes of these correlations vary with latitude and elevation. ENSO climate indices better predicted SP conditions north of 31 • S, whereas the SAM better predicted SP south of 31 • S.

Aim In this study we examine fire history (i.e. c. 500 yr bp to present) of Araucaria-Nothofagus forests in the Andes cordillera of Chile. This is the first fire history developed from tree rings for an Araucaria-Nothofagus forest landscape.Location The fire history was determined for the Quillelhue watershed on the north side of Lanin volcano in Villarrica National Park, Chile. The long-lived Araucaria araucana was commonly associated with Nothofagus pumilio and N. antarctica in more mesic and drier sites respectively.Methods Based on a combination of fire-scar proxy records and forest stand ages, we reconstructed fire frequency, severity, and the spatial extent of burned areas for an c. 4000 ha study area. We used a composite fire chronology for the purpose of determining centennial-scale changes in fire regimes and comparing the pre-settlement (pre-1883) and post-settlement fire regimes. In addition, we contrasted Araucaria and Nothofagus species as fire-scar recorders.