Ecological and climatic controls of modern wildfire activity patterns across southwestern South America

Abstract

Abstract. Understanding how patterns of wildfire activity across biomes are shaped by heterogeneity in biomass resources to burn and atmospheric conditions conducive to burning is a high research priority in the context of global environmental change. Along a latitudinal gradient (25 to 568 S) from semi-arid scrublands through Mediterranean-type vegetation to wet forests in southwestern South America (SSA) we analyzed influences of mean climate and interannual climate variability on fire activity using documentary fire records from 1984 to 2008. We identified large regions with common temporal variability in annual area burned, related this variability to local interannual climate variability and in turn to modes of the major tropical and extratropical climate drivers of the southern hemisphere-El Niño-Southern Oscillation (ENSO) and the Antarctic Oscillation (AAO). Differences in fire activity response to interannual climate variability were related to the relative influences of available biomass to burn, and to weather effects on amounts of fine fuels and fuel moisture conditions. The pattern of average fire activity along this latitudinal moisture/productivity gradient corresponds well with the varying constraints model. This model predicts low fire activity towards the arid extreme due to reduced burnable biomass and again towards the humid extreme due to infrequent weather suitable for drying fuels, and predicts a broad zone of high fire activity at intermediate locations where resources to burn are abundant in all years and fuel moisture dries under reliably dry summer conditions. The dominant influence on interannual climate variability is AAO, which explained most of the variability in fire activity both by reducing seasonal precipitation in mesic and wet forests where fire is dependent on infrequent drought and by enhancing fine fuel production in Mediterranean-type vegetation where fuel amount and continuity constrain fire activity. In the context of the drying and warming trends in SSA related to the continued positive anomaly in AAO, our results underscore the importance of the varying constraints on fire activity and modulation of fire-climate relationships by different vegetation types, which is a much needed step toward developing fire projections under future climate.

Habitat distribution modeling reveals vegetation flammability and land use as drivers of wildfire in SW Patagonia

“…The peak probability of fire at intermediate precipitation levels observed in all study areas is consistent with biomass limitation to fire in the drier areas and the fuel desiccation limitation towards the moister end of the gradient Bradstock 2007, Krawchuk andMoritz 2011). The three study areas that include xeric ecosystem types (CL, AY, MA) exhibit sharply reduced probabilities of fire at the dry extremes where fuel continuity in the steppe vegetation is limiting to fire spread (Kitzberger et al 1997, Holz et al 2012b. Towards the moist end of gradients, fire probability drops sharply in all study areas with the exception of CL; however, if we consider CC as a continuation of the precipitation gradient of CL it becomes clear that fire probability also drops at the moister extreme of this extended gradient (Fig.…”

“…1). These four regions represent a north-to-south gradient of decreasing temperature and annually less frequent weather conditions suitable for wildfire (Holz et al 2012b). The three northern study areas are separated from the southernmost study area by ca.…”

“…After the large-scale forest v www.esajournals.org burning period lasting from the late 1800s to the mid-1900s, depending on the region, national policies of fire suppression were adopted and continue to be implemented with varying degrees of effectiveness across the study area (Veblen et al 2008). Throughout southwestern Patagonia, although humans are the most common source of ignitions, fire spread and variability in annual area burned is determined primarily by annual climate variability (Holz et al 2012b). …”

Effects of volcanic and hydrologic processes on forest vegetation: Chaitén Volcano, Chile

“…Annual precipitation varies by a factor of 2 to 3 from the coast to the crest of the Andes, but sparse records limit knowledge of precipitation distribution; cold spells occur year-round (Garreaud, 2009). Forest fires are an infrequent, but important non-volcanic disturbance type in the region; only rarely do fuels dry sufficiently for easy spread of fire (Holz et al, 2012).…”

Análisis espacio-temporal de incendios forestales en la región del Maule, Chile

“…De acuerdo a estudios recientes, esta relación se explicaría por inviernos y primaveras más lluviosas en años "Niño" que favorecerían la producción y acumulación de combustible, generando condiciones para la ignición y propagación de incendios, no en la misma temporada sino en la temporada siguiente, especialmente en temporadas más secas de lo normal, asociadas al fenóme-no de la Niña (González et al 2011). Adicionalmente, la Oscilación Antártica (AAO), que tiene una gran influencia en la variabilidad climática interanual, es indicada -junto a El Niño Oscilación del Sur (ENSO)-como un factor que también explicaría la actividad de incendios en esta región geográfica (Holz et al 2012).…”