Fire history of Araucaria-Nothofagus forests in the Andean cordillera of South-Central Chile.

摘要

Fire history was investigated in relation to its role in stand development patterns and in the context of inter-annual variability of climate and changes in human land-use in Villarrica National Park, Chile. Araucaria-Nothofagus forests are characterized by a mixed fire regime that includes surface and stand-replacing fires. This type of mixed-severity fire regime and particular species traits and life history attributes have a strong influence on the subsequent post-fire vegetation responses and recovery patterns. Due to the high frequency of fires in relation to the life span of the tree species, the catastrophic regeneration mode is the dominant pattern in forest regeneration dynamics.; Changes in human land-use had a strong influence on the fire regimes in the Araucarian region. A dramatic increase in fire occurrence is evident in the fire record during Euro-Chilean settlement (after 1880s) when compared to the Native American period. Both the current vegetation mosaic and the conspicuous increases in fire occurrence during the 1900s resulted from the massive burning and livestock grazing activities carried out by the settlers. Thus, the current Araucaria-Nothofagus forested landscape is largely dominated by early and mid-successional stands younger than 150 years. Also, large areas formerly dominated (c. 60 years ago) by relatively dense forests today are sparcely vegetated or covered by dense bamboo thickets due largely to severe and repeated burning and heavy grazing.; Fire occurrence is strongly associated with regional inter-annual drought conditions connected with the coupled effects of El Niño-Southern Oscillation (ENSO) events and variability in the southeast Pacific anticyclone. Years of widespread burning are associated with warmer and drier climatic conditions during the current year. Also, years of extensive fire activity tend to be favored by preceding years of dry conditions that may predispose the vegetation to fire occurrence. Variability in the El Niño-Southern Oscillation and its strong influence on large-scale atmospheric features is an important force promoting fire. Years of high fire activity coincide with warm and dry summers following El Niño years.