CSIRO PUBLISHING International Journal of Wildland Fire 2008, 17, 724–741 www.publish.csiro.au/journals/ijwf The historical range of variability of fires in the Andean–Patagonian Nothofagus forest region Thomas T. Veblen A,E , Thomas Kitzberger B , Estela Raffaele B , Mónica Mermoz C , Mauro E. González D , Jason S. Sibold A and Andrés Holz A A Department of Geography, University of Colorado, Boulder, CO 80309, USA. B Consejo Nacional de Investigaciones Científicas y Técnicas de Argentina and Laboratorio Ecotono (CONICET)-Universidad Nacional del Comahue, Quintral 1250, Bariloche, 8400, Argentina. C Administración de Parques Nacionales,Vicealmirante O’Conner 1188, Bariloche, 8400, Argentina. D Facultad de Ciencias Forestales, Universidad Austral de Chile,Valdivia, Casilla 567, Chile. E Corresponding author. Email: veblen@colorado.edu Abstract. The present synthesis addresses key questions about several extreme fire events that occurred in the Nothofagus forest region of southern Argentina and Chile in the late 1990s and early 2000s: (1) are there historical precedents for the extent and severity of these recent wildfires? (2) To what extent can large, severe fires be attributed to influences from modern humans, either indirectly through land-use practices or directly through ignition? (3) What are the relationships of these fire events to interannual climatic variability and trends? (4) What are the medium-term ecological consequences of these fire events, particularly in terms of the resiliency of the burned ecosystems? Historic fire regimes vary greatly across the different ecosystem types in the southern Andean region, and the tree-ring record shows that before the 20th century, large severe fires also played a significant ecological role in shaping even the wettest forests. Recent severe droughts at an annual time scale have been facilitated by a trend towards higher temperatures since the mid-1970s. In large parts of the region, the risk of wildfire ignition and spread has been exacerbated by increases in lightning associated with higher temperatures, increased ignitions associated with exurban development, and conversion of less flammable native vegetation to more flammable plantations of exotic conifers. Additional keywords: Argentina, Chile, fire ecology, fire history. Introduction Reports of large wildfires in many parts of the world since the early 1980s, including in temperate and tropical ecosystems, have received substantial attention in the popular media and contributed to a widespread view among resource managers and ecological researchers that these large, severe fires are symp- tomatic of fire regimes that have been altered either directly or indirectly by modern humans (Myers 2006; Shlisky et al. 2007). Public concern about large fire events in recent decades is driven by the perception that recent wildfires in many regions have been unusually extensive or burned with unusual severity due to either land-use practices (e.g. fire suppression or logging) or climate change. Initial steps to create a knowledge base for develop- ing locally appropriate integrated fire management (as in Myers 2006) are to assess the ecological role of wildfire in the area of interest and to determine if historical fire regimes have been altered by land-use practices and climate change (Shlisky et al. 2007). Thus, our objective in the present review is to synthe- sise existing research to assess the precedents and consequences of extreme fire events in the Nothofagus forest region of the southern Andes (south of ∼38 ◦ S). A key element in examining the issues above, and in inform- ing fire policy discussions, is a sound understanding of the historical range of variability of local fire regimes and associated ecosystem conditions. In the modern paradigm of ‘ecosystem management’(Christensen et al. 1996), the focus of management is on sustaining ecosystems, while also sustaining yields of par- ticular ecosystem products and services. For resource managers, it is important to know the range of critical ecological processes and conditions that have characterised particular ecosystems over specified time periods and under varying degrees of human influences. This range of critical processes and ecosystem condi- tions has been termed natural range of variability or historical range of variability (HRV). HRV is viewed as a coarse-filter guide in ecosystem management because it identifies the pro- cesses and conditions that in the recent past (i.e. the past several centuries) have sustained ecosystem function, and helps man- agers set limits to desired future conditions (Landres et al. 1999). In the present synthesis, the concept of HRV is used to examine the role played by fire historically and in modern times (i.e. after 1900) in shaping ecosystem structures in the Nothofagus forest region of southern South America. © IAWF 2008 10.1071/WF07152 1049-8001/08/060724