Fire history and climate influences on Pilgerodendron uviferum (Guaitecas cypress) in the coastal temperate rainforests of southern South America

Background/Question/Methods
The temperate rainforests of southwestern South America (ca. 42° S) have experienced widespread wildfires in recent history. However, there is no information clarifying the natural role and scale of modern fires in this region. One of the dominant tree species in this region is Pilgerodendron uviferum; an endemic, slow growing, long-lived species, and the southernmost conifer worldwide. Due to a recent history of massive burning and logging P. uviferum is listed under CITES (Appendix I) and IUCN (Vulnerable).

What is the fire history of P. uviferum coastal temperate rainforests and the relative influences of climatic variability and trends, and human activities on fire occurrence on the Chiloé Island in southern Chile for the past 300 years?

Fire history was reconstructed using tree cores and fire scars sampled in nine sites in Chiloé. The potential influence of low- and high-frequency climatic variability on the occurrence of fire (both extensive and small fires) was investigated using the instrumental climate record, existing and new tree-ring chronologies, and published tree-ring reconstructions of indices of broad-scale climatic anomalies.

Results/Conclusions
A tree-ring fire record based on two new chronologies and 90 fire scars from P. uviferum forests in Chiloé shows the presence of large fires prior to the European colonization period (prior to ~1890s). An increase in fire frequency occurred primarily during the past four decades (post ~1970s), and secondarily during the last decades of the European colonization period (ca. ~1940s).

Preliminary results show widespread fire years are negatively (positively) correlated with spring and summer precipitation (temperature) of the current fire season. These conditions are associated with interannual climatic variability, driven by broad-scale anomalies in Pacific sea-surface temperatures (ENSO). Years of high fire activity tend to follow El Niño events and were more frequent during the drier 1977-2000 period.

Widespread fires are a natural yet infrequent component of the historical fire regimes of these coastal temperate rainforests on the Chiloé Island (even prior to the widespread European settlement). However, higher fire activity coincides with recent, more severe, interannual droughts that have been facilitated by a decadal trend towards warmer temperatures across the region since the mid-1970s.