Tree-ring, stratigraphic, and palynological evidence for volcanic and climatic controls on Fitzroya cupressoides forests in southern Chile over the last  5700 years.
by
Alexia Wolodarsky-Franke
Instituto de Silvicultura, Facultad de Ciencias Forestales, Universidad Austral de Chile, Casilla 567, Valdivia, Chile
Coauthors: Patricio I. Moreno (Depto. de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile), Antonio Lara (Instituto de Silvicultura, Facultad de Ciencias Forestales, Universidad Austral de Chile, Valdivia, Chile) Mario Pino (Instituto de Silvicultura, Facultad de Ciencias Forestales, Universidad Austral de Chile, Valdivia, Chile) and Gustavo Villarosa (CRUB, Universidad Nacional del Comahue, Argentina)

We report a 5666-year tree-ring composite chronology based on Fitzroya cupressoides samples collected on the foothills of Volcán Apagado (VA) (41º35’S; 72º30’W), southern Chile (Wolodarsky-Franke, 2002). This record, which constitutes the longest chronology in the Southern Hemisphere, shows a high correlation with other chronologies from the area, and significant relationships with temperature and precipitation variables. The record consists of three stacked independent chronologies (Fig.1): (i) VAP2, derived from living trees in VA, with ages ranging from 448 to 1994 AD (1547 years long); (ii) VAP1 (3675 to 345 BC, 3327 years long) with ancient trees from VA which did not overlap in time with VAP2, but cross-dated satisfactorily with the nearby (iii) Lenca chronology (LEN), which spans between 1634 BC to AD 1987 (Lara & Villalba 1993). Thus, the ~700-year gap which separates VAP1 and VAP2 between 345 BC and AD 448 (Fig.1), can be filled with LEN to develop a continuous master chronology (VAL) (Fig.2) spanning 5666 years.

Preliminary results on radiocarbon-dated stratigraphic sections and lake sediment cores from VA and nearby areas indicate the occurrence of a prominent volcanic event at ~350 BC, which is recorded as a 2-cm thick tephra in eastern Isla Grande de Chiloé, ~100 kms from VA. Our results suggest that ash deposits blanketed the Fitzroya cupressoides forests in the VA area killing the trees.

A conspicuous below-average tree-growth period is evident in LEN between 80 BC and AD 160 (Fig.1), possibly caused by temperatures above the mean (Lara & Villalba 1993). This anomalous-growth period is also present in another nearby tree-ring chronology (AYA), south of VA. These data indicate that climate is the most probable forcing factor during this period. Ongoing multidisciplinary studies (vegetation, fire, volcanic, and lake level history) will aid in refining the paleoenvironmental history of the region from annual to millennial timescales.

Aknowledgements

We thank Project Fondecyt Nº 1000445 and Nº 1030766 for funding this investigation.

References

Lara, A. & R. Villalba. 1993. A 3620-year temperature record from Fitzroya cupressoides tree rings in southern South America. Science, 260: 1104-1106.

Wolodarsky-Franke, A. 2002. Fluctuaciones ambientales de los últimos 1000 años a partir de anillos de crecimiento de Fitzroya cupressoides ((Molina) Johnston) en el área del Volcán Apagado, Décima Región, Chile. M.Sc. Thesis, Facultad de Ciencias, Universidad Austral de Chile.

Date received: November 18, 2004