Climate–Fire–Vegetation interactions during the Late Holocene in Las Yungas upper montane forest, Lagunas de Yala. Northwestern Argentina
by
Liliana Concepción Lupo
CONICET, Laboratorio de Palinología-Grupo Yavi/UNJu, Argentina
Coauthors: María Martha Bianchi (CONICET-CRUB, Argentina) and Martin Grosjean (NCCR Climate, University of Bern, Switzerland)

In the area of the upper Montane forest of Las Yungas, fire is a remarkable disturbance agent.

The rol of both natural and antropic fires in moduling climate influences at the forest-montane grassland boundary at different temporal scales is a main topic of discussion.

Pollen charcoal and sedimentological records from lake sediments obtained at Lake Comedero and Lake Rodeo, Potrero de Yala (24°06’S 65°29’W, 2100 m a s l) were correlated.

At Laguna Rodeo a 20 cm long core, dated with 210Pb showed variations in sedimentation rates and charcoal concentration during the XX century.

A 700 cm long obtained at the same lake with a basal date of 1700 yr BP showed alternate sedimentary phases (decadal or seasonal regime?).

High values of herbs are shown by the pollen record between 1700 and 300 AP, while the pollen of major montane forest tree, Alnus acuminata (60%), increased thereafter, pointing out the establishment of the forest in this watershed.

Poaceae pollen strongly dicreases in relation with grazing during former hispanic times while charcoal abundance shows variations.

At Laguna Comedero a 30 cm long core showed that the abundance of charcoal is higher during the first part of the XX century with peaks at ca. 1920; 1943 and 1985-1995, in correspondence with dry periods charcaterized by mineralogical analyses. A noticeably reduction in charcoal abundance is shown from 1945 to recent times.

This preliminary results showed the potencial of the area for fire history studies, alowing us to place questions about the causes of fires ( climate - land use) in this watershed and in the upper montane forest during the XX century and late Holocene.

Date received: November 19, 2004