Holocene Fire history in the humid forest of Northwestern Patagonia, Argentina

GIACHÉ. Y. S; BIANCHI M. M.,; DEL FUEYO G.M.,

Salvador

Congreso; XIV International Palynological Congress - X International Organization of Palaeobotany Conference; 2016

Universidade Estadual de Feira de Santana

Holocene Fire history in the humid forest of Northwestern Patagonia, ArgentinaYamila Soledad Giaché1, María Martha Bianchi1,2, Georgina Marisa Del Fueyo21 Instituto Nacional de Antropologia y pensamento Latinoamericano (INAPL), Buenos Aires, Argentina, yamilagiache@gmail.com2 Museo Argentino de Ciencias Naturales?Bernardino Rivadavia?, CONICET (MACN), Buenos Aires, ArgentinaFire is recognized as a critical agent in the earth system. A strong interaction between climate variabilityand regional fire regimes exists in Patagonia, with human influences having a more localized impact. InNorthern Patagonian rainforest disturbed sites, the cane Chusquea culeou is the dominant understory species,contributing to burning biomass. Pollen and charcoal records of El Laguito del Morro lake (41°31?54.0? S,71°48?25.2? W) allowed us to identify five palynological zones showing major changes in the rain foreststructure an its relation to changes in fires frequency and severity during the last 14000 cal. Yr B.P. Charredgrass fragments were identified under SEM as Chusquea culeou foliar epidermis. In Zone 1 (14000 ? 8300 calyr BP) N.dombeyi-type pollen increased from 65 % to 95% whereas rainforest elements, Cupressaceae andshrubland/steppe types were lower than 10%. Poaceae, probably Chusquea culeou, reached 15%. Charcoalvalues (woody and charred grass) were high. This period was characterized by open Nothofagus forest withfrequent fires. In Zone 2 (8300 - 5300 cal yr BP) N.dombeyi-type, remained high while Cupressaceae andshrubland/steppe types decreased to the lowest values of the entire record. This period was characterizedby a closed low diversity Nothofagus forest. Concentration of woody and grass charcoal declined suggestingless fires and an increase in moisture. In zone 3 (5300 - 3800 cal yr BP) Cupressaceae increased sharplywhile Poaceae and shrubland/steppe types were in low percentages. Charcoal concentrations were initiallylow and gradually increased pointing the early expansion of mixed Nothofagus-Austrocedrus forest. In zone 4(3800 ? 1200 cal yr BP) N.dombeyi-type remained at ca 80% and Cupressaceae declined while Shrubland andsteppe types increased. The mixed forest was established. Woody and grass charcoal concentrations increasedtowards 1200 cal yr BP. The highest concentration of woody charcoal of the entire sequence was recordedat 1500 cal. yr BP indicating high fire frequencies. In zone 5 (1200 cal yr BP to present) the expansion andestablishment of scrub ?matorral? occurred. Rainforest and steppe herbs also became more abundant whileCupressaceae decreased. Grass charcoal increased but woody charcoal steadily declined suggesting morefrequent and less severe fires. Our results at El Laguito del Morro indicate that forest vegetation dynamicswas mostly determined by low severity and high fire frequencies along most part of the Holocene period.First evidences of the role of Chusquea culeou burning events in long term forest dynamics are shown. It is acontribution to grants ANPCyT PICT 2012/528, 2012/ 471 and CONICET PIP 112-201201-00212Keywords: Patagonia, rainforest, fire history, charcoal, Holocene