PARENT SESSION
Poster Session #15: Paleoecology.
Monday, August 5. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Late Holocene vegetation history and climate in NW Sierra Madre Occidental, Sonora, Mexico.

Ortega Rosas, Carmen^*,1, Peñalba, Cristina¹, ¹ Instituto de Ecología, Universidad Nacional Autónoma de México, Hermosillo, Sonora, México

ABSTRACT- The Sierra Madre Occidental (SMO) is a physiographic province that separates the Sonoran and Chihuahuan Deserts in northern Mexico and enclose high biodiversity and a variety of climates. A paleoecological study based on pollen analysis was carried on in the Ciénega de Camilo, a peatbog located in northwestern SMO (28°25'34"N, 108°34'09"W, 1520 m elevation). The site is surrounded by Pine-Oak woodlands, lies on a slope in a wet canyon and is covered by Sphagnum palustre; this habitat is unique in Sonora. Annual precipitation is about 1000 mm. No previous paleoecological or paleoclimatic records are known for northwestern SMO, although they would be essential for the understanding of present species distribution. Sediment cores were obtained with a Livingstone corer at the center of the site. The sediment (dark gray organic clay) was 3.60 m-deep at CAM3. Pollen extraction from sediments followed typical procedures in palynology including: hot hydrofluoric acid (HF), acetolysis and sodium polytungstate. Preliminary results show three dominant taxa: Quercus, Pinus and Pteridophyta, with variations along the sequence. Pollen frequencies of Pinus decrease, while those of Quercus increase from the bottom to the top. Fern spore presence range from 3 to 40%, but almost disappear in the recent pollen spectra. Vegetation fluctuations at this site could be caused by Holocene climatic changes (wet and dry phases) recorded in other paleoecological studies in NW Mexico, but human activity cannot be disregarded.

KEY WORDS: Sphagnum palustre, Holocene, pollen, Sierra Madre Occidental