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Abstract We examine major reorganizations of the terrestrial ecosystem around Mono Lake, California during the last deglacial period from 16,000–9,000 cal yr BP using pollen, microcharcoal, and coprophilous fungal spores (Sporormiella) from a deep-water sediment core. The pollen results record the assemblage, decline, and replacement of a mixed wooded community of Sierran and Great Basin taxa with Alkali Sink and Sagebrush Steppe biomes around Mono Lake. In particular, the enigmatic presence ofSequoiadendron-type pollen and its extirpation during the early Holocene hint at substantial biogeographic reorganizations on the Sierran-Great Basin ecotone during deglaciation. Rapid regional hydroclimate changes produced structural alterations in pine–juniper woodlands facilitated by increases in wildfires at 14,800 cal yr BP, 13,900 cal yr BP, and 12,800 cal yr BP. The rapid canopy changes altered the availability of herbaceous understory plants, likely putting pressure on megafauna populations, which declined in a stepwise fashion at 15,000 cal yr BP and 12,700 cal yr BP before final extirpation from Mono Basin at 11,500 cal yr BP. However, wooded vegetation communities overall remained resistant to abrupt hydroclimate changes during the late Pleistocene; instead, they gradually declined and were replaced by Alkali Sink communities in the lowlands as temperature increased into the Early Holocene, and Mono Lake regressed.
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Paleoecological evidence for late Holocene aridification from the Taolambiby subfossil site of southwestern Madagascar
Taolambiby, a key subfossil site in southwestern Madagascar, has yielded many bones of extinct large lemurs and associated fauna in excavations spanning more than a century. In 2004 our group collected a 4.4 m sediment profile from deposits near prior excavations. Our aim was to use sedimentological and palynological inferences to examine the interaction between climate change and human activities, in order to better understand how each may have contributed to local extirpations. The basal age of this profile was ca. 3500 cal yr BP. Lithology of the excavated and cored material showed many changes in sediment regime, reflecting the variable natureof the basin’s hydrology. After ca. 1500 cal yr BP, the record shows successive drying of the site and subsequent erosion and redeposition. After this time, pollen and spores were not preserved but charcoal particles continued to provide a record of local and regional fires up to the present. Between 340 and 250 cm below surface, pollen was well-preserved, showing evidence for a mixture of mesic and xeric vegetation, including many trees, shrubs, forbs, and ferns, most still found in the adjacent Bezà Mahafaly Special Reserve. This pollen record, spanning the period from ca. 3000 - 1500 cal yr BP, shows evidence for increased wetness at the beginning of the period and subsequent aridification. Coprophilous fungus spores (Sporormiella) are high during this same interval, suggesting the local presence of abundant megafauna, but decline with increasing aridification.
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- Award ID(s):
- 1750598
- PAR ID:
- 10317010
- Date Published:
- Journal Name:
- Malagasy nature
- Volume:
- 15
- ISSN:
- 2661-9032
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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