The paleoecology and stratigraphy of Nichols Meadow, Sierra National Forest, California, USA

Sediment stratigraphy and pollen, plant macrofossil and charcoal analyses, along with nine radiocarbon dates from Nichols Meadow, provides the most intensive investigation of Sierra Nevada montane meadow development and paleoecology. During pollen zone NM-I (ca. 18,500-12,500 yr B.P.) the Nichols Meadow area contained a stream during the Tioga glacial stage. The presence of high Artemisia and Gramineae pollen percentages along with a very low pollen influx rate reflects a cold-dry steppe-woodland environment. Pollen zone NM-II (ca. 12,500-8800 yr B.P.) documents the development of a lower montane forest and giant sequoia (Sequoiadendron giganteum) community which existed around a small meadow. The higher sediment accumulation rates suggest that fallen trees contributed to the aggregation of meadow sediments. arly Holocene aridity is recorded in pollen zone NM-III (ca. 8800-6000 yr B.P.) by poorly preserved pollen. We infer that the forest trees closed in on the meadow and occupied the meadow floor. The reduction in available moisture caused giant sequoia to become locally extinct in the Nichols Meadow area probably moving into their current distribution within the Nelder Grove. Pollen zone NM-IV (6000 yr B.P.-present) reflects the development of the modern Nichols Meadow. Less sand in the meadow sediments, due to stable vegetation surrounding Nichols Meadow, allowed the increased retention of ground water. This along with the neoglacial cooling trend at ca. 3000 yr B.P. caused ground water to rise and saturate the meadow. These events excluded the conifers from the meadow surface and allowed herbaceous vegetation associated with wet meadows to dominate. Overgrazing and channeling of the meadow's outflowing stream caused the water table to drop, resulting in the incision of the meadow.