Pollen records from lake sediment have yielded a developing
record of Holocene vegetation and climate in the central and southern Rocky
Mountains, USA.
Absent from these records are alpine and subalpine
areas of southeastern Wyoming.
We recovered sediment cores totaling 2.27 m depth from East
Glacier Lake,
near alpine treeline at 3280 m elevation in the Snowy Range,
on the Medicine Bow National Forest.
Present vegetation is open, “parkland” forest dominated by Picea engelmannii (Engelmann spruce). The cores cover the entire Holocene, containing
glacial diamict at the base and gytja at the surface.
The samples were processed and pollen counted according to standard laboratory
methods. Six 14C dates were obtained, yielding an average sediment
accumulation rate of 67.5 yr cm-1. Deglaciation
occurred by at least 15400 cal yr BP, with vegetation dominated by Artemisia and graminoids
until ca. 11600 cal yr BP, when these species declined and coniferous pollen (primarily
Pinus and Picea) began to increase. These
trends continued until ca. 8000 cal yr BP
when vegetation resembled the modern community. The period 6500-5200 cal YBP
showed a considerable increase in coniferous pollen and a further decrease in Artemisia, Cheno-am (saltbush species) and
graminoid pollen, possibly indicating a closed
coniferous forest present on the site, and a higher alpine treeline. The
corresponding section of the core contains coarse plant material. Vegetation
and inferred climate trends are broadly similar to those found at sites in Colorado's Front Range and other locations in the
southern Rocky Mountains.