Postglacial vegetation, fire, and climate history of Blacktail Pond, Northern Yellowstone National Park, WY

Abstract

Previous studies in Yellowstone National Park (YNP) suggest intensification of the summer-dry and summer-wet patterns in Yellowstone during the early Holocene when increased summer insolation caused atmospheric circulation patterns to strengthen. To examine this hypothesis further, pollen and high-resolution charcoal records were analyzed from Blacktail Pond to reconstruct fire and vegetation histories near the present transition between summer-wet and summer-dry conditions. The site currently lies in Pseudotsuga parkland with Artemisia steppe at lower elevations around the pond. The site supported sparse tundra prior to 12,000 cal yr B.P. and fires were uncommon. Between 12,000 and 11,000 cal yr B.P, fire activity increased and Picea-Pinus parkland was established. These changes are consistent with increasing temperature and moisture. Between 11,000 and 7600 cal yr B.P., pollen evidence of a Pinus-Picea-Abies forest is consistent with increased winter moisture, while high fire activity at this time indicates that summers had lower effective moisture than at present. Between 7600 and 4000 cal yr B.P., vegetation around the site shifted to parkland dominated by Pinus, Picea, Pseudotsuga, and Artemisia indicating that effective winter moisture decreased. Fire activity continued to be high during this time suggesting summers maintained low effective moisture. The development of Artemisia steppe around the site over the last 4000 years indicates that effective winter moisture decreased, while decreased fire activity indicates that effective summer moisture increased during this time. Winter conditions during the early Holocene that resemble a summer-wet site along with summer conditions at the same time resembling a summer-dry site could be a result of the geographical setting of Blacktail Pond near the boundary between these two precipitation regimes. Poaceae/Artemisia pollen ratios were used to infer wet/dry climate oscillations during the late Holocene. The fluctuations correspond well with other paleoclimate data from northern Yellowstone National Park (Gennett and Baker, 1986; Hadly, 1996; Meyer et al., 1995), and suggest that conditions were drier from 3775-3125, 2475-2225, 1700- 675, and 425-75 cal yr B.P.