Vegetation and climate changes at Spicer Lake, Indiana, during the Holocene

Abstract

Many paleoclimate studies have shown that the midcontinent of North America experienced a warmer and drier-than-present climate during the early and middle Holocene and relatively humid climate during the late Holocene, interspersed with several centennial-scale megadroughts. In response to this climate variability, the ranges of individual taxa shifted and some tree taxa (e.g. Tsuga canadensis, Fagus grandifolia) experienced episodic declines in their abundances, which appear to be linked to hydroclimatic variability. This study focuses on climate and vegetation changes during the Holocene at Spicer Lake in northern Indiana (41� 44'52" N, 86� 31'19" W, 237 elevation), a kettle lake located in New Carlisle, near the southeastern edge of Michigan. Reported data include radiocarbon dates, loss-on-ignition data, and fossil pollen analysis, which together are used to reconstruct the vegetation, climate and environment at Spicer Lake. Picea-dominated conifer forest was the main vegetation type at Spicer Lake before 11,800 years BP, followed by a period of high Pinus abundances. After 10,300 years BP, conifer forest decreased and deciduous forest expanded during this time, resulting in deciduous forests with high abundances of Acer, Quercus, Ulmus and Fagus pollen. Fagus increased and became highly abundant after about 6,800 years BP. Fagus pollen abundances during the middle and late Holocene are highly variable, with declines at roughly 5,000, 4,000, 3,800 -- 1,900 and 1,000 years BP. These declines at Spicer Lake may be associated with Fagus pollen declines at other lakes in north central United States, perhaps caused by regional drought events, but cross-correlation is confounded by dating imprecision in earlier records. Bayesian time-series models also suggest that Fagus pollen abundance changes may be partly related to LOI variability at Spicer Lake. The LOI variability in the lake sediment may be a signal of changing lake-level and hence moisture balance, but the exact reasons for the increases or decreases of minerals may change according to the different relative position of lake level and core position.