Late Quaternary vegetation near Battle Ground Lake, southern Puget Trough, Washington
Pollen and plant-macrofossil records from Battle Ground Lake, along with published data, are used to reconstruct the late-Quaternary vegetation history of the nonglaciated southern Puget Trough. Coinciding with the end of the Evans Creek Stade (circa 20,000-17,000 yr B.P.) of Fraser Glaciation, Gramineae, Artemisia , herbs, and Picea cf. engelmannii grew in a parkland/tundra around Battle Ground. This assemblage, recorded throughout the southern Puget Trough, implies cold, relatively dry conditions similar to subalpine environments east of the Cascade Range. The presence of Pseudotsuga, Picea sitchensis , and Alnus rubra as macrofossils suggests a slight interstadial warming between 17,000 and 15,000 yr B.P. Cool, humid conditions prevailed during the Vashon Stade when, south of the Cordilleran Ice Sheet, open forest or parkland featured mesophytic subalpine taxa. At Battle Ground Lake, temperate conifers were part of forest communities circa 11,200 yr B.P., but elsewhere they were present as early as 12,500 yr B.P. From 10,000 to 4500 yr B.P., Pseudotsuga-Quercus savannah spread into the Battle Ground area, offering evidence for summer drought more severe than today. Pseudotsuga and Thuja forest was established in the late Holocene with the introduction of the modern humid climate. Consideration of all the pollen data from the southern Puget Trough and the available radiometric chronology suggests that postglacial migration of most lowland conifers into the Puget Trough was rapid and not necessarily from southern refugia.