PARENT SESSION
Oral Session 68: Paleoecology I: Pollen.
Presiding: G Uzochukwu and M Edwards
Wednesday, August 4, 8:00 AM to 10:45 AM, Meeting Room D 136.
A stand-scale pollen record improves understanding of no-analogue pollen assemblages in the Puget Lowlands. WA.
Brubaker, Linda*,1, Crausbay, Shelley2, 1 University of Washington, Seattle, WA2 University of Wisconsin, Madison, WI
ABSTRACT- The interpretation of late-glacial and early-Holocene pollen assemblages in lakes of the Puget Lowland, WA, has long been challenging because the dominant tree species of these spectra do not occur together in modern forests. Small-hollow pollen and charcoal records from upland landforms of Marckworth Forest reveal stand-level forest composition that can resolve unanswered questions about past forest composition and disturbance regimes during these periods. Late-glacial pollen spectra (ca.12,000-11,000 cal BP) from Marckworth Forest hollows resemble assemblages from Puget Lowland lakes, confirming that trees presently common at low elevations (Picea sitchensis, Tsuga heterophylla) occurred in the same stands with trees currently restricted to high elevations (Abies amabilis). Thus regional forests of the Puget Lowlands were likely characterized by diverse species mixtures within individual stands. Though one fire occurred during this interval, the period is too brief to estimate fire frequency. In contrast, forest-hollow assemblages are strikingly different from lake pollen assemblages during the early Holocene (ca.11,000-8000 cal BP), with much higher percentages of Pseudotsuga menziesii and Pteridium aquilinium and lower percentages of Alnus rubra in hollow than in lake records. These differences document that the major tree species of the period, A. rubra and P. menziesii, occupied different landscape locations. Open stands of P. menziesii, with understories of P. aquilinium and Poaceae, were present on the Marckworth uplands, and A. rubra stands likely dominated river floodplains ca.10 km to the north. In addition, pollen and charcoal content indicates several stand-replacing fires, with differing successional responses. These interpretations differ from any of the previous interpretations of early-Holocene forest composition and disturbance based on lake sediment records.
Key words: charcoal, forest, pollen, no-analogue