A 6000-year soil pollen record of subalpine meadow vegetation in the Olympic Mountains, Washington, USA

1 Subalpine meadow communities are influenced by edaphic and microclimatic gradients, and should be affected by climate change that affects these loca l controls. We used pollen preserved in meadow soils to investigate the lon g-term interaction of these factors in a 1-ha subalpine meadow in the Olymp ic Mountains, Washington, USA. 2 To describe the spatial scale at which soil pollen is related to neighbou ring vegetation, pollen in 46 soil surface samples was compared with plant cover within concentric circular plots (0.5-1 m radii). Regression analysis of percentage pollen with plant cover at different distances from the surf ace sample had the highest correlation with radii < 1 m, confirming that en tomophilous meadow species have very small relevant pollen source areas. 3 We analysed pollen records in soil columns at three sites representing a range of growing season lengths and community types within the meadow. Soil s had aggraded by the deposition of eolian silt. Radiocarbon dates of polle n concentrates were similar to or older than radiocarbon dates on charcoal pieces at the same depth, suggesting negligible downwards movement of polle n in the soil profile. 4 The oldest soil pollen profile was from the wettest microsite, currently dominated by a snowbed Carex nigricans community. This site was occupied by a dry Juniperus community prior to c. 6000 BP (before present), when it sh ifted to more mesic communities dominated by Poaceae and Polemonium. The fi rst appearance of a snowbed Calex nigricans community at this site, c, 2500 -1500 BP suggests a change to cooler and/or wetter regional climate. 5 High levels of Polygonum bistortoides at all sites indicated a shift to l ong snow-free periods and mesic summer conditions during an interval corres ponding to the Medieval Warm Period (c. 1200-700 BP). After 500 BP (during the Little Ice Age) Carex nigricans re-established in the wet microsite, wh ile relatively little change occurred at the other two sites. Overall, the greater magnitude of change at this microsite than at the longer growing-se ason sites indicates that, in these subalpine meadows, short growing season sites are most sensitive to regional climate change.