A 5999!year soil pollen record of subalpine meadow vegetation in the Olympic Mountains\ Washington\ USA

0 Subalpine meadow communities are in~uenced by edaphic and microclimatic gradi! ents\ and should be a}ected by climate change that a}ects these local controls[ We used pollen preserved in meadow soils to investigate the long!term interaction of these factors in a 0!ha subalpine meadow in the Olympic Mountains\ Washington\ USA[ 1 To describe the spatial scale at which soil pollen is related to neighbouring vegetation\ pollen in 35 soil surface samples was compared with plant cover within concentric circular plots "9[4Ð0m radii#[ Regression analysis of percentage pollen with plant cover at di}erent distances from the surface sample had the highest correlation with radii 3 0m\ con_rming that entomophilous meadow species have very small relevant pollen source areas[ 2 We analysed pollen records in soil columns at three sites representing a range of growing season lengths and community types within the meadow[ Soils had aggraded by the deposition of eolian silt[ Radiocarbon dates of pollen concentrates were similar to or older than radiocarbon dates on charcoal pieces at the same depth\ suggesting negligible downwards movement of pollen in the soil pro_le[ 3 The oldest soil pollen pro_le was from the wettest microsite\ currently dominated by a snowbed Carex ni`ricans community[ This site was occupied by a dry Juniperus community prior to c[ 5999 BP "before present#\ when it shifted to more mesic com! munities dominated by Poaceae and Polemonium[ The _rst appearance of a snowbed Carex ni`ricans community at this site\ c[ 1499Ð0499 BP\ suggests a change to cooler and:or wetter regional climate[ 4 High levels of Poly`onum bistortoides at all sites indicated a shift to long snow!free periods and mesic summer conditions during an interval corresponding to the Med! ieval Warm Period "c[ 0199Ð699 BP#[ After 499 BP "during the Little Ice Age# Carex ni`ricans re!established in the wet microsite\ while relatively little change occurred at the other two sites[ Overall\ the greater magnitude of change at this microsite than at the longer growing!season sites indicates that\ in these subalpine meadows\ short growing season sites are most sensitive to regional climate change[