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Royal Basin, Olympic National Park, Washington, USA
Reference
Gavin, D.G. and Brubaker, L.B. 1999. A 6000-year pollen record of subalpine meadow vegetation in the Olympic Mountains, Washington, USA. Journal of Ecology 87: 106-122.

Description
Working in Royal Basin (47°49'N, 123°12'30" W), which is a north-facing glacial valley at the headwaters of Royal Creek in northeastern Olympic National Park in the state of Washington, the authors extracted three 18-cm-deep soil cores from three different sites within a subalpine meadow they refer to as Meadow Ridge, from which they constructed depth (= time) profiles of pollen types and abundances that pertained to the past six millennia. Then, based on current associations of the plants that produced the pollen with various climatic parameters, primarily temperature and precipitation, they reconstructed a climatic history of the three sites. This work revealed, in their words, that in the part of the soil profiles "corresponding to the Medieval Warm Period (c. 1200-700 BP)," all sites showed an increase in the abundance of Polygonum bistortoides, which is "an indicator of mesic conditions." At one of the sites, in fact, it reached a maximum abundance of 50%, which they say is "more than three times the value in any modern surface sample at Meadow Ridge." In addition, one of the sites showed "a decline in Cyperaceae (cf. Carex nigricans)," which, as they describe it, "suggests earlier snow-melt dates." Based on these observations, they concluded that the observed changes "suggest long and moist growing seasons" during the Medieval Warm Period. What is more, they note that the pollen-plant relationship they developed for P. bistortoides over this period "corresponds to c. 75% cover," which they say is "higher than any reported Polygonum bistortoides cover in the Olympic Mountains (Schreiner, 1994)," which would seem to suggest that the MWP of AD 800-1300 was very likely significantly warmer than the Current Warm Period in that part of the world has been to date.

Additional Reference
Schreiner, E.G. 1994. Subalpine and alpine plant communities. In: Houston, D.B., Schreiner, E.G. and Moorhead, B.B. (Eds.) Mountain Goats in Olympic National Park: Biology and Management of an Introduced Species. Olympic National Park, National Park Service, Port Angeles, Washington, pp. 242-250.