Holocene treeline and climate change in the subalpine zone near Stoyoma Mountain, Cascade Mountains southwestern British Columbia, Canada

Multiproxy paleoecological investigation of a small lake in the high subalp ine zone near Stoyoma Mountain, northern Cascade Mountains of British Colum bia, reveals significant change in vegetation, limnic conditions, and infer red climate throughout the Holocene (last 10,000 radiocarbon years). Three zones of distinct pollen, plant macrofossil, and chironomid assemblages are apparent in the sediment core from 3M Pond (informal name). A dry, sparsel y vegetated spruce parkland and a warm-adapted chironomid community existed in and around the study sites in the early Holocene (ca. 10,000 to 7000 C- 14 yr BP). Between 7000 and 3500 C-14 Yr BP, Engelmann spruce-subalpine fir forest conditions established and then declined around 3M Pond leading to modern subalpine parkland conditions from 3500 C-14 yr BP to present. Chiro nomid communities at 3M Pond between 7000 and 3500 C-14 yr BP are indicativ e of warmer waters than present, but show a transition to modern assemblage s. Three climatic regimes are identified near Stoyoma Mountain: (1) the ear ly Holocene xerothermic period (10,000 to 7000 C-14 yr BP, (2) a period of climatic transition in the mid-Holocene (7000 to 3500 C-14 yr BP), and (3) cool, modern neoglacial conditions (after 3500 C-14 yr BP). These findings confirm vegetation and inferred climate changes identified at Cabin Lake, B ritish Columbia (a nearby lake in the subalpine forest). Changes in treelin e position, plant communities, chironomid communities, and inferred climate are nearly synchronous and validate the multiproxy approach for paleoecolo gical reconstruction Chironomid-based paleotemperature reconstructions conf irm earlier evidence that the early Holocene was significantly warmer than present, with estimated summer water surface temperatures up to 4 degrees C higher than today.