Paleoecology of range limits: beech in the Upper Peninsula of Michigan.

Fossil pollen was used to map American beech (Fagus grandifolia) populations in Wisconsin and Michigan during the last 8000 yr. Among questions addressed were: (1) What were routes and rates of range expansion? (2) Did range expansion follow a @'wave-front@' model or occur by coalescene of outliers? (3) Has the range of beech been determined by environmental tolerance or by dispersal rate? Presettlement distributions were mapped from survey records. Range expansion was reconstructed using pollen diagrams from 34 sites, most in a 30-50 km grid. We show beech moving through southern Michigan into Wisconsin and Michigan's Upper Peninsula. During much of the last 8000 yr the range of beech was relatively stable and presumably environmentally controlled. Brief delays may have been occasioned by dispersal barriers. Range expansions occurred during the last millennium, as well as 3000-2500 yr ago and 8000-5000 yr ago. Several separate colonizations across Lake Michigan formed temporary outliers. No other past outliers were detected, although modern outliers are known; however, even with closely spaced sites, outliers may have been undetected.