Pollen whiskers, rational limits and cryptic refugia: Determining the local presence of spruce on lateglacial landscapes of eastern Canada
The 20% spruce isopoll has traditionally been used to identify the range limit of spruce in eastern North America. Using plant macrofossils and stomates in a network of 25 lateglacial-aged sites throughout Nova Scotia, we identified sites where spruce was locally present but contributed as little as 4% to the pollen rain. Our data suggest that 8% pollen abundance is a more reasonable limit that consistently indicates the local presence of trees. Using 8% to define the presence of spruce, we find that the number of sites likely to contain spruce increases from 3 to 11 as compared to using the 20% isopoll. The resulting increase in the estimated distribution of spruce leads to a reduction in the apparent migration lags and migration rates of spruce into the region. Reducing the error in distribution histories will provide better-constrained estimates of climate change and its impact on the local vegetation.