XVI International Botanical Congess

In January 1998, an ice storm with record breaking precipitation hit parts of Quebec and Ontario in Canada, and the adjacent U.S. We surveyed the amount of gap opening due to the ice storm at Mont St. Hilaire, Quebec, which is located near the northern limit of deciduous forest in eastern North America. Mont St. Hilaire was one of the locations hit hardest by the ice storm, receiving nearly 100 mm of freezing rain over a 3-day period. We assessed the amount of opening by taking hemispheric photographs before and after the ice storm at 115 different locations. The photographs were digitized to obtain gap fraction values, and pre- and post-values were then compared. There was a considerable spatial variation in increase of gap opening: the range of pre-ice storm gap fraction values was 8 - 22%, while the post-ice storm range was 12 - 47%. Gap opening was greater for locations that had 1) less open canopy prior to the ice storm, and 2) greater presence of Fagus grandifolia in the canopy.