Response of Forest Understory Vegetation to a Major Ice Storm

Abstract

DARWIN, A.T., D. LADD, R. GALDINS, T. A. CONTRERAS AND L. FAHRIG (Dept. of Biol., Carleton University, Ottawa, ON, Canada KiS 5B6). Response of forest understory vegetation to a major ice storm. J. Torrey Bot. Soc. 131:45-52. 2004.-In January of 1998, Ottawa, Ontario was hit with a major ice storm. Detailed pre-storm vegetation data had been collected in 1997 in 164 forest interior sampling plots across a 3,000 km2 region. These data included information on shrubs/saplings, woody seeds and seedlings, herbaceous seeds and ground cover, and canopy cover. For the four growing seasons following the ice storm (1998-2001), we resampled the same 164 plots. In addition, in 1998 we estimated an ice storm damage index for each plot, and the volume of downed coarse woody debris due to the ice storm in each plot. The objectives of this paper were to examine changes in shrubs/saplings and ground vegetation in response to ice storm damage over the four-year period following the storm. Contrary to our initial expectations, we found that woody seedlings showed a large decrease in density immediately following the storm (1998). Woody seedling density recovered to pre-storm levels by 2001. We hypothesize that the decrease in woody seedling density resulted from reduced seedling germination due to lower light availability on the forest floor, which resulted from the large amount of woody debris created by the storm. We also found that shrub/sapling counts showed a large increase in 1999, most likely due to increased light to the understory, due to opening of the upper canopy. Herbaceous cover increased from 1998 to 2000, but returned to pre-storm levels the following year (2001). The between-plot variation in these understory changes was positively correlated to plot damage from the ice storm, indicating that they resulted from the storm. Overall, it appears that the forest understory plant structure is rapidly returning to pre-ice storm conditions.