Effects of Logging History and Hurricane Damage on Canopy Structure in a Northern Hardwoods Forest

PEART, D. R., C. V. COGBILL AND P. A. PALMIOTTo (Department of Biological Sciences, Dartmouth College, Hanover, NH 03755). Effects of logging history and hurricane damage on canopy structure in a northern hardwoods forest. Bull. Torrey Bot. Club 119: 29-38. 1992.Canopy structure following the 1938 hurricane and subsequent salvage logging was evaluated from 1942 aerial photographs for six gauged watersheds in the northern hardwoods forest at the Hubbard Brook Experimental Forrest, N.H. Three of the six watersheds that have not been cut since the hurricane were also evaluated from 1978 aerial photographs. A total of 1635 points were sampled on a grid system and categorized as high canopy, low canopy, exposed understory or open, as assessed through a stereoscope. Archival reports on logging and hurricane effects were used to supplement the photographic interpretations. In 1942, percent openness (area whithout canopy cover) ranged from 13% to 38%. From 1942 to 1978, percent openness decreased by a mean of 18%. The reduction in canopy cover due to the hurricane and salvage logging was apparently less than 20% in the gauged watersheds. However, damage was patchy: the most heavily damaged area (72% open) was that which was logged least before the hurricane, and watersheds with most evidence of young second growth prior to the hurricane were apparently the least damaged. Although effects were locally severe, large areas were apparently only lightly damaged in 1938. Recovery of the canopy in the heavily damaged area was rapid: in 1978, only 9% of the area was open, and canopy structure was similar to that in the gauged watersheds. Thus, 40 years of canopy development effectively masked the patchy effects of hurricane damage. Photographic evidence, together with other historical records, provides a better assessment of past disturbance to forest canopies than unquantified eyewitness accounts, and can be evaluated more rapidly and over larger areas than more intensive, field-based investigations.