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COPYRIGHT 2003 Indiana Academy of Science
ABSTRACT. In April 1974 a tornado severely damaged the sugar maple/Ohio buckeye forest in Happy Valley, Jefferson County, Indiana. Virtually all canopy trees were destroyed or damaged. In the fall of 1974, the forest was sampled on three transects across the valley. The most damaged portion of the valley forest was characterized as a sugar maple/white oak spp./white ash community. Seven years later the forest was sampled on the same transects, and the most damaged part was described as a sugar maple/elm spp./ Ohio buckeye/redbud community. Fifteen years after the tornado the forest was sampled on the same transects, and the most damaged part was described as a sugar maple/slippery elm community. Twenty and twenty-five years after the tornado the most damaged portion of the forest is still a sugar maple/ slippery elm community, with chinkapin oak, Ohio buckeye, American basswood, white ash and hackberry of secondary importance. The less damaged portion of the valley is dominated by sugar maple, with black walnut, box-elder, white ash, slippery elm and red oak of secondary importance. Important changes in overall forest structure that occurred between 20 and 25 years after the tornado are described, and predictions of future changes are included.
Keywords: Forest composition, forest structure, Jefferson County, Indiana, oaks, Ohio buckeye, secondary succession, slippery elm, sugar maple
Temperate forests in the midwestern United States have been subjected to natural disturbances since they evolved. One dramatic cause of such disturbance is tornadic winds. On the afternoon of 3 April 1974, a series of tornadoes ripped across Indiana. One traveled through the town of Hanover, traversed the Hanover College campus, and continued northeast across the adjacent wooded Happy Valley creating extensive damage. The tornado left nine people dead in the county and damaged nearly every building on the college campus (Larking 1974; Anonymous 1974).
Bailey and MacMillan (1977) completed a census of the Happy Valley forest in the fall of 1974 and found that 90% of the canopy vegetation was removed and approximately one-third of the trees (dbh[greater than or equal to]5) had been destroyed. The valley floor was so littered with logs that one was forced to climb over them. Forest destruction was most severe at the northern end of the Valley. Destruction of the canopy allowed sunlight to reach the forest floor, which in turn supported abundant herbaceous plant growth. Within a few years, woody shrubs and tree saplings emerged above the piles of fallen stems and branches; and many of the damaged standing stems branched profusely and leafed out. After seven years (1981), emergent trees began to form a canopy creating an environment that supported more shade tolerant plants (Martin & MacMillan 1982).
Data on the Happy Valley forest, gathered before the tornado of 1974, was not systematically collected; but it suggested that the forest had been a sub-climax, sugar maple/Ohio buckeye community. The summer following the tornado, Bailey & MacMillan (1977) established three west-to-east transects across the valley to census the forest. They found the remaining forest to be composed primarily of sugar maple. White ash, elm spp. and white oak spp. were of secondary importance, while Ohio buckeye was a very minor component of the forest. Prior to and since the tornado, sugar maple is the dominant species. However, many changes have taken place in the sub-dominant or secondary tree species since the tornado. Seven years later (1981), the same three transects were recensused. The dominant species in the most severely damaged (northern) portion of the valley was sugar maple, with Ohio buckeye and slippery elm of secondary importance. In the less disturbed (southern) portion of the valley, sugar maple was by far the most dominant tree with white ash, white oak spp., and box-elder of secondary importance (Martin & MacMillan 1982). In 1989, 15 years after the tornado, the valley forest was described as a sugar maple/slippery elm community (MacMillan 1996). American basswood, black maple and sycamore were of secondary importance in the more damaged (northern) part of the valley, while black walnut, white ash, northern red oak, and box-elder were of secondary importance in the less damaged (southern) portion of the valley.
The objectives of this present study were to (1) describe the composition and structure of the Happy Valley forest 20 and 25 years after the tornado of 1974, (2) compare the current valley forest composition and structure with the predictions made 15 years after the tornado, and (3) predict future changes in the forest composition and structure.
STUDY SITE
Happy Valley is located at 38[degrees]43'N and 85[degrees]27'W, just east of the Hanover College campus, in Jefferson County, Indiana. The valley contains a small intermittent stream that drains from the northwest to the southeast and empties into the Ohio River. The east- and west-facing sides descend steeply (25-50% slope) ca. 250 ft (75 m) to a narrow valley floor. The wooded valley slopes are composed of Eden-Caneyville soils, and the valley floor is composed of Dearborn channery silt loam soils (Nickell 1985). Three west-to-east transects were laid out in 1974. These transects have been used in each subsequent survey (Fig. 1). Transects 1 and 2 are located in the more severely damaged north and central areas of the valley, Transect 3 is in the less-damaged southern portion.
[FIGURE 1 OMITTED]
METHODS
The point-center-quarter method described by Cottam & Curtis (1956) was used to sample the trees at 15 m intervals along each of three transects. Transect 1 (northern) is 345 m long and included 92 trees (23 points); Transect 2 (middle) is 405 m long and included 109 trees (27 points); Transect 3 (southern) is 390 m long and included 104 trees (26 points).
Data collected in the field included diameter at breast height (dbh) in cm, point-to-tree distance in meters, tree species, and any notes that might prove to be important such as the death of a previously measured tree along the transect line. Relative density, relative frequency, and relative dominance were calculated for each species using the methods of Cox (1990), and those values were summed to determine importance values. Finally, comparisons were made using Sorenson's quotient of similarity (Brower et al. 1990) and the Bray & Curtis (1957) similarity index. Sorenson's quotient of...
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