Effect of fire intensity on understory composition and diversity in a Kalmia-dominated oak forest, New England, USA.

Published source details Ducey M.J., Moser W.K. & Ashton P.M.S (1996) Effect of fire intensity on understory composition and diversity in a Kalmia-dominated oak forest, New England, USA. . Plant Ecology (formerly Vegetatio 1948-1996), 81-90.
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Summary

Evidence suggests that recurrent fire played a major role in promoting the pre- and post-European settlement dominance of oak Quercus forests in eastern North America. The absence of fire or other disturbance has been suggested as a potential cause for oak regeneration failure and conversion of many former oak-dominated forests to other woodland types. Despite the importance of fire to oak forest ecosystems, the relationship between fire intensity and oak forest dynamics is not clearly understood. This is particularly true of the herbaceous and woody understory. This study examines the effects of fire on understory diversity and composition at two sites in Connecticut, northeast USA.

Study sites: Two mixed-oak stands (each c. 4 ha) in the Yale-Myers Forest in Eastford, Connecticut (41º55' N, 72º05' W) northeast USA, were selected. Prior to burning, both had a homogenous overstory tree canopy, with an understory dominated by a dense growth of mountain laurel Kalmia latifolia.

Prescribed burns: Burning was undertaken in August, 1993. At each site, 16, 4.047 mÂ² circular plots were systematically located in each of three treatments: unburned control, moderate burn with light overstory damage; and severe burn with heavy overstory damage.

Composition and diversity of woody and herbaceous species in the understory were measured in the two stands 7-8 years after the prescribed burns in each of the three treatment areas.

Most species increased in density and frequency following fire; only wild sarsaparilla Aralia nudicaulis and white oak Quercus alba showed statistically significant decreases. Overall, 29 species increased in density and eight declined after fire; 29 increased in frequency and six declined. However, plant diversity was depressed on the moderately burned sites due to rapid regrowth of the previously dominant Kalmia. No common herbaceous or woody species disappeared following burns, and different species responded in different ways both to burning and site variation.

Among the herbaceous species, Aster divaricatus, Desmodium ciliare, Fragaria virginiana, Galium boreale, Gaultheria procumbens, Mitchella repens and Rubens pubescens increased in density on burned sites, while Aralia nudicaulis declined. Uncommon species found only on burned sites included Epitobium hirsutum, Impatiens capensis, Monotropa uniflora and Solidago bicolor; Cypripedum reginae and Epigaea repens were found only in unburned plots; both species are characteristic of wet habitats and may thus not survive in the relatively open, dry environment after a severe burn.

Among the woody species, Betula papyrifera, Kalmia latifolia, Pinus resinosa, Pinus strobus, Quercus rubra, Quercus vetutina, Rubus idaeus and Vitis labrusca increased in density on the burned sites; only Quercus alba and Aralia nudicaulis declined.

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