Long-term effects of a prescribed fire regime on tree seedling density in an oak-hickory woodland
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The massive of oak-hickory forests and woodlands, in combination with the decline of dominant overstory oaks, is becoming an important management issue in the Central Hardwoods Region. Suppression of understory-tolerant species, as well as the recruitment of oaks, hickory, and shortleaf pine is a common land-management goal across the Central Hardwoods, including the Missouri Ozarks. After decades of fire suppression, land managers in the Missouri Ozark Highlands began applying prescribed fire to promote the regeneration of oak and hickory species, and to prevent the recruitment of mesophytic understory species into the overstory. In this study, 13 years of prescribed fire data were examined to determine the response of oak, hickory, and shortleaf pine tree seedling density, as well as the densities of various understory and fire tolerant species, after repeated low - to moderate-intensity periodic burns at the Ozark National Scenic Riverways. Seedling density data were collected pre-burn, then after 1, 2, 3, or 4 burns, in xeric and mesic woodland plots. Seedling density was greater in mesic woodlands than xeric woodlands, overall. Oak, hickory, and shortleaf pine seedling densities did not change due to the periodic prescribed fire regime. In xeric woodlands, seedling density increased for both intermediately understory-tolerant and understory-intolerant seedlings, while fire-tolerant species seedling density increased. No long-term changes were significant in mesic woodlands, suggesting th at prescribed fire may be affecting xeric woodlands more intensely than mesic areas, and that other ecological factors, not fire, are likely keeping understory-tolerant species at low densities. Since mesophication does not appear to be a prominent issue, and fire is disproportionately affecting xeric woodlands, recruitment may be improved by increasing the fire return interval to allow seedling growth.