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Abstract: The survival and growth of oak advance regeneration is often limited by shade-tolerant species that are abundant in the understory of oak stands. Evidence of historic burning has prompted the use of prescribed fire as a tool to improve the competitive status of oak regeneration in mature stands. A primary shortfall of fire effects research in oak forests has been a lack of long-term studies on the effects of multiple fires. Here we describe the effects of repeated fires on stand structure and tree regeneration over a 13-year period in mature mixed-oak forests located in southern Ohio, USA. Three stands were burned 3–5 times from 1996 to 2005 with low-intensity dormant-season fires, and two stands remained unburned. Woody vegetation was sampled periodically on nine 0.125ha plots per stand. Plots were located across the upland landscape and were characterized by an Integrated Moisture Index. Fire altered stand structure by reducing the density of large saplings (3.0–9.9cm DBH) and midstory trees (10–25cm DBH) by 76% and 34%, respectively. Fire had little impact on trees >25cm DBH. Small saplings (1.4m tall to 2.9cm DBH) were dynamic over time on dry plots that were burned. After being repeatedly topkilled from year 1–8, the small sapling layer had redeveloped on dry burned plots by year 13 and species composition had shifted from dominance by shade-tolerant species to a more equal distribution of shade-tolerants, oaks+hickories, and sassafras. The density of oak+hickory and sassafras advance regeneration (stems 30cm tall to 2.9cm DBH) was significantly greater on burned plots than on unburned plots in year 13, though variability among plots was high. Advance regeneration of shade-tolerant species was equally abundant on burned and unburned plots. Density of oak+hickory advance regeneration in year 13 was positively related to its weighted frequency (a surrogate for size and abundance) in year 0 (r 2 =0.67, p <0.0001) and inversely related to stand density (r 2 =0.33, p <0.0001) and canopy cover (r 2 =0.31, p <0.0001), both of which were reduced by fire. Although oak+hickory advance regeneration was more abundant on burned plots, we conclude that other methods (e.g., herbicide, partial cutting) are necessary to further reduce stand density and promote the development of larger oak+hickory regeneration, particularly on mesic sites. [Copyright &y& Elsevier]

Oak dominance is declining in the central hardwoods region, as canopy oaks are being replaced by shade-tolerant trees that are abundant in the understory of mature stands. Although prescribed fire can reduce understory density, oak seedlings often fail to show increased vigor after fire, as the canopy remains intact. In this study, we examine the response of tree regeneration to a sequence of repeated prescribed fires followed by canopy gap formation. We sampled advance regeneration (stems >30 cm tall) in 52 gaps formed by synchronous mortality of white oak ( Quercus alba L.); 28 gaps were in three burned stands and 24 gaps were in three unburned stands. Five years after gap formation, unburned gaps were being filled by shade-tolerant saplings and poles and were heavily shaded (7% of full sun). By contrast, tolerant saplings had been virtually eliminated in the burned gaps, which averaged 19% of full sun. Larger oak and hickory regeneration was much more abundant in burned gaps, as was sassafras, while shade-tolerant stems were equally abundant in burned and unburned gaps. Our results suggest that the regeneration of oak, particularly that of white oak, may be improved with multiple prescribed fires followed by the creation of moderate-sized canopy gaps (200-400 m2). [ABSTRACT FROM AUTHOR]

We used dendrochronology to examine the influence of past fires on oak and maple establishment. Six study units were located in southern Ohio, where organized fire control began in 1923. After stand thinning in 2000, we collected basal cross sections from cut stumps of oak (n = 137) and maple (n = 204). The fire history of each unit was developed from the oaks, and both oak and maple establishment were examined in relation to fire history. Twenty-six fires were documented from 1870 to1933; thereafter, only two fires were identified. Weibull median fire-return intervals ranged from 9.1 to 11.3 years for the period ending 1935; mean fire occurrence probabilities (years/fires) for the same period ranged from 11.6 to 30.7 years. Among units, stand initiation began ca. 1845 to 1900, and virtually no oak recruitment was recorded after 1925. Most maples established after the cessation of fires. In several units, the last significant fire was followed immediately by a large pulse of maple establishment and the cessation of oak recruitment, indicating a direct relationship between fire cessation and a shift from oak to maple establishment. [ABSTRACT FROM AUTHOR]