Prescribed Fire in Oak Savanna: Fire Frequency Effects on Stand Structure and Dynamics (original) (raw)
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Ecosphere, 2021
Due to decades of fire suppression, much of the Upper Midwest savanna habitat has converted to oak woodland. In efforts to restore oak savanna habitat, fire has been re‐introduced in many of these woodlands. A primary purpose of these burns is to kill the fire‐sensitive mesophytic tree species, which had established themselves during the decades of fire suppression, reduce the number of understory trees, and preserve the larger more widely spaced oaks. It is clear from ongoing efforts that restoring oak savannas will require frequent fires over decades, but frequent fires over the long term can also threaten the desirable oaks. Long‐term demographic studies at savanna restoration sites experiencing frequent fires are necessary to determine the extent to the frequent burns are supporting and/or confounding restoration goals. Results presented here are from a twenty‐five‐year demographic study of an Upper Midwest bur oak (Quercus macrocarpa) savanna/woodland experiencing frequent fire...
Fire History and Stand Structure of High Quality Black Oak ( Quercus velutina ) Sand Savannas
Natural Areas Journal, 2013
We surveyed high quality, remnant black oak sand savannas across four sites in northeastern Illinois to compare characteristics of stand structure and tree vigor with fire history. Dendrochronological methods were applied to 289 dated fire scars identified on 60 Quercus velutina trees. Stand structure was characterized using 30 circular plots (0.04 ha each) per stand during summer 2007. Tree recruitment dynamics differed among the four stands, suggesting that canopy decline dynamics among them is likely to differ in coming decades. Frequent fire intervals (less than two years) were associated with canopy openness, but also a paucity of future canopy trees. Under these frequent fire regimes, we predict a loss of canopy cover, as no smaller trees were present to assume dominance. Fire intervals longer than two years were associated with transition to closed canopy forests. These results suggest that savanna managers should consider other disturbances, such as selective cutting and or grazing, along with fire to sustain both herbaceous and canopy tree components.
Tree Density and Fire Scarring in Minnesota Oak Savanna: Implications for Restoration
Due to fire suppression subsequent to European settlement, Midwestern oak savanna has become one of the rarest ecosystems in North America, with only 0.02% of the original range surviving today. Because of the necessity of fire in perpetuating this ecosystem, restoration and management is difficult, especially because little is known about original conditions and fire dynamics of oak savanna. To address these uncertainties, fire scarring was studied at one of the longest-managed remnants of oak savanna at the Cedar Creek Natural History Area in Central Minnesota, which has been burned periodically since 1964. Fire scars lead to a lower life expectancy, therefore high levels of scarring can indicate the beginnings of a shift towards prairie or oak scrub. Both contact and non-contact scarring are prevalent in oak savanna at Cedar Creek, with scarring on as much as 80% of trees over 10 cm DBH. Contact scarring is more prevalent in areas with higher tree densities prior to the start of ...
Canadian Journal of Forest Research, 2019
Understanding the effects of fire on advance regeneration of oak (Quercus L.) species and their competitors is an important step in determining the role of prescribed fire in regenerating and restoring upland oak ecosystems. Our study aimed to understand how dormant-season prescribed fire affects advance regeneration of chinkapin oak (Quercus muehlenbergii Engelm.), black oak (Quercus velutina Lam.), and their major competitors at sites targeted for woodland restoration and management. We analyzed relationships between stem size and survival probability; determined the effect of fire temperature on survival probability; and compared how mortality, sprouting, and survival differed among species. For chinkapin oak, black oak, and bitternut hickory (Carya cordiformis (Wangenh.) K. Koch), mortality was low and rate of sprouting was high after shoot dieback. Initial basal diameter was significantly related to survival probability after one fire for all species except chinkapin oak and bl...
Forest Ecology and Management, 2012
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 13year 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 0.125 ha 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 (3.0-9.9 cm DBH) and midstory trees (10-25 cm DBH) by 76% and 34%, respectively. Fire had little impact on trees >25 cm DBH. Small saplings (1.4 m tall to 2.9 cm 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 30 cm tall to 2.9 cm 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.
Silvicultural considerations for managing fire-dependent oak woodland ecosystems
2014
Oak woodlands are characterized by open understories and dense ground flora composed of forbs, grasses, and sedges. They once were common in the western Central Hardwood Forest region and the prairie-forest transition zone where lowintensity fires occurred frequently. In the absence of fire, many of the woodland ecosystems throughout much of this region have succeeded to compositions and structures resembling those of mesophytic forests. Consequently, forest managers are increasingly interested in restoring the structure and composition of oak woodlands by thinning and prescribed burning. Presently, there are few guidelines based upon silvicultural principles for restoring and managing woodland ecosystems. However, many silvicultural concepts, principles, and methods used for managing forests can also be used for managing woodlands, but the application and timing of treatments may differ to meet the objectives of woodland management. In this paper, we summarize findings from a number of studies and offer guidelines for restoring and managing oak woodlands.
Changes in Hoosier Prairie Oak Savanna During 27 Years of Prescribed Fire Management
The Michigan Botanist, 2007
Hoosier Prairie Nature Preserve, located in northwestern Indiana, protects a rare and unusually high quality example of a Midwestern (USA) oak savanna. Although many savannas in the region have been lost to agriculture, urbanization, and fire suppression, parts of the 178 hectare preserve never lost its historic community structure. A program of prescribed burning was initiated in 1978 and monitoring of two 10 × 10 m sample areas (Blocks) began in 1979. Throughout the 27 year observation period each Block retained a distinct understory composition even though subjected to similar fire regimes. At the same time, each underwent notable and individualistic changes from their original species composition (SSI = 64-69%) but continued to support a remarkably high diversity of xeric and mesic forbs. Native species richness ranged from 34-58 species per Block and as high as 16.8 species per 0.67 m 2 quadrat. Additionally, according to the Floristic Assessment metrics, the species quality of contemporary Hoosier Prairie is comparable (mean C = 4.9) to that expected in regional pre-settlement oak savanna communities.
Forest Ecology and Management, 2005
This study quantifies prescribed fire effects at four sites in southern Ohio, from 1995 to 2002. Each site had three treatment units: an unburned control, a unit burned 2 x (1996 and 1999), and a unit burned 4 x (1996-1 999). Vegetation plots were stratified by an integrated moisture index (IMI) into xeric, intermediate, and mesic classes. Prior to treatments, oak (Quercus spp.) and hickory (Carya spp.) comprised 74-83% of basal area among sites but shade-tolerant species (e.g., Acer rubmm) were abundant in the midstory and completely dominated the sapling layer. Fires were conducted in March and April. Fire intensity, estimated by temperature-sensitive paints, was highest on the 2 x bum units. Fires had little effect on large tree (>25 cm DBH) density and stand basal area. By contrast, the density of small trees (10-25 cm DBH) was reduced by 31% on 2 x burn units and by 19% on 4x burn units. "Fire-induced" mortality (i.e., mortality on bum units above that of unburned units) for the most common species of small trees was: A. rubrum = 33%; Quercus alba = 17%; Carya spp. = 13%; Nyssa sylvatica = 10%; Acer saccharwn = 4%; Quercus prinus = 2%. Sapling density was reduced by 86% on burn treatments. Despite reduced small tree and sapling densities on burned units, canopy openness, estimated by hemispherical photography, remained low (<6%). In general, the composition of tree regeneration was not substantially altered by fire treatments. On bum units, a significant initial decrease in A. rubncrn seedling density and a significant increase in Liriodendron tulipifera from the seed bank did not persist throughout the study. Oak + hickory seedling density was not significantly affected by fire nor was the density of shade-tolerant seedlings. Post-treatment (2002) sampling of large seedlings (>30 cm height) indicated no significant differences in the abundance of oak + hickory nor that of shade-tolerant seedlings among fire treatments. For most vegetation response variables, fire effects tended to be similar among IMI classes. The application of fire alone, without partial harvesting, failed to improve oak regeneration consistently. However, given that two fires reduced stand density, the longer term application of periodic fire, coupled with natural gap dynamics, may still be a feasible management strategy for improving the sustainability of oak forests where harvesting is not permitted or desired.
Atti del Secondo Congresso Internazionale di Selvicoltura = Proceedings of the Second International Congress of Silviculture, 2015
Variability in historic fire regimes in eastern North America resulted in an array of oak savannahs, woodlands and forests that were dominant vegetation types throughout the region. In the past century, once abundant savannahs and woodlands have become scarce due to conversion to agriculture, or development of forest structure in the absence of fire. In addition, the future dominance of oak forests is uncertain due to chronic low regeneration potential of oak across the region and insufficient overstory recruitment. Restoration of oak savannahs and woodlands, and sustaining oak forests are primary goals for land management agencies and conservation organizations. Insights learned from fire history research can be used to guide silviculture prescriptions to achieve these goals. Restoration of oak savannahs and woodlands requires a long-term regimen of prescribed burning, but it takes a combination of prescribed fire, timber harvesting and forest thinning to efficiently produce desired structure and composition. Sustaining oak savannahs and woodlands requires an occasional longer fire-free period to allow for replacement of the overstory by recruitment of trees from the reserve of oak sprouts that have accumulated in the understory. Prescribed fire is useful for sustaining oak forests, but it must be used judiciously to minimize timber damage and decreases in value. Integrating fire in a silvicultural prescription that uses the shelterwood regeneration method to promote competitive oak reproduction has been successfully applied in the eastern US to sustain oak forests. Restoration of oak ecosystems is possible but requires innovative combinations of traditional practices, including prescribed burning.