To investigate hypotheses regarding effects of competitors and site quality on oak regeneration, we documented site factors and oak seedling composition, size, and abundance in the Ridge and Valley Province of Tennessee. Small oak seedlings were most abundant on productive soils and mesic landform positions, whereas large oak seedlings were most abundant on less productive soils and drier landform positions. Patterns in the abundance of large oak seedlings and saplings were consistent with the hypothesis that oaks are most competitive on drier and poorer sites. Results were mixed with regard to existing hypotheses concerning particular competitors and competition for light.
—The effect of season of cutting on the stump sprouting of white and Shumard oaks was investigated. Replicate plots were cut at 2-month intervals from January through November, 2001. The number of sprouts and the heights and basal diameters of the three tallest sprouts per stump were recorded bi-monthly after cutting. After 4 months of growth following cutting, mean heights of white and Shumard oak sprouts were substantially greater in the September, November, and January cutting treatments than in the May treatment, with nearly a two-fold difference in mean height of Shumard oak sprouts between the September and May treatments. Similarly, mean basal diameters of Shumard oak sprouts were significantly greater in the September and November cutting treatments than in the May treatment. The greatest mean numbers of white and Shumard oak sprouts were produced in the July, September, and November treatments, but differences were not statistically significant. These patterns likely resulted from seasonal differences in stored carbohydrate reserves, and suggest that late summer, fall, and winter cutting is preferable to spring and early summer cutting in order to regenerate oak by coppicing, or to maximize the growth of sprouts from stems damaged during harvesting. Oak stump sprouts are an important means of regenerating oak stands whenever oak advance reproduction from seed is lacking and survival of oak seedlings and saplings into larger size classes is low due to interspecific competition and additional factors such as deer browsing. The rate of height growth in oak stump sprouts often exceeds that of oak seedlings and saplings originating from seed as a result of the extensive residual root systems of stumps, which contain large amounts of stored carbohydrate reserves (Johnson 1979, Reich et al. 1980, Cobb et al. 1985). The rate of height growth in oak sprouts is very important during the first growing season for establishing their competitive position in the regeneration layer, and also influences the amount of time they are near the ground and are most susceptible to deer browsing and late frosts. The relationship between stump diameter and the rate of stump sprout growth has been investigated in several studies. Sprout growth generally increases as stump diameter increases (Sander 1971, 1972, Johnson, 1979, Reich et al. 1980). The correlation between stump diameter and sprout growth can weaken, however, at diameters greater than 10-20 cm (Johnson 1979, Reich et al. 1980). Working with sprouts from large oak advance reproduction, Sander (1971) recommended ground-line diameters of oak advance reproduction between 1.27 and 2.54 cm in order to produce sprouts with sufficient growth rates to be competitive with sprouts and saplings of other species, yet limited in number. Oak species have a very large number of buds or bud bank that facilitates regrowth of stems, branches, and foliage following a variety of injuries (Ward 1964, Wilson and Kelty 1993). The ability of oak stumps to produce desirable sprouts, however, diminishes with increasing stump diameter and age (Johnson 1977, McGee 1978, Weigel and Johnson 1998). Long-term survival of hardwood stump sprouts is influenced by a number of factors, including intraand interspecific competition, the type and location of buds producing sprouts, and the ability of the overall sprout clump to maintain the residual root system (Wilson 1968, Kramer and Kozlowski 1979, Johnson et al. 2002). A number of stump sprout thinning or grooming studies (Haney 1962, Lamson 1983, Johnson and Rogers 1984, Lowell et al. 1989) have been conducted to explore means of increasing the growth, form and survival of one or a small number of sprouts on a single stump. Due to the apparent correlation between stump sprout growth and amounts of carbohydrate reserves stored in residual stump root systems, it can be hypothesized that additional factors affecting amounts of stored reserves could also affect sprout growth, regardless of stump diameter and the associated size of the residual †Assistant Professor (DSB), University of Tennessee, Agricultural Experiment Station, Department of Forestry, Wildlife and Fisheries, 274 Ellington Plant Sciences Building, Knoxville, TN 37996-4563; and Superintendent (RME), University of Tennessee, Forestry Experiment Stations, 901 South Illinois Avenue, Oak Ridge, TN 37830. DSB is corresponding author: to contact, call (865) 974-7126 or e-mail at dbuckley@utk.edu.
Oak regeneration has declined significantly over the past century in many regions of the United States. Pre- scribed burning, herbicides, and cutting are all potentially viable methods of favoring oak regeneration by removing competi- tors, but evaluation of these methods in all regions of the Eastern United States is incomplete. We compared effects of four treatments on oak regeneration and competitors: Shelterwood cutting, wildlife thinning using herbicide, wildlife thinning using herbicide combined with prescribed burning, and prescribed burning with no overstory treatment. Light, soil moisture, herbs, shrubs, woody reproduction, and overstory structure were measured to quantify treatment effects. Shelterwood harvests and wildlife thinnings significantly increased light availability and reduced overstory and midstory cover. Prescribed fire signifi- cantly increased the density of oak seedlings and sprouts < 10 cm tall. Prescribed fire also reduced the density of red maple regeneration, but significantly increased the density of sassafras and yellow-poplar regeneration.
Oak savanna remnants contribute substantially to the biodiversity of graminoid-dominated landscapes in the Great Plains Region. Most of these ecologically important ecosystems have either been altered or lost altogether since the arrival of Europeans in the early to mid-1800s. Changes in land use have been accompanied by reduced oak regeneration, which may be attributable to grazing and other management practices. At present, numbers of surviving oak seedlings are insufficient for sustaining the recruitment of oaks into savanna overstory strata. Herbivore exclosures were used to distinguish sources of mortality in first-year bur oak (Quercus macrocarpa) seedlings to determine the impacts of large mammalian herbivores, small mammals, and drought on oak regeneration in savanna remnants in Custer County, Nebraska. Results suggested an uncertain future for extant oak savannas on private land in central Nebraska. Seedlings without exclosures exhibited 97% mortality over the first growing season, and 100% mortality was observed during the subsequent dormant season in seedlings without exclosures that had survived the growing season. Although drought and small mammals contributed to overall oak seedling mortality, cattle and deer impacts were the leading causes of mortality in seedlings without exclosures. Trampling, grazing, and browsing may compromise efforts to restore and sustain these ecologically valuable ecosystems. However, effects of these factors may be reduced through management involving exclosures and limiting grazing to seasons when young oaks are less susceptible to damage.
A prominent diffi culty during bottomland hardwood aff orestation is that sites are often fl ooded during the preferred months of planting (January-March), which results in delayed planting (April-June) and reduced survival. We monitored growth and survival of oak seedlings planted in 11 diff erent months (February through December) after varying periods of humidifi ed cold storage to investigate the hypothesis that seedlings held over the summer months in cold storage and planted in autumn months would fare better than seedlings planted in late spring and summer. Results for Nuttall oak (Quercus nuttallii Palmer) generally agreed with this hypothesis, whereas results for overcup oak (Quercus lyrata Walt.) did not. Both species' height growth during the second growing season decreased with increased time in cold storage. Th ese results suggest that although reduced height growth can be expected, long-term storage over the summer months and subsequent planting in autumn need not result in heavy mortality of some bottomland oak species.
Abstract Invasion by emerald ash borer (EAB; Agrilus planipennis Fairmaire), an exotic pest, is disrupting natural processes and hindering our ability to conserve genetic diversity and perpetuate ash ecosystem services and functions. The goal of this project was to identify forest communities most at risk in terms of having altered ecosystems following EAB invasion. Using recent data available from the USDA, Forest Service, Forest Inventory and Analysis program, we calculated Shannon–Wiener species diversity index values for forests containing each of the six native ash species found in the eastern United States. These forest communities differed in their species diversity index values, and diversity indices varied across ecosystem provinces and states. In addition, communities containing ashes that are restricted by a narrow range of suitable environmental conditions consistently had lower diversity index values than communities of ash species with greater geographical ranges. Finally, forest stand cohorts (i.e., seedlings, saplings, and canopy trees) had similar species diversity indices across forest communities containing a single ash species. The tree species diversity index values quantified for communities with a single ash species will provide managers with additional information for prioritizing EAB control measures and restoration efforts following EAB invasions.
Abstract As insect pollinator populations continue to decline, it is essential to understand the impacts of anthropogenic activities, including forest management, on pollinator communities. Although multiple studies have shown that clearcutting is beneficial for bees, other less intense, selective silvicultural methods that result in disproportionate increases in edge habitat within stands are less well understood. We investigated bee community characteristics across microsites (center of cut, edge of cut, and closed-canopy forest) in three mixed-mesophytic forest stands subjected to group selection cuttings. Results revealed bee communities in the center of cuts and their edges to differ from those in forest microsites, and their diversity measures were higher than in forest microsites. Within-stand edge microsites did not differ from their cut centers in terms of their communities or their diversity. Finally, center of cut and edge microsites combined, and forest microsites, were characterized by different indicator species, thereby exemplifying differences between these two microsite groupings. These results suggest that group selection harvests support differing communities of bees across microsites and sustain a wide range of bee species, and that edges within these forest stands behaved more like extensions of canopy gap openings despite differences in forest physiognomy.
