Eric J. Holzmueller

Influence of calcium, potassium, and magnesium on Cornus florida L. density and resistance to dogwood anthracnose

Dogwood anthracnose, a major disease of Cornus florida L., has caused heavy mortality of C. florida in eastern United States forests. Disease severity and rate of infection have been shown to vary with several environmental factors, but the link between soil cation availability and anthracnose has not been examined. We hypothesized that soil cation availability, particularly calcium (Ca), potassium (K), and magnesium (Mg), would influence dogwood survival from anthracnose. In forested stands, positive correlations between soil Ca, K, and Mg saturation and C. florida stem density and basal area were found. The effect of these cations at four levels (0, 50, 100, and 200%) of a standard nursery fertilization rate on C. florida seedling survival and resistance to dogwood anthracnose was tested. Although most of the seedlings died after one season of exposure to dogwood anthracnose, seedlings that had lower inputs of Ca and K cations showed higher levels of disease severity sooner than seedlings in other treatments, suggesting that these nutrients play a role in C. florida survival from anthracnose. Magnesium treatment levels did not appear to have an effect on C. florida disease severity or mortality.

Early impacts of hemlock woolly adelgid in Tsuga canadensis forest communities of the southern Appalachian Mountains1

Abstract Throughout much of its range, Tsuga canadensis (L.) Carr. (eastern hemlock) is severely threatened by the hemlock woolly adelgid (HWA; Adelges tsugae Annand), an exotic, invasive insect introduced from Japan. HWA causes defoliation and mortality, which presents a serious threat to the survival of T. canadensis in forests of eastern North America. Although HWA has been extensively studied in the forests of New England and the Mid-Atlantic, its spread into forested ecosystems throughout the southern Appalachian Mountains is relatively recent, and few studies have addressed the early impacts of this biological invasion. This study utilized forest inventory data collected in 2003, and again in 2008–2009 to quantify T. canadensis mortality and consequential shifts in species composition resulting from infestations of HWA throughout Great Smoky Mountains National Park. We observed significant decreases in the density of overstory and understory T. canadensis. The majority of the surviving overstory T. canadensis trees are in severe decline, and will likely die in the coming years. Furthermore, understory T. canadensis trees have experienced greater rates of mortality than overstory trees. No individual site or stand characteristic was correlated with mortality. Overstory and understory species composition did not significantly change over the observation period, but the overwhelming presence of Rhododendron maximum L. (rosebay rhododendron) in the understory may influence future successional trends in forests of the southern Appalachian Mountains.

Biomass production for biofuels using agroforestry: potential for the North Central Region of the United States

As demand for energy increases in the United States, alternative energy sources are being sought both domestically and abroad. Biofuels have been promoted as a major source of alternative energy, but sustainable supply of biomass still remains a major challenge. Agroforestry offers a potential way to integrate perennial woody bioenergy crops with traditional agricultural crops to satisfy energy demands without sacrificing food production in the North Central Region of the United States. We suggest shelterbelts, alley cropping and working riparian buffer strips as ideal candidates for biomass production in agroforestry settings in this region. In addition to satisfying domestic energy demands, these systems could also potentially increase water quality, sequester carbon, improve aesthetics, and provide critical wildlife habitat. However, obstacles to implementing agroforestry systems for biomass production, such as a competitive price structure and stable markets, must be overcome before large-scale adoption by landowners.

Invasion success of cogongrass, an alien C4 perennial grass, in the southeastern United States: exploration of the ecological basis

Cogongrass (Imperata cylindrica) is considered one of the worst invasive species in the world. The species is readily adaptable to a wide range of environmental conditions and upon invasion reduces forest productivity, alters nutrient cycling, and threatens native species biodiversity. This paper explores seven major ecological hypotheses (Propagule Pressure Hypothesis, Natural Enemies or Enemy Release Hypothesis, Empty Niche Hypothesis, Invasional Meltdown Hypothesis, Evolution of Increased Competitive Ability Hypothesis/Superior Competitor Hypothesis, Novel Weapons Hypothesis, and Diversity—Invasibility (Elton’s) Hypothesis) that explain the invasiveness of cogongrass in the southeastern United States. Information gathered from this review can be used to reduce the spread of cogongrass and is applicable for control of other invasive species as well.

The Response of Understory Species Composition, Diversity, and Seedling Regeneration to Repeated Burning in Southern Appalachian Oak-Hickory Forests

ABSTRACT: Understory plant composition and diversity levels in oak-hickory (Quercus-Carya) forests have historically been maintained by periodic low-intensity ground fires, but fire suppression has altered the structure and function of these communities. We examined burned and unburned oak-hickory stands to determine the influence of repeated burning on understory communities. We compared understory herbaceous, shrub, and tree species diversity and composition among four burn categories: unburned stands, and stands that had burned once, twice, and three times over a 20-year period (late 1960s to late 1980s). We hypothesized that stands that have received repeated burns will have greater understory diversity and reduced importance of shade-tolerant mesophytic species. We found that burned stands had greater species richness than unburned stands, regardless of burn frequency. Species composition was not drastically different among the four burn categories; however, individual species were indicative of particular burn categories. More forest herbs were associated with the single burn category, while more disturbance-dependent species (Desmodium spp. and Solidago spp.) were associated with the repeated burn categories. Burned stands contained greater densities of white oak (Quercus alba L.) and hickory species seedlings. Our results suggest that restoring and maintaining the historic fire return interval (10–15 years) will promote herbaceous species diversity and favor the regeneration of oak and hickory species. However, it has been 15–22 years since the stands we sampled last burned, and the similarity among burn categories suggests that additional burning is needed to prevent these stands from reverting to a suppressed condition.

Using prescribed fire to protect flowering dogwood from dogwood anthracnose (Illinois).

Using Prescribed Fire to Protect Flowering Dogwood from Dogwood Anthracnose (Illinois) Eric J. Holzmueller (Dept of Forestry, center for Ecology, 1205 lincoln Dr—Mc 4411, southern illinois University, carbondale, il 62901, 618/453-3708, eholzmue@siu.edu), David J. gibson (Dept of Plant Biology, center for Ecology, southern illinois University, 1125 lincoln Drive, carbondale, il 62901) and Paul F. suchecki ( Johnston city High school, 1500 Jefferson ave, Johnston city, il 62951)

Black Walnut Allelopathy: Implications for Intercropping

Black Walnut (Juglans nigra L.) produces the chemical juglone that has an allelopathic effect on some companion species in intercropped systems. Nevertheless, black walnut continues to be a popular planted species in alley cropping, silvopastoral, and mixed species systems. Recent advances in management techniques, including the use of polyethylene root barriers, trenching or disking, and planting and managing the companion species during the early establishment of black walnut, have proven to be effective in alleviating the allelopathic effects of juglone. While allelopathic interference is a reality in black walnut intercropped systems, management intervention may help sustain the production potential so that they become an economically viable option for landowners.

Managing Wicked Environmental Problems as Complex Social-Ecological Systems: The Promise of Adaptive Governance

Lessons learned from the failure of rational-comprehensive planning approaches to the management of water and other natural resources have led to a rethinking of the nature of resource management problems. The concept of wicked problems is increasingly used to describe problems that lack consensus in terms of their definition and solutions. In line with the ongoing search for appropriate conceptual frameworks and institutions for managing wicked problems, this chapter argues for a reconceptualization of wicked problems as complex social-ecological systems . Such a reconceptualization calls for a resilience-based approach to managing wicked problems through adaptive governance institutions. Adaptive governance provides a multi-level institutional framework for managing the uncertainties and conflicts that characterize wicked environmental problems. This argument is illustrated using the case of the Cache River watershed in southern Illinois, USA.

Tree Response to Experimental Watershed Acidification

Forest ecosystems in the Eastern USA are threatened by acid deposition rates that have increased dramatically since industrialization. We utilized two watersheds at the Fernow Experimental Forest in West Virginia to examine long-term effects of acidification on ecological processes. One watershed has been treated with ammonium sulfate (approximately twice the ambient deposition rate) since 1989 to simulate elevated acidic deposition, while the other served as a control. Prior to treatment, both watersheds were similar in age and species composition. Ten dominant overstory Prunus serotina and Liriodendron tulipifera trees were selected and cored from each watershed to measure bolewood concentrations of essential elements through time. In addition, changes in tree species basal area were analyzed utilizing 50 long-term growth plots. Results of this experiment show lower calcium and magnesium concentration and increased acidic cation concentration for both species in the treated watershed, indicating a negative treatment effect. Growth response, measured through relative growth rates of cored trees and changes in basal area from growth plots, was not as conclusive and appeared to differ by species. The resulting difference in species response indicates that acidification sensitivity is something that land managers should consider when managing forests affected by acidification.

Response of Cogongrass to Imazapyr Herbicides on a Reclaimed Phosphate-Mine Site in Central Florida, USA

Cogongrass (Imperata cylindrica) is a globally recognized invasive weed; it has caused land management problems and threatened critical habitat in the southeastern United States as well as on most continents. We tested four rates of imazapyr (1.17, 2.34, 3.51 and 4.68 L/ha), the most effective active ingredient available for cogongrass control, as two formulations (Chopper and the new generation Chopper known as Chopper GEN2) on cogongrass cover over a 27–month period in central Florida. One month after the June treatment, Chopper GEN2 provided significantly greater cover reduction than the original Chopper formulation. Twelve months after treatment, cogongrass top regrowth cover was similar among all herbicide treatments, ranging from 1% to 3%. However, 15 months after treatment, cogongrass cover was significantly higher at the lowest rates of Chopper treatments than for the Chopper GEN2 treatments, and this trend continued throughout the experiment. Overall, Chopper GEN2 provided immediate control (one month after treatment) that continued to 27 months after treatment.