Rose-Marie Muzika

Dynamics of an anthropogenic fire regime

Human interaction with fire and vegetation occurs at many levels of human population density and cultural development, from subsistence cultures to highly technological societies. The dynamics of these interactions with respect to wildland fire are often difficult to understand and identify at short temporal scales. Dendrochronological fire histories from the Missouri Ozarks, coupled with human population data, offer a quantitative means of examining historic (1680–1990) changes in the anthropogenic fire regime. A temporal analysis of fire scar dates over the last 3 centuries indicates that the percent of sites burned and fire intervals of anthropogenic fires are conditioned by the following four limiting factors: (a) anthropogenic ignition, (b) surface fuel production, (c) fuel fragmentation, and (d) cultural behavior. During an ignition-dependent stage (fewer than 0.64 humans/km2), the percent of sites burned is logarithmically related to human population (r2 = 0.67). During a fuel-limited stage, where population density exceeds a threshold of 0.64 humans/km2, the percent of sites burned is independent of population increases and is limited by fuel production. During a fuel-fragmentation stage, regional trade allows population densities to increase above 3.4 humans/km2, and the percent of sites burned becomes inversely related to population (r2 = 0.18) as decreases in fuel continuity limit the propagation of surface fires. During a culture-dependent stage, increases in the value of timber over forage greatly reduce the mean fire interval and the percent of sites burned. Examples of the dynamics of these four stages are presented from the Current River watershed of the Missouri Ozarks.

What causes outbreaks of the gypsy moth in North America

Abstract The gypsy moth has been present in North America for more than 100 years, and in many of the areas where it has become established outbreaks occur with varying degrees of periodicity. There also exists extensive spatial synchrony in the onset of outbreaks over large geographic regions. Density-dependent mortality clearly limits high-density populations, but there is little evidence for strong regulation of low-density populations. Predation by small mammals appears to be the major source of mortality affecting low-density populations, but because these are generalist predators and gypsy moths are a less preferred food item, mammals do not appear to regulate populations in a density-dependent fashion. Instead, predation levels appear to be primarily determined by small mammal abundance, which is in turn closely linked to the production of acorns that are a major source of food for overwintering predator populations. Mast production by host oak trees is typically variable among years, but considerable spatial synchrony in masting exists over large geographic areas. Thus, it appears that the temporal and spatial patterns of mast production may be responsible for the episodic and spatially synchronous behavior of gypsy moth outbreaks in North America. This multitrophic relationship among mast, predators, and gypsy moths represents a very different explanation of forest insect outbreak dynamics than the more widely applied theories based upon predator–prey cycles or feedbacks with host foliage quality.

Effect of Forest Structure and Fragmentation on Site Occupancy of Bat Species in Missouri Ozark Forests

Abstract Changes in structure and arrangement of forests may influence the distribution of bat communities by affecting roosting and foraging habitat. Using Anabat bat detectors, we determined presence of bat species at 316 sample plots in southeastern Missouri, USA, through qualitative identification of echolocation calls collected. We used maximum-likelihood estimation techniques incorporating detection probabilities into estimation of site occupancy by species of bats. We compared a priori models at 2 geographic scales using information theoretic methods. At the local-site scale, eastern pipistrelle (Pipistrellus subflavus) and red bat (Lasiurus borealis) occupancy was most influenced by structural characteristics of forested areas, whereas Indiana bats (Myotis sodalis) were influenced most by density of large-diameter snags that could provide roosting habitat. At the landscape scale, occupancy of Indiana bats was directly related to amount of nonforested land cover. Northern long-eared bat (M. septentrionalis) occupancy was inversely related to edge. These data describe implications of forest fragmentation and provide information that can be used when integrating forest-management practices into bat conservation.

HISTORICAL CO2 GROWTH ENHANCEMENT DECLINES WITH AGE IN QUERCUS AND PINUS

Despite experimental evidence showing that elevated C02 levels increase growth in most plants, the isolation of a signal consistent with anthropogenically caused increases in atmospheric C02 from the dendrochronological record has shown mixed results. Our extensive sets of tree ring data from the Ozark Mountains in Missouri showed that since 1850, Quercus velutina Lam., Quercus cocc?nea Muench., and Pinus echinata Mill, trees increased in stem growth coincidently with increases in atmospheric C02. Those long-term increases in radial growth appear unrelated to historical disturbance levels for the region, to long-term changes in relevant climatic variables, or to productivity of sites sampled for the purpose of creating a time sequence of tree ring growth. It is still unclear what the potential role of nitrogen deposition might have been for tree growth. We cross-dated a large number of increment cores and aligned the ring width data by pith date for accurate age constant assessments of growth over the past 150 years. Thus, we circumvented changes in growth trend associated with differences in physiological functioning during development, as well as the need for statistical detrending that removes an unknown degree of long-term environmental signal, the so called segment length curse that applies to standard dendrochronological investigations. When the positive relationship between C02 and ring width was examined at different ages, an ontogenetic decline in the rate of growth stimulation was found. Specifically, both the pooled Quercus spp. and P. echinata were characterized by a negative exponential pattern of response over a developmental sequence through age 50. Further knowledge of an intrinsic decline in C02 sensitivity with tree age or size such as this may be important for increased accuracy in estimating terrestrial carbon stocks across successional landscapes.

Effects of alternative prey on predation by small mammals on gypsy moth pupae

Previous work shows that predation by small mammals is a dominant cause of mortality of low-density gypsy moths in North America and that declines in small mammal density result in increases in gypsy moth density. Here we examined whether predation by small mammals is density dependent by way of a type III functional response, and how predation is influenced by alternative prey. First we showed that the preference of predators for gypsy moth pupae was low compared to other experimental prey items, such as mealworm pupae and sunflower seeds. Predation on gypsy moth pupae was characterized by a type II functional response with percent predation highest at the lowest prey densities, whereas the functional response to sunflower seeds was characterized by a type III functional response in which predation increased with increasing prey density. These results suggest that predation by small mammals is unlikely to stabilize low-density gypsy moth populations.

Estimating Probabilities of Detection for Bat Echolocation Calls: An Application of the Double-Observer Method

Abstract Differential detectability is an issue of great practical importance in bat species (Order Chiroptera) surveys. Bat echolocation recorders increasingly are being used in survey efforts, but recorder-based surveys have not measured differences in detection probability quantitatively. A recently developed avian survey technique uses 2 observers at a site to estimate the probability of detection by comparing birds recorded independently by the 2 observers. We applied this method to bat surveys using remotely operated Anabat echolocation recorders. We placed 2 detectors at each sample point, which were randomly selected from forested habitat within 2 watersheds in Indiana and 2 in Missouri. The first detector was oriented toward the most open area of forest and the second was set 5 m away and oriented toward the most open area that allowed sampling of an area distinct from the first detector. We estimated detection probabilities using the Huggins closed-capture model in program MARK. We compared models of detection probability using the corrected quasi-likelihood Akaikes Information Criterion adjusted for overdispersion (QAICc). The best models accounted for detector placement and region but not species. Overall probability of detection for bats using 2 detectors was 0.62 in Indiana and 0.42 in Missouri. Results confirmed that a second detector increased the probability of detecting different species of bats at a site. Future regional comparisons should account for differences in detection probability to avoid biases associated with surveys relying solely on recorded calls.

Interactive effects of harvest and deer herbivory on the population dynamics of American ginseng.

Few demographic models for any species consider the role of multiple, interacting ecological threats. Many forest herbs are heavily browsed by white-tailed deer (Odocoileus virginianus) and a number of these are also harvested for the medicinal, floral, or horticultural trades. Previous studies of the viability of American ginseng (Panax quinquefolius) have separately examined the effects of harvesting and deer herbivory. We followed individually marked ginseng plants in 6 populations for 8 years and documented deer browse levels, conducted helicopter surveys to estimate the deer herd size, and documented 2 ginseng harvests. We used this long-term data set to develop a stochastic demographic model that quantified the separate and interactive role of these threats to ginseng viability. Although harvesting and deer herbivory negatively affected ginseng population growth, their effects were not additive. Deer herbivory negatively affected population growth in the absence but not in the presence of harvesting. Life table response experiments revealed that in the presence of harvesting, deer herbivory had some positive effects on vital rates because browsed plants were less apparent to harvesters. Ginseng populations that were harvested responsibly (i.e., planting seeds from harvested individuals) had higher growth rates than those that were harvested irresponsibly. We concluded that both deer populations and harvesting must be managed to ensure sustainable populations of American ginseng. Our findings underscore the importance of long-term monitoring to assess threats to viability and the need for a broad ecological understanding of the complexity of ecosystem management.

The Influence of Forest Stand and Site Characteristics on the Composition of Exotic Dominated Ambrosia Beetle Communities (Coleoptera: Curculionidae: Scolytinae)

ABSTRACT Economic and biological consequences are associated with exotic ambrosia beetles and their fungal associates. Despite this, knowledge of ambrosia beetles and their ecological interactions remain poorly understood, especially in the oak—hickory forest region. We examined how forest stand and site characteristics influenced ambrosia beetle habitat use as evaluated by species richness and abundance of ambrosia beetles, both the native component and individual exotic species. We documented the species composition of the ambrosia beetle community, flight activity, and habitat use over a 2-yr period by placing flight traps in regenerating clearcuts and older oak—hickory forest stands differing in topographic aspect. The ambrosia beetle community consisted of 20 species with exotic ambrosia beetle species dominating the community. Similar percentages of exotic ambrosia beetles occurred among the four forest habitats despite differences in stand age and aspect. Stand characteristics, such as stand age and forest structure, influenced ambrosia beetle richness and the abundances of a few exotic ambrosia beetle species and the native ambrosia beetle component. Topographic aspect had little influence on ambrosia beetle abundance or species richness. Older forests typically have more host material than younger forests and our results may be related to the amount of dead wood present. Different forms of forest management may not alter the percent contribution of exotic ambrosia beetles to the ambrosia beetle community.

Evaluation of Continuous In Situ Monitoring of Soil Changes with Varying Flooding Regimes

Abstract To support investigations of flood tolerance occurring at a field‐based research facility, changes in soil volumetric water content, temperature, redox potential, dissolved oxygen content, and pH over the course of flood events were monitored. Electronic sensors connected to dataloggers for continuous monitoring of these parameters were installed, and soil redox potential and pH were also monitored manually for comparison. Soil volumetric water content showed that soils became saturated quickly following inundation. Soil redox potentials revealed a reduction of the soil with inundation; however, stagnant water treatments did not result in lower redox potentials than flowing water treatments. Similarly, dissolved oxygen content was not lower in the stagnant water treatment. The automated and manual systems detected similar trends in redox potential response to flooding; however, redox potentials measured manually were generally higher and significantly different from those obtained with the automated system. Anomalous readings were detected with the automated measurement of soil pH, indicating further need for improvement of this system.

More than Drought: Precipitation Variance, Excessive Wetness, Pathogens and the Future of the Western Edge of the Eastern Deciduous Forest

For many regions of the Earth, anthropogenic climate change is expected to result in increasingly divergent climate extremes. However, little is known about how increasing climate variance may affect ecosystem productivity. Forest ecosystems may be particularly susceptible to this problem considering the complex organizational structure of specialized species niche adaptations. Forest decline is often attributable to multiple stressors including prolonged heat, wildfire and insect outbreaks. These disturbances, often categorized as megadisturbances, can push temperate forests beyond sustainability thresholds. Absent from much of the contemporary forest health literature, however, is the discussion of excessive precipitation that may affect other disturbances synergistically or that might represent a principal stressor. Here, specific points of evidence are provided including historic climatology, variance predictions from global change modeling, Midwestern paleo climate data, local climate influences on net ecosystem exchange and productivity, and pathogen influences on oak mortality. Data sources reveal potential trends, deserving further investigation, indicating that the western edge of the Eastern Deciduous forest may be impacted by ongoing increased precipitation, precipitation variance and excessive wetness. Data presented, in conjunction with recent regional forest health concerns, suggest that climate variance including drought and excessive wetness should be equally considered for forest ecosystem resilience against increasingly dynamic climate. This communication serves as an alert to the need for studies on potential impacts of increasing climate variance and excessive wetness in forest ecosystem health and productivity in the Midwest US and similar forest ecosystems globally.