Erik V. Nordheim

Estimating the leaf area index of North Central Wisconsin forests using the landsat thematic mapper

Abstract Leaf area index (LAI) is an extremely important structural characteristic of vegetation because it is directly related to the exchange of energy, CO2 and mass from plant canopies at a variety of scales. Research investigating the relationship between forest LAI and satellite data for hardwood and mixed conifer-hardwood forests is lacking, however. The objective of this study was to explore the utility of Landsat-5 Thematic Mapper (TM) data for accurately estimating the LAI of conifer, hardwood, and mixed conifer-hardwood forests in north central Wisconsin. Individual bands and vegetation indices (VIs) calculated from satellite measures of exoatmospheric reflectance were related to the litterfall-estimated LAI of 24 stands. The results showed that individual bands or VIs containing at least one infrared (IR) band (either near- or mid-infrared) or a strong IR component divided data into at least two groups, with each group requiring a different regression line. The primary division was between conifer-dominated and hardwood-doin inated stands. Of the individual bands and VI.s considered, seven were strongly correlated to the LAI of conifer stands (r2=0.69–0.73). For the hardwoods, the best individual band or VI was Green/mid-IR#1 (r2=0.35), although an additional individual band and two VIs did much better using re subset of lower LAI stands (r2=0.60–0.75). For individual bands and VIs not requiring a conifer-hardwood distinction, the sixth Tasseled Cap component was most closely related to LAI (r2=0.60). Multiple-variable models (using LAI as the dependent variable) were found to offer substantial improvement over single-variable models, especially for hardwood stands. We recommend for further consideration a four-variable model for the conifers, and one four-variable and two eight-variable models for the hardwoods.

Foliar quality influences tree-herbivore-parasitoid interactions: effects of elevated CO2, O3, and plant genotype

This study examined the effects of carbon dioxide (CO2)-, ozone (O3)-, and genotype-mediated changes in quaking aspen (Populus tremuloides) chemistry on performance of the forest tent caterpillar (Malacosoma disstria) and its dipteran parasitoid (Compsilura concinnata) at the Aspen Free-Air CO2 Enrichment (FACE) site. Parasitized and non-parasitized forest tent caterpillars were reared on two aspen genotypes under elevated levels of CO2 and O3, alone and in combination. Foliage was collected for determination of the chemical composition of leaves fed upon by forest tent caterpillars during the period of endoparasitoid larval development. Elevated CO2 decreased nitrogen levels but had no effect on concentrations of carbon-based compounds. In contrast, elevated O3 decreased nitrogen and phenolic glycoside levels, but increased concentrations of starch and condensed tannins. Foliar chemistry also differed between aspen genotypes. CO2, O3, genotype, and their interactions altered forest tent caterpillar performance, and differentially so between sexes. In general, enriched CO2 had little effect on forest tent caterpillar performance under ambient O3, but reduced performance (for insects on one aspen genotype) under elevated O3. Conversely, elevated O3 improved forest tent caterpillar performance under ambient, but not elevated, CO2. Parasitoid larval survivorship decreased under elevated O3, depending upon levels of CO2 and aspen genotype. Additionally, larval performance and masses of mature female parasitoids differed between aspen genotypes. These results suggest that host-parasitoid interactions in forest systems may be altered by atmospheric conditions anticipated for the future, and that the degree of change may be influenced by plant genotype.

Inference from Nonrandomly Missing Categorical Data: An Example from a Genetic Study on Turner's Syndrome

Abstract The process leading to partial classification with categorical data is sometimes nonrandom. A particular model accounting for incomplete data, which allows the probability of uncertain classification to depend on category identity, is utilized for an analysis of data obtained from a genetic study on Turners syndrome. Estimates of population proportions are obtained from maximum likelihood. A method for handling nonrandomly missing data arrayed in contingency tables is discussed. Sensitivity analyses incorporating parameters related to the missing-data mechanism are recommended for estimation and testing.

Estimating Gap Origin Probabilities for Canopy Trees

A method is presented for estimating the probability that existing canopy trees were growing in gaps during the sapling stage, given observed mean 5—yr radial growth rates starting at the point where the trees were 4 cm diameter at breast height (dbh). Required calibration data are frequency distributions of radial growth rate for existing saplings that are currently suppressed in the forest understory vs. those of saplings growing in gaps. Threshold growth rates for high confidence of gap origin are calculated in an iterative fashion using growth rate data and interpretation of radial increment patterns. The method is illustrated with data from sugar maple (Acer saccharum) and eastern hemlock (Tsuga canadensis) in mature and old northern hardwood forests of western Upper Michigan. The proportion of canopy trees that had been growing in gaps during the sapling stage ranged from 35—67% in different stands. This wide range suggests the adaptability of these two late—successional, shade—tolerant species to a...

Charring rate of wood for ASTM E 119 exposure

Analytical methods that predict the endurance of structural wood members in a fire are based on the reduction of the cross section of the member caused by wood being charred. To define the charring rate in terms of more fundamental properties, empirical models were established. Eight species were tested for charring rates and material properties. Regression analysis was used to develop the models. The predictor variables for the initial factorial design included density, moisture content, treatability, and hardwood-softwood classification. The addition of char contraction simplified the model and reduced the predictor variables to the char contraction factor, density, and moisture content. Our results show the importance of surface recession and moisture content to wood charring.

How many choices can your test animal compare effectively? Evaluating a critical assumption of behavioral preference tests

Abstract. Behavioral choice tests comprise one of the most commonly used experimental designs in ecology. However a critical assumption of these assays, that the outcome is independent of the number of choices, has not been tested explicitly. We developed a methodology for testing this assumption, and discuss how it can be incorporated into experimental design. The model with which we performed this test consisted of an insect herbivore, the gypsy moth Lymantria dispar L., feeding on a clonal host plant, Populus. We established a dose-response feeding gradient by amending leaves of a single age class with defined concentrations of a diterpene, isopimaric acid, that exhibits feeding deterrent properties. We selected various concentrations that elicited different levels of feeding for subsequent tests in which we modified the number of choices. A sample size of 30 assay units per test generated statistically significant separations in two-way choice tests, yielded statistically significant but somewhat inconsistent results when four concentrations were offered, and failed to provide complete separation when five concentrations were offered. Other factors associated with the number of choices that affected results included specific combinations of doses, physical arrangement of choices, and total consumption per assay unit. We used our results to develop procedures for estimating the sample sizes needed to compare a specified number of choices. We based these methods on power considerations, the requirements for data transformation and inclusion of covariates. We develop a general approach for estimating the number of replicates needed to support a particular number of choices for a test organism, and discuss factors to be considered when relating this approach to various types of behavioral choice assays.

Hypothesis tests for normal means constrained by linear inequalities

Likelihood ratio tests for a set of k normal means are studied when both the null and alternative hypotheses impose homogeneous linear inequality constraints on the means. Examples of such constraints include hypotheses that the means are equal, that they are nonnegative, that they are linear, or that they are monotone. Several tests involving such constraints have appeared recently, and here we present theory that unifies and extends many of these results. Our approach makes use of the properties of polyhedral cones. We define conditions under which the exact distribution of the likelihood ratio statistic is available, and show that this distribution is of the chi-bar-square form. When the exact distribution is unavailable, it may still be possible to find a stochastic ordering of the test statistic, and thereby derive a conservative test. The asymptotic distribution of the test statistic is also studied. Our results do not require that estimates of the k means be independent, provided that their covaria...

Population Dynamics of Ips pini and Ips grandicollis in Red Pine Plantations in Wisconsin: Within- and Between-Year Associations with Predators, Competitors, and Habitat Quality

Abstract We sampled bark beetle (Coleoptera: Scolytidae) populations in 17 declining and healthy red pine plantations in Wisconsin over 3 yr. We tested for potential relationships among numbers of bark beetles, conspecifics and competitors, and predators within and among flight seasons to help identify factors affecting population densities. The two most common bark beetle species obtained were Ips pini (Say) and Ips grandicollis (Eichhoff). The predominant predators obtained were Thanasimus dubius (F.) (Cleridae), Platysoma cylindrica (Paykull) (Histeridae), and Platysoma parallelum Say. Declining stands contained significantly more Ips than did healthy stands during the early portion of the season. Healthy stands had more predators than declining stands. There were strong delayed inverse relationships between I. pini and predators at the site level, both within and between flight seasons. The number of I. pini caught during the late portion of the season was lower when each of the above predators was more abundant earlier in the season, during both 1998 and 1999. Likewise, numbers of I. pini and I. grandicollis caught during the early portion of the year were inversely related to numbers of predators caught during the previous year. Although Ips trap counts showed significant correlations with each predator species, simple predator-prey models did not necessarily improve fits based on habitat quality (i.e., Ips numbers regressed on prior Ips numbers). We did not observe evidence for interspecific competition among Ips spp. This pattern is consistent with the view that host plant quality and predation jointly affect I. pini and I. grandicollis population dynamics. These results emphasize the importance of interactions among host tree physiology, predation, and dispersal in the population dynamics of phloeophagous herbivores, and have implications to forest management.

Fungi, leaves, and the theory of island biogeography.

Species dynamics of fungi (filamentous fungi and yeasts) on apple leaves were studied within the framework of the theory of island biogeography by following “immigration” and “extinction” patterns on individual apple leaf “islands” over time. Total fungi were censused on unmanipulated leaves collected throughout two seasons; filamentous fungi only were monitored additionally for several weeks in one season on newly created, axenic, model (seedling) islands introduced to the orchard, and on surface-sterilized, preexisting leaves. Analyses based on both the natural and the surface-sterilized systems showed that an equilibrium in species number was reached and turnover in species composition occurred in both. Immigration and extinction events were strongly related to number of species present on each island. The balance between immigration and extinction implies that species number on leaves and “real” (oceanic) islands is determined by a common mechanism, and emphasizes the need to regard leaf microbial communities as dynamic.

Spatial Controls of Pre–Euro-American Wind and Fire Disturbance in Northern Wisconsin (USA) Forest Landscapes

We elucidate spatial controls of wind and fire disturbance across northern Wisconsin (USA), where climatic and topographic gradients are not strong, using data from the original US Public Land Survey (PLS) notes. These records contain information on the location and extent of heavy windthrows and stand-replacing fires prior to Euro-American settlement. The spatial patterns of windthrow and fire were spatially clustered at all scales in this historical environment, with stronger associations at local than regional scales. Logistic regression shows environmental variables to have a strong influence on this pattern. In the case of heavy windthrow, environmental drivers of disturbance pattern are fairly consistent across the region. The effects of climate and vegetation are predominant at all scales, but effects are often indirect, with strong interactions between them. Interactions between these two drivers and soil characteristics are also sometimes present. In contrast, models of stand-replacing fire show simple and direct control within and across fire-prone landscapes of historical northern Wisconsin, with climate and physiography as the main factors explaining the distribution of fire disturbance. This simple and direct control is lost at the regional scale, where climate, physiographic, soil, and vegetation variables, along with interactions between them, are significant factors. Contrary to other regions, the topographic effects are generally not important in predicting either wind or fire disturbance. Our work suggests that, in landscapes that lack strong environmental patterning, climate maintains its role as a primary driver of these natural disturbances, but topography is replaced by interactions and feedbacks with other forms of environmental heterogeneity.