TABLE OF CONTENTS Page CHAPTER 1 Introduction 1 Life History of Lymantria dispar L3 Study Objectives 5 Design of The Study 5 Criteria Used in Plot Selection 5 Plot Design and Vegetation Measurement 6 Summary 8 Literature Cited 9 CHAPTER 2 – Defoliation and mortality associated with outbreaks of the European gypsy moth (Lymantria dispar L.): A regional review of the literature. Introduction 12 New England 14 The Melrose Highlands Study 14 Other Studies 21 New Jersey and New York 35 Pennsylvania 40 The Pocono Mountains 40 Central Pennsylvania, Ridge and Valley Province 42 Western Pennsylvania, Appalachian Plateau 47 The Pennsylvania Damage Appraisal Surveys 48 Virginia and West Virginia 52 Virginia 52 West Virginia 57 Michigan 58 Summary 59 Literature Cited 60 CHAPTER 3 – Tree mortality subsequent to defoliation by the European gypsy moth (Lymantria dispar L.) in the United States: a review. Introduction 68 Factors Influencing Tree Mortality Following Defoliation 73 Relationships Between Defoliation and Tree Mortality 77 Initial Stand Composition 81 Effect of Site Quality on Tree Mortality 88 Tree Mortality in Initial and Subsequent Outbreaks 92 Summary 97 Literature Cited 98 iii CHAPTER 4 – The European gypsy moth in Coastal Plain mixed pine-hardwood stands: defoliation patterns and prediction of stand susceptibility. Introduction 108 Methods 110 Study Area and Site Selection 110 Plot Design and Vegetation Measurements 113 Statistical Analysis 114 Results and Discussion 116 Stand Characteristics 116 Gypsy Moth Population Dynamics 119 Trends in Defoliation 122 Modeling Defoliation Relationships 141 Model Validation 146 Conclusions 150 Literature Cited 151 CHAPTER 5 – The European gypsy moth in Coastal Plain mixed pine-hardwood stands: patterns of tree mortality and prediction of individual tree mortality. Introduction 157 Methods 159 Study Area and Site Selection 159 Plot Design and Vegetation Measurements 160 Stand Characteristics and Defoliation History 163 Statistical Analysis 165 Model Development 168 Results and Discussion 169 Tree Mortality Subsequent to Defoliation 169 Influence of species composition 171 Influence of canopy position and tree vigor 178 Influence of factors other than defoliation 185 Prediction of the Probability of Tree Mortality 187 Model Development 187 Model Validation 190 Conclusions 197 Literature Cited 198 CHAPTER 6 - Summary Summary 205 Using the Models to predict defoliation and tree mortality 207 Literature Cited 212 VITA 214 iv LIST OF TABLES Page CHAPTER 2 Table 2.1. The effect of crown condition, crown class and frequency of 19 defoliation episodes on five year stem mortality rates in a composite mixed stand of oaks (Quercus rubra, Q. velutina, Q. coccinea, Q. alba); mortality rates for crown condition were calculated following a single heavy defoliation, while those for defoliation frequency were calculated following a single severe defoliation and two consecutive heavy defoliations. From Campbell and Sloan (1977). Table 2.2 The effect of crown condition on five year stem mortality rates of 22 dominant trees, intermediate/suppressed trees, mixed oaks and resistant species following a single heavy defoliation in a composite mixed stand of oaks (Quercus rubra, Q. velutina, Q. coccinea, Q. alba). From Campbell and Sloan (1979). Table 2.3 Estimated mortality losses from gypsy moth to merchantable timber in 25 the New England States from 1932 to 1952. From Perry, 1955. Table 2.4 Five year mortality rates observed in defoliated and undefoliated 27 stands in New England; trees were defoliated either 100 or 90 percent. From House (Turner, 1963) Table 2.5 Percent stem mortality of eastern white pine and eastern hemlock in 31 western Connecticut stands three years after a heavy defoliation. From Stephens (1988). Table 2.6 Species composition as a percentage of stand basal area, on three sites 39 within the Greenbrook Sanctuary, NJ, prior to defoliation by the gypsy moth. From Stalter and Serrao (1983). Table 2.7 Influence of site quality on stem and basal area mortality subsequent 44 to defoliation in Central Pennsylvania. From Gansner (1987). CHAPTER 3 Table 3.1 Examples of some trees and shrubs common to the Eastern United 70 States, and their classification according to currently accepted gypsy moth host preference classes; adapted from Montgomery, 1991; Twery, 1991 and Liebhold et al., 1995. v Table 3.2 Five year stem mortality rates for intermediate/suppressed and 79 dominant trees in a composite mixed stand of oaks (Quercus rubra, Q. velutina, Q. coccinea, Q. alba) following a single heavy defoliation. From Campbell and Sloan (1977). Table 3.3 Crown condition and five year stem mortality rates for a composite 80 mixed stand of oaks (Quercus rubra, Q. velutina, Q. coccinea, Q. alba) subjected to a single severe defoliation and two consecutive heavy defoliations. From Campbell and Sloan (1977). Table 3.4 The effect of duration of defoliation episodes on oak mortality in oak- 82 hickory forests of Clarke County and the Lee Ranger District of the George Washington National Forest, Virginia. Comparisons were made between stands experiencing either zero, one, two, or three defoliations; mortality was based on the percentage of the original oak basal area that had been killed. From Tigner (1992). Table 3.5 Total mortality as a percentage of initial stand basal area, and oak 84 mortality as a percentage of initial oak basal area, observed in stands with varying proportions of oak basal area prior to defoliation. Table 3.6 Mortality subsequent to gypsy moth defoliation observed within forest 90 stands growing on sites of varying productivity; total mortality is expressed as a percentage of initial stand basal area (or stem density), oak mortality is expressed as a percentage of initial oak basal area (or stem density). Table 3.7 Total mortality in predominantly oak stands following an initial gypsy 94 moth outbreak, and following subsequent outbreaks; total mortality is expressed as a percentage of initial stand basal area (or stem density), oak mortality is expressed as a percentage of initial oak basal area (or stem density CHAPTER 4 Table 4.1 Year of study plot establishment, the number of years of vegetation 112 measurements and the number of years of egg mass surveys of sixteen mixed pine-hardwood stands. Table 4.2 Total stand basal area, stem density, mean diameter, age, and basal 117 area of species and host preference classes of sixteen mixed pine- hardwood stands at the time of plot establishment. vi Table 4.3 Tree species, by host preference class, that were found in seven pine- 118 oak and nine pine-sweetgum stands. Table 4.4 Basal area of pines, oaks, sweetgum, resistant and immune tree 120 species as a percentage of total basal area in seven pine-oak and nine pine-sweetgum stands. Table 4.5 Annual gypsy moth population size, based on number of egg masses 121 per hectare within seven pine-oak stands and nine pine-sweetgum stands. Table 4.6 Mean total stand defoliation from 1992 to 1996 in seven pine-oak 131 stands and nine pine-sweetgum stands. Table 4.7 Results of simple linear regressions of mean total stand defoliation 135 (%) on the percentage basal area and quadratic mean diameter of pine, oak, sweetgum and susceptible species (combined oak and sweetgum). Table 4.8 Pearson correlation coefficients of six independent variables; the 142 values in parentheses are the p values for r under Ho: Rho = 0. Table 4.9 Regression statistics for the top four models identified by all possible 144 regressions using Mallows' Cp statistic (SAS, 1992). Table 4.10 Actual defoliation values and the defoliation predictions using Model 148 3 for a random sample (n=20 observations) of the development data set. CHAPTER 5 Table 5.1 Stand characteristics of sixteen mixed pine-hardwood stands at the 164 time of plot establishment. Table 5.2 Listing of the discrete variables used in the formulation of logistic 167 regression equations, the coded value refers to the descriptive term used for the variable in the logistic regression equations. Table 5.3 Cumulative basal area mortality in m2/ha and as a percentage of the 170 initial basal area, and cumulative stem mortality in stems/ha and as a percentage of the initial number of stems in pine-oak and pine sweetgum stands. vii Table 5.4 Cumulative basal area and stem mortality separated by host 174 preference class in pine-oak and pine-sweetgum stands; basal area mortality and stem mortality are measured in m2/ha and stems/ha and as percentages of the initial basal area and initial number of stems. Table 5.5 Cumulative stem mortality of different oak species within pine-oak 175 stands of the Atlantic Coastal Plain; numbers in parentheses are the initial number of stems sampled within each stand. Table 5.6 Initial number of stems, initial basal area, stem mortality, and basal 177 area mortality of overstory and understory pines in six pine-oak and four pine-sweetgum stands in which pine mortality was observed; overstory consists of dominant and codominant trees, understory consists of intermediate and suppressed trees. Table 5.7 Cumulative basal area and stem mortality of understory and 181 overstory trees in pine-oak and pine-sweetgum stands defoliated by the European gypsy moth. Table 5.8 Cumulative basal area and stem mortality of trees in good, fair, and 183 poor condition, as a percentage of the initial basal area and number of stems, in pine-oak and pine-sweetgum stands defoliated by the European gypsy moth. Table 5.9 Results of stepwise logistic regression using the development data 189 sets for the pine-oak and pine-sweetgum cover types; variable abbreviations are those used in Table 5.1 and the text. Table 5.10 Classification results for Models 1, 2, and 3, using the pine-oak and 192 pine-sweetgum validation data sets.