Sunghoon Baek

Date of Graduation

2015

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Agricultural and Resource Economics

Committee Chair

Yong-Lak Park

Committee Co-Chair

Rakesh Chandran

Committee Member

Andrew Liebhold

Committee Member

William MacDonald

Committee Member

Patrick Tobin

Abstract

Eastern hemlock, Tsuga canadensis (Pinales: Pinaceae) is an important tree species in eastern North America ecosystems. During the past 65 years, eastern hemlock stands have been threatened by the hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae). The goal of this research was to determine the spatial and temporal distribution of A. tsugae populations. First, the appropriate sample unit for A. tsugae was determined based on within-branch and -tree distribution of A. tsugae. The results of this study showed that A. tsugae ovisacs were more frequently found at the tip of a branch and no significant (P > 0.05) differences in A. tsugae ovisac density were found among four cardinal directions (i.e. north, south, east, and west). However, A. tsugae ovisacs were found more frequently on upper third branches ( P < 0.05). Based on coefficient of variation values, a 50-cm branch sample approximately 3 m above the ground would be the optimal unit for sampling A. tsugae ovisacs. Using the optimal sample unit, spatial associations between A. tsugae ovisacs and surrounding environmental factors were investigated. The results showed that trees infested with A. tsugae ovisacs were spatially aggregated regardless of three study sites and two A. tsugae generations. Elevation, plant species diversity and basal area showed inconsistent spatial relationships with A. tsugae ovisac populations. This study provides fundamental information to develop efficient sampling plans and management strategies for A. tsugae..

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