Influence of Hemlock Woolly Adelgid Infestation Levels on Water Stress in Eastern Hemlocks within the Great Smoky Mountains National Park, U.S.A.

Carla Coots,Rusty Rhea,Jennifer Franklin,Paris Lambdin,Jerome Grant

doi:10.3390/f6010271

Carla Coots, Rusty Rhea + Show 3 more

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https://doi.org/10.3390/f6010271

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Journal: Forests	Publication Date: Jan 20, 2015
Citations: 18	License type: CC BY 4.0

Affiliation: University of Tennessee at Knoxville, US Forest Service

Abstract

Extensive mortality of eastern hemlock, Tsuga canadensis (L.) Carrière, resulting from infestation by hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), has occurred throughout the eastern United States. Although imidacloprid treatment can reduce tree mortality, its effectiveness can be influenced by several factors including tree water stress. The relationship between water stress and infestation rates is unknown, and an understanding of these could greatly increase the efficiency of management for this invasive insect. The primary objective of this study was to assess water stress at three levels of hemlock woolly adelgid infestations. Water stress was measured monthly for 13 months in eastern hemlocks classified as <25%, 25%–75%, and >75% infested. The highest level of water stress was found in those trees with hemlock woolly adelgid infestation levels greater than 75%. The lowest level of water stress was found in those trees with less than 25% hemlock woolly adelgid infestation levels. Knowledge of these effects can contribute to development of more effective chemical management strategies.

Highlights

Large scale mortality of eastern hemlock, Tsuga canadensis (L.) Carrière, resulting from infestation by hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), has occurred throughout the eastern United States over the past decade
Eastern hemlocks with high infestation levels (>75%) had significantly higher water stress (Student-Newman-Keuls test; p < 0.05)
The results from this study indicate a strong relationship between hemlock woolly adelgid infestations and water stress

Summary

Introduction

Large scale mortality of eastern hemlock, Tsuga canadensis (L.) Carrière, resulting from infestation by hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), has occurred throughout the eastern United States over the past decade. Imidacloprid treatment can reduce tree mortality, its effectiveness is influenced by several factors, including tree water stress [2]. Adelgid infestation has recently been found to influence tree water relations in mature stands [2] and saplings [3] but this relationship between water stress and infestation rates is basically unknown, and an understanding of these could greatly increase the efficiency of management for this invasive insect. Eastern hemlock, Tsuga canadensis (L.) Carrière, and Carolina hemlock, Tsuga caroliniana Engelmann, are found in the eastern United States. Eastern hemlock is a shade-tolerant, slow growing and drought intolerant conifer species [4] found on nearly eight million hectares of forest in the eastern United States. It is formerly considered to be the dominant tree on about one million of those hectares [4] and comprises approximately 1528 hectares in the Great Smoky

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