Silvicultural Disturbances Affect on Root-Feeding Bark Beetle
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Silvicultural Disturbances Affect on Root-feeding Bark Beetle Populations and the Incidence of Ophiostomatoid Fungal Species Contributing to Southern Pine Decline in Pinus taeda Stands by Yuan Zeng A thesis submitted to the Graduate Faculty of Auburn University in partial fulfillment of the requirements for the Masters Degree Auburn, Alabama May 7, 2012 Keywords: Hylastes spp., ophiostomatoid fungi, mechanical thinning, harvesting, Southern Pine Decline Copyright 2012 by Yuan Zeng Approved by Lori Eckhardt, Chair, Associate Research Professor, School of Forestry and Wildlife Sciences David Held, Assistant Professor of Entomology Edward Loewenstein, Associate Dean, Academic Affairs, Associate Professor, School of Forestry and Wildlife Sciences Abstract Root-feeding beetles and weevils are known to be vectors of ophiostomatoid fungi which contribute to Southern Pine Decline (SPD) in the southeastern United States. This study examined population changes of Hylastes spp. in response to either mechanical thinning or harvesting in Pinus taeda L. stands and the factors associated with the incidence of ophiostomatoid fungi. In addition, the study also quantified ophiostomatiod fungal response to mechanical thinning in central Alabama and Georgia. Three different insect traps were used during the two-and-half-year study. Pinus taeda roots were excavated and assayed for ophiostomatoid fungal infections from both pre- and post- treatments in thinned and control plots. Of the 46,865 total insects captured, 22,495 were Hylastes spp. Populations of the Hylastes spp. significantly increased after thinning treatments at study sites. Although Hylastes spp. decreased in response to harvesting in some plots, their populations recovered to pre-treatment levels and were stable over the study duration. The dominant fungus recovered was Leptographium procerum (Kendr.) Wingf. followed by other species including L. terebrantis Barras & Perry, Grosmannia alacris T.A. Doung, Z.W. de Beer & M.J. Wingf. sp. nov., G. huntii (Rob.-Jeffr.) Zipfel, Z.W. de Beer & M.J.Wingf., and Ophiostoma ips (Rumbold) Nannf. Grosmannia alacris and O. ips were recovered from tree roots in plots with severe decline symptoms. Sites with mechanical thinning had increased incidence of ophiostomatoid fungal species that may serve as a source to infest the remaining trees in the stand leading to SPD. ii In general, thinning and harvesting are recommended as bark beetle management strategies. However, in the current study, recent mechanical thinning significantly increased pathogen-vectoring Hylastes spp. and ophiostomatoid fungi which contribute to SPD. Thus, future research should consider either how to thin or how to control the insect vectors to reduce possibility of SPD infestation in P. taeda stands. iii Acknowledgments I would like to thank my major professor, Dr. Lori Eckhardt for creating all the opportunities to let me perform this research at the School of Forestry and Wildlife Sciences in Auburn University. I would like to thank my committee members, Dr. David Held and Dr. Edward Loewenstein for providing me with academic and research guidance. In particular, I would like to thank Dr. Scott Enebak, for all his suggestions and comments made on my thesis. I must also thank my lab mates in the Forest Health Dynamics Labratory, without their help I would not have succeed in the field. Additionally, appreciation to my family and friends, their love and surport enabled me to complete this work. Finally, thanks are due to Forest Health Cooperative for their funding and allowing me access to their forest stands to set up my research plots. iv Table of Contents Abstract ........................................................................................................................................ ii Acknowledgments ....................................................................................................................... iv List of Tables ................................................................................................................................ x List of Figures ............................................................................................................................. xii Chapter 1 Introduction and Review of Literature ........................................................................ 1 1.1 Tree and Forest Decline ......................................................................................... 1 1.1.1 Germ Theory ................................................................................................ 3 1.1.2 Climate and Weather Stress ......................................................................... 4 1.1.3 Cohort Senescence or Natural Succession ................................................... 5 1.1.4 Human Impacts and Complex Interactions of Factors ................................. 5 1.2 Loblolly Pine Decline and Associated Factors .................................................... 7 1.2.1 Loblolly Pine (P. taeda L.) .......................................................................... 7 1.2.2 Damage Agents for Loblolly Pine ............................................................... 8 v 1.2.3 Loblolly Pine Decline ............................................................................... 10 1.2.3.1 Abiotic Factors .............................................................................. 13 1.2.3.2 Biotic Factors ................................................................................ 14 1.2.3.2.1 Insect Associations......................................................... 14 1.2.3.2.2 Ophiostomatoid Species Associations ........................... 17 1.3 Forest Management Affect on Insect and Fungus Populations ........................... 23 1.4 Central Theme ...................................................................................................... 27 Chapter 2 Thinning and Harvesting Effects on Root-feeding Bark Beetle Population Dynamics in Pinus taeda L. Plantations in Central Alabama and Georgia .............. 28 2.1 Abstract ................................................................................................................ 28 2.2 Introduction ........................................................................................................ 29 2.3 Methods and Materials ......................................................................................... 32 2.3.1 Study Site and Plot Measurements ............................................................ 32 2.3.2 Insect Trapping .......................................................................................... 34 2.3.3 Tree Measurements .................................................................................... 36 2.3.4 Stump Sampling ......................................................................................... 37 2.4 Data Analysis ...................................................................................................... 38 vi 2.5 Results ................................................................................................................. 38 2.5.1 Description of Study Area ......................................................................... 39 2.5.2 Relationship of Hylastes spp. and Stand Age and Crown Parameters ....... 39 2.5.3 Insect Activity ............................................................................................ 47 2.5.3.1 Population Trends of Hylastes spp. and Seasonal Effects on Populations ..................................................................................... 49 2.5.3.2 Correlation among Hylastes spp., D. terebrans and I. grandicollis ..................................................................................... 52 2.5.3.3 Hylastes spp. Responses to Thinning Treatment ........................... 53 2.5.3.4 Insect Diversity Response to Thinning Treatment ......................... 61 2.5.3.5 Hylastes spp. Responses to Harvesting Treatment ........................ 66 2.5.3.6 Insect Diversity Responses to Harvesting Treatment .................... 78 2.5.3.7 Stump Observations ....................................................................... 83 2.6 Discussion ............................................................................................................ 85 Chapter 3 Factors Associated with Incidence of Ophiostomatoid Fungal Species Contributing to Southern Pine Decline ..................................................................... 91 3.1 Abstract ................................................................................................................ 91 3.2 Introduction ........................................................................................................ 92 vii 3.3 Methods and Materials ......................................................................................... 95 3.3.1 Study Sites ................................................................................................. 95 3.3.2 Tree Vigor and Site Characteristic Measurements .................................... 96 3.3.3 Insect Trapping .......................................................................................... 97 3.3.4 Root Sampling ........................................................................................... 98 3.4 Data Analysis .................................................................................................... 100 3.5 Results ..............................................................................................................