Vegetation, Coarse Woody Debris, and Cerambycid Communities in Riparian Forests Invaded by the Emerald Ash Borer
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VEGETATION, COARSE WOODY DEBRIS, AND CERAMBYCID COMMUNITIES IN RIPARIAN FORESTS INVADED BY THE EMERALD ASH BORER By Patrick Engelken A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of Entomology – Master of Science 2019 ABSTRACT VEGETATION, COARSE WOODY DEBRIS, AND CERAMBYCID COMMUNITIES IN RIPARIAN FORESTS INVADED BY THE EMERALD ASH BORER By Patrick Engelken This thesis, presented in three chapters, focused on evaluating the effects of emerald ash borer (EAB) on forest overstories, regeneration dynamics, and associated woodboring cerambycid beetles in riparian forests across Michigan. In chapter one, forests bordering first order streams were evaluated in three watersheds, representing a temporal gradient of the EAB invasion across southern Michigan. Canopy gap overstories were originally dominated by ash species but >85% were killed by EAB across all sites. Coarse woody debris (CWD) was most abundant in southeastern sites, with the longest history of EAB invasion. Gap regeneration was dominated by ash but seedlings were rare and understories were dominated by dense sedge mats (Carex spp.). In chapter two, I conducted trapping surveys of cerambycid beetles in the sites from chapter one. Beetle assemblages differed among invasion stages, and between traps at different heights. Several species were more abundant in southeast sites than southcentral and southwest sites and appear to be exploiting the abundant CWD in southeast Michigan. In chapter three I evaluated riparian forests bordering economically important northern lower Michigan rivers. Canopy gaps from EAB killed ash trees comprised 15-20% of the riparian buffer within 100 m of river banks. Prior to the EAB invasion, green and black ash dominated riparian forests, but >95% had died. Most dead ash trees were standing and ash CWD was not yet abundant. In gaps, green ash dominated regeneration, but black ash was uncommon. As in southern Michigan, dense sedges dominated gap understories, and seedlings were rare. iii ACKNOWLEDGEMENTS I thank my advisor, Dr. Deborah G. McCullough, for her guidance, leadership and invaluable insight throughout this project. Deb introduced me to the world of forest insects, for which I’ll always be grateful. Thank you for not only broadened my horizons but for imparting to me the value of being a more inquisitive researcher. I also would like to thank my guidance committee members: Dr. Therese Poland, Dr. M. Eric Benbow, and Dr. Michael Walters. Thank you for your encouragement and assistance along the way. These projects would not have been possible without the help and support from my fellow lab mates and undergraduate students in the Forest Entomology Lab. A special thanks goes to Justin Keyzer and Ryan Rupp for the countless hours spent collecting data in the field. No matter how unpleasant the conditions were or how thick the mosquitoes got, these two never wavered and were always great to work with. Additionally, I would like to thank James Wieferich for lending insight and advice in both the lab and the field. I thank my parents for loving me, supporting me and always pushing me to be my best self. Thank you for teaching me to love nature, and for always believing in me. Without you guys I would undoubtedly not be where I am now. I thank my fiancé, Angelica for enduring me through my highs and my lows, and for supporting and loving me throughout this process. You never stopped believing in me and kept me motivated even when I was at my worst. I love you unconditionally and you know that you’re my favorite. Funding for this research was provided through the Evaluation Monitoring program of the USDA Forest Service, Forest Health Protection, Northeastern Area. Partial funding to enable iii presentation of this research was provided by The College of Agriculture and Natural Resources, and the Ray and Bernice Hutson Memorial Entomology Endowment Travel Funds. iv PREFACE Emerald ash borer (EAB) (Agrilus planipennis Fairmaire) (Coleoptera: Buprestidae), a phloem-boring beetle native to Asia was first detected in the greater metropolitan area of Detroit, Michigan, USA in 2002. The range invaded by EAB has continued to progress and now encompasses much of the eastern U.S. and Canada. Previous studies have quantified mortality of ash (Fraxinus spp.) trees following EAB invasion, particularly in forests in southeast Michigan and Ohio, but little is known about the impacts of EAB in riparian forests bordering streams and rivers. In the northeastern U.S., black ash (F. nigra Marsh.) and green ash (F. pennsylvanica Marsh.) are abundant in riparian forests and are both highly preferred and vulnerable EAB hosts. In riparian forests where ash trees were abundant prior to the EAB invasion, mortality could result in cascading effects in both terrestrial and aquatic environments. My research, which is presented in three chapters of this thesis, focused on evaluating effects of EAB on forest overstories, regeneration dynamics, and associated woodboring cerambycid beetles in riparian forests of Michigan. Each chapter is intended to be submitted as a manuscript for publication in scientific journals. In Chapter One, I assessed the overstory trees, regeneration, shrubs, herbaceous plants, coarse woody debris, and photosynthetically active radiation in canopy gaps formed from EAB killed ash trees and in adjacent forests in riparian forests bordering first order streams. Sites were located in three distinct watersheds across southern Michigan and were selected to represent a temporal gradient of the EAB invasion. In canopy gaps along streams, green ash (F. pennsylvanica) and black ash (F. nigra) dominated the overstory before the EAB invasion but more than 85% were killed by EAB in all sites, resulting in canopy gaps. In southeastern sites v with the longest EAB invasion history, dead ash trees had begun to fall and coarse woody debris (CWD) volumes were higher than in areas of more recent EAB invasion, where most of the dead ash remain standing. Regeneration in canopy gaps was dominated by ash but seedlings were rare and gap understories were dominated by dense sedge mats (Carex spp.). In Chapter Two, I captured cerambycid beetles (Coleoptera: Cerambycidae) in cross vane panel traps baited with (R) 3-hydroxyhexan-2-one, an aggregation pheromone attractive to several genera of cerambycids. Traps were deployed in the canopy and at ground level at the perimeter of the canopy gaps described in Chapter 1. Trapping took place during summer months of 2017 and 2018, and captured beetles were collected at 2-3 week intervals. During both trapping seasons, the majority of species were initially captured early in the summer. Beetle captures were similar among watersheds and between canopy and ground level traps, but canopy traps captured more species than ground traps. Several species captured in high abundance were notably more common in different watersheds, and are perhaps responding to forest changes in the aftermath of the EAB invasion. In Chapter Three, I evaluated riparian forests along three rivers in northwest lower Michigan that are economically important for recreation, provide habitat for spawning Great Lake trout and salmon and drain into reservoirs that empty into Lake Michigan. Forests were evaluated in a similar manner as in Chapter One. In these northern forests, canopy gaps from EAB killed ash trees comprised 15-20% of the forest area near river banks. Prior to the EAB invasion, green ash (F. pennsylvanica) and black ash (F. nigra) dominated overstories in all gaps, but >95% of those trees had died. Most dead ash trees remained standing and ash CWD was limited in all canopy gaps. Green ash saplings and recruits dominated the advance vi regeneration in canopy gaps, but black ash regeneration was minimal. As in southern Michigan, seedlings were rare in gaps, where understory vegetation was dominated by dense sedge mats. Overall, results from this research provide a baseline of the post-EAB invasion status of riparian forests across Michigan. Green ash and black ash have been functionally lost in the overstory, and canopy gaps now make up a large component of the riparian corridors. While ash regeneration is present in canopy gap understories, dense sedge mats may inhibit future seedling recruitment. If the remnant ash cohort is unable to persist, large areas where ash was abundant prior to the EAB invasion may transition away from forests towards sedge dominated meadows. This may present long term changes in terrestrial and aquatic conditions. Ash mortality appears to be altering assemblages of cerambycid species, indicating EAB can indirectly affect other taxa. Effects of EAB related changes in riparian forests on aquatic ecosystems are as of yet largely unknown. vii TABLE OF CONTENTS LIST OF TABLES ...............................................................................................................x LIST OF FIGURES ......................................................................................................... xiii CHAPTER 1: LEGACY EFFECTS OF EMERALD ASH BORER ON RIPARIAN FOREST VEGETATION AND STRUCTURE ..............................................1 Introduction ..............................................................................................................1 Materials and Methods .............................................................................................6 Study Sites ...................................................................................................6