BUYING TIME: PRELIMINARY ASSESMENT OF THE POTENTIAL ROLE OF BIOCONTROL IN THE RECOVERY OF NATIVE FOREST VEGETATION FOLLOWING THE INVASION OF EMERALD ASH BORER by Elan Margulies A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science (Natural Resources and Environment) at the University of Michigan August 2017 Faculty Advisors Professor Inés Ibáñez Professor Leah Bauer Abstract: Introduced forest pests have become one of the major threats to forest ecosystems in North America. Once the spread phase is underway, biological control is one of the few environmentally acceptable and sustainable practices available for the management of destructive invasive pests in natural ecosystems. Assessing the impact of a biocontrol program progresses from evaluating the establishment of biocontrol agents, to control of the target pest, to impacts on the affected organism, and ultimately, to the indirect impacts that biocontrol may have on the whole community. In our study, we assessed the recovery of forest vegetation following the mortality of overstory ash trees caused by the emerald ash borer (EAB) invasion and ongoing management of EAB using biological control. We collected data on the forest structure and composition of stands affected by this pest and where biocontrol agents were released or not (biocontrol and no-biocontrol plots). We then used a multilevel modeling framework to evaluate the potential indirect effects of a biocontrol agent on native tree seedling forest regeneration. We found that the impacts of biocontrol on ash saplings had community- level effects by protecting native seedlings from invasive and weedy saplings. Our results showed a higher number of ash saplings with increasing numbers of the dominant EAB biocontrol agent T. planipennisi, while the number of invasive and weedy saplings was negatively associated with number of ash saplings. Density of native seedlings was negatively associated with invasive and weedy saplings. As disturbance events produce gaps in the canopy, the protection of ash saplings by the biocontrol agent may help native recruitment during forest transition by supporting the growth of native hardwood seedlings over invasive and weedy saplings. We found that evaluating the efficacy of the ash biocontrol program will need to include varied ash size classes and the community dynamics of the co-occurring species. i Keywords: Agrilus planipennis, Fraxinus, gap dynamics, invasive species, Oobius agrili, southeastern Michigan, Spathius agrili, temperate forests, Tetrastichus planipennisi Acknowledgements I would like to thank my advisor Inés Ibáñez and my committee member Leah Bauer for their support throughout the research process. I am grateful to have worked with the Global Change Ecology Laboratory, especially Natalie Tonn and Daniel Katz, who helped me with the field work and encouragement throughout. This work would not have been possible without the support of the University of Michigan, Michigan State University, United States Department of Agriculture (USDA) Forest Service, USDA Animal and Plant Health Inspection Service, USDA Agricultural Research Service, Michigan Department of Natural Resources, Huron-Clinton Metroparks, Michigan Nature Association, and the Rackham Graduate School. I would like to particularly give thanks to Inés for her help and allowing me to work on this project from afar. This has given me the opportunity work with educators to build an environmental organization that touches the lives of thousands of school children. ii Table of Contents Abstract ............................................................................................................................................ i Acknowledgements ......................................................................................................................... ii 1. Introduction ............................................................................................................................. 1 2. Methods ................................................................................................................................. 10 2.1. Study Sites ...................................................................................................................... 10 2.1.1. Release of biocontrol .................................................................................................. 10 2.1.2. Vegetative Sampling................................................................................................... 11 2.1.3. Environmental data ..................................................................................................... 11 2.2. Statistical Analysis ......................................................................................................... 12 3. Results ................................................................................................................................... 15 4. Discussion .............................................................................................................................. 16 Tables and Figures .................................................................................................................... 22 Appendix ................................................................................................................................... 27 Literature Cited ......................................................................................................................... 40 iii List of Figures Figure 1. a) Visual representation of the forest transition with and without biocontrol. b) Graphical representation of the analysis testing the hypothesis…………………………………24 Figure 2. Location of 21 vegetative study sites and EAB introduction epicenter in Michigan...25 Figure 3. Posterior parameter means and 95% credible intervals (CI) of each of the parameters included in the analyses….......................................................................................................…..26 List of Tables Table 1. Posterior means and 95% credible intervals (CI) for all the parameters included in the analysis…………………………………………………………………………………………...22 iv Introduction Ash (Fraxinus spp.) trees grow in a variety of habitats contributing to the species diversity in key niches of North American forests (Gleason & Cronquist 1991). Ash trees also host a unique array of birds, mammals, and at least 98 species of invertebrates are closely associated or dependent on ash (Martin et al. 1951; Wagner & Todd 2016; Jennings et al. 2017). USDA Forest Service Forest Inventory and Analysis (FIA) data showed that in 2003, the United States timberlands had over 7.5 billion ash trees (Nowak et al. 2003). Ash were present in the Midwest and northeast on 32% of all forested land; of these 78% of these were on private property, 17% on state and local land, and 5% on federal land (Desantis et al. 2013). In 2008, there were an estimated 4.3 billion saplings between 2.5 – 12.6cm diameter at breast height (DBH) in the Midwest and northeast (Desantis et al. 2013). Ash is also a common ornamental species which has been widely planted in North American cities to replace the loss of elm in urban forests (Federal Register 2003). From FIA surveys in the 1980’s until 2009, ash (>2.5cm DBH) volume increased 80% in the Great Lakes region, totaling ~427 million m3 in 2008 (MacFarlane & Meyer 2005; Pugh et al. 2011; Desantis et al. 2013). Michigan, our study region, had nearly 700 million ash trees that comprised 4.6% of the total forest basal area (Nowak et al. 2003). There are 16 species of ash (Fraxinus spp.) in North America, five of which can be found in Michigan (MacFarlane & Meyer 2005; Desantis et al. 2013; USDA NRCS 2017). The most common species is white ash (F. americana), which grows in mixed upland hardwood forests. Green ash (F. pennsylvanica) tolerates both mesic and hydric soils and has the largest distribution (Kennedy 1990; Gucker 2005). Blue ash (F. quadrangulata) occupies calcium-rich upland sites, while both black ash (F. nigra) and pumpkin ash (F. profunda) can be dominant in hydric soils (Kennedy 1990; Gleason & Cronquist 1991; Harlow et al. 1991; Gucker 2005; MacFarlane & Meyer 2005; Desantis et al. 2013; USDA NRCS 2017). 1 Currently, one of the major challenges facing North American forests are invasive forest pests (Lovett et al. 2016). In recent decades, the increase in new species introductions, mainly associated with an increase in global trade, have exacerbated the frequency and impact of invasive pest outbreaks (Niemeli & Mattson 1996; Work et al. 2005; Aukema et al. 2010). Outbreaks of forest pests can decimate forests and, in some instances, locally eliminated tree species (e.g., Busby & Canham 2011), or substantially change forest ecosystems (e.g., Chapin et al. 2000; Lovett et al. 2006; Moser et al. 2009; Kovacs et al. 2010; Morin et al. 2017). Gypsy moth (Lymantria dispar) and Asian longhorned beetle (Anoplophora glabripennis) are examples of generalist pests that attack an array of tree species, while pests such as chestnut blight (Cryphonectria parasitica), hemlock woolly adelgid (Adelgis tsugae), Dutch elm disease (Ophiostonza novo-ulmi), and beech scale (Cryptococcus fagisuga) target specific tree species (Gavin & Peart 1993; Paillet 2002; Sharov et al. 2002; Smith et al. 2009; Dix et al. 2010; Potter et al. 2011). For instance, Dutch elm disease killed ~200 million elms (Ulmus spp.) in the 20th century, and currently reduces the lifespan of elm