Restoration of the Forest Herbaceous Layer: Genetic Differentiation
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Iowa State University Capstones, Theses and Graduate Theses and Dissertations Dissertations 2016 Restoration of the forest herbaceous layer: genetic differentiation, phenotypic plasticity, and opportunities for conservation and nursery professionals Emily Anne Altrichter Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/etd Part of the Environmental Sciences Commons Recommended Citation Altrichter, Emily Anne, "Restoration of the forest herbaceous layer: genetic differentiation, phenotypic plasticity, and opportunities for conservation and nursery professionals" (2016). Graduate Theses and Dissertations. 15105. https://lib.dr.iastate.edu/etd/15105 This Thesis is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Graduate Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Restoration of the forest herbaceous layer: Genetic differentiation, phenotypic plasticity, and opportunities for conservation and nursery professionals by Emily A. Altrichter A thesis submitted to the graduate faculty in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Major: Environmental Science Program of Study Committee: Janette R. Thompson, Co-Major Professor Catherine M. McMullen, Co-Major Professor Matthew J. Helmers Randall K. Kolka Iowa State University Ames, Iowa 2016 Copyright © Emily A. Altrichter, 2016. All rights reserved. ii TABLE OF CONTENTS ABSTRACT iii CHAPTER 1: GENERAL INTRODUCTION 1 Research Questions 4 Thesis Organization 6 Author Contributions 7 Literature Cited 7 CHAPTER 2: GENETIC DIFFERENTIATION AND PHENOTYPIC PLASTICITY OF HERBACEOUS LAYER SPECIES USEFUL FOR FOREST RESTORATION 11 Abstract 11 Introduction 12 Methods 15 Results 18 Discussion 20 Acknowledgements 25 Literature Cited 25 Tables 29 Figures 39 CHAPTER 3: CONSERVATION AND NURSERY PROFESSIONALS’ PERCEPTIONS OF LOCAL ECOTYPE USE IN WOODLAND RESTORATION 40 Abstract 40 Introduction 41 Methods 45 Results 49 Discussion 55 Conclusion 60 Acknowledgments 60 Literature Cited 60 Tables 66 CHAPTER 4: GENERAL CONCLUSIONS 79 Acknowledgments 84 Literature Cited 84 APPENDIX A: SURVEY OF CONSERVATION PROFESSIONALS 86 APPENDIX B: SURVEY OF NURSERY PROFESSIONALS 99 APPENDIX C: INSTITUTIONAL REVIEW BOARD APPROVAL 113 iii Abstract The forest herbaceous layer provides important ecosystem services, but land use changes have led to a decline in native herbaceous perennial species in the Midwest, including Iowa. Restoration focused on the herbaceous layer is uncommon, and best practices have not been established. Significant debate has developed over appropriate plant sources for restoration: geographically distant populations of the same species are often genetically distinct, and this phenomenon may affect restoration success. In the first part of this study, I examined genetic variability and phenotypic plasticity of local and nonlocal populations of six herbaceous perennial understory species. I used a common garden study to test for genetic variation in vegetative and reproductive traits and a field study to test for phenotypic plasticity. I detected genetic differences between local and nonlocal populations for about half of the measured traits, and observed that few trait differences in greenhouse trials were also consistently expressed by plants in the field due to phenotypic plasticity. In the second component of this study, I examined the recommendation to practitioners to use local ecotypes in restoration. I surveyed two stakeholder groups, conservation professionals and nursery professionals, to learn if there were differences between the two groups in terms of perception, use, or sale of native and local ecotype plant material. I found that 78% of conservation professionals use native plants for a majority of their restoration projects, while only 9% of nursery professionals sell a majority of native plants. There was also a time lag between demand and supply for these plants: 67% of conservation professionals have been buying native plants for >10 years, while only 25% of nursery professionals have been selling native plants for that long. Although conservation professionals indicated interest in using local iv ecotype plant material, only 30% of survey respondents and 22% of their organizations have plant sourcing guidelines. Members of both groups reported that they rely on trusted authorities and professional training for information on local ecotypes, representing an opportunity to encourage collaboration and create sources of native plant materials, particularly herbaceous perennial species. 1 CHAPTER 1: GENERAL INTRODUCTION Temperate deciduous forests in the northeastern United States provide important ecosystem services, including maintenance of air, water, and soil quality, filtering of dust particles, habitat for maintenance of biological diversity, and recreation and aesthetic values (Dobbs et al. 2010). However, many forests throughout the Midwestern region have been replaced by agricultural or urban land uses. For example, the landscape of Iowa was historically a mosaic of tallgrass prairie, prairie pothole wetlands, and upland and riparian forests (Thompson 1992), but 78% of its land area is currently used for intensive row-crop farming or pasture (Gallant et al. 2011). Remnant forests in this landscape tend to be located on land that is too steep, stony or wet to farm, or in urban and urbanizing landscapes, often as gallery forests along rivers and streams (Thompson 1992). Forests in the transition zone between the eastern deciduous forest and the tallgrass prairie region are dominated by Quercus alba, Q. macrocarpa, Q. rubra, and Q. velutina, Carya ovata, Acer nigrum, Tilia americana and Prunus serotina (Mabry 2004, van der Linden and Farrar 2011). The herbaceous understory layer is an important component of deciduous forests. Forest understory species, which are variously defined, but here refer to non-woody vascular plants, provide diversity and contribute to erosion control and nutrient capture (Gilliam and Roberts 2003). They are particularly important in nutrient cycling, capturing a disproportionate amount of nitrogen and phosphorus relative to their biomass (MacLean and Wein 1997). One group of herbaceous plants, spring ephemerals, is critical to nutrient capture; they grow when canopy trees are coming out of dormancy, and their growth period coincides with the time of maximum leaching from crop fields. These 2 plants take up nutrients, particularly nitrogen and phosphorus, thus decreasing runoff and nutrient pollution in streams (Likens et al. 1970, Mabry et al. 2008, Gerken Golay et al. 2013b). However, Iowa’s history of cattle grazing, deer overabundance, nonnative earthworms, and heavy recreational use in urban areas have led to the degradation of the forest herbaceous layer (Mabry 2002, Rooney et al. 2004, Andrés-Abellán et al. 2005, Nuzzo et al. 2009, Cameron et al. 2015). Currently, many forests in Iowa have understories composed of generalist or invasive species or bare ground (Mabry 2002, Gerken Golay et al. 2013a). The functional importance of perennial herbaceous species and their relative scarcity in Iowa forests make them a strong candidate for potential restoration. However, few restorations of forest herbaceous plants have been attempted in Iowa (but see Mottl et al. 2006, Gerken Golay et al. 2013a). Natural reestablishment of the herbaceous layer is partially limited by lack of seed in the forest seed bank and/or limited seed dispersal. Many primary and secondary woodlands (abandoned farmlands or logged areas) may be partially recolonized via natural processes. However, since many herbaceous species do not persist in the forest seed bank, populations may not return with the cessation of disturbance (Pickett and McDonnell 1989). They are also unlikely to colonize new sites (Matlack 1994, McLachlan and Bazely 2001) because they disperse over only limited distances, up to a few meters (Willson 1993, Cain et al. 1998). The most restricted woodland species produce few, heavy seeds, which limits their ability to reach unoccupied patches (Mabry 2004). These factors make forest herbaceous species unlikely to colonize new areas, so they need to be actively restored (McLachlan and Bazely 2001). 3 In addition, perennial herbaceous plants do not restore well from seed. Large, fleshy seeds do not dry or store well, and have limited seed production and low germination rates (Cullina 2000, Mabry 2004). Perennial herbs are very long-lived, and may take years to reach reproductive maturity if planted from seed (Bierzychudek 1982). Transplanting seedlings may be the best method (McLachlan and Bazely 2001), with some demonstrated long-term success (Mottl et al. 2006). However, there are still questions about where and how to obtain seedlings and other plant materials for restoration. One of the primary debates among restoration researchers and practitioners relates to identifying and obtaining genetically and geographically appropriate plant material. Genetic differentiation and phenotypic plasticity are two phenomena that influence restoration protocols and prevailing opinions on plant material sources. The first, genetic or local differentiation, is based on the idea that populations adapt to local conditions because they cannot move to escape adverse environments.