The forest herbaceous layer provides important ecosystem services in the central United States. However, human impacts have caused declines of many of these species. Restoration of this layer is uncommon in temperate forests, so best practices are not yet established. There has been widespread concern about negative outcomes (for example, failure due to genetic swamping or outbreeding depression) when plant material is transferred beyond a local scale. Current practice is to use local sources under the assumption that they are optimal genotypes for the site. However, few local sources are available for many species. We examined genetic variability and phenotypic plasticity by comparing performance of local and non-local populations (from sites approximately 250 km apart) of six forest herbaceous species. We used a common garden study to test for genetic differences in plant traits, and a field study to test for phenotypic plasticity. Based on the common garden we found genetic differences between local and non-local populations for each species. Trait differences we observed in greenhouse trials we also detected in the field in the first year. However, these differences diminished in the second year of the field study and we did not detect them in the four species measured in the third year. This provided evidence that phenotypic plasticity was operating, as plant characters responded plastically to local conditions. We found no evidence that local plants consistently outperformed non-local plants. These results suggest less need for strict adherence to locally sourced seeds or transplants.
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 Author Contributions The candidate was responsible for data collection, analysis, and the preparation of the text. Drs. Janette Thompson and Catherine McMullen provided help with experimental design, data collection, manuscript editing, and project guidance. Dr. McMullen was particularly instrumental in the design, analysis and interpretation of Chapter 2, and Dr. Thompson assisted with survey design, construction, administration and interpretation described in Chapter 3. Drs. Matthew Helmers and Randy Kolka provided comments and editorial recommendations on all chapters.
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