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How predictable are evolutionary responses to environment? Comparing trait-environment relationships among three species of Asteraceae forbs in the Great Basin
AuthorBartz, Tessa A
AdvisorLeger, Elizabeth A
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Restoring native forbs in the Great Basin Desert is an important part of regenerating a healthy landscape that benefits wildlife, plant communities, and humans. Despite their importance and contribution to plant diversity, forbs have been understudied relative to grasses and shrubs. To begin bridging this knowledge gap, we examined three Asteraceae species (Chaenactis douglasii, Dieteria canescens, Erigeron pumilus) collected from a wide geographic area and grown in common garden experiments, asking how variable these species and populations are, how their traits were associated with environment of origin, and how two of the three species responded to water addition in direct-seeding environments. We also asked if trait-environment relationships were similar among these three species. As expected, we found that populations were extremely variable, and that much of this variation was significantly different among populations, with some variation explained by the ecoregion where populations were gathered. All three species had at least one trait strongly correlated with an environmental variable, sometimes in similar ways. For example, we found a consistent relationship where plants from higher elevation locations flowered earlier across all species, as well as a relationship with plant height and mean annual temperature, with taller plants sourced from warmer areas. Across species, the strongest trait-environment relationships we found were found for plant height, flowering phenology, and flower production, though there was variation in which environmental variables were most correlated with these responses. Our results suggest that approaches that generalize across species, even closely related ones, may not be adequate when determining whether a potential seed-source is well-matched to a target restoration site. Instead, our results support the idea that species-specific seed zones (areas where seeds can be moved without loss of performance) should be developed to help make this decision. Additionally, we found that environmental variables such as mean annual temperature and elevation were highly associated with traits that are typically considered important in restoration, i.e. phenology, number of inflorescences, and plant size. Therefore, before species-specific seed zones are available, we may be able to use these environmental factors as proxies to help us better match seed sources to target restoration sites. Finally, we also found that at least one species (C. douglasii) emerged from seed more readily when it was sourced from a drier origin, in both ambient and water addition conditions. Although more research needs to be done in this area, this suggests that seeds sourced from drier locations may be better suited for restoration projects that are being direct-seeded.