Microclimate Effects on the Germination of Pitcher's thistle (Cirsium pilcheri)
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Cirsium pitcheri (Torr. Ex Eaton), or Pitcher's thistle, has been identified as a federally threatened species since 1998. While several projects have successfully reintroduced greenhouse-grown plants, less research has focused on reintroduction of this species through seed. In this study, I attempt reintroduction from seed, and provide evidence showing how these efforts may be optimized to promote seedling germination and survival. Pitcher's thistle seeds were planted in the West Beach of the Indiana Dunes National Lakeshore, Indiana. Seedling emergence and size were studied for fourteen weeks, along with soil moisture, soil temperature, slope, sand burial, and elevation. Seeds germinated throughout the Spring in all subplots, confirming successful planting methods. Seeds in south-facing subplots germinated at higher rates at the start of the study, but also had the lowest survival rates. North-facing subplots had higher germination rates later in the study and a higher survival rate, with both being attributed to cooler sand temperatures and higher soil moisture. Seedling survival was also significantly higher in subplots furthest from the lake. These data suggest that seeds should be planted on north-facing slopes and far from the lakeshore to have the best microclimate to favor seedling germination and survival.