The Effect of Drought on the Comparative Fitness of Purple Needle Grass (Stipa pulchra) in the Presence of an Invasive Weed

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Research Poster

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Studies on the relative health of Stipa pulchra, a California native perennial bunchgrass, were conducted at the transplant garden on the Drescher campus of Pepperdine University in the Spring semesters of 2016 and 2017. Following the trend of other perennial native grasses, Stipa pulchra is dwindling due to competition with Avena fatua and other invasive species introduced by human activities. In 2016, in the midst of historic five-year drought in California, stomatal conductance, dark adapted fluorescence, water potential, and height of S. pulchra and A. fatua were recorded and compared. As hypothesized, the wild S. pulchra exhibited greater overall fitness-- in stomatal conductance, height, and water potential than the transplanted S. pulchra, and surprisingly also exhibited greater fitness than the A. fatua. After the abnormally high winter rainfall of 2017, it was hypothesized that all plants would exhibit higher fitness than the previous year, and A. fatua would have greater relative fitness than wild or transplanted S. pulchra. A. fatua exhibited a higher relative fitness than both the transplant and wild S. pulchra, as indicated by significantly higher stomatal conductance and height. The low levels of water potential indicated stress in transplanted S. pulchra. Comparison to the previous year also revealed an overall increase in plant growth. The findings demonstrate the impact of competitive invasive species on the growth of a struggling native species, especially in conditions of stress.

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