Effects of Sunlight and Fire on Autumn Olive (Elaeagnus umbellata) Fruit Sugar Concentration: Do Burns Help or Hinder an Invasive Plant?

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Dr. Kathy Winnett-Murray, Hope College

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Fire has often been used as a control mechanism for invasive plant species, such as Autumn Olive (Elaeagnus umbellata). However, little is known about the impact of burning on Autumn Olive’s reproductive success. A contributing factor for plant reproductive success is seed dispersal which is hypothesized to be correlated with the sugar concentration of fruit. Research has demonstrated that fruits with higher sugar concentrations are preferentially chosen by birds and mammals and therefore should be dispersed more often than fruits with lower sugar concentrations. In this study, we examined environmental factors that may influence the sugar concentration of Autumn Olive fruits, thus theoretically impacting seed dispersal. We sampled fruits from four plant treatment groups: (1) previously burned Autumn Olive plants in high light conditions, (2) previously burned plants in shade conditions, (3) unburned in higher light, and (4) unburned in shade. Whereas average sugar concentrations did not vary significantly between burned and unburned plants, we did determine that sugar concentration was higher among plants growing in higher light conditions (mean in light: 19.51 ± 2.57% sugar, mean in shade: 17.78 ± 3.21% sugar). Furthermore, there was an interactive effect of light environment and burn treatment, suggesting that burning Autumn Olive reduces the affect of light on sugar concentration. Unburned plants had significantly lower sugar concentrations when growing in the shade (t= 5.48, df= 27.8, p<0.00001), but burned plants had statistically similar sugar concentrations whether in the shade or in direct sunlight (t= 0.33, df= 26.2, p>0.05). Variation in factors such as light, temperature, and foliage structure at the microhabitat level could interact with animal seed dispersers’ preferences and behavior in ways that strongly influence individual plant dispersal success.

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