Rachel Nettles, Brigham Young University
Plant and Wildlife Sciences
Background/Questions/Methods
The invasion of red brome (Bromus rubens L.), a winter annual, is altering fire regimes in desert ecosystems in the southwestern USA. In this study, the primary objective was to determine the environmental conditions (temperature and water potential) that best stimulate germination in this exotic species. A laboratory study was conducted to compare germination ratios of red brome seed under gradients of water availability and temperature to better predict how climate conditions are likely to affect fire potential. Samples were prepared using different solutions of polyethylene glycol (0, -0.5, -1, -1.5, -2 bar). These samples were then placed in incubators at six temperature settings (0, 5, 10, 20, 25, 30°C) for a 28 day period during which seed germination was scored.
Results/Conclusions
The hydrothermal time value of this pop- ulation of Bromus rubens is 47.2 (°C Mpa days). In order for a population of red brome to germinate in temperatures ranging from 0-20°C, the minimum water potential requirement is -1.3 Mpa. At 25°C, the requirement is at least -0.49 Mpa, while for 30°C, the water potential requirement is a minimum of -0.9 Mpa. This data suggests that the optimal temperature for the germination of this population of red brome is around 25°C. In contrast, the lowest temperature at which germination occurs is 0.16°C. It can be expected that in a fall season of above average precipitation, if the average temperatures remain mild, then optimal germination rates are likely to result in high fine fuel loads that will increase the probability of fire.