Timing and duration of precipitation pulses and interpulses influence seedling recruitment in the Great Basin

Abstract

Precipitation pulses and interpulse dry periods are major drivers of dryland ecosystem function globally, yet how the patterning and timing of precipitation inputs and dry periods influence seedling recruitment in these systems is poorly understood. We conducted two experiments to understand how limited and variable patterns of precipitation inputs may influence recruitment of bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Löve). In the first experiment, we evaluated how precipitation magnitude and dry-d interval during spring influenced recruitment. Ambient precipitation was excluded during spring, and we experimentally applied 5 levels of water (25, 35, 45, 55, and 65 mm) and 5-dry-d durations (1, 2, 4, 6, or 8 dry d between waterings) to plots sown with P. spicata. In the second experiment, we evaluated how the seasonal timing and duration of dry d influenced recruitment. All ambient precipitation was excluded through late winter and spring, and we experimentally applied three levels of dry-d duration (10, 20, and 30 d) four times during the growing season (February, March, April, and May) to plots sown with P. spicata. We observed strong, nonlinear interactive effects of precipitation amount and dry-d interval on recruitment where the midpoint dry-d treatment (4 d) interacted with low water availability to drive a major decline in recruitment. We also found strong evidence that recruitment was limited by dry periods occurring in late winter as opposed to dry periods occurring through spring, with recruitment decreasing over 40% during February dry periods compared with dry periods in March, April, or May. By understanding how precipitation pulses and interpulse dry periods interact to drive recruitment, we can refine efforts to develop weather-centric restoration frameworks, as well as hone ongoing efforts to identify plant materials and seed enhancement technologies that may buffer effects of variable precipitation on recruitment.