Emerging research suggests a large portion of extreme weather events can be attributed to climate change and the frequency of such events is increasing. Extreme weather can significantly impact the reproductive capacity of plant populations, leading to loss in community persistence, resistance and habitat quality with impacts that extend across a landscape. To address this issue, we hypothesized that shrubs can facilitate fecundity of plant community members in extreme weather years. We asked if this is a possible mechanism for plant communities to resist deleterious effects of extreme weather, by measuring floral production of 6 dominant perennial bunchgrass species. Our main hypothesis was tested via a replicated full-factorial experiment across two sites in the Northern Great Basin Experimental Range in eastern Oregon. Shrub canopy removal, extreme precipitation and extreme drought events were crossed for 6 total treatments: Canopy Intact (control), Canopy Intact + Water, Canopy Intact + Drought, Canopy Removed, Canopy Removed + Water and Canopy Removed + Drought. Simulated extreme drought and precipitation events were actively manipulated in the field through the use of irrigation and rain-out shelters. We predicted that Canopy Removal and Canopy Intact + Water would yield the greatest floral production; Canopy Intact + Drought and Canopy Removed + Water would yield similar floral production as Control; and Canopy Removal + Drought would yield the least floral production.
Our main finding was that in the Canopy Removed + Drought treatment, floral production was on average 53% less than most other treatments in Site A and on average 70.8% less than all other treatments in Site B. Contrary to our prediction Canopy Removal and Canopy Intact + Water did not result in significantly greater floral production. In fact, we found that beyond the highly significant results of the Canopy Removal + Drought treatment, all other results were largely species-specific. For example, Canopy Removal + Water resulted in significantly higher floral yield for one species but lower for another, possibly indicating certain species in this semi-arid environment are equally as sensitive to extreme moisture as extreme drought. Our findings illustrate how shrubs can act as a buffer, facilitating fecundity among plant community members in extreme weather years. With this study, we add support to growing research on fecundity facilitation as a mechanism for mitigating short and long-term impacts on plant population resistance and persistence in a changing climate.