Infrequent, high-volume rainfall events modulate acorn production for two common oak species in Western North Carolina, USA

Variations in landscape-scale acorn production have been studied across the Quercus genus to understand its role in ecosystem ecology and forest regeneration. Multiple weather conditions may influence annual acorn production, especially the positive influence of seasonal rainfall. Prior studies have assessed the effects of rainfall measured over monthly and seasonal scales, but have not focused on the potential influence of daily rainfall events (e.g., frequency and volume) on acorn production. Here, we examined 19 years of daily rainfall data with annual acorn data collected from Quercus montana and Quercus alba at the Bent Creek Experimental Forest, North Carolina, USA to understand how daily rainfall modulates acorn production. We organized daily rainfall data into three percentile thresholds (50th, 90th, and 99th) and examined how well linear models were able to explain variations in mean annual acorn production with and without previous-year high-volume daily rainfall (i.e., the highest volume rainfall days). We discovered model strength remained strong, and sometimes improved, when removing the frequent, low-volume rain events, and daily rainfall at or above the 90th percentile (21.9 mm/day) was crucial for establishing statistical relationships with annual acorn production. Our results indicate the importance for high-volume daily rainfall events to explain precipitation-acorn production relationships for two common oak species in North Carolina. Further, our results provide insights into the importance of daily high-volume rainfall for above average acorn production, which could have implications under future climate change.