LAUSR

Alterations in global climate via extreme precipitation will have broadscale implications on ecosystem functioning. The increased frequency for drought coupled with heavy, episodic rainfall will likely generate impacts to biotic and abiotic processes across aquatic and terrestrial ecosystems. Despite demonstrated shifts in global precipitation, less is known about how extreme precipitation interacts with biophysical factors at controlling future demographic processes, especially those sensitive to climate extremes such as organismal recruitment and survival. We utilized a field-based precipitation manipulation experiment in 0.1 ha forest canopy openings to test future climate scenarios characterized by extreme precipitation on temperate tree seedling survival. The effect of planting seedbed (undisturbed leaf litter/organic material versus scarified, exposed mineral soils), seedling ontogeny, species, and functional traits were examined against four statistically defined precipitation scenarios. Results indicate seedlings grown within precipitation treatments characterized by heavy, episodic rainfall preceded by prolonged drying responding similarly to drought treatments lacking episodic inputs. Moreover, among all treatment conditions tested, scarified seedbeds most strongly affected seedling survivorship (odds ratio 6.9). Compared to any precipitation treatment, the effect size (predicted probabilities) of seedbed was over twice as important at controlling seedling survivorship. Yet, the interaction between precipitation and seedbed resulted in a 27.9% improvement in survivorship for moisture sensitive species. Seedling sensitivity to moisture was variable among species, most closely linked to functional traits like seed mass. For instance, under dry moisture regimes, survivorship increased linearly with seed mass (log transformed; adjusted R2 = 0.72, p < 0.001), although no relationship was apparent under wet moisture regimes. Although precipitation influenced survival, extreme rainfall events were not enough to offset moisture deficits nor provide a rescue effect under droughty conditions. The relationships reported here highlight the importance of plant seedbed and species (e.g., functional traits) as edaphic and biotic controls that modify the influence of extreme future precipitation on seedling survival in temperate forests. Ultimately, we demonstrate the biophysical factors most influential to early forest development that may override the negative effects of increasingly variable precipitation. This work contributes to refinements of species distribution models and can inform reforestation strategies intended to maintain biodiversity and ecosystem function under increasing climate extremes.