Data from: Earthworm invasion, white-tailed deer and seedling establishment in deciduous forests of northeastern North America

1. Earthworm invasions and high deer populations are among many stressors threatening long-term population viability of forest understorey plants in northeastern North America. Stressor effects are typically tested one at a time, however, stressors often co-occur, and plants respond to effects of multiple stressors simultaneously. 2. We used a factorial design to test independent and combined effects of non-native earthworms and native white-tailed deer on survival of seedling transplants of 15 native understorey plants in 5 forests in New York State. 3. Earthworm biomass was negatively correlated with survival of 12 of 15 species. We found no interactive effect of deer and earthworms, but did find a positive, non-consumptive effect of deer on Geranium maculatum and P. virginianum survival. 4. Deer and earthworm presence/absence indirectly influenced other trophic levels: earthworm presence increased the likelihood of insect attack, and deer exclusion increased the likelihood of rodent attack disturbance of transplants. 5. Synthesis: Invasive earthworms negatively affected seedling survival of many understorey plants, including species previously thought to benefit from earthworm associations. This effect was a function of earthworm biomass, a surrogate for earthworm activity. We expect deer herbivory to increase in importance, including indirect effects, as seedlings grow into browse height over the next years. Investigations of co-occurring stressors can result in ‘ecological surprises’ including previously overlooked non-consumptive effects or effects on other trophic levels.