Complex interactions of deer herbivory, soil chemistry, and competing vegetation explain oak-hickory forest tree regeneration in central Pennsylvania, USA

The root causes of forest tree regeneration failure are difficult to
resolve, although numerous studies show ungulate herbivory, soil
conditions, and competition from undesirable vegetation as likely
contributors. To better understand the relative importance of each issue,
we conducted a 7-year manipulative experiment to assess the interactive
effects of white-tailed deer (Odocoileus virginianus) herbivory, soil
acidity, and competing vegetation on tree regeneration in oak-hickory
forests of central Pennsylvania, USA. Outcomes depended on initial tree
seedling abundance, and all three factors had significant interactions. At
low initial seedling abundance, fencing resulted in the greatest increase,
but all treatments had a positive effect on seedling growth and abundance.
At higher initial seedling abundance, abundance failed to recover 7 years
after herbicide treatment and soil pH was an important predictor. When
soil pH was > 4.6 from lime application, seedling growth and
abundance in unfenced controls with high initial abundance was comparable
to the fenced-only treatment. Competing vegetation, assumed to be a
symptom of excessive, long-term deer herbivory, does not seem to be the
primary factor limiting tree regeneration in our study area. Ameliorating
acid deposition warrants greater consideration as a management action
because it could provide long-lasting benefits compared to short-term
fence installations.