Climate, light, earthworms, nutrients and deer herbivory as predictors of seedling growth at the prairie-forest ecotone in western Minnesota
Results/Conclusions All four tree species exhibited substantially greater height growth when protected from deer herbivory. T. americana seedlings have grown the most both inside deer exclosures (+301%) and in adjacent control plots (+121%), and T. americana has the largest gap in height growth for protected versus unprotected seedlings. At the other extreme, Q. macrocarpa in our control plots have not, on average, grown at all. To examine the effects on growth of climate versus other stressors, we performed an analysis of deviance and compared predictors and suites of predictors to a base model. Climate (temperature and moisture), soil nutrients (considered together), light, earthworms (count and biomass), and deer density all substantially improved growth predictions over the base model, though not equally so. For example, climate reduced overall deviance by 63% more than did earthworms and 25% more than the suite of soil nutrients, but light was more important than climate by 19%. For trees growing in our control plots, deer density was 94% more important for predicting growth than was climate. Thus we conclude that while climate change of the magnitude predicted for the coming century will impact tree growth, other factors are of similar or even greater importance.