Northern hardwoods seedlings respond to a complex of environmental factors when deer herbivory is limited

Deer herbivory has a reputation for suppressing tree seedling development in Northern hardwood forests. We examined survival and growth of sugar maple (Acer saccharum) and ash (Fraxinus spp.) seedlings in a controlled factorial experiment with differing light conditions and levels of deer access in a Northern hardwoods forest in Wisconsin, USA. Measurements were made in similar to 380 m(3) harvest gaps, in transition zones adjacent to gaps, and under closed canopy conditions, both inside and outside of deer exclosures. Browse incidence was initially greater in unfenced treatments, but a general decline through time eliminated this difference. Seven-year sur-vival of both species groups was correlated positively with initial root collar diameter (RCD) and was greater in transition zones. Ash seedling survival was greater in plots with greater overall seedling aggregate height. Soils were primarily differentiated by available nitrogen, which positively influenced height growth of sugar maple in transition zones but did not influence ash growth. Although sugar maple height growth was correlated positively with initial RCD, greater initial height reduced growth rates, both as a simple effect (sugar maple) and in combination with initial RCD (ash). Ash growth correlated negatively with seedling aggregate height in gaps but was unaffected in transition or canopy zones. Allometric coefficients of RCD:height indicated some influence of deer herbivory which was not detected in other analyses. Coefficient values trended downward from year 2 to year 9, but wide confidence intervals limit the value of this metric as an indicator of seedling community resilience with regard to deer.

Automated summary

This study examines the effects of deer on the survival and growth of sugar maple and ash seedlings in a Northern hardwood forest. The results show that the survival of seedlings is positively correlated with initial root collar diameter and is higher in transition zones. The study also finds that soil nitrogen positively influences the height growth of sugar maple but has no effect on ash growth.