Impact of deer herbivory on leaf nutrient content and leaf thickness of Betula lenta in Black Rock Forest, New York

Background/Question/Methods

The physiological response of black birch (Betula lenta) tree leaves to overbrowsing by white-tailed deer was examined at Black Rock Forest in southeastern New York state.  Since a major environmental problem affecting the forests in the eastern U.S. is excessive deer browsing, this was an important question to consider.  Leaf samples from 120 black birch trees collected from paired plots (one fenced to exclude deer and the other open) were processed for leaf mass per unit area (LMA), photosynthetically active radiation (PAR) and percent nitrogen per leaf area (%N).   It was hypothesized that deer herbivory would create a higher light environment in the control (browsed plot) which would cause black birch trees to respond in two ways: (1) trees under deer pressure would produce thicker leaves, and (2) leaves would produce more nitrogen (due to the higher light environment).

Results/Conclusions

LMA, PAR and %N were shown to be significantly higher in the control where deer have free access to the trees. It seems that, through herbivory, deer create a higher light environment in the control and the black birch trees respond by producing thicker leaves with increased nitrogen content.   There is some uncertainty about the cause of the increased leaf nitrogen in the browsed plot. My future research would be to see if the soil in the browsed versus unbrowsed plot has different amounts of nitrogen too.  In conclusion, the higher PAR, LMA, and %N in the control plot suggest that herbivores such as the white-tailed deer may have the ability to impact habitat conditions and leaf physiology in an eastern deciduous forest to the point where the nitrogen cycle is affected.