The Relationship Between Deer Density and Forest Regeneration

Deer can be too many, too few, or just enough for healthy forests [PDF], March 31, 2012 NRS Research Review, No. 16, Spring 2012
... Deer populations at the time of European settlement in areas of “prime habitat” (3 million square miles) ranged from 8 to 20 per square mile ... they found that deer population levels at or below 20 per square mile allowed undergrowth to recover. The study surprised scientists, though, when there was some regrowth even at very high deer densities.... when deer populations were reduced to just-right densities (from about 28 to about 15 deer per square mile in that particular landscape) populations of wildflower indicator species such as trilliums and Canada mayflower started to recover ... one species of small tree/shrub, pin cherry, that had become overabundant at the lowest levels of deer density (10 per square mile in that study). They soon realized that this phenomenon was early evidence of such a thing as too few deer. Pin cherry, a shrubby cousin of black cherry (a desirable lumber tree), can outcompete other species when highly abundant.  
     Meanwhile, in West Virginia, where deer populations were lower compared to the carrying capacity of the landscape, NRS scientists Royo and Mary Beth Adams (Parsons, WV), and colleagues looked at the effects of interactions of deer browsing, fire, and the creation of gaps in the forest canopy on the forest ecosystem. In fact, this research suggested that the levels of deer were just right for the West Virginia landscape where the study occurred because the mix of disturbances experienced by these forests historically—ground fire, canopy gaps, and some deer—increased diversity, compared to exclosures where there were clearly too few (zero) deer, and the same shrubby plants dominated the understory... 
     Scientific reports of the long-term trophic cascade have resulted in efforts by game commissions and other hunting regulators to encourage hunting of more female deer (does) for meat in addition to trophy males (bucks). When this is successful, the effects of deer browsing are not so severe and forests are healthier—and so are the deer herds ...

Direct and indirect effects of white-tailed deer in forest ecosystems,  Forest Ecology and Management Volume 181, Issues 1–2, 3 August 2003, Pages 165–176
Thomas P Rooney, , Donald M Waller
As reported in Figure 2, the density of yellow birch seedlings measured in the forest ecosystem fell off dramatically when the deer density fell much below 18 deer per square mile (about 7 deer per square km) or when deer density was much above about 44 deer per square mile (about 17 deer per square km).

... Understanding and predicting the effects of deer (Cervidae) on forest ecosystems present significant challenges in ecosystem ecology. Deer herbivory can cause large changes in the biomass and species composition of forest understory plant communities, including early life-cycle trees (i.e., seedlings and saplings).... Our findings highlight the indirect effects of white-tailed deer on the growth of adult individuals of Q. rubra in a way opposite of what would be expected from previous studies based on immature or understory tree populations. We suggest the increased growth of adult trees in the presence of deer may be explained by increased nutrient inputs through deer fecal and urine deposits and the alteration of the competitive environment belowground through the reduction of understory vegetation by browsing. Underscoring the ecological and demographic importance of adult trees in forest ecosystems, results from this study suggest the direct and indirect effects of deer on mature trees should not be overlooked.

Effects of Deer Settling Stimulus and Deer Density on Regeneration in a Harvested Southern New England Forest  [PDF] KJ Barrett, OJ Schmitz - International Journal of Forestry Research, 2013
... Elevated deer densities have led to reports of forest regeneration failure and ecological damage. However, there is growing evidence that the biophysical conditions of a forest thatmake it attractive to deermay be a contributing factor in determining browsing levels.
Thus, an understanding of settling stimulus—how attractive an area is to deer in terms of food-independent habitat requirements— is potentially important to manage deer browsing impacts. We tested the settling stimulus hypothesis by evaluating the degree
to which thermal settling stimulus and deer density are related to spatial variation in browsing intensity across different forest harvesting strategies over the course of a year. We determined if deer were impacting plant communities and if they resulted in
changes in plant cover.We quantified the thermal environment around each harvest and tested to see if it influenced deer density and browsing impact.We found that deer had an impact on the landscape but did not alter plant cover or diminish forest regeneration
capacity. Deer density and browse impact had a relationship with thermal settling stimulus for summer and fall months, and deer density had a relationship with browse impact in the winter on woody plants. We conclude that thermal settling stimulus is an
important predictor for deer density and browsing impact.

The effects of deer herbivory and forest type on tree recruitment vary with plant growth stage  MN Bugalho, I Ibáñez, JS Clark - Forest Ecology and Management, 2013
... We assessed how deer herbivory and forest-type affected the diversity of seedlings and saplings of dominant tree species in a temperate forest of Eastern USA, during four consecutive years. Fenced and unfenced plots were established in hardwood and pine forests and tree seedlings and saplings identified and monitored annually. Tree recruitment patterns varied widely from year to year, particularly for seedlings. Sapling communities were richer in species, more diverse and with lower indexes of dominance than seedling communities. The diversity of seedlings and saplings was significantly affected by inter-annual variation of tree recruitment but not by deer herbivory or forest type. Herb cover was reduced for more than fourfold in unfenced hardwood plots. Results show that inter-annual variation of recruitment, herbivory and forest type can combine to shape the composition of tree seedlings and saplings...

Southwestern CT: A 5 Year Update January 4, 2013 Connecticut, E. Faison. Highstead, Redding, CT 
     The towns of Redding and Ridgefield CT began deer hunting on several town preserves in 2006.  In 2007 Highstead established forest monitoring plots in these preserves and nearby unhunted properties to document any changes to forest understories resulting from deer management.  These plots were resampled for the first time in 2012, and the results are presented here. 
     From 2007 to 2012, tree seedling (≥30 cm<2.5 cm diameter) density increased in both hunted and unhunted properties (Fig. 1), whereas species richness of tree seedlings (the number of different tree seedlings per plot) changed little from 2007 to 2012 in either management category.   [tree density increased more in unhunted properties]