Research Studies - Habitat

Relationship Between Deer and Habitat - Richard D. Sample

Over-browsing by deer can severely reduce habitat quality, so there is a need to accurately assess the impact deer have on vegetation communities. Deer densities and landscape context vary spatially across Indiana, thus techniques are needed to assess impacts of herbivory across a range of conditions. We have three overall objectives to help determine the effect deer have on their habitats. First, we seek to evaluate three different metrics of browse intensity. The use of all three methods will provide a more accurate estimation of the intensity of deer browsing across Indiana forests. In addition, a comparison of the efficiency and efficacy of the methods will identify the method that most reliably and efficiently estimates browse intensity across different regions of Indiana. Secondly, we will determine the relationship between deer densities, browsing intensity, and vegetation communities. Lastly, we will determine deer diet composition and how it relates to plant species availability.

We will use four different techniques to measure browse intensity. The first technique is the twig aging method, which involves aging twigs of common tree species back to a browsed parent twig. Aging is done by counting the number of bud scale scars, which are areas on the twigs where the previous year’s growth started. Therefore, one bud scale scar represents one year of twig age. This method allows for an estimate of the number of years since a twig was browsed and is therefore an indicator of the intensity of deer browse.

A second method for evaluating deer browsing intensity is known as the stump sprout method. Forest managers are frequently challenged to sustain vegetation diversity and structure in landscapes experiencing high browsing pressure. Often, managers monitor browse damage and risk to plant communities using vegetation as indicators. Many hardwood tree species such as maple and ash produce multiple stump sprouts when they are cut. These sprouts grow quickly and may be rich in nutrients, as they are able to draw on the large energy reserves and uptake capacity of the tree’s full root system. Because of this, they make an excellent browse resource for deer, and their vigorous growth allows them to persist when browsed heavily with potentially large consequences for vegetation dynamics, community composition, and species coexistence. Most of our knowledge of resprouting strategies comes from fire-prone systems, but this cannot be readily applied to other systems where disturbances are less intense.

A third technique, the oak sentinel method, is similar to the stump sprout method. Oak species are highly favored by deer, especially during the spring months, and deer browsing is known to reduce heights of oak. However, naturally occurring oak seedlings are rare in the forests of Indiana and across most of the Central Hardwood Region. Planting oak seedlings provides a favored yet rare food source for deer and serves as a standardized food source to assess the rate of deer browsing. Therefore, planting oak seedlings and evaluating their growth and survival when protected or unprotected from deer browse (by use of fences) provides a rapid assessment of deer browse intensity.

deer exclosures video

A final technique to assess browsing intensity is the indicator species technique. Three common Indiana plant species (sweet cicely, jack-in-the-pulpit, and white baneberry) have been shown to be useful indicators of deer browse intensity. The heights of these plants can be used to determine the impacts of browsing, as taller average heights of these species have been shown to correlate with lower intensity of deer browsing.