Saturday, January 21, 2012

Winter forage

With the problem of deer overpopulation in Ozark woodlands ever burgeoning, snow covered landscapes tend to be desirable for the simple fact of allowing for aerial deer counts. In the absence of snow, and often in consort with the aerial census, another method to measure deer impacts to biodiversity can be employed. This time intensive process tracks deer browse on woody stems, both the desirable species and those normally less palatable to deer.

Winter twig browse surveys usually begin in mid-February in the Ozarks, before leaf on and yet still winter when deer begin browsing on small shrubs and trees. Ice cream twigs for deer include dogwood, white oaks, sassafras, aromatic sumac, winged sumac. In my experience running long transects for winter twig browse surveys, these are often the first shrubs and trees deer will browse in late winter months. The less favorable plants include black oaks, buckeye, bitternut hickory, vaccinium--when these are browsed intensely, it probably indicates deer overpopulation.

Here's the drill: Walk along transects that harbor enough small woody species to fill a page with each species of 50 spaces; clones on each plant are grasped and the number of browsed twigs and unbrowsed twigs are recorded. So, grab a stem on a sassafras and you may have three browsed twigs and one unbrowsed, recorded as 3/1 in one of the spaces. Find another sassafras and another and so forth until the page is filled with browsed/unbrowsed numbers. This is accomplished for about 10-15 species and at least 10 transects scattered across the landscape. Time consuming, yes, but valuable information results when the browsed/unbrowsed are calculated into percentages. In woodlands with high deer numbers, dogwood gets hit on the nose, and even black oak buds are clipped off. When this happens repeatedly, erect trees and shrubs take on a multibranching habit or, under intense pressure, they never leaf out and subsequently die.

The deer problem in the Ozarks is growing at an alarming rate, leading us to homogenized ecosystems full of plants unpalatable to deer. Measuring the impacts of deer overpopulation to biodiversity is a top priority for me. Spending the days running twig browse transects each February-March gathering valuable data are indeed days well spent.


Elizabeth said...

Interesting - I ought to do this in my yard in Illinois. I went out to check on my witch hazel tree, and noticed the deer have pretty well rubbed the bark off it as well as other adjacent trees,and I can see where they are bedding down. Imagine there is foraging going on as well, would be interesting to see how it compares to the Ozarks.

Allison Vaughn said...

Oh you should! If you send me a list of shrubs and small trees, I can tell you which are preferred and not preferred. I wonder how Illinois is faring in the deer problem with so much land in agriculture? I imagine the natural places that remain may be threatened. One you look closely at the stems, it's pretty easy to see if they've been browsed. I hope you don't have a deer problem.