Saturday, February 22, 2014

Twig Browse Time

After three days of much needed sun and highs in the 40s, only small patches of snow remained in this exquisite post oak woodland filled with warm season grasses and the churling calls of red-headed woodpeckers. As late February rolls around, just before all the tender shoots of herbaceous vegetation come up in the spring, deer begin looking for the fresh green buds of woody shrubs for forage. By examining how many buds have been browsed, one can determine how much pressure a deer population is having on the landscape.

My twig browse surveys have occurred here every winter since 2008. Since then, in combination with aerial deer censuses and sampling of deer exclosures to calculate deer impacts on the herbaceous layer, I’ve seen the deer population fluctuate from a high of 75 deer/mi2 to a manageable 20 deer/mi2. During these past seven years, I’ve also amassed a list of ice cream shrubs for deer, those shrubs that deer prefer to browse compared to the unpalatable species. The ice cream shrubs, much like the herbaceous ice cream plants, really get hit on the nose during winter months, sometimes to the degree that they can’t flower since all the buds have been clipped off.

Deer do seem to love aromatic sumac, smooth sumac, white oak, post oak, and sassafras. Discovering heavy browse on these species generally indicates a lot of deer activity in the woods, but when the unpalatable species are being clipped at the same rate, plants like buckeye and black oak, then the deer population is probably pretty well out of control, indicating they're desperate enough to eat plants they don’t really prefer.

By the end of the day, I had counted 314 browsed stems of aromatic sumac, and 165 unbrowsed which resulted in 65% browsed. Dogwood: 81 browsed, 99 unbrowsed, 45% browsed. Sassafras: 731 browsed, 934 unbrowsed, 43% browsed. Smooth sumac: 226 browsed, 38 unbrowsed, 85% browsed. And black oak, a plant deer don't seem to like too much: 93 browsed, 161 unbrowsed, 36% browsed, which is pretty high for an unpalatable species.

The deer exclosures are equally revealing, with species richness and abundance greater in the protected exclosures and the absence of signature species for the area. No asters, goldenrods, even wild petunia are present outside the exclosure. Beyond the cattle fencing it's a monoculture of dogbane, sedges, some crotons and wild rye. Sadly, I've seen this transformation occur in the past 7 years. Deer are having a serious negative impact on biodiversity in Missouri, and hardly anyone notices because so few of us are looking.


DW said...

I googled deer predators. Looks like Missouri needs more mountain lions and wolves, but people are pretty scared of those guys. I don't know what the answer is.

Allison Vaughn said...

You're right, we do need more large predators....unfortunately, once our predator populations start growing, our state will probably start hunting them down.