Thursday, February 21, 2013

Deer, we have a problem

Aromatic sumac doesn't stand a chance of survival in the deer infested woods I visited earlier this week. For the past four years, with increased urbanization and a changing demographic in the area, the deer problem in these woods has escalated to mind-boggling levels, such as it has throughout the Ozarks in similar settings.

Due to circumstances beyond my control, we conducted our winter twig browse surveys a few weeks earlier than normal, in mid-February rather than March, because, in the absence of snow, helicopter deer counts could not occur. Since moving to the Ozarks, every summer I've sampled deer exclosures to measure the impacts of deer herbivory on herbaceous vegetation. The winter twig counts are simply another way of measuring the ever burgeoning pressure deer have on biodiversity. Granted, I know a deer problem when I see it, but I fly by data collection to guide decisions rather than anecdotal evidence.

So, in a feverish 8 hour period, I tallied all of the multiple thousands of browsed twigs and unbrowsed twigs on preferred and unpalatable winter stems. Ice cream plants for deer include sassafras (72% browsed), all of the sumacs, dogwood, white oaks, hazelnut and bitternut hickory, with its tender orange buds. In years past, I didn't detect a lot of browsing on buckeyes, but this year, 68% of the buckeyes I sampled had their big bulging buds snipped off. Only 15% of the black oaks showed signs of browse (which is high for an unpalatable species), and deer are apparently not very interested in the green stems on box elder. Alarming is the amount of winter twig browse this early in the season. I suspect that if we resample in early March, the percentages of browsed twigs will be even greater. If there is substantial browsing going on in mid February, it bolsters my data collected from the deer exclosures that illustrates significant browsing occurring on herbaceous flora as well.

In the past few years, I've amassed quite a list of ice cream plants, those tender (usually high C value species) perennial forbs that form a rich matrix of heterogeneity in nice, restored Ozark woodlands. In one 5,000 acre tract I sample every year, the only place in the whole acreage one can find Triosteum perfoliatum is inside a deer exclosure; undoubtedly it existed throughout the area historically but the deer have extirpated its population everywhere else. Deer love the asters, especially Aster patens, Aster anomalus, and Aster drummondii. They're not crazy about Verbesina helianthoides, so much so that in one 854 acre tract I sample, it is the sole forb in the woodland understory. It's not very fun to botanize in deer problem woods. Deer also browse heavily on the juicy stalks of jewelweed and the flowering heads of Ratibida pinnata, Ohio horsemint, and even the stickery heads of the Echinaceas.

The deer problem began in the Ozarks like a wave from the east, quickly and resolutely. Biotic homogenization is taking its toll on once healthy woodlands and there seems to be no end in sight until the woodland understory is a carpet of sedges and fragile fern.

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