Sunday, November 02, 2014

Paradox Lost, or, Less Irony in the Woodland Diet

The woodlands of Princeton have long held a paradox. Abundant food in the form of non-native species has gone begging while deer and other wildlife stubbornly maintain their preference for eating natives. The result is a continuing imbalance as the non-natives gain competitive advantage and dominate the understory, forming what is essentially an inedible landscape.

Here's the classic example--a native spicebush with one main trunk large enough to escape the deer, but with any new shoots from the base getting eaten down. Those stubs of new shoots--dense stunted growth reminiscent of witch's broom--are a sign of heavy deer browsing. I hadn't seen anything similar on the nonnative shrubs like winged euonymus, Linden viburnum, privet, and asian photinia.

Last week, though, I saw something that would suggest that the forests grip on paradox is loosening. Here's a typical winged euonymus, showing off its pink in autumn's color-coded forest. If it were in full sun, the fall color would be bright red--thus the common name burning bush. Its ability to successfully invade and dominate in our preserves owes much to its inedibility. The native Euonymus shrub (E. americana) by contrast is a favorite of the deer, and is browsed so thoroughly that it survives only as sprouts here and there on the forest floor, a few inches high.

But what's going on there in the photo, down near the ground, to the left of the trunk?

This nonnative Euonymus has sprouts that look a lot like the browsed sprouts of the native spicebush.

And this invasive Linden Viburnum, cut down by volunteers with the Friends of Herrontown Woods maintaining Autumn Hill Reservation's trails--the new sprouts from the stump are getting browsed by the deer.

These are heartening signs that the deer may be, with an emphasis on "may", expanding their diet to include more invasives. The question for land managers is whether we could help this process along. I recently heard a testimonial that the mint-flavored sprays used on hostas and other plants to discourage deer browsing are actually effective. Perhaps there's a spray that would attract deer to invasives, and begin training them to consume them more. Is food preference learned or instinctive? Does one generation steer the next towards particular foods?

In the meantime, we walk the trails cutting invasives here and there, deer-like, applying the sort of steady browsing pressure on exotics that deer have shown can be so transformative when applied to natives. Normally, without a little dab of glyphosate applied to the cut stump, the shrubs would simply resprout and need to be cut again the next year to keep the trail clear. But if the deer cooperate and browse the resprouts, then some progress towards shifting the balance towards native species could actually be made, even without the stump treatment. If this is over-optimistic, blame it on the uplifting nature of a brisk autumn walk in the woods.

Some other observations during a beautiful fall day in Autumn Hill Reservation:

Slow-mo wrestling match. The bark of a dogwood trunk has completely enveloped a Japanese honeysuckle vine that had grown around it. The vine was squeezing the trunk, and now the trunk is squeezing the vine. I cut the vine at the bottom to improve the dogwood's prospects.

A lone hazelnut, with a lone female flower bud. Autumn color-coding in the forest makes it easier to discover the solitary hazelnut shrubs scattered across Princeton. I know of one in Autumn Hill Reservation, two in Herrontown Woods, and four at Mountain Lakes Preserve.

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