ARBORETUM NEWS (NATURALISTS’ NOTES)
What’s Happening? – that cycle of beginnings and endings which we call a year, Aldo Leopold
SUNDAY, JANUARY 10, 2010It was a pleasant 12 degrees or so, with sunshine and an intermittent breeze, for the Sunday public tour on January 10th. I decided to take the group through Wingra Woods for a winter look at Big Spring (winter/spring, get it?).
We paused just after entering the trail for a quick quote from Aldo Leopold. The first essay in A Sand County Almanac is called “January Thaw”, and while a thaw is certainly not what was happening that day, I did want to share Leopold’s take on winter phenology: “that cycle of beginnings and endings which we call a year … January [nature] observation can be almost as simple and peaceful as snow, and as continuous as cold.”
The main reason Leopold found January observations simple is that—to put it plainly—they are few and far between. Before long new appearances and events will crowd the calendar, but for now, “skunk tracks” or “woodpeckers drumming” might be the only notations made in half an hour’s time. For exactly that reason I find them precious.
In fact a hairy woodpecker, tapping vigorously on a dead snag, was our first sighting of the day. We never did see enough of the bird to be sure if it was male or female. It was partially turned away from us, and the telltale red patch (if it was there) was hidden from our view.
We are privileged to have at the Arboretum a very precious data set – phenological observations made by Aldo Leopold and Sara Elizabeth Jones between 1935 and 1945. From birdsong to blooming dates, they charted some of the annually observable phenomena in the Arboretum, and since 2005, we have been attempting to update those records. Perhaps in doing this we will learn something about the local effects of global climate change.
It’s tricky doing phenology just right. To be a true scientist about it, one must perform the observations exactly the same way, not only from year to year, but from place to place. Keeping track of the first date that silver maple flowers are in pollen is meaningless if it’s just any silver maple tree anywhere in the Arboretum; rather, one is required to observe the very same silver maple tree, the same number of times, on the same dates, at the same time of day, each year. Otherwise there are too many other factors which could influence the event: amount of sunlight received, the wetness or dryness of the site, tiny differences in soil nutrients available to the tree, the observer’s absence on a critical day, and a host of others.
Sometimes that strict consistency isn’t possible. In 75 years, trees die or get cut down; buildings go up which may cast shade; alterations are made to the hydrology; in short, the landscape changes. But to the best of our ability, we’re seeking to replicate the Leopold and Jones data, to keep the faith with their scientific practice and to see what we may learn.
On Sunday afternoon our group wasn’t doing formal phenology, of course—just keeping a sharp eye out for what might be happening in the woods. Our next notable sighting was “buck rub”. There is a place on the Wingra Woods trail, past the edge of the golf course and just before you skirt the Sinaiko Prairie, where there is very dramatic scraping on two balsam fir trees standing opposite one another, right along the trail. I am not a good enough interpreter of animal sign to be sure just how long ago the scratches were inflicted, but the raw wood revealed by the missing bark areas looks orange-colored and quite fresh.
Which brings me to a short discussion of white-tailed deer. It just so happens that last week on Wednesday I heard a presentation by UW faculty member Don Waller about indicators of deer overabundance.
Waller teaches in the botany department; he has been studying the impact of white-tailed deer on forest ecosystems for more than two decades. For all of my years as an Arboretum guide I have been carrying around a card with a summary of his research findings: at a density of 10 deer per square mile, you will see a reduction in woodland wildflower richness and abundance; 20 deer per square mile will eat enough of the understory that there will be less bird diversity in response; and 30 deer per square mile will accomplish major shifts in the forest’s structure and composition.
The Arboretum covers two square miles … you do the math. And much of northern Wisconsin features deer densities of 40-45 per square mile. The question must be asked, do we even know what our state’s forests would look like if the deer population were more appropriate?
Most people know that wolves prey on deer, and that the great reduction in wolf numbers in the upper Midwest has a lot to do with our increased deer population. But Waller points out that it’s not that simple a relationship: cougars and wolverines are also predators for white-tails, and were formerly present here; not only that, but pre-settlement and pre-logging, there were other large ungulates around to compete with the deer (moose, elk, and woodland caribou).
You might say “it’s not only what eats you, it’s what competes with you” that helps to keep any given species in balance.
I don’t mean to be down on deer. They are beautiful, graceful animals, and my heart pounds when I see one just like anyone else’s. But it is a Jekyll-Hyde relationship, since deer can also be very damaging to ecosystems when they become overabundant. And in a relatively small “island” of natural area like the Arboretum, where there is a generous food supply and no 4-legged predator or significant grazing competition present, they can quickly overpopulate. That is why we have a deer control program – humans must become the force that thins the herd.
Of course the Wisconsin deer population has been the subject of many newspaper articles recently, with much finger-pointing between hunting groups and the DNR. I am not going to take a position on that except to say that from a forest-ecology perspective, the number of deer in our state is higher than optimal no matter whose numbers you believe.
But back to Wingra Woods and the Sunday afternoon walk. We paused at Big Spring for a quick reading of a Ho-Chunk story called “The Sky Man”, a legend collected in the 1930s by archaeologist Charles E. Brown and probably referring to the very spring above which we stood.
Wending our way uphill from there, we passed between two large effigy mounds, looking like giants sleeping under the snow. We noted mouse tracks and tunnels in several places along the trail. After crossing the road, we angled through Longenecker Gardens back to the Visitor Center, and were treated to the sight of wild turkeys feeding on and under crabapple trees. The sight of such a large bird perched in such a small tree always seems incongruous to me. It reminds me of stylized representations of a “partridge in a pear tree”, a la the Twelve Days of Christmas.
We’ll see what’s happening next along the Arboretum’s trails. Will you be there?