Arboretum Sampler

Marcescent oak leaves

Marcescent oak leaves

Last Sunday’s walk was a fun one with a great group (and a pretty large group, too). The walk theme was “Sampler” so we took about a 2-mile loop to check out late November highlights of the Arb. We started in Longenecker where there was lots of bird activity, including reports from earlier in the day of a pileated woodpecker (no, we didn’t see it). We were lucky, however, to have fellow naturalist and expert birder Levi Wood along with us. There’s a lovely stick nest in a big willow right behind the service buildings. Levi confirmed that it was probably a crow’s nest, based on shape, size, and materials. On the bird front, we saw plenty of turkeys, a red-bellied woodpecker, nuthatches, robins, and a blue jay. We later couldn’t remember specifically but think that we also saw at least a few sparrows and juncos.

American chestnut burs
American chestnut burs

We stopped at the chestnuts in Longenecker, a favorite spot this time of year (if there’s no snow) because of the amazing American chestnut hulls that carpet the ground around the tree. The hulls are both exquisitely prickly (outside) and exquisitely velvety (inside). They are beautiful. A visitor asked if these trees are treated (against chestnut blight). I wasn’t sure but got the answer later: no, the chestnuts are not treated. Although the low numbers of American chestnut in the region helps to limit airborne transmission, there are other sources of the pathogen. As Molly Fifield Murray (outreach and education manager) noted, the pathogen could be tracked in on someone’s boots. In her words, the trees are “not presumed safe.” Alas.

There’s also beautiful little black/blue cup fungi under the chestnut trees. Plectania, perhaps?

We walked through Gallistel Woods from G7 to G5 and then crossed over to Wingra Woods. We stopped to discuss the effigy mounds, now very visible with the undergrowth leafless.

Speaking of leafless, several visitors noticed that there were many trees, in Wingra woods in particular, that still had dry leaves attached to their branches. (Did you guess which tree? Beech? Yes! Also common on oaks.) There’s a term for everything botanical, and “marcescence” describes the condition of holding onto leaves after the leaves are dead and would be expected to have fallen to the ground. There are a few hypotheses about why some types of trees do this, and the most compelling, in my opinion, is that it’s an adaptation that helps to prevent herbivory. Tree buds and twigs are nutritious treats for hungry herbivores in the winter months, and if these tasty parts are covered by inedible cellulose (the dead leaves) then it might deter nibbling.

Big spring in the fog
Big spring in the fog

At Big Spring in Wingra Woods we stopped to consider how runoff water from our built landscape—called the sewershed—affects Lake Wingra. We looked at a fabulous map (made by Mark Wegener, assistant director) that shows the locations and magnitude of the runoff water entering Lake Wingra. The UW–Madison and City of Madison Engineering work together to manage the runoff water before and as it enters Arboretum natural areas and Lake Wingra. Runoff water moves through a city-engineered, largely invisible system of underground culverts. This runoff water carries pesticides, fertilizers, sediment, salts, debris, and other contaminants. Water that runs over pavement and built surfaces moves quickly. Fast-moving water can carry lots of sediment. The city, in partnership with UW–Madison Facilities Planning and Management, has built ponds on Arboretum land to treat the runoff flows. As the runoff enters the constructed pond, the water slows down and much of the sediment settles out. Some phosphorous is also left behind, attached to the sediment. This moderates some of the flow and helps filter the water that continues through Arboretum lands and into Lake Wingra. (See our Stormwater page for maps of the Lake Wingra watershed and Arboretum stormwater flow.)

We also compared this year’s prospects of lake freezing with the last couple of years.

Smaller Lake Wingra has ice cover before Mendota or Monona, usually around Nov. 29. The record latest date of ice cover was Dec. 29 in 1877, with a second latest date of Dec. 24 in 2001. With the current 10-day forecast, it’s easy to imagine we might set a new record this year—we’ll find out soon enough.

As you walk the Arb in the mild December weather, watch out for mud. Walking through mud can degrade trails, but walking around mud can trample off-path plants. Our Sunday route ended with a bit more mud than ideal. Try to carefully keep to the path, even if you encounter mud.

—Sara Christophersen

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