Autumn Woodland Walk

American bittersweet

Considering the unseasonably cold weather forecast for the upcoming week, our tour conditions today were pleasant with calm winds and partly sunny skies.

On our way to the east access trail to Wingra Woods, we stopped to take a look at the native bittersweet that lounges along the Longenecker fenceline. Although the native and invasive forms can hybridize, generally the native vine flowers and fruits only at the terminal ends of branches. The oriental bittersweet vine can pose a significant problem in wooded areas where it circles itself around tree trunks to climb into the canopy for sunlight, essentially preventing the tree from transporting water and nutrients along the vascular cambium. Active management of the oriental bittersweet vine occurs in several woodland units of the Arboretum.

Refocusing our efforts on more upbeat items, we walked through Wingra Woods to visit White Clay Spring and Big Spring. Hydrologists classify a groundwater seepage as a ‘spring’ when it has a flow rate at least 0.25 cubic feet per second (cfs). While White Clay Spring has a fairly low discharge rate, Big Spring flows well above 1 cfs, making it eligible as one of the 300 springs in Wisconsin that are legally protected. Historically, there were several dozen springs around Lake Wingra. The dozen or so that remain are an important source of water and respite for resident bird populations and other non-hibernating animals during the winter months. As we sauntered through Wingra Woods, we noted the presence of both yellow birch and beech trees. These species were planted sometime between the 1940s and 1960s to mimic the tree composition of a typical northern Wisconsin mesic forest.

Beech trees produce millions of seeds in a mast year, each weighing less than a paper clip. Many of the seeds that fall to the forest floor are covered by leaf litter and do not survive. These seedlings germinate best on a fertile, moist substrate, such as a moss-covered stump. This preference explains the post roots often exhibited by beech that have grown up over a rotting stump or log. The beech is a tree species more traditionally found in eastern Wisconsin, along the Lake Michigan forests coastline. They are distinct trees with the smooth gray bark and can have a lifespan up to 400 years. Along with many of our oaks, the beeches also retain their leaves throughout the winter. Various theories attempt to explain this phenomenon. Some scientists suggest that the delayed leaf drop is a means of preserving a nutrient source for spring or that the dried leaves serve as a defense for the young buds from deer browse or frost damage. Whatever the reason, both oak and beech trees are in the beech family, so there may be some evolutionary connection to occupying the realm between evergreen and deciduous tree strategies.

Along the path we ran across evidence of both brown rot and white rot fungi activity right next to each other. From the viewpoint of an amateur mycologist, this was an exciting find. Brown rot and white rot fungi have different capacities for degrading wood substrates, and leave behind either the chunky, brown, resistant lignin compounds (brown-rot fungi) or the white, stringy, soft, simple carbon compounds (white-rot fungi). These treasures reveal the various fungi functional guilds needed to process and decompose the woody debris that falls in the forest. For example, the well-known turkey tail is a white-rot fungi, which is why it’s being researched as a natural substitute for chemicals currently used to make paper. Aren’t they amazing organisms?!

We also investigated some lichen, being more obvious in the autumn woodland where trees are defoliated and ground layer forbs have mostly gone dormant. There are three main growth forms of lichen – foliose, fruticose and crustose. We were only able to find the flat, leafy, rosette-like foliose forms today, but I know the other forms are out there, waiting for appreciation.

Our last stop was in Longenecker Gardens to check on the native autumnal witch hazel tree (Hamamelis virginiana). Unfortunately it was getting a little too late to see the delicately splendid blooms as the slender, yellow petals had already fallen off. I did remind people to visit the vernal witch hazels in the collection during springtime.

Although we didn’t see much wildlife, it was a very nice day for a final fall foray in the woods before the cold north winds and snow set in on us.

Amy Jo Dusick