Wingra Oak SavannaSUNDAY, AUGUST 5, 2012
Enter from either parking lot off Nakoma Road (Spring Trail Lot) or Monroe Street (Arbor Drive Lot) and venture into a patch of plant and animal life drawn to this little oasis of wetlands, ponds and forest/savanna tucked in between the busy city life on Monroe Street and Lake Wingra. From thousands of years ago through the present day, this land on the northwest corner of Lake Wingra has also been bustling with human activity. The present day southwest commuter bike path was the path taken by the freight cars of the Illinois Central Railway four generations ago. Upwards of a thousand freight cars a day would come and return to the Chicago area. A staple commodity throughout the winter was 400-pound blocks of ice cut from Lake Wingra. One of my father’s earliest childhood memories of life in Chicago was the ice man coming up the steps with the block of ice to place in their icebox. However, the massive ice cube coming up the steps to my father’s apartment was not from here. The Lake Wingra operation shut down the year he was born in 1937.
Thirty four percent of the water feeding Lake Wingra comes from surface water, mostly rain and ice and snow melt. If you drive east down Odana Road towards Lake Wingra you can feel and see the slope. All this surface flow sends dissolved fertilizer from our lawns, salt from the roads, and all kinds of debris and nutrients sheeting into Lake Wingra. This has prompted the Arboretum and several industrious and active neighborhood groups into action – educating business owners and residents about retaining water on their properties. Rain gardens, settling ponds and buffer zones, like the Wingra Oak Savanna slow down and filter the water into the ground in efforts to decrease some of this surface flow into the lake. Other threats to lake quality include invasive plant species, like Eurasian water-milfoil, and a large, aggressive population of carp brought from Europe.
Under pressure from European immigrants who enjoyed eating carp in their home countries, the U.S. Commission of Fish and Fisheries began an intensive effort of European carp importation and cultivation in 1877. Carp were introduced into lakes all over the United States. They are highly tolerant of pollution, reproduce in great numbers, and foul up the waters and reduce sunlight filtration as they are feeding and filtering out muck from the lake bottom. By the early and mid-1900’s ecologists realized that carp introduction was a mistake, and eradication programs are in place on many lakes, including Lake Wingra.
The Friends of Lake Wingra produced a brochure, Lake Wingra: a vision for the future, that details the issues and goals towards a healthier watershed that their organization and other interested parties are working on. Real progress is being made on most of these goals. One of the goals is to increase spring flow. Unlike the Lake Mendota, Lake Monona, and the lakes down the chain that are fed through waters flowing down the Yahara River and flowing from lake to lake – Lake Wingra is not fed by a river system or from another lake. About equal in percentage to the 34% surface water that feeds Lake Wingra, 35% of it’s input comes from underground seepage and springs. You can see two of these springs on a walk through the Wingra Oak Savanna. In case you are wondering, the remaining amount of input, 31%, is from direct precipitation.
The spring waters do have higher than desirable levels of nitrate, but they do not have the phosphorous, chloride, and other chemicals that our surface water has. So, the plan is to decrease the amounts of water sheeting into the lake and increase the amount that will re-charge the springs and seep in through the surrounding land.
Since 1992, there has been a plan and steady work in place to restore and maintain the edge of this area adjacent to Monroe Street as an Oak Savanna. The savanna is an environment with a dominant tree species of oak and tree cover that provides typically more than 20% shade, but not more than 50% shade. With less than 20% shade in our area, the system tends toward grassland that has been created and will be maintained that way by fairly frequent fires and/or grazing. More than 50% shade is categorized as forest habitat and there are less grasses and different species of forbs or showy flowering plants, usually spring ephemerals. So, the oak savanna is its own unique ecosystem. To me, it is very attractive, and well adapted and functional in our area. And also a valuable legacy to keep alive – because it was the dominant ecosystem in this area of southern Wisconsin prior to farming and the ecosystem pressures and inputs of immigrant settlement and urbanization that took hold in the 1830’s through the 1850’s. And these pressures are ongoing through to the present day challenges.
After 20 years of work, the oaks are favored and doing well along with a variety of black walnuts, black cherries, hackberries, and some silver maple trees. The savanna is also supportive of an interesting mixture of understory plants. We saw glade mallow (Napaea dioica), joe pye-weed (Eutrochium maculatum), and high bush cranberry (Viburnum trilobum). Because many spots are fairly sunny in the savanna, similar to the prairie, we saw a number of plants that are also common to the prairie: boneset (Eupatorium perfoliatum), yellow coneflower (Ratibida pinnata), pale Indian plantain (Arnoglossum atriplicifolium), grey dogwood (Cornus racemosa), and a variety of goldenrods (Solidago).
Much of the paths in this area are raised boardwalks, because this narrow strip of land transitions from oak savanna to wetlands and ponds before it flows into the lake. In the shade at the edges of the pond and in the shallow backwaters, we could see small fish swimming. And, we weren’t the only ones attracted to gazing into the water. Before we started the tour, I walked out a short way onto the boardwalk and as I turned the corner I heard a deep loud, crackling croak and the slow deliberate flutter and lift off of a large bird with a wingspan of what looked to me like the maximum for this bird, which is a bit over six feet. This great blue heron (Ardea herodias) had been stalking lunch from a stand on top of a dead branch that fell out into the pond. A full-grown great blue can be over four feet tall and can weigh almost eight pounds. The croak startled me and sent me back on my feet. Was that what he or she (hard for us humans to tell the difference) meant to do? The croak did alert me to where it was – however by then it was too late (for photo capture or any other type of capture). As far as non-terrestrial threats, there are no flying creatures that are larger enough to be predators of great blue herons. Since, the herons hunt alone – an alarm call would not benefit any mate or chicks hunting with this bird. Whatever the evolution of this startle or alarm call, it seems like it still could have some present-day advantage of delaying/startling a predator. Alarm calls have been on my mind, as on my last walk to the Grady Tract I had to wonder what the purpose was for the alarm call of the chipmunks. They forage alone. However, they may have a neighbor (who may or may not be related) nearby. So, the alarm function to alert a nearby chipmunk. In my backyard (and others who have infestations) this alarm call is counterproductive for them, as it may ultimately lead to their demise by the neighborhood cats and dogs, or to capture and relocation by we humans.
I frequently hear a higher pitched croak, far less big, deep and archaic than the croak of the great blue heron – given by the little green heron. Which I would have appreciated today – but was denied. As I turned a corner ahead of the group, I spotted a little green heron fishing. It also spotted me about 150 yards away, but didn’t make the alarm or startle call that I have come to expect. It just flew up into a tree where none of the rest of the group could see it. I feel I did make a believable case for its presence – though that is never as interesting as the communal sighting experience.
We did have a communal experience before we ended the walk. A few days before this walk, my friend and fellow naturalist who is very familiar with this area, Kathy Miner, showed me the lay of the land and gave me a good history lesson (with supporting documents). If you’re interested in more history go on her walk next year and/or see if you can get a copy of the pamphlet, Dudgeon Monroe Past and Present, published in 1998. Kathy and I spotted a plant growing along the edge of what was a larger area of prairie plants that looked like wild lettuce. Sure enough it was. More specifically – blue or woodland lettuce (Lactuca floridana).
Other notable edibles that caught our eyes where white water lilies on the pond, and ripe blackberries, elderberries, and mulberries along the edges of the sidewalk – and a puffball mushroom – bigger than a softball, smaller than a soccer ball – also edible – tucked under a few trees 20 yards or so in from the sidewalk. If you are on Monroe Street, take a little detour – you won’t be disappointed.