ARBORETUM NEWS (NATURALISTSNOTES)

Grady Tract Oak Savanna and Greene Prairie

SUNDAY, JUNE 2, 2013

“Like a walk in the park.” That’s how some have described oak savannas. At the entrances to the Grady Tract are maps and posters describing the major restoration work being done aimed at restoring and replicating the oak savanna ecosystem. A few people in the group weren’t familiar at all with the term savanna, and the rest said they would pass at trying to come up with a definition. That is to be expected. Although approximately 75% of present day southern Wisconsin was oak savanna over 150 years ago, today there is almost none of that ecosystem left.

Similar to prairies, which were also common in this area before European settlement, today most savannas are remnants or restorations. However, it is difficult for remnants to survive on their own, because a major component in the creation and maintenance of savannas is virtually gone – fire. Set off by thunderstorms or by Native People – periodic fires would eliminate most trees and shrubs, allowing for grasses, wildflowers, and fire resistant/resilient trees like oaks, especially burr oak, that create and maintain the landscapes of savanna and prairie in this area. The prairie in the Grady Tract, we call Greene Prairie, is maintained in part by periodic burning. The oak savanna areas adjacent to the prairie are currently being encouraged through selective tree and shrub removal. Today, we could see the work the crews have done recently cutting large trees and using a monster mower, called a forestry mower, to go through and grind up the shrub layer and the smaller trees – leaving many of the oaks. The oak savanna will typically have a density of mostly oaks that will cast a 20 – 50% shadow when the trees are fully leaved out. Prairies typically range from no trees to less than a 20% tree cover. So, there will be more shade tolerant plants in the savanna, however there is much overlap in the plants of prairies and savannas in our area. We saw some of that today.

Although designed to attract bumblebees and other pollinators, wild blue lupine (Lupinus perennis) will surely catch your eye when it is in bloom. Rising above the interesting beds of two inch long leaflets that fan out in circular fashion, are 4-10 inch long stem-like structures called racemes that display 20 or more purplish blue and white pea-like flowers in all directions. Other than their distinctive and attractive shape and color, we noticed that they grew in patches – extending along the edges of the paths and into the savanna and prairie areas. Many plants, like some creeping Charlie we saw sneaking into the Grady Tract, can grow vegetatively – one plant sending out many stolons, shoots, or rhizomes. It is true that one lupine plant may grow several shoots (sometimes emerging a few feet away from the original), but this behavior of growing in extended patches is a result of the plants ability to throw their seeds around as the pods dry out, sprouting new plants next year. An individual plant may produce several hundred seeds and can pop them out anywhere from 3-16 feet away. As far as I know the champion seed thrower around here would be wild geranium (Geranium maculatum), which we saw in the shaded edges of the forested areas of the Grady Tract. They have leaves that fan out and form a carpet-like cover with small purple saucer shaped flowers rising above the leaves. The geranium tosses its seeds on average 10 feet away and can hit a spot of soil up to 30 feet away. Their throwing advantage comes from a pod that not only bursts when it is dry but also gets a catapult from a structure that curls up and helps whip out the seeds when they are dry.

Whether plants are sowing/throwing their seeds, winding around the forest floor and climbing trees – like the Virginia creeper we saw throughout the woods – plants respond to their environment – they move, adapt, and behave in a variety of ways. The more I learn about plants, the more I see them as competitive and enterprising creatures. Just because a plant can toss its seeds around, doesn’t mean it will get the upper hand on its territory. I found that lupine’s taproot was also classified as a proteiod root. What this means is that when the plant senses that there is not enough of a needed nutrient in the soil (mostly phosphorous in the case of lupine), it will start a chemical reaction that will lead to the growth of hairs or rootlets along the taproot and its branches. In some plants of the lupine genus this can lead to a fifteen-fold increase in root surface area and can lead up to a thirteen-fold boost in absorption of phosphorous.

Another interesting interaction that lupine and all members of the bean family have with the soil is that they “fix” atmospheric nitrogen into a usable form through bacteria that grow on their roots. This not only enriches the soil for plant’s own benefit, this nitrogen becomes available in the soil for other plants when the roots of the bean family plants die off. All types of natural areas and gardens and cropland can benefit by having a population of nitrogen fixing plants. Sprinkled throughout the prairie another member of the bean family, cream wild indigo (Baptisia leucophaea), was in bloom. It is a shrub-like plant with densely packed creamy light yellow to white pea-like flowers.

As we approached Greene Prairie we saw the cream wild indigo and could make out a few leaves of prairie plants that were familiar to some of us – but as we got out on the boardwalk and took a closer look, we were greeted with the first blooms of the great variety that we have to look forward to the rest of the summer and into fall. The other plants in bloom on the prairie were: the small flowers and grass-like leaves of yellow star-grass (Hypoxis hirsuta), the many shades of purple, pink and white of downy or prairie phlox (Phlox pilosa), the last pale purple flowers of Jacob’s ladder (Polemonium reptans) were going to seed, the interesting whorls of curved long yellow flowers of the short, stout wood betony (Pedicularis canadensis), and the tight spikes of white flowers of Seneca snakeroot (Polygala senega). It was also a treat to see a threatened species that blooms for a short time – small white lady’s-slipper (Cypripedium candidum). Two prairie plants that seem to be doing well this year are shooting stars (Dodecatheon meadia) and golden Alexanders (Zizia aurea). These plants are both growing heartily on my small prairie in my front yard, on Curtis Prairie, today on Greene Prairie, and on some other small prairie plantings I’ve seen around town. The shooting stars are loosing their petals and going to seed. As we headed out we took a last look at the three lady’s slipper plants and also saw a patch of sensitive ferns (Onoclea sensibilis), some smooth scouring rush or smooth horsetail (Equisetum laevigatum) and the bright yellow flowers of northern ragwort (Packera paupercula). We got a good look at two sandhill cranes foraging, and saw several tree swallows darting above us. Leading the way on the path along the prairie and up the West knoll were robins and Carolina grasshoppers skirting ahead of us. Heard but not seen in this area included: possibly a tree frog, some crickets, wild turkeys, and a common yellowthroat.

The lacy leaved yarrow (Achillea millefolium) was growing well along the disturbed and compacted paths around the side and on top of the knoll. We also saw large-flowered beard tongue (Penstemon grandiflorus) about to bloom, the leaves of common milkweed (Asclepias syriaca), smooth sumac (Rhus glabra), and the last flowering of field pussy toes (Antennaria neglecta) – all growing on the sandy edges of the knoll on the west and north sides. Into the shade and around some of the woody areas of the Grady Tract you can get a lesson in distinguishing the differences and identifying poison ivy, Virginia creeper, and sugar maple and boxelder saplings. Also on a blooming march in the wooded areas of the Grady Tract were patches of wild geranium, black raspberries, wild strawberry, and Virginia waterleaf (Hydrophyllum virginianum). Cardinals and chickadees were flitting about the woods, and we also saw one eastern towhee in the trees and a few song sparrows pulling on low growing plant leaves and foraging on the forest floor. Heard in the pine trees above, but not seen, was a Northern flicker.

One other interesting area we walked was the short path that loops around the top of the west knoll. A young lady (Libellula Lydia) or common whitetail, a dragonfly in the skimmer family, nervously zipped in front and then behind us, maintaining a claim to patches of warm sun she found on the path. As we walked in from the main path we saw some clumps of low growing sedges (Carex pensylvanica), and then the brilliant bright, yellow-orange flowering of the hoary puccoon (Lithospermum canescens). Along the path we also saw more patches of the enterprising lupine and cream wild indigo scattered throughout the knoll.

Paul Borowsky
Arboretum Naturalist

Located between Lake Wingra and the West Beltline Highway at 1207 Seminole Highway, the University of Wisconsin-Madison Arboretum features the restored prairies, forests and wetlands of pre-settlement Wisconsin. This 1,260-acre arboretum also houses flowering trees, shrubs and a world-famous lilac collection. Educational tours for groups and the general public, science and nature-based classes for all ages and abilities, and a wide variety of volunteer opportunities for groups, families and individuals are available.