April 3 was the only sunny and warm day within a stretch of many cold/windy/rainy/snowy days, so it was not too surprising that about 70 of us gathered for the walk. Barely out the back door of the Visitor Center and into the native garden, we were greeted by a bald eagle soaring in circles far above. The theme of Sunday’s tour was Transitions. And although it may seem that we are just barely transitioning into spring time weather, a number of native trees and plants have already completed their flowering—a transition out of one stage, but of course into the next. For example, our native hazelnuts’ magenta-colored female flowers are already dried and brown. This plant, visible in the native plant garden as well as in restored areas, has already completed its annual flowering and fertilization processes. It has transitioned from fertilization to fruit development. In the native garden, under the sugar maples, hepatica was in full bloom. Toothwort greens and buds are visible throughout the Arb and we noticed one flower already open. Virginia bluebell greens are up, no buds evident as of Sunday. With such a large group we likely flushed most birds and other animals, but a birder-visitor was quick to recognize the call of a tufted titmouse as we crossed Arboretum Drive from Gallistel into Wingra woods.
We noticed a number of sugar maples in Wingra Woods with wet bark, drenched in sap. On one tree, the source of the sap leakage was low enough to see: a small hole made from a woodpecker—likely a small woodpecker commonly called a sapsucker. We spotted a mourning cloak butterfly on one wet sugar maple trunk, drinking the sap. These butterflies overwinter as adults, and tree sap is a main component of their springtime diet. Tree “sap” is, more specifically, the xylem. Xylem is primarily water and dissolved minerals, taken up from soil, but also contains some sugars that had been stored within the tree—hence the sweetness of maple sap. (Of course, sap is boiled down extensively to concentrate the sweetness into a syrup.) The number and extent of sap-drenched maple trunks was greater than I remember ever noticing before. I had some questions about this observation and I appreciated input about it from Brad Herrick (Arb ecologist), Molly Fifield Murray (Arb outreach programs manager), and David Stevens (Longenecker Horticultural Gardens curator). Based on everyone’s comments, it sounds to me like our Sunday observations were nothing out-of-the-ordinary—I guess I’ve just never had quite that exact timing to see so many trees sap-drenched at once. David said that sugar maples (and a few others that tend to leak sap, including birch and walnut) are known as “bleeders.” I hadn’t heard that moniker before but it fits! With the end of freezing nighttime temperatures and the soon-to-be leafing out of trees, the sap will soon stop running—another transition.
We checked in on the skunk cabbage, which are toward the end of their flowering. With the flecked purplish spathe open, the flowers on the spadix within are visible. Some yellow pollen still remains but many plants show browner tones on the spadix, indicating that stages of active reproduction are nearing their end . . . more transitions.
Happy spring . . . transitions!