An Inconsistent Spring

We have had a real roller coaster of a spring this year. Temperatures have jumped between the low twenties and the high seventies, and our April showers have changed into blinding snow storms right before our eyes. We have adjusted to these unpredictable changes by putting on (or taking off) sweaters, coats, hats and, of course, by complaining a lot. But how are the plants and animals of the Nature Trail dealing with this “unexpected” weather?

The first thing we have to remember is that this “unpredictable” weather is actually incredibly expected. Almost every year we get an early hint of warmth in March that quickly fades back into a period of cold and gray in April. Almost every year spring comes on early and then retreats back into winter complete with snow storms and freezing temperatures. So, the plants and animals that we have been seeing on the Nature Trail for the past six weeks must have some special adaptations to tolerate and survive these wildly fluctuating conditions.

Deborah and I saw the first mourning cloak butterfly over a month ago. These butterflies overwinter as adults in tree holes or in the tiny spaces under flaking tree bark. They emerge on the first sunny days of early spring and feed on the rising tree sap as it drips from scars in the bark (and even from fresh woodpecker holes in the tree trunks!). When temperatures fall, the mourning cloaks respond by seeking out new hideouts. They wedge themselves back into protected spaces and “sleep” their way to the next warm, sunny day.

Similarly, we have seen large, bumble bees flying noisily about on the Nature Trail. These first bees of the spring are young queens that were born at the end of last year’s bee-colony cycle. They mated when they left their birth colonies and then overwintered in tiny hibernacula in the soil. Stimulated by rising soil temperatures, these bees emerge and warm themselves both in the sun and via rapid contractions of their flight muscles. They gather nectar and pollen from the early spring wildflowers and eventually find a suitable site, often an abandoned rodent burrow, to start their own colony. In the meantime, if temperatures suddenly turn cold, they return to protected spaces (under leaves, in the soil, in tree holes, etc) and, like the mourning cloak, sleep away the cold days and nights. Not all of these queens find their new hibernacula quickly enough, though. These unlucky individuals die from the cold exposure. Their bodies can be found on sidewalks, parking lots, and roadways often in the middle of open expanses that have little in the way of shelter or refuge. A number of these “unlucky” bees, in fact, have been seen this year (L. Pollock, personal communication).

Several people have told me that the snow drops and crocuses around their houses not only sprouted but even started to bloom back in January! Many of these earliest sprouts survived being buried in the snow and withstood both buried and exposed weeks of cold temperatures. More recently the daffodils and tulips have also starting sprouting and blooming and have had to withstand many nights (and days) of sub-freezing conditions. One of the ways that these plants are able to withstand prolonged cold is the presence of ethylene glycol (“antifreeze”) and also rising levels of glucose (“sugar”) in their cells and tissue fluids. These chemicals help to keep both plant saps and cytoplasm from freezing and provide a degree of insurance against transient cold snaps. Very cold temperatures, though, can overwhelm this protective system and can result in the death of the plant.

An even more spectacularly cold- adapted plant than these domesticated flowers, though, is the skunk cabbage. Skunk cabbage can be found on the scattered wetlands along our Nature Trail stream. In late February the yellow-streaked, brownish-purple spathe of this plant pushes up through the covering layer of snow and ice. The spathe houses and protects the yellow flower structures of the central spadix. The ability of this plant to not only push its way up through frozen coverings but also thrive under the continuing wintery conditions of February and March (not to mention Aprils like this!) is greatly enhanced by its physiology. The skunk cabbage has a set of enzymes (called “alternative oxidative enzymes” (AOX)) that use atmospheric oxygen to rapidly breakdown stored root polysaccharides with the subsequent generation of heat. During the two weeks or so of spathe emergence and spadix flowering, a skunk cabbage plant will use as much oxygen as a comparably sized mammal in order to keep this heat generation system running. Further, the spadix is able to homeostatically control the activity of AOX through temperature monitoring and feedback systems and can, thus, keep its intra-spathe temperature up to 20 degrees C warmer than the surrounding environment and maintain it at a constant and optimal level for flower maturation and pollination. The skunk cabbage is, then, a “warm-blooded” plant!

There is more spring on the way!

See you at Clean-Up Day!

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