Created: 10/8/2012 Updated: 8/10/2016
The last, tremulous notes of the ice cream truck have faded into the distance. Sales of fun-sized candy bars are spiking. And all across this great nation, people are attaching their egos to teams of large, colorfully outfitted men battling over oblong balls. Yes, fall is here, and leaves are raining to the ground like opponents’ home runs onto the bleachers of Wrigley Field. But why? Why would otherwise perfectly reasonable trees decide to shamelessly expose their naked limbs? (In front of the saplings, no less!)
Thanks, guys. You know I'm gonna have to rake that, right?
Well, winter is hard on us all. For plants, the main problem is water, which, like most people, becomes sedentary and expands during cold weather. Sedentary water (by which I mean ice and snow) can’t be absorbed by a plant’s roots. So when the ground is frozen, water lost through its leaves can’t be replaced. Most plants in our area avoid the problem by stripping bare.
As for expansion, water is quite odd in that it becomes less dense when it freezes, so the same amount of water takes up more space when it becomes ice. This is a big deal for plants, since it causes their cells to quite literally explode as the water inside them swells. Try freezing a salad and you’ll know what I mean.
So instead of risking death by dehydration or cell destruction, a clever tree ditches its leaves for the winter. But, you say, ever the contrarian, what about evergreens? Well, your average pine or spruce has small leaves with thick 'skin' to slow water loss. And it's quite industrious, churning out resins and antifreeze compounds to prevent cell damage. Deciduous (leaf-losing) trees can't be bothered to spend as much energy on such nonsense. What antifreeze they do get around to manufacturing is concentrated in their buds in preparation for spring.
All this hard work gives evergreens a competitive advantage in early spring, when temperatures are warm enough for efficient photosynthesis. Deciduous trees can’t get moving until they stop hitting the snooze button and get to work cranking out leaves, while Joe Spruce is already soaking up the vernal sun and adding inches. The tables turn in summer, when the larger leaves of deciduous trees allow them to collect more light and grow faster than our work-a-day friend Mr. Spruce. These differing strategies are one reason evergreens dominate the landscape of northern latitudes. Short summers don’t allow those deciduous layabouts enough time to catch up.
Seth Harper - Museum HorticulturistView Comments
Created: 10/5/2012 Updated: 8/10/2016
It's been a wild year for butterflies in the Chicago area. Heat and drought seem to be the catchwords of the year. The season got off to an extraordinarily early start. It's not all that unusual to see a few butterflies in March, as species like Mourning Cloaks that hibernate as adults sometimes venture out on warm days. The prolonged hot spell in March brought a lot of species out, many over a month early. These Spring Azures were photographed at Bluff Spring Fen on St. Patrick's Day.
As the season settled in, the east central part of the US and Canada was overrun by an enormous population explosion of Red Admirals. In April the wave of Red Admiral migration crossed northern Illinois, with numbers about ten times their normal levels. As impressive as that was, the huge migration was even bigger in eastern Canada, where it was estimated that hundreds of millions of the butterflies were passing through.
Not surprisingly given the early and very warm season, 2012 saw the influx of several butterfly species that normally fly further to the south. Pipevine Swallowtails, Dainty Sulphurs (photo below), and Sachem skippers were all conspicuous in the Chicago area for much of the summer. These species are typically either rare or absent this far north. It will be interesting to compare data collected by the Illinois and Ohio butterfly monitoring networks to see if similar trends were observed in both of these states.
The news wasn't all good. The drought seems to have taken a toll on some of the region's rare butterflies- those species that require remnant prairies or wetlands. The Nature Museum's Butterfly Restoration Project made very little progress this year due to the very low numbers of these species that we encountered. Species that were present in very low numbers this summer included Silver-bordered Fritillaries, Baltimore Checkerspots (photo below), and Regal Fritillaries. With luck, conditions will be more favorable in 2013 and their numbers will rebound.