Needle Ice

While hiking up to Summit Peak in the Porcupine Mountains this past weekend (not quite as impressive as it sounds; as I said at the time, “peak” is a relative term and we were in Michigan), we came across a patch of mud at the edge of the trail with some unusual ice crystals sprouting out of it.

The shape actually reminded us of string cheese, only smaller – delicate curlicues of ice growing out of the surface of the soil. I’d never seen anything like it before, but we found several more patches of them as we walked, all growing out of exposed mud.

It turns out this phenomenon is called “needle ice.” It only occurs when the air temperature is below freezing but the soil temperature isn’t – in other words, in the fall before the soil freezes for the winter. Liquid water in the soil is drawn up to the surface through capillary action and is extruded in columns through pores in the soil as it freezes. This is more or less what we’d guessed was happening.

And if you’re wondering, here’s what the view from Summit Peak, the highest point in Michigan’s Upper Peninsula, looked like this first weekend in November. That’s Lake Superior on the horizon, although it blends so seamlessly with the sky that it’s hard to tell. (Click to enlarge.)

Blowsy Seedheads

It seems like a lot of people are still posting photos of fall color and even butterflies. Here in the North Woods, the leaves are already mostly off the leaves, and we keep waking up in the morning to a dusting of snow that melts off by mid-day. The bogs are lovely, though. The golden color of the tamaracks peaks just as the maples, oaks, etc. have lost their leaves.

This morning I walked along the edge of one of the lakes and took photos of the seedheads of the various plants I found. I’m being a lazy naturalist and not identifying all of these (a couple of them I already know, but not all). I just like all the shapes and textures.

Stocked up on hot chocolate this weekend, dropping my wool coat off today for dry-cleaning – I’m ready for winter. How about you?

Putting the Lakes to Bed

As the days grow colder, the lakes are getting ready to turn over. This phenomenon, which happens every fall, is related to the unique chemistry of water.

In summer, the water in a lake is typically separated into two distinct zones, separated by a boundary called the thermocline. Near the surface, closer to air and sunlight, the water is relatively warm and oxygenated. Deeper, below the thermocline, it’s colder and contains less oxygen. Because of the different densities of water at different temperatures, these two zones don’t mix much – think of oil and water. If you’ve ever gone swimming in a lake you might have even felt where the water abruptly becomes colder at a certain depth.

I’m sure I could find a perfectly good public domain illustration of this online, but it’s so much more fun to make my own in MS Paint.

As winter approaches, the surface water cools along with the air. When it gets cold enough and dense enough, it sinks. The two distinct zones break up and all the water in the lake circulates and mixes freely. This is the “turnover.”

Ta-da!

Here’s what’s really cool. Almost any other liquid becomes denser and denser as it cools and gets densest of all as a solid. Water is densest at 4°C or 39°F, several degrees above its freezing point. This is why ice floats – and why lakes freeze from the surface down than from the bottom up. The water under the ice, freshly re-oxygenated from the fall turnover, remains at 4°C all winter long, allowing the fish and other aquatic live to survive until the spring thaw.

Yes, this lake is inhabited by goldfish. Stop judging me.

There’s nothing like walking over the frozen surface of a lake in the dead of winter and imagining all the sleeping life sealed beneath your feet. This morning we woke up to another dusting of snow… it won’t be long.

Fall Dragonflies

This is a meadowhawk – probably, according to the helpful folks at BugGuide, a Saffron-winged Meadowhawk, although all the dragonflies in this genus look the same to my eyes. (Apparently this one has “long pterostigma,” which is a word I had to look up. It’s that colored cell at the front of each wing.) These are everywhere along the edges of the lakes right now, and some of them are hard at work making more meadowhawks.

We’re supposed to get three inches of snow tonight. One of the advantages of keeping a blog is that I know exactly when the first significant snow was last year, because I posted photos of it – it was November 9. Much earlier this year!

Photos, a Reminder, and an Invitation

FIRST, a couple photos from my morning walk. It’s a cool, gray, misty day, and autumn is definitely here.

SECOND, a reminder that International Rock Flipping Day is Sunday. Participating is easy and fun, whether you have your own blog or not! Details here.

THIRD, a week from Sunday I’ll be leaving for a week-long backpacking trip in Porcupine Mountains Wilderness State Park. For work. Don’t you wish you had my job? Anyway, that obviously means I’ll be unplugged from the internet for an entire week, and I thought I’d see if anyone would be interested in writing a guest post for this blog to appear while I’m gone. The requirements would be pretty simple – write a little something (say, 200ish words? but very flexible) about the natural history of the area where you live or somewhere you’ve traveled to, and illustrate it with at least one photo you took yourself. If you have your own blog, I’ll gladly link back to it, but this is also an opportunity for anyone who doesn’t have their own blog but has a favorite photo or nature fact to share.

If you might be interested, get in touch with me sometime in the next couple days using the “Contact Me” link above. If I don’t get any takers I’ll either pre-schedule some posts of my own or just let the blog go dark for a week. Not a big deal either way, but I thought I’d throw the possibility out there!

Update – I’ve already had about four replies to this, which will be more than enough for a week. Thank you so much!

Frosted Gold

I snapped this photo on the morning of November 3. I was on my way to an environmental education conference in the central part of the state, and despite the fact it was well into mid-morning there was still a heavy cover of frost over everything, sparkling in the autumn sunlight as I drove south. Every time I passed a bog and saw the leatherleaf, spruces, and golden tamaracks frosted silver, I wished I could stop and take a photo. Finally I came to two realizations: first, I had packed my camera in my bag for the conference, and second, I was in no particular hurry and had time to stop if I wanted to. So at the next bog I passed I pulled over onto the shoulder and did my best to capture what I was seeing.

I’m entering the last three weeks of my first semester of grad school (hard to believe I’ll soon be a fourth done with my master’s degree – time flies). This means that all of my various final projects and assignments for my classes are all coming due at once, and when you add that to my assistantship duties my time available to spend wandering around outside looking for birds and taking photos dwindles to near zero. The fact that there’s a depressing lack of snow at the moment doesn’t help my motivation, either – when there’s snow on the ground this place looks like Narnia, but without it winter is just cold and dark and depressing. Still, I need to remember to take time out occasionally to ramble in the woods before I leave for nearly a month for the holiday break.

Hope everyone is taking care of themselves. I didn’t say it on Thanksgiving, but thank you to all of you who read this blog; the feedback and discussion you provides adds so much richness to my experiences as a naturalist and educator.

Why Do the Leaves Change Color?

There are things that you think you know until someone asks you to explain them and you suddenly realize you have no idea what you’re talking about. This happened to me recently when a student asked what causes the northern lights. “Well, they’re – they’re caused by – by the sun. And the Earth’s magnetic field. Interacting. Somehow.” While not inaccurate, this is a far from satisfying answer! So when I recently realized that I don’t really know why leaves change color in autumn (“It’s because… um… because the chlorophyll goes away!”), I thought I’d better find out.

Luckily for me, the U.S. Forest Service has a nice webpage devoted to answering this exact question. Turns out there are three different pigments that play a role in fall color.

  • Chlorophyll, which, as everyone knows, is green and is essential to the tree’s survival because it facilitates photosynthesis.
  • Carotenoids, the familiar yellow-orange pigments that produce the color of everything from carrots to cardinals.
  • Anthocyanins, water-soluble pigments found in cranberries, blueberries, etc. – apparently a deeper red-purple color.

In autumn, deciduous trees respond to the lengthening nights by halting their production of chlorophyll. As the chlorophyll is broken down, the colors of the carotenoids, which are present in chloroplasts year-round, become more visible. Trees then clog the “veins” that transport fluids and sugars in and out of the leaves, causing a build-up of excess sugar that can trigger the production of anthocyanins, which are not present year-round. (I suppose this might explain why, even on an individual sugar maple tree, some leaves are solid yellow while some are much more pink – differing amounts of anthocyanins?) Once these connecting tissues have been sealed off all it takes is a puff of wind to dislodge the leaf from the tree.

Of course, this is all the proximate cause of leaf color change and fall. What’s the ultimate cause, the reason why it’s adaptive in the first place? While stems, buds, etc. are hardy enough to withstand the harsh conditions of winter, delicate leaf tissue is not. Since there’s not much sunlight in winter to power photosynthesis anyway, energetically it makes more sense for trees to just ditch their existing leaves in the fall and grow new ones when milder conditions return in the spring.

I am not a plant physiologist, so it’s possible I’ve oversimplified this by quite a bit. Feel free to set me straight in the comments. (Hey Dr. Wolverton, you’re a plant physiologist, do you still read this…?)