Over the weekend a friend and I checked out a stand of trees that burned back in May. It wasn’t a natural forest, rather a plantation of red pines, but forest fires aren’t nearly as common here around the Great Lakes as they are out west and it was interesting to see up-close what woods look like in the aftermath of a fire. Because this particular fire only burned for a few hours, the trees are still standing, but they are mostly dead and dying with blackened trunks.
In some spots a lush carpet of grass and ferns had sprung up, probably in response to the burst of nutrients the fire released.
Wood-boring beetles are slowly working on demolishing the standing dead trees, and we could literally see and hear the process. Sawdust slowly drifted through the air around us and settled at the bases of the trunks.
Most amazing of all, we could literally hear the sound of the beetles chewing and gnawing all around us. Listen!
At the edge of the stand of pines a fire break was created to keep the blaze contained, and the contrast between burned on one side and not-burned on the other was sharp.
Last spring I was in the woods with a group of kids and stopped to point out rows of small, neat holes that had been drilled into the trunk of a paper birch, standing out dark against the white bark. “That’s from a sapsucker,” I told them. We’d already looked at the gaping cavities the Pileated Woodpeckers had excavated in the nearby cedars, but now I explained how Yellow-bellied Sapsuckers, another woodpecker species, make small, shallow holes like this and ate the sap that seeps out, rather than tearing the wood apart in search of insects.
“So is their favorite tree the sugar maple?” asked one of the kids.
What a good question – and not one I knew the answer to. We talked a bit about what trade-offs sapsuckers would face when selecting a tree, like the sugar content of the sap versus the hardness of the wood, and then we moved on to something else. The idea stuck with me, though. Do sapsuckers have a favorite tree species? What factors affect which trees they make their sap wells in?
We currently seem to be experiencing a bumper crop of acorns – enough so that it’s noticeable even though oaks aren’t all that common here. The technical term for this is mast. We are having a mast year.
Oaks don’t produce large amounts of acorns every year (same goes for other nut trees). Instead, the trees in area will synchronize themselves so that, at irregular intervals, they all go acorn-crazy at the same time. The most popular theory as to why is that when all of the trees go all out at the same time, there are just so many nuts around that the squirrels and other nut-eating critters can’t eat them all even if they gorge themselves, so at least a few will get to germinate and grow. If one oak tree were to be a rebel and produce a lot of acorns in a year when the other trees were holding back, all the squirrels in the forest would descend on that one tree and it wouldn’t get to reproduce. (Squirrels aren’t the only animals that eat acorns, of course – earlier this summer one of the people I work with spotted a black bear way up in the highest branches of an oak tree, feasting on them.)
Of course, the real question here is how the heck are a bunch of trees spread across a forest communicating with each other and reaching a consensus on when to produce mast? And how are they balancing this cooperation with competition, natural selection favoring the trees that manage to reproduce more than their neighbors?
The simple answer seems to be that no one is really sure, but that doesn’t mean there aren’t a couple ideas. Plants can communicate with each other through chemical signals, messages like “look out everybody, there are lots of herbivores around.” A new study that’s gotten some media coverage even suggests that some communicate by producing clicking sounds in their roots that other plants can sense – plants don’t have ears, but maybe they can sense vibrations? So maybe our oaks are doing something like this, but they’re not in dense stands here like the maples and hemlocks are, they’re scattered in among the other more common trees. It’s questionable whether chemicals and clicks would really be effective at transmitting information across an entire forest.
There are other ideas too, like maybe trees are responding to some environmental cue and we just don’t know what it is, or maybe they need a certain number of years to store up energy before they flower and, since they need each other’s pollen to produce acorns, eventually they all either get on the same cycle or fail to pass on their genes.
In any case, tree mast is a really cool phenomenon, and if you know more about it than this feel free to jump in via the comments. Is it a mast year where you are?
This is a satellite photo of the area in Wisconsin where I live, courtesy of Google Maps. You can see why it’s called “Land O’ Lakes” (no relation to the butter, though we sometimes call the abandoned lumber mill on the edge of town “the butter factory” to confuse people). We also have a lot of bogs. These two facts are not unrelated.
These are kettle lakes that were formed by retreating glaciers 10,000 years ago. Many of them have Sphagnum moss growing around their edges. Sphagnum is amazingly absorbent, holding up to twenty times its dry weight in water, and the mats it forms eventually grow thick enough that they act as a substrate for a whole community of other plants we associate with bogs – leatherleaf, wild blueberry and cranberry, orchids, carnivorous plants like pitcher plant and sundew, and many more.
Slowly the lake fills with sediment, and the sphagnum eats away more and more at its edges, growing thicker and absorbing more water as it does. As the lower layers of spagnum die, they decompose very slowly due to anaerobic (oxygen-poor), acidic conditions, so that over time you get rich, moist deposits of peat. Below is an old lake on this property that’s been almost completely bog-ified, with only a small area of open water left in the middle.
Eventually the sphagnum and peat build up to the point where they can even support trees, mostly tamarack and black spruce.
This is all just one more example of the powerful process of ecological succession – one natural community transforming into another through time.
Never, ever take sugar maples for granted. Not only do they provide us with a sweet and tasty breakfast condiment, they perform a very cool function called hydraulic lift.
All plants take up water through their roots and evaporate it through their leaves. Sugar maples (along with some other plants) take it a step further. During the day, their roots draw water up from deep underground; at night, when water isn’t evaporating from the leaves, the excess is released into soil near the surface. Sugar maples essentially irrigate the soil around their bases. To read more about this phenomenon, check out this article from Cornell.
So if you like wildflowers, next time you see a sugar maple… tell it thank you.
Jack, who always leaves such lovely comments, asked about tamarack, and I took a couple photos of tamarack a while ago that have been sitting on my hard drive, so the topic of my next post is obvious.
Larix laricina, commonly known as tamarack, American larch, or hackmatack. (Gesundheit on that last one.) Where I am now in northern Wisconsin seems to be a sort of transition zone between the harsh boreal forests to the north and the more diverse forests to the south, with boreal species like tamarack, spruce and aspen found side-by-side with maple, oak, birch and basswood. Some species I was familiar with in Ohio, like sycamores, are missing entirely, and some, including most of the conifers, are new to me. Tamarack ranges north to the very limits of the tree line.
Its needles, which grow in tuft-like bunches, are incredibly soft to the touch. During a portage on my canoe trip over the weekend, I leaned back to let someone pass me on the trail, and when I felt something silky brush my arm I didn’t have to turn around to know the tree behind me was a tamarack. What’s even more interesting is that this is a deciduous conifer. These needles will turn gold in the autumn and then fall.
When old lakes fill in and turn into bogs, like the one above, moisture-loving tamaracks will be one of the pioneering tree species (along with spruce). Although I can’t rationally explain why, I have a lot of fondness for these slightly oddball trees. Come autumn I’ll have to take some photos to show you the color change.
Interesting though they are (see the downward-facing hairs, to keep insects from crawling out and escaping?), the pitchers aren’t the only carnivorous plant in our bog. To spot the other one, though, you’ll practically have to rub your nose against the sphagnum.
This is sundew, its odd, round leaves surrounded by sticky-tipped hairs. (The fact that the sticky glands look like water droplets gives the plant its name.) The secretions are sweet and tempting, but when an insect makes the mistake of landing here, it’s trapped and the leaf curls around it and digests it.
I’ve never witnessed this plant eat. Maybe sometime I’ll catch an insect to feed to it. It would have to be a very small insect, though.
Because I promise I have a normal-sized thumb, and as you can see, this is a very, very small plant.