During the break…

leaf

During the break…

…I’ve been hard at work on the moth proofs. I’m at 45 hours (and counting) spent bent over my drafting table, red pen in hand. Most of these hours have been spent in drawing in the arrows that I dearly hope all you good folks are going to make effective use of in identifying your unknown moths. Doing it forced me to really pause and think about what features I refer to when I recognize a species, how it is I know a species is what it is and not something similar. I’ve learned some interesting and, on occasion, surprising things about the identification of even the moths I’m already familiar with.

White Underwing

…I’ve been setting out my moth light most nights it’s warm and dry enough. Trying to lure in some interesting species so I can take their photos to include among the selection we’ll send to our book’s designer for use on the title pages. We sent them some already, but they turned out to mostly be the wrong orientation. A few nights ago I had some eight underwings come in, half of which were White Underwings like this guy.

leaves

…the leaves have been turning. In the past few years our autumn colour has peaked around Thanksgiving weekend, which here in Canada is the second weekend of October. Next weekend, this year.

fall trees

But it feels like our trees have already peaked. There were vibrant colours among our fields last week, which I’d appreciate when I took the dogs out for some exercise and so I could straighten my back for a brief period.

fall maple

I wonder if it’s because of how dry and sunny it’s been this year? There seem to be a whole lot more reds than there were the year before. The maples in our yard have turned fairly orange, but last year they seemed more yellow (though maybe it’s my imagination). Reds are controlled by light levels and temperatures (I explained the process in more detail in this post), with bright, cool days producing the most colour, so perhaps. The cool weather has definitely arrived, though we managed to hold off our first fireplace fire (the sole source of heating for our home) until October 1, which I thought was doing better than usual.

Milkweed snow

…the milkweed has peaked, too. We had a stretch of beautiful sunny days where all the pods seem to split and the fluffy seeds puffed out, waiting to catch the wind. I couldn’t resist kicking at the stalks as I passed, spreading the down in a snowy blanket across the grass.

Tiny Woolly Bear

…and the Woolly Bears have started trundling from the plants where they grew up to look for a spot to spend the winter. This has got to be the tiniest Woolly Bear I’ve ever encountered. I presume he’s very young, relative to most of the ones I find. I hope he finds someplace cozy

Two curious trees

Path of lightning strike

That is to say, two strange and interesting trees (I doubt the trees feel all that much curiosity, although we do suffer from something of a language barrier, so who’s to say, really; it’s probably a little presumptuous of us to think we know what they’re feeling). I spotted this first tree the same day I returned to the beetle-hole-turned-sapsucker-well grove over at the 100-acre woods; it was the subject of my pushed-luck photos, the ones I managed to take following the resurrection of my camera battery. I wouldn’t’ve been heartbroken had the battery returned to the dead and I’d been forced to return home without the photos, but I did stop and puzzle over what I was seeing for a few minutes.

What caught my eye, initially, was this ridge that seemed to run along the side of the trunk. It was about two inches wide and nearly the same high, sticking out from the trunk proper. It looked an awful lot like the thick trunk of an ancient climbing vine, a Virginia Creeper or grapevine (our Poison Ivy doesn’t climb here). It took close examination to convince me that it wasn’t external to the tree (or previously-external-but-now-being-grown-over). No, it actually appeared to be an old wound, now healed and thick with scar tissue. The fact that the ridge broke and jumped slightly sideways at eye-level confirmed that it wasn’t (or hadn’t been) a vine.

Intrigued and still puzzled, I circled the tree and followed the ridge as it rose up the length of the trunk – in a spiral, all the way up to where the branches started, thirty or forty feet from the ground. Any guesses?

Twisting path of lightning strike

I believe this is the scar left from a lightning strike many years ago. I wrote a whole post about how lighting works a few years ago (I initially wrote a couple, and then realized it had been longer than that; I’ve been blogging more than three years. Goodness.), after a tree behind my parents’ house had been hit and destroyed by a strike. Trees are often hit by lightning not just because they’re tall, but also because they’re wet – whether on the outside, from rain, or the inside, from sap – and therefore conduct electricity extremely well. The lightning, once it reaches the tree, takes the path of least resistance. Although this can sometimes be down inside the heart of the tree (as it was for the pine), usually with disastrous results, it can also (perhaps more often) be down the outside of the tree, either through the water that’s soaked the outer bark, or through the sapwood just under the bark.

While lightning traveling the outside of the tree will likely do little damage beyond superficial burns, if the electricity enters the tree it can be more problematic. Lightning is incredibly hot, even hotter than the surface of the sun (which means little to most of us, since none of us have been there to experience it firsthand, but does at least give you the understanding that lightning is really, really hot). It should come as no surprise that any liquid that comes in contact with lightning is instantly vapourized. When the lightning travels through the inside of the tree, through the sap, the sap is instantly vapourized, turned into a gas. Gas takes up more space than liquid – it’s all the same atoms, just spaced a whole lot farther apart (yes, you can have solid/frozen oxygen, if you can somehow get the temperature down to −362°F/−219°C) – so you can imagine what effect this has if the liquid had been in a confined space. Yup, that’s right: kaboom.

If the lightning travels through the outer sapwood, rather than down through the heart of the tree, the effect is the same, but less pronounced. The outer bark and probably the layers of sapwood (the phloem and xylem) will be stripped along the route the lightning takes, but the rest of the tree will remain intact. As the tree heals over the open wound, it will inevitably form a ridge of scar tissue, and that’s what I think I was seeing here.

Dead tree with twsting wood pattern

Why the spiral, though? Well, although we can’t often tell from the outside, under the thick outer bark the inner wood of the tree is sometimes slightly twisted. It’s easiest to see this on dead trees where the outer bark has all sloughed off over time. This is such a one that I found last fall, for instance. I’m not sure what caused the two wood colours, but it does help to make the twists and waves of the trunk pretty obvious. As you can see, the wood doesn’t necessarily grow straight. Some trees have a very pronounced spiral. (I do actually have photos – somewhere – of such a dead trunk, but don’t ask me to find them.)

So what I think happened, why I think the lightning traced a spiral route down the tree, is it was simply following the path of the bark. Pretty neat. The tree seems to be doing well these days, despite the incident.

Broken and healed limb, pine tree

This tree I’ve seen a few times. It’s also over at the 100-acre woods, but at the edge of one of the fields. I’ve walked by it a number of times, and when I photographed it a couple of days ago, it wasn’t the first time I’d noticed it. In fact, I think the first time I’d consciously taken note of it was during the winter; this year or last, I can’t remember. I do remember, however, thinking that the branch had been torn in one of our ice storms. Pines seem particularly susceptible to this sort of damage, because they have so many long needles which catch not only ice but snow, and because they’re a softwood, and their limbs aren’t quite as sturdy as, say, a maple or oak.

So I’d noticed it before and not thought too much of it, but when I walked by the other day I realized two things: first, the limb was still alive, and second, that it wasn’t even a recent, open wound. Looking more closely (below) it’s obvious that this happened quite some time ago. Not only is there no recent wound, there’s barely any evidence of a wound at all. Like the lightning-struck tree, the damage was minimal; the pine’s limb was still connected by enough tissue that it simply grew over and sealed the wound, and carried on.

I love seeing resiliency in nature.

Broken and healed limb, pine tree

Done in by a sapsucker

Sorry to keep you in suspense! Here’s the final photo:

Eastern Hemlock trunk with holes

It was a sapsucker after all.

Of course, you all knew that, didn’t you? If not by the photos/evidence, then simply by the title of yesterday’s post and which way it was clearly going. But still, I was surprised – and relieved, I have to admit – to discover this, some ways up one of the trees. An answer. Classic (to me) sapsucker sign: stacked, rectangular holes.

But that didn’t explain why five trees were absolutely peppered with little holes, as if someone had come out for shotgun practice there. I’ve seen some worked-over trees, but I’ve never seen sapsucker feeding sign like that. Could these be the favoured trees of a pair that nested in the little swampy bit just a couple dozen meters away? Since sapsuckers don’t winter here, and would be unlikely to remain in one spot long enough during migration to create such a multitude of holes, it would have to have been birds present during the summer months.

To try to find an answer, I pulled out the Birds of North America account for Yellow-bellied Sapsucker and began reading. It makes the note that pairs will usually return to the same breeding site as in previous years, and also indicates that the longevity record for a wild bird (these are usually inferred through the time between two captures of a banded bird, whose age was known when it was first banded) is approaching 7 years. So perhaps if the same pair came back to this site for four or five years, they’d have time enough to riddle a few trees.

Fresh sapsucker wells
Active sapsucker wells. I'd forgotten about these photos, which I took a few years ago, back in Toronto.

Something else I came across, though, which I found interesting, and which may also help to explain what I was seeing here: sapsuckers make two types of wells, one that penetrates to the xylem, and the other to the phloem.

Each ring of a tree ring has both xylem and phloem; the xylem is found closer to the center of the tree, while the phloem is found outward, closer to the bark. The xylem is a network of capillary tubes used primarily for the transport of water, and some nutrients, from the roots of the tree to its leaves. Movement of fluids upwards (against gravity) in this network is passive. Water molecules climb the sides of these tiny tubes through capillary action, drawn upward (usually) by transpiration (the tree “breathing”, losing water through its leaves), or sometimes pushed upward by excess water pressure in the root system.

The phloem, the outer layer, transports sugars and other nutrients throughout the plant, to wherever they need to go. Unlike the xylem, which is actual tubes, the phloem is composed of cells, which pass contents from one to another like a bucket brigade. The phloem is where the sap flows, and where the sugar content is highest. The reason that girdling will kill a tree is that with the phloem destroyed all the way around the trunk, the sugars have no way of making it down to the roots to keep the roots alive.

Consider the two systems as your arteries and veins, with the roots as the heart and the leaves as the lungs. The water starts in the roots (your heart) and is pumped up through the tree’s xylem (your arteries) to the leaves (your lungs). There it picks up sugars (oxygen, in this analogy) which it then carries back through the rest of the tree by the phloem (your veins) before returning to the roots to be cycled through again. Of course, this isn’t a perfect analogy because in our bodies the switchover between arteries and veins isn’t at the lungs as I’ve drawn here but at the tissues where the oxygen is dropped off. But you get the idea. Also, just as there remains a small amount of oxygen in the blood that the veins carry back to the heart and lungs, so too is there a little big of sugar in the water going back up from the roots in the xylem.

Yellow-bellied Sapsucker at well
We actually got to see a sapsucker visiting its wells. The one and only time I've observed this behaviour.

Back to the sapsuckers; the wells that they drill into the xylem are circular, usually in horizontal rows of 3 to 15 holes. Those bored into phloem, however, are typically rectangular and stacked vertically for as much as 20 cm (8 in). What I’m used to thinking of as “sapsucker holes” are their phloem wells.

I’m not entirely clear on why they bore two types, but I would guess it has to do with energetics. Although phloem sap contains >10% sucrose and xylem sap only 2-3% (according to the BNA), xylem sap, by virtue of its density/viscosity and its transport method, flows faster. Although the bird may not need to consume as much phloem sap to obtain the same energy, it would need a lot more wells because of the flow rates. (That said, the BNA indicates that sapsuckers will preferentially choose trees with higher sugar content over trees with lower sugar but higher sap flow. Perhaps in the summer, when they don’t want to be flying all over the territory, they settle for the faster-but-lower-sugar xylem sap flow.)

Incidentally, in the spring the tree has no leaves yet, and so the sugar movement is all unidirectional – from the storage location in the roots, up through the xylem to the branches so the tree can use it to start making new leaves. Maple syrup is made from xylem sap. As soon as the leaves start to bud out and begin photosynthesizing, and the phloem sap starts flowing, the taste of the collected sap changes (not for the better) and maple syrup season is over. [In the spirit of full disclosure, I deduced this paragraph from everything I’ve just learned about the two types of sap, except for the bit about maple syrup season ending at leaf out because the taste changes, which I already knew.]

What about why sapsuckers arrange the two types of wells differently? This, too, isn’t specifically stated in the BNA account but I have a guess. Because the xylem operates passively, putting a second well above the first does you no good – the sap would leak out at the first well it gets to and the well above wouldn’t function. So they put them side-by-side. They could also do this with the phloem wells, and you do sometimes see multiple stacks of phloem wells side-by-side. But (and here the BNA account does say) sugars tend to back up in the phloem above a wound/well where the transport cells have been damaged (remember, they’re headed down toward the roots, so they accumulate above the well), so when the first well starts to seal up, the sapsuckers drill their second well above it, where the sugars have become concentrated.

I feel I’ve learned a lesson here. (Ironic, because I’m usually pretty careful about double-checking my info, or using language such as “probably”, “might be”, or “I think” if I’m not thoroughly certain.) Hopefully you have, too, and without having had to eat your words! Still, I feel it was a worthwhile lesson, to have learned that cool stuff about sapsucker wells.

Jumping to conclusions

Eastern Hemlock trunks with holes
Part of the grove with the trees in question. The four trunks on the right were peppered with holes, while the two on the left had none.

A little over a year ago, in December of 2009, I was snowshoeing through our woods when I came across a small grove of trees with some peculiar sign on them (sign being the term used for evidence left behind by a living creature, whether vertebrate or invertebrate). Curious, I took several photos and then came home to puzzle it over. Then, feeling I’d reached a conclusion, I posted about it. Last winter I wrote:

My first thought was Yellow-bellied Sapsucker, which drill their sap-producing holes in straight lines. But they weren’t really sapsucker-ish enough. … These were in straight lines alright, but the holes were small, round, and packed together, the lines widely spaced, and man, were there a lot of them. This didn’t look like the work of sapsuckers. I’m fairly sure that these are exit holes of wood-boring beetles, and more specifically, I suspect the Hemlock Borer, Melanophila fulvoguttata. It seems to be a fairly widespread species, never widely abundant but reasonably common. As its name suggests, its primary host is Eastern Hemlock

I finished the post, posted it, and thought little more about it.

Eastern Hemlock trunk with holes (and dog)
A single trunk, showing the extent of the holes. From the thin twiggy branch that comes off the trunk to the left, near the top, all the way down to just above Raven's head... so thick with holes, I don't think there was anywhere where two vertical inches remained hole-free.

Then a couple of weeks ago I got a Flickrmail from someone who’d been trying to find photos of the emergence holes of Hemlock Borers. She wrote to say she kept being directed to my post and Flickr photos, but that she wasn’t entirely sure that I had them ID’d correctly – to her, the straight lines seemed more like the work of sapsuckers. So I went back to my post, had another look, and then wrote her back to politely disagree. I didn’t know what they actually were, perhaps, but I felt confident they weren’t the work of sapsuckers.

I explained my reasoning:

First was simply the tree species in question. I almost exclusively see sapsucker wells on thin-barked species such as birch or aspen. This isn’t to say that other species might not be used, but just that in my experience sapsuckers seem to have a preference for these trees. We have no shortage of either of these, or even of maples or other thin-barked hardwoods, so it seems odd that they would target the hemlocks. (Unless these are very old holes made when the tree was smaller?)

Second was the diameter of the trees. Again, my experience has been that sapsuckers tend to target smaller-diameter trees, usually no more than 6 to 8 inches DBH, though this doesn’t necessarily mean all sapsuckers will do this. But all of the trees showing this sign were at least a foot in diameter.

Third was the fact that there were SO many holes on each tree, and that every hemlock within this grove had such an excess but none of the surrounding trees showed any signs of damage. I’ve seen worked-over sapsucker trees before, but they typically have a favourite tree or two, not a whole grove of them, and the holes are concentrated in an area of a few or several feet, not as extensive as these were.

Fourth was the arrangement of the holes in the tree. When sapsuckers re-visit trees, they usually drill their new holes clustered near the old ones, like so:

Old sapsucker wells

I would consider it unusual for the lines to be so separated from each other.

(Also, sapsuckers typically drill rectangular holes, though I have seen some that are more circular so this isn’t as strong a clue.)

Eastern Hemlock trunk with holes
Many of the holes were in straight rows, like this.

At the end of the post, I’d closed with the comment that I was looking forward to the publication of Tracks & Sign of Insects by Charley Eiseman and Noah Charney. It wasn’t out yet at the time. But now it is, and I have a copy on my shelf! So before I hit send to fire off the email back to her, I thought I’d have a browse through to look for photos of borer holes or other possibilities.

Well, there wasn’t anything in there that looked right. Not giving up, though, I decided I’d go straight to the source, and contact Charley Eiseman himself. He’s helped me out with puzzling identifications in the past, and I thought he might be willing and able to shed some light on this strange sign. I said I’d get back to her once I got a reply from him.

Eastern Hemlock trunk with holes
But there were quite a lot of them that appeared pretty random, too.

He wrote back, expressing similar thoughts to the woman who’d contacted me initially, though he was very generous in offering some room for doubt at the end:

I don’t have experience with that species, but here are my thoughts: The holes in the third photo are what I think of as classic sapsucker holes. In certain tree species sapsuckers make vertical stacks of rectangular-ish holes, but in most cases (from what I’ve seen in New England–and Mark Elbroch agrees, in his “Bird Tracks & Sign” book, which I used as a model for my own book) they make neat horizontal rows of circular holes, just like that. I’ve watched sapsuckers visit these rows and sip from all the holes in a line, one at a time (in one case taking turns with a hummingbird, which was really neat to see). I also feel comfortable calling the holes in the last photo the work of sapsuckers, albeit slightly sloppier ones. The first photo I’m not sure about, but they seem to be similarly round holes, and the exit holes of a buprestid should be distinctly flattened. It also would be very unusual to see buprestids occurring in that density–I don’t think even an emerald ash borer infestation would look quite like that. I have seen holes like this in hemlocks that seemed to be beetle holes, but I’ve never figured out who makes them, although my first guess would be a scolytine bark beetle of some sort. I’ll let you know if I find anything out about them, and I hope you’ll do the same!

Eastern Hemlock trunk with holes
And all of them were old. Some of them were beginning to lose their shape.

Instead of clarifying the situation, Charley’s comments only served to muddy the water. I knew that they weren’t sapsucker holes, and he didn’t know what they were but didn’t think they were beetle holes, either. So I resolved that, next time I made it back to the woods, I’d return to the grove of trees and have another look.

Which I did, a couple of days ago. I ran off a whole bunch of photos, counted the trunks that had been affected, examined the holes, posed Raven for scale, looked at the trunks from the other side, checked out the neighbouring, unaffected trees, came back and puzzled over them some more.

And then!

And then my camera battery died, just as I went to take the photo of what I noticed that clinched the ID. What spectacular timing, I thought. I stood there and glared at it for a minute or so while I debated whether I should just post the topic with what I had, or defer writing about it until I could come back with a charged camera to get this last photo. Finally, in that hopeful way of someone who doesn’t like the options they’re presented with and wishes the thing would just work, dammit, I flipped the on switch again.

And it turned on!

So I took the photo quick, before it could change its mind. And then I took ten more, of another, unrelated subject, figuring I might as well press my luck since I was out there anyway. And it was still on when I finally turned for home. Not precisely sure what happened with the battery, but maybe it knew I needed a good interlude here to keep you all in suspense.

And you’ll have to stay that way till tomorrow! When I finished up this post it was ridiculously long, over 2600 words, so I thought I’d break it into two parts. (Even this part is still 1400 words!) So check back tomorrow for the answer. But it’s super cool and I promise will be worth it. (At least, I thought so.)

Marking the passage of time

Cross-section of tree trunk - 51 years old

My goodness, is it Saturday already? Where has the week gone? Apparently it’s been a busy week for me. Just a quick post today, too, as I’m headed out to my parents’ for the weekend.

When out hiking the 100-acre woods last week, I found this sawn tree. In any woods, trees fall with some regularity as they become old, diseased, or are taken down by weather phenomenon such as lightning or heavy snow or ice. I’m not sure why this one came down, though I think it was probably killed by insects, given that it didn’t look all that large. It’d come down across the trail, and I’d noticed it a few times over the last year of hiking the woods. Last week when I went by I noticed that the neighbour, who tends the trails in exchange for being able to ride his ATV there, had brought his chainsaw and cleared out some of the fallen logs.

I love to count tree rings, when I find stumps like this. You can’t do it on most natural stumps, of course, because they rarely break cleanly enough for you to see the individual layers. But a sawn log is easy to read. I snapped a photo and when I got home, counted the rings using Photoshop to keep track (otherwise I lose my place when I get halfway through).

This tree was 51 years old when it died. I think it came down in 2009, though it’s possible it had died sometime before that. That means that, at the latest, it started growing in 1958. I look at those rings, and try to think what each one represents, what was happening that year while the tree stood stolidly here, time flowing by. I can find the year I was born, halfway in.

I like how you can see the knots formed by the bases of branches. These would have grown when the tree was smaller, and as it continued to lay down wood each year, the bases of the branches would get overgrown and incorporated into the trunk of the tree.

tree growth rings

We can discern the individual rings of growth because wood grown at different times of the year tends to have a different colour. The highest rate of growth is during the spring and early summer. It’s lighter coloured and usually thicker in width than the stuff that’s grown later in the summer. By fall growth has nearly stopped as the tree prepares for winter dormancy.

The light-coloured part of the ring is called “early wood” or “spring wood”, to reflect the time of year it was grown, and the darker stuff is “late wood” or “summer wood”. The lighter colour is probably due to the more porous nature of spring wood compared to the denser material of the summer wood.

Variation in the width of the bands reflects growing conditions of that particular season. Years with good rainfall and temperatures will result in more wood growth, while especially dry years, or cold years, will cause stunted growth for the year. If you count back 8 or 9 years there’s a really broad band with thick growth of both spring wood and summer wood. My guess is that the summer was wetter than normal, allowing the tree to keep growing longer than it would normally. Just a few years later the weather had flipped, and thin rings suggest a particularly dry year.

Younger trees tend to put down more wood per season than older trees, too, which is why inner rings are often wider than outer ones (compare the width of the second and third decades in the top photo to the fifth decade). It could also be an indication of localized growing conditions – perhaps when it took root as a seedling the canopy was closed, but somewhere late in its first decade a neighbouring tree fell, opening up the canopy and letting in more light and rain. I’m sure a dendrologist (one who studies trees) would know better the life story of this individual, but I enjoy hypothesizing.