One of the last big burly oaks on campus

Species name: Quercus macrocarpa

Common name: bur oak (sometimes burr oak or even burl oak), mossycup oak

Location: Western University campus

Burr oak trees (that's how I spell it since that's how I was taught to spell it, but Bur oak is just as common a spelling) are native to the Carolinian forest of eastern North America, and are still present throughout much of their native range. Unlike most oak species, the burr oak does best in open areas like savannahs (depending on the area, they can sometimes be the only oak species in a traditional Oak Savannah habitat) and actually does rather poorly in forested areas. It is very shade-intolerant but grows very quickly, and these two characteristics have made it one of the most popular boulevard trees (or landscaping tree). The burr oak is also incredibly long-lived, with some individuals reaching ages of 350 years or more! That's one old tree!

Like most oak species, the burr oak is known for its masting. Masting is when a tree over-produces fruit in an attempt to overwhelm seed predators so that some of their offspring (fruits are the structures produced by plants to carry and protect their seeds, which are their babies) make it to the next generation. Burr oak seeds are some of the most prized nuts in the eyes of wildlife (like squirrels, deer, and in some places even bears), and they will selectively eat burr oak acorns over any other type of acorn. There are a few reasons why this occurs: first, the acorns are the largest of any oak species ("macrocarpa" means "big fruit"). Second, the acorn wall, or that tough shell you have to crack through to get to the yummy meat of the nut, is quite thin compared to other oak species so it's much easier to eat. Third, there are fewer tannis in the acorns of the burr oak, which make it much more palatable than other oak species. They are rumoured to even be choice edibles to humans, although I've never tried one. As long as you roast it a bit I could see them being at the very least edible, but tasty? I don't know if I'd go that far. I would make a terrible forager! When tree seeds are the most eaten food item of an animal species that has co-evolved with the tree, they tend to use really odd yearly cycles to over-produce fruits. These masting years, depending on the species, are every 7, 9, or 11 years. Our red oak in the front yard had a masting year a couple years ago. It sounded like it was raining acorns every time the wind lightly blew through the tree! It was incredible. The squirrels didn't know what to do with themselves :) To put it into perspective just how many burr oak acorns are eaten by wildlife, there are reports of certain trees in Tennessee and Kentucky in "bear country" near the Great Smokey Mountains having a 0% reproductive rate in some years (non-masting years, that is). When you set up video cameras to check out what's going on with these trees reproducing less than their neighbours, you catch bears climbing the trees and eating every single acorn they encounter. They'll even rip off branches or shake the trunk of the tree to get the ones higher than they can climb (bears are heavy, you know!), and then scramble down the tree to eat what dropped. Something tells me you don't want to come between a burr oak and a bear...

Unfortunately, the burr oak that I took a picture of and its nearest equally old neighbour are on their way out as far as tree lifetimes go. The third picture above shows where a branch broke off many, many years ago and a massive hole has formed in its place. I have no idea if the hole is occupied, but it's large enough to be an ideal place for a Great Horned Owl to build a nest. And those birds are huge! It would also be a good nesting place for a raccoon family, or the equivalent of a Hollywood mansion for a family of squirrels. The fourth picture shows where on that same tree the bark is starting to come off the tree. Unlike in my previous blog post about the butternut (which you can read HERE), this is not a direct result of a fungal infection. There is now likely a fungus that has exploited the tree's old age and exposed wood, but that bark fell off because the tree is just getting old and nearing the end of its natural life. The last picture shows where more bark is coming off the tree near the base, and you can see that it, at one point, was heavily infested with insects. Again, that's likely not what caused the bark to come off in the first place, but once the old rotting wood was exposed the insects took advantage. The tree is also likely hollow, because the old inner wood of trees is often decayed by fungi before the tree is completely dead; this is called heart rot. This also doesn't directly kill the tree, but rather creates a standing hollow tube. Doesn't take much of a wind storm to knock the tree down once the structural integrity is compromised. I personally have no idea how old this tree is (I might be "old" according to my students, but I'm not THAT old!), but I'm guessing upwards of 250 years. It will be a shame to see this tree come down in a storm, and I'm sure it's not that many more years before it does.

Aside from being some of the oldest trees that can be found around southern Ontario and the eastern half of the United States, burr oaks can also be some of the largest. They grow to be very, very tall trees but also grow to an enormous girth. It's hard to tell from the above pictures, but the burr oak I was taking pictures of is one of the largest trees on campus. To put it into perspective, I took a picture of the width of the tree at "breast height" (about 4 feet off the ground; this is traditionally a way to determine if a tree is ready for logging) with the arboretum label for size:

Still doesn't really look like much, but that arboretum label measures 2.5 by 5 inches (or about 6 x 14 centimetres). So if you figure out what the diameter of the tree is (by my rough estimation, 63 inches or 160 centimetres), that's...enormous. That would make it about 196 inches in circumference (or almost 5 meters!). You would need three people joining hands to comfortably circle the tree. That's bigger than enormous! There are two trees of this size that are burr oaks, and a couple hackberries (look for this species to be covered in my next blog), all in the same general location. Standing here looking at the trees, I often wonder what these trees have "seen". They would have survived the entire outwards growth of the city I live in, and would have been here long before London, Ontario actually became a city. I wonder who planted them? Or was this an acorn that sprouted there? If it was, where was the tree it came from? It would be long gone by now. Did anyone care for this tree when it was a wee seedling? If so, who were they? What did they do? Did the Kingsmill family, the ones that owned the property that Western University is built on for many generations before Western purchased all of the land in 1919, ever use this tree for a rope swing? When there were bears living in southwestern Ontario, did bears used to climb this tree to get the acorns? So many questions and no one left to ask...

When I helped Jane Bowles with an arboretum tour back in June, she said that the four trees in this small patch of campus were "some of" the largest, oldest trees on campus. I never thought to ask her where the biggest or the oldest trees were. I guess I'll have to go exploring to find them myself now (and learn a bit about how to determine the age of a really big tree depending on the species). Until then, I'll just have to be content with the geezer trees I know :)

The unfortunate case of the butternut tree

Species name: Juglans cinerea

Common name: butternut, white walnut

Location: UWO campus

The butternut is a rather unfortunate tree, and a great example of how "world connectedness" is sometimes a bad thing. The butternut is native to the Carolinian forest, but is now completely absent from North and South Carolina in the United States, and almost completely absent from Ontario in Canada (the two extremes in the natural range of this species). Towards the middle of the range of this species in Ohio, numbers are dwindling quickly. Why is the population of butternut decreasing, you ask? Well, the saying "when in doubt blame it on a fungus" certainly applies here. In fact, when in doubt blame it on two fungi is even more appropriate.

Before we go blaming things on fungi, let's talk a bit about the butternut tree itself. It looks incredibly similar to the black walnut (which you can read all about HERE), but differs in two major ways. The first way that a butternut differs from a black walnut is in the shape of the leaves. Both butternuts and black walnuts have numerous leaflets in their compound leaf (and this number often depends on maturity of the leaf which determines the length of the petiole or the "leaf branch", rather than genetics determining number of leaflets in a compound leaf), but the butternut leaf ends in a terminal leaflet where the black walnut leaf ends in a terminal pair of leaflets. Unfortunately, the wind can shear off the terminal leaflet (pictured in the second image near the pink arrow) so the leaves end up looking identical. So when using leaves to identify species, make sure you look at more than just one! The second way to tell them apart can be seen in the third image above, but admittedly this is a terrible picture of the fruit (the pink arrow points to the fruit in the third image). On this entire tree there was only one single fruit produced this year, so I didn't have much to work with for angles to photograph. But in a nut shell (pun intended), the fruit (or nut) of the black walnut is spherical, but the fruit (or nut) of a butternut is shaped like a football. This can even be distinguished by looking at the shell casings on the ground, so take a poke around the base of the tree if you're trying to identify a butternut or black walnut. Like the black walnut, the meat on the inside of the nut is completely edible, and apparently tastes wonderful when roasted slightly in the oven or pan-fried a bit (I haven't ever had the pleasure of eating a butternut, so I don't speak from experience on this one; see below for why I DON'T recommend eating butternuts).

I guess there's no time like the presence to talk about an evil fungus. The steady decline of butternuts isn't just due to habitat loss (and there is quite a bit of that happening in the Carolinian deciduous forest in Eastern North America!). It's actually because of a disease called Butternut Canker, which is caused by a fungus. :( I know, sad face. But, of course, that's a boring story so I wouldn't just tell you about a single fungus. Recent evidence shows that it's not just one fungus that's responsible for the butternut canker disease, it's actually two. The first one comes in and attacks the tree, causing a localized disease that, theoretically, the tree should be able to overcome. Unfortunately, this causes open wounds in the bark of the tree, exposing the underlying wood and the juicy vascular tissue. This vascular tissue is critical for the survival of the tree, and is the only living part out of all of the wood in the trunk in the tree. Because it is located just under the bark, this is one of the reasons why cracking bark is a critical step in so many fungal infections (sometimes even insect infections or bacterial infections) of trees. Once this vascular tissue has been exposed, the second fungus comes in and completely kills the tree. It will start off being one or two limbs of the tree near the crown (a fancy word for the top), and once the branch loses all of its leaves it won't grow them back the next year. Even pruning these dead branches won't save the tree; once limb death starts it's only a matter of time before the rest of the tree is killed. Because it's a combination of two different fungi that cause the death of the tree, it is exceedingly difficult to come up with a solution to prevent infection. The first fungus that attacks the tree (it has a ridiculously long name: Sirococcus clavigignenti-juglandacearum) is carried by potentially hundreds of different vectors, from the wind to other plant species to insects, and nearly all of these are impossible to prevent from coming in contact with the tree. You might think that lone trees would be most susceptible to this disease, but actually that's not the case. The canopy of the forest traps a lot of pathogens in the circulating air within the forest, so it actually increases the incidence of butternut canker. Lone trees often survive much longer without the disease. This fungus, an invasive fungus introduced from Asia, has managed to infect nearly 90% of all butternut trees left in existence. It won't be long before this species goes extinct, as there is no way of preventing the disease. It's an incredibly unfortunate set of circumstances for butternut trees, and for the Carolinian forest in general. We're about to lose one of the most majestic trees in the deciduous forest of eastern North America. Because this species is so critically endangered, do the world a favour: if you happen to find an intact butternut fruit, don't eat it! Instead, hold it in your hands, do a little "rain and good health to butternuts" dance, and lovingly plant it in the ground. Cover it with some chicken wire (I recommend making a box, and burying it at least 4 inches into the ground over where you planted the seed), and hope for the best. These are one of the preferred food sources for deer and squirrels, so not many seeds manage to escape being eaten (especially considering how few are left). I'm not going to suggest you take a seed home and try to grow it in a pot; that would be illegal in Canada according to our Species At Risk Act (SARA). Even if you plant the seedling back exactly where you found the nut, it would still be against Canadian endangered species laws, and much the same regulations exist in the United States. You might ask who enforces these laws and how common these people are in butternut territory...

Instead of ending on a sour note, let's end on a happy note! There is currently an effort underway in both Canada and the United States to try to protect the butternut in some way from disease. The method developed currently will not save the trees that are dying, but will instead protect the new generation of butternut trees. When butternuts are hybridized with the Asian walnut, the tree has almost complete resistance to the butternut canker. This is great, but unfortunately it dilutes the genetic pool of butternuts with Asian walnut genes. To try to combat this (since hybrids don't actually have any status according to any endangered species act anywhere in the world), hybridizing this hybrid with a different butternut tree causes the tree to have characteristics that are nearly identical to the butternut, but still have the disease resistance of the Asian walnut. This process is known as "back-crossing," and is commonly done with agricultural plant species to introduce disease resistance. This still doesn't make a "true butternut," but the resulting tree is nearly identical to a genetically pure butternut. There might come a day when we have forests containing this "butternut" (technically called a "Butter-Buart" which to me just sounds strange) in abundance once again. I wonder if anyone has tested the edibility of the butternuts of this backcrossed hybrid to determine tastiness... :)

The blackest of the walnuts

Species name: Juglans nigra

Common name: Black walnut

Location: Ontario

This tree was once incredibly rare in Canada, but now is starting to bounce back in population numbers due to the planting of ornamental specimens. The black walnut is native to the Carolinian Forest, which extends from the Carolinas northward to southwestern Ontario. The black walnut is now relatively common in British Columbia for its attractiveness as an ornamental species, but also its value as a lumber tree.

Black walnut has been used for centuries as one of the most valuable lumber trees in North America. Since these trees have one main trunk (unlike many oak species which tend to fork after about 40 or 50 years) that is usually incredibly straight, they make very long boards suitable for furniture building. At one time, walnut was even used as a siding for houses and as material to build decks. Not a smart use since it isn't as resistant to decay like a gymnosperm wood would be (like pine or cedar), and incredibly expensive! Since the grain and colour of the wood is so attractive, the wood is so easily worked, and the wood is not very likely to bend or warp when used indoors, the prices for black walnut wood soared in the late 1800s and early 1900s. Getting a piece of furniture made of solid walnut is rare today, and would cost thousands of dollars. It is much more common to have furniture made out of a wood like oak (or, worse yet, particleboard or plywood) and either veneered or stained to look like walnut. Sometimes, too, only the exterior parts of a piece of furniture will be made out of walnut, and all of the "guts" of the piece, the parts you can't see, will be made out of a much cheaper wood.

The black walnut is a great example of a tree with a compound leaf. It is by far not the most impressive example, either in Canada or around the world, but it has a very distinctive leaf that is easily identified. If you look at the third picture down, you can see where the petiole of the leaf (the green "leaf stalk" onto which all of the leaflets are attached) is swollen at the base and wraps almost all the way around the branch that it's attached to. There is a very similar and closely related species of tree in Canada, the butternut (also called the white walnut) that has one major characteristic of the leaves that is different from the black walnut. If you look at the end of the leaf, you'll notice that there's no terminal leaflet in the black walnut (sometimes there is, but it is never the same size as the rest of the leaflets). The butternut always has a terminal leaflet, and it's always at least the same size (sometimes bigger) as the rest of the leaflets.

Yes, the walnuts you buy at the store are the fruit of this tree! The best way to harvest them is to pull them off the tree when the fruit is still green and unripe since that's when the flesh on the inside tastes best. The green outer husk is incredibly difficult to remove (just sit and listen to a squirrel trying to get inside a walnut!), and the best and easiest way is to run over the fruit with an SUV. I'm not kidding! Line them up on the driveway or in a parking lot, and give it a go! Once the outer husk is removed, the nut on the inside (with the hard shell that's sold in grocery stores as "in-shell walnuts") will start to look familiar. Take a nut-craker, crack open the outer shell and enjoy! They don't need to be roasted in the oven first, but some people enjoy them more that way. Unfortunately, what's sold most often in grocery stores is the Persian walnut which is much easier to harvest (and probably accounts for its higher popularity). This is causing more and more Persian walnut trees to be planted in favour of the native species, which is always a downside of agriculture! A word of caution: if you're going to harvest your own black walnut nuts, make sure you wear gloves! Anyone who has seen the remnants of squirrels gnawing their way through a walnut on the sidewalk knows just how potent the dye from the husk, made up of juglone, plumbagin and tannins, can be! It will permanently dye your hands for weeks, and was actually often used as a permanent hair dye (and sometimes still is in "natural beauty products").

One downside of having black walnut in your yard is the fact that walnuts produce juglone in all of their tissues, including the roots. This chemical prevents the growth of most species of plants (and is incredibly toxic to some animals), so under most black walnut trees is a "dead zone" where nothing grows. This chemical is so potent that even black walnut seedlings, who can produce the chemical themselves, are sensitive to it and will die! This phenomenon is referred to as allelopathy, and one of the species I've already talked about, Norway Maple, is another good example of an allelopathic plant. Another good reason to wear gloves when harvesting walnuts is that some people are sensitive to juglone on their skin and it can cause an itchy rash (but the rash doesn't last as long as the dye on your hands does!).