Saturday, September 1, 2012

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!).