Election Section

Ash Trees Both Strong, Beautiful By RON SULLIVAN Special to the Planet

Tuesday June 21, 2005

Some ash trees are among the last to leaf out in Berkeley every spring—along with certain sycamores—and I’ve caught myself giving up on a few of the oldest specimens every year, supposing them dead at last. So many of our senior trees have been so grotesquely pruned for powerline clearance that I’ve become a bit of a pessimist about them.  

I can’t entirely blame utility crews. Part of the problem is that either trees that get too tall have been planted under utility wires, or utility wires have been strung over trees that get too tall. In most neighborhoods, I suppose the wires are of longer standing than the street trees.  

Another problem is bad pruning, and I think that is a result of bad pruning schedules—too many years between cuts. To compensate, tree workers cut heavily, and we end up with disproportionately spindly scaffold branches, sometimes with silly tufts of leafy twigs on the ends, sometimes with lots of watersprouts that make the whole thing too heavy to hold itself up. 

I didn’t intend to write another malpruning screed, but there is a connection, honest.  

Ash trees are lovely. They have handsome bark—pale gray in most of the ash species we see on city streets—and graceful, feathery compound leaves in encouraging shades of pale and bright green. They take a “vase-shaped” form, roughly a point-down triangle atop a straight trunk, that gives a street a sort of stately Gothic-arch bower as they get large enough for their branches to meet over it.  

Part of that vase shape, though, involves what tree folks call “narrow crotch angles.” Limbs join trunks at acute upward angles, making a “V” rather than a “U.” It looks pretty but increases the chance of a bark inclusion between the limb and trunk, or branch and limb. 

Look at the nearest tree. See that rumple of bark like a rough turtleneck where a limb emerges? If it’s rolled outward and kind of rough, like a keloid scar, that’s a good thing. As the limb grows thicker, the bark at the junction is being forced outward, where it’s harmless. If it’s rolled inward to make a neat little crease like the inside of your bent elbow, there might be trouble brewing. 

Bark that’s rolled inward can effectively dam the live flow of the tree, so what looks like a thickening branch is actually being cut off from nutrients at that upper edge, while the bark is growing into the wood. It replaces live tissue with dead “skin,” and leaves less wood to hold the limb up. That’s the kind of branch that’s most likely to rip off the trunk under stress from wind, weight (from outside forces or just from sudden fast water intake, which adds a surprising amount), or just gravity and time.  

What I find interesting is that ash trees don’t do as much of this self-pruning, in my experience, as sweetgums and acacias do. Maybe it’s just that the strong white wood they make is capable of holding itself up. Ash is what your classic Louisville Slugger baseball bat is made of, after all, and tool handles and other things that need to withstand hard knocks.  

You want strength? Yggdrasil, the World Tree of Norse mythology, is widely supposed to have been an ash. (And the first human man was made of ash; the first human woman, alder.)  

Mostly what you see planted around here are velvet ash, especially the ‘Modesto’ cultivar (Fraxinus velutina ‘Modesto’) and shamel ash (Fraxinus uhdei). Just to add to our instant California tour of names, “fresno” is the Spanish word for the shamel ash. That one is evergreen if it’s growing far enough to the south; it’s native to semitropical Mexico.  

There’s a potentially serious threat to our ash trees – it’s already devastating urban and rural ash groves in the Midwest. The emerald ash borer, a beetle imported accidentally in freight from Asia, has killed more than six million ash trees in Michigan, and is spreading in spite of quarantines. When you think about chestnut blight and Dutch elm disease and how they’ve changed our landscape, it’s a lot more scary than the prospect of the occasional falling limb.