Care for the future, care for the trees

This gash was left after a huge limb broke off a blue oak

 recently. (Photos: Kathy Morrison)

They are more vulnerable than we realize

By Kathy Morrison

It takes a long time for a mature tree to die. 

Yet we've all seen it, maybe without noticing the symptoms. The canopy grows sparse, or it starts dropping leaves and twigs at the wrong time of year, or there are holes all over the trunk. Years may go by before a windstorm blows it over. With the shade in that area now gone, the plants nearby are affected, and maybe the character of the site changes.

Trees are easily taken for granted.

I was reminded of this earlier in the week when I strolled over to our neighborhood park. I hadn't been in awhile, and I always enjoy seeing the changes that fall brings. Also, a flock of magpies lives there, and the birds are amusing to watch.

This park has been part of my landscape for nearly 25 years -- I've photographed most of the trees at one time or another -- so it was a bit of a shock to see a giant wound on my favorite blue oak. This tree stands probably 50 feet tall, just to the side of a small park building that formerly was a restroom and now is a utility room for the park district. A small muddy creek runs nearby about 10 feet away.

Here's what the full-size blue oak looked like in January 2018.

The tree had recently lost its leader, its largest vertical limb, probably in the windstorm that blew through Oct. 26. About half the canopy was gone. Chunks of the giant branch still were on the crushed roof of the utility building. Parks district workers clearly had a big job just removing the limb from where it fell-- more cross-sections littered the ground nearby. The rounds were so big -- roughly 24 inches across -- they could have been mistaken for parts of a tree trunk.

Blue oaks (Quercus douglasii) are tough native trees. In the book "Oaks of California" (Cachuma Press), the authors note, "Although other oaks are resistant to drought, few of them combine all the mechanisms of opportunism, conservation, tolerance and resiliency that are known in blue oak." The tree also is one of the "Shady Eighty," trees recommended by the Sacramento Tree Foundation. This particular specimen undoubtably was growing here long before the neighborhood was built in the 1960s.

So why did this giant lose such a big section at this time?

And here it is earlier this week.

The best clue is in those huge cross-sections of limb, and in the gash on the side of the tree. There were dime-size holes through the center (the pith and heartwood) of the rounds, and some of them were not fresh. The broken bit of branch still attached to the tree shows holes and rot.

This likely is evidence of borer insects, which years ago sensed a stressed tree and made this oak their home. Clearwing moths are among the insects whose larvae leave dime-size tunnels in trees, but it could have been another pest. SacTree notes of the blue oak: "Wood and root rots occur, borers and chewing insects can also be a problem."

Whatever caused the branch to weaken and break, this tree may not survive the injury. The remaining canopy, with the exception of one other smaller branch, still sported the tree's distinctive blue-green leaves. But since the tree stands next to a public walkway, it may pose too much of a liability to remain where it's grown for so many years. If it goes, I will miss it. Its fate also serves as an excellent reminder to care for our trees, before we're forced to notice them.

If you have questions about caring for any trees,  not just oaks, the Sacramento Tree Foundation is an excellent source of information: sactree.org