This is not an expert's "how-to," though I hope to transmit a few useful links and tips. It's just a "how-I-did."
Bert Wilson of Las Pilitas Nursery (laspilitas.com) says that they don't prune their oaks themselves; they get an expert. Well, I could certainly use the services of an expert, but I have a lot of small oaks, mostly coast live oaks, Quercus agrifolia, and scrub oaks (Quercus berberidifolia or Quercus dumosa (with indeterminate individuals that are hard to place in either camp), and I don't think I can afford the services of a good arborist to take care of them all.
Also I love pruning.
The trees of greatest concern are growing along the road. I picked this one to start with.
The foliage reaches down to a couple feet off the ground, creating a "fire ladder" that could allow a wildfire to spread into the crown of the tree. And it's on the dry chaparral-habitat slope below our home.
(Fun fact: the word chaparral comes from the Spanish name for scrub oak: chaparro.)
Here is the same tree from another angle:
The weather has been pretty dry lately. Usually in August and September it's very dry but this year has been cooler and foggier - and dry is what you want when pruning.
Damp wounds are more easily infected, and we are wounding the tree, unfortunately, when we prune. With oaks around here, we always worry about Sudden Oak Death Syndrome, caused by the pathogen Phytophthora ramorum, which thrives in moist conditions (as you can learn on the California Oak Mortality Task Force web site). Cases have been found in Santa Cruz county, but I don't know of any around here. I live in blissful ignorance, perhaps.
I also read on the Oak Tree Help page of laspilitas.com that it is important to leave the oak leaf litter in place, and to plant under oaks only plants that grow under oaks natively - because the oak is "obligately mycorrhizal" meaning that it depends on fungus (of various sorts) for its good health.
It's important to keep the area under the oaks as close to their natural state as possible, to keep a natural balance. Similarly, don't water California native oaks in summer. They need to be dry. And weed free. Weeds apparently (again this info is from laspilitas.com) harm the health of the oak considerably. Deviating from their natural habitat upsets the balance and makes it more easy for pathogens - "bad fungus" and such - to take hold.
Anyway, regarding this small oak, I had a pretty clear idea what to do: For fire safety remove up to but no more than the lower third of the tree. Also make sure its foliage wouldn't obstruct vehicles like the UPS truck. And I worry a bit about the tree being top heavy. Another little oak fell over last year in a storm.
I'm hardly an expert myself. I have read various pruning guides, attended two classes, and practiced on the ornamental fruit trees that were ruined long before I got my hands on them. But I think I'm getting a feel for pruning in general.
An excellent pruning guide is produced by the Forest Service Northeastern Area. It's very short and gets to the point.
- I know to cut at a node (where branch joins larger branch).
- I know not to cut into the branch collar, or to leave a stub.
- I know to cut to a stub before making the final cut, so you don't rip the bark when a limb or large branch falls down.
- I know that crossing and rubbing branches are bad.
- Also dead branches.
- Favor strong branches that come out at a generous angle (not narrowly attached to the tree by a very acute angle).
- Favor branches that enhance the overall structure of the tree, its balance.
- To trim a branch back, you cut it to just above a bud (a quarter inch or so for smaller branches) whose direction is desirable, usually out and up.
- Or cut it back to a smaller branch that is at least a third of the width of the one you're cutting.
- It's important to leave enough branches along the trunk and main limbs to "feed the trunk." Trimming up too far is called "lion tailing" and it can weaken the tree.
And I learned that even small trees require use of a ladder. We have a very sturdy and stable one. I can't get much use out of pruning saws on sticks, though I have one. I use big loppers for small branches and rough cuts, and a Japanese style pruning saw to make the final cuts.
I know to step back often and look at the tree from different angles.
Take short breaks and come back with a refreshed view.
But I did break the dead branch rule a bit. The interior of the oak is fairly thick with lichen covered dead twigs, and I was going to trim them off when I thought about fog drip, and the health of this tree. In our area fog drip is an important part of nature's irrigation system. We don't get as much as in the valleys below us, but we get some. I know redwoods rely on it. I think they require 150 gallons of water a day, of which a good percentage comes from fog drip. I believe the oaks make use of fog drip too (along with their lichens).
And interestingly I was just reading last night that salamanders actually live in rotten wood in trees, and that to be too tidy in this regard takes away their habitat.
A neighbor came by, out on a walk with his dog. That's what's nice about working along the road. We chatted, and he also advised against pruning further - because those branches are part of the beauty of the oak.
So I stopped. I can always take a little more off another day, but I can't stick it back on!