A tree talk with master
Story by Carolyn Males
On a sunny morning, master arborist Michael Murphy and I meet up for some tree talk beneath the live oaks in Whitehall Park on Lady’s Island. Here at the edge of the salt marsh, we position ourselves in front of a stand of live oaks dominated by the park’s Mother Tree, a taller, broader and leafier specimen. I soon will learn that there’s a lot of root movement and “conversations” between the Mother Tree and her arboreal neighbors going on in the soil beneath our feet; conversations that involve life and death. It makes me want to put an ear to the ground. But the bird calls echoing over the Beaufort River are preempting this, not to mention there’s my dignity to consider.
Plus, the above-ground conversation is compelling, and Murphy has made me an intriguing promise. “You’ll soon know more about live oaks than most horticulturists who actively prune trees.” For an hour or so he tutors me here. Then we drive over to a wooded bluff on Battery Creek to see Beaufort County’s oldest and largest documented tree, the Cherry Hill Plantation Live Oak, whose massive trunk rises up from a thicket of yaupons and wildflowers. At its foot lies the grave of Mary Pope, an enslaved young woman who once sat and read beneath its canopy. It turns out that the tree, which won the 2013 South Carolina Heritage Tree Award, measures 113.75 inches in diameter, slightly wider than its more celebrated cousin, Charleston’s Angel Oak. Furthermore, we’re only viewing part of the original tree, Hurricane Gracie having split away its other half in 1959. Both places turn out to be the perfect spots to contemplate these iconic beauties.
[Q] What is a Mother Tree and why is it important? [Michael Murphy] It’s a term used in forestry for a giant tree with a bunch of younger trees of that same species around it. What they’ve discovered is that these live oaks have huge root systems that talk to each other. The roots graft and interlock and they can tell when another tree is sick or dying. The mycorrhizae, beneficial fungi that grow off of them, absorb nutrients and moisture in the soil and transfer them to the other trees.
People used to think the root system went to the drip line, but it goes at least double that length. In undisturbed soil, the roots grow many times faster than the limbs. A leaf just has to sit out there and catch the sun, while roots have to mine the soil for nutrients they need. These feeder roots are dynamic so the new ones grow and grow. Then they die and new ones grow and then they die. It just keeps going on forever.
[Q] You mentioned that there’s a new and better way to prune live oaks to make them safer and stronger, especially in hurricanes. [MM] We used to think thinning out live oaks would make them “hurricane safe.” The theory was that by thinning out the heavier crowns, winds could blow through them, and there’d be less of “a sail” effect. To do that we’d take out as much interior wood as possible, allowing you to see the crown from underneath. So if you stood away from the tree and looked back, it would look exactly the same as before because hardly anything was removed from the outer canopy.
[Q] But it turns out, that wasn’t a good idea. What changed? [MM] We’re now preserving live oaks with a method called reduction pruning. The idea is to make bigger trees smaller and safer.
At the University of Florida, researchers developed a giant fan that would imitate hurricane-force winds. They pruned one set of trees the old way, thinning them out and opening them up on the inside. On the other set of trees, they did reduction pruning, leaving in most of the interior crown and just removing the outer live growth to reduce the weight on the tree.
Then they turned on the wind machine and recreated category one, two, and three hurricanes. Afterward, they looked at films of how both sets of trees responded. When they slowed them down, they discovered that the trees that had been thinned out the old way were flopping back and forth, flailing and breaking. Meanwhile, the trees with their interior branches left in were dancing in the same wind with no damaging effects.
So for years, we’d been telling people –– and some horticulturists are still doing this –– that we’re going to take all these interior branches out of the trees to make them safer in storms. But we’d actually been making them more susceptible to wind damage.
[Q] I’m noticing that none of these trees we’re looking at have dramatic “angel wings” like that of Charleston’s Angel Oak.[MM] [He nods.] If a tree has lower limbs that touch the ground, some people like to call that tree “an angel oak” because it was like angel wings that hit the ground. But the Angel Oak in Charleston actually got its name from its location, the Angel Plantation.
Generally, it’s not very good for the tree to have those branches touching the ground. That’s because the bark, even though it can have rain hit upon it, needs to stay relatively dry, while roots have to stay as semi-moist as possible. If you have a smaller tree and you put too much mulch around it, that can create a lot of moisture on the bark and the bark may rot and the tree die. So when these “angel” limbs hit the ground and stay on the ground too long, the bark starts to decay, and sometimes it decays back into the tree and causes problems.
[Q] So does that mean you have to cut away branches that touch the ground? [MM] Not necessarily, but if you do have a limb like that, you should buffer it by digging out the earth beneath it and placing something like railroad ties or pilings below it to separate it from the ground. Reduction pruning is also important. You’re helping the branch out by taking off that part that is hitting the ground, but you’re also helping the entire tree by removing some of that weight.
[Q] This Mother Tree looks as if it doesn’t have a very full inner crown. [MM] Before it was pruned, this tree had been full of vines. Vines like wild grape or poison ivy are very invasive to trees because they always grow faster than the tree, and they take sunlight needed for photosynthesis and growth away from the leaves. Some people have trees on their property that are so covered with vines, they just see green and don’t realize their trees could be dead. Getting rid of that vine is the first step in getting the tree to reproduce its inner canopy.
[Q] What about Spanish moss? And resurrection fern? I’m always amazed when it rains and the latter pops up along branches and trunks. [MM] Spanish moss doesn’t sap any nutrients from the tree itself, but it does block the light and creates weight, especially at the ends. If it’s heavy on the limbs, it might not let the sprouts come out. So every time a tree is pruned, you should remove as many of the clumps as possible. Resurrection fern, on the other hand, grows just on the thicker part of the bark, and since the bark is all dead cells, it doesn’t have any effect on the tree, and it’s not big enough to create shade. It looks dead, but it’s not.
[Q] I’m seeing a freshly cut and a healed-over spot on the trunk where branches were pruned. [MM] The fresh-cut was probably deadwood that was removed. The wound directly below it was made fifteen or twenty years ago. Trees create what we call wound wood similar to calluses on our hands. With us, the wound heals and goes away. A tree eventually covers up and seals that wound wood, encapsulating that part of that history in its wood. Dendrochronologists who study tree rings can tell you climate conditions over thousands of years. (By the way, if you’re on the fence about climate change, read some of their documentation of weather patterns.)
[Q] Should you always remove a dead limb? [MM] You don’t have to. On a smaller tree with a dead branch, absolutely, it can come off because young trees are energetic, and the wound is going to seal over. But as a tree gets older and the limbs get bigger, taking off a giant limb is a decision that an arborist has to make. It could do more damage. Making that cut closer to the trunk, it might never seal over. But if you leave the limb on, it will delay any decay that might get into the trunk.
[Q] You mentioned that live oaks are different from most trees. [MM] Live oaks respond differently than other trees to pruning; it’s called differential species response. When you prune a tree, every cut you make is wounding, so you have to be careful how you make that cut because on most kinds of trees, decay can start right away. But trees are actually built to fail. Their purpose in life is to grow up, die and become food for the trees around them. In a real forest atmosphere, hundreds of trees die for one that lives. Those are the things that help nourish other trees.
Live oaks, however, have a capacity not to decay as easily in response to cutting. You can take off more than the rules or standards that arborists have to follow (for example, what percentage of wood can come off at one time, what size limb can be removed in relation to another size limb and so on). Live oaks push the envelope on that. Taking off more of that outer weight helps keep them stable. And so technically if you can keep a live oak stable, it might not fall over like the Succession Oak did. Then it can live forever.
[Q] Ah, the Succession Oak — that’s the historic tree in Bluffton where, in 1844, the seeds of succession were sown as hundreds rallied to protest tariffs they felt were unfair to the South. [MM] Earlier this year it broke apart into two giant pieces, and they had to take away everything that fell over the roadway. Two pieces of the trunk are still there, and I think one side is still alive. We’ll see what sprouts out on the other side.
[Q] This brings me to a strange question. If someone wanted to move a big tree like this Mother Oak, could it be done? [MM] That would be a monumental project. This tree probably weighs hundreds of tons. When we pruned it, we took off about twelve thousand pounds of end-weight plus vines and Spanish moss. But the fact is, live oaks can lose quite a bit of their root system so yes, it could be done. People that move big trees say that there’s no tree that they can’t move. When Disney was building Animal Kingdom in Orlando, they would box trees up, root prune them, put misters in their canopies and move them to their nursery. Then when construction was finished, they would bring the trees back to their original spots or use them in other places.
Lesson over, Murphy heads off to consult on another tree matter, and I head home armed with new knowledge. And while I’m not about to join an arbor maintenance work crew or move a massive tree, after today I will never look at live oaks in quite the same way