November 25, 2021

Leave This Soapberry? Or Uproot This Chinese Pistache? How Can I Tell?

In the woods of Central Texas, you will find saplings of both the native western soapberry (Sapindus drummondii) and the highly invasive Chinese pistache (Pistacia chinensis). We want to preserve and nurture the soapberry, and to do so we must control competition from exotic invaders. But there is a special challenge here: because both species produce even-pinnate compound leaves, sometimes produce wings along the rachis (especially when young), and often produce odd-pinnate compound leaves (again, especially when young), telling them apart takes more than a cursory inspection.

Most guides rely on the scent of the leaves:

  • The leaves of S. drummondii have a nondescript aroma—the kind of smell produced by the crushed leaves of just about any plant not noted for its scent.
  • For most people, the scent of P. chinensis is a repulsively overwhelming mix of pine, citrus, camphor, and kerosene. (As with wine or fine chocolate, different people pick up different notes.) Personally, I put it somewhere on the scale between demonic and downright horrid, but a few people actually find it attractive.

So usually telling whether a sapling is one or the other is as simple as rubbing a leaf and sniffing. But what about that second sapling? Are you smelling its scent, or the residual pistache from the first sapling's leaves? And what if reaching the sapling means going through poison ivy? Or greenbrier? Wouldn't it be nice to be able to tell the two apart visually?

Fortunately, you can. And often the answer is quick: If the leaves or immature stems show any hint of redness—even a shade just barely to the orange side of lemon yellow—it is not a soapberry. If you have otherwise narrowed it down to these two species, it's Chinese pistache.

Failing that, telling the two apart is still easy, if you look closely. You will find differences in these traits:

  • Bark. On the western soapberry, the bark of just-hardened stems is usually light gray—in fact, almost white. On Chinese pistache, it's usually cinnamon colored. (If you have narrowed the identification down to these two species and any segment of the tree has cinnamon-colored bark, it's Chinese pistache.)
  • Tips of the twigs. On western soapberry, bud breaks near the end of the twigs are usually very short. The direction of growth varies slightly from one bud break to the next, so the tips of the twigs are almost always slightly crooked. On Chinese pistache, the bud breaks tend to be much longer, so usually the end of a twig, stem, or trunk will be ramrod straight.
  • Branch angles. The branches of western soapberry emerge at moderately wide angles—say, 15 to 50 degrees or so, but branches of Chinese pistache emerge at angles much closer to 90 degrees. Often when you're examining the growing tip of a sapling you will see near the tip a lateral branch that has emerged at no more than a 30-degree angle, cinching the identification.
  • Branching pattern. In addition to the wide branching angle, Chinese pistache tends to branch out in an idiosyncratic pattern—a pattern you will never see on a soapberry. It won't appear everywhere on the tree, but you can usually detect it somewhere. Starting from the lowest node (branching point), follow the central stem of the sapling. Usually there will be a relatively wide span with no lateral branches at all, and then bam! Several branches come out at about the same wide angle, and the next segment of the central stem continues for another relatively long uninterrupted span before several branches appear at once again. The groups of branches are nearly whorls, but they don't all emerge from the same node. They are all close to the bud break, but not all at it. Examining the whorl-ish groups more closely, you will see that the more branches each includes the more unequal the branches are in strength. Often one is much, much stronger than all the rest; occasionally two or three are all the same strength; often most are very weak. This general pattern will repeat itself along the trunk and all significant branches. Sometimes it does so only sporadically, but you usually can find it at least once on saplings no more than knee high and two or three times on saplings that have reached head high. As the trunk or main branch increases in size, the number of laterals branching out in each of these whorl-ish groups will increase. The disparity in the strength of the laterals increases, too.

I'm sure there are many more structural details we could use to differentiate these two species, but these macroscopic cues have worked very well for me.

Oh, there is one more, very important test: If the tree passes all of the above tests for Chinese pistache, check out its root system. Be sure to separate every bit of dirt from every one of its roots. Look at it, and then toss it into an appropriate place—a compost pile, a shredder, or up in the branches of another tree or bush. Come back and reexamine it in a week. If it dies, it was Chinese pistache. If it lives, repeat the test, just to be sure.

Unless, of course, you are observing the trees in China.

Posted on November 25, 2021 20:36 by baldeagle baldeagle | 1 comment | Leave a comment

November 23, 2021

Girdling: What's It All About?

Fully vaccinated but still careful to mask up, I am trying to get back in a rhythm of assailing invasive trees in my vicinity. If that sounds like something you would like to do, a good start would be to watch the instructional video on girdling glossy privet a good friend of mine, Dave Dauber, produced for the Austin Water Department's Wildlands Conservation Division.

This video shows how to girdle trees by the method I developed for volunteers in Austin's Walnut Creek Metropolitan Park. Using no herbicides and no power tools, we have killed all the mature ligustrums on more than 20  of the park's forested acres.

What's so special about this method?

Following techniques taught elsewhere, I and other volunteers like me found that girdled trees almost always recovered fully. (Actually, I can't recall a single tree that didn't fully recover.)

Others gave up on the technique, but after the third variation failed, I returned to the job site daily to monitor the recovery of the girdled trees. Right away I learned that the tissue that bridged the girdle wasn't growing in from the ends of the girdle. Instead, it was growing from tissue left behind on the surface of the sapwood in the girdled gap.

In other words, we didn't need a tool that was sharper or larger or more powerful. Instead, we needed to make sure we removed every cell of tissue from the trunk in a band at least 3/4 of an inch wide:

  • It turns out that it's easier to remove a wider strip of bark, so we remove about a hand's width.
  • If the tree has forks, you can girdle each trunk at a convenient height, so long as every leaf remaining on the tree is separated from the ground by a girdle.

Need more details?

For the details on why girdling works, what tools to use, where to get them, and other techniques for eradicating invasives, check out my presentation to the 2019 annual meeting of the Texas Master Naturalists. This PDF of the slide deck includes not just the slides my audience saw but also what I said while they were displayed and information added to answer questions raised by the audience. It is pretty thorough. The PDF is weird; somehow in creating it they wound up with the images at the lower right corner of each screen, but the information is complete.

Got massive trunks?

Girdling works no matter how large the tree is. I've stripped individual trunks up to 26 inches in diameter (a chinaberry), and I've girdled trees with a combined diameter at breast height of 42 inches. When the bark gets really thick, you might need a bigger tool. Watch how backyard birder Jeff Hansen of South Dakota can remove thick bark with a pry bar.

Even with trees as big as Jeff's, I suggest you add my final step of scrubbing the residual phloem and cambium from the surface of the sapwood. You can get by with scrubbing a band just a couple of inches wide, so long as it goes all the way around the trunk. As with peeling the bark, wider is usually easier, but if the pry bar removes a whole foot-wide strip of bark, you don't have to scrub the whole width.

Now get out there and kill some privets!

Posted on November 23, 2021 21:38 by baldeagle baldeagle | 1 comment | Leave a comment

March 09, 2020

Coming Soon to the Heard Museum and Sanctuary…

Soon this glossy privet will have an important question to ask itself: "Do I feel lucky?" The date was set for May 16, but I fear that will have to be reset as the Covid-19 pandemic unwinds. But sometime before long I will be teaching my girdling techniques at the Blackland Prairie Master Naturalists' Third at the Heard—their Third Saturday Nature Talks at the Heard Museum. The talk begins at 9:30 a.m. Unless you are a member of the Heard, you do have to pay for admission to the museum, but once you're in the talk and workshop are free.

I will do my best to keep the talk to less than an hour, because the real fun will be when we go outside for a hands-on workshop. Many glossy privets on the grounds of the wildlife sanctuary—as many as we can reach—will learn the peril of the girdling knife on that day.

And so the little privets won't feel neglected, I will bring my suite of uprooting tools, too.

Posted on March 09, 2020 03:16 by baldeagle baldeagle | 1 comment | Leave a comment

July 19, 2019

Glossy Privet: Slayer of Native Shade Trees

Every weekend I walk through the woods of Walnut Creek Metropolitan Park to see how things are turning out for the trees we have girdled and the plants we need to grow in their place. The first weekend of July 2019 I came across a large live oak, shown in the second picture below, that is suffering the damage glossy privets do to larger shade trees:

  • They fill every bit of open space. Everywhere you look up under this oak, you see the leaves of glossy privet.
  • They grow year-round, piercing the oak's canopy.
  • As they grow into the canopy, they shade out—and kill—all the branches they pass by. In this oak, one large branch has died and is hanging in the canopy. Another large branch above it is dying, if not already dead. Both are in the shade of the same four glossy privets.
  • In Central Texas, glossy privets grow to be at least 40 feet tall. That's taller than our treasured live oaks. In fact, glossy privet competes with or towers above every species of tree found in Walnut Creek Metropolitan Park other than our pecans. And it can compete with pecans enough to do serious harm. For example, the pecan shown in the first picture below lost all of its leaves below 30 feet to a dense stand of glossy privet that grew in its shadow. (I'll have more later about the grove where this tree grew.) And for this live oak, it means that the glossy privets are already just as tall and are about to break above it, taking the first bite at the available sunshine.

    Whenever I see a native shade tree in this condition, it becomes an immediate priority. Instead of continuing our march through the woods on the other side of the trail, this weekend we focused on saving this tree.

    In three hours, three of us managed to uproot 27 Nandina domestica and girdle each of the 46 trunks of the 13 glossy privets (Ligustrum lucidum)—that's right; in the same area taken up by the canopy of this one live oak, there are 13 glossy privets—and to reach half of them we had to uproot the Nandina first.

    So today, July 13, 2019, this live oak's chance to recover begins. Over the coming year, I will report on the response of the glossy privets to their girdling and the response of this tree to its increasing access to all the available sunlight.

    Posted on July 19, 2019 23:10 by baldeagle baldeagle | 2 observations | 0 comments | Leave a comment

    June 18, 2019

    Diary of the Glossy Privet's Grim Reaper

    Several years ago, I took on the task of eradicating Ligustrum lucidum, also called glossy privet, and other invasive plants rom Austin's Walnut Creek Metropolitan Park. The idea that we could eradicate them is ambitiously optimistic, but I have a feeling we will do far better than just to manage them. Besides, with that goal in mind, I am inspired to keep trying new twists on my techniques for reducing their numbers.

    In this series of posts, I plan to share my observations of the impact of glossy privet on the plant communities in this park and the results—successful and otherwise—of our attempts to bring them under control. Follow me and you will find facts worth discussing, with details to back them up:

    • Glossy privet is so beautiful every spring, and it's a bulletproof evergreen. What makes it the most perniciously invasive woody plant in Central Texas?
    • Not all tree extractors are alike—and it isn't just the trade name that makes the difference. When you put them in the hands of volunteers, which ones work best? Why?
    • How does girdling work? If you have tried and failed, I can show you the way to succeed—and it's probably easier than whatever you've done before.
    • Nature abhors a vacuum. If we can get rid of the ligustrum, what will we put in its place?
    • What other invasive plants are making inroads in the park—and how can we show them the way out?

    One thing you won't hear me discuss is herbicide. At least three friends of mine have died from cancers linked to herbicides. It's better for us and our planet if we don't use them. And even if that weren't my position, I would still have to figure out how to get the job done without them. In Austin's parks, greenbelts, and preserves, volunteers are not allowed to use power tools or herbicides.

    As a teaser, the photo associated with this post shows 55 glossy privets uprooted in 90 minutes by one of my volunteers last weekend. In the background, you can see larger glossy privets that we girdled in the same project. In my posts, I'll follow this and other areas as the ligustrums decline and the new habitat emerges.

    And your comments will always be welcome.

    Posted on June 18, 2019 03:39 by baldeagle baldeagle | 1 observation | 5 comments | Leave a comment

    Leafcutter ants: An ally against glossy privet

    I have known for some time that leafcutter ants will attack glossy privet. I had even noticed that they seem to do so preferentially. In Austin's Walnut Creek Metropolitan Park, a couple of large colonies seem to be eating nothing else.

    I had not realized that leafcutter ants could kill ligustrums. They certainly strip the leaves, but they don't seem to be able to keep up with the plant's growth.

    All around this huge leafcutter ant mound we can find dead ligustrums. Volunteers working with me have girdled many in the area—but not these. We meant to get to these glossy privets eventually, but the leafcutters beat us to it.

    Perhaps if left to their own devices these ants would never have killed the ligustrums. Perhaps it is that we removed so many seedlings, saplings, and mature trees that the ants overwhelmed whatever remained behind. But they also seem not to have cultivated a taste for other plants in the area.

    If only I could convince them to try Chinese pistache, chinaberry, and giant reed…

    Posted on June 18, 2019 02:48 by baldeagle baldeagle | 1 observation | 2 comments | Leave a comment

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