Invasives - the battle of land rights amongst flora

PART TWO: REMINDERS AND TECHNIQUES– WHO IS AT STAKE HERE?

In our last blog post, we reviewed the guidelines that are generally used to determine

whether or not an organism is considered an invasive species. Here they are, one more

time:

Liggustrum

Ligustrum vulgare

1. The organism traveled to a new location with the help of humans or our tools

(intentional or not!)

2. The organism fundamentally changes its new environment to more suit its

needs, to the detriment of other organisms that live in the area. This completely alters

the ecosystem and typically reduces the overall biodiversity of the space.

3. A lack of relationships. The new organism has not formed reciprocal

relationships with other plants and animals within the ecosystem, and disrupts the

relationships that existed in the area prior to its arrival.

We also named three organisms that are invasive in Texas– Chinaberry Tree (Melia

azedarach), Vitex (Vitex agnus-castus), and Glossy-Leaf Privet (Ligustrum lucidum).

There are many other organisms that are considered to be invasive in Texas, but South

Austin Creek Alliance (SACA) focuses mainly on the removal of Ligustrum with a

technique called girdling.

SACA chooses to girdle invasive trees for a couple of reasons:

- Girdling is a fantastic opportunity for public education and direct engagement

with landscape management. We are a part of our ecosystems!

- Girdling helps keep our landscapes free of herbicides, which is especially

important in areas where water is present– healthy riparian areas are key for clean

water.

- Girdled trees continue to hold soil in place with their roots and provide

temporary shade to any young saplings under their canopies, protecting native species

and allowing replacement trees more time to mature before full exposure to the

elements.

- Girdling also creates standing deadwood, which is a critical resource for many

insects and birds.

- And, most of all– girdling is fun!

How do we decide where and when to girdle?

The most important part of this process is to be familiar with the land you want to

work on. Walk to and through the area frequently, during different seasons. Observe

who is there– what organisms are you sharing the space with? What animals and plants

will be impacted by girdling? How much of the canopy (tallest tree layer) is made up of

invasive trees, and how much of the understory (baby replacement trees) is composed

of invasive species? Is the area a monoculture? What other restoration activities might

benefit the area? Try to think about how the area changes over time, too.

Most urban creeks are heavily altered and disturbed by human activities. This

predisposes the land to be colonized by invasive species, which are typically organisms

that can survive extremes and possess extraordinarily high reproduction capabilities.

Native species can flourish in these areas, too– but they are still often outcompeted

when invasive species are introduced. Another reason why invasive plants are often

found in disturbed areas is that they are used in landscaping more often than native

species, so it's very easy for them to 'escape' into the woods. While this is beginning to

change, it's still extraordinarily common for developers to use invasive plants in their

projects.

Before committing to a girdling project, it's very important to make sure that

you've weighed the potential risks of additional disturbance to an area. The general rule

of thumb is that intervening to remove an invasive tree is usually a good idea, but there

are some situations where it might do more harm than good. Here are a couple

examples of things to watch out for:

Is the tree casting shade on water? If the tree died, will the sun hit the water and

heat it up? Keeping water cool is critical for organisms in hot places like Texas– if the

water temperature rises too much, most of the animals and plants living in it will die.

Is the tree the sole source of shade for a group of young native saplings? Are the

saplings large enough to survive without a nurse tree? (A good rule of thumb is that the

saplings should be at minimum waist height before exposure to full sun)

Is the invasive tree holding the bank / preventing erosion?

In cases like the above, it may be best to leave the invasive tree alone

temporarily and formulate a plan to address the tree without accidentally damaging the

ecosystem.

It's also a really good idea to prioritize girdling invasive trees that have

surrounded a mature native tree. This helps the native tree survive when times are

tough (like a drought is present) and allows the mature organism to continue

reproducing.

Another great place to prioritize is any place on the brink of becoming a

monoculture– i.e., all of the understory replacement trees are invasives while the

canopy is still predominantly native trees. If the invasive trees are removed, the native

overstory plants have a chance to reproduce.

REFRAMING A VIEW

Despite advocating for their removal, I believe the organisms that become

invasive are pretty extraordinary. They have found a way to survive and thrive in

situations where they are almost completely severed from the relationships they formed

with others as they evolved over millennia. Most organisms can't do this! We need

mutual relationships to survive: interdependency is the norm. Think about it– if you

removed a panda from the forest it evolved alongside and stuck it in the middle of the

Central Texas woods, the likelihood of that panda surviving and somehow reproducing

is extraordinarily small–much less becoming so successful that it completely alters the

Central Texas ecosystem!

And yet organisms are doing this every single day. If these plants and animals

weren't excluding other species from our ecosystems and dramatically altering our

landscapes, we would probably have a very different relationship to them. Kudzu, for

example, was originally introduced to the Americas with the intent that it be a resource

for people– it's a crop plant and provides wonderful, deep shade (a characteristic which

also contributes to its ability to completely alter the understory of a forest)– clearly, this

did not work (Blaustein, 2001).

But are there hidden opportunities here?

While we're doing habitat restoration and removing invasive species, is there a

way for us to benefit not only the ecosystem*, but ourselves directly? What I mean is

that funding for restoration activities is always shaky, but if we can demonstrate that a

project can boost the local economy by providing unique opportunities to the people

living there, a stable source of funds might be secured in addition to getting the public

directly engaged. Also, are there unique opportunities for research and learning that are

afforded by these species? Can we incorporate their harvest into industry or use them

to improve the soils where they had previously lived? What kinds of relationships do

these organisms have with others from their homelands? What niche are they filling

here? Why did they become invasive anyway– was the ecosystem in disrepair before?

It's also important to think about long-term management and expectations. How

can we shift our culture to incorporate better land management practices? How do we

convince developers to use native plants in their plantings instead? What do our long

term goals look like?

*Setting aside the fact that any benefits towards an ecosystem also benefit human

beings as we are a part of this Earth.

PART THREE: WHY GIRDLING WORKS

My favorite part of girdling is teaching people why this technique works, because

it means I get to gab about plant phytotomy (aka, anatomy).

The very basic idea is that plants are collections of tubes. Complicated, beautiful

bundles of tubes, capable of incredible feats– but tubes nonetheless.

Some of these tubes gather water from soil and transport it upwards through the

body of the plant (xylem). Other tubes bring down from the leaves delicious sugars–aka,

food–which were created via photosynthesis (phloem). The roots require these sugars

in order to live and continue to acquire water.

Different types of plants have different arrangements of their food and water

tubes (called vascular bundles). If you took cross sections of an oak tree trunk and a

palm tree trunk, and compared the arrangement of their xylem and their phloem tubes,

they would be completely different.

Monocot Vascular Bundle Arrangement (This is what the palm tree would look like,

approximately– the vascular bundles are the smaller, darker clusters of cells interspersed

throughout the stem). Photo courtesy of libretexts. https://bio.libretexts.org/Bookshelves/Botany/

Plant_Anatomy_and_Physiology_(Bellairs)/03%3A_Stem_Leaf_and_Root_Anatomy/3.01%3A_Stems

Dicot Cross Section of Vascular Bundle Arrangement (this is what the Oak tree would look like,

approximately). Photo courtesy of libretexts. https://bio.libretexts.org/Courses/Coalinga_College/

Introduction_to_Plant_Science_(Hochman_Adler)/09%3A_Tissues_and_Organs_-_How_the_Plant_is_Built/9.04%3A_The_Stem/

9.4.01%3A_Inside_Stems

Note that monocots like the palm "tree" have their water and food tubes scattered all

throughout the cross section of the trunk, whereas the dicot's vascular bundles are

arranged in a ring around the edges of the stem, right under the bark. The location of

sugar-laden vessels under the bark (also called cork) in many dicots allows humans to

access them, harvest their contents (yum! Maple syrup!)– or, in the case of an unlucky

few– kill the organism entire.

Girdling works by severing the sugar carrying tubes and preventing the tree from

feeding itself. It's simple: remove a strip of bark and the phloem layer beneath it, all the

way around a trunk, and that trunk will cease transporting food to the roots below. Do

this to all of the trunks on a tree, and it will die– slowly, by inches. It can take up to two

years for a girdled tree to starve, though most succumb in a year or less, so long as the

bark doesn't reconnect itself.

And on that dark note– thank you for reading! We hope that you join SACA for our next

restoration event. Keep your eyes on September and October!

Resources:

https://www.srs.fs.usda.gov/pubs/ja/ja_blaustein001.pdf (Blaustein, Richard J. 2001)

Please note that this article, like many others about invasive species, uses pretty loaded

language and is strongly biased– keep this in mind if you check it out.

Introduction to Botany:

https://bio.libretexts.org/Courses/Coalinga_College/

Introduction_to_Plant_Science_(Hochman_Adler)

https://bio.libretexts.org/Bookshelves/Botany/Plant_Anatomy_and_Physiology_(Bellairs)

Beginner Friendly Books about plants (available through the Austin Public Library):

The Nature of Plants: An introduction into how plants work by Craig Norman Huegel

The Light Eaters by Zoë Schlanger– synopsis / collection of most recent research into

plant behavior, learning, and similar.