Weeds? Pests? Invaders? Are invasive species really detrimental to our native habitats?

by Nadia Rhudy

PROLOGUE:

Invasive Chinese Pistache, Pistacia chinensis frequently seen along urban waterways

Environments are in a constant state of flux: weather sweeping across the landscape, organisms living and moving and eventually dying to return into the earth. These processes build up soils that may be blown away by the winds after a particularly bad drought, or a scorching fire carrying particles up into the air to be deposited elsewhere. The waters, churning through banks and twisting their shapes to spread and carve and sculpt our landscape. Austin is a river valley. Central Texas bows to this like every other place on our planet. Our beautiful, unique landscape with all its various organisms dancing in ancient lockstep with each other again, and again, and again.

Life cycles are roughly circular when you take a broad enough view. Ultimately though, everything leads to this: organisms influence and shape their environment just as much as their environment shapes the organisms themselves. Plants and animals are enormous ecosystem engineers if you take a step back– life produces more life, and nothing is wasted. The relationships between organisms are particularly important, and when these relationships are broken or damaged, our ecosystems change in ways that are usually undesirable for most everything that lives in the area.

Loss of biodiversity through poor land management is an overwhelming issue for everyone on our planet, and South Austin Creek Alliance is invested in being part of the solution here. Some organisms are particularly adept at altering their environments rapidly to more suit their needs. Trees, beavers, and humans beings are all examples of organisms that are incredibly good at changing landscapes rapidly to more suit them (for brevity's sake we will not touch on the complex history of land management practices, colonialism, and human movement in this newsletter/blog– but it's a fascinating topic that is absolutely relevant to today's socioeconomic, political, and ecological landscape. Resources for further reading are

Chinaberry tree, Melia azedarach, often found in riparian zones is a noxious plant that is highly invasive. In the state of Texas, it is illegal to sell, distribute, or import.

appended at the bottom of this article! I am also required to say here that any opinions expressed by these articles, journals, and books are not necessarily endorsed by SACA per se, and etc.-- you get the idea).

There are many reasons to love Central Texas. Whether it's a penchant for our volatile weather, or the people who live here, or a particular group of animals and plants that you might like, or the history, or simply economic opportunities– the list can go on and on. Many people move here for love of place, and this movement brings many changes. Not all of these changes are great for organisms (and people!) that already lived here– but if we step up our game in being better neighbors to wildlife and careful participants in our ecosystem, we can create a system where meeting human needs and conservation can coexist.

It is up to us to protect our water, our food, and our landscapes. The time is now, and every little bit can make a big difference! South Austin Creek Alliance is dedicated to conserving these resources. When we talk about habitat restoration at our events, what we mean is this: managing land so that native species flourish once more, water quality is improved in areas where it is poor, and our resources not only remain intact but increase to historical levels. One aspect of this process involves identifying and removing invasive organisms from the environment, and that's where this essay really begins.

PART ONE: DEFINITIONS

The topic of invasive species is convoluted and simple at the same time. The science might be the least tangled portion of the topic– in terms of definitions– but we still lack a complete understanding of the ways that new organisms to an area change it fundamentally. The questions of human social structures, history, and how they impact our land management is even more complex. This is why SACA will be approaching this topic over the course of several discussions. We're also trying to keep a relatively neutral stance– it's up to you to form your own opinion!

These may be some helpful guidelines and questions to keep in mind when working with invasive species:

1. Am I applying human social structures, politics, and pressures to these organisms? I.e., are you attaching human values to the organisms themselves that effect your attitude about them? How might your attitude about these organisms impact or extend to people?

2. What is your goal with management? Is that goal consistent with your internal ethics?

3. How are the actions you are taking to reduce the total number of organisms of one species going to affect other organisms in the area? How can you do these practices to strengthen the number and effectiveness of relationships between organisms?

4. Are you exploring all avenues for education that these invasives can provide? How can you reshape our cultural approaches and assumptions about land management?

5. How careful are you when determining what an organism is and whether it's actually invasive? Who are you asking for this information and resources? What are their goals, and do those align with yours?

6. Who are you inviting to participate with you? Keeping these in mind when working with invasive species can be pretty challenging but also extremely rewarding!

   
   

Chaste Tree, Vitex, Vitex agnus-castus This invasive is also deceptively referred to as "Texas Lilac" however, it is not native and will out-compete those that are. Often found in riparian areas as the seeds spread easily through storm run-off.

There is a wealth of opportunity for reflection and connection. There are also loads of common misconceptions about invasive species. We will address some of them now:

- Human beings are not an invasive species. We have lived in almost every ecosystem on Earth for thousands of years. While we're a relatively young species (Homo sapiens emerged approximately 200,000 years ago, though our oldest ancestors were present circa 2 to 6 million years ago), we have formed plenty of extremely specific relationships with other organisms and places.

- Not all nonnative organisms in an environment are considered to be invasive species. "Weeds" are not always an invasive species– a "weed" potentially could be an invasive species, but most often they are not!

- Many people believe that Juniper trees ("cedar trees"-- Juniperus ashei) are invasive in Central Texas. This is completely false. Juniper trees would not be the sole source of nesting material for golden-cheeked warblers if they were invasive– a specific relationship like that takes many hundreds if not thousands of years to develop.

There are approximately three conditions that must be met before a species can be considered invasive (though like everything in biology, this determination can be fraught).

1. The organism could not have traveled to its new environment on its own– it must have had help moving from a human (or our tools), intentional or not.

2. The organism must be able to significantly alter the new ecosystem it's in to the detriment of other organisms living there– i.e., it makes such fundamental changes to the land that it excludes other forms of life. Often, this leads to a loss of diversity, which means that other organisms here might become more susceptible to extinction during disturbances (fires, new pathogen, flooding, fragmentation, weather events, etc).

3. The new, invasive organism does not support the lives of any other organisms in its environment. Many plants and animals have extremely specific relationships where they both benefit– pollinators and flowering plants are a great example. Many invasive species fall outside of these cooperative relationships, and cause problems by disrupting them without opportunities for reciprocity.

Ligustrum/Chinese Privet, Ligustrum lucidum This tree-like shrub will produce large thickets along riparian areas and outcompete native plants. It is incredibly prolific along our urban waterways in Austin.

It's important to remember that any organism– plant, animal, etc– has the potential to become an invasive species. It's also important to consider that environments are constantly in states of flux and change, and that the ecology of the planet shifted broadly when people began to travel long distances frequently.

Most of the invasive species SACA focuses on right now is management of Ligustrum lucidum, an understory tree brought here by developers in search of a landscaping element. We'll cover the process we use to identify and remove these trees with minimal disturbance to the ecosystem in an upcoming blog post!

Here are just a few helpful resources on the topics of changing ecology, land management, and invasive species:

Wong, J., & Hendry, L. (n.d.) The origin of our species. Natural History Museum. https://

www.nhm.ac.uk/discover/the-origin-of-our-species.html

For Further Learning:

1491; 1493, Charles C. Mann (these two books focus on ecological and social changes that

began at the onset of colonization in the Americas)

texasinvasives.org; tiscc.texas.gov (lists of state-recognized invasive species)

wildflower.org/plants-main (Ladybird Johnson Wildflower Center list/search for native plant

species)

Native Plant Society of Texas, https://www.npsot.org/

xerces.org (great general information about regional-specific habitat restoration for pollinators

and other native insects)