Invasive Plant Species: The Threat They Pose to Native Ecosystems

Many readers are familiar with the concept of an invasive animal species and how these animals can decimate entire ecosystems. Invasive animals can overburden food sources, prey on native species, or breed prolifically, resulting in extinctions, displacement, and a massive loss in local biodiversity. The thing is, invasive plant species can be just as destructive.

Though not everyone has heard of an invasive plant species, they are a growing concern in habitats and communities across the globe. Invasive plants pose significant threats to native ecosystems and biodiversity, just as invasive animals do, but they also have sweeping, often catastrophic effects on human livelihoods.

Somewhat ironically, many of these invasive plant species are introduced into ecosystems by humans either intentionally or accidentally. Once they take root, invasive plants often spread rapidly, outcompeting native vegetation for vital resources. The presence of these alien species disrupts the natural balance in a number of detrimental ways.

In this article, we will try to describe and define the characteristics of invasive plant species. We will explore their various impacts on native ecosystems while examining some notable invasive plants worldwide. Finally, we will conclude by discussing several ways that humans can prevent and control their spread.

Understanding Invasive Plant Species

Invasive plants are defined as non-native species that through transplantation establish themselves in new environments. Most invasive species have a high capacity for growth and reproduction. That said, not all non-native plants can be categorized as or eventually become invasive. The truly invasive ones are distinguished by their ability to spread aggressively, negatively affecting ecosystems wherevere they take root. A list of some common traits of invasive plant species can be found below:

• Rapid Growth and Reproduction: Invasive plants grow and reproduce faster than their native neighbors, quickly establishing themselves and spreading across large areas.
• High Adaptability: These plants tend to be highly adaptable to different soil types, climates, and environmental conditions, rendering them particularly adept at conquering most relatively-similar ecosystems.
• Resilience to Predators: Once they have established themselves in a new environment, invasive plants will run roughshod over local species. This is because invasive plants often lack natural predators or diseases. This allows them to proliferate without checks and balances.
• Allelopathy: Interestingly, some invasive plants release chemicals into the soil that inhibit the growth of other plants, which effectively suppresses native vegetation.

As you can see, these unique characteristics give invasive plants a competitive advantage over indigenous plant species.

How Invasive Plants Impact Native Ecosystems

Invasive plant species disrupt ecosystems in several terrible ways. When scientists look at these plants, they view their impact at multiple levels, from soil quality and water availability to the overall biodiversity of an area. Below, we have gathered some primary ways invasive plants affect native ecosystems:

Reduction of Native Biodiversity

We’ve touched on biodiversity several times thus far, and there is a very good reason fort that. Biodiversity is essential for the perpetual survival of an ecosystem. When biodiversity is robust, plants, animals, and microorganisms work in concert with one another. As long as this continues, the ecosystem remains healthy and life goes on. Invasive plant species can cut into an areas biodiversity, disrupting this existing homeostatic balance.

This is because invasive plants compete directly with native plants for sunlight, water, and nutrients. The fact that many invasive plants grow so aggressively, doesn’t help, as this aggressive growth pattern allows them to outcompete native species for these resources. If this goes on long enough, it can lead to the decline or even extinction of indigenous flora. In most cases, even the fauna eventually suffers and declines. The native plants disappear and the animals that depend on them, including insects, birds, and mammals, lose their homes or meal tickets, causing a ripple effect through the food chain.

Alteration of Soil Composition

We touched on it earlier, but some invasive species have a very interesting effect on soil quality in a new area. Take, for example, the black locust tree (Robinia pseudoacacia). This plant can alter the chemical composition of the soil by enriching the soil heavily with nitrogen. Sure, we know that high nitrogen levels in soil can help plants grow, but too much nitrogen can have an opposite effect, especially if the native plants surrounding the locust are used to lower nitrogen levels. Altered soil compositions like this can lead to significant shifts in plant communities, and the new soil type usually favors certain invasive plants over native ones.

Water Resources Depletion

Invasive plants are thirsty, greedy buggers when they want to be. We’re not just talking about little weeds either here, large shrubs and trees can also be invasive, and they consume significant amounts of water. If one such invasive plant ends up taking root in an area, it can easily dry out local streams, rivers, and wetlands.

The tamarisk (salt cedar) tree, for example, has become invasive in the southwestern United States. This tree needs a lot of water to survive, but in the American southwest, so does every other living thing. Tamarisk trees consume so much water that they regularly deplete local water resources which critical for other plants, animals, and human communities located nearby. They can even impact water availability for agricultural use.

Increased Fire Risk

These days, thanks to climate change, wildfires are something of a regularity in many parts of the world Certain invasive plants, such as cheatgrass (Bromus tectorum), increase the frequency and intensity of these wildfires. No, it’s not a fire flower from Super Mario Bros., it’s just highly flammable and it grows like….well, a weed. When these newly-grown acres of cheatgrass dry out during the summer they a vast grassland of highly flammable kindling.

We have already seen this happen in regions like the western United States, where invasive cheatgrass has contributed to a higher incidence of wildfires. These fires can devastate entire ecosystems, decimate populations, destroy homes, and endanger human lives.

Displacement of Native Fauna

When invasive plants butt their way in to replace native vegetation, they disrupt the habitat and food sources for native insect and animal species. Native animals are often highly-specialized, which means they have specific dietary or habitat requirements. The loss of their homes and food sources could be devastating to local populations of fauna, which can then disrupt ecosystem dynamics.

Notable Invasive Plant Species Around the World

Invasive plants are a global issue. They have insinuated their way into countless ecosystems in various regions and climates. We could go on for days, but have pulled just a handful of the most notable invasive plant species and their impacts below:

Kudzu (Pueraria montana var. lobata) – United States

Originally introduced from Asia to the southeastern United States for erosion control, kudzu quickly became invasive. Kudzu is distinguished by its fast-growing vines, which can cover and choke native trees, shrubs, and ground cover. This quick, dense coverage shades local plants out, killing them and disrupting entire southern ecosystems. Kudzu’s rapid spread has led to its notorious nickname, “the vine that ate the South.”

Water Hyacinth (Eichhornia crassipes) – Global

Native to the Amazon Basin, water hyacinth are gorgeous water plants that are beautiful to behold. Unfortunately, they have also become one the most invasive plants for freshwater ecosystems around the world. The water hyacinth has found its way across entire oceans into Africa, Asia, and North America. Its thick, floating mats block sunlight and reduce oxygen levels in the water, which can lead to anoxia. This affects local fish and other aquatic life. In terms of human beings, mats of water hyacinth can wind up clogging valuable waterways, impacting navigation, fishing, and water access for local human communities.

Japanese Knotweed (Fallopia japonica) – Europe and North America

Originally introduced as an ornamental plant, the Japanese knotweed has made its way to Europe and North America, where it has spread aggressively. The tenacious root system of this once lovely plant damages buildings, roads, and flood defenses wherever it grows. At the same time. knotweed also outcompetes native plants, especially in riparian zones, where it alters the ecosystem structure.

Tamarisk (Tamarix spp.) – Southwestern United States

We mentioned the infamous salt cedar earlier, but didn’t discuss how the tamarisk was introduced in the first place. This plant was originally brought in for landscaping and erosion control. but ended up consuming entire wetlands and waterways once it had taken root. These plants also deposit salt into the soil, making it inhospitable for native plants. Their presence in the American southwest has dramatically affected ecosystems by contributing to the decline of native species and altering fire patterns.

Australian Pine (Casuarina equisetifolia) – Florida, United States

The Australian pine is now a Florida native. Like the python before it, the Australian pine has had a detrimental effect on its Floridian neighbors since it was brought over. Originally, introduced for landscaping and windbreaks, the invassive pine has has since invaded coastal areas.

The shallow roots and dense canopy of these tree allow it to outcompete native dune plants, which has led to beach erosion and loss of natural habitat for already threatened coastal wildlife populations. In addition, the Australian pine also poses a threat to nesting sea turtles, as its dense canopy blocks access to nesting sites.

How Invasive Plants Spread

Invasive plants can spread in numerous ways on their own, which is a problem in and of itself. Unfortunately, their penchant for rapid proliferation is often unwittingly aided by human activities. Still, understanding these methods might help us prevent future invasions:

• Intentional Introduction: Many invasive plants were intentionally brought into their new environments for ornamental purposes, agriculture, or erosion control. However, once established, these plants have somehow found ways to escape cultivation and spread more rapidly.
• Accidental Introduction: Other invasive plants are introduced unintentionally, often through contaminated soil, seeds, or cargo. If these seeds hitch a ride on vehicles, equipment, clothing, or even animals, they can fall off anywhere, finding new environments to grow in.
• Natural Dispersal Mechanisms: Many invasive plants have efficient natural dispersal methods, such as seeds that float on the wind or water. This allows them to spread over long distances without much help from the likes of us.
• Climate Change: The effects of climate change have made it possible for many invasive plant species to hitchhike and thrive once transplanted. The rising temperatures and changing precipitation patterns wrought by climate change often create new habitats where invasive plants can thrive, further expanding their range.

Methods for Controlling and Managing Invasive Plants

If we are to continue on as a species, we need to learn how to manage some of these invasive plants. It isn ‘t easy, given that some of these plants grow so quickly and so prolifically, but it isn’t impossible. It would seem that a multifaceted approach, which combines prevention, early detection, eradication, and restoration, might be the key. Below are some common methods used to control invasive plant species:

Mechanical Removal

Ripping the plants out of the ground seems like a good idea at face value. Mechanical removal involves physically uprooting or cutting invasive plants, and it’s effective for small infestations. Unfortunately, mechanical removal can be labor-intensive and could end up doing more harm that good by potentially causing soil disturbance, which might even allow other invasive plants to take root.

Chemical Control

Chemical herbicides can be an effective way to combat invasive plants, but they are rarely used as carefully as they ought to be. Chemicals can inadvertently harm other native flora and fauna and can have long-term effects on soil and water quality in the ecosystem.

Biological Control

Biological control involves introducing natural predators, such as insects or pathogens into the mix. But as we have seen with the cane toad and other such invasive deterrents, this can have an opposite effect on the local ecosystem. Using this method requires careful study and planning to avoid any unintended consequences or potential ecological disasters.

Controlled Burning

While it seems dangerously counterproductive, prescribed burns can be used to help control certain invasive plants, such as cheatgrass. However, this method is only feasible in certain environments and must be carefully managed and timed to avoid unwanted wildfires.

True Investigator Says…

Today we learned why invasive plant species are such a pervasive, proliferous threat to our global ecosystems. These interloping plants endanger biodiversity, alter entire landscapes, and create costly environmental problems for humans and animals alike. We as humans need to be more mindful of which plants we introduce to an area, not just for our sakes, but for that of our plant and animal neighbors.