One of the biggest challenges we face at Wild Basin Wilderness Preserve is the presence of invasive plant species. They weren’t intentionally planted here, but journeyed here by hitching a ride on animal fur, the wind, the movement of water, dumped landscape trimmings, or through an animal’s digestive system. Why do we consider this one of our biggest challenges? To answer this, we must dig a little deeper.
Let’s start with what we are calling invasive species. In this article, we’ll use the definition put forth in the Executive Summary of the National Invasive Species Management Plan (NISMP) in which an invasive species is defined as ‘‘a species that is non-native to the ecosystem under consideration and whose introduction causes or is likely to cause economic or environmental harm or harm to human health”. This is how we will approach this topic, but just for the record native species can also become invasive and cause ecosystem problems given the right conditions. Animals can also be invasive, but the current threats to Wild Basin center around plants.
Why should we care about invasive plants? These species, when introduced to a new environment, do really well. So well, in fact, they can outcompete native plants and can take over. At Wild Basin, our most common invasive is one called Waxleaf ligustrum, or Japanese privet (Ligustrum japonicum). Ligustrum can propagate from its roots or grow from seeds (self-seeding or animal/bird droppings) and can outcompete all the native trees and shrubs around it. If left unchecked it can grow into a monoculture forest that allows very little light to reach the ground, allowing for little understory growth. This leads to less biodiversity and a potential increase in erosion. Roots are important in holding the soil in place. Think this is bad? Wait - there’s more.
Invasives don’t have many natural “predators” around here to keep them in check – they are not considered a tasty treat by most of our native wildlife species. Some animals do find ligustrum berries to be yummy, but in eating them they just spread more ligustrum seeds – what goes in must come out! Native wildlife prefers to feed and browse on native plants. Think about it – would you rather eat barbeque from New York or Texas? It’s kind of the same with our Texas wildlife. In areas with high numbers of invasives, this preference leads to reduced growth and reproduction of native plants. This allows invasives more room to take over. It can completely change the ecosystem it has invaded. Less native plants leads to less native wildlife and puts the ecosystem out of balance.
Even if they like the taste, invasive plants don’t offer much in the way of nutritional value to most native species. If they do eat it, it may be toxic. Another invasive we constantly battle at Wild Basin is a shrub called Nandina (Nandina domestica), also known as Heavenly bamboo. Nadina is toxic to grazing animals, and can kill birds if eaten excessively (all parts of the plant contain a type of cyanide). Not all invasives are this toxic to wildlife, but few offer anything akin to the sustenance they get from native plants. Think of it as “junk food” to our native animals.
So who is responsible? If invasive plants are so bad, why were they brought here in the first place? All of these plants have their positive qualities that made them inviting. Ligustrum is evergreen, fast-growing, drought-tolerant, and has lovely smelling flowers. Nandina is deer-resistant, spreads readily, and is an attractive shrub that grows beautiful red berries. These plants make a lot of money in the nursery trade, and due to that are not classified as invasive by the Texas Department of Agriculture (TDA). The TDA must consider other impacts when deciding whether to classify a plant as “noxious” or “invasive”. There are currently only 32 species on their list (follow this link for the list - https://texreg.sos.state.tx.us/fids/201300604-1.html). The City of Austin lists 61 species on its “Invasives of Central Texas” guide (consider printing this guide and referring to it when buying plants - https://www.austintexas.gov/sites/default/files/files/Watershed/invasive/2013_Invasives_guide_small.pdf). Why such a big difference in numbers? If the plant is important to ranching, agriculture, horticulture, aquaculture, etc., it will not necessarily be classified as invasive, even if it is. For example, invasives have been planted to stabilize soils, provide greater forage for cattle, and to be sold for aquarium environments. Unless a plant is listed on the TDA list, it can be sold in Texas. To be fair, no one brought these plants here to sabotage our native ecosystems. Unfortunately, though, that is what is happening. They are one of the greatest threats to native habitats, and they are incredibly hard to get rid of.
We are only starting to fully realize the economic and environmental benefits of NOT classifying many of these species as invasive. According to USFWS, the annual cost of invasives in the US is $120 billion. This just includes monitoring and control costs. It doesn’t include long term impacts to wildlife, ecosystems, watersheds, and biodiversity. It may not even include all the species that are truly invasive for many of the reasons already discussed.
Will we ever be rid of invasive species? It isn’t likely, but that doesn’t mean we shouldn’t try. There are many ways we can prevent further introductions. By being informed consumers, we can dictate what is sold in nurseries – if it isn’t making money, they won’t sell it. Ask your local nursery for native plants, and investigate plants before you buy them. Complain when you see them selling invasives. Volunteer to remove invasive species and/or restore ecosystems with native plants (come to Wild Basin – we can put you to work!). Talk to your friends and neighbors about considering natives in their landscape – they are often much easier to care for. They also offer entertainment in the wildlife they attract such as hummingbirds and butterflies. Search the internet to find native plant sales in your area. No, we will not completely eliminate invasives, but we must try to protect our natural heritage and ecosystem heath.
