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Invasive Species and the Reserve

December 1, 2021

I wanted to write about something close to my heart for the November blog post, so I chose invasive species. Mary and I have been working on removing invasive species from around the lodge recently. However, before we get to that, let’s kick things off with some dry definitions and depressing statistics.

First off: what is an invasive species?

According to the Invasive Species Advisory Council (ISAC) the definition is “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” (ISAC 2006). That definition might sound a little vague, but the distinction of invasive species can have many nuisances. Most non-native species are not invasive. For example, you could bring a tropical houseplant that is native to Central America to Minneapolis, thus making it a “non-native” species. But if you release your houseplant into the winter of Minnesota, your houseplant likely will not survive long enough to do any harm. Many ornamental and agricultural plants fall under this umbrella of “non-native ” but not necessarily “invasive.”  Let’s move on to an example of an invasive species: West Nile Virus (WNV). WNV was introduced to the US from its native range in Africa, therefore making it non-native. It also causes harm to humans and the ecosystem, making it invasive. That example is easy to understand because West Nile Virus causes direct harm to humans by making them sick and harm to the environment by killing native bird species. Other examples aren’t so straightforward. Many invasive plant species cause harm to the environment, but indirectly. Invasive plants can reduce forage for wildlife, outcompete native plants for resources, impact water systems, and change the ecosystem around them by altering soil chemistry, fire regimes, and biome type.

One example of an invasive species that is well known in the western United States is cheatgrass (Bromus tectorum).  Cheatgrass is a cool-season annual that has invaded the Great Basin from its native range in Eurasia. It takes over sagebrush steppe and creates so much thatch that it increases the frequency of fires from every 70-100 years to every 3-5 years. Sagebrush is not able to reestablish within such a short fire regime, so cheatgrass effectively alters the ecosystem from sagebrush steppe to annual grassland (Knapp 1996). This is terrible news for biodiversity. Native birds that nest in sagebrush such as sage grouse and other sage-dependent species cannot survive in a cheatgrass monoculture. Native grasses and forbs are outcompeted for water and sunlight. Cheatgrass is unpalatable for wildlife and livestock after it dries out and its seed heads can cause infections in the eyes and mouth. Mammal and insect communities that rely on native plants cannot find food or shelter. Within decades, a once vibrant ecosystem that has been “invaded” can become increasingly biologically desolate, even if it still looks “natural.”

Female Sage Grouse, a charismatic sage dependent species. Credit: Aidan Sullivan

In the US, it is estimated that 42% of threatened and endangered species are at risk from invasive species (NWF). Globalization has already introduced many invasive species to high Human Development Index (HDI) countries. Within the next century, it is predicted that air travel/global trade, expansion of agriculture, and changes in native plant communities, due to climate change, will lead to many more invasions in low HDI countries (Early, et al 2016). So, what can be done?

As with many issues, prevention is the best option. On the national level, requiring agricultural inspections at all ports of entry, setting strict standards for horticultural and animal imports, funding early detection rapid response teams (EDRR), and sharing data and expertise internationally are some of the best prevention tools.  When invasive species slip past prevention measures, then it’s time to look at your management options.

Oftentimes there are more invasive plant species to control than there is available funding so it is necessary to prioritize. A good prioritization scheme considers an invasive species’ potential to spread further, its risk to threatened/endangered species, human health, or agriculture, economic damage, and the chance to be successfully eradicated. Once you’ve ranked your invasive species, then you’re ready to select your control methods:

  • Cultural. This means getting people to adjust their practices. Examples include only buying certified weed-free livestock feed or sanitizing heavy timber harvesting/wildfire equipment before going to a new worksite. Livestock and heavy machinery are common vectors for invasive species.
  • Mechanical. An example would be a volunteer pulling up invasive species at a weekly volunteer event or a land manager mowing their field to stop an invasive mustard before it has the chance to go to seed.
  • Biological. A biological control can be a fungus, insect, or an animal like a goat. This method often sounds frightening, since people often associate biological controls with such ecological nightmares as private individuals with the sugarcane industry releasing mongooses in Hawaii. However, biological controls are rigorously researched and only released if they will only impact the intended invasive species. Many non-native species have natural checks and balances in their native range that don’t exist in the introduced range. For example, in the 1940s, St. John’s Wort (Hypericum perforatum) covered over 400,000 acres of Northern California’s rangeland. St. John’s Wort induces photosensitivity in livestock when ingested and threatened the cattle/sheep industry. A beetle (Chrysolina quadrigemina) that fed on St. John’s Wort was found in its native range in Europe. After the beetle was put through extensive tests to see if it would damage crops or wreak ecological havoc, it was released in California. Within 10 years this beetle had reduced St. John’s Wort to just 1% of its original range, saving California an estimated $3,500,000 per year between 1953 and 1959 (Shelton, A).
  • Chemical. Also a controversial control method, but if used correctly an invaluable tool in any ecologist’s toolbox. Many invasive species cannot be managed with cultural or mechanical methods, and no effective biological control agent has been found for them yet. Tree of heaven (Ailanthus altissim) is one of many such invasive species. It grows in dense monocultures and releases allelopathic chemicals, meaning it inhibits other plants from growing near it (Heisey 1990). If you simply try to cut one down, it will send up shoots all around the stump. The only viable method of controlling tree of heaven is called cut-stumping. Cut-stumping involves painting on a small amount of concentrated herbicide on the phloem of a freshly cut stump. This method will treat the invasive species without causing unintended damage to native plants.

Here at the Reserve

I am just starting to learn the native and non-native plants of the Ecuadorian cloud forest but one thing that struck me right away was how few invasive plant monocultures I saw at the Reserve. In the Bay Area or western Montana, one didn’t have to look too hard to see an invasive species taking over. At the Reserve, there is no shortage of plant life, but there are no monotypic stands of invasive plants that we have found. Except one. Many years ago, Brazilian red-cloak (Megaskepasma erythrochlamys), was planted around the lodge to attract hummingbirds. Despite the common name, it is a mid-sized shrub native to Venezuela. As with the introduction of most ornamental plants that become invasive species, it was done with good intentions. Unfortunately, Brazilian red-cloak is a voracious grower and has few natural checks to keep it from out-competing native plants. Simply cutting it down just spreads the plant. It can re-root from just about any piece of stem, even one that is just a few inches long. When Mary and I got here, we found that red-cloak surrounded the lodge to the depth of a few meters, and it was advancing into the forest. We have been working hard to get the Brazilian Red-Cloak under control and we are excited to choose native plant species with which to replace it.

So what can an individual do?

  • Clean your outdoor gear. Especially your boots, socks, and bottoms of your pant legs and undercarriage of your car if you’re driving off-road. While this is a good idea when traveling locally, it is especially important before traveling long distances. Seeds can be very small, and travel in the soil or as burs stuck to clothing. Throw any seeds in the trash. It is also important to clean your waders and boat if you are traveling between water bodies.
  • Plant locally native plants. They are often better adapted to local environmental conditions and provide food and habitat for wildlife.  The Xerces society will often have regional guides that focus on native plants that benefit pollinators. You might also be able to find local chapters of native plant societies. They can provide great information and often have native plant sales. Don’t plant anything from the internet called something like “native wildflower mix” unless it specifies to where specifically it is native.
  • Manage invasive species on your own property. It is a good idea everywhere and some states like Montana you have a legal obligation to remove noxious weeds on your property.
  • Write to your local city council and ask them to landscape with native plants. I linked a great podcast below about how urban forestry can create habitat for wildlife.  
  • “Burn it where you buy it” We hear the phrase all the time. It boils down to: don’t travel more than 30 miles with firewood. It can be an easy vector for invertebrates and plant pests.
  • Never dump pets, the contents of an aquarium (including the fish), or houseplants in the wild.
  • Volunteer with your local land management agency. All land management agencies from local parks to the National Park Service must do invasive species management. Many agencies are underfunded and unstaffed and really appreciate volunteers helping out.
Volunteers planting native plants at a restoration site in the Golden Gate National Recreation Area (Credit: Aidan Sullivan)

Thank you for sticking around through the end. Something I didn’t get a chance to touch on was invasive pathogens. Sudden Oak Death (SOD), Rapid Ohia Death (ROD), White-nose syndrome, chytrid, and even the death of the American chestnut are all caused by invasive pathogens. Maybe I will do my next blog post about that. Hopefully, this blog post inspired you to plant some native species in your yard or volunteer with your local land management agency. Or hey, you could even volunteer here at the Reserve.

Awesome podcasts

Work Cited

Early, R., Bradley, B., Dukes, J. et al. Global Threats from Invasive Alien Species in the Twenty-First Century and National Response Capacities. (2016) Nat Commun 7, 12485.

Heisey RM. Evidence for allelopathy by tree-of-heaven (Ailanthus altissima). J Chem Ecol. 1990 Jun;16(6):2039-55. doi: 10.1007/BF01020515. PMID: 2426400

Invasive Species Advisory Council (ISAC) Invasive Species Definition Clarification and Guidance (2006)

Knapp P. A. Cheatgrass (Bromus tectorum L.) domi­nance in the Great Basin Desert: History, persistence, and influences to human activities. (1996) Global Environ. Change 6(1):37–52.

The National Wildlife Federation (NWF) Invasive Species,and%20economy%20cost%20billions%20of%20dollars%20each%20year.

Shelton, A. Eccleston, J. Successes in Biological Control. Cornell University

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