Using Native Plants to Outcompete Invasive Plant Species

Dense growth of Sporobolus airoides along a path in New Mexico

I’ve listened to and participated in many discussions about how to outcompete invasive plants using native plant species. Competition could be used to prevent new invasions or to aid in restoration after removing invasive plants. A recent article in Restoration Ecology reports results of a sowing study done in Hungary looking at native grassland species competing against three different invasive plant species. They note that the timing of seed germination of the native and invasive species was similar and that as you might expect, high seeding rates of the native species increased their early competitive ability. A perennial grass species was the most competitive against the three (non-grass) invasive plant species.

Csákvári, E., Sáradi, N., Berki, B., Csecserits, A., Csonka, A.C., Reis, B.P., Török, K., Valkó, O., Vörös, M. and Halassy, M. (2023), Native species can reduce the establishment of invasive alien species if sown in high density and using competitive species. Restor Ecol, 31: e13901.

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Flowering Rush a Threat to Wetlands

Controlling flowering rush in Mentor Marsh, Mentor, OH

Introduced as an ornamental plant, and perhaps also accidentally introduced through ballast, flowering rush, Butomus umbellatus, has spread into lakes, ponds, marshes, and irrigation ditches across southern Canada and the northern United States. Several characteristics make it a great invader. It comes in two forms, a flowering diploid and a seldom-flowering triploid. Although diploid populations produce numerous seeds, both types tend to spread mainly through vegetative reproduction. They both produce rhizome buds that easily break off and float to new sites. Diploids also produce vegetative bulbils in the inflorescences. They can grow submerged, although their biomass declines in deeper water. The plant is hardy to zone 3, and in its native Europe grows from Spain to Finland.

File:Butomus umbellatus Sturm04007.jpg
Illustration by Jacob Sturm, 1796

When it isn’t flowering, the leaves tend to blend in among other aquatic vegetation like cattails, sweet flag, burr-reed, and iris. The sword-like leaves are weakly triangular in cross section.

Dr. John D. Madsen, researcher with USDA ARS, has been studying control methods for flowering rush and has several papers published on chemical, mechanical, and drawdown techniques,

Still sold in the nursery trade, the plant is listed as a noxious weed in several states.

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Japanese eelgrass in the Pacific Northwest

My dad was out kayaking on a slough near Newport, OR with some botanists and learned

Japanese eelgrass rests on the muddy edge of a slough near Newport, OR.

about Japanese (or dwarf) eelgrass, Zostera japonica.  It often occurs in the same locations as the native common eelgrass, Z. maritima, but higher in the intertidal if both species are present.  It has narrower and shorter leaf blades than common eelgrass.

Japanese eelgrass probably arrived in the 1930s in shipments of Pacific oysters.  It reproduces prolifically by seed and spreads by rhizomes.  It has established from Humboldt Bay in CA north to the Strait of Georgia in Canada.

You can read an excellent summary about this eelgrass written by Levy Hay at University of Washington in 2011.

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Hybrid Tumbleweeds

In another couple months the tumbleweeds will be rolling along in the western United States.  Wells and Ellstrand (2016) at the University of California – Riverside documented a new hybrid species of tumbleweed, Salsola ryanii, rapidly expanding its range.  Salsola ryanii is an allopolyploid species with 2 complete sets of genes from its parent species, S. tragus and S. australis.

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Eating invasives

Spring is here and along with it some of the more edible invasive plants.  Anyone for a dish of knotweed kimchi or garlic mustard pesto pasta?  Pittsburgh has gone to great lengths developing edible uses for Japanese knotweed, Fallopia japonica.   One business sells it by the pound to enterprising brewers and bakers.  Watch a video from the Wall Street Journal on Pittsburgh’s knotweed gourmets here,

The ultimate online resource for eating invasive plants (and animals) is probably Eat the Invaders.  Here you can find all sorts of information and recipes on edible invaders.  Bon appetit!

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Murdannia keisak is making a name for itself

According to the Virginia Department of Conservation and Recreation Murdannia has no known common name and generally goes by Anielema, its former Latin name.  The USDA PLANTS website calls it wartremoving herb and calls it marsh dayflower.  Maryland Extension calls it marsh dewflower or Asiatic dayflower.  The leaves and stems do resemble Asiatic dayflower (Commelina communis).  I don’t know about it’s wart-removing powers.

Murdannia keisak

Murdannia keisak in a marsh on the Maryland Coastal Plain.

Look for mats of Murdannia keisak in freshwater ponds and marshes and along the edges of streams and canals.   It probably arrived in the US from eatern Asia in the 1920s or 30s as a weed of rice cultivation but it has unfortunately spread to natural areas.  It forms dense mats blocking light to plants below. Plants produce thousands of small seeds eaten by ducks and other waterfowl, and the plants spread vegetatively.

Small stands could be hand-pulled before flowering taking care to remove all fragments of the plant.  Larger stands are usually treated using biodegradable herbicides.

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Giant knotweed keeps coming up

Wallace Kaufman pauses on the battlefield

Wallace Kaufman pauses on the battlefield

Wallace Kaufman and Knot-weed stalks

April 24, 2015. Along the west bank of Poole Slough, 4 miles east of the Pacific Ocean and Newport, OR.  Here begins the first battle of the third year against the dense stand of giant knotweed that took over about an acre of land where an old barn and a few apple trees stood 60 years ago. When the first battle began in late summer 2012 the knotweed stood in an almost pure stand, stalks up to 10 feet high and two inches thick, two or three stalks from one root, plants 6 to 12 inches apart. Although I cut before they flower, the roots send out new stalks all summer and again in the spring. The stalks are hollow cylinders closed off at knots every 6 to 12 inches. Dried stalks make good pan pipes and flutes. Fresh young stalks can be peeled and cooked as vegetables.

Since the plants begin storing carbohydrates in the roots in early summer, I’ll cut again then and again in the fall. As the lower growing natives begin to compete, the prospects are that I can begin regular mowing with a blade set high to allow low natives to grow while preventing the knotweeds from replenishing their roots.

Each year the stand has been slower growing, stalks slimmer, and height diminished. Here is a scene from the very first attack 3 years ago.



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Water hyacinth used for counteracting algal blooms

In a controversial experiment in Florida, researchers are stocking King’s Bay with floating pens of water hyacinth (Eichornia crassipes) to reduce algal blooms.  Water hyacinth was removed from the bay beginning in the late 1950s, but Hydrilla replaced it and now algal blooms have become an issue in the lake.  Water hyacinth is good at removing pollutants from water and shading out algae.  In addition, manatees love it!

The pens also contain two other non-native species (called native in the original article), water lettuce and frog’s bit, considered less invasive by the some, but the article does not address whether these two plants would serve the same function as the water hyacinth.

Read more at the University of Washington’s Conservation web site and for updates see the Florida Springs Institute.

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