Invasive Plant Dispersal – Hitchhiker Awareness
Plant Dispersal
Plants disperse seeds using an impressive variety of techniques. This helps to maximize the distance between the new plant and the parent, which reduces competition for light, nutrients, and water. Some plants can disperse seeds on their own, while others need hosts or environmental factors to disperse. The most successful plants use a combination of seed dispersal methods, and this is especially true for invasive species.
There are six main methods of dispersal:
- 1) Gravity – Seed falls to the ground dispersing close to the parent plant, unless combined with other methods like wind and/or water.
- 2) Wildlife Ingestion – Birds are primary spreaders and their droppings spread invasives great distances. Certain berries have a laxative effect on birds that help spread berries even further.
- 3) Phoresy – The seed travels on the body of another, using adaptations such as hooks, barbs spines facilitate seeds in doing this.
- 4) Ballistic (Explosive dehiscence) – Under the right timing and with some pressure, seeds explode away from parent plant.
- 5) Wind – Seeds are blown off parent plant and travel across surfaces until meeting an obstacle.
- 6) Water – Floating seeds travel with the currents establishing downstream from parent plant.
Species Examples:
Gravity
Wild Cucumber (Learn more)
An annual plant that produces prickly, oval-shaped fruit which release the plant's seed directly below when it has reached maturity.
Photo Credit: Green Thumb Photography
Wildlife Ingestion
Glossy Buckthorn (Learn more)
Seeds of this perennial are primarily spread by birds. They are low in nutritional value so birds are required to consume more than native berries, and they also have a laxative affect.
Photo Credit: Green Thumb Photography
Phoresy
Common Burdock
The burr (seed or dry fruit or infructescence that has hooks or teeth) of this species contains 40 seeds on average and a single plant can have 100 burrs. The burr is carried by passerby's until they are eventually removed in a new area.
Photo Credit: Green Thumb Photography
Ballistic
Himalayan Balsam (Learn more)
Explosive to the touch these seeds are launched meters from the parent plant.
Photo Credit: Green Thumb Photography
Wind
Giant Hogweed (Learn more)
Each plant can contain up to 10,000 winged seeds. The high stalks of this plant persist into winter, the winged seeds then blow off easily catching the wind, drifting over hard snow to new locations. The wings also allow this seed to float and establish downstream.
Photo Credit: Green Thumb Photography
Water
Yellow Flag Iris (Learn more)
Each 2-4 inch seed pod contains hundreds of small brown seeds. Seeds have a hard casing with an attached air pocket that is designed to help them float. They can remain buoyant for over 7 months, and this allows them to travel downstream and establish in wet soils.
Photo Credit: Green Thumb Photography
Human Impact on Dispersal
Humans disperse seed both accidentally and intentionally. Accidental introductions can be avoided if recreationalists:
- Stay on the trail
- Clean their boots with a boot brush before and after leaving a site.
- Brush off their pants, bags and pets before and after leaving a site.
A study done in Illinois tested the effectiveness of boot brush stations by looking at the seeds found underneath a brush stationed at the head of a trail – they confirmed the presence of over 39 seeds (14 from invasive species). It is important to take the time to clean our gear, pack a boot brush to ensure you always hike responsibly!
Intentional introductions are sometimes done by well-meaning recreationalists looking to beautify a space.
One common mistake made is by those who purchase wildflower seeds to plant in ditches. Many people mistakenly believe they are helping pollinators in doing so. Unfortunately, these packets often contain invasive species, and many packets don't list what species they contain or even misrepresent their contents. Pollinators thrive in rich biodiverse habitats which invasive species do not support. Please never buy wildflower mixes.
Learn more about invasive species by taking our course and becoming a certified spotter.
(Coming Soon)
