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Characteristics of an Invasive Species
Top 10 Pests in West Maui

Feral Cattle trample soils and uproot native plants Photo: Chris Brosius
Pampass Grass (Cortaderia selloana ) Photo on CGAPS website
Strawberry Guava (Psidium cattleianum) Photo: Forest and Kim Starr
Tibouchina herbacea Photo: Forest and Kim Starr
Clidemia hirta Photo: Forest and Kim Starr
Feral pigs cause enormous damage to the watershed
Axis Deer are becoming a larger problem in Maui Photo: Star Bulletin
Small mammals, like the mongoose, eat bird eggs and spread disease.
Plant pathogens, like Endoraecium acaciae, can severly harm our native forests. This pathogen affects specis of Koa trees. Photo: Don Garnder,
Invasive insects can be harmful in many ways, like the fruitflies are to our agriulture!

A Silent Invasion

A silent invasion of Hawaii by insects, disease organisms, snakes, weeds, and other pests is the single greatest threat to Hawaii's economy and natural environment and to the health and lifestyle of Hawaii's people.

Pests already cause millions of dollars in crop losses, the extinction of native species, the destruction of native forests, and the spread of disease. But many more harmful pests now threaten to invade Hawaii and wreak further damage. Even one new pest - like the brown tree snake - could forever change the character of our islands.

Stopping the influx of new pests and containing their spread is essential to Hawaii's future well-being.

Exerted from "A Silent Invasion", a  presentation by the Coordinating Group on Alien Pest Species

What is an invasive species?
What can I do to help?

Characteristics of an Invasive Species

Invasives species grow quickly, spread easily, and out-compete others for food, water and living space.  They are better at survival than our native plants, animals, and insects, most likely because they came from a place where competition was stiff.  Or perhaps they do better in Hawai'i because their natural predator doesn't exist here, so there's nothing to keep it in check.

Here's a list of characteristics of invasive species [link to 'invasive plants' pdf] and the advantages they have.  Excerpted from the Ho'ike curriculum - an environmental education curricula designed by and for teachers.  Available at

Top 10 Pests in West Maui

1. Pampass grass
2. Strawberry guava
3. Tibouchina and Clidemia
4. Fire
5. Feral Ungulates
6. Small mammals
7. Forest pathogens
8. Invasive insects
9. Global Warming
10. Humans

1. Pampas grass - Pampas grass is a large bunchgrass from South America. The leaves are narrow and have sharp, serrated edges, and the showy white to purple flower plumes are sometimes used in floral arrangements. Both species of pampas grass are considered serious pests in California and New Zealand, where they out compete native species and create a fire hazard. Both species of pampas grass were planted as ornamentals in upcountry Maui, and Cortaderia jubata has spread to other yards, pastures, and native forests.  Unfortunately it is also found in the most remote and unthinkable places within our watersheds.

2. Strawberry guava - Psidium cattleianum - Like other invasive species this plant creates forests all to its own. Shade tolerance, prolific fruiting, and genetic variability helps this species out-compete and displace other native vegetation. Establishing dense, single-species stands from primarily pig-dispersed seeds, this species also has the ability to leave a chemical in the soil that prevents other plants from growing there later. It has been estimated that a single pig can disperse around 8 million Strawberry Guava seeds a month during the peak fruiting season in a densely infested area (1). In the last two hundred years on Maui, this tree has dominated and claimed thousands of acres.  It's so good at reducing competition that it allows nothing else to grow under it, causing huge losses in forest complexity that is precious to our watershed.
(1. Excerpted from the Element Stewardship Abstract for Psidium cattleianum, The Nature Conservancy and Tim Tunison).

3. Glory bush and Koster's curse - Tibouchina herbacea and Clidemia hirta -  Like their taller cousin, Miconia (which has been found close to WMMWP lands), these plants also dominate the habitats in which they are established.  Standing three to six feet tall these plants tower over native shrub lands and and ground cover.  Found in moist areas of the watershed and seizing pockets of disturbance created by animals and humans alike, WMMWP is working hard to keep this species from spreading.

4. Fire - This living, breathing, and all consuming element is a current and historic threat to our dry forests.  Fire is not part of the Hawaiian ecosystem and it extremely damaging to our leeward native forests and shrub lands which are rare in Hawaii and even more so in West Maui.  Since 1998 more than 12,000 acres have been burned in West Maui, leaving openings in the forest which makes it exceedingly easy for invasive species to establish themselves and permanently displace native cover.  Species that take their place reduce forest moisture and make fires more common.  In times of drought even wet forests can be threatened by this problem.

5.Feral Ungulates - If you place a cow in a pasture, it will eat the most nutritious plants first, and leave the weeds for later.  They do the same thing in a native forest.  Feral ungulates such as pigs, goats, deer, and cattle were once domestic and have now established wild populations in the watershed.  Their selective palates can drive native plants to extinction.  In the wake of their browsing and digging weeds can become established.  If left unchecked, the native forests of West Maui will convert into a degraded forest that has a diminished capacity to provide the water you drink.  Wild populations of ungulates may drop feces and spread disease into our clean mountain streams.  Their digging also speeds up erosion, which washes silt and nutrients downstream, choking our nearshore reefs.

6.Small mammals - Small mammals like mongoose, mice, rats and cats cause considerable harm to watershed resources.  These animals spread diseases like typhus, toxoplasmosis, and leptospirosis  into our streams.  They can cause the extinction rare forest birds and other species by feeding on eggs, nestlings and adults.  Rodents often have an affinity for seeds and plants which can greatly reduce a plant’s reproductive success.

7. Forest pathogens - Currently the worst forest pathogen to come to Hawaii is 'Ohi'a rust,  Puccinia psidii; []  First detected in April of 2005 it has now spread state wide and severely impacted thousands of acres of non-native rose apple trees and infected several related species.  One of these is our native 'Ohi'a, the most common plant of our forest. Scientists hope that a more virulent strain of the disease does not become established in Hawaii.  Thought to have come to Hawaii on nursery stock from Florida or California this is an example of how bad things come in many different packages or forms from all over the world.   WMMWP supports careful inspection of imported materials to prevent the establishment of unwanted forest diseases.

8.Invasive insects - What's the size of pinhead and can render an object a billion times its size defenseless? The Erythrina Gall Wasp has become widely established throughout the state. First discovered in Hawaii in spring of 2005 it quickly spread and crippled host species including ornamental coral trees, and our precious native Wiliwili trees.  Wiliwili are being devastated by this little bug that lays its eggs in the leaves.  The leaves respond by forming galls which dramatically reduce the plants vigor and seed production.  This is yet another example of a pest that might have been detected with adequate screening and quarantine procedures.

9. Global warming - It might be "global" but this phenomenon effects even our local watershed. Small changes in the earth's temperature may lead to dramatic shifts in our forest structure at a rate which may upset its delicate balance. Global warming could cause local droughts, native species loss and increased fires.

10. Humans - Like it or not, we all have an impact on the environment that supports us.  The decisions we make day to day can either help or burden the fragile ecosystem that is our island home.  The watershed provides us clean and fresh water, but this resource is limited and its sustainability is tied to the health of our forests.  Do your part by educating yourself about invasive species so you can help prevent their establishment and secure our communities future. Support Watershed management in West Maui.

How you can help

To help stop the silent invasion of harmful plants, insects, and other pests, follow these tips from West Maui Watershed and other organizations:

* Living Responsibly - things you can do to minimize the negative impact of your daily actions

* Stop the Alien Invasion - tips from CGAPS, the Coordinating Group on Alien Pest Species

* Report-a-Pest - learn about Maui County's target species and join the early detection "eyes & ears" team from the Maui Invasive Species Committee.