EPOW - Ecology Picture of the Week

Explanation:  Pretty yellow flowers, you say?  They belong to a terribly invasive weedy shrub called gorse.  We are on the Big Island of Hawai'i at about 6,000 feet elevation on the southern flank of Mauna Kea.  Before us stretches a foggy landscape, not of native island flora, but mostly of an introduced spiny shrub -- gorse -- that has spread to cover much of the land.  

Helping to disperse this weedy invader are introduced cattle ... and roads created by "introduced" humans.  

Although the cattle can trample and kill some of the gorse, the cattle are numerous and damaging enough to the ecosystem themselves that there has been an annual lottery for being able to shoot them.  No, the same does not exist for controlling tourists.

Gorse was originally introduced as an ornamental from the Mediterranean region and has become a noxious weed in many parts of North America as well as here on Hawai'i.  Its spiny branches cling well to passing mammals, probably including livestock.  

Thus, gorse spreads ... becomes a fire hazard in some drier ecosystems ... and outcompetes much of the local native plant life.  

This brings us to a tiny hero, the Gorse Spider Mite.  It is used on Hawai'i and elsewhere, such as in New Zealand, as a biological control agent  The mites produce a webbing and can generate such numbers that kill gorse plants.  

However, local coccinellid beetles ("lady bugs") and native predatory mites might prey on the introduced Gorse Spider MItes, reducing their effectiveness.  Oh what a tangled web we -- and the Gorse Spider Mite -- weave, when first we practice uncontrolled introductions of exotic species.  

Other measures to control gorse can include mechanical ripping, chemical and herbicide treatment, introduction of other insects as biological control agents, and controlled fire.  

In Hawai'i, gorse is being successfully controlled at least on Molokai'i island.  But it remains a battleground in much of its introduced range in many parts of the world.