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Gorse Crisis: Making Way for Native Plants

Amanda and Amy remove some invasive gorse.

It goes without saying that wild bird populations are dependent upon good quality, natural habitat for foraging, nesting, and escaping from predators, to survive. The native forest birds of Hawaii face a multitude of threats, and the loss and degradation of habitat is one of the primary reasons for the decline of these unique species. Invasive plants and animals are taking over and destroying their forest home. For example, introduced pigs and deer browse on the plants and churn up the forest floor in search of food, killing native seedlings and providing an opening for faster-growing, invasive plants to gain a foothold in native environments. In many cases, in order to restore native plants, we must first remove the nonnative ones.

Gorse in bloom. Note the nasty thorns!

Gorse is one such invasive plant common in parts of Maui as well as the Big Island. The dense, prickly shrub, introduced to Hawaii in the 1800s, originated in western Europe, where it is still valued as a living fence for livestock. In addition to its aggressive tendencies, gorse grows much more quickly than most of Hawaii’s indigenous species and easily out-competes them for space and sunlight. Today, gorse is considered to be a serious weed, and all attempts to eradicate it have failed. The International Union for Conservation of Nature recognizes gorse as one of the top 100 worst invasive species in the world; so far, the best-recognized method for combating gorse is to plant faster-growing plants that are able to shade out sun-loving gorse.

At the Maui Bird Conservation Center, we have our own gorse crisis. Fellow intern Amy Kuhar and I are tackling our gorse invasion head on. Because the gorse defends itself with innumerable thorny spikes, we have started by taking down different sections of the weed in phases. We start by trimming back branches with loppers, then we use hand saws to sever each plant at the base. When possible, we also dig out the roots. The process is very time consuming, and we have worked many hours on the project. “Painstaking” would be the best adjective to describe the effort, because the gorse fights back, and after an afternoon of gorse eradication, we are left with innumerable itchy, tiny thorns embedded under the skin of our hands, arms, and legs!

A mamane sapling planted at the MBCC.

In addition to rescuing resident koa, ‘ohia, and mamane trees choked by gorse around the facility, we also began the process of replacing the invasive vegetation with native plants such as `a`ali`i and more mamane. In one area alone, we have planted more than two dozen new trees and are excited to see them growing over the newly cleared area! But the battle does not end there. One of gorse’s greatest weapons is its massive production of seeds, which can lay dormant in the soil for many years. As the older gorse is cleared, the seeds rapidly germinate, and within a few weeks there is a bed of new gorse seedlings. To stay on top of these, we must spray with herbicide to prevent another new invasion, allowing the native plants to flourish.

Hopefully, future interns will continue to clear gorse to make way for more native planting, all of which will someday create habitat for our wild, feathered friends such as the `amakihi. We hope the native plants will also eventually provide a source of perching, nesting material, berries, and seedpods for the birds in our care.

Amanda Maugans is an intern at the San Diego Zoo Maui Bird Conservation Center.