Manoa Cliff Forest Restoration

Native sweet-smelling Hibiscus (Hibiscus arnottianus)

Now we’re getting into the meat of things. Helping restore a native forest has been one of the most satisfying things I’ve done here in Hawai’i.

The Manoa Cliff Trail is part of a very popular and well maintained trail system in the hills behind Honolulu. The restoration site is a fenced, 6 ac. area located at the confluence of Manoa Cliff, Puu Ohia, and Pauoa Flats trails. One of the main reasons this area was chosen was the fact that many native plants are still found there.

The native plants on O’ahu have a sad story to tell. Overgrazing by livestock in the 1800’s left the hills behind Honolulu (where the site is located) pretty much denuded. The immediate problems that caused at the time were erosion and water loss. Much of the rain that falls here is in the mountains (orographic lifting) and without montane forest acting as a sponge to hold and slowly release the water over time, fresh water was lost quickly.

So the answer, which made sense at the time, was to bring in non-native plants to help rebuild the watershed. Millions of plants were brought in, with an emphasis on quick-growing ones to help protect the watershed faster: aka weeds. The results, which mind you did help solve the water issues, have been an unmitigated disaster for native plants.

These kind of alarming statements are common with environmental issues. They are calls to action. But what action? Holding a fundraiser? Donating money to some 501(c)(3)? The great thing about the Manoa Cliff Forest Restoration is that you get to see clear, direct results of your efforts.

Take strawberry guava (Psidium cattleianum) for example. It is just one of many invasive plants found in the area. The problem is its aggressive growth: in areas where strawberry guava is established, it’s literally the only plant found.

Trail through monotypic stand of guava

Here are some of the other troublesome plants we have at the site:



Cutting and girdling trees

Gingers (Heydychium gardnerianum & H. coronarium) and Bamboo (Phyllostachys nigra) will also form monotypic stands and out-compete other plants. So a lot of what we have to do is control the invasive plants and give the native plants room to breathe. Our most common tasks are pulling weeds, girdling plants, and cutting down trees. This is as direct conservation as you can get.

What has surprised me is just how much I’ve enjoyed these tasks. Imagine Godzilla.

And Tokyo is whatever stand of invasive plant is in my way. Oddly, it has been very therapeutic for me to take out whatever frustrations that has built up on these stands of non-native plants. Those invasives don’t have a chance!

But the ultimate joy is seeing the results of your hard work over time. The project itself was initiated about 5 years ago. To go from this:

All guava, all the time

To this:

… is quite the satisfaction.

Through all this what I’ve learned is that even with all these issues, all these problems that are causing the contraction of range and eventually extinction of native plants, this is still their native habitat. We don’t have to hook up monitors and watch them 24/7. We don’t have to put additives into the ground. They will still grow. Its nice to know that if we do our part, the plants will do theirs. Clear the invasives, and the native plants will grow. That realization is quite a marvelous thing.

Hope for the future

We have public workdays ever 1st and 3rd Sunday of the month. If you are on O’ahu and would like to join us, please visit

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