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Our third and final service learning for the Fall 2014 semester was held at Piliokahe (also known as ‘Tracks’) Beach Park on the west side of O’ahu, near Kapolei. This site is the most publicly accessible and picturesque of the restoration locations we have visited. So picturesque in fact, that not one, but *two* wedding parties visited the beach during our morning restoration activities to take wedding photos.
Like the other service learning events, Bruce Koebele supervised the students and provided the native plants for the restoration. Unlike the other locations, this site is an open recreation beach, meaning the dune ecosystems in Piliokahe are threatened not just by invasive plants, but also by human and vehicular disturbances, all of which can severely erode the sandy dunes. UHWO students worked on two locations at Piliokahe. The first was a dune overtaken by invasive buffelgrass (Cenchrus ciliaris), and the second was a dune that had been partially restored by Malama Learning Center, but which was facing severe erosion before the native plants could establish root systems large enough to protect the sandy soil.
First Location: dune covered with invasive buffelgrass
As with the other locations, our first step here was to remove the invasive buffelgrass. Buffelgrass was introduced to Hawaii in the early 1930s and is native to Africa and tropical Asia. Buffelgrass is particularly problematic because it is fire-adapted, having a low ignition threshold and the ability to quickly reestablish after fire. Native Hawaiian plants along the dunes are not fire-adapted, so this shift in disturbance regime allows buffelgrass to rapidly dominate the habitat after being introduced. Unlike our other restorations, where we fully dug out invasive plants, we wanted to retain the buffelgrass root systems to protect the sandy soil from erosion. For this removal, then, we simply gave the buffelgrass a ‘haircut’ (as Bruce likes to say), while keeping the root system relatively intact. Bruce had sprayed much of the buffelgrass with an herbicide prior to our arrival, to make it easier to remove. The remaining grasses would be hit again with an herbicide to give the native plants a good chance of establishing.
The herbicide treatment was particularly relevant for my biology students as the herbicide Bruce uses specifically targets monocots (the buffelgrass) while not affecting the native eudicots. Last week’s lab focused on the physiological differences in these two groups (leaf venation, internal structure of stems and roots, etc) but the herbicides act on a biochemical differences in acetyl coenzyme A in each group (which is important in lipid synthesis). The herbicide inhibits production of acetyl coenzyme A in monocots, which disrupts cell division in the meristematic tissue (growth regions) of the grass stem and ultimately kills the plant.
As with the other sites, our restoration here involved three steps: 1) remove invasive plants, 2) prepare the ground for planting (dig a hole and fill it with water) and 3) plant native plants. The plants Bruce provided for this ecosystem included:
‘Ohelo kai oh-hello-kye (Lyceum carolinianum var. sandwicense) In Hawai’ian, kai means water or sea, and ‘ohelo kai has berries that are similar to the ‘ohelo plant that grows on Big Island, hence the name ‘ohelo kai (‘ohelo by the sea).
Pa’u-o-Hi’iaka, pah-ooh-oh-hee-eee-ah-ka (Jacquemontia ovalifolia subsp sandwicensis) this vine is said to have protected Hi’iaka, the infant sister of the volcano goddess Pele, from the harsh Hawaiian sun as she lay on the beach while Pele was fishing. Pa’u-o-hi’iaka translates to ‘the skirt of Hi’iaka’ and can also be used to treat thrush. The vine produces rather pretty thick green leaves and small bluish purple flowers. Pa’u-o-hi’iaka already spreads throughout the dune areas where our restoration was taking place, and mature plants can be seen in many of the photos below.
‘Akulikuli, ah-coo-lee-coo-lee (Sesuvium portulacastrum) This indigenous shrub is common in coastal areas, marshes, lagoons, and rocky shorelines and can grow directly out of exposed coral beds. It is so well-adapted to shore life that it can take up moisture directly from sea-spray off the ocean, despite the salt content of this water source. ‘Akulikuli bears a strong physical resemblance to the invasive pickleweed, and the two are sometimes confused.
Naio, nye-oh (Myoporum stellatum) This rare shrub is found only in Kalaeloa and Nanakuli, and was part of our restoration at Kalaeloa Heritage Park last month. Our site today is found between the two current populations of naio, and so was a likely habitat for this plant in the past. Despite being quite rare, naio is not listed as endangered. It was sometimes substituted for ‘iliahi during the sandalwood trade, giving it the unfortunate nickname of ‘bastard sandalwood.’
Ma’o, mah-oh (Gossypium tomentosum) Known as Hawaiian cotton, this shrub is federally listed as vulnerable and is a close relative of commercial cotton (Gossypium hirsutum). Ma’o is much more resistant to herbivory by insects than G. hirsutum, and the two have been bred in order to confer insect resistance into G. hirsutum. Ma’o also produces yellow flowers which can be used to create a vibrant green dye.
Bruce and his crews had previously restored a nearby dune last year, and the plants there have established quite well. We hope in a year that our dune will look this good!
Second Location: dune threatened by erosion
The Malama Learning Center provides hands-on learning experiences to link art, science, conservation, and culture in order to promote sustainable living in Hawaii. One such learning experience in August of this year focused on restoration at Piliokahe Beach. Unfortunately, the dune restored during that exercise did not retain enough underground root mass to prevent significant wind, water, and human-caused erosion to threaten the native plants on the dune. Malama Learning Center built a series of small terraces to aid in soil retention, but more effective, longer-term means of soil retention and erosion control were still needed. Since this dune had already been cleared, our efforts focused solely on planting new plants lower on the dune to protect the bottom half from erosion. Later this month, Bruce will return with students from Leeward Community College in Pearl City to plant on the upper portion of the dune to protect the dune from erosion higher up. We planted only two plants on this dune, specifically chosen by Bruce to aid in soil retention. Bruce also strategically placed the plants to maximize their effect (as opposed to letting the students choose locations, as has been the case in other sites).
Pohinahina, poh-hee-nah-hee-nah (Vitex rotundifolia) This indigenous shrub is named for its tendency to pohina or ‘fall over’ as it grows. Pohinahina has aromatic leaves described as sage-like in smell, which are used to make lei. Rapid nodal rooting and vegetative reproduction create dense mats reaching up to 10 feet from the parent plant, making pohinahina excellent for erosion control and soil retention.
‘Aki’aki, ah-kee-ah-kee (Sporobois virginicus) This indigenous grass is common along many Hawaiian coastlines. ‘Aki’aki forms extensive underground root and stem systems, making it also an excellent choice for erosion control and soil retention.
Currently, there is no signage indicating restoration efforts in this area, meaning much of the human disturbances (though walking, dune sliding, and all-terrain-vehicles) of these dunes may be unintentional and preventable. To assist in reducing human disturbances, restoration groups active in the area are considering posting small signs informing the public that restoration is currently active in this area. Hopefully, such signage may support the efforts of the students and other groups and allow the native plants to establish and grow uninhibited.