Final Comprehensive Conservation Plan - U.S. Fish and Wildlife ...

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
„akiapōlā„au. In addition, natural regeneration of koa through root sprouting and seed is also
occurring in planting areas (USFWS 1996b).
The survival rates of these koa reforestation efforts and studies have produced varying results, with
differences mainly attributed to microsite conditions such as soil depth, moisture content, rockiness,
and exposure to weather and sunlight. Survival rates are also affected by elevation, drought, spacing,
topography, and other annual climatic differences (USFWS 1996b). In general, poorer survival rates
occur at higher elevations than lower elevations as a result of frost. Frost protection devices have
been designed to enhance seedling survival and growth. Set up on the east side of the seedling, these
devices are the most cost-effective and least labor intensive technique (USFWS 1996b, Jeffrey, pers.
comm.). Scowcroft and Jeffrey (1999) found that use of this device increased survival from 15-
100 percent. By blocking the night sky, the frost protection devices reduce radiative cooling and
moderate leaf temperatures (Scowcroft et al. 2000). They also increase moisture by catching fog or
mist. Spacing may have a minor affect on survival rates, with 84 percent survival for seedlings
spaced 6.6 ft apart and 74 percent survival for seedlings spaced 8.2 ft apart (USFWS 1996b). The
average spacing for corridor plantings at the Refuge is a grid of 12 ft.
Seedling survival is also dependent on site preparation methods. In an experiment where discing,
burning, herbicide treatment, hand scarifying, and no treatment were used, discing a continuous 6.6 ft
strip proved to be the most effective method for preparing a site for planting, but erosion proved to be
a problem (USFWS 1996b). When an existing seed bank is present, mechanical soil scarification can
also enhance koa regeneration (USFWS 1996b, Jeffrey, pers. comm.). Since 1996, the Refuge has
used a modified bulldozer blade attachment to scarify the ground for koa outplanting. A 3-ft wide
“mini blade” is attached to the bulldozer blade. As the dozer moves forward, the blade is dropped,
scraping the grass off a 3 ft wide by 3 ft long area, exposing the top soil. Koa seedlings grown in
dibble tubes are then planted in the sites by volunteers. The planters follow the bulldozer tracks
through the grasslands, poking holes in the ground within the scarified sites with a dibble stick. Three
holes, 8 in deep and a 1 ft apart are made at each site. The koa seedling is planted into the center hole
and fertilizer is placed in the other two.
4.10.2 ‘Ōhi‘a (Metrosideros polymorpha)
„Ōhi„a (Metrosideros polymorpha) is the dominant species on lava flows and in mature native rain
forests in the Hawaiian Islands. Occurring from sea level-9,515 ft, „ōhi„a has a wide ecological
distribution colonizing habitats of various elevations, substrate ages, soil moistures, and temperatures
(Cordell et al. 1997, Mueller-Dombois and Fosberg 1998, Friday and Herbst 2006, Crawford et al.
2008). „Ōhi„a is reported in dry areas with less than 16 in of annual precipitation, as well as wet
forests with more than 400 in per year. Furthermore, „ōhi„a can thrive in various soil types, including
nutrient-poor sites, and are shade tolerant (Friday and Herbst 2006, Crawford et al. 2008). This
endemic tree is considered a pioneer species because it is one of the first species to establish on
recent volcanic lava flows. As a result, „ōhi„a forests tend to be comprised of relatively even-aged
trees (USFWS 1996b, Mueller- Dombois and Fosberg 1998).
„Ōhi„a is a slow growing species. On average, „ōhi„a are estimated to grow 12 - 24 in in height
annually and by 0.04 - 0.12 in in diameter each year (Hatfield et al.1996, Friday and Herbst 2006).
Seedlings grow between 2 - 4 in each year (USFWS 1996b). In spite of the slow growth rates, „ōhi„a
can grow up to 100 ft tall and reach a peak diameter of 85 in (Wagner et al. 1999, Friday and Herbst
2006). Thus, the species has a relatively long lifespan. Some trees have been dated to approximately
4-78 Chapter 4. Refuge Biology and Habitats