Koa Demonstration Exclosures
LHWRP has been monitoring experimental koa demonstration exclosures in Kahikinui and Nu’u over the last several years. We will continue to work collaboratively with DOFAW to explore additional restoration techniques for secondary forest species to use in regional forest restoration. LHWRP will collaborate with Nick Dudley at the Hawaii Agricultural Research Center (HARC) and the Maui Koa Network to collect, genetically screen and plant regional koa. The goals of genetic exploration with koa are two-fold, 1) to screen for resistance to the highly damaging forest pathogen fusarium and 2) to create seed farms to encourage leeward Haleakalā koa genetic augmentation to give maximum genetic resilience as we head into uncertainties of climate change and unknown diseases that could challenge koa forests in the future.
A 1-5 acre seed farm will be established in the leeward watershed
and out-planted with regional koa and additional native forest species that are seed limited and needed for holistic regional koa forest restoration. Four demo exclosures have been constructed and parallel experiments implemented in two (5 grass and 16 bare ground) to test similar treatments in the two different substrates, grass dominated and bare ground. Seed balls consisting of an inert, art-grade natural clay (free of any seeds or chemicals), filled with regionally collected ohi’a seeds, and a’ali’i seeds, and koa seeds inoculated with Bradyrhizobium, (a Nitrogen-fixing bacteria) were placed in plots consisting of disturbed, scarified, herbicide-treated and untreated substrate both inside and outside the grass exclosure, and on rocky and bare ground in the bare ground exclosure. Initial monitoring at both sites had some germination occurring both inside and outside the exclosures. Monitoring will be continued on a quarterly basis for several years to determine and compare the long-term effectiveness of all treatments. Koa, a’ali’i, and ohi’a seedlings are growing at the nursery now for the other two exclosures, which will be testing different restoration methods including out-planting.
The southern leeward slopes of Haleakala are in a rain shadow and depend on a temperature inversion between the mountain and coast to create the vertical lift required to form low level clouds and naulus rains (Leopold1949). Tree foliage intercepts these low-level clouds and rakes the precipitation out of them creating fog drip. Fog drip contributes a significant proportion of the total precipitation these leeward forests receive. Removing trees from fog drip zones can eliminate fog drip and lead to dramatic deficiencies in rainfall. Recent studies in Hawaiian forests have shown that forests comprised of native trees use less water than forests dominated with non-native trees, thereby promoting groundwater recharge. Restoration of a highly diverse and highly degraded dry forest at Auwahi, Maui has transformed the vegetation from grazed non-native pastureland to a native shrub understory with scattered remnant native trees. An initial rapid hydrologic assessment performed by Perkins et al. with the USGS at Auwahi showed promising results with the forest restoration site having greater soil hydraulic conductivity, subsurface wetting, and hydrophobicity.
Thanks to support from the Department of Water Supply, preliminary findings from soil moisture studies at Auwahi show that these vegetation changes have led to three important signs of recovered
hydrologic function in the restored area compared to the non-native grasslands: 1) soil moisture transfers more rapidly down through the soil column, 2) soil moisture reaches greater depth, and 3) soils maintain a cooler and less variable temperature across depths. LHWRP is encouraged by these findings within the watershed as we launch into large scale restoration efforts with hopes of recovering both biogeochemical and hydrological processes for increasing watershed function.
Click to download the following research paper on EcoHydrology: Assessing effects of native forest restoration on soil moisture dynamics and potential aquifer recharge, Auwahi, Maui – Perkins et al. 2014