The mamane-naio ecosystem is a dry, high elevation forest and shrubland that occurs in a ring around Mauna Kea Volcano from approximately 2000 meters elevation to treeline at 2850 meters (6,600 to 9,400 feet). It is dominated by two tree species, mamane (Sophora chrysophylla) and naio (Myoporum sandwicense). This habitat type has been severely impacted throughout Hawaii by cattle ranching, browsing by feral sheep and goats, and fires. Mauna Kea supports the best remaining example of this habitat type, and the largest area of intact mamane-naio forest occurs on the southwestern slope of Mauna Kea near Puu Laau.
The area is characterized by steadily sloping terrain that is punctuated by steep volcanic cinder cones. The soil is cinder or loosely compacted volcanic ash. The forest is fairly low in stature, with the largest trees only 10-12 meters tall. Trees grow slowly in this cold, dry environment. Large mamane trees often have a twisted, ancient-looking growth form, and even small trees may be quite old. The forest becomes more stunted at higher elevations, eventually giving way to montane shrubland and then bare ash, cinder, and rock toward the 13,796 foot summit of Mauna Kea. Rainfall is low, less than 400 mm (15.7 in) per year over the western slope, but clouds and mist roll up from the lowlands on many afternoons, providing another source of moisture. Rainwater runs off or percolates rapidly due to the steep terrain and porous volcanic soil. Freezing temperatures occur on many nights, especially during the winter months, but snow is infrequent and occurs only at the upper limit of the habitat in association with winter storms.
Mamane-naio forest also occurs at similar elevations on Mauna Loa and Hualalai and formerly occurred at lower elevations, but it has been more severely degraded in those areas, and on Mauna Loa it does not extend as high in elevation due to more recent volcanic activity.
The mamane-naio forest on Mauna Kea contains the entire world population of Palila (Loxioides bailleui), a Hawaiian honeycreeper endemic to the island of Hawaii, and the last finch-billed honeycreeper in the main islands. Adult Palila feed almost exclusively on mamane seed pods and also nest primarily in mamane. Roughly 96% of the Palila population occurs on the southwestern slope of Mauna Kea where the widest and most intact belt of mamane forest exists. A few Palila occur in remnant forest on the southern slope of Mauna Kea, and a few were found near Puu Kanakaleonui on the eastern side of Mauna Kea, but none have been observed there for several years. A combination of translocations and releases of captive-bred birds has resulted in establishment of a small Palila population in a mamane-naio forest remnant on the northern slope of Mauna Kea near Puu Mali. The population of Palila at Puu Mali is still very small (less then 20 birds), but in 2006 there were several successful nests.
The mamane-naio forest also supports populations of several other endemic birds. Hawaii Amakihi (Hemignathus virens) are particularly abundant and reach some of their highest known densities, up to 940 birds per square kilometer. Apapane (Himatione sanguinea) and Iiwi (Vestiaria coccinea) are less common but substantial numbers of these nectarivorous species may visit seasonally from lower elevations when mamane flowers are in bloom. This dry forest supports an isolated population of Elepaio that is currently regarded as a distinct subspecies (Chasiempis sandwichensis bryani) and is found only in this area. The Pueo or Hawaiian Short-eared Owl (Asio flammeus sandwichensis) is commonly observed hunting over the mamane forest and adjacent grassland. The Io or Hawaiian Hawk (Buteo solitarius) is rarely seen in this area. Small numbers of Akiapolaau formerly occurred in the mamane forest, particularly at Kanakaleonui, but they are now rarely observed.
The most serious threats to mamane-naio forest are browsing by non-native ungulates and invasive alien plants that displace native plants and provide fuel for fires. Predation by feral cats has been documented on forest birds including Palila, and mongoose (Herpestes auropunctatus) and rats (Rattus spp.) also may prey on birds and nests. Disturbance by vehicle traffic is a minor threat, but recent establishment of an off-road vehicle track has increased potential disturbance, introduction of alien weeds, and fire. Browsing by feral cattle, sheep, goats, and mouflon sheep introduced for hunting has degraded mamane-naio habitat over large areas for decades. Browsing lowered tree line, reduced tree density, and lowered productivity. In the early 1900s over 46,000 feral sheep, cattle, goats, and pigs were removed to protect the Mauna Kea Forest Reserve. Populations of sheep were allowed to rebuild and mouflon sheep were introduced to promote sport hunting, again causing widespread damage. The mamane-naio forest on Mauna Kea was designated as critical habitat for the Palila in1977. Lawsuits filed under the Endangered Species Act resulted in court rulings that required all feral sheep, goats, and mouflon be removed from Palila critical habitat. Goats have been eliminated and sheep and mouflon have been reduced, but some areas still suffer from browsing. Fire is a serious threat to the dry mamane-naio forest, and fire risk is increased by accumulation of fine fuels from alien grasses and other weeds. Fire could directly destroy forest, and Palila could be deprived of food resources for several years until mamane regenerates. Fountain grass is a fire-promoting grass that forms monotypic stands and has become established on the southern and western slopes of Mauna Kea. Cape ivy threatens forest by climbing on and smothering native trees and shrubs. Gorse is a spiny shrub that occurs on the eastern slope and may spread from pastures below Mauna Kea Forest Reserve.
Land comprising the Mauna Kea mamane-naio forest IBA is owned almost entirely by the State of Hawaii. Some of the land is leased to the U.S. Army as part of the Pohakuloa Training Area. Onwership information was unavailable or unlisted for 8% of the area. Less than 1% of the land is privately owned, and these lands are narrow slivers on the edges of the IBA.
The Mauna Kea mamane-naio forest IBA consists of dry, high elevation evergreen forest and shrubland. Vegetation is taller in stature at lower elevations, with forest canopy height reaching a maximum of about 12 meters. The forest becomes progressively shorter and sparser as temperature and rainfall decline with increasing elevation, giving way to montane shrubland around 2750 meters. The dominant tree species are mamane (Sophora chrysophylla) and naio (Myoporum sandwicense). Areas of sparse ohia (Metrosideros polymorpha) forest occur in some lower elevation regions on the southern side of the IBA. Sandalwood (Santalum paniculatum) was much more prevalent historically, but most sandalwood trees were cut and exported over a century ago and recovery has been slow. Other widespread plant species include aalii (Dodonaea viscosa), akoko (Chamaesyce olowaluana), and, especially at higher elevations, pukiawe (Leptecophylla tameiameiae). The highest slopes of Mauna Kea consist of bare volcanic cinder and ash with very sparse herbaceous vegetation or none at all, and this habitat type occurs intermittently over the higher portions of the IBA. Habitat disturbance has been extensive throughout the area, due to browsing and grazing by cattle, feral sheep, and mouflon, and wildfires. Alien grasses introduced for grazing now dominate some areas, particularly fountain grass (Pennisetum setaceum), buffel grass (Cenchrus ciliaris), and in some lower elevation areas, kikuyu grass (Pennisetum clandestinum).
Two-thirds of the Mauna Kea mamane-naio IBA is used for conservation purposes and is designated as the Mauna Kea State Forest Reserve. However, substantial areas of mamane-naio habitat with important native bird populations are found on the adjacent Kaohe and Mauna Kea Game Management Areas, which are managed for hunting of feral pigs and non-native game birds. Most of the game management area is administered by the State of Hawaii, but some is leased to the U.S. Army as part of the Pohakuloa Training Area and is managed cooperatively by the Army and the State. The ?Kaohe Lease? was formerly leased by the State for cattle grazing and is severely degraded, but is no longer leased and could be restored, which would provide a much-needed opportunity to increase the amount of mamane-naio habitat. The IBA does not include the Mauna Kea State Recreation Area, which consists of mostly open habitat and contains many buildings and non-native plant species.