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

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
Pi‘ihonua silty clay loam, 6-20 percent slopes (PND):
The Pi‘ihonua series, located from 4,500 - 6,500 ft on the windward side of Mauna Kea, consists of
well-drained silty clay loams that have a banded appearance. The surface layer is about 6 in thick and
comprised of very dark brown silty clay loam that is extremely stony in certain areas. The subsoil is
dark-brown to dark-red silty clay loam about 44 in thick, while a weakly cemented layer of volcanic
ash occurs at a depth of 17-25 in. Acidity varies between very strongly acid to extremely acid.
Pi‘ihonua extremely stony silty clay loam, 6-20 percent slopes (POD):
In addition to the characteristics of Pi‘ihonua silty clay loam, 6-20 percent slopes, stones cover
3-15 percent of the surface in this soil.
‘Akaka soils (rAK):
The ‘Akaka series consists of moderately well-drained silty clay loams that formed from volcanic
ash. These are gently sloping to steep soils on upland rain forests ranging from 1,000 - 4,500 ft. On
the HFU, these soils are found in the mid- to lower-portion of the Refuge and comprise the majority
of the Refuge area. ‘Akaka soils typically have a slope between 3-20 percent, but are dissected by
small steep drainages, with slopes between 40-50 percent. Small, swampy areas of shallow soils
underlain by pāhoehoe bedrock also occur in the soil type.
Table 3-2. Soil Types Found Within the Hakalau Forest Unit and Key Characteristics.
Permeability Runoff Erosion
Hazard
PUC Moderately rapid Slow Slight
LAD Moderately rapid Medium Moderate
HCD -- Slow Slight
PND Rapid Slow Slight
POD Rapid Slow Slight
The Natural Resources Conservation Service (NRCS) operates a soil moisture and temperature
station at Pua ‘Ākala at 6,394 ft. This station, which has been operating since February 2005, records
soil moisture and temperature to a depth of 27 inches.
3.2.2 Kona Forest Unit Geology and Soils
The surface of the KFU is covered in a sheath of Mauna Loa lava flows of the Ka‘ū Basalt series.
Lava flows in the northern two-thirds of the unit are older ranging between 1,500 - 3,000 years old,
while the younger southern portion is estimated between 750-1,500 years old. A small area in the
central region of the Refuge is composed of Ka‘ū Basalt flows between 3,000 - 5,000 years old.
South of the KFU, more recent twentieth century lava flows are present (USFWS 2008a).
A thin layer of organic soil covers the highly permeable basalt that remains from the lava flows. The
following eight soil types have been identified within the KFU:
3-6 Chapter 3. Physical Environment