Physiographic features

This ecological site occurs on volcanic ash fields deposited over lava flows on interfluves and ridges of sloping mountainsides of shield volcanoes.

Table 2. Representative physiographic features

Table 3. Representative physiographic features (actual ranges)

Climatic features

Summary for this ecological site
Average annual precipitation ranges from 75 to 400 inches (1875 to 10,000 millimeters). Rainfall occurs throughout the year, with the heaviest precipitation occurring from October through April. Landscapes are shrouded in fog or overcast during much of the day throughout the year, which reduces evapotranspiration and adds additional moisture from condensation of fog on vegetation. Mean annual temperature ranges from 59 to 60 degrees F (15 to 16 degrees C). Frost free and freeze free periods are 365 days per year.

General principles
Air temperature in the Hawaiian Islands is buffered by the surrounding ocean so that the range in temperature through the year is narrow. This creates “iso-“ soil temperature regimes in which mean summer and winter temperatures differ by less than 6 degrees C (11 degrees F).

The islands lie within the trade wind zone. Significant amounts of moisture are picked up from the ocean by trade winds up to an altitude of more than about 6000 feet (1850 meters). As the trade winds from the northeast are forced up the mountains of the islands their moisture condenses, creating rain on the windward slopes; the leeward sides of the island receive little of this moisture.

Two seasons can be defined during the year: a seven-month winter season from October through April and a five-month summer season from May through September. Summer has warmer temperatures, steadier and stronger trade winds, few widespread rainstorms, and generally lower average monthly rainfall than winter. Differences in rainfall amounts between winter and summer are most marked in low elevation dry areas; wetter areas exhibit less seasonal variation in rainfall.

On the windward sides of the island, cool, moist air at higher elevations descends toward the ocean where it meets the trade winds; this process brings rainfall, often at night, to lower elevation areas.

Extensive low-pressure systems often approach the islands from the west, producing heavy rainstorms that primarily affect the leeward sides, but can envelope the entire island. These major storms occur most frequently between October and March.

Sea-to-land naulu winds regularly flow up the western and southern slopes of Haleakala on Maui, forming clouds on these faces of the mountain between about 3000 to 6000 feet (925 to 1850 meters). These clouds form a shadow at lower elevations and produce fog drip at higher elevations where the clouds contact the mountain (Leopold 1949; Schroeder 1981).

Table 4. Representative climatic features

Influencing water features

Streams exist in shallow to deep gulches. Vegetation in small gulches is similar to that of the rest of the ecological site. Ponding is common in depressions.

Soil features

One soil series, Amalu peat, is correlated with this ecological site. Amalu soils are classified within the Inceptisols soil order (soils with weak soil horizon development). They are in the Histic subgroup, meaning they have a histic (organic, in this case peat) surface horizon, and are saturated with water, and are reduced (“anaerobic” is a partial definition of this term) for some time in normal years.

These soils formed in organic matter over basic volcanic ash over residuum weathered from basalt. Soil temperature regimes are isothermic. Soil moisture regimes are aquic, which is a reducing regime in a soil that is virtually free of dissolved oxygen because it is saturated by water. They are poorly drained and are shallow (typically 10 to 20 inches or 25 to 50 centimeters) to the root-restricting placic (thin, solid ironstone horizon). The organic surface horizon is typically about 8 inches (20 centimeters) thick. Directly beneath it is the gleyed (gray, anaerobic, reduced) mineral horizon. Plant roots appear to be exclusively in the surface peat horizon and underlying gleyed horizon.

This ecological site correlated with Amalu soils, which are the same soil series correlated with Ecological Site F164XY501 Sphagnum Peat Dwarf Forest on Kohala on the island of Hawaii. This ecological site, on Maui and Molokai, differs from F164XY501 by having a peaty or mucky soil surface horizon that is not formed in sphagnum moss. Sphagnum occurs only on Kohala and on Mt. Eke in West Maui (Wagner et al. 1999, page 102). On Kohala, Amalu soils have an Oi horizon that is pale yellow (2.5Y 7/4) peat; on Maui and Molokai, Amalu soils have an Oi horizon that is black (5YR 2/1) peat.

Large areas of Miscellaneous Land Types adjoin this ecological site. These are areas that were mapped in very little detail. Parts of these areas contain soils described as Tropaquods, which are considered to be “similar to Amalu” in the 1972 Five Islands Soil Survey. Tropaquods occur in a large area mapped as Hydrandepts-Tropaquods association (map unit rHT) on Maui and as Tropaquods (map unit rTO) on Molokai.

Tropaquods are in the Spodosols soil order (soils with a spodic horizon having coarse texture, high pH-dependent charge, and few base cations). They are poorly drained soils that formed in basic igneous materials and organic material. Their surface horizon is peat or sometimes muck; see Definitions in Other Information section); this overlays a gleyed horizon (water-saturated and reduced). Beneath this is a placic horizon (solid, thin ironstone) that restricts root penetration and water percolation.

Table 5. Representative soil features

Other references

ANNOTATED REFERENCES

Abrahamson I. 2013. Fire regimes in Hawaiian plant communities. In: Fire Effects Information System, US Dept. of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. Available" www.fs.fed.us/database/feis/fire_regimes/Hawaii/all.html Review of fire regimes and history for multiple generalized plant communities in the Hawaiian Islands.

Armstrong RW. 1973. Atlas of Hawaii. University of Hawai`i Press, Honolulu. General reference for climate, land use, land forms, etc.

Athens JS. Ch. 12 Hawaiian Native Lowland Vegetation, IN Prehistory in Historical Ecology in the Pacific Islands – Prehistoric Environmental and Landscape Change. Kirch, PV and TL Hunt, eds. 1997. Yale U. Press, New Haven. General discussion of effects of prehistoric Polynesians on native lowland vegetation.
Burney DA, HF James, LP Burney, SL Olson, W Kikuchi, WL Wagner, M Burney, D McCloskey, D Kikuchi, FV Grady, R Gage II, and R Nishek. 2001. Fossil evidence diverse biota from Kauai and its transformation since human arrival. Ecological Monographs 71:615-641. Investigation of fossil evidence to trace changes in Hawaiian biota over time; generally applicable to all Hawaiian islands.

Craighill ES and EG Handy. 1991. Native Planters in Old Hawaii – Their Life, Lore, and Environment. Bernice P. Bishop Museum Bulletin 233, Bishop Museum Press, Honolulu, HI Discussion of early agriculture in Hawaii.

Cuddihy LW and CP Stone. 1990. Alteration of Native Hawaiian Vegetation: Effects of Humans, Their Activities and Introductions. Honolulu: University of Hawaii Cooperative National Park Resources Study Unit. General account of human effects on native Hawaiian vegetation.

Deenik J and AT McClellan. 2007. Soils of Hawaii. Soil and Crop Management, Sept. 2007, SCM-20. Cooperativve Extension Service, College of Tropical Agriculture and Human Resources. University of Hawaii at Manoa. Available online at: https://www.ctahr.hawaii.edu/oc/freepubs/pdf/SCM-20.pdf Discussion of soil orders and their practical implications in Hawaii.

Division of Forestry and Wildlife. 2009. Molokai Forest Reserve Draft Management Plan. Department of Land & Natural Resources, State of Hawaii. Discussions of vegetation types in the forest reserve, including wetlands.

Dixon JB and Schulze DG, eds. 2002. Soil Mineralogy with Environmental Applications. Volume 7. Soil Science Society of America. Available online at: https://acsess.onlinelibrary.wiley.com/doi/book/10.2136/sssabookser7 Exhaustive treatment of basics of soil mineralogy and implications for environmental management.

Giambelluca TW and TA Schroeder. 1998. Climate. In Atlas of Hawaii, 3rd edition. SP Juvik, JO Juvik, and RR Paradise, eds. pp. 49-59. Honolulu: University of Hawaii Press. Standard geographical reference work for Hawaii.

Hazlett RW and DW Hyndman. 1996. Roadside Geology of Hawaii. Mountain Press Publishing Company, Missoula MT. General account of geologic history of Hawaii.

Henke LA. 1929. A Survey of Livestock in Hawaii. Research Publication No. 5. University of Hawaii, Honolulu. Early assessment and history of effects of European livestock on Hawaiian ecosystems.

Imada, C. 2012. Hawaiian Native and Naturalized Vascular Plants Checklist (December 2012 update). Bishop Museum Technical Report 60. Bishop Museum Press, Honolulu. Constantly-updated list of vascular plants of Hawaii, including latest nomenclature and species occurrences on each island.

Jacobi JD. 1989. Vegetation Maps of the Upland Plant Communities on the Islands of Hawaii, Maui, Molokai, and Lanai. Technical Report 68. Cooperative National Park Resources Studies Unit, University of Hawaii at Manoa and National Park Service. Shapefiles of upland vegetation communities with canopy types, stature, environment types, and general species information.

Juvik JO and D Nullet. 1993. Relationships between rainfall, cloud-water interception, and canopy throughfall in a Hawaiian montane forest. In: Tropical Montane Cloud Forests. Proc. Int. Sym., San Juan, PR. Hamilton LS, JO Juvik, and FN Scatena, eds. East-West Center. Discussion of importance of fog drip to total precipitatiion in a montane forest.

Kirch PV. 1982. The impact of the prehistoric Polynesians in the Hawaiian ecosystem. Pacific Science 36(1):1-14. General discussion of effects of prehistoric Polynesians on native vegetation.

Kirch PV. 1985. Feathered Gods and Fishhooks: An Introduction to Hawaiian Archaeology and Prehistory. Honolulu: University of Hawaii Press. General discussion of effects of prehistoric Polynesians on native vegetation.

Kirch PV. 2000. On the Road of the Winds: An Archaeological History of the Pacific Islands Before European Contact. Berkeley: University of California Press. General discussion of effects of prehistoric Polynesians on native vegetation.

Kitayama K and D Mueller-Dombois. 1992. Vegetation of the Wet Windward Slope of Haleakala, Maui, Hawaii. Pacific Science 40(2):197-220. University of Hawaii Press, Honolulu. Vegetation transect through an area with Amalu soils on Maui.

Little EL Jr. and RG Skolmen. 1989. Common Forest Trees of Hawaii (Native and Introduced). US Department of Agriculture-US Forest Service Agriculture Handbook No. 679. (out of print). Available at www.fs.fed.us/psw/publications/documents/misc/ah679.pdf Information on common native and introduced tree species in Hawaii. Especially useful for introduced species.

Mueller-Dombois D and FR Fosberg. 1998. Vegetation of the Tropical Pacific Islands. Springer-Verlag New York, Inc. General account of tropical Pacific Island vegetation, with section on Hawaii. Discussion of likely effect of stoniness on soil moistue storage in dry habitats.

Palmer DD. 2003. Hawaii’s Ferns and Fern Allies. University of Hawaii Press, Honolulu. Standard reference for Hawaiian ferns and fern allies.

Pratt HD. 1998. A Pocket Guide to Hawaii’s Trees and Shrubs. Mutual Publishing, Honolulu. Useful guide to common tree and plant species, with color photos.

Reppun F, Silva JHS, Wong K, and Deenik JL. 2017. A Soil Phosphorus Primer for Hawaiian Soils. Soil and Crop Management, August 2017, SCM-33. College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa. Available online at: https://www.ctahr.hawaii.edu/oc/freepubs/pdf/SCM-33.pdf Practical discussion of soil phosphorus for Hawaii.

Ripperton JC and EY Hosaka. 1942. Vegetation zones of Hawaii. Hawaii Agricultural Experiment Station Bulletin 89:1-60. Broad-scale map of vegetation zones in Hawaii.

Rock JF. The Indigenous Trees of the Hawaiian Islands. 1st edition 1913, reprinted 1974, Charles E. Tuttle Company, Rutland, VT and Tokyo, Japan. Very useful account observations of native vegetation in Hawaii from early 20th century. Can be paired with GIS layer of place names to locate species observations.

Shoji SD, M Nanzyo, and R Dahlgren. 1993. Volcanic Ash Soils: Genesis, Properties and Utilization. Elsevier, New York. Detailed discussion of volcanic ash soils. Not specific to Hawaii, but very informative.

Silva JA and R Uchida, eds. 2000. Plant Nutrient Management in Hawaii’s Soils, Approaches for Tropical and Subtropical Agriculture. College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa. Available online at: https://www.ctahr.hawaii.edu/oc/freepubs/pdf/pnm0.pdf Practical discussion of plant nutrient management for Hawaii.

Sohmer SH and R Gustafson. 2000. Plants and Flowers of Hawaii. University of Hawaii Press, Honolulu. A good general discussion, with color photographs, primarily of native Hawaiian plants and vegetation types.

Soil Survey Staff. 2014. Soil Taxonomy, Twelfth Edition. USDA – NRCS. Standard book of soil taxonomy; useful for terminology and interpretation of soils, also.

Steadman DW. 1995. Prehistoric extinctions of Pacific island birds: biodiversity meets zooarchaeology. Science 267:1123-1131. Discussion of loss of many bird species, including flightless birds.

USDA-NRCS-PIA Threatened & Endangered Species GIS files. Not publicly available. Specific locations of observations of many native Hawaiian plant species.

USDA-NRCS. 2011. Soil Survey Laboratory Information Manual. Soil Survey Investigations Report No. 45, Version 2.0. National Soil Survey Center, Lincoln, Nebraska.

USDA-NRCS. 2006. Major Land Resource Regions. USDA Agriculture Handbook 296. http://soils.usda.gov/MLRAExplorer Description of MLRAs of Hawaii.

USDA-NRCS. Island of Hawaii Soil Surveys 801 and 701. Available online at https://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm The latest NRCS soil survey for the island of Hawaii.

USDA-SCS. 1972. Soil Survey of Islands of Kauai, Oahu, Maui, Molokai, and Lanai, State of Hawaii. Foote DE, Hill EL, Nakamura S, and F Stephens, in cooperation with The University of Hawaii Agricultural Experiment Station. The latest NRCS soil survey for these islands. Some of the taxonomic names are outdated.

USDI-USGS. 2006. A GAP Analysis of Hawaii. Final Report and Data. GIS map of vegetation types and land use in Hawaii based on remote sensing. Very general, occasionally inaccurate, but useful.

Vitousek P. 2004. Nutrient Cycling and Limitation: Hawai`i as a Model Ecosystem. Princeton University Press, Princeton and Oxford. Discussion of development of soils, soil nutrients, and plant species in Hawaiian Archipelago.

Wagner WL, DR Herbst, and SH Sohmer. 1999. Manual of the Flowering Plants of Hawaii, Revised Edition. Bishop Museum Press, Honolulu. Standard reference of flowering plants of Hawaii.

Western Regional Climate Center, cited 2020. Climate of Hawaii. Available: https://wrcc.dri.edu/Climate/narrative_hi.php Detailed summary of climate of Hawaiian Islands.

Whistler, WA. 1995. Wayside Plants of the Islands: A Guide to the Lowland Flora of the Pacific Islands. Isle Botanica, Honolulu. Reference of common introduced plant species in lowland areas of the Pacific Islands including Hawaii; with color photographs.


DEFINITIONS

Aa lava: A type of basaltic lava having a rough, jagged, clinkery surface and a vesicular interior.

Aquic soil moisture regime: A regime in which the soil is free of dissolved oxygen because it is saturated by water. This regime typically exists in bogs or swamps.

Ash field: a land area covered by a thick or distinctive deposit of volcanic ash that can be traced to a specific source and has well defined boundaries. The term “ash flow” is erroneously used in the Physiographic section of this ESD due to a flaw in the national database.

Ashy: A “soil texture modifier” for volcanic ash soils having a water content at the crop wilting point of less than 30 percent; a soil that holds relatively less water than “medial” and “hydrous” soils.

Available water capacity: The amount of soil water available to plants to the depth of the first root-restricting layer.

CaCO3 equivalent: The amount of free lime in a soil. Free lime exists as solid material and typically occurs in regions with a dry climate.

Canopy cover: The percentage of ground covered by the vertical projection downward of the outermost perimeter of the spread of plant foliage. Small openings within the canopy are included.

Community pathway: A description of the causes of shifts between community phases. A community pathway is reversible and is attributable to succession, natural disturbances, short-term climatic variation, and facilitating practices, such as grazing management.

Community phase: A unique assemblage of plants and associated dynamic soil properties within a state.

Dominant species: Plant species or species groups that exert considerable influence upon a community due to size, abundance, or cover.

Drainage class: The frequency, duration, and depth of a water table in a soil. There are seven drainage classes, ranging from “excessively drained” (soils with very rare or very deep water tables) to “well drained” (soils that provide ample water for plant growth but are not so wet as to inhibit root growth) to “very poorly drained” (soils with a water table at or near the surface during much of the growing season that inhibits growth of most plants).

Electrical conductivity (EC): A measure of the salinity of a soil. The standard unit is deciSiemens per meter (dS/m), which is numerically equivalent to millimhos per centimeter (mmhos/cm). An EC greater than about 4 dS/m indicates a salinity level that is unfavorable to growth of most plants.

Gleyed: A condition of soil from which iron has been reduced (in the redox chemistry sense) and removed during soil formation or that saturation with stagnant water has preserved a reduced state. If iron has been removed, the soil is the color of uncoated sand and silt particles. If iron is present in a reduced state, the soil is the color of reduced iron (typically bluish-gray). Redox concentrations (spots of oxidized iron, formerly called mottles are often present.

Isomesic soil temperature regime: A regime in which mean annual soil temperature is 47 degrees F (8 degrees C) or higher but lower than 59 degrees F (15 degrees C) and mean summer and mean winter soil temperatures differ by less than 11 degrees F (6 degrees C) at a specified depth.

Isothermic soil temperature regime: A regime in which mean annual soil temperature is 59 degrees F (15 degrees C) or higher but lower than 72 degrees F (22 degrees C) and mean summer and mean winter soil temperatures differ by less than 11 degrees F (6 degrees C) at a specified depth.

Major Land Resource Area (MLRA): A geographic area defined by NRCS that is characterized by a particular pattern of soils, climate, water resources, and land uses. The island of Hawaii contains nine MLRAs, some of which also occur on other islands in the state.

Makai: a Hawaiian word meaning “toward the sea.”

Mauka: a Hawaiian word meaning “toward the mountain” or “inland.”

Muck: Organic material of which virtually all the material has undergone sufficient decomposition to limit recognition of the plant parts.

Naturalized plant community: A community dominated by adapted, introduced species. It is a relatively stable community resulting from secondary succession after disturbance. Most grasslands in Hawaii are in this category.

Parent material: Unconsolidated and chemically weathered material from which a soil is developed.

Peat: Organic material of which virtually all of the organic remains are sufficiently fresh and intact to permit identification of plant forms.

Perudic soil moisture regime: A very wet regime found where precipitation exceeds evapotranspiration in all months of normal years. On the island of Hawaii, this regime is found on top of Kohala and on parts of the windward side of Mauna Kea.

pH: The numerical expression of the relative acidity or alkalinity of a soil sample. A pH of 7 is neutral; a pH below 7 is acidic and a pH above 7 is basic.

Reference community phase: The phase exhibiting the characteristics of the reference state and containing the full complement of plant species that historically occupied the site. It is the community phase used to classify an ecological site.

Reference state: A state that describes the ecological potential and natural or historical range of variability of an ecological site.

Restoration pathway: A term describing the environmental conditions and practices that are required to recover a state that has undergone a transition.

Sodium adsorption ratio (SAR): A measure of the amount of dissolved sodium relative to calcium and magnesium in the soil water. SAR values higher than 13 create soil conditions unfavorable to most plants.

Soil moisture regime: A term referring to the presence or absence either of ground water or of water held at a tension of less than 1500 kPa (the crop wilting point) in the soil or in specific horizons during periods of the year.

Soil temperature regime: A defined class based on mean annual soil temperature and on differences between summer and winter temperatures at a specified depth.

Soil reaction: Numerical expression in pH units of the relative acidity or alkalinity or a soil.

State: One or more community phases and their soil properties that interact with the abiotic and biotic environment to produce persistent functional and structural attributes associated with a characteristic range of variability.

State-and-transition model: A method used to display information about relationships between vegetation, soil, animals, hydrology, disturbances, and management actions on an ecological site.

Transition: A term describing the biotic or abiotic variables or events that contribute to loss of state resilience and result in shifts between states.

Udic soil moisture regime: A regime in which the soil is not dry in any part for as long as 90 cumulative days in normal years, and so provides ample moisture for plants. In Hawaii it is associated with forests in which hapuu (tree ferns) are usually moderately to highly abundant.

Contributors

David Clausnitzer
John Proctor
Mike Kolman
Carolyn Auweloa
Jennifer Higashino
Amy Koch
Kendra Moseley
Mathew Cocking

Approval

Kendra Moseley, 5/08/2025

Acknowledgments

Assistance, advice, review, and/or insights:

Randy Bartlett, Puu Kukui Watershed Preserve
Alison Cohan, The Nature Conservancy
Michael Constantinides, NRCS-PIA
Gordon Cran, Kapapala Ranch
Diana Crow, Ulupalakua Ranch
Lance DeSilva, Hawaii DLNR
Kerri Fay, Waikamoi Preserve, The Nature Conservancy
Alex Franco, Kaupo Ranch
Ranae Ganske-Cerizo, NRCS
Carl Hashimoto, NRCS
Bob Hobdy, consultant, Maui
Wallace Jennings, NRCS
Mel Johansen, The Nature Conservancy
Jordan Jokiel, Haleakala Ranch
David Leonard, volunteer
Penny Levin
Reese Libby, GIS - NRCS
Hannah Lutgen, Maui SWCD
Joseph May, NRCS
Scott Meidel, Haleakala Ranch
Anna Palomino, Hoolawa Farms Inc.
Jon Price, USGS
Tamara Sherrill, USFWS, Maui Nui Botanical Garden
Amber Starr, Hana Ranch
Kahana Stone, NRCS
Mark Vaught, Water Resources, Alexander & Baldwin
Jacqueline Vega, NRCS
Rich von Wellsheim, Whispering Bamboos, Kipahulu