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Ecological site QX197X01X503

Lavaflow Forest

Last updated: 6/12/2025
Accessed: 12/05/2025

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General information

Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site.

MLRA notes

Major Land Resource Area (MLRA): 197X–Volcanic Islands of American Samoa

This MLRA consists of the islands of Tutuila, Aunuu, Ofu, Olosega, and Tau. The islands have extremely steep, highly dissected mountains, small valleys, and a narrow coastal plain. More than half of the area has slopes of more than 70 percent. The highest elevations are 3,056 feet (931 meters) on Tau and 2,142 feet (653 meters) on Tutuila. The islands consist of Pleistocene-age, basic igneous rocks, mainly basalt with some andesite and trachyte.

The climate is moist, warm, and humid. Average annual rainfall ranges from 125 inches (3,175 millimeters) to more than 250 inches (6,350 millimeters). Rainfall varies over short distances due to topography. The driest months are June through September; the wettest months are December through March. Average annual temperature is 81 degrees F (27 degrees C). Relative humidity is 73 to 90 percent throughout the year. Prevailing winds are easterly trade winds. Cyclones occasionally strike the area.

Soils are Mollisols, Andisols, Entisols, Oxisols, and Histosols. Soil moisture regimes are udic or perudic; the soil temperature regime is isohyperthermic. Natural vegetation is mostly tropical hardwood forest.

Classification relationships

This ecological site occurs within Major Land Resource Area (MLRA) 197 – Volcanic Islands of American Samoa.

Ecological site concept

This ecological site occurs on the island of Tutuila and on a small part of Tau in American Samoa. It occurs on gently to strongly sloping (3 to 15 percent) aa lava flows at elevations ranging from 0 to 150 feet (0 to 46 meters) elevation. It is easily accessible on the southern side of Tutuila.

Soils are Folists (Histisols) that formed in organic matter deposited over relatively recent aa lava flows. Soil temperature regimes are isohyperthermic; soil moisture regimes are udic. Average annual rainfall ranges from 120 to 175 inches (300 to 438 centimeters). Water runoff is very slow. Effective rooting depths are variable in spaces between aa fragments and in bedrock cracks.

This forest type has high plant diversity. The upper canopy grows up to 100 feet (30 meters) tall. Ground cover is dense. Epiphytes are sparse to common; climbing plants are common.

Associated sites

QX197X01X504	Alluvial Valley Forest Alluvial Valley Forest adjoins Lavaflow Forest in the few locations where alluvial valleys descend to young aa lava flows near the coast. Alluvial Valley Forest has somewhat poorly drained, mineral soils; Lavaflow Forest has well drained, organic soils in the interstices between aa rocks.
QX197X01X507	Dry Coastal Forest Dry Coastal Forest adjoins Lavaflow Forest where uplands and mountain slopes descend to young aa lava flows near the coast. Dry Coastal Forest has mineral soils formed from volcanic ash deposited over hard tuff, or, in one case, in the interstices between aa rocks; Lavaflow Forest has organic soils that formed in the interstices between aa rocks.

QX197X01X504

Alluvial Valley Forest

Alluvial Valley Forest adjoins Lavaflow Forest in the few locations where alluvial valleys descend to young aa lava flows near the coast. Alluvial Valley Forest has somewhat poorly drained, mineral soils; Lavaflow Forest has well drained, organic soils in the interstices between aa rocks.

QX197X01X507

Dry Coastal Forest

Dry Coastal Forest adjoins Lavaflow Forest where uplands and mountain slopes descend to young aa lava flows near the coast. Dry Coastal Forest has mineral soils formed from volcanic ash deposited over hard tuff, or, in one case, in the interstices between aa rocks; Lavaflow Forest has organic soils that formed in the interstices between aa rocks.

Similar sites

QX197X01X505	Skeletal Pachic or Fulvic Forest Skeletal Pachic or Fulvic Forest adjoins Lavaflow Forest where talus slopes, uplands, and mountain slopes descend to young aa lava flows near the coast. Skeletal Pachic or Fulvic Forest has mineral soils with high organic carbon content and high rock content, slopes of 6 to 60 percent, elevations of 0 to 900 feet, and mean annual rainfall of 150 to 250 inches. Lavaflow Forest has organic soils with high rock content, slopes of 3 to 15 percent, elevations of 0 to 150 feet, and receives 120 to 175 inches.

QX197X01X505

Skeletal Pachic or Fulvic Forest

Skeletal Pachic or Fulvic Forest adjoins Lavaflow Forest where talus slopes, uplands, and mountain slopes descend to young aa lava flows near the coast. Skeletal Pachic or Fulvic Forest has mineral soils with high organic carbon content and high rock content, slopes of 6 to 60 percent, elevations of 0 to 900 feet, and mean annual rainfall of 150 to 250 inches. Lavaflow Forest has organic soils with high rock content, slopes of 3 to 15 percent, elevations of 0 to 150 feet, and receives 120 to 175 inches.

Table 1. Dominant plant species

Tree	(1) Nephelium (2) Planchonella
Shrub	Not specified
Herbaceous	(1) Asplenium nidus (2) Phymatosorus grossus

Legacy ID

F197XY503AS

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Physiographic features

This ecological site occurs on aa flows.

Table 2. Representative physiographic features

Landforms	(1) Island > Aa lava flow
Runoff class	Very low
Flooding frequency	None
Ponding frequency	None
Elevation	151 ft
Slope	3 – 15%
Water table depth	60 in
Aspect	NW, SE

Climatic features

The area is characterized by abundant rain and warm, humid days and nights. Average annual precipitation in this ecological site ranges from 120 to 174 inches (3000 to 4420 millimeters). Mean annual air temperature is 80F (27C). The driest period is June through September (winter), and the wettest is December through March (summer), although heavy showers and long, rainy periods can occur in any month. June, July, and August are the coolest months, and January, February, and March are the warmest. Daytime temperatures typically reach the upper 80s in summer and the middle 80s F in winter, while nighttime temperatures are in the middle 70s in summer and low 70s in winter.

The prevailing winds throughout the year are the easterly trade winds. They tend to be more directly from the east in December through March and mostly from the east-southeast and southeast during the rest of the year. The trade winds are less prevalent in summer than in winter. About 25 to 30 thunderstorms occur in an average year, mainly during the rainy season. The area lies across the path of tropical disturbances, including cyclones, that come usually from the north, but occasionally from east or west.

Table 3. Representative climatic features

Frost-free period (characteristic range)	365 days
Freeze-free period (characteristic range)	365 days
Precipitation total (characteristic range)	120-174 in
Frost-free period (actual range)	365 days
Freeze-free period (actual range)	365 days
Precipitation total (actual range)	120-174 in
Frost-free period (average)	365 days
Freeze-free period (average)	365 days
Precipitation total (average)	147 in

Characteristic range

Actual range

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Figure 1. Monthly precipitation range

Characteristic range

Actual range

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Figure 2. Monthly minimum temperature range

Characteristic range

Actual range

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Figure 3. Monthly maximum temperature range

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Figure 4. Monthly average minimum and maximum temperature

Figure 5. Annual precipitation pattern

Figure 6. Annual average temperature pattern

Climate stations used

(1) PAGO PAGO WSO AP [AQW00061705], AS

Soil features

TAFUNA

The soils in this ecological site are in the Histisols soil order. They formed from organic matter deposited in the interstices between aa lava rocks. They are well drained. Soil temperature regimes are isohypothermic (very warm) with a mean temperature of 80F (27C). Soil moisture regimes are udic.

Table 4. Representative soil features

Parent material	(1) Organic material
Surface texture	(1) Extremely stony
Drainage class	Well drained
Permeability class	Very slow
Depth to restrictive layer	43 – 60 in
Soil depth	43 – 60 in
Surface fragment cover <=3"	Not specified
Surface fragment cover >3"	9%
Available water capacity (0-40in)	3 in
Calcium carbonate equivalent (0-40in)	Not specified
Electrical conductivity (0-40in)	Not specified
Sodium adsorption ratio (0-40in)	Not specified
Soil reaction (1:1 water) (0-40in)	6.1 – 7.3
Subsurface fragment volume <=3" (0-40in)	23%
Subsurface fragment volume >3" (0-40in)	44%

Ecological dynamics

Although annual rainfall is high and well distributed throughout the year, the soil depth (average 9 inches or 22 centimeters) results in dry conditions as indicated by the low waterholding capacity of the soils. However, water may accumulate on top of the blue rock below the soil material zone. This has not been observed but is suggested by the abundant plant growth and presence of mosquitos in aa lava flow areas with organic soils on the Pacific Islands.

The main natural disturbance is strong storms that can damage or kill vegetation by high wind speeds. The forest is susceptible to human-caused fires in the drier season, especially in drought years. The main human disturbance is clearing of native vegetation to plant coconut plantations and abandonment of plantations that results in at least temporary dominance of introduced weedy plants.

Very little of this ecological site exists because it has been used for homesites.

State and transition model

Custom diagram

Standard diagram

Figure 7. State and Transition Model (STM) for F197XY503AS (Lavaflow Forest)

More interactive model formats are also available. View Interactive Models

More interactive model formats are also available. View Interactive Models
Click on state and transition labels to scroll to the respective text

Ecosystem states

1. Reference State

2. Coconut Plantation

3. Cleared and Abandoned State

T1A	-	State 1 Reference transitions to State 2 Coconut Plantation by removal of native vegetation and planting coconut palms (Cocos nucifera).
T1B	-	State 1 Reference transitions to State 3 Abandoned if Cleared and Abandoned. This allows heliophytes, both native and introduced, to temporarily cover the understory.
R2A	-	State 2 Coconut Plantation could theoretically be restored to State 1 Reference by removal of coconut palms and other vegetation and replanting with native species.
T2B	-	State 2 Coconut Plantation transitions to State 3 Cleared and Abandoned if cleared and abandoned. This allows heliophytes, both native and introduced, to temporarily cover the understory.
R3B	-	State 3 Cleared and Abandoned may be restored to State 1 Reference. The intensity of active restoration measures will be determined by the presence or lack of nearby native forest or, at least, some native trees as well as the density and species mix of grasses, vines, shrubs, and trees present on the site, especially if many competitive introduced species are present.
R3A	-	State 3 Cleared and Abandoned may be restored to State 2 Coconut Plantation by land clearing, weed control, and replanting coconut palms.

State 1 submodel, plant communities

1.1. Tava - mamalava/bird’s nest fern – musk fern/fue manogi

1.2. Tava - toi/bird’s nest fern – musk fern

P1.1A	-	Storms or fires that damage or kill trees causes a phase change from 1.1 to 1.2 typified by a partial, temporary change in dominant tree species and a temporary increase in ground level vegetation.
P1.2A	-	This community phase will revert to phase 1.1 with gradual regrowth of native species when given adequate time to recover after disturbance.

State 2 submodel, plant communities

2.1. Coconut palm

State 3 submodel, plant communities

3.1. Coconut palm – white leadtree/giant sensitive plant/romerillo or syn. beggar’s tick/merremia

State 1
Reference State

This diverse ecological site has a very tall (80 to 100 feet or 25 to 30 meters) tree canopy. Ground cover is dense, epiphytes are sparse to moderately abundant, and climbing vines are common.

Community 1.1
Tava - mamalava/bird’s nest fern – musk fern/fue manogi

Common large trees are tava (Pometia pinnata or syn. Nephelium spp.), mamalava (Planchonella samoensis), asi (Syzygium inophylloides), maali (Canarium samoense), maota (Dysoxylum maota), mamala (Homalanthus nutans), auauli (Diospyros samoensis), and atone (Myristica inutilis).

Dominant plant species

nephelium (Nephelium), tree
planchonella (Planchonella), tree
Hawai'I birdnest fern (Asplenium nidus), other herbaceous
musk fern (Phymatosorus grossus), other herbaceous
pepper (Piper), other herbaceous

Community 1.2
Tava - toi/bird’s nest fern – musk fern

The same tree species as in Community Phase 1.1 remain in this phase, but other tree species, commonly toi (Alphitonia zizyphoides) and tavai (Rhus taitensis) can join the canopy as the forest regrows. Ground vegetation, especially bird’s nest fern and musk fern, increase in abundance with increased light availability. Epiphytes are less common than in 1.1.

Dominant plant species

nephelium (Nephelium), tree
alphitonia (Alphitonia), tree
Hawai'I birdnest fern (Asplenium nidus), other herbaceous
musk fern (Phymatosorus grossus), other herbaceous

Pathway P1.1A
Community 1.1 to 1.2

Storms or fires that damage or kill trees causes a phase change from 1.1 to 1.2 typified by a partial, temporary change in dominant tree species and a temporary increase in ground level vegetation.

Pathway P1.2A
Community 1.2 to 1.1

This community phase will revert to phase 1.1 with gradual regrowth of native species when given adequate time to recover after disturbance.

State 2
Coconut Plantation

This state consists of one community phase that has been cleared of natural vegetation and planted with coconut palms (Cocos nucifera).

Community 2.1
Coconut palm

This community phase consists of planted coconut palms (Cocos nucifera). Highly variable low ground cover is present.

Dominant plant species

coconut palm (Cocos nucifera), tree

State 3
Cleared and Abandoned State

This state consists of one community phase dominated by a variable mixture of native and introduced small trees, shrubs, vines, forbs, and grasses that thrive in sunny environments. Remnant coconut palms are likely be present.

Community 3.1
Coconut palm – white leadtree/giant sensitive plant/romerillo or syn. beggar’s tick/merremia

This community phase contains remnant coconut palms with a variable understory of native and/or introduced shrubs, forbs, vines, and grasses that thrive in sunny environments. White leadtree (Leucaena leucocephala), an introduced small tree, is often abundant. The introduced shrub giant sensitive plant (Mimosa diplotricha) is common, as is the introduced forb beggar’s tick (Bidens pilosa). Merremia (Merremia peltata), a highly invasive introduced vine, may be very abundant. A wide variety of other species may occur depending on location of the site.

Dominant plant species

coconut palm (Cocos nucifera), tree
white leadtree (Leucaena leucocephala), tree
giant false sensitive plant (Mimosa diplotricha), shrub
romerillo (Bidens alba), shrub
merremia (Merremia peltata), other herbaceous
romerillo (Bidens alba), other herbaceous

Transition T1A
State 1 to 2

The Reference State (1) transitions to the Coconut Plantation State (2) by removal of native vegetation and planting coconut palms (Cocos nucifera).

Transition T1B
State 1 to 3

The Reference State (1) transitions to the Cleared and Abandoned State (3) if cleared and abandoned. This allows heliophytes, both native and introduced, to temporarily cover the understory.

Restoration pathway R2A
State 2 to 1

State 2 Coconut Plantation could theoretically be restored to State 1 Reference by removal of coconut palms and other vegetation and replanting with native species.

Transition T2B
State 2 to 3

The Coconut Plantation State (2) transitions to the Cleared and Abandoned State (3) if cleared and abandoned. This allows heliophytes, both native and introduced, to temporarily cover the understory.

Restoration pathway R3B
State 3 to 1

The Cleared and Abandoned State (3) may be restored to the Reference State (1). The intensity of active restoration measures will be determined by the presence or lack of nearby native forest or, at least, some native trees as well as the density and species mix of grasses, vines, shrubs, and trees present on the site, especially if many competitive introduced species are present.

Restoration pathway R3A
State 3 to 2

The Cleared and Abandoned State (3) may be restored to the Coconut Plantation State (2) by land clearing, weed control, and replanting coconut palms.

Additional community tables

Supporting information

Other references

Annotated References for F197XY503AS Lavaflow Forest

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.

Forestry Program, Division of Community and Natural Resources. 2010. American Samoa Forest Assessment and Resource Strategy. American Samoa Community College, Pago Pago, American Samoa. Some discussion of disturbances, threats, and invasive species.

Green K, G Kittel, C Lopez, A Ainsworth, M Selvig, V Vaivai, K Akamine, M Tukman, and G Kudray. Vegetation Mapping Inventory Project, National Park of American Samoa. USDI-NPS Natural Resource Stewardship and Science. Fort Collins, Colorado. Discussion and maps of fine-scale vegetation associations, including Appendix with data including elevation ranges, litter, bare, and surface rockiness.

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.

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

Sene DM. 2020. Forest Action Plan. Forestry Program, American Samoa Community College, Pago Pago, American Samoa. Discussions of forest types, disturbances, and succession.

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

Space JC and T Flynn. 2000. Observations on invasive plant species in American Samoa. USDA Forest Service, Pacific Southwest Research Station, Honolulu. http://www.hear.org/pier/references/pierref000021.htm Recent, detailed report on invasive and potentially-invasive plants in American Samoa.

USDA-NRCS. 2011. Soil Survey Laboratory Information Manual. Soil Survey Investigations Report No. 45, Version 2.0. National Soil Survey Center, Lincoln, Nebraska. Provides additional insight for interpretation of soils information.

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

USDA-SCS. 1984. Soil Survey of Islands of American Samoa. Nakamura S, Chavez CL and MW Roybal, in cooperation with the Government of American Samoa. The latest NRCS soil survey for these islands. Some of the taxonomic names are outdated.

USDI-FWS. 1982. Woldlife and Wildlife Habitat of American Samoa. II. Accounts of Flora and Fauna. R Banks, editor. Washington DC. Discussion of vegetation as habitat types for local fauna. Good climate discussion.

USDI-NPS. 2009. Natural History Guide to American Samoa, 3rd Edition. P. Craig, editor. National Park of Samoa, Department of Marine and Wildlife Resources-American Samoa, American Samoa Community College-Community and Natural Resources Division. General reference for terrestrial and marine resources of American Samoa, with color photographs.

Webb EL. 2009. A Guide to the Native Ornamental Trees of American Samoa. Department of Marine and Wildlife Resources, Government of American Samoa. Guide to the more common and/or useful native trees recommended for planting in American Samoa, with color photographs and individual descriptions.

Webb EL and S Fa`aumu. 1999. Diversity and structure of tropical rain forest of Tutuila, American Samoa: effects of site age and substrate. Plant Ecology 44: 257-274. Information on wind disturbances and their effect on forest succession on Tutuila.

Whistler WA. 2004. Rainforest Trees of Samoa. Isle Botanica, Honolulu. A guide to the common lowland and foothill forest trees of the Samoan archipelago.

Whistler WA. 2002. The Samoan Rainforest. Isle Botanica, Honolulu. A guide to the various vegetation types of the Samoan archipelago, with some reference to landscape and soils, and based on extensive fieldwork.

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 American Samoa; with color photographs.

Whistler WA. 1994. Botanical Inventory of the Proposed Tutuila and Ofu Units of the National Park of American Samoa. Technical Report 87. National Park Service. Honolulu. Discussion of vegetation types within area of American Samoa National Park on Tutuila and Ofu.

Whistler WA. 1992. Botanical Inventory of the Proposed Ta`u Unit of the National Park of American Samoa. Technical Report 83. National Park Service. Honolulu. Discussion of vegetation types within area of American Samoa National Park on Ta`u.

Contributors

David Clausnitzer PhD
John Proctor
Ann Tan
Carolyn Auweloa
Daniel Bowman
Jennifer Fedenko
Amy Koch
Kendra Moseley
Sarah Quistberg
Jill Ficke-Beaton
Daniel Block
Brendan Brazee
Curtis Talbot

Approval

Kendra Moseley, 6/12/2025

Acknowledgments

Assistance, advice, review, and/or insights:

Michael Constantinides, NRCS-PIA
Jennifer Higashino, USFWS and NRCS
Mike Kolman, NRCS

Rangeland health reference sheet

Interpreting Indicators of Rangeland Health is a qualitative assessment protocol used to determine ecosystem condition based on benchmark characteristics described in the Reference Sheet. A suite of 17 (or more) indicators are typically considered in an assessment. The ecological site(s) representative of an assessment location must be known prior to applying the protocol and must be verified based on soils and climate. Current plant community cannot be used to identify the ecological site.

Author(s)/participant(s)
Contact for lead author
Date	06/13/2025
Approved by	Kendra Moseley
Approval date
Composition (Indicators 10 and 12) based on	Annual Production