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Ecological site QX197X01X506

Tuff or Rock Subsurface 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 islands of Tutuila, Aunuu, Ofu, Olosega, and Tau in American Samoa. It occurs on gently sloping to very steep (6 to 70 percent) mountainsides and uplands at elevations ranging from 0 to 1500 feet (0 to 462 meters) elevation. Easiest access is on the eastern side of Tutuila and restricted elsewhere.

Soils are in the Oxisols order or Andic Hapludolls (Mollisols) subgroup. They formed in residuum, residuum with volcanic ash, or volcanic ash over a layer of highly weathered tuff. Soil temperature regimes are isohyperthermic; soil moisture regimes are udic. Average annual rainfall ranges from 150 to 230 inches (375 to 575 centimeters). Water runoff is slow to rapid. Effective rooting depths range from 20 to more than 60 inches (50 to more than 150 centimeters). Rock fragment content is low.

This forest type has high plant species diversity. The tree canopy grows up to 100 feet (30 meters) tall. Ground cover is moderate to dense; epiphytes and climbing plants are abundant.

Associated sites

QX197X01X001	Coastal Marsh Coastal Marsh adjoins Tuff or Rock Subsurface Forest where uplands and mountain slopes descend to coastal depressions near sea level. Coastal Marsh ascends to 20 feet elevation and has very poorly drained soils, in contrast with Tuff or Rock Subsurface Forest, which occurs on slopes up to 1500 feet elevation and has well drained soils.
QX197X01X501	Mangrove Swamp Mangrove Swamp adjoins Tuff or Rock Subsurface Forest where uplands and mountain slopes descend to partially-protected areas of the coast that are open to seawater. It ascends to 20 feet elevation and has very poorly drained soils, in contrast with Tuff or Rock Subsurface Forest, which occurs on slopes up to 1500 feet in elevation and has well drained soils.
QX197X01X502	Sandy Littoral Forest Sandy Littoral Forest adjoins Tuff or Rock Subsurface Forest where uplands and mountain slopes descend to sandy coastlines. It ascends to 15 feet elevation, undergoes occasional, very brief to brief flooding by seawater, and has somewhat excessively to excessively drained soils, in contrast with Tuff or Rock Subsurface Forest, which occurs on mountain slopes up to 1500 feet in elevation, undergoes no flooding, and has well drained soils.
QX197X01X509	Very Steep Forest Very Steep Forest adjoins Tuff or Rock Subsurface Forest in mountainous areas where very steep slopes border on less steep slopes. Its soils are Andisols and Andic Mollisols on slopes of 70 to 130 percent; Tuff or Rock Subsurface Forest consists of Andisols, Andic Mollisols, and Oxisols on slopes of 6 to 70 percent.

Table 1. Dominant plant species

Tree	(1) Syzygium (2) Dysoxylum
Shrub	Not specified
Herbaceous	(1) Angiopteris evecta (2) Lomagramma cordipinna

Legacy ID

F197XY506AS

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Physiographic features

This ecological site occurs on mountain slopes on residuum or volcanic ash overlying either basic igneous rock or hard weathered tuff.

Table 2. Representative physiographic features

Landforms	(1) Island > Mountain
Runoff class	Medium to high
Flooding frequency	None
Ponding frequency	None
Elevation	1,499 ft
Slope	6 – 70%
Water table depth	60 in
Aspect	Aspect is not a significant factor

Table 3. Representative physiographic features (actual ranges)

Runoff class	Low to high
Flooding frequency	Not specified
Ponding frequency	Not specified
Elevation	2,099 ft
Slope	Not specified
Water table depth	Not specified

Climatic features

The area is characterized by abundant rain and warm, humid days and nights. Average annual precipitation in this ecological site ranges from 115 to 197 inches (2920 to 5005 millimeters). Mean annual air temperature is 79 to 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 4. Representative climatic features

Frost-free period (characteristic range)	365 days
Freeze-free period (characteristic range)	365 days
Precipitation total (characteristic range)	115-197 in
Frost-free period (actual range)	365 days
Freeze-free period (actual range)	365 days
Precipitation total (actual range)	104-230 in
Frost-free period (average)	365 days
Freeze-free period (average)	365 days
Precipitation total (average)	169 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

FAGASA, OFU, OFU VARIANT, SOGI VARIANT

Soils are in the Oxisols order or are Andic Hapludolls (Mollisols with andic characteristics) subgroup. They formed in residuum, residuum with volcanic ash, or volcanic ash over a layer of rock or hard, weathered tuff. Soil temperature regimes are isohyperthermic; soil moisture regimes are udic. They are moderately deep to deep and well drained.

Table 5. Representative soil features

Parent material	(1) Residuum (2) Volcanic ash
Surface texture	(1) Silty clay
Family particle size	(1) Fine
Drainage class	Well drained
Permeability class	Very slow to moderate
Depth to restrictive layer	29 – 72 in
Soil depth	29 – 72 in
Surface fragment cover <=3"	Not specified
Surface fragment cover >3"	Not specified
Available water capacity (0-40in)	3 – 5 in
Calcium carbonate equivalent (0-40in)	Not specified
Electrical conductivity (0-40in)	Not specified
Sodium adsorption ratio (0-40in)	1
Soil reaction (1:1 water) (0-40in)	5.6 – 7.3
Subsurface fragment volume <=3" (0-40in)	3 – 28%
Subsurface fragment volume >3" (0-40in)	14 – 15%

Ecological dynamics

The main natural disturbances are landslides and strong storms that can damage or kill vegetation by high wind speeds. The main human disturbance is burning or clearing of native vegetation that results in at least temporary dominance of introduced weedy plants.

State and transition model

Custom diagram

Standard diagram

Figure 7. State and Transition Model (STM) for F197XY506AS (Tuff or Rock Subsurface 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. Cleared and Abandoned

3. Invaded Forest

T1A	-	State 1 Reference transitions to State 2 Cleared and Abandoned by removal of native vegetation and allowing colonization by local species.
T1B	-	State 1 Reference transitions to State 3 Invaded Forest by localized landslides or wind damage to the forest when there is a nearby source of seeds of invasive species or, more gradually, by damage to the forest understory by ungulates, especially feral pigs, when there is a source of seeds of invasive species.
R2A	-	State 2 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 invasive trees present on the site, especially if many competitive introduced species are present.
T2A	-	State 2 Cleared and Abandoned transitions to State 3 Invaded Forest by growth of an overstory of trees with an understory of shade-tolerant shrubs, vines, ferns, forbs, and grasses. The species mix is variable but may be mostly introduced species or a combination of native and introduced species.
R3A	-	State 3 Invaded Forest can be restored to the Reference State. The difficulty, cost, and likelihood of success will depend on the species composition and amount and competitiveness of introduced species present on a given site.
R3B	-	State 3 Invaded Forest can be restored to State 2 Cleared and Abandoned. After this “restoration,” State 2 is likely to rapidly transition back to State 3 due to presence of an abundant tree seed bank in the soil.

State 1 submodel, plant communities

1.1. Asi – mamala/Oriental vessel fern – lomagramma

1.2. Tavai – afa

P1.1A	-	Landslides or storms 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. Lantana – Honolulu rose/fua lele/mile-a-minute vine Lantana camara – Clerodendrum chinense/Crassocephalum crepidioides/Mikania micrantha

State 3 submodel, plant communities

3.1. Asi – African tulip tree/Koster’s curse/mile-a-minute vine/running mountaingrass Syzygium inophylloides – Spathodea campanulata/Clidemia hirta/Mikania micrantha/Oplismenus compositus

State 1
Reference State

This ecological site is forest with a highly diverse, very tall (80 to 100 feet or 25 to 30 meters) tree canopy. Ground cover is moderately dense to dense. Epiphytes and lianas are abundant.

Community 1.1
Asi – mamala/Oriental vessel fern – lomagramma

Dominant tree species are asi (Syzygium inophylloides), mamala (Homalanthus nutans), atone (Myristica inutilis), maali (Canarium samoense), afa (Neonauclea forsteri), mamalava (Planchonella samoensis), and moso oi (Cananga odorata). Nontree species include the native creeping and climbing fern lomagramma (Lomagramma cordipinna). Other ferns are bird’s nest fern (Asplenium nidus), Asplenium polyodon, and Tectaria dissecta. There are many orchid species.

Dominant plant species

syzygium (Syzygium), tree
(Dysoxylum), tree
Oriental vessel fern (Angiopteris evecta), other herbaceous
(Lomagramma cordipinna), other herbaceous

Community 1.2
Tavai – afa

The same tree species as in Community Phase 1.1 remain in this phase, but other native tree species, commonly tavai (Rhus taitensis) and afa (Neonauclea forsteri) can join the canopy as the forest regrows. Ground vegetation becomes temporarily more abundant. Epiphytes are less common than in 1.1.

Dominant plant species

(Rhus taitensis), tree
(Neonauclea forsteri), tree

Pathway P1.1A
Community 1.1 to 1.2

Landslides or storms 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
Cleared and Abandoned

This state consists of one community phase dominated by a variable mixture of shrubs, vines, forbs, and grasses that thrive in sunny environments.

Dominant plant species

lantana (Lantana camara), tree
stickbush (Clerodendrum chinense), tree
redflower ragleaf (Crassocephalum crepidioides), other herbaceous
mile-a-minute (Mikania micrantha), other herbaceous

Community 2.1
Lantana – Honolulu rose/fua lele/mile-a-minute vine Lantana camara – Clerodendrum chinense/Crassocephalum crepidioides/Mikania micrantha

This community phase consists of a variable array of shrubs, forbs, vines, and young trees that thrive in sunny environments. Shrubs such as lantana (Lantana camara), Honolulu rose (Clerodendrum chinense), comb bushmint (Hyptis pectinata), mautofu (Triumfetta rhomboidea), and nettleleaf velvetberry (Stachytarpheta urticifolia) are dominant. The shrub layer may also include seedlings and saplings of any native trees that may have persisted on or near the site or invasive, introduced tree species such as African tulip tree (Spathodea campanulata), red beadtree (Adenanthera pavonina), and tamaligi or peacock’s plume (Falcataria moluccana). Mile-a-minute vine (Mikania micrantha) and the large, introduced forb fua lele (Crassocephalum crepidioides) may be present (Forestry Program, Division of Community and Natural Resources, 2010; Green et al., 2015; Sene, 2020; Space and Flynn, 2000; Webb and Fa`aumu, 1999; Whistler, 2002; Whistler, 1994; Whistler, 1992).

State 3
Invaded Forest

This state consists of one community phase. It is forest with both overstory and understory composed of a variable mix of native and introduced species. The actual species composition on a given site depends on the original native species composition, the disturbance history, and the species composition existing near the site before, during, and after disturbances (Forestry Program, Division of Community and Natural Resources, 2010; Green et al., 2015; Sene, 2020; Space and Flynn, 2000; Webb and Fa`aumu, 1999; Whistler, 2002; Whistler, 1994; Whistler, 1992).

Dominant plant species

syzygium (Syzygium), tree
African tuliptree (Spathodea campanulata), tree
soapbush (Clidemia hirta), shrub
running mountaingrass (Oplismenus compositus), grass
mile-a-minute (Mikania micrantha), other herbaceous

Community 3.1
Asi – African tulip tree/Koster’s curse/mile-a-minute vine/running mountaingrass Syzygium inophylloides – Spathodea campanulata/Clidemia hirta/Mikania micrantha/Oplismenus compositus

The overstory consists of large trees. Any of the native species listed for State 1 Reference may be present. Introduced tree species are likely to be present; common examples of these are African tulip tree (Spathodea campanulata), tamaligi or peacock’s plume (Falcataria moluccana), and red beantree (Adenanthera pavonina) (Forestry Program, Division of Community and Natural Resources, 2010; Green et al., 2015; Sene, 2020; Space and Flynn, 2000; Webb and Fa`aumu, 1999; Whistler, 2002; Whistler, 1994; Whistler, 1992). The understory consists of an unpredictable mixture of native and introduced shrubs, ferns, vines, forbs, and grasses that have some shade tolerance. See State 1 Reference for examples of native species. Common examples of introduced understory species are the shrubs Koster’s curse (Clidemia hirta) and Honolulu rose (Clerodendrum chinense), mile-a-minute vine (Mikania micrantha), and running mountaingrass (Oplismenus compositus) (Forestry Program, Division of Community and Natural Resources, 2010; Green et al., 2015; Sene, 2020; Space and Flynn, 2000; Webb and Fa`aumu, 1999; Whistler, 2002; Whistler, 1994; Whistler, 1992).

Transition T1A
State 1 to 2

The Reference State (1) transitions to the Cleared and Abandoned State (2) by removal of native vegetation and allowing colonization by local species.

Transition T1B
State 1 to 3

The Reference State (1) transitions to the Invaded Forest State (3) by localized landslides or wind damage to the forest when there is a nearby source of seeds of invasive species or, more gradually, by damage to the forest understory by ungulates, especially feral pigs, when there is a source of seeds of invasive species.

Restoration pathway R2A
State 2 to 1

The Cleared and Abandoned State (2) 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 invasive trees present on the site, especially if many competitive introduced species are present.

Transition T2A
State 2 to 3

The Cleared and Abandoned State (2) transitions to the Invaded Forest State (3) by growth of an overstory of trees with an understory of shade-tolerant shrubs, vines, ferns, forbs, and grasses. The species mix is variable but may be mostly introduced species or a combination of native and introduced species.

Restoration pathway R3A
State 3 to 1

The Invaded Forest State (3) can be restored to the Reference State (1). The difficulty, cost, and likelihood of success will depend on the species composition and amount and competitiveness of introduced species present on a given site.

Restoration pathway R3B
State 3 to 2

The Invaded Forest State (3) can be restored to the Cleared and Abandoned State (2). After this “restoration,” the Cleared and Abandoned State (2) is likely to rapidly transition back to the Invaded Forest State (3) due to presence of an abundant tree seed bank in the soil.

Additional community tables

Supporting information

Other references

Annotated References for F197XY506AS Tuff or Rock Subsurface 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