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Ecological site QX197X01X509

Very Steep 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, Ofu, and Olosega in American Samoa. It occurs on very steep (70 to 130 percent) mountain side slopes at elevations ranging from 0 to 2100 feet (0 to 646 meters) elevation. Access is very difficult.

Soils are in the Mollisols and Andisols orders. They formed in volcanic ash and residuum overlying basic igneous rock or cinders. Soil temperature regimes are isohyperthermic; soil moisture regimes are udic. Average annual rainfall ranges from 150 to 250 inches (3750 to 6250 millimeters), and cloud cover and fog occur frequently at the higher elevations of the ecological site. Water runoff is very rapid.

The forest canopy grows to 60 to 80 feet (18 to 25 meters) tall. Ground cover is sparse under the trees and there are few epiphytes.

Associated sites

QX197X01X502	Sandy Littoral Forest Sandy Littoral Forest adjoins Very Steep Forest where very steep mountain slopes descend to the sea coast. Sandy Littoral Forest 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 Very Steep Forest, which occurs on slopes up to 2100 feet in elevation, undergoes no flooding, and has well drained soils.
QX197X01X504	Alluvial Valley Forest Alluvial Valley Forest adjoins Very Steep Forest where very steep mountain slopes descend to alluvium-filled valleys near the coast. Alluvial Valley Forest ascends only to 250 feet elevation, undergoes occasional brief flooding, and has somewhat poorly drained soils, in contrast with Very Steep Forest, which occurs on slopes up to 2100 feet in elevation, undergoes no flooding, and has well drained soils.
QX197X01X505	Skeletal Pachic or Fulvic Forest Skeletal Pachic or Fulvic Forest adjoins Very Steep Forest where higher-elevation, very steep mountain slopes descend to lower-elevation, less-steep slopes. Skeletal Pachic or Fulvic Forest consists of Fulvudands and Pachic Mollisols on slopes of 6 to 60 percent that have high organic carbon content and high rock content. Very Steep Forest consists of Andisols and Andic Mollisols on slopes of 70 to 130 percent and have variable rock content and lower organic carbon content.
QX197X01X507	Dry Coastal Forest Dry Coastal Forest adjoins Very Steep Forest where very steep mountain slopes descend to meet lower-elevation, less-steep slopes. Dry Coastal Forest consists of Andisols on slopes of 0 to 40 percent, at elevations of 0 to 400 feet, and having mean annual rainfall of 120 to 160 inches. Very Steep Forest consists of Andisols, Andic Mollisols, and Mollisols on slopes of 70 to 130 percent, at elevations of 0 to 2100 feet, and having mean annual rainfall of 150 to 250 inches.
QX197X01X508	Cinder Subsurface Forest Cinder Subsurface Forest adjoins Very Steep Forest where very steep slopes border on less-steep slopes on mountainsides at high elevations. Cinder Subsurface Forest has slopes of 6 to 40 percent and occurs at elevations of 900 to 3000 feet. Very Steep Forest has slopes of 70 to 130 percent and occurs at elevations of 0 to 2100 feet.

Table 1. Dominant plant species

Tree	(1) Syzygium (2) Canarium
Shrub	Not specified
Herbaceous	(1) Freycinetia storckii

Legacy ID

F197XY509AS

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Physiographic features

This ecological site occurs on very steep to nearly vertical mountain slopes.

Table 2. Representative physiographic features

Landforms	(1) Island > Mountain slope
Runoff class	Medium
Flooding frequency	None
Ponding frequency	None
Elevation	2,099 ft
Slope	70 – 75%
Water table depth	60 in
Aspect	Aspect is not a significant factor

Climatic features

The area is characterized by abundant rain and warm, humid days and nights. Average annual precipitation in this ecological site ranges from 170 to 194 inches (4320 to 4930 centimeters). Rainfall varies over short distances due to topography. Cloud cover and fog occur frequently at the higher elevations of the ecological site, resulting in addition to soil moisture by fog drip. Air temperatures range from 74 to 80 F (23 to 27 C). 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)	170-194 in
Frost-free period (actual range)	365 days
Freeze-free period (actual range)	365 days
Precipitation total (actual range)	112-213 in
Frost-free period (average)	365 days
Freeze-free period (average)	365 days
Precipitation total (average)	182 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, OLOAVA

Soils are in the Mollisols and Andisols orders. They formed in volcanic ash and residuum overlying basic igneous rock or cinders. Soil temperature regimes are isohyperthermic; soil moisture regimes are udic to perudic. Effective rooting depths range from 11 to over 31 inches (28 to 79 centimeters).

Table 4. Representative soil features

Parent material	(1) Residuum (2) Volcanic ash (3) Cinders
Surface texture	(1) Silty clay loam
Family particle size	(1) Fine (2) Medial over pumiceous or cindery
Drainage class	Well drained
Permeability class	Slow to moderate
Depth to restrictive layer	11 – 31 in
Soil depth	11 – 31 in
Surface fragment cover <=3"	Not specified
Surface fragment cover >3"	Not specified
Available water capacity (0-40in)	2 – 4 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)	5.1 – 6.5
Subsurface fragment volume <=3" (0-40in)	12 – 33%
Subsurface fragment volume >3" (0-40in)	Not specified

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 clearing or burning 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 F197XY509AS (Very Steep 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 State

3. Invaded Forest State

T1A	-	State 1 Reference transitions to State 2 Cleared by landslides or severe windstorms when a nearby seed source for introduced plant species is present.
T1B	-	State 1 Reference transitions to State 3 Invaded Forest 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 may be restored to State 1 Reference. The intensity of active restoration measures will be determined by the slope of the site, the presence or lack of nearby native forest or, at least, some native trees, and 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 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 slope of the site, the species composition, and the amount and competitiveness of introduced species present on a given site.
T3A	-	State 3 Invaded Forest can transition back to State 2 Cleared due to damage by landslide, a severe storm, or clearing by humans. 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 – maali/ieie

1.2. Tavai – asi/lau maile

P1.1A	-	Storms or landslides that damage or kill trees or clearing of small plots by humans when there is no significant source of invasive introduced plant species nearby 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 typical dominant 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

State 3 submodel, plant communities

3.1. Asi – red beadtree/Koster’s curse/mile-a-minute vine

State 1
Reference State

This ecological site is a native forest with a tree canopy that is 60 to 80 feet (18 to 25 meters) tall. Ground cover is sparse. Epiphytes are few.

Community 1.1
Asi – maali/ieie

Among the dominant tree species are asi (Syzygium inophylloides), maali (Canarium samoense), Buchanania merrillii, tamanu (Calophyllum inophyllum), auauli (Diospyros samoensis), mafoa (Canarium harveyi), atone (Myristica inutilis), and ifilele (Intsia bijuga). Common ferns include asaua (Dicranopteris linearis) under canopy openings, bird’s nest fern (Asplenium nidus), leather fern (Davallia solida), musk fern (Microsorum grossum), and Asplenium polyodon. The scandent shrub gau (Alyxia bracteolosa) is common. Climbers and lianas include 'ie'ie (Freycinetia storckii), maile (Alyxia stellata), and Gynochthodes epiphytica.

Dominant plant species

syzygium (Syzygium), tree
olive (Canarium), tree
freycinetia (Freycinetia storckii), other herbaceous

Community 1.2
Tavai – asi/lau maile

The same tree species as in Community Phase 1.1 remain in this phase, but other native tree species, commonly tavai (Rhus taitensis) and beach hibiscus (Hibiscus tiliaceus), 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
syzygium (Syzygium), tree
Maile (Alyxia stellata), other herbaceous

Pathway P1.1A
Community 1.1 to 1.2

Storms or landslides that damage or kill trees or clearing of small plots by humans when there is no significant source of invasive introduced plant species nearby 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 typical dominant native species when given adequate time to recover after disturbance.

State 2
Cleared State

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

Community 2.1
Lantana – Honolulu rose/ fua lele/mile-a-minute vine

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), Koster’s curse (Clidemia hirta), and nettleleaf velvetberry (Stachytarpheta urticifolia) are dominant. The shrub layer may also include seedlings and saplings of any native trees that have persisted on or near the site or invasive, introduced tree species such as African tulip tree (Spathodea campanulata). Mile-a-minute vine (Mikania micrantha) and the large, introduced forb fua lele (Crassocephalum crepidioides) are commonly present.

Dominant plant species

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

State 3
Invaded Forest State

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.

Community 3.1
Asi – red beadtree/Koster’s curse/mile-a-minute vine

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 peacocks plume (Falcataria moluccana), and red beantree (Adenanthera pavonina). 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).

Dominant plant species

syzygium (Syzygium), tree
red beadtree (Adenanthera pavonina), tree
soapbush (Clidemia hirta), shrub
mile-a-minute (Mikania micrantha), other herbaceous

Transition T1A
State 1 to 2

The Reference State (1) transitions to the Cleared State (2) by landslides or severe windstorms when a nearby seed source for introduced plant species is present.

Transition T1B
State 1 to 3

The Reference State (1) transitions to the Invaded Forest State (3) 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 State (2) may be restored to the Reference State (1). The intensity of active restoration measures will be determined by the slope of the site, the presence or lack of nearby native forest or, at least, some native trees, and 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 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) Invaded Forest can be restored to the Reference State (1). The difficulty, cost, and likelihood of success will depend on the slope of the site, the species composition, and the amount and competitiveness of introduced species present on a given site.

Transition T3A
State 3 to 2

The Invaded Forest State (3) can transition back to the Cleared State (2) due to damage by landslide, a severe storm, or clearing by humans. The Cleared 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 F197XY509AS Very Steep 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