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Ecological site QX192X01X002

Deep Alfic Soils on Volcanic Uplands

Last updated: 5/08/2025
Accessed: 05/20/2025

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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): 192X–Volcanic Highlands of the Mariana Islands

This MLRA is in the southern half of Guam. Topography consists of mountains and plateaus that are dissected by streams. The highest elevation is 1,336 feet (410 meters). The geology consists of deeply weathered volcanic rock with some limestone inclusions. Average annual rainfall ranges from 85 to 100 inches (2,160 to 2,540 millimeters) in the northern half of this MLRA and from 95 to 118 inches (2,410 to 3,000 millimeters) in the southern half. Average annual temperature is 79 degrees F (26 degrees C). The dry season occurs from January through April; the rainy season occurs from July through November. Trade winds are persistent during the dry season. Typhoons are frequent. Soils are Entisols, Alfisols, Inceptisols, Mollisols, or Oxisols. The dominant soil moisture regime is ustic. The soil temperature regime is isohyperthermic. Except for remnants of native forest in gulches and river valleys, forest vegetation has been largely replaced by grasses through repeated burning. Introduced deer, pigs, goats, and water buffalo are common (USDA-NRCS, 2006).

Classification relationships

This ecological site occurs within Major Land Resource Area (MLRA) 192 – Volcanic Islands of the Mariana Islands.

Ecological site concept

This ecological site occurs on the island of Guam in the Mariana Islands. It occurs on nearly level to very steep (0 to 60 percent slopes) volcanic uplands at elevations ranging from 30 to 985 feet (9 to 300 meters) (USDA-SCS, 1988).

Tate soils are deep, well drained, Inceptisols (Oxic Haplustalfs) which formed in residuum derived from tuff and tuff breccia (USDA-SCS, 1988). Sasalaguan soils are moderately deep Inceptisols (Udertic Haplustepts) derived from tuffaceous sandstone (Soil Survey Staff, 2025). Soil temperature regimes are isohyperthermic; soil moisture regimes are ustic. Soil temperature regimes are isohyperthermic; soil moisture regimes are ustic. Mean annual precipitation is 104 inches (2,640 millimeters) (PRISM, 2006). Water runoff is low to high; permeability is very slow to moderately slow (USDA-SCS, 1988). Effective rooting depth ranges from 28 to 43 inches (70 to 110 centimeters (USDA-SCS, 1988). Available water-holding capacity is 4 inches (10 cm). Base saturation is moderately high (greater than 35 percent); pH is ranges from 5.5 to 5.8 such that aluminum toxicity is not a limiting factor to plant growth. Most of the area is vegetated by forest, grasses, and forbs (Amidon et al., 2017; Fosberg, 1960; USDA-SCS, 1988).

Associated sites

QX192X01X003	Shallow Soils on Volcanic Uplands Both ecological sites occur adjacent to each other on volcanic uplands. Soils of the Deep Alfic Soils on Volcanic Uplands Ecological Site (QX192X01X002) are primarily deep Alfisols on hillslopes with low available water holding capacity (4 inches), moderately high base saturation, and no aluminum toxicity which support forest, grasses, and forbs. Soils of the Shallow Soils on Volcanic Uplands (QX192X01X003) are shallow Mollisols with very low available water holding capacity (2 inches), high base saturation, and no aluminum toxicity that support upland grasses, forbs, and forest.
QX192X01X004	Very Deep Soils on Volcanic Uplands Both ecological sites occur adjacent to each other on volcanic uplands. Soils of the Deep Alfic Soils on Volcanic Uplands Ecological Site (QX192X01X002) are primarily deep Alfisols on hillslopes with low available water holding capacity (4 inches), moderately high base saturation, nearly level to very steep (0 to 60 percent) slopes, and no aluminum toxicity, and support upland grasses, forbs, and forest. Soils of the Very Deep Soils on Volcanic Uplands (QX192X01X004) are very deep Alfisols on upland slopes, concave areas, and drainageways, have moderate available water holding capacity (4 inches), moderate base saturation, gently sloping to strongly sloping (3 to 15 percent) slopes, no aluminum toxicity, and support a variety of grasses and forbs.
QX191X01X506	Somewhat Poorly and Poorly Drained Valley Bottoms and Coastal Plains The Somewhat Poorly and Poorly Drained Valleys and Alluvial Coastal Plains Ecological Site (QX191X01X506) occurs below this ecological site in coastal plains and broad valleys rather than on the mountain slopes. The soils have high water tables, occasional flooding, slightly brackish ground water in coastal areas, and support wetland forest, grasses, and sedges. The Deep Alfic Soils on Volcanic Uplands Ecological Site (QX192X01X002) occur on volcanic uplands, have steeper slopes, are well drained, have deep water tables, no flooding, and support upland grasses, forbs, and forest.
QX192X01X001	Moderately Deep Oxic Soils on Volcanic Uplands Both ecological sites occur adjacent to each other on volcanic uplands. Soils of the Moderately Deep Oxic Soils on Volcanic Uplands Ecological Site (QX192X01X001) are primarily moderately deep Oxisols on mountain slopes with primarily low to high available water holding capacity (3 inches), low base saturation, nearly level to very steep (0 to 90 percent) slopes, and aluminum toxicity, and support mostly Pacific Island silvergrass (swordgrass). Soils of the Deep Alfic Soils on Volcanic Uplands Ecological Site (QX192X01X002) are primarily deep Alfisols on upland slopes, have slightly higher available water holding capacity (4 inches), moderately high base saturation, nearly level to very steep (0 to 60 percent) upland slopes, no aluminum toxicity, and support forest, grasses, and forbs.
QX191X01X505	Very Low Available Water Capacity Soils on Limestone Plateaus and Escarpments The Very Low Available Water Holding Capacity Soils on Limestone Plateaus and Escarpments Ecological Site (QX191X01X505) occurs on limestone plateau that may border on volcanic uplands. Depending on slope (0 to 99 percent), water runoff ranges from very slow to high. Available water holding capacity is very low (1 inch), slightly less than in this ecological site. Water that does not run off very steep slopes seeps through the underlying porous limestone. Where this groundwater encounters volcanic uplands, it can flow out to the surface as seeps or springs. Soils in QX191X01X505 formed over porous limestone, have high base saturation, no aluminum toxicity, and are mostly vegetated by native forest, unlike this ecological site, which has soils formed from volcanic materials, moderately high base saturation, and supports grasses, forbs, and forest.
QX191X01X503	Very Shallow to Moderately Deep Soils on Limestone Plateaus The Very Shallow to Moderately Deep Soils on Limestone Plateaus Ecological Site (QX191X01X503) occurs on limestone plateaus that may border on volcanic uplands. Depending on slope (0 to 30 percent), water runoff ranges from slow to medium. Available water holding capacity is very low to low, as in this ecological site. Water that does not run off the steeper slopes seep through the underlying porous limestone. Where this groundwater encounters volcanic uplands, it can flow out to the surface as seeps or springs. Soils in QX191X01X503 formed over limestone, have high base saturation and no aluminum toxicity, and where they have not been farmed it’s soils support vegetation consisting of introduced grass, forb, and tree species, including forests of tangantangan (white leadtree) and some native forest. Soils in this ecological site formed on volcanic materials, have moderately high base saturation and no aluminum toxicity, and support grasses, forbs, and forest, but very little tangantangan.
QX192X01X501	Somewhat Poorly Drained Alluvium The Somewhat Poorly Drained Alluvium Ecological Site (QX192X01X501) occurs in stream channels, depressions, and seeps surrounded by this ecological site, which occurs on adjacent hillslopes. As such water will move from this ecological site into QX192X01X501. Soils in the Deep Alfic Soils on Volcanic Uplands Ecological Site (QX192X01X002) have low available water holding capacity (4 inches), a very deep-water table, and support upland grasses, forbs, and forest. Soils in the QX192X01X501 have moderate water holding capacity (7 inches), a moderately deep water table (30 inches), occasional flooding, and support wetland forest, grasses, and sedges.

Similar sites

QX191X01X002	Moderately Deep Alfic Soils on Volcanic Uplands The Moderately Deep Alfic Soils on Volcanic Uplands Ecological Site (QX191X01X002) occurs in Saipan, Tinian, and Rota, while this ecological site (QX192X01X002) occurs on volcanic uplands in Guam. Their soils are classified differently (Udertic Haplustepts and Oxic Haplustalfs in QX192X01X002; Kandiustalfic Eutrustox in QX191X01X002) and the sites are correlated with different soils (Soil Survey Staff, 2025). However, the soils of the two ecological sites are similar in every important characteristic and support the same types of vegetation.

QX191X01X002

Moderately Deep Alfic Soils on Volcanic Uplands

The Moderately Deep Alfic Soils on Volcanic Uplands Ecological Site (QX191X01X002) occurs in Saipan, Tinian, and Rota, while this ecological site (QX192X01X002) occurs on volcanic uplands in Guam. Their soils are classified differently (Udertic Haplustepts and Oxic Haplustalfs in QX192X01X002; Kandiustalfic Eutrustox in QX191X01X002) and the sites are correlated with different soils (Soil Survey Staff, 2025). However, the soils of the two ecological sites are similar in every important characteristic and support the same types of vegetation.

Table 1. Dominant plant species

Tree	Not specified
Shrub	(1) Mimosa pudica
Herbaceous	(1) Dimeria chloridiformis (2) Miscanthus floridulus

Legacy ID

R192XY002GU

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Physiographic features

This ecological site occurs in uplands on the mountain slopes of an extinct volcano (USDA-SCS, 1988). The depth to water table is greater than 72 inches (185 centimeters).

Table 2. Representative physiographic features

Landforms	(1) Upland > Mountain slope
Runoff class	Low to high
Flooding frequency	None
Ponding frequency	None
Elevation	30 – 985 ft
Slope	60%
Water table depth	72 in
Aspect	Aspect is not a significant factor

Climatic features

Summary for this ecological site

Rainfall statistics were determined from Guam PRISM rainfall raster data (PRISM, 2006). Representative (20th and 80th percentiles) values for mean annual precipitation range from 100 to 108 inches (2,540 to 2,745 millimeters) while actual (10th and 90th percentiles) values for mean annual precipitation range from 97 to 110 inches (2,465 to 2,795 millimeters). Extreme values range from 92 to 116 inches (2,340 to 2,950 millimeters). The average annual precipitation is 104 inches (2,640 millimeters), and the median annual average precipitation is 103 inches (2,615 millimeters).

Temperature statistics were determined from Guam PRISM temperature raster data (PRISM, 2006) Representative (20th and 80th percentiles) values for mean annual temperatures range from 79 to 81 degrees F (26 to 27 degrees C) while actual (10th and 90th percentiles) values for mean annual temperatures also range from 79 to 81 degrees F (26 to 27 degrees C). Extreme values range from 77 to 82 degrees F (25 to 28 degrees C). The average annual temperature is 79 degrees F (26 degrees C), and the median annual temperature is 81 degrees F (27 degrees C).

The data presented in the climate normals table below are from the PRISM rainfall raster data presented above (PRISM, 2006). I did not use the Western Region Climate Center weather stations which were available for Guam as they did not provide a good representation of the spatial distribution of this ecological site (Western Regional Climate Center, 2020).

General Concepts

The climate of Guam is uniformly warm and humid throughout the year. Afternoon temperatures typically are about 86 degrees F (30 degrees C); nighttime temperatures are about 68 degrees F (20 degrees C). Relative humidity is 65 to 75 percent in the afternoon to 85 to 100 percent at night. Though temperature and humidity vary only slightly throughout the year, rainfall and wind conditions vary markedly. There are two main seasons on Guam, the dry season from January through April and the rainy season from mid-July to mid-November. Moisture deficit occurs between January and June. Mean annual rainfall ranges from about 98 inches (2,490 millimeters) on the windward (east) side of the higher mountains to about 79 inches (2,005 millimeters) along the coast of the west side of the southern half of the island. On average, about 15 percent of the annual rainfall occurs during the dry season and 55 percent during the rainy season (Fosberg, 1960; USDA-SCS, 1988).

Throughout the year, the dominant winds in Guam are the trade winds that blow from the east or northeast. The trade winds are strongest and most constant during the dry season, when windspeeds of 15 to 25 mph (25 to 40 kph) are common. Coastal areas that have east, and northeast exposures are subject to salt spray and buffeting winds (Fosberg, 1960; USDA-SCS, 1988).

During the rainy season the trade winds may break down and be replaced by a weak, westerly monsoon influence that brings heavy showers or steady and sometimes torrential rains. Guam lies in the path of typhoons from the southeast and east. They bring heavy rains and violent winds that may result in a surge of water onto low-lying coastal areas. They occur most frequently during the latter half of the year. The chance of having one or more typhoons pass close to Guam in any particular year is about once in three years. The chance of having a typhoon move directly across Guam is about once in eight years (Fosberg, 1960; USDA-SCS, 1988).

Table 3. Representative climatic features

Frost-free period (characteristic range)	365 days
Freeze-free period (characteristic range)	365 days
Precipitation total (characteristic range)	100-108 in
Frost-free period (actual range)	365 days
Freeze-free period (actual range)	365 days
Precipitation total (actual range)	97-110 in
Frost-free period (average)	365 days
Freeze-free period (average)	365 days
Precipitation total (average)	104 in

Influencing water features

Ravines in this ecological site carry water during the rainy season. This ecological site consists of the uplands surrounding stream courses; the ravines support other ecological sites (USDA-SCS, 1988).

Number of National Wetland Inventory (NWI) features overlapping ecological site: Riverine (67), freshwater emergent wetland (33), freshwater forested/shrub wetland (33), freshwater pond (5), and lake (1) (USFWS, 2023).

Soil features

The soil components associated with this ecological site are Atate and Sasalaguan.

Atate soils are deep, well drained Alfisols (Oxic Haplustalfs) which formed in residuum derived from tuff and tuff breccia (USDA-SCS, 1988). Sasalaguan soils are moderately deep Inceptisols (Udertic Haplustepts) derived from tuffaceous sandstone (Soil Survey Staff, 2025). Soil temperature regimes are isohyperthermic; soil moisture regimes are ustic. These soils have vertic (shrink-swell) properties (USDA-SCS, 1988). Most of the soils have an argillic (accumulated translocated clay) horizon. Their pH is high enough (5.5 to 5.8) so that aluminum toxicity is not a limiting factor to plant growth. These soils are susceptible to erosion and slumping that can lead to formation of badlands.

Table 4. Representative soil features

Parent material	(1) Residuum – tuff (2) Residuum – tuff breccia
Surface texture	(1) Silty clay (2) Clay
Family particle size	(1) Very-fine
Drainage class	Well drained
Permeability class	Very slow to moderately slow
Depth to restrictive layer	24 – 43 in
Soil depth	24 – 43 in
Surface fragment cover <=3"	Not specified
Surface fragment cover >3"	Not specified
Available water capacity (0-40in)	4 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) (0-10in)	5.5 – 5.8
Subsurface fragment volume <=3" (0-40in)	Not specified
Subsurface fragment volume >3" (0-40in)	Not specified

Ecological dynamics

The main human disturbance is intentional and frequent burning of highly flammable Pacific Island silvergrass or swordgrass (Miscanthus floridulus); this prevents survival of trees and increases erosion (Amidon et al., 2019; Amidon et al., 2017; Fosberg, 1960; Stone, 1970; USDA-SCS, 1988; Wagner and Grether, 1948; Willsey et al., 2019).

The main natural disturbance is strong storms that can damage or kill vegetation by high wind speeds (Amidon et al., 2019; Amidon et al., 2017; Athens and Ward, 2004; Fosberg, 1960; Stone, 1970; USDA-SCS, 1988; Wagner and Grether, 1948; Willsey et al., 2019).

State and transition model

Custom diagram

Standard diagram

Figure 1. State-and-Transition Model for the Deep Alfic Soils on Volcanic Uplands Ecological Site (R192XY002GU).

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. Native Forest State

3. Tree-Invaded State

4. Grazed State

5. Badlands State

States 1, 5 and 2 (additional transitions)

1. Reference State

5. Badlands State

2. Native Forest State

R1A	-	The Reference State (1) can be restored to the Native Forest State (2) by fire protection, weed control, erosion control (Vetiver grass is useful), mulching, fertilizing, and replanting of native plant species.
T1B	-	The Reference State (1) transitions to the Tree-Invaded State (3) when fire is infrequent, allowing the growth of trees and shrubs.
R1B	-	The Reference State (1) can be restored to the Grazed State (4) by fire protection, weed control, erosion control, and planting desired forage grass species.
T1A	-	The Reference State (1) transitions to the Badlands State (5) through destruction of vegetation cover and surface litter by fire, leading to loss of surface soil horizons by erosion and slumping (Amidon et al., 2019; Amidon et al., 2017; Fosberg, 1960; Stone, 1970; USDA-SCS, 1988; Wagner and Grether, 1948; Willsey et al., 2019).
T2A	-	The Native Forest State (2) transitions to the Reference State (1) by destruction of the forest by human-caused fire in adjacent stands of Pacific Island silvergrass or swordgrass.
R3A	-	The Tree-Invaded State (3) is restored to the Reference State (1) by fire.
R3C	-	The Tree-Invaded State (3) may be restored to the Native Forest State (2). The intensity of active restoration measures will be determined by the presence or lack of native trees already on the site as well as the density and species mix of grasses, vines, shrubs, and introduced trees present on the site, especially if many competitive introduced species are present.
R3B	-	The Tree-Invaded State (3) may be restored to Grazed State (4) by clearing the forest, maintaining erosion control, weed control, and seeding desired forage grasses.
T3A	-	The Tree-Invaded State (3) transitions to the Badlands State (5) through destruction of tree cover and surface litter by fire, leading to loss of surface soil horizons by erosion and slumping. Soil slumping is considered rare in forested sites in the Marianas Islands (Amidon et al., 2019; Amidon et al., 2017; Fosberg, 1960; Stone, 1970; USDA-SCS, 1988; Wagner and Grether, 1948; Willsey et al., 2019).
T4A	-	The Grazed State (4) can transition the Reference State (1) by reinvasion of weedy species, particularly Pacific Island silvergrass or swordgrass (Miscanthus floridulus) and forbs.
T4B	-	The Grazed State (4) can transition to the Tree-Invaded State (3) by abandonment or light grazing that allows establishment of trees and shrubs.
T4C	-	The Grazed State (4) can transition to the Badlands State (5) by overgrazing that reduces cover of vegetation and litter to a point at which soil erosion removes the upper soil horizons.
R5A	-	The Badlands State (5) can be partially restored to the Reference State (1) in areas that are reasonably accessible by instituting erosion control measures that result in patches of soil accumulation.
R5C	-	The Badlands State (5) can be started on a path to restoration towards the Native Forest State (2) by instituting erosion control measures and excluding fire. Replanting native plant species can then be successful with mulching, fertilization, and addition and maintenance of soil organic matter.
R5B	-	The Reference State (5) can be restored to the Tree-Invaded State (3) by instituting erosion control measures and excluding fire. Replanting trees, either native, introduced, or both, can then be successful with mulching, fertilization, and reducing acidity and aluminum toxicity by lime application and maintenance of soil organic matter.

State 1 submodel, plant communities

1.1. Dimeria - Pacific Islands Silvergrass (Swordgrass)/Shameplant

1.2. Dimeria - Pacific Island Silvergrass (Swordgrass)/Shameplant/Beach Sheoak

1.1A	-	Phase 1.1 changes to phase 1.2 over time if fire does not occur over a period that allows scattered trees and shrubs to seed into a site and grow.
1.2A	-	Fire kills beach sheoak (Causarina equisetifolia) and any other woody vegetation that may have established, causing a change back from Phase 1.2 to Phase 1.1.

State 2 submodel, plant communities

2.1. Chosga – Mago

2.2. Sea Hibiscus – Tahitian Screwpine

2.1A	-	Storms that damage or kill trees causes a phase change from phase 2.1 to phase 2.2 typified by a partial, temporary change in dominant tree species and a temporary increase in ground level vegetation.
2.2A	-	Community phase 2.2 will revert to phase 2.1 with gradual regrowth of a more diverse array of native species when given adequate time to recover after disturbance (Amidon et al., 2019; Amidon et al., 2017; Fosberg, 1960; Stone, 1970; USDA-SCS, 1988; Wagner and Grether, 1948; Willsey et al., 2019).

State 1
Reference State

The Reference State (1) is medium to tall (to 6.5 feet or 2 meters) grassland. The consensus of most authors indicates that these grasslands did not exist in the southern Marianas Islands until humans arrived and started burning the ubiquitous forests of these islands (Athens and Ward, 2004). However, naturally occurring grassland is considered to occur on certain locations on the young stratovolcano islands of the northern end of the island chain (Amidon et al., 2019; Amidon et al., 2017; Fosberg, 1960; Stone, 1970; USDA-SCS, 1988; Wagner and Grether, 1948; Willsey et al., 2019). The Reference State (1) is highly prone to fire; most fires appear to be set intentionally. The soils are vulnerable to erosion and slumping, especially when vegetation cover is low. This condition can lead to development of patches of badland (Amidon et al., 2019; Amidon et al., 2017; Fosberg, 1960; Stone, 1970; USDA-SCS, 1988; Wagner and Grether, 1948; Willsey et al., 2019). The grass and forb species in this state are sometimes used for grazing. However, the forage value is low (USDA-SCS, 1988).

Community 1.1
Dimeria - Pacific Islands Silvergrass (Swordgrass)/Shameplant

The Reference State (1) is a grassland that includes some forbs and a few shrubs. Typical species are dimeria (Dimeria chloridiformis), Pacific Islands silvergrass or swordgrass (Miscanthus floridulus), mission grass or foxtail (Pennisetum polystachion), golden false beardgrass (Chrysopogon aciculatus), pignut (Hyptis suaveolens), false ironwort (Hyptis capitata), Philippine ground orchid (Spathoglottis plicata), shameplant (Mimosa pudica), and porterweed (Stachytarpheta spp.). Indian mulberry (Morinda citrifolia), a shrub, can occur (Amidon et al., 2019; Amidon et al., 2017; Fosberg, 1960; Stone, 1970; USDA-SCS, 1988; Wagner and Grether, 1948; Willsey et al., 2019).

Dominant plant species

shameplant (Mimosa pudica), shrub
(Dimeria chloridiformis), grass
Pacific Island silvergrass (Miscanthus floridulus), grass

Community 1.2
Dimeria - Pacific Island Silvergrass (Swordgrass)/Shameplant/Beach Sheoak

This community is dominated by dimeria (Dimeria chloridiformis) and Pacific Islands silvergrass or swordgrass (Miscanthus floridulus) but contains scattered small trees and shrubs such as shameplant (Mimosa pudica). The most common tree species by far is beach sheoak (Casuarina equisetifolia) (Amidon et al., 2019; Amidon et al., 2017; Fosberg, 1960; Stone, 1970; USDA-SCS, 1988; Wagner and Grether, 1948; Willsey et al., 2019).

Dominant plant species

beach sheoak (Casuarina equisetifolia), tree
shameplant (Mimosa pudica), shrub
(Dimeria chloridiformis), grass
Pacific Island silvergrass (Miscanthus floridulus), grass

Pathway 1.1A
Community 1.1 to 1.2

Phase 1.1 changes to phase 1.2 over time if fire does not occur over a period that allows scattered trees and shrubs to seed into a site and grow.

Pathway 1.2A
Community 1.2 to 1.1

Fire kills beach sheoak (Causarina equisetifolia) and any other woody vegetation that may have established, causing a change back from Phase 1.2 to Phase 1.1.

State 2
Native Forest State

The Native Forest State (2) has two community phases consisting of native forest species. No intact examples of the original native forest remain, so the species list is historical and based on remnant plants and species persisting in ravines. The consensus of authors suggests that fire was probably not an important disturbance in these forests before humans arrived. The main disturbance was storm damage due to typhoons (Amidon et al., 2019; Amidon et al., 2017; Fosberg, 1960; Stone, 1970; USDA-SCS, 1988; Wagner and Grether, 1948; Willsey et al., 2019).

Community 2.1
Chosga – Mago

Common trees of this forest include chosga (Glochidion marianum), mago (Hernandia sonora), grand devil’s-claws (Pisonia grandis), sea hibiscus (Hibiscus tiliaceus), bakong (Pandanus dubius), Alexandrian laurel (Calophyllum inophyllum), sea putat (Barringtonia asiatica), Tahitian screwpine (Pandanus tectorius), and tropical almond (Terminalia catappa) (Amidon et al., 2019; Amidon et al., 2017; Fosberg, 1960; Stone, 1970; USDA-SCS, 1988; Wagner and Grether, 1948; Willsey et al., 2019).

Dominant plant species

(Glochidion marianum), tree
mago (Hernandia sonora), tree

Community 2.2
Sea Hibiscus – Tahitian Screwpine

Community phase 2.2 is dominated by sea hibiscus (Hibiscus tiliaceus) and Tahitian screwpine (Pandanus tectorius) for some years until the more diverse native forest regrows between typhoons (Amidon et al., 2019; Amidon et al., 2017; Fosberg, 1960; Stone, 1970; USDA-SCS, 1988; Wagner and Grether, 1948; Willsey et al., 2019).

Dominant plant species

sea hibiscus (Hibiscus tiliaceus), tree
Tahitian screwpine (Pandanus tectorius), tree

Pathway 2.1A
Community 2.1 to 2.2

Storms that damage or kill trees causes a phase change from phase 2.1 to phase 2.2 typified by a partial, temporary change in dominant tree species and a temporary increase in ground level vegetation.

Pathway 2.2A
Community 2.2 to 2.1

Community phase 2.2 will revert to phase 2.1 with gradual regrowth of a more diverse array of native species when given adequate time to recover after disturbance (Amidon et al., 2019; Amidon et al., 2017; Fosberg, 1960; Stone, 1970; USDA-SCS, 1988; Wagner and Grether, 1948; Willsey et al., 2019).

State 3
Tree-Invaded State

The Tree-Invaded State (3) consists of one community phase dominated by a variable mixture of small trees, shrubs, vines, forbs, and grasses that thrive in the absence of fire (Amidon et al., 2019; Amidon et al., 2017; Fosberg, 1960; Stone, 1970; USDA-SCS, 1988; Wagner and Grether, 1948; Willsey et al., 2019).

Community 3.1
Beach Sheoak – Small Philippine Acacia/Limeberry/Dimeria

Dimeria (Dimeria chloridiformis), Pacific Island silvergrass or swordgrass (Miscanthus floridulus), and other grasses are still present where not shaded out by trees. The most common tree species are native beach sheoak (Casuarina equisetifolia) and introduced small Philippine acacia (Acacia confusa). Introduced limeberry shrub (Triphasia trifolia) is also common. Over time, more tree and shrub species could establish. These might include the native species listed within community phase 2.1. Some possible introduced species include betel palm (Areca catechu) and ilang-ilang (Cananga odorata). White leadtree or tangantangan (Leucaena leucocephala) is not common in this ecological site (Amidon et al., 2019; Amidon et al., 2017; Fosberg, 1960; Stone, 1970; USDA-SCS, 1988; Wagner and Grether, 1948; Willsey et al., 2019).

Dominant plant species

beach sheoak (Casuarina equisetifolia), tree
small Philippine acacia (Acacia confusa), tree
limeberry (Triphasia trifolia), shrub
(Dimeria chloridiformis), grass

State 4
Grazed State

The Grazed State (4) is grassland with one community phase.

Community 4.1
Hilograss – Kodomillet

This community phase is dominated by grasses that have fair to good forage value. Typically, they are hilograss (Paspalum conjugatum), an introduced species, and kodomillet (Paspalum scrobiculatum), a native species. Golden false beardgrass (Chrysopogon aciculatus) may also be present; it has fair forage value when young. Good grazing management will help maintain the desired forage mix. Care must be taken to suppress or control undesirable species such as Pacific Island silvergrass or swordgrass (Miscanthus floridulus), pignut (Hyptis suaveolens), false ironwort (Hyptis capitata), Philippine ground orchid (Spathoglottis plicata), shameplant (Mimosa pudica), and porterweed (Stachytarpheta spp.) (Amidon et al., 2019; Amidon et al., 2017; Fosberg, 1960; Stone, 1970; USDA-SCS, 1988; Wagner and Grether, 1948; Willsey et al., 2019).

Dominant plant species

hilograss (Paspalum conjugatum), grass
kodomillet (Paspalum scrobiculatum), grass

State 5
Badlands State

The Badlands State (5) consists of one community phase. It is sparsely vegetated with much bare ground. Most of the upper soil horizons have been eroded away, leaving highly acidic and infertile subsoil that supports few plant species (Amidon et al., 2019; Amidon et al., 2017; Fosberg, 1960; Stone, 1970; USDA-SCS, 1988; Wagner and Grether, 1948; Willsey et al., 2019).

Community 5.1
Old World Forkedfern/Golden False Beardgrass

Vegetation consists of sparse, low-stature ferns, fern allies, shrubs, and grasses. Typical species are Old World forkedfern (Dicranopteris linearis), midsorus fern (Blechnum orientale), staghorn clubmoss (Lycopodiella cernua), the shrubs Myrtella bennigseniana, Wikstroemia elliptica, beach naupaka (Scaevola sericea), Geniostoma micranthus, Malabar melastome (Melastoma malabathricum), and golden false beardgrass (Chrysopogon aciculatus) (Amidon et al., 2019; Amidon et al., 2017; Fosberg, 1960; Stone, 1970; USDA-SCS, 1988; Wagner and Grether, 1948; Willsey et al., 2019).

Dominant plant species

golden false beardgrass (Chrysopogon aciculatus), grass
Old World forkedfern (Dicranopteris linearis), other herbaceous

Restoration pathway R1A
State 1 to 2

The Reference State (1) can be restored to the Native Forest State (2) by fire protection, weed control, erosion control (vetivergrass (Vetiveria sp.)) is useful, mulching, fertilizing, and replanting of native plant species.

Transition T1B
State 1 to 3

The Reference State (1) transitions to the Tree-Invaded State (3) when fire is infrequent, allowing the growth of trees and shrubs.

Restoration pathway R1B
State 1 to 4

The Reference State (1) can be restored to the Grazed State (4) by fire protection, weed control, erosion control, and planting desired forage grass species.

Transition T1A
State 1 to 5

The Reference State (1) transitions to the Badlands State (5) through destruction of vegetation cover and surface litter by fire, leading to loss of surface soil horizons by erosion and slumping (Amidon et al., 2019; Amidon et al., 2017; Fosberg, 1960; Stone, 1970; USDA-SCS, 1988; Wagner and Grether, 1948; Willsey et al., 2019).

Transition T2A
State 2 to 1

The Native Forest State (2) transitions to the Reference State (1) by destruction of the forest by human-caused fire in adjacent stands of Pacific Island silvergrass or swordgrass.

Restoration pathway R3A
State 3 to 1

The Tree-Invaded State (3) is restored to the Reference State (1) by fire.

Restoration pathway R3C
State 3 to 2

The Tree-Invaded State (3) may be restored to the Native Forest State (2). The intensity of active restoration measures will be determined by the presence or lack of native trees already on the site as well as the density and species mix of grasses, vines, shrubs, and introduced trees present on the site, especially if many competitive introduced species are present.

Restoration pathway R3B
State 3 to 4

The Tree-Invaded State (3) may be restored to Grazed State (4) by clearing the forest, maintaining erosion control, weed control, and seeding desired forage grasses.

Transition T3A
State 3 to 5

The Tree-Invaded State (3) transitions to the Badlands State (5) through destruction of tree cover and surface litter by fire, leading to loss of surface soil horizons by erosion and slumping. Soil slumping is considered rare in forested sites in the Marianas Islands (Amidon et al., 2019; Amidon et al., 2017; Fosberg, 1960; Stone, 1970; USDA-SCS, 1988; Wagner and Grether, 1948; Willsey et al., 2019).

Transition T4A
State 4 to 1

The Grazed State (4) can transition the Reference State (1) by reinvasion of weedy species, particularly Pacific Island silvergrass or swordgrass (Miscanthus floridulus) and forbs.

Transition T4B
State 4 to 3

The Grazed State (4) can transition to the Tree-Invaded State (3) by abandonment or light grazing that allows establishment of trees and shrubs.

Transition T4C
State 4 to 5

The Grazed State (4) can transition to the Badlands State (5) by overgrazing that reduces cover of vegetation and litter to a point at which soil erosion removes the upper soil horizons.

Restoration pathway R5A
State 5 to 1

The Badlands State (5) can be partially restored to the Reference State (1) in areas that are reasonably accessible by instituting erosion control measures that result in patches of soil accumulation.

Restoration pathway R5C
State 5 to 2

The Badlands State (5) can be started on a path to restoration towards the Native Forest State (2) by instituting erosion control measures and excluding fire. Replanting native plant species can then be successful with mulching, fertilization, and addition and maintenance of soil organic matter.

Restoration pathway R5B
State 5 to 3

The Reference State (5) can be restored to the Tree-Invaded State (3) by instituting erosion control measures and excluding fire. Replanting trees, either native, introduced, or both, can then be successful with mulching, fertilization, and reducing acidity and aluminum toxicity by lime application and maintenance of soil organic matter.

Additional community tables

Supporting information

Other references

References for the Deep Alfic Soils on Volcanic Uplands Ecological Site (R192XY002GU)

Amidon F., C. Brunson, J. Flores, R. Frager, F. Galsim, S.E. Miller, R. Pe`a, and M.K. Reeves. (2019). Savannas of the Mariana Islands Archipelago. Encyclopedia of the World's Biomes. Elsevier Inc. Https://doi.org/10.1016/B978-0-12-409548-9.11986-4

Amidon F., M. Metevier, and S.E. Miller. (2017). Vegetation Mapping of the Mariana Islands: Commonwealth of the Northern Mariana Islands and Territory of Guam. US Fish and Wildlife Service and Pacific Islands Climate Change Cooperative. Final Report November 2017.

Athens J., and J.V. Ward. (2004). Holocene vegetation, savanna origins and human settlement of Guam. In A Pacific Odyssey: Archaeology and Anthropology in the Western Pacific. Papers in Honour of Jim Specht, ed. Val Attenbrow and Richard Fullagar, pp. 15–30. Records of the Australian Museum, Supplement 29. Sydney: Australian Museum.

Fosberg F.R. (1960). The Vegetation of Micronesia. I. General descriptions, the vegetation of the Marianas Islands, and a detailed consideration of the vegetation of Guam. Bulletin of the American Museum of Natural History 199:1.

PRISM Climate Group, Oregon State University. (2006). https://prism.oregonstate.edu, data created 4 Feb 2014, accessed 09 Oct 2024. Pacific Islands Project: Average monthly precipitation, minimum and maximum temperature, relative humidity, and mean dew point temperature for the period 1971-2000 (completed 2006). Covers Hawaii, Kosrae, Manua, Pohnpei, Tutuila, Guam, CNMI, and Palau. Project sponsored by USDA Natural Resources Conservation Service.

Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Official Soil Series Descriptions. Available online. Accessed [April/08/2025].

Stone B.C. (1970). The Flora of Guam. A Manual for the Identification of the Vascular Plants of the Island. Micronesica – Journal of the University of Guam, vol. 6, July 1970.

USDA-NRCS. (2006). Major Land Resource Regions. USDA Agriculture Handbook 296. http://soils.usda.gov/MLRAExplorer

U. S. Department of Interior, Fish & Wildlife Service. (2023). Download seamless wetlands data by state. National Wetlands Inventory website. U.S. Department of the Interior, Fish and Wildlife Service, Washington, D.C. Accessed September 16, 2024. [https://www.fws.gov/program/national-wetlands-inventory/download-state-wetlands-data].

USDA-Soil Conservation Service. (1988). Soil Survey of Territory of Guam.

Wagner W.H. and D.F. Grether. (1948). The Pteridophytes of Guam. Occasional Papers of Bernice P. Bishop Museum, volume XIX, number 2. Honolulu, Hawaii.

Western Regional Climate Center, (2020). Climate of Hawai’i. Available: [https://wrcc.dri.edu/Climate/narrative_hi.php].

Willsey T., J.A. Kwon, M.K. Reeves, F. Amidon, and S.E. Miller. (2019). Mariana Islands Forest. Encyclopedia of the World's Biomes. https://doi.org/10.1016\B978-0-12-409548-9.12012-3

Contributors

David Clausnitzer PhD
John Proctor
Ann Tan
Amy Koch
Kendra Moseley
Daniel Bowman
Sarah Quistberg
Brendan Brazee
Daniel Block
Jennifer Ficke-Beaton

Approval

Kendra Moseley, 5/08/2025

Acknowledgments

Assistance, advice, review, and/or insights:

Bart Lawrence, NRCS
Michael Constantinides, NRCS-PIA
Jennifer Higashino, USFWS and NRCS
Carolyn Auweloa, NRCS
Jay Doronila, NRCS
Michael 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	05/10/2025
Approved by	Kendra Moseley
Approval date
Composition (Indicators 10 and 12) based on	Annual Production