Natural Resources
Conservation Service

Ecological site QX192X01X001

Moderately Deep Oxic Soils on Volcanic Uplands

Last updated: 5/08/2025
Accessed: 05/19/2025

Home / Esd catalog / MLRA 192X / Ecological site QX192X01X001

USC

Metric

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 Marianas Islands. It occurs on nearly level to very steep (0 to 90 percent slopes) volcanic uplands at elevations ranging from 0 to 1,080 feet (0 to 325 meters) (Amidon et al., 2017; USDA-SCS, 1988).

Soils are moderately deep to deep, well drained Oxisols that formed in residuum derived from volcanic tuff and tuff breccia (USDA-SCS, 1988). Soil temperature regimes are isohyperthermic; soil moisture regimes are ustic. Mean annual rainfall is about 102 inches (2,590 millimeters) (PRISM, 2006). Depending on slope, water runoff ranges from low to high; permeability is moderately slow. Effective rooting depth is greater than 72 inches (185 centimeters) (USDA-SCS, 1988). Available water-holding capacity is primarily 3 inches (8 centimeters) in the upper 40 inches (100 centimeters) of soil. Base saturation is low (less than 35 percent); pH is 5.1 or lower, such that aluminum toxicity limits the growth of most plant species. Most of the area is vegetated by Pacific Island silvergrass or swordgrass (Miscanthus floridulus). Human-caused fires are frequent and intense.

Associated sites

QX192X01X501	Somewhat Poorly Drained Alluvium Soils of QX192X01X501 (The Somewhat Poorly Drained Alluvium Ecological Site) occur in stream channels, depressions, and seeps surrounded by QX192X01X001 (The Moderately Deep Oxic Soils on Volcanic Uplands Ecological Site), which occurs upslope on hills. As such water will move from QX19X01X001 into F192X01X501GU. Soils in QX192X01X001 are very strongly acidic to strongly acidic (4.9 to 5.1), have primarily low to occasionally moderate available water-holding capacity (3 to 7 inches), very deep-water tables (greater than 72 inches), and aluminum toxicity which supports mostly Pacific Island silvergrass (swordgrass). Soils of F192XY501 are strongly acidic to moderately acidic (5.3 to 5.8), have moderate water holding capacity (7 inches), a water table as shallow as 30 inches (75 centimeters) below the surface, rare and brief flooding, and support wetland forest, grasses, and sedges.
QX192X01X003	Shallow Soils on Volcanic Uplands Both ecological sites occur adjacent to each other on volcanic uplands. Soils of QX192X01X001 (The Moderately Deep Oxic Soils on Volcanic Uplands Ecological Site) are moderately deep (24 inches) Oxisols which are very strongly acidic to strongly acidic (4.9 to 5.1), have primarily low to occasionally moderate available water holding capacity (3 to 7 inches), low base saturation, and aluminum toxicity which supports mostly Pacific Island silvergrass (swordgrass). Soils of the QX191X01X003 (The Shallow Soils on Volcanic Upland Ecological Site) are shallow (about 14 inches) Mollisols which have very low available water holding capacity (2 inches), high base saturation, and no aluminum toxicity that supports upland grasses, forbs, and forest.
QX191X01X506	Somewhat Poorly and Poorly Drained Valley Bottoms and Coastal Plains Soils of QX191X01X506 (The Somewhat Poorly and Poorly Drained Valleys and Alluvial Coastal Plains Ecological Site) border QX192X01X001 (The Moderately Deep Oxic Soils on Volcanic Uplands Ecological Site) in select locations in Guam where it occurs in coastal plains and broad valleys rather than volcanic uplands. The soils have high water tables (wet at about 30 inches), occasional flooding, slightly brackish ground water in coastal areas (0 to 2 mmhos/centimeter), and support wetland forest, grasses, and sedges. Soils of QX192X01X001 has steeper slopes (0 to 90 percent), are well drained, have very deep water table (greater than 72 inches), no flooding, and support mostly Pacific Island silver grass (swordgrass).
QX191X01X503	Very Shallow to Moderately Deep Soils on Limestone Plateaus Soils of QX191X01X503 (The Very Shallow to Moderately Deep Soils on Limestone Plateaus Ecological Site) occur on limestone plateaus that may border on volcanic uplands. Depending on slope (0 to 60 percent), water runoff ranges from very low to very high. Available water holding capacity is very low to low (2 to 3 inches). 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. They formed over limestone, have high base saturation, neutral to slightly acidic to moderately alkaline pH levels (6.5 to 7.9), and no aluminum toxicity (where not been farmed), and support vegetation consisting of introduced grass, forb, and tree species, including forests of white leadtree or tangantangan (Leucaena leucocephala) and some native forest. Soils of QX192X01X001 (The Moderately Deep Oxic Soils on Volcanic Uplands Ecological site formed on volcanic materials, have primarily low to occasionally moderate available water holding capacity (3 to 7 inches), very low base saturation, very strongly acidic to strongly acidic pH levels (4.9 to 5.1), aluminum toxicity, and support mostly Pacific Island silvergrass (swordgrass).
QX192X01X004	Very Deep Soils on Volcanic Uplands Both ecological sites occur adjacent to each other on volcanic uplands. Soils of QX192X01X001 (The Moderately Deep Oxic Soils on Volcanic Uplands Ecological Site) are primarily moderately deep (24 inches) Oxisols on mountain hillslopes with primarily low to occasionally moderate available water holding capacity (3 to 7 inches), low base saturation, nearly level to very steep (0 to 90 percent) slopes, very strongly to strongly acidic pH levels (4.9 to 5.1), and aluminum toxicity which supports mostly Pacific Island silvergrass (swordgrass). Soils of QX192X01X004 (The Very Deep Soils on Volcanic Uplands Ecological Site) are very deep (greater than 72 inches) Alfisols on lower slopes, concave areas, and drainageways, with slightly higher available water holding capacity (4 inches), moderate base saturation, gently sloping to moderately sloping (3 to 15 percent) slopes, moderately acid pH levels (5.6), no aluminum toxicity, and support a variety of grasses and forbs.
QX192X01X002	Deep Alfic Soils on Volcanic Uplands Both ecological sites occur on volcanic uplands. Soils of QX192X01X001 (The Moderately Deep Oxic Soils on Volcanic Uplands Ecological Site) are primarily moderately deep (24 inches) Oxisols on mountain slopes with primarily low to occasionally moderate available water holding capacity (3 to 7 inches), low base saturation, nearly level to very steep (0 to 90 percent) slopes, and aluminum toxicity which support mostly Pacific Island silvergrass (swordgrass). Soils of QX192X01X002 (The Deep Alfic Soils on Volcanic Uplands Ecological Site) are primarily deep (43 inches) Alfisols. However, Sasalaguan soils are shallow (28 inches) Inceptisols. These Alfisols and Inceptisols soils occur on mountain slopes, have slightly higher available water holding capacity (4 inches), high base saturation, nearly level to very steep sloping (0 to 60 percent) slopes, moderately acidic pH levels (5.5 to 5.8), and no aluminum toxicity, and support forest, grasses, and forbs.
QX191X01X505	Very Low Available Water Capacity Soils on Limestone Plateaus and Escarpments Soils of QX191X01X505 (The Very Low Available Water Capacity Soils on Limestone Plateaus and Escarpments Ecological Site) occur on limestone plateaus that may border on volcanic uplands. Depending on slope (0 to 99 percent), water runoff ranges from very low to high. Available water holding capacity is very low (1 inch). 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 of QX191X01X505 formed over porous limestone, have very low available water holding capacity (1 inch), high base saturation, neutral pH levels (7.0 to 7.2) no aluminum toxicity, and are mostly vegetated by native forest, unlike the soils of QX192X01X001 (The Moderately Deep Oxic Soils on Volcanic Uplands Ecological Site) which have primarily low to occasionally moderate available water holding capacity (3 to 7 inches), low base saturation, very strongly to strongly acidic pH levels (4.9 to 5.1), aluminum toxicity, and supports mostly Pacific Island silvergrass (swordgrass).

Similar sites

QX191X01X001	Moderately Deep Oxic Soils on Volcanic Uplands Soils of QX191X01X001 (The Moderately Deep Oxic Soils on Volcanic Uplands Ecological Site) occurs on upland hillslopes on the islands of Saipan and Rota, while soils of QX192X01X001 (The Moderately Deep Oxic Soils on Volcanic Uplands Ecological Site) occurs on upland on the island of Guam. They are correlated with different soils but are similar in every important characteristic and support the same types of vegetation. Both ecological sites occur on moderately deep Oxisols with low available water holding capacity (3-5 inches), low base saturation, low pH levels, and have aluminum toxicity which supports mostly Pacific Island silvergrass (swordgrass).

QX191X01X001

Moderately Deep Oxic Soils on Volcanic Uplands

Soils of QX191X01X001 (The Moderately Deep Oxic Soils on Volcanic Uplands Ecological Site) occurs on upland hillslopes on the islands of Saipan and Rota, while soils of QX192X01X001 (The Moderately Deep Oxic Soils on Volcanic Uplands Ecological Site) occurs on upland on the island of Guam. They are correlated with different soils but are similar in every important characteristic and support the same types of vegetation. Both ecological sites occur on moderately deep Oxisols with low available water holding capacity (3-5 inches), low base saturation, low pH levels, and have aluminum toxicity which supports mostly Pacific Island silvergrass (swordgrass).

Table 1. Dominant plant species

Tree	Not specified
Shrub	Not specified
Herbaceous	(1) Miscanthus floridulus

Legacy ID

R192XY001GU

Download full description

Physiographic features

This ecological site occurs on upland slopes of extinct volcanoes (USDA-SCS, 1988). The water table depth is greater than 72 inches (185 centimeters).

Table 2. Representative physiographic features

Landforms	(1) Upland > Hillslope
Runoff class	Low to high
Flooding frequency	None
Ponding frequency	None
Elevation	1,080 ft
Slope	90%
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 98 to 106 inches (2,490 to 2,690 millimeters) while actual (10th and 90th percentiles) values for mean annual precipitation range from 96 to 110 inches (2,440 to 2,795 millimeters). Extreme values range from 91 to 116 inches (2,310 to 2,945 millimeters). The average annual precipitation is 102 inches (2,590 millimeters) and the median annual average precipitation is also 102 inches (2,590 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 81 degrees F (25 to 27 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)	98-106 in
Frost-free period (actual range)	365 days
Freeze-free period (actual range)	365 days
Precipitation total (actual range)	96-110 in
Frost-free period (average)	365 days
Freeze-free period (average)	365 days
Precipitation total (average)	102 in

Influencing water features

There are ravines in this ecological site that carry water during the rainy season. This ecological site consists of the uplands surrounding these stream courses; areas within the ravines constitute other ecological sites (Amidon et al., 2017; Fosberg, 1960; USDA-SCS, 1988).

Number of National Wetland Inventory (NWI) features overlapping ecological site: Riverine (463), freshwater emergent wetland (119), freshwater pond (14), estuarine and marine deepwater (8), estuarine and marine wetland (8), and lake (1) (USFWS, 2023).

Soil features

The soil components associated with this ecological site are all Akina series, which are in the Oxisols soil order.

Soil temperature regimes are isohyperthermic; soil moisture regimes are ustic (USDA-SCS, 1988). They are moderately deep to deep, well drained, and have kaolinitic clay mineralogy. Their low pH induces aluminum toxicity that limits growth of most plant species. Soils are often complexed with badlands caused by erosion and slumping.

Table 4. Representative soil features

Parent material	(1) Residuum – tuff (2) Residuum – tuff breccia
Surface texture	(1) Silty clay
Family particle size	(1) Very-fine
Drainage class	Well drained
Permeability class	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)	3 – 7 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)	4.9 – 5
Subsurface fragment volume <=3" (0-40in)	2%
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; Athens and Ward, 2004; Fosberg, 1960; Stone, 1970; 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; Wagner and Grether, 1948; Willsey et al., 2019).

State and transition model

Custom diagram

Standard diagram

Figure 1. State-and-Transition Model for R192XY001GU (Moderately Deep Oxic Soils on Volcanic Uplands).

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. Badlands State

R1A	-	The Reference State (1) can be restored to the Native Forest State (2) by fire protection, weed control, erosion control (vetiver-grass (Vetiveria sp) is useful), mulching, fertilizing, liming, 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.
T1A	-	The Reference State (1) transitions to the Badlands State (4) by loss of upper soil horizons to erosion due to human caused grassland fires on soils which developed over volcanic bedrock resulting in vegetation and litter cover which are inadequate to protect soils from run off caused by strong storms and typhoons (Guampedia, 2025).
T2A	-	The Native Forest State (2) transitions to the Reference State (1) by destruction of the forest by human-caused fire. Moreover, areas with low can result in aluminum toxicity which favors swordgrass monocultures over diverse grass, forb, shrub plant communities.
R3B	-	The Tree-Invaded State (3) is restored to the Reference State (1) by fire.
R3A	-	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.
T3A	-	The Tree-Invaded State (3) transitions to the Badlands State (4) through destruction of trees 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.
R4A	-	The Badlands State (4) can be restored to the Reference State (1) by instituting erosion control measures and temporarily excluding fire.
R4B	-	The Badlands State (4) 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. Pacific Islands Silvergrass (Swordgrass)

1.2. Pacific Island Silvergrass (Swordgrass)/Beach Sheoak

1.1A	-	In the absence of fire over time community phase 1.1 may change to community phase 1.2 as scattered trees and shrubs will begin to colonize the site.
1.2A	-	Fire kills beach sheoak (Casuarina equisetifolia) and any other woody vegetation that may have established, causing a phase change from 1.2 back to 1.1.

State 2 submodel, plant communities

2.1. Glochidion Tree – Mago

2.2. Sea Hibiscus – Tahitian Screwpine

2.1A	-	Storms that damage or kill trees causes a phase change from 2.1 to 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 community phase 2.1 with gradual regrowth of a more diverse array of native species when given adequate time to recover after disturbance.

State 3 submodel, plant communities

3.1. Beach Sheoak – Small Philippine Acacia/Limeberry/Pacific Island Silvergrass (Swordgrass)

State 4 submodel, plant communities

4.1. Old World Forkedfern/Golden False Beardgrass

State 1
Reference State

The Reference State (1) is tall (to 6.5 feet or 2 meters) grassland. The near-consensus of authors indicates that this Miscanthus-dominated grassland did not exist in the southern Marianas Islands until humans arrived and started burning the ubiquitous forests of these islands. However, naturally occurring Miscanthus 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; Athens and Ward, 2004; Fosberg, 1960; Stone, 1970; Wagner and Grether, 1948; Willsey et al., 2019).

Community 1.1
Pacific Islands Silvergrass (Swordgrass)

Pacific Islands silvergrass or swordgrass (Miscanthus floridulus); an introduced grass species is by far the dominant species. It is not palatable to grazing animals, grows dense and tall, and excludes most other species. It is highly flammable in the dry season and it resprouts after burning. As it is a bunchgrass, there is bare ground around each plant that allows erosion to occur between plants (Amidon et al., 2019; Amidon et al., 2017; Athens and Ward, 2004; Fosberg, 1960; Stone, 1970; Wagner and Grether, 1948; Willsey et al., 2019). Some other species that can co-occur with Pacific Islands silvergrass are mission grass or foxtail (Pennisetum polystachion), which has some forage value when young, dimeria grass (Dimeria chloridiformis), false ironwort (Hyptis capitata), Philippine ground orchid (Spathoglottis plicata), and porterweed (Stachytarpheta spp.) (Amidon et al., 2019; Amidon et al., 2017; Athens and Ward, 2004; Fosberg, 1960; Stone, 1970; Wagner and Grether, 1948; Willsey et al., 2019).

Dominant plant species

Pacific Island silvergrass (Miscanthus floridulus), grass

Community 1.2
Pacific Island Silvergrass (Swordgrass)/Beach Sheoak

Community phase 1.2 is dominated by Pacific Islands silvergrass or swordgrass (Miscanthus floridulus) but contains scattered small trees and shrubs. The most common tree species is beach sheoak (Casuarina equisetifolia) (Amidon et al., 2019; Amidon et al., 2017; Athens and Ward, 2004; Fosberg, 1960; Stone, 1970; Wagner and Grether, 1948; Willsey et al., 2019).

Dominant plant species

beach sheoak (Casuarina equisetifolia), tree
Pacific Island silvergrass (Miscanthus floridulus), grass

Pathway 1.1A
Community 1.1 to 1.2

In the absence of fire over time community phase 1.1 may change to community phase 1.2 as scattered trees and shrubs will begin to colonize the site.

Pathway 1.2A
Community 1.2 to 1.1

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

State 2
Native Forest State

The Native Forest State (2) consists of 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; Athens and Ward, 2004; Fosberg, 1960; Stone, 1970; Wagner and Grether, 1948; Willsey et al., 2019). Measurements of soil pH on forested sites and grassland sites indicate lower acidity and aluminum toxicity on the forested sites (Amidon et al., 2019).

Community 2.1
Glochidion Tree – Mago

Common trees of this historical forest include Glochidion tree or 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; Athens and Ward, 2004; Fosberg, 1960; Stone, 1970; Wagner and Grether, 1948; Willsey et al., 2019).

Community 2.2
Sea Hibiscus – Tahitian Screwpine

Community phase 2.2 would have been historically dominated by sea hibiscus (Hibiscus tiliaceus) and Tahitian screwpine (Pandanus tectorius) for some years until the more diverse native forest regrew between typhoons (Amidon et al., 2019; Amidon et al., 2017; Athens and Ward, 2004; Fosberg, 1960; Stone, 1970; 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 2.1 to 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 community phase 2.1 with gradual regrowth of a more diverse array of native species when given adequate time to recover after disturbance.

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.

Community 3.1
Beach Sheoak – Small Philippine Acacia/Limeberry/Pacific Island Silvergrass (Swordgrass)

Pacific Island silvergrass or swordgrass (Miscanthus floridulus) is 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). The introduced shrub, limeberry (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) tends not to grow on these highly acidic soils (Amidon et al., 2019; Amidon et al., 2017; Athens and Ward, 2004; Fosberg, 1960; Stone, 1970; 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
Pacific Island silvergrass (Miscanthus floridulus), grass

State 4
Badlands State

The Badlands State (4) consists of one community phase. It is sparsely vegetated with much bare ground. Most of the upper soil horizons has been eroded away, leaving highly acidic and infertile subsoil that supports few plant species (USDA-SCS, 1988).

Community 4.1
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 micranthum, Malabar melastome (Melastoma malabathricum), and golden false beardgrass (Chrysopogon aciculatus) (Amidon et al., 2019; Amidon et al., 2017; Athens and Ward, 2004; Fosberg, 1960; Stone, 1970; 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, liming, 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.

Transition T1A
State 1 to 4

The Reference State (1) transitions to the Badlands State (4) by loss of upper soil horizons to erosion due to human caused grassland fires on soils which developed over volcanic bedrock resulting in vegetation and litter cover which are inadequate to protect soils from run off caused by strong storms and typhoons (Guampedia, 2025).

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. Moreover, areas with low can result in aluminum toxicity which favors swordgrass monocultures over diverse grass, forb, shrub plant communities.

Restoration pathway R3B
State 3 to 1

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

Restoration pathway R3A
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.

Transition T3A
State 3 to 4

The Tree-Invaded State (3) transitions to the Badlands State (4) through destruction of trees 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.

Restoration pathway R4A
State 4 to 1

The Badlands State (4) can be restored to the Reference State (1) by instituting erosion control measures and temporarily excluding fire.

Restoration pathway R4B
State 4 to 3

The Badlands State (4) 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 Moderately Deep Oxic Soils on Volcanic Uplands Ecological Site (R192XY001GU)

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.

https://www.guampedia.com/badlands-in-southern-guam/ (Accessed 04/04/2025).

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.

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
Daniel Bowman
Amy Koch
Kendra Moseley
Sarah Quistberg
Brendan Brazee
Daniel Block
Jill Ficke-Beaton

Approval

Kendra Moseley, 5/08/2025

Acknowledgments

Assistance, advice, review, and/or insights:

Michael Constantinides, NRCS-PIA
Jennifer Higashino, USFWS and NRCS
Mike Kolman, NRCS
Bart Lawrence, NRCS
Carolyn Auweloa, NRCS
Jay Doronila, 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	05/09/2025
Approved by	Kendra Moseley
Approval date
Composition (Indicators 10 and 12) based on	Annual Production