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Ecological site QX191X01X506

Somewhat Poorly and Poorly Drained Valley Bottoms and Coastal Plains

Last updated: 8/19/2025
Accessed: 09/19/2026

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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): 191X–High Limestone Plateaus of the Mariana Islands

This MLRA consists of the northern half of Guam and the islands of Saipan), Tinian, Rota, and Aguijan. Topography consists mostly of limestone plateaus. The highest elevations are 1,700 feet (520 meters) on Rota, 1,485 feet (450 meters) on Saipan, 655 feet (200 meters) on Tinian, and 860 feet (260 meters) in the northern part of Guam. The limestone plateaus were uplifted by tectonic activity. Deeply weathered volcanic rock is exposed on some ridges and slopes. Average annual rainfall is 100 inches (2,540 millimeters) on northern Guam and 80 inches (2,030 millimeters) on Saipan, Tinian, Aguijan, and Rota. The rainy season occurs from July through November; the dry season occurs from December through June. Trade winds blow from the northeast. Average annual temperature is 79 degrees F (26 degrees C). Typhoons are frequent. Soils are Alfisols, Andisols, Entisols, Mollisols, or Oxisols. The dominant soil moisture regime is ustic. The soil temperature regime is isohyperthermic. Native vegetation consists of mixed tropical hardwoods; introduced white leadtree or tangantangan trees (Leucaena leucocephala) are abundant. Introduced deer, pigs, goats, and water buffalo are common (USDA-NRCS, 2006). The main human disturbance is clearing land for cultivation. Feral pigs, feral cattle, brown tree snakes, stray dogs (Boonie dogs), and introduced deer are destructive to the native forest (Amand, 2000; CNMI SWARS Council, 2010; Donnegan et al., 2011; Liske-Clark, 2015; Willsey et al., 2019).

Classification relationships

This ecological site occurs within Major Land Resource Area (MLRA) 191 – High Limestone Plateaus 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 gently sloping (0 to 4 percent slopes), wide river valley bottoms and long, narrow coastal plains at elevations ranging from 0 to 330 feet (0 to 100 meters) (USDA-SCS, 1988).

Soils are very deep (greater than 72 inches), somewhat poorly and poorly drained Entisols that formed in alluvium derived from volcanic and limestone uplands. On the coast, alluvium is derived from beach deposits. Soil temperature regimes are isohyperthermic; soil moisture regimes are aquic. Average annual precipitation is about 97 inches (2,465 millimeters) and ranges from 92 to 103 inches (2,335 to 2,615 millimeters) (PRISM, 2006). Water runoff is medium; permeability is slow. Effective rooting depth is greater than 72 inches (185 centimeters). Available water-holding capacity is moderate (5 to 6 inches). The water table fluctuates seasonally between about 20 and 40 inches (50 and 100 cm). Flooding is occasional and brief in the rainy season (USDA-SCS, 1988). Most of the area is vegetated by grasses, forbs, and wetland forest (Amidon et al., 2017; Fosberg, 1960; Marshall et al., 2020; Stemmermann, 1981; Stone, 1970; Wagner and Grether, 1948; Willsey et al., 2019).

Associated sites

QX192X01X004	Very Deep Soils on Volcanic Uplands Soils of QX192X01X004 (The Very Deep Soils on Volcanic Uplands Ecological Site) are very deep, well drained Alfisols on the lower slopes, concave areas, and drainageways of volcanic uplands, have low (4 inches) available water holding capacity (but relatively high for soils on volcanic uplands), moderate base saturation, gentle to moderate slopes (3 to 15 percent), no aluminum toxicity, and support a variety of grasses and forbs. Soils of QX191X01X506 (The Somewhat Poorly and Poorly Drained Valleys and Alluvial Coastal Plains Ecological Site) occurs in broad river valley bottoms and narrow coastal plains. Soils formed in alluvium or beach deposits, are somewhat poorly and poorly drained, have aquic moisture regimes, moderately deep water tables, fresh groundwater except in areas near the coast that have slightly saline groundwater, occasional flooded. Most of the area is vegetated by grasses, forbs, and wetland forest.
QX192X01X501	Somewhat Poorly Drained Alluvium Soils of QX192X01X501 (The Somewhat Poorly Drained Alluvium Ecological Site) consists of streams and seeps at higher elevations that feed into QX191X01X506 (The Somewhat Poorly Drained Valleys and Alluvial Plains Ecological Site). Soils, drainage, water tables, and flooding regimes in both ecological sites are similar, except that ground water in coastal areas of QX191X01X506 (The Somewhat Poorly and Poorly Drained Valleys and Alluvial Coastal Plains Ecological Site) are slightly saline rather than fresh. Both ecological sites support wetland forest, grasses, and sedges.
QX191X01X503	Very Shallow to Moderately Deep Soils on Limestone Plateaus Soils of QX19101X503 (The Very Shallow to Moderately Deep Soils on Limestone Plateaus) formed in fine materials over porous coralline or argillaceous limestone. They are well drained, have ustic moisture regimes, very deep water tables, only fresh groundwater, and no flooding. Areas not farmed are vegetated by mostly introduced grass, forb, and tree species, with some areas of native upland forest.
QX191X01X501	Excessively and Somewhat Excessively Drained Coastal Strand Soils of QX191X01X501 (The Excessively and Somewhat Excessively Drained Coastal Strand Ecological Site) formed in coral sand near the sea and fine materials over limestone where it borders inland limestone plateaus and escarpments. Soil drainage is somewhat excessive to excessive. Effective rooting depth is 4 to 63 inches or greater; available water holding capacity is very low to low (0 to 3 inches). Windborne salt spray and rare flooding by seawater affect the entire area. It is mostly forested. Soils of QX191X01X506 (The Somewhat Poorly and Poorly Drained Valleys and Alluvial Coastal Plains Ecological Site) occur in broad river valley bottoms and narrow coastal plains. Soils formed in alluvium or beach deposits, are somewhat poorly and poorly drained, have aquic moisture regimes, moderately deep water tables, fresh groundwater except in areas near the coast that have slightly saline groundwater, occasionally flooded. Most of the area is vegetated by grasses, forbs, and wetland forest.
QX192X01X003	Shallow Soils on Volcanic Uplands Soils of QX192X01X003 (The Shallow Soils on Volcanic Uplands Ecological Site) formed in volcanic materials in uplands, are well drained, have effective rooting depths of about 15 inches or less, and have very low (2 inches) available water holding capacity. Most of the area is vegetated by grasses, forbs, and forest. Soils of QX191X01X506 (The Somewhat Poorly and Poorly Drained Valleys and Alluvial Coastal Plains Ecological Site) occur in broad river valley bottoms and narrow coastal plains. Soils formed in alluvium or beach deposits, are somewhat poorly and poorly drained, have aquic moisture regimes, moderately deep water tables, fresh groundwater except in areas near the coast that have slightly saline groundwater, occasional flooded. Most of the area is vegetated by grasses, forbs, and wetland forest.
QX192X01X001	Moderately Deep Oxic Soils on Volcanic Uplands Soils of QX192X01X001 (The Moderately Deep Oxic Soils on Volcanic Uplands Ecological Site) formed in volcanic materials, are well drained, and have effective rooting depths between 16 and 45 inches, low to moderate (2 to 7 inches) available water holding capacity, low base saturation, low pH (4.5 to 6.0), and aluminum toxicity. Most of the area is vegetated by Pacific silver grass or swordgrass (Miscanthus floridulus). QX191X01X506 (The Somewhat Poorly and Poorly Drained Valleys and Alluvial Coastal Plains Ecological Site) occurs in broad river valley bottoms and narrow coastal plains. Soils formed in alluvium or beach deposits, are somewhat poorly and poorly drained, have aquic moisture regimes, moderately deep water tables, areas of slightly saline groundwater, and are occasionally flooded. Most of the area is vegetated by grasses, forbs, and wetland forest.
QX192X01X002	Deep Alfic Soils on Volcanic Uplands Soils of QX191X01X002 (The Moderately Deep Alfic Soils on Volcanic Uplands Ecological Site) formed in volcanic materials, are well drained, and have effective rooting depths of 20 to 40 inches, low (4 inches) available water holding capacity, fairly high base saturation, pH ranging from 5.1 to 6.5, and no aluminum toxicity. Most of the area is vegetated by upland forest, grasses, and forbs. QX191X01X506 (The Somewhat Poorly and Poorly Drained Valleys and Alluvial Coastal Plains Ecological Site) occurs in broad river valley bottoms and narrow coastal plains. Soils formed in alluvium or beach deposits, are somewhat poorly and poorly drained, have aquic moisture regimes, moderately deep water tables, areas of slightly saline groundwater, and are occasionally flooded. Most of the area is vegetated by grasses, forbs, and wetland forest.
QX191X01X505	Very Low Available Water Capacity Soils on Limestone Plateaus and Escarpments Soils of Q191X01X505 (The Very Low Available Water Capacity Soils on Limestone Plateaus and Escarpments Ecological Site) formed in fine materials over porous coralline limestone. They are well drained. Effective rooting depth is 2 to 16 inches; available water holding capacity is very low (1 inches). Most of the area is vegetated by native forest. This ecological site is limited to an area that is often shrouded in clouds and fog. Moisture is added to the soil by fog drip, which maintains soils in moist condition most of the time. It is mostly forested with native species. QX191X01X506 (The Somewhat Poorly and Poorly Drained Valleys and Alluvial Coastal Plains Ecological Site) occurs in broad river valley bottoms and narrow coastal plains. Soils formed in alluvium or beach deposits, are somewhat poorly and poorly drained, have aquic moisture regimes, moderately deep water tables, areas of slightly saline groundwater, and are occasionally flooded. Most of the area is vegetated by grasses, forbs, and wetland forest.
QX191X01X507	Very Poorly Drained Mucky Clay Soils of QX191X01X507 (The Very Poorly Drained Mucky Clay Ecological Site) occur on coastal valley bottoms and plains. Soils formed in alluvium from mixed sources, are very poorly drained, have aquic moisture regimes, water tables that are at the soil surface to 18 inches (45 centimeters) below the soil surface, slightly to moderately saline ground water, and frequent flooding. Most of the area is vegetated by wetland grasses and sedges and, in some locations, mangrove forest. Soils of QX191X01X506 (The Somewhat Poorly and Poorly Drained Valleys and Alluvial Coastal Plains Ecological Site) occur in broad river valley bottoms and narrow coastal plains. Soils formed in alluvium or beach deposits, are somewhat poorly and poorly drained, have aquic moisture regimes, moderately deep water tables, fresh groundwater except in areas near the coast that have slightly saline groundwater, occasional flooded. Most of the area is vegetated by grasses, forbs, and wetland forest.

Table 1. Dominant plant species

Tree	(1) Barringtonia racemosa
Shrub	Not specified
Herbaceous	Not specified

Legacy ID

F191XY506MP

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Physiographic features

This ecological site occurs on valley floors and coastal plains (USDA-SCS, 1988).

Table 2. Representative physiographic features

Landforms	(1) Coastal plain (2) Valley floor
Runoff class	Medium
Flooding frequency	Occasional
Ponding frequency	None
Elevation	0 – 330 ft
Slope	0 – 4 %
Water table depth	18 – 42 in
Aspect	Aspect is not a significant factor

Climatic features

Summary for this Ecological Site

Rainfall statistics were determined from PRISM rainfall raster data (PRISM, 2006). Representative (20th and 80th percentiles) values for mean annual precipitation range from 92 to 103 inches (2,335 to 2,615 millimeters) while actual (10th and 90th percentiles) values for mean annual precipitation also range from 92 to 103 inches (2,335 to 2,615 millimeters). Extreme values range from 88 to 107 inches (2,235 to 2,720 millimeters). The average annual precipitation is 97 inches (2,465 millimeters) and the median annual average precipitation is also 97 inches (2,465 millimeters).

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

The data presented in the climate normals tables below are from select climate stations in Guam. I used the data from these stations because they are representative of the spatial distribution of this ecological site and because the values for mean annual rainfall of 98 inches (2,490 millimeters) and mean annual temperature values of 81 degrees F (27 degrees C) are reasonably comparable.

General Principles

The climate 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, the dry season from December through June 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 (eastern) side of the higher mountains to about 79 inches (2,005 millimeters) along the coast of the western side of the islands. 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; USDA-SCS, 1989).

Throughout the year, the dominant winds 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; USDA-SCS, 1989).

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. The islands lie 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 the islands in any particular year is about once in three years. The chance of having a typhoon move directly across an island is about once in eight years (Fosberg, 1960; USDA-SCS, 1988; USDA-SCS, 1989).

Table 3 Representative climatic features

Frost-free period (characteristic range)	370 days
Freeze-free period (characteristic range)	370 days
Precipitation total (characteristic range)	90-100 in
Frost-free period (actual range)	370 days
Freeze-free period (actual range)	370 days
Precipitation total (actual range)	90-110 in
Frost-free period (average)	370 days
Freeze-free period (average)	370 days
Precipitation total (average)	100 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) GUAM INTL AP [GQW00041415], GU

Influencing water features

Number of National Wetland Inventory (NWI) features overlapping ecological site: Riverine (256), Freshwater forested/shrub wetlands (99), freshwater emergent wetlands (78), estuarine and marine wetland (35), estuarine and marine deepwater (29), and freshwater pond (7) (USFWS, 2023).

Soil features

One soil, Inarajan (Entisols) is associated with this ecological site.

Inarajan soils formed in alluvium derived from volcanic rock, limestone, and beach deposits. Soil temperature regimes are isohyperthermic; soil moisture regimes are aquic. They are very deep (greater than 72 inches) and are somewhat poorly to poorly drained (USDA-SCS, 1988).

Table 4. Representative soil features

Parent material	(1) Alluvium
Surface texture	(1) Clay (2) Sandy clay loam
Family particle size	(1) Very-fine
Drainage class	Poorly drained to somewhat poorly drained
Permeability class	Slow
Depth to restrictive layer	72 in
Soil depth	72 in
Surface fragment cover <=3"	Not specified
Surface fragment cover >3"	Not specified
Available water capacity (0-40in)	4.8 – 5.9 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) (0-10in)	5.1 – 7.3
Subsurface fragment volume <=3" (0-40in)	0 – 2 %
Subsurface fragment volume >3" (0-40in)	Not specified

Ecological dynamics

The main natural disturbance is strong storms that can damage or kill vegetation by high wind speeds. The main human disturbance is clearing of native vegetation for agriculture and abandonment of plantations that results in at least temporary dominance of introduced weedy plants (Amidon et al., 2017; Fosberg, 1960; Marshall et al., 2020; Stemmermann, 1981; Stone, 1970; Wagner and Grether, 1948; Willsey et al., 2019).

State and transition model

Custom diagram

Standard diagram

Figure 7. State-And-Transition Model for F191XY506MP (Somewhat poorly and Poorly Drained Valley Bottoms and Coastal Plains).

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Ecosystem states

1. Reference State

2. Naturalized Grassland State

3. Cleared and Abandoned State

4. Invaded Forest State

T1A	-	The Reference State (1) transitions to the Naturalized Grassland State (2) by removal of native vegetation and planting, or allowing colonization by, introduced grass species.
T1B	-	The Reference State (1) transitions to the Cleared and Abandoned State (3) if previously cleared of forest and then abandoned. This allows heliophytes, both native and introduced, to temporarily cover the ground.
T1C	-	The Reference State (1) transitions to the Invaded Forest State (4) by wind damage to the forest when there is a nearby source of seeds of invasive species or, more gradually, by damage to the forest understory by ungulates, especially feral pigs, when there is a source of seeds of invasive species.
R2A	-	The Naturalized Grassland State (2) could theoretically be restored to the Reference State (1) by suppression of grassland vegetation and replanting with native species. Natural reseeding by native forest species can be expected if there is a nearby stand of suitable species.
T2B	-	The Naturalized Grassland State (2) transitions to the Cleared and Abandoned State (3) upon abandonment of grasslands, which are invaded by low-statured, native and/or introduced heliophytes.
R3B	-	The Cleared and Abandoned State (3) may be restored to the Reference State (1). The intensity of active restoration measures will be determined by the presence or lack of nearby native forest or, at least, some native trees as well as the density and species mix of grasses, vines, shrubs, and invasive trees present on the site, especially if many competitive introduced species are present.
R3A	-	The Cleared and Abandoned State (3) may be restored to the Naturalized Grassland State (2) by land clearing, weed control, and replanting grasses.
T3A	-	The Cleared and Abandoned State (3) transitions to the Invaded Forest State (4) 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.
R4A	-	The Invaded Forest State (4) can be restored to the Reference State (1). The difficulty, cost, and likelihood of success will depend on the species composition and amount and competitiveness of introduced species present on a given site.
T4A	-	The Invaded Forest State (4) may transition to Cleared and Abandoned State (3) due to mechanical clearing or fire. State 3 is likely to rapidly transition back to State 4 due to the presence of an abundant tree seed bank in the soil.

State 1 submodel, plant communities

1.1. Putat

1.2. Putat – Sea Hibiscus/Kodomillet – Tall Reed

1.1A	-	Storms that damage or kill putat (Barringtonia racemosa) trees cause a phase change from 1.1 to 1.2 typified by a partial, temporary change in dominant tree species and a temporary invasion by ground level vegetation.
1.2A	-	Community phase 1.2 will revert to phase 1.1 with dominance by putat (Barringtonia racemosa) when given adequate time to recover after disturbance.

State 2 submodel, plant communities

2.1. Para Grass/Greenleaf Ticktrefoil

2.2. Porterweed – Linearleaf Primrose-Willow/Para Grass – Hilograss

2.1A	-	Community phase 2.1 will change to 2.2 by invasion of the site by shrubs and forbs. This process is facilitated by excessive grazing, which reduces the competitive advantage of para grass (Urochloa mutica).
2.2A	-	Community phase 2.2 can shift back to phase 2.1 by reducing grazing pressure on paragrass (Urochloa mutica) and, when necessary, performing spot weed control on shrubs and forbs.

State 3 submodel, plant communities

3.1. Sea Hibiscus/Jack In The Bush/Para Grass – Tall Reed

State 4 submodel, plant communities

4.1. Sea Hibiscus – Tahitian Screwpine/Emperor’s Candlesticks/Linearleaf Primrose-Willow

State 1
Reference State

The Reference State (1) is a forest that is 32 to 48 feet (10 to 15 meters) tall. There is little or no undergrowth (Amidon et al., 2017; Fosberg, 1960; Marshall et al., 2020; Stemmermann, 1981; Stone, 1970; Wagner and Grether, 1948; Willsey et al., 2019).

Community 1.1
Putat

The only tree species is Barringtonia racemosa (locally known as putat) (Amidon et al., 2017; Fosberg, 1960; Marshall et al., 2020; Stemmermann, 1981; Stone, 1970; Wagner and Grether, 1948; Willsey et al., 2019).

Dominant plant species

(Barringtonia racemosa), tree

Community 1.2
Putat – Sea Hibiscus/Kodomillet – Tall Reed

Some putat (Barringtonia racemosa) trees from Community Phase 1.1 remain in this phase, but other sea hibiscus (Hibiscus tiliaceus) and Tahitian screwpine (Pandanus tectorius) can join the canopy as the forest regrows. Ground vegetation becomes temporarily common, particularly tall reed (Phragmites karka) as well as kodomillet (Paspalum scrobiculatum) (Amidon et al., 2017; Fosberg, 1960; Marshall et al., 2020; Stemmermann, 1981; Stone, 1970; Wagner and Grether, 1948; Willsey et al., 2019).

Dominant plant species

(Barringtonia racemosa), tree
sea hibiscus (Hibiscus tiliaceus), tree
tall reed (Phragmites karka), grass
kodomillet (Paspalum scrobiculatum), grass

Pathway 1.1A
Community 1.1 to 1.2

Storms that damage or kill putat (<a class="species-link" href="https://plants.usda.gov/core/profile?symbol=BARA5" target="_blank" title="Open in plants.usda.gov">Barringtonia racemosa</a>) trees cause a phase change from 1.1 to 1.2 typified by a partial, temporary change in dominant tree species and a temporary invasion by ground level vegetation.

Pathway 1.2A
Community 1.2 to 1.1

Community phase 1.2 will revert to phase 1.1 with dominance by putat (<a class="species-link" href="https://plants.usda.gov/core/profile?symbol=BARA5" target="_blank" title="Open in plants.usda.gov">Barringtonia racemosa</a>) when given adequate time to recover after disturbance.

State 2
Naturalized Grassland State

The Naturalized Grassland State (2) consists of two community phases that have been cleared of natural vegetation and planted or colonized with introduced grass species. It can be used for grazing. Soil compaction will become a problem if wet areas are heavily used by grazing animals (Amidon et al., 2017; Fosberg, 1960; Marshall et al., 2020; Stemmermann, 1981; Stone, 1970; Wagner and Grether, 1948; Willsey et al., 2019).

Community 2.1
Para Grass/Greenleaf Ticktrefoil

This community phase is dominated by para grass (Urochloa mutica). When not excessively grazed, it includes the legume greenleaf ticktrefoil (Desmodium intortum). There may be small amounts of hilograss (Paspalum conjugatum) present (Amidon et al., 2017; Fosberg, 1960; Marshall et al., 2020; Stemmermann, 1981; Stone, 1970; Wagner and Grether, 1948; Willsey et al., 2019).

Dominant plant species

para grass (Urochloa mutica), grass
greenleaf ticktrefoil (Desmodium intortum), other herbaceous

Community 2.2
Porterweed – Linearleaf Primrose-Willow/Para Grass – Hilograss

Resilience management. This community phase consists largely of para grass (<a class="species-link" href="https://plants.usda.gov/core/profile?symbol=URMU" target="_blank" title="Open in plants.usda.gov">Urochloa mutica</a>) and some hilograss (<a class="species-link" href="https://plants.usda.gov/core/profile?symbol=PACO14" target="_blank" title="Open in plants.usda.gov">Paspalum conjugatum</a>). Shrubs, vines, and forbs occupy some of the site due to reduction of grass competitiveness by excessive grazing and/or soil compaction. Some common species include: Porterweed (Stachytarpheta spp.), linearleaf primrose-willow (<a class="species-link" href="https://plants.usda.gov/core/profile?symbol=LUHY6" target="_blank" title="Open in plants.usda.gov">Ludwigia hyssopifolia</a>), false ironwort (<a class="species-link" href="https://plants.usda.gov/core/profile?symbol=HYCA12" target="_blank" title="Open in plants.usda.gov">Hyptis capitata</a>), Philippine ground orchid (<a class="species-link" href="https://plants.usda.gov/core/profile?symbol=SPPL" target="_blank" title="Open in plants.usda.gov">Spathoglottis plicata</a>), and pygmy smartweed (<a class="species-link" href="https://plants.usda.gov/core/profile?symbol=POMI21" target="_blank" title="Open in plants.usda.gov">Polygonum minus</a>), a native forb (Amidon et al., 2017; Fosberg, 1960; Marshall et al., 2020; Stemmermann, 1981; Stone, 1970; Wagner and Grether, 1948; Willsey et al., 2019).

Dominant plant species

para grass (Urochloa mutica), grass
hilograss (Paspalum conjugatum), grass
porterweed (Stachytarpheta), other herbaceous
linearleaf primrose-willow (Ludwigia hyssopifolia), other herbaceous

Pathway 2.1A
Community 2.1 to 2.2

Community phase 2.1 will change to 2.2 by invasion of the site by shrubs and forbs. This process is facilitated by excessive grazing, which reduces the competitive advantage of para grass (<a class="species-link" href="https://plants.usda.gov/core/profile?symbol=URMU" target="_blank" title="Open in plants.usda.gov">Urochloa mutica</a>).

Pathway 2.2A
Community 2.2 to 2.1

Community phase 2.2 can shift back to phase 2.1 by reducing grazing pressure on para grass (<a class="species-link" href="https://plants.usda.gov/core/profile?symbol=URMU" target="_blank" title="Open in plants.usda.gov">Urochloa mutica</a>) and, when necessary, performing spot weed control on shrubs and forbs.

State 3
Cleared and Abandoned State

The Cleared and Abandoned State (3) consists of one community phase dominated by a variable mixture of small trees, shrubs, vines, forbs, and grasses that thrive in sunny environments. Remnant para grass (Urochloa mutica) and hilograss (Paspalum conjugatum) are present (Amidon et al., 2017; Fosberg, 1960; Marshall et al., 2020; Stemmermann, 1981; Stone, 1970; Wagner and Grether, 1948; Willsey et al., 2019).

Community 3.1
Sea Hibiscus/Jack In The Bush/Para Grass – Tall Reed

This community phase contains remnant stands of para grass, hilograss, and tall reed with a variable array of shrubs, forbs, vines, and young trees that thrive in sunny environments. Trees such as sea hibiscus (Hibiscus tiliaceus), Tahitian screwpine (Pandanus tectorius), and white leadtree or tangantangan (Leucaena leucocephala) may be present. Shrubs such as emperor’s candlesticks (Senna alata) and native embrert (Clerodendrum inerme) may occur. Jack in the bush or masiksik vine (Chromolaena odorata) and the large, introduced forb redflower ragleaf or fua lele (Crassocephalum crepidioides) may be present. Common forbs are porterweed (Stachytarpheta spp.), linearleaf primrose-willow (Ludwigia hyssopifolia), false ironwort (Hyptis capitata), Philippine ground orchid (Spathoglottis plicata), Colombian waxweed (Cuphea carthagenensis), and pygmy smartweed (Polygonum minus), a native species (Amidon et al., 2017; Fosberg, 1960; Marshall et al., 2020; Stemmermann, 1981; Stone, 1970; Wagner and Grether, 1948; Willsey et al., 2019).

Dominant plant species

sea hibiscus (Hibiscus tiliaceus), tree
Jack in the bush (Chromolaena odorata), shrub
para grass (Urochloa mutica), grass
tall reed (Phragmites karka), grass

State 4
Invaded Forest State

The Invaded Forest State (4) consists of one community phase. It is a forest with both an 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 (Amidon et al., 2017; Fosberg, 1960; Marshall et al., 2020; Stemmermann, 1981; Stone, 1970; Wagner and Grether, 1948; Willsey et al., 2019).

Community 4.1
Sea Hibiscus – Tahitian Screwpine/Emperor’s Candlesticks/Linearleaf Primrose-Willow

The overstory consists of trees, particularly sea hibiscus (Hibiscus tiliaceus) and Tahitian screwpine (Pandanus tectorius). Emperor's candlesticks (Senna alata) may be present in the shrub layer. Linearleaf Primrose-Willow (Ludwigia hyssopifolia) is a common forb in the ground cover. Any of the native species listed for the Reference State (1) may be present. Other native plants that may occur are the tree Cynometra ramiflora, the vine threeleaf derris (Derris trifoliata), the vine (Dalbergia candenatensis), and the shrub embrert (Clerodendrum inerme) (Amidon et al., 2017; Fosberg, 1960; Marshall et al., 2020; Stemmermann, 1981; Stone, 1970; Wagner and Grether, 1948; Willsey et al., 2019).

Dominant plant species

sea hibiscus (Hibiscus tiliaceus), tree
Tahitian screwpine (Pandanus tectorius), tree
emperor's candlesticks (Senna alata), shrub
linearleaf primrose-willow (Ludwigia hyssopifolia), other herbaceous

Transition T1A
State 1 to 2

The Reference State (1) transitions to the Naturalized Grassland State (2) by removal of native vegetation and planting, or allowing colonization by, introduced grass species.

Transition T1B
State 1 to 3

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

Transition T1C
State 1 to 4

The Reference State (1) transitions to the Invaded Forest State (4) by wind damage to the forest when there is a nearby source of seeds of invasive species or, more gradually, by damage to the forest understory by ungulates, especially feral pigs, when there is a source of seeds of invasive species.

Restoration pathway R2A
State 2 to 1

The Naturalized Grassland State (2) could theoretically be restored to the Reference State (1) by suppression of grassland vegetation and replanting with native species. Natural reseeding by native forest species can be expected if there is a nearby stand of suitable species.

Transition T2B
State 2 to 3

The Naturalized Grassland State (2) transitions to the Cleared and Abandoned State (3) upon abandonment of grasslands, which are invaded by low-statured, native or introduced heliophytes.

Restoration pathway R3B
State 3 to 1

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

Restoration pathway R3A
State 3 to 2

The Cleared and Abandoned State (3) may be restored to the Naturalized Grassland State (2) by land clearing, weed control, and replanting grasses.

Transition T3A
State 3 to 4

The Cleared and Abandoned State (3) transitions to the Invaded Forest State (4) 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 R4A
State 4 to 1

The Invaded Forest State (4) can be restored to the Reference State (1). The difficulty, cost, and likelihood of success will depend on the species' composition and amount and competitiveness of introduced species present on a given site.

Transition T4A
State 4 to 3

The Invaded Forest State (4) may transition to Cleared and Abandoned State (3) due to mechanical clearing or fire. State 3 is likely to rapidly transition back to State 4 due to presence of an abundant tree seed bank in the soil.

Additional community tables

Table 5. Community 1.1 plant community composition

Group	Common name	Symbol	Scientific name	Annual production ()	Foliar cover (%)

Table 6. Community 1.2 plant community composition

Group	Common name	Symbol	Scientific name	Annual production ()	Foliar cover (%)

Table 7. Community 2.1 plant community composition

Group	Common name	Symbol	Scientific name	Annual production ()	Foliar cover (%)

Table 8. Community 2.2 plant community composition

Group	Common name	Symbol	Scientific name	Annual production ()	Foliar cover (%)

Table 9. Community 3.1 plant community composition

Group	Common name	Symbol	Scientific name	Annual production ()	Foliar cover (%)

Table 10. Community 4.1 plant community composition

Group	Common name	Symbol	Scientific name	Annual production ()	Foliar cover (%)

Supporting information

Other references

References for F191XY506MP (The Somewhat Poorly and Poorly Drained Valleys and Alluvial Coastal Plains Ecological Site)

Amand, A. (2000). Boiga irregularis (Brown Tree Snake) on Guam and Its Effect on Fauna. Restoration and Reclamation Review, 6 1-6.

Amidon, F., Metevier, M., and Miller, S. E. (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.

CNMI SWARS Council. (2010). Commonwealth of the Northern Mariana Islands (CNMI) Statewide Assessment and Resource Strategy 2010-2015+. CNMI Forestry. Contains good information about fire, invasive species, reforestation, and badlands.

Donnegan, J. A., Butler, S. L., Kuegler, O., Hiserote, B. A. (2011). Commonwealth of the Northern Mariana Islands’ Forest resources, 2004. Resource. Bull. PNW-RB-261. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 40 p. Forest survey based on randomized plots. Contains species lists by vegetation type, some soil and disturbance information, and size and cover data.

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.

Liske-Clark, J. (2015). Wildlife Action Plan for the Commonwealth of the Northern Mariana Islands, 2015-2025. CNMI DLRN-Division of Fish and Wildlife, Saipan, MP. Extensive review of habitat types with their plant species; discusses disturbances, invasive species.

Marshall, A.P., Willsey, T., Reeves, M., Amidon, F., and Miller, S., (2020). Wetlands of the Mariana Islands. In: Goldstein, M.I., DellaSala, D.A. (Eds.), Encyclopedia of the World's Biomes, vol. 4. Elsevier, pp. 295–315.

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.

Stemmermann, L. (1981). A Guide to Pacific Wetland Plants. US Army Corps of Engineers, Honolulu District.

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

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

USDA-Soil Conservation Service. (1989). Soil Survey of the Islands of Aguijan, Rota, Saipan, and Tinian, Commonwealth of the Northern Mariana Islands.

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 April 24, 2024. [https://www.fws.gov/program/national-wetlands-inventory/download-state-wetlands-data].

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

Willsey, T., Kwon, J. A., Reeves, M. K., Amidon, F., and Miller, S. E. (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
Daniel Bowman
Amy Koch
Kendra Moseley
Daniel Block
Sarah Quistberg
Bandan Brazee
Ann Tan
Jill Ficke-Beaton

Approval

Curtis Talbot, 8/19/2025

Acknowledgments

Assistance, advice, review, and/or insights: Assistance, advice, review, and/or insights: Michael Constantinides, NRCS-PIA Jennifer Higashino, USFWS and NRCS Mike Kolman, NRCS Bart Lawrence, NRCS Pamela Sablan, 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	08/19/2025
Approved by
Approval date
Composition (Indicators 10 and 12) based on	Annual Production

Indicators

Number and extent of rills:
Presence of water flow patterns:
Number and height of erosional pedestals or terracettes:
Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
Number of gullies and erosion associated with gullies:
Extent of wind scoured, blowouts and/or depositional areas:
Amount of litter movement (describe size and distance expected to travel):
Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
Functional/Structural Groups (list in order of descending dominance by above-ground annual-production or live foliar cover using symbols: >>, >, = to indicate much greater than, greater than, and equal to):

Dominant:

Sub-dominant:

Other:

Additional:
Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
Average percent litter cover (%) and depth ( in):
Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
Potential invasive (including noxious) species (native and non-native). List species which BOTH characterize degraded states and have the potential to become a dominant or co-dominant species on the ecological site if their future establishment and growth is not actively controlled by management interventions. Species that become dominant for only one to several years (e.g., short-term response to drought or wildfire) are not invasive plants. Note that unlike other indicators, we are describing what is NOT expected in the reference state for the ecological site:
Perennial plant reproductive capability:

Download reference sheet

Natural ResourcesConservation Service

Ecological site QX191X01X506

Somewhat Poorly and Poorly Drained Valley Bottoms and Coastal Plains

Last updated: 8/19/2025 Accessed: 09/19/2026

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General information

MLRA notes

Classification relationships

Ecological site concept

Associated sites

Table 1. Dominant plant species

Legacy ID

Natural Resources
Conservation Service

Last updated: 8/19/2025
Accessed: 09/19/2026