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Ecological site QX192X01X501

Somewhat Poorly Drained Alluvium

Last updated: 5/08/2025
Accessed: 09/20/2026

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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): 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 centimeters). 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 moderately sloping (0 to 15 percent slopes) hillslopes in steeps, narrow stream channels, and depressions at elevations ranging from 33 to 984 feet (10 to 300 meters) (USDA- SCS, 1988).

Soils are very deep, somewhat poorly drained Entisols (Aquic Ustifluvents) that formed in alluvium derived from weathered tuff and tuff breccia (USDA-SCS, 1988). Soil temperature regimes are isohyperthermic; soil moisture regimes are ustic with an aquic intergrade, meaning water tables are high except during the distinct dry season. Mean annual precipitation is about 101 inches (2,565 millimeters) (PRISM, 2006). Water runoff is low to medium; permeability is slow (USDA-SCS, 1988). The water table in the rainy season is at a depth of 30 inches (75 centimeters). As such the effective rooting depth is about 30 inches (75 centimeters). Flooding is rare and brief in the rainy season. Available water-holding capacity is moderate (7 inches). pH is strongly acidic to moderately acidic (5.3 to 5.8). Groundwater is fresh (electronic conductivity is 0.0 dS/cm). Most of the area is vegetated by wetland forest, grasses, and sedges (Amidon et al., 2017; Fosberg, 1960; Marshall et al., 2020; Stemmermann, 1981; Stone, 1970; Wagner and Grether, 1948; Willsey et al., 2019).

Associated sites

QX192X01X003	Shallow Soils on Volcanic Uplands Soils of QX192X01X003 (The Shallow Soils on Volcanic Uplands Ecological Site) occur on steeper slopes surrounding QX192X01X501 (The Somewhat Poorly Drained Alluvium Ecological Site), which occurs downslope in depressions, stream channels, and seeps. Water will move from QX192X01X003, which has slow permeability and low to medium runoff, into QX192X01X501. Soils of QX192X01X003 have effective rooting depths of about 0 to 14 inches, very low available water holding capacity (2 inches), neutral soils reactions (6.7), are a very deep-water table, and support upland grasses, forbs, and forest. Soils QX192X01X501 have effective rooting depths greater than 72 inches, moderate water holding capacity (7 inches), moderately acidic to strongly acidic soil reactions (5.3 to 5.8), and have a water table as shallow as 30 inches below the surface, occasional and brief flooding, and support wetland forest, grasses, and sedges.
QX192X01X001	Moderately Deep Oxic Soils on Volcanic Uplands Soils of QX192X01X001 (The Moderately Deep Oxic Soils on Volcanic Uplands Ecological Site) occur on steeper slopes surrounding QX192X01X501 (The Somewhat Poorly Drained Alluvium Ecological Site), which occurs downslope in depressions, stream channels, and seeps. Water will move from QX192X01X001, which has slow permeability and low to high runoff, into this ecological site, carrying eroded alluvium that forms the parent material of QX192X01X501. Soils of QX192X01X001 have a very deep-water table, low available water holding capacity (3 inches), very strongly acidic to strongly acidic soil reaction (4.9 to 5.1), and high aluminum toxicity such that this site mostly and support mostly Pacific Island silvergrass (swordgrass). While soils of QX192X01X501 have moderate water holding capacity (7), are moderately acidic to strongly acidic (5.3 to 5.8), and have a water table as shallow as 30 inches below the surface, rare and brief flooding, and support wetland forest, grasses, and sedges.
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) occur in lower areas and broader valleys than QX191X01X501 (The Somewhat Poorly Drained Alluvium Ecological Site). Water from streams and seeps in QX192X01X501 feeds into QX192X01X506. Soils, water tables, and flooding regimes in both ecological sites are similar, except that ground water in coastal areas of QX191X01506 are slightly brackish rather than fresh. Both ecological sites support wetland forest, grasses, and sedges.
QX192X01X002	Deep Alfic Soils on Volcanic Uplands Soils of QX192X01X002 (The Deep Alfic Soils on Volcanic Uplands Ecological Site) occur on steeper slopes surrounding QX19WX01X501 (The Somewhat Poorly Drained Alluvium Ecological Site), which occurs in the depressions, stream channels, and seeps below. Water will move from QX192X01X002, which has very slow to moderately slow permeability and low to high runoff, into QX192X001X501, carrying eroded alluvium that forms the parent material of this ecological site. Soils of QX192X01X002 have low available water holding capacity (4 inches), a very deep-water table, and moderately acidic soil reaction (5.5 to 5.8) which support upland forests, grasses and forbs. While soils in QX19X01X501 have a higher water holding capacity (7 inches), a water table as shallow as 30 inches below the surface, rare and brief flooding, and support wetland forest, grasses, and sedges.
QX192X01X004	Very Deep Soils on Volcanic Uplands Soils of QX192X01X004 (The Very Deep Soils on Volcanic Uplands Ecological Site) occur on lower slopes, concave areas, and in drainageways, some of which surround or feed into QXY19201X501 (The Somewhat Poorly Drained Alluvium Ecological Site), which also occurs in depressions, stream channels, and seeps. Water will move from QX192X01X004 which has moderately slow permeability and medium runoff, into QX192X01X501, carrying eroded alluvium that forms the parent material. Soils of QX192X01X004 have low available water holding capacity (4 inches), very deep water tables, and can support diverse upland forests, grasses and forbs. While soils of QX192X01X501 have a higher water holding capacity (7), a water table as shallow as 30 inches below the surface, rare and brief flooding, and support wetland forest, grasses, and sedges.
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 QX192X01X501 (The Somewhat Poorly Drained Alluvium Ecological Site) on volcanic uplands. Soils of QX191X01X503 have water runoff ranging from very low to very high, very low available water holding capacity (1 inch), neutral to mildly alkaline soil pH (6.7 to 7.9) and vegetation which is mostly farmed. Where it is not farmed, the vegetation consists of introduced grass, forb, and tree species, including forests of white leadtree or tangantangan and some native forest. While soils of QX192X01X501 are primarily deep Alfisols on mountain slopes with low available water holding capacity (4 inches), moderately acidic soils (5.5 to 5.8), high base saturation, occur on strongly sloping to very steep (0 to 60 percent) slopes, 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 Holding Capacity Soils on Limestone Plateaus and Escarpments Ecological Site) occur on limestone plateaus that may border QX192X01X501 (The Somewhat Poorly Drained Alluvium Ecological Site) which occurs on volcanic uplands. Subsurface soils of QX191X01X505 contain 13 to 40 percent rock fragments greater than 3 inches resulting in a very low to low available water holding capacity (2 to 3 inches). Depending on slope (0 to 99 percent), water runoff ranges from very slow to very rapid, pH is neutral (7.0 To 7.9), and the area is mostly vegetated by native forest. Soils of QX192X01X501 have a higher water holding capacity (7), a water table as shallow as 30 inches below the surface, rare and brief flooding, and support wetland forest, grasses, and sedges.

Table 1. Dominant plant species

Tree	(1) Hibiscus tiliaceus (2) Ficus prolixa
Shrub	Not specified
Herbaceous	Not specified

Legacy ID

F192XY501GU

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Physiographic features

This ecological site occurs in stream channels, depressions, and seeps on volcanic hillslopes (USDA-SCS, 1988). The water table depth ranges from 30 inches to greater than 72 inches (75 to 185 centimeters).

Table 2. Representative physiographic features

Landforms	(1) Upland > Hillslope (2) Upland > Depression (3) Upland > Seep (4) Stream > Channel
Runoff class	Low to medium
Flooding frequency	Rare
Ponding frequency	None
Elevation	33 – 984 ft
Slope	0 – 15 %
Water table depth	30 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 97 to 103 inches (2,465 to 2,615 millimeters) while actual (10th and 90th percentiles) values for mean annual precipitation range from 96 to 106 inches (2,435 to 2,690 millimeters). Extreme values range from 92 to 116 inches (2,335 to 2,945 millimeters). The average annual precipitation is 101 inches (2,565 millimeters), and the median annual precipitation is also 101 inches (2,565 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 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 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 F degrees (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 (2490 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)	370 days
Freeze-free period (characteristic range)	370 days
Precipitation total (characteristic range)	100-100 in
Frost-free period (actual range)	370 days
Freeze-free period (actual range)	370 days
Precipitation total (actual range)	100-110 in
Frost-free period (average)	370 days
Freeze-free period (average)	370 days
Precipitation total (average)	100 in

Influencing water features

Small seasonal or perennial streams are present in this ecological site. The site receives runoff from surrounding slopes (USDA-SCS, 1988). 
 
Number of National Wetland Inventory (NWI) features overlapping ecological site: Riverine (272), freshwater emergent wetland (79), freshwater forested/shrub wetland (62), freshwater pond (7), estuarine and marine deepwater (2), and estuarine and marine wetland (1) (USFWS, 2023).

Soil features

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

These soils are Aquic Ustifluvents. They have an aquic soil moisture regime, meaning they are saturated with water near the surface (as low as 30 inches or 75 centimeters) and are anaerobic for much of the year. They formed in alluvium derived from weathered tuff and tuff breccia. Soil temperature regimes are isohyperthermic. They are very deep and somewhat poorly drained (USDA-SCS, 1988).

Table 4. Representative soil features

Parent material	(1) Alluvium – tuff breccia
Surface texture	(1) Clay
Family particle size	(1) Fine
Drainage class	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)	7 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)	5.3 – 5.8
Subsurface fragment volume <=3" (0-40in)	0 – 5 %
Subsurface fragment volume >3" (0-40in)	Not specified

Ecological dynamics

The main natural disturbance is strong storms that can damage or kill vegetation by flooding in rivers and drainageways and by high wind speeds. The main human disturbances are fires, invasion by introduced plant species, and damage to vegetation and soils by introduced ungulates (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 1. State-and-Transition Model for the Somewhat Poorly Drained Ecological Site (F192XY501GU).

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. 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) when the overstory plants of the forest are removed and then the site is abandoned. This allows increased light available to shade-intolerant 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 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.
T2A	-	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.
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.
R4B	-	The Invaded Forest State (4) can be restored to the Cleared and Abandoned State (3). After this “restoration,” State 3 is likely to rapidly transition back to State 4 due to presence of an abundant tree seed bank in the soil, unless fire is frequent.

State 1 submodel, plant communities

1.1. Sea Hibiscus - Fig

1.2. Sea Hibiscus – Tahitian Screwpine/Kodomillet – Tall reed

1.1A	-	Storms that damage or kill trees by high wind speeds or flooding causes a phase change from 1.1 to 1.2 typified by a partial, temporary change in dominant tree species and a temporary increase in ground level vegetation.
1.2A	-	Community phase 1.2 will revert to phase 1.1 with gradual regrowth of native species when given adequate time to recover after storm 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 introduced shrubs and forbs. This process is facilitated by excessive grazing, which reduces the competitive advantage of para grass.
2.2A	-	Community phase 2.2 can shift back to phase 2.1 by reducing grazing pressure on para grass (Urochloa mutica) and, when necessary, performing spot weed control on shrubs, forbs, and vines.

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 Sate (1) is forest with a tree canopy of variable height often determined by the depth of the ravine, which protects trees from the destructive effects of typhoons (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
Sea Hibiscus - Fig

Common, native tree species are sea hibiscus (Hibiscus tiliaceus), Tahitian screwpine (Pandanus tectorius), bakong (Pandanus dubuis), fig (Ficus prolixa), Glochidion marianum, malbau (Premna serratifolia), and cynometra (Cynometra ramiflora). Clerodendrum inerme is a common native shrub. Two common native vines are threeleaf derris (Derris trifoliata) and dalbergia (Dalbergia candenatensis) (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
fig (Ficus prolixa), tree

Community 1.2
Sea Hibiscus – Tahitian Screwpine/Kodomillet – Tall reed

The same tree species as in community phase 1.1 remain in phase 1.2 including sea hibiscus (Hibiscus tiliaceus), Tahitian screwpine (Pandanus tectorius), bakong (Pandanus dubuis), fig (Ficus prolixa), Glochidion marianum, malbau (Premna serratifolia), and cynometra (Cynometra ramiflora). However, other tree species such as Tahitian screwpine can become more abundant as the forest regrows. Ground vegetation including kodomillet (Paspalum scrobiculatum) and tall reed (Phragmites karka) become temporarily more abundant.

Dominant plant species

sea hibiscus (Hibiscus tiliaceus), tree
Tahitian screwpine (Pandanus tectorius), tree
kodomillet (Paspalum scrobiculatum), grass
tall reed (Phragmites karka), grass

Pathway 1.1A
Community 1.1 to 1.2

Storms that damage or kill trees by high wind speeds or flooding causes a phase change from 1.1 to 1.2 typified by a partial, temporary change in dominant tree species and a temporary increase in ground level vegetation.

Pathway 1.2A
Community 1.2 to 1.1

Community phase 1.2 will revert to phase 1.1 with gradual regrowth of native species when given adequate time to recover after storm 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 livestock grazing. The Naturalized Grassland State often occurs after fire removes the natural vegetation.

Community 2.1
Para Grass/Greenleaf Ticktrefoil

Community phase 2.1 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) and weedy forbs 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

This community phase consists largely of para grass (Urochloa mutica) and some hilograss (Paspalum conjugatum). Shrubs, vines, and forbs occupy some of the site due to reduction of grass competitiveness by excessive grazing. Some common species include: porterweed (Stachytarpheta spp.), linearleaf primrose-willow (Ludwigia hyssopifolia), false ironwort (Hyptis capitata), Philippine ground orchid (Spathoglottis plicata), Jack in the bush (Chromolaena odorata), common bamboo (Bambusa vulgaris), Colombian waxweed (Cuphea carthagenensis), and Johnsongrass (Sorghum halepense) (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 introduced 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, forbs, and vines.

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.

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

Community phase 3.1 contains remnant stands of para grass (Urochloa mutica) and hilograss (Paspalum conjugatum). Wetter spots may support dense stands of tall reed (Phragmites karka). Sea hibiscus (Hibiscus tiliaceus) and Tahitian screwpine (Pandanus tectorius) may be present and are likely to increase over time. Jack in the bush (Chromolaena odorata) may be very abundant. A wide variety of species are possible, including white leadtree or tangantangan (Leucaena leucocephala), guineagrass (Urochloa maxima), false ironwort (Hyptis capitata), Philippine ground orchid (Spathoglottis plicata), porterweed (Stachytarpheta spp.), linearleaf primrose-willow (Ludwigia hyssopifolia), Polygonum minus (a native forb), common bamboo (Bambusa vulgaris), and betel palm (Areca catechu) (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 forest with both overstory, and understory composed of a variable mix of native and introduced species. The actual species composition on a given site depends on the original native species composition, the disturbance history, and the species composition existing near the site before, during, and after disturbances.

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

Any of the native tree species listed for the Reference State (1) may be present including sea hibiscus (Hibiscus tiliaceus) and Tahitian screwpine (Pandanus tectorius). Introduced tree species are typically present; common examples of these are African tuliptree (Spathodea campanulata), white leadtree or tangantangan (Leucaena leucocephala), and betel palm (Areca catechu) (Amidon et al., 2017; Fosberg, 1960; Marshall et al., 2020; Stemmermann, 1981; Stone, 1970; Wagner and Grether, 1948; Willsey et al., 2019).

The understory consists of an unpredictable mixture of native and introduced shrubs, ferns, vines, forbs, and grasses that have some shade tolerance. Common examples of introduced understory species are the shrub emperor’s candlesticks (Senna alata), linearleaf primrose-willow (Ludwigia hyssopifolia), and vines such as mile-a-minute (Mikania micrantha) and Jack in the bush (Chromolaena odorata) (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) when the overstory plants of the forest are removed and then the site is abandoned. This allows increased light available to shade-intolerant 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 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 T2A
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.

Restoration pathway R4B
State 4 to 3

The Invaded Forest State (4) can be restored to the Cleared and Abandoned State (3). After this “restoration,” State 3 is likely to rapidly transition back to State 4 due to presence of an abundant tree seed bank in the soil, unless fire is frequent.

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 the Somewhat Poorly Drained Alluvium Ecological Site (F192XY501GU)

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.

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.

Marshall, A.P., Willsey, T., Reeves, M., Amidon, F., 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

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
Daniel Block
Jill Ficke-Beaton
Brendan Brazee

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	09/20/2026
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 QX192X01X501

Somewhat Poorly Drained Alluvium

Last updated: 5/08/2025 Accessed: 09/20/2026

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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: 5/08/2025
Accessed: 09/20/2026