
Natural Resources
Conservation Service
Ecological site QX190X01X502
Loamy Sand
Last updated: 6/12/2025
Accessed: 10/19/2025
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): 190X–Stratovolcanoes of the Mariana Islands
This MLRA occurs on the Northern Islands group of the Commonwealth of the Northern Mariana Islands. It consists of the islands of Pagan, Anatahan, Agrigan, Alamagan, Sarigan, and five smaller islands. The islands are largely unpopulated due to volcanic activity. The islands are cone-shaped stratovolcanoes covered with volcanic ash and cinder deposits on steep and very steep slopes. Agrigan has the highest elevation, ranging from sea level to 3,185 feet (970 meters). Average annual precipitation is about 80 inches (2,030 millimeters). Rainfall decreases northwards and increases slightly with elevation. Two-thirds of the precipitation falls between July and November. Average annual temperature is 79 degrees F (26 degrees C). The cooler dry season is between January and May. Trade winds blow from the northeast and east-northeast. Typhoons are frequent. Soils are Andisols, Inceptisols, or Entisols. The soil moisture regime is mostly ustic. The soil temperature regime is isohyperthermic. Abandoned coconut plantations occur on low elevation coastal sites. Areas above 330 feet (100 meters) are dominated by Pacific Island silvergrass or swordgrass (Miscanthus floridulus). Forest species are mixed tropical hardwoods. Large numbers of feral cows, pigs, and goats are on some of the islands (USDA-Natural Resources Conservation Service, 2006).
Classification relationships
This ecological site occurs within Major Land Resource Area (MLRA) 190 – Stratovolcanoes of the Mariana Islands.
Ecological site concept
This ecological site occurs on the island of Pagan in the Marianas Islands. It occurs on
nearly level to steep (0 to 45 percent) slopes of lava plains, hills, and lower slopes of calderas that have been smoothed by recent volcanic fallout of ash and cinders on stratovolcanic islands at elevations ranging from 20 to 1,000 feet (6 to 305 meters) (Soil Survey Staff 2025; Amidon et al., 2017; Carlisle et al., 2001; Fosberg, 1960; Kessler, 2011; Liske-Clark, 2105; USDA-Natural Resources Conservation Service, 2001; Willsey et al., 2019).
Soils are very deep (greater than 72 inches or 183 centimeters), well drained Entisols (Vitrandic Ustorthents) that formed in recent basaltic and andesitic volcanic ash and cinders. Soil temperature regimes are isohyperthermic; soil moisture regimes are ustic. Effective rooting depth is about 18 inches (46 cm) where plant roots are concentrated at the next horizon boundary. Texture of the soil surface horizon is ashy loamy fine sand. Average annual rainfall is about 80 inches (2,030 millimeters). Water runoff is negligible to low; permeability is very rapid. Available water holding capacity is very low (2 inches). Native and naturalized vegetation includes trees and ferns (Soil Survey Staff, 2025; Amidon et al., 2017; Carlisle et al., 2001; Fosberg, 1960; Kessler, 2011; Liske-Clark, 2105; USDA-Natural Resources Conservation Service, 2001; Willsey et al., 2019).
Similar sites
QX190X01X504 |
Silt Loam Although QX190X01X504 (The Silt Loam Ecological Site) and QX190X01X502 (The Loamy Sand Ecological Site) share some landscape types and similar elevation ranges, they differ in that the soils of the Silt Loam Ecological Site formed in older, more weathered volcanic ash and cinders, have much greater effective rooting depths, finer textures, and much greater available water holding capacity than the soils in the Loamy Sand Ecological Site. This results in the Silt Loam Ecological Site having greater productivity and ability to support forests than the Loamy Sand Ecological Site. The two sites co-occur only on the island of Pagan and do not directly border on each other. |
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Table 1. Dominant plant species
Tree |
(1) Aglaia mariannensis |
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Shrub |
Not specified |
Herbaceous |
(1) Phymatosorus scolopendria |
Legacy ID
F190XY502MP
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Ecosystem states
States 1, 5 and 2 (additional transitions)
T1A | - | The Reference State (1) may transition to the Cleared and Abandoned State (4) by mechanical clearing of the land followed by invasion by introduced species and increase of native nondominant species. |
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R2A | - | The Grassland State (2) can be restored to a facsimile of the Reference State (1) by suppressing grasses and replanting native trees. Protection from ungulates will likely be needed. |
T2A | - | The Grassland State (2) will transition to the Pioneer Tree-Invaded State (3) from Community Phase 2.2 as beach sheoak (Casuarina equisetifolia) gradually forms denser stands and outcompetes other vegetation. |
R2B | - | The Grassland State (2) can be restored to the Farmed State (5) by removing grass species and cultivating for crops or planting agroforest. |
R3B | - | The Pioneer Tree-Invade State (3) can be restored to a facsimile of the Reference State (1) by removal of beach sheoak (Casuarina equisetifolia) followed by replanting of a variety of native tree species commonly found in State 1. |
R3A | - | The Pioneer Tree-Invaded State (3) may be restored to the Grassland State (2) by fire. |
R3C | - | The Pioneer Tree-Invaded State (3) can be restored to the Farmed State (5) by clearing the land and cultivating for crops or planting agroforest. |
R4A | - | The Cleared and Abandoned State (4) may be restored to a facsimile of the Reference State (1) by brush and weed control followed by replenishing native tree species and numbers. |
T4B | - | The Cleared and Abandoned State (4) may transition to the Grassland State (2) if fire clears a site before development of closed forest with little understory and where Pacific Island silvergrass or swordgrass (Miscanthus floridulus) is either still present or seed sources are nearby. |
T4A | - | The Cleared and Abandoned State (4) may transition to the Pioneer Tree-Invaded State (3) if few or no seed sources for trees other than beach sheoak (Casuarina equisetifolia) are near the site during the temporary stage dominated by grasses, forbs, and shrubs. |
R4B | - | The Cleared and Abandoned State (4) may be restored to the Farmed State (5) by clearing site, followed by cultivation or planting agroforest. |
R5A | - | The Farmed State (5) may be restored to a facsimile of the Reference State (1) by weed control followed by replanting of native trees. |
T5A | - | The Farmed State (5) will transition to the Cleared and Abandoned State (4) if tree seed sources are present on the site after farmed lands are abandoned. |
State 1 submodel, plant communities
1.1A | - | Community phase 1.1 may shift to phase 1.2 by damage from powerful storms. |
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1.2A | - | Community phase 1.2 reverts to phase 1.1 by regrowth of the original dominant species if given enough time between strong storm events. |
State 2 submodel, plant communities
2.1A | - | Community phase 2.1 will shift to phase 2.2 upon invasion by native beach sheoak (Casuarina equisetifolia). |
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2.2A | - | Community phase 2.2 will revert to phase 2.1 with fire, which kills beach sheoak (Casuarina equisetifolia). |