
Natural Resources
Conservation Service
Ecological site AX004A01X403
Udic Moist Forest
Last updated: 5/06/2025
Accessed: 10/18/2025
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): 004A–Sitka Spruce Belt
This area consists of a long and narrow band of marine terraces, coastal estuaries, sand dunes, low relief hills, and mountain slopes that parallels the Pacific Ocean. This area is entirely within the Pacific Border Province of the Pacific Mountain System in Oregon and Washington. In Washington, this area ranges in elevation from sea level to a maximum of 1800 feet (550 meters) inland. The portion of this area in northern Washington consists primarily of glacial deposits, with some scattered young Tertiary sedimentary rocks. The climate is cool and moist, with minimal changes between seasons. Summer temperatures are moderated by the proximity of cool ocean water and fog. Sitka spruce forests are characteristic of this area. The average annual precipitation is 52 to 60 inches (1,320 to 1,525 millimeters) near the beach and can be as much as about 150 inches (3,800 millimeters) at the higher elevations along the inland edge of the MLRA. Most of the rainfall occurs during low-intensity, Pacific frontal storms. Precipitation is evenly distributed throughout fall, winter, and spring; summers are cool and dry. Snowfall accumulation is rare on the ocean side of this area, but some snowfall occurs along the eastern boundary. This area lies within the coastal fog belt zone, and heavy fogs are common in summer. Supplemental moisture is provided by fog condensation. Dominant soil orders in this MLRA are Andisols, Inceptisols, Spodosols, and Entisols.
Ecological site concept
Isomesic Udic Moist Forest sites occur on stable landscape positions on colluvial aprons in the isomesic fog belt. Runoff generated from less stable Isomesic Udic Forest sites accumulates on Isomesic Udic Moist Forest sites, resulting in increased available water. As a result, Isomesic Udic Moist Forest sites characteristically favor the growth and production of moist mesophytic understory species, such as salmonberry (Rubus spectabilis) and threeleaf foamflower (Tiarella trifoliata).
Isomesic Udic Moist Forest sites are characterized by a dense overstory of western hemlock (Tsuga heterophylla) and Sitka spruce (Picea sitchensis), accompanied by an understory shrub community of salmonberry (Rubus spectabilis) and cascara buckthorn (Frangula purshiana). The herbaceous layer is dominated by common ladyfern (Athyrium filix-femina), western swordfern (Polystichum munitum), horsetail (Equisetum spp.), threeleaf foamflower (Tiarella trifoliata), redwood-sorrel (Oxalis oregana), water parsley (Oenanthe sarmentosa), and threepetal bedstraw (Galium trifidum). Western redcedar (Thuja plicata) is commonly present in the overstory.
Associated sites
AX001X01X200 |
Temperate Wet Meadow Temperate Wet Meadow sites may be found adjacent to or surrounded by Isomesic Udic Moist Forest sites. Temperate Wet Meadows occur on depressions and seeps. Temperate Wet Meadow sites lack tree cover. |
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AX004A01X404 |
Isomesic Aquic Forest Isomesic Aquic Forest sites may occur downslope or in mosaic with Isomesic Udic Moist Forest sites. Isomesic Aquic Forest sites occur on depressions and seeps and are subject to ponding. |
AX004A01X401 |
Isomesic Udic Forest Isomesic Udic Forest sites may be found upslope of Isomesic Udic Moist Forest sites and frequently generate run-off moisture that is captured by Isomesic Udic Moist Forest sites. |
Similar sites
AX001X01X402 |
Mesic Udic Moist Forest Mesic Udic Moist Forest sites occur at higher elevations and lack Sitka spruce (Picea sitchensis). |
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AX001X01X407 |
Frigid Udic Moist Forest Frigid Udic Moist Forest sites occur at much higher elevations and support Pacific silver-fir (Abies amabilis). |
Table 1. Dominant plant species
Tree |
(1) Tsuga heterophylla |
---|---|
Shrub |
(1) Rubus spectabilis |
Herbaceous |
(1) Athyrium filix-femina |
Legacy ID
F004AA403WA
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Ecosystem states
State 1 submodel, plant communities
Communities 1 and 5 (additional pathways)
1.1B | - | Minor disturbance |
---|---|---|
1.1A | - | High-intensity disturbance |
1.2A | - | Time without disturbance |
1.2B | - | High-intensity disturbance |
1.3A | - | Time without disturbance |
1.4B | - | High-intensity disturbance |
1.4A | - | Time without disturbance |
1.5A | - | Time without disturbance |
1.5B | - | High-intensity disturbance |