Natural Resources
Conservation Service
Ecological site AX001X01X403
Mesic Udic Dry Forest
Last updated: 5/15/2025
Accessed: 12/06/2025
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): 001X–Northern Pacific Coast Range, Foothills, and Valleys
This area consists of a long and narrow range of mountains with associated foothills and valleys that parallels the Pacific Ocean. This area is entirely within the Pacific Border Province of the Pacific Mountain System in Oregon and Washington. MLRA 1 is bounded on the north by the highest elevations of the Olympic Mountains and the strait of Juan de Fuca, and by the Klamath Mountains on the south. The Washington portion of this MLRA is primarily composed of young Tertiary sedimentary rocks (siltstone and sandstone) mixed with some volcanic rocks of the same age. Glacial till and outwash deposits are also found in the northern half of this area in Washington. Much of this area is accreted terrane formed by tectonic processes. The average annual precipitation ranges from 60 to 200 inches (1,525 to 5,580 millimeters), increasing with elevation. Most of the precipitation in this area occurs during low-intensity, Pacific frontal storms and is evenly distributed throughout fall, winter, and spring.
The dominant soil orders in this MLRA are Andisols, Inceptisols, and Ultisols. Soil depths broadly range from shallow to very deep. Soils are primarily well drained, however poorly drained soils may be found in depressional areas and on alluvial floodplains. Surface textures are typically medial and loamy or clayey. Soils in this area dominantly have a mesic or frigid temperature regime and a udic moisture regime. Soils with aquic moisture regimes and cryic temperature regimes also occur.
Ecological site concept
Mesic Udic Dry Forest sites occur on less stable landscape positions on glacial valley walls and colluvial aprons in the mesic temperature zone. These sites are located on the leeward side of the Olympic Mountains where precipitation is relatively low. Additionally, relatively high slope gradients limit water infiltration on these sites, generating runoff to more stable Mesic Udic Moist Forests, Mesic Aquic Forests, and Temperate Wet Meadows. Mesic Udic Dry Forests are indicated by the presence of dry mesophytic species such as oceanspray (Holodiscus discolor) and dwarf rose (Rosa gymnocarpa). These species may or may not be abundant on Mesic Udic Dry Forest sites, but their presence serves as a strong indicator of this site.
Mesic Udic Dry Forest sites are characterized by an overstory canopy of western hemlock (Tsuga heterophylla) and Douglas-fir (Pseudotsuga menziesii), accompanied by an understory shrub community of oceanspray and dwarf rose. The herbaceous layer is dominated by western swordfern (Polystichum munitum) and sweet after death (Achlys triphylla), locally known as deerfoot vanilla leaf. Western redcedar (Thuja plicata) may be present as a minor overstory component, particularly in microtopographic depressions. Cascade barberry (Mahonia nervosa) is commonly present in the understory shrub and subshrub layers in greater abundance than on Mesic Udic Forest sites. Salal is a common component in the understory shrub layer. Site indices for Mesic Udic Dry Forests are generally lower than for Mesic Udic Forests.
Associated sites
| AX001X01X200 |
Temperate Wet Meadow Temperate Wet Meadow sites may be found adjacent to or surrounded by Mesic Udic Dry Forest sites. Temperate Wet Meadows occur on depressions and seeps. Temperate Wet Meadow sites lack tree cover. |
|---|---|
| AX001X01X402 |
Mesic Udic Moist Forest Mesic Udic Moist Forest sites may occur downslope of Mesic Udic Dry Forest sites and generally have more stable slope gradients. Mesic Udic Moist Forest sites have higher productivity. Mesic Udic Moist Forest sites typically support salmonberry (Rubus spectabilis). |
| AX001X01X004 |
Mesic Aquic Forest Mesic Aquic Forest sites may occur downslope or in mosaic with Mesic Udic Dry Forest sites. Mesic Aquic Forest sites occur on depressions and seeps and are subject to ponding. |
Similar sites
| AX001X01X401 |
Mesic Udic Forest Mesic Udic Forest sites are located on the windward side of the Olympic mountains and receive higher precipitation. Production on Mesic Udic Forest sites is significantly higher. |
|---|---|
| AX001X01X408 |
Frigid Udic Dry Forest Frigid Udic Dry Forest sites are located at higher elevations and support Pacific silver-fir (Abies amabilis). |
Table 1. Dominant plant species
| Tree |
(1) Tsuga heterophylla |
|---|---|
| Shrub |
(1) Holodiscus discolor |
| Herbaceous |
(1) Polystichum munitum |
Legacy ID
F001XA403WA
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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 |
| 1.5B | - | High-intensity disturbance |
| 1.5A | - | Time without disturbance |