Some Representative Ideal Soil Types for Hybrid Poplar
in Western Washington State

Hybrid poplar, as mentioned before, thrives in rich, moist, alluvial soils. The topography, climate, vegetation, and geology of western Washington State have interacted to provide these soils in relative abundance. Mountain ranges with abundant precipitation have produced great rivers, which provide the alluvium. As the great rivers find their way to the gentle lowlands, the churning water slows. The great burden of silts and sands is deposited, sometimes in deltas, sometimes on dry land as floodwaters recede. The forces of erosion and andesitic volcanism provide rich alluvium, which is made even more productive by accumulation and integration of organic matter and nutrients.

This section showcases some western Washington soils from three counties that provide an ideal substrate for the intensive culture of hybrid poplar, as identified by Cellier. It is intended to support generalizations about the type of soils preferred for this industry.

Whatcom County

Mt. Vernon silt loam
This soil is a very deep, moderately well-drained soil in alluvium. Found on river terraces, flood plains, and levees. Admixture of volcanic ash with fine sandy loam. The Douglas-fir 50 year site index is 130.
0-7": dark brown fine sandy loam
7-13": very dark grayish brown fine sandy loam
13-20": dark grayish brown stratified fine sandy loam and sand
20-31": olive gray stratified fine sandy loam
42-60": dark grayish brown stratified sand and very fine sandy loam

Eliza-Tacoma silt loams
This series is found on flood plains, deltas, and tidal flats. Formed in alluvium. The red alder 50 year site index is 90.
0-4": dark grayish-brown mottled silt loam
4-12": olive gray, mottled silt loam
12-24": dark gray, mottled silt loam
24-60": dark gray, mottled, stratified sandy loam and loamy sand

Briscot-Oridia silt loam
Again, a series formed in alluvium on flood plains. Very deep, poorly drained soil. Red alder 50 year site index is 90.
2-0": fibric horizon- twigs and leaves
0-4": very dark grayish brown silt loam
4-12": olive brown silt loam
12-37": dark grayish brown or brown mottled loam
37-60": dark grayish brown fine sandy loam

Lewis County

Clato-Mud Flow
This is an example of the dynamic nature of the soil where poplars are grown. The 1980 eruption of Mt. St. Helens added a layer of fresh alluvium to many of the riparian soils in this area. The Clato series is well to poorly drained.
variable depth: recent mud flow silt loam and sand
0-11": dark yellowish brown silt loam
11-19": dark brown silt loam
19-42": dark yellowish brown heavy silt loam
42-69": dark yellowish brown silt loam

Siler silt loam/ash admixture
The Siler series was formed in alluvium and volcanic ash. It is very deep and ranges from well drained to poorly drained. Sometimes artificial drainage expedites certain land uses, such as agriculture and forestry. Very productive- Douglas-fir 50 year site class index of 50.
0-14": dark brown silt loam
14-21": light gray, sand-sized volcanic ash
21-60": dark brown silt loam

Schooley silt loam/ash admixture
Shallow depressional areas on river flood plains and low terraces are where the Schooley series is found. This series is formed in recent alluvium overlying sand-sized volcanic ash. It is typically very deep, poorly drained, and has a high organic matter content.
0-6"- mottled, very dark grayish brown silt loam
6-21"- mottled dark brown silt loam
21-31": white, sand-sized volcanic ash
31-40": mottled, dark grayish brown silt loam
40-60+" very dark brown muck

Grays Harbor County

Grehalem silt loam
This series is very deep and moderately drained. It is formed in alluvium and found on natural levees on flood plains. Incredibly productive 50 year site index for Douglas-fir: 140. Compactable, subject to rut formation.

Chehalis silt loam
The Chehalis series is very deep and well drained. It is a very productive site, with a Douglas-fir 50 year site index of 130. It is subject to compaction and erosion. Any area of this series experiencing repeated traffic requires an artificial surface to prevent loss of productivity.

Ocosta silty clay loam
Very deep and very poorly drained soils make up the Ocosta series. The alluvium forming this series is mostly clay deposited in quiet backwaters protected from tidal overflow. Because of the fine texture, permeability is low and drainage may be a problem.

Summary
This sample clearly displays some characteristic traits of soils with a high suitability for poplar production. High soil moisture availability, proximity to rivers, high fertility as expressed by site index ratios for other species, and alluvial parent material all seem to point to high site quality for hybrid poplar plantations.


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