FOREST SOILS - web.mala.bc.ca

FOREST SOILS
FORESTRY 151
SOIL TAXONOMY
As everything in science, soils are classified for the purpose of identification. This way, when someone
describes a soil as being a BRUNISOL, everyone to whom that is communicated, within the environmental
sciences, knows (or should know) of what that person speaks.
Generally speaking, there are three (3) mineral horizons (in most cases) within a soil profile; the "A" at the top
of the profile which is either eluviated (Ae) or humified (Ah) (in some cases, both can be found in the same
profile); the "B" horizon located below the "A" (sometimes, there is more than one "B" horizon) which is an
altered form of the "C", or lower horizon, by pedogenesis; and the "C" horizon which is unaltered (more or
less) parent material. On top of it all, there is an organic horizon referred to as the humus or LFH.
Not all soils are the same; they will vary a great deal in appearance based on the environment in which they
have evolved and the type of material that they evolve from.
Climate very strongly influences the process of soil formation and evolution both directly and indirectly; the
latter by controlling other factors such as plant and wildlife communities. As such, soils are classified,
primarily, according to the powers of influence and what causes them to be the way they are.
The Canadian System of Soil Classification
The System of Soil Classification for Canada has six levels of generalization or categories
as outlined below:
Order Level
This is the highest level of generalization. The pedons (the smallest 3 dimensional unit of soil that
can be used for classification purposes - generally 1 - 2 m deep by 1 - 3.5 m wide) are grouped
according to their properties that reflect the nature of the soil forming processes. For
example, the total effect of soil processes in the soils of the Chernozemic order leads mainly to
the accumulation of organic matter in the topsoil under grassland vegetation. The number of
specific statements that can be made about this category are few; only general statements are
possible. Ten orders are recognized, eight for mineral soils, one for organic soils, and one which
can contain both.

Great Group Level
This class is a subdivision of the order and is, therefore, more specific and more precise
statements can be made about it. Great groups are based on properties that reflect
differences in the strength of the dominant processes or a major contribution of a process
in addition to the dominant one. In the Chernozemic order the great groups are differentiated
on the basis of the colour of the topsoil. This is an indication of the amount of organic matter that
has accumulated. The Brown soils in the driest areas have the least and the Black soils in the
coolest and wettest areas have the most. The Dark Gray soils occur near the forest-grassland
transition where a secondary process of the leaching of organic matter and clay from the topsoil
becomes important.
Subgroup Level
A subdivision of the great group that defines the central concept of the great group (Orthic) or
certain variations from that concept which are grading towards other orders, e.g. a Gleyed Brown
Chernozemic or a Solonetzic Brown Chernozemic, where the normal features of a Brown
Chernozemic soil are being modified by the occurrence of excessive water or soluble salts
respectively. Special features of the soil profile such as thin iron pans (Placic) or repeated organic
layers (Cumulic) are also used to classify sub-groups. The subgroup is visualized as having a
particular assemblage of horizons and the Canadian System of Soil Classification specifies the
horizons that each subgroup category must have, along with others that it may have.
Family Level
A subdivision of the subgroup which identifies a group of soils that are relatively homogeneous in
mineralogy, texture and soil climate as well as genetic soil horizons. Because of the more precise
nature of this class many statements can be made about the use and management of the soils in
relation to plant growth, hydrology and engineering characteristics.
Series Level
A subdivision of the family, this is a group of pedons (a polypedon) with horizons whose features
such as colour, texture, structure and thickness fall within a narrow range. The pedons have all
been developed from similar parent material. This is probably the most important category of soils
for consideration of use and management since it applies to real soil bodies - polypedons.
There used to be a further category called a TYPE based on the texture of the topsoil. This has
now been dropped but may be found in some early reports.
The higher classes of the Soil Classification (order, great group, subgroup and family) are
especially important in studying genetic relationships, drawing inferences and allowing
correlations which are often required for regional studies. The two lower categories are more
suited to local and site specific studies and to land utilization programs.
The nomenclature used for the four higher categories is descriptive of either the soil morphology
or the kinds of environments in which the soils are found. The soil series, because of its more local
character and precise nature, is named after a geographic or cultural feature near the site where
the soil was first observe.

The classification system down to this level is as follows:
Order Great Group General Description
Brunisolic
Podzolic
Cryosolic
Gleysolic
Luvisolic
Organic
Regosolic
Chernozemic
Solonetzic
Dystric Brunisol
Eutric Brunisol
Sombric Brunisol
Melanic Brunisol
Humic
Ferro-humic
Humo-ferric
Organic Cryosol
Static Cryosol
Turbic Cryosol
Humic Gleysol
Gleysol
Luvic Gleysol
Gray Brown Luvisol
Gray Luvisol
Fibrosol
Mesisol
Humisol
Folisol
Regosol
Humic Regosol
Brown
Dark Brown
Black
Dark Gray
Solod
Solodized Solonetz
Solonetz
Vertisolic No Great Groups
These soils are common in milder forest environments such as the south
coast. They tend to be marginally developed soils as demonstrated by the dull
brown "B" horizons. They could be classified as transitional soils between
REGOSOLS and some other great group such as PODZOLS.
Podzols have "B" horizons with various accumulation levels of humified
organic materials and Al and/or Fe (Bh/Bhf/Bf), and tend to occur in cooler
wetter coniferous forest environments.
Soils that have permafrost within one metre of the surface.
These soils tend to be saturated for prolonged periods of time and, as such,
tend to experience intense reduction. They have a characteristic low chroma
or have very prominent mottles of high chroma within 50 cm of the surface.
These soils are common in depressions with poor drainage.
These soils have strongly illuvial "B" horizons in which high levels of clay has
accumulated (Bt) and demonstrate the "classic" clay skins on the peds.
These soils are composed of at least 40 cm of organic materials that are
saturated for extended periods of time.
These are very young, poorly developed, soils and lack a genetic horizon.
These are typical prairie or grassland soils with dark "Ah" horizons greater
than 10 cm thick with a base saturation greater than 80%.
These soils are common in areas were the parent material is saline. They
tend to be quite hard when dry and very sticky when wet and demonstrate the
classic columnar or prismatic macrostructure.
These are soils developed on Aheavy@ clay parent materials composed mainly
of smectite - a swelling type clay. As a result, the soil tends to shrink and
expand quite significantly resulting in prominent vertical cracking obliterating
well-defined horizons. Common on the prairies and east of the Rocky
mountains in BC.
THE MOST COMMON SOIL ORDERS OF BRITISH COLUMBIA
THE BRUNISOLIC ORDER
Soils of the Brunisolic order have undergone only moderate development from the original parent
material. Physical, chemical and biological weathering has proceeded far enough to change the
morphology of the parent material. There are no drastic translocations or transformations of the
material that characterize many of the other orders.
There are a number of reasons for this type of soil occurring in British Columbia. Firstly in many
areas the climate has restricted the progression of soil weathering. Long winters and low
temperatures restrict the rate of many of the transformations which constitute soil weathering.
This is the reason why Brunisolic soils cover much of the high plateaus of central and northern
British Columbia. Lack of soil moisture also limits transformations such as chemical weathering.
Thus, Brunisolic soils are also found in the sub-humid to semiarid zones of the southern interior.
Secondly, some Brunisolic soils have developed on very coarse textured materials such as

fluvio-glacial sands and gravels in areas where the climate is not normally a limiting factor in soil
development. Because clay-sized particles, the principal active fraction in chemical
transformations, make up only a small volume of the total mineral soil, little weathering has taken
place. Most of the soil is relatively inert gravel and quartz sand. Moreover the parent material has
a low water-holding capacity, so that soil water content is low and thus chemical transformations
are further restricted. The droughtiness of these soils means that the vegetation is often limited to
open lodgepole pine and pinegrass in the interior. Therefore, organic matter additions to the
topsoil are limited, and well-structured Ah horizons are thin or absent. Thirdly, Brunisolic soils are
found on very young geological sediments. In this case the time available for soil development
since deposition has not been sufficient for anything more than a moderate amount of weathering
to have taken place. Many of the soils on the recent alluvium of the Fraser Valley fall into the
Brunisolic order.
Soils of the Brunisolic order are often regarded as being in a transitional stage of development.
We think that given time, the translocation of weathered products will begin within the soil to
produce Podzols or possibly Luvisols. The Brunisolic soils on Fraser River alluvium are a
probable example. However, there are many areas in British Columbia where Brunisolic soils
occur on sediments that have been exposed to sub-aerial weathering since the ice melted about
11,000 years ago; for example the soils in the semiarid southern interior valleys. In other words, it
is necessary to decide whether transitional is to mean in the short or in the long term.
The main processes involved in the formation of Brunisolic soils are the removal by
leaching of soluble salts and carbonates, the in situ weathering of the mineral fraction to
form secondary minerals and hydrated iron and aluminum oxides, and the development of
soil structure in the finer textured materials that is different from the original structure of
the parent material. These are the processes that form the Bm horizon which is diagnostic
of Brunisolic soils. In the field it is recognized by its browner or redder colour as
compared with the parent material, by its structure and by its lack of major accumulations
of any materials translocated from the A horizon, such as clay. A common horizon
sequence for these soils would be LFH, Ah, Bm, C or Ck.
The great groups of the Brunisolic order are separated on the basis of the presence or absence of
an A horizon in which the mineral and organic fractions have been mixed together by soil fauna
(an Ah horizon), and on the base status of the soils as shown by the pH. The Ah horizon indicates
that there is a net addition of organic matter to the soil and that organic nutrients are available. A
high base status shows that the soil can retain inorganic nutrients such as calcium and potassium,
or that leaching is limited. The specific characteristics of the four great groups are as follows:
Melanic Brunisol: Thick Ah horizon + high base status (pH over 5.5)
Eutric Brunisol: No or thin Ah horizon + high base status (pH over 5.5)
Sombric Brunisol: Thick Ah horizon + low base status (pH. less than 5.5)
Dystric Brunisol: No or thin Ah horizon + low base status (pH less than 5.5)
THE PODZOLIC ORDER
Soils of the Podzolic order have been formed under subarctic to cryoboreal and perhumid
to humid soil climates. Their parent materials are mostly coarse textured and well drained.
They contain much silica and few bases such as calcium or magnesium carbonate. The
vegetation growing on them is usually coniferous forest, but some Podzolic soils develop under
heather (alpine).
Under these conditions there is an abundance of water moving through the soil during the year.
Chemical and biological transformations are intense in the upper horizons. Organic matter is
decomposed and primary minerals are broken down releasing iron and aluminum in the

non-calcareous (soils with limited amounts of calcium carbonates) soil environment. These three
weathering products are readily moved out of the A horizon and into the B in the porous parent
materials. It is the accumulation, in various combinations, of organic matter, iron and
aluminum in the B horizon that is the distinguishing characteristic of Podzolic soils.
Podzolic soils have a striking appearance. There is a black LFH organic litter layer on the
surface under which the top of the mineral soil is light gray. This is the Ae horizon from
which bases, organic matter, iron and aluminum have been translocated down into the B
horizon. There is little left apart from silica silt and sand. The B horizon is in sharp contrast, a
reddish brown layer enriched with organic matter, iron and aluminum, the colour
becoming more yellow with depth. A typical horizon sequence would therefore be LFH, Ae,
Bhf, Bf, BC, C.
There are some variations of this classic podzol profile in British Columbia. In many areas
of coastal forest there is no bleached Ae horizon in the profile. The addition of organic matter
to, and the weathering of iron and aluminum in, the upper mineral horizon is so great that despite
the heavy leaching there is no net depletion to form an Ae horizon. In other areas the organic
matter simply masks the Ae horizon under moist field conditions.
Many of the Podzolic soils of the west coast mountains have compacted horizons in the subsoil.
These may be at various depths, have varying thicknesses and contain different cementing
agents. They are given different names - ortstein, placic, duric or fragic - according to their
morphology and mode of origin. They have the common effect of restricting root penetration and
permeability.
Over much of southern British Columbia, especially in the mountains, volcanic ash makes
up a significant proportion of the topsoil. As it weathers, the ash releases large amounts
of iron and especially of aluminum. When the iron and aluminum are translocated into the
B horizon a Podzolic soil profile is produced. This can happen in areas that do not have a
typically high rainfall, nor dense conifers nor an acid bedrock. The profile has been formed
because the parent material was able to supply large quantities of moveable iron and aluminum.
The result is an example of comparable soils being formed in two different environments where
the lack of one factor is compensated for by the excess of another.
There are three great groups in the Podzolic order. They differ according to the relative amounts
of organic matter and iron plus aluminum that have accumulated in the upper B horizon as
follows:
Humic Podzol: Accumulation of organic matter with a limited supply of Fe to give a Bh
horizon. These soils occur in wet environments such as the coastal forests
or at high elevations inland; common on the BC coast.
Ferro-Humic Podzol: Accumulation of organic matter Fe plus Al to give a Bhf horizon. These
soils occur under humid coniferous forest conditions on the west coast
where there is often a thick ground cover of moss.
Humo-Ferric Podzol: Accumulation of Fe plus Al and little organic matter to give a Bf
horizon. These soils occur in less humid or cooler areas than the other
two great groups such as higher elevations on the eastern side of
Vancouver Island or the subalpine forests of the interior.

HORIZON QUALIFIERS
Due to pedogenesis, soil horizons will vary in their physiological make-up from soil order to soil order. To note
these differences, lower case suffixes are used. Of the twenty qualifiers used, the following are the most
common.
c Denotes a cemented horizon.
e A horizon characterized by the eluviation of clay, Fe, Al, or organic matter. Used with the "A"
horizon
f A horizon enriched with Al and Fe combined with organic matter. It usually has a hue of 7.5
YR or redder. Used with the "B" horizon.
g Denotes a gleyed horizon. Characterized by grey colours, or prominent mottling. Can be
used with the B and/or C horizons.
h A horizon enriched with organic matter. Used with either the "A" or "B" horizons.
m A horizon slightly altered by hydrolysis, oxidation or solution, or all three. Used with the "B"
horizon when it is slightly redder or brighter than the underlying material.
t An illuvial horizon enriched with silicate clays. Used with the "B" horizon.
j A modifier of suffixes such as f, e, t, m, g, h, used to denote that the horizon does not quite
meet the criteria of the suffix it is used with.
n A horizon in which the ratio of exchangeable Ca to Na is less than 10. The horizon must also
have prismatic or columnar structure, dark coatings on the peds, and hard to very hard
consistence when dry. It is used with B master horizons.
Other qualifiers include s for salts, k for carbonates, p for disturbed by man, z for frozen, y for affected by
cryoturbation, and u for markedly disrupted by physical or faunal activity such as blowdown, mass movement,
or burrowing animals.