Lichen
Communities
Glossary
Acidity, active The activity of hydrogen ion in the
aqueous phase of a soil expressed as a pH value. Acidity, residual Soil acidity that is neutralized
by lime or a buffered salt solution to raise the pH to a
specified value (usually 7.0 or 8.0) but which cannot be
replaced by an unbuffered salt solution. It can be calculated
by subtraction of salt replaceable acidity from total acidity. Acidity (exchangeable) The aluminum and hydrogen
that can be replaced from an acid soil by an unbuffered salt
solution such as KCl or NaCl Adsorption The attraction of ions or compounds to
the surface of a solid
Air-filled porosity The fraction of the bulk volume
of soil that is filled with air at any given time or under
a given condition, such as a specified soil-water content
or soil-water metric potential.
Anion A negatively charged ion (e.g., PO4-, NO3-) Bulk density The mass of dry soil per unit bulk volume.
The value is expressed as grams per cubic centimeter (g cm-3) Carbon cycle The sequence of transformations whereby
carbon dioxide is converted to organic forms by photosynthesis
or chemosynthesis, recycled through the biosphere (with partial
incorporation into sediments), and ultimately returned to
its original state through respiration or combustion. C:N ratio The ratio of the mass of organic carbon
to the mass of organic nitrogen in soil, organic material,
plants, or microbial cells. Cation A positively charged ion (e.g., Na+, Ca++) Cation Exchange
Capacity (CEC) The sum of exchangeable bases plus
total soil acidity at a specific pH values,usually 7.0 or
8.0. Expressed in centimoles of charge per kilogram of exchanger
(cmolc kg-1). Clay (i) A soil separate consisting of particles <0.002
mm in equivalent diameter. (ii) A textural class. (iii) A
naturally occurring material composed primarily of fine-grained
minerals, which is generally plastic at appropriate water
contents and will harden when dried or fired. Effective Cation
Exchange Capacity
(ECEC) When acidity is expressed as salt extractable
acidity, the cation exchange capacity is called the effective
cation exchange capacity (ECEC) because this is considered
to be the CEC of the exchanger at the native pH value.
Expressed in centimoles of charge per kilogram of exchanger
(cmolc kg-1). Erosion The wearing away of the land surface by rain
or irrigation water, wind, ice, or other natural or anthropogenic
agents that abrade, detach and remove geologic parent material
or soil from one point on the earth's surface and deposit
it elsewhere Exchangeable
Nutrient A plant nutrient that is held by the adsorption
complex of the soil and is easily exchanged with the anion
or cation of neutral salt solutions. Litter The surface layer of the forest floor which
is not in an advanced stage of decomposition, usually consisting
of freshly fallen leaves, needles, twigs, stems, bark, and
fruits. Mineral Soil A soil consisting predominantly of products
derived from the weathering of rocks (e.g., sands, silts,
and clays). Nutrient Elements or compounds essential as raw materials
for organism growth and development. O horizon A layer of organic material having undergone
little or no decomposition (fibric material). On the forest
floor this layer consists of freshly fallen leaves, needles,
twigs, stems, bark, and fruits. Organic soil For the purposes of FIA, an organic
soil is defined as any soil in which the organic horizon
is greater than 8 inches (20 cm) in thickness. These soils
are prevalent in wetland areas such as bogs and marshes and
may be frequently encountered in certain regions of the country
(e.g., Maine, northern Minnesota, coastal regions) pH The pH of a solution in equilibrium with soil.
It is determined by means of an electrode or other indicator
at a specified soil-solution ratio in a specified solution,
usually distilled water, 0.01 M CaCl2, or 1 M KCl. Plant nutrient An element which is absorbed by plants
and is necessary for completion of the normal life cycle.
These include C, H, O, N, P, K, Ca, Mg, S, Cu, Fe, Zn, Mn,
B, Cl, Ni, and Mo. Porosity The volume of pores in a soil sample (nonsolid
volume) divided by the bulk volume of the sample Restrictive layer In FIA, defined as any soil condition
that increases soil density to the extent that it may limit
root growth. This limitation may be physical (hard rock)
or chemical (acid layer) or both. Sampling frame In FIA, a frame used to collect forest
floor samples from a known area. A bicycle tire 12 inches
in diameter has been selected as the national standard. Soil profile A vertical section of the soil through
all its horizons and extending into the C horizon. Water content The water lost from the soil upon drying
to constant mass at 105 ° C; expressed either as the
mass of water per unit mass of dry soil or as the volume
of water per unit bulk volume of soil.
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