Physiographic region An area of similar geologic structure and topographic relief that has
a unified geomorphic history; e.g., the Great
Plains of Fenneman (1928).
Piedmont Sequence of landforms along the
margins of uplands.
Plankton Small, floating or weakly swimming
plants and animals, found in salt and fresh
water; primarily microscopic algae and
protozoa.
Plant adaptation region Large area based on
both ecological (ecoregion) and climatic
(hardiness zone) characteristics that can be
used to guide collecting and evaluating plant
materials for potential adaptations.
Plant formation class A world vegetation type
dominated throughout by plants of the same
life form.
Plate tectonics The large-scale motions of the
earth’s lithosphere.
Playa A desert lake existing only temporarily
after a rain.
Pleistocene The most recent major ice age.
Generally the Pleistocene is considered to
have begun approximately two million years
ago and to have ended 8 to 10 thousand years
ago.
Podzol Soil order consisting of acid soil in
which surface soil is strongly leached of
bases and clays.
Polar front Boundary lying between cold polar
air masses and warm tropical air masses.
Potential natural vegetation Naturally occurring plant cover known to occur in areas
undisturbed by human activity and assumed
to grow in a disturbed area if human intervention should be removed.
Prairie (Also known as tall-grass prairie)
grassland characterized by grasses 1 m tall or
taller, those grasses growing close together
and exposing little or no bare soil, and shrubs
conspicuously absent except for isolated sitespecific patches.
Predictive model See growth and yield model.
Regolith Layer of weathered inorganic and
organic debris overlying the surface of the
earth.
Salinity A saline quality
Salinization Precipitation of soluble salts
within the soil.
Savanna forest The forest component of the
savanna.
Savanna Closed grass or other predominantly
herbaceous vegetation with scattered or
widely spaced woody plants usually including
some low trees.
Seed transfer zone Identifiable area, usually
with definite topographic bounds, climate,
and growing conditions, containing plants
with relatively uniform genetic (racial)
composition.
Sclerophyll or sclerophyllous Refers to plants
with predominantly hard, stiff leaves that are
usually evergreen.
Selva An alternative term for tropical rainforest,
originally applied to the Amazon Basin.
Semideciduous forest Composed partly of
evergreen and partly deciduous species.
Semidesert (Also called half-desert) is an area
of xerophytic shrubby vegetation with a
poorly developed herbaceous lower layer, e.
g., sagebrush.
Shrub savanna Closed grass or other predominantly herbaceous vegetation with scattered or
widely spaced shrubs.
Shrub A woody plant less than 5 m in height.
Sierozem See desert soil.
Silvicultural practices Generally: the science
and art of cultivating and managing forest
crops based on silvics, the collective knowledge of both tree and forest ecology.
Site The smallest, or local, ecosystems.
Small-leafed As used here, refers to birch and
aspen.
Soil Great group third level of classification of
soils, defined by similarities in kind, arrangement, and distinctiveness of horizons, as well
as close similarities in moisture and temperature regimes, and base status.
Soil orders Those ten soil classes forming the
highest category in the classification of soils.
Source region Extensive land or ocean surface
over which an air mass derives its
characteristics.
Glossary of Technical Terms
157
a unified geomorphic history; e.g., the Great
Plains of Fenneman (1928).
Piedmont Sequence of landforms along the
margins of uplands.
Plankton Small, floating or weakly swimming
plants and animals, found in salt and fresh
water; primarily microscopic algae and
protozoa.
Plant adaptation region Large area based on
both ecological (ecoregion) and climatic
(hardiness zone) characteristics that can be
used to guide collecting and evaluating plant
materials for potential adaptations.
Plant formation class A world vegetation type
dominated throughout by plants of the same
life form.
Plate tectonics The large-scale motions of the
earth’s lithosphere.
Playa A desert lake existing only temporarily
after a rain.
Pleistocene The most recent major ice age.
Generally the Pleistocene is considered to
have begun approximately two million years
ago and to have ended 8 to 10 thousand years
ago.
Podzol Soil order consisting of acid soil in
which surface soil is strongly leached of
bases and clays.
Polar front Boundary lying between cold polar
air masses and warm tropical air masses.
Potential natural vegetation Naturally occurring plant cover known to occur in areas
undisturbed by human activity and assumed
to grow in a disturbed area if human intervention should be removed.
Prairie (Also known as tall-grass prairie)
grassland characterized by grasses 1 m tall or
taller, those grasses growing close together
and exposing little or no bare soil, and shrubs
conspicuously absent except for isolated sitespecific patches.
Predictive model See growth and yield model.
Regolith Layer of weathered inorganic and
organic debris overlying the surface of the
earth.
Salinity A saline quality
Salinization Precipitation of soluble salts
within the soil.
Savanna forest The forest component of the
savanna.
Savanna Closed grass or other predominantly
herbaceous vegetation with scattered or
widely spaced woody plants usually including
some low trees.
Seed transfer zone Identifiable area, usually
with definite topographic bounds, climate,
and growing conditions, containing plants
with relatively uniform genetic (racial)
composition.
Sclerophyll or sclerophyllous Refers to plants
with predominantly hard, stiff leaves that are
usually evergreen.
Selva An alternative term for tropical rainforest,
originally applied to the Amazon Basin.
Semideciduous forest Composed partly of
evergreen and partly deciduous species.
Semidesert (Also called half-desert) is an area
of xerophytic shrubby vegetation with a
poorly developed herbaceous lower layer, e.
g., sagebrush.
Shrub savanna Closed grass or other predominantly herbaceous vegetation with scattered or
widely spaced shrubs.
Shrub A woody plant less than 5 m in height.
Sierozem See desert soil.
Silvicultural practices Generally: the science
and art of cultivating and managing forest
crops based on silvics, the collective knowledge of both tree and forest ecology.
Site The smallest, or local, ecosystems.
Small-leafed As used here, refers to birch and
aspen.
Soil Great group third level of classification of
soils, defined by similarities in kind, arrangement, and distinctiveness of horizons, as well
as close similarities in moisture and temperature regimes, and base status.
Soil orders Those ten soil classes forming the
highest category in the classification of soils.
Source region Extensive land or ocean surface
over which an air mass derives its
characteristics.
Glossary of Technical Terms
157