at high latitudes, to the tropical wet climate at
low latitudes.
Trewartha (1968) describes them briefly.
The low latitudes contain a winterless, frostless
belt with adequate rainfall. This is the tropical
humid climate, or the A group. It is subdivided
into two types, tropical wet (Ar) and tropical
wet-and-dry (Aw). On the low-latitude margins
of the middle latitudes, where winters are mild
and killing frosts only occasional, is the subtropical belt, or C group. Here two subdivisions
are recognized: subtropical dry summer (Cs)
and subtropical humid (Cf). Poleward from the
subtropics is the temperate belt, or D group. It
contains two types, temperate continental (Dc)
and temperate oceanic (Do). Two subtypes of
temperate continental are recognized: a more
moderate one with hot summers and cold
winters (Dca), and a more severe subtype
(Dcb), located poleward, which has warm summers and rigorous winters. Still farther poleward is the boreal of subarctic belt, the E
group. It has not been subdivided. In the very
high latitudes are the summerless, polar
climates (F group), subdivided into the tundra
climate (Ft) and ice-cap climate (Fi). The dry
climates, group B, are subdivided into semiarid
or steppe type (BS) and an arid or desert type
(BW). A further subdivision separates the hot
tropical–subtropical deserts and steppes (BWh,
BSh) from the cold temperate–boreal deserts
and steppes (BWk, BSk) of middle latitudes.
Highland climates, which are lowtemperature variants of climates at low
elevations in similar latitudes, are designated by
the letter H.
4.3
Distribution of the Continental
Regions
Although we can define ecoregions climatically,
they are most effectively treated by combining
and rearranging the 15 climatic types to maximize correspondence with major plant
formations. Through this process I have mapped
the Earth into zones called ecoregion provinces,
each of which has characteristic ecosystems.
This map is based on a world map of natural
climate–vegetation landscape types in the
Fiziko-geograficheskii atlas mira (Gerasimov
1964). Eight-six such subdivisions are
recognized (Bailey 1989), but for simplification
I have grouped them into 15 divisions. They
range from the tundra at high latitudes to the
rainforest at low latitudes. Mountains exhibiting
elevational zonation and having the climatic
regime of the adjacent lowlands are distinguished
according to the character of the zonation.
We can further simplify this classification of
ecosystems by grouping the divisions into four
large regions called domains. Four such subdivision are recognized—three are humid zones,
thermally differentiated: polar, with no warm
season; humid temperate, rainy with mild to
severe winters; humid tropical, rainy with no
winters. The fourth, dry, is defined on the basis
of moisture alone, and transects the otherwise
humid domains.
These domains can be described briefly. In the
very high latitudes lie the polar domain,
differentiated on the basis of ice formation and
plant development into icecap, tundra, and subarctic tayga divisions. In the mid latitudes is the
humid temperate domain of mid-latitude forests,
differentiated according to the importance of
winter frost into warm continental, hot continental, subtropical, marine, prairie, and mediterranean divisions. In low and middle latitudes is the
dry domain, differentiated on the basis of rainfall
(steppe versus desert), and winter temperature
(cold versus warm), into tropical/subtropical
steppe, tropical/subtropical desert, temperate
steppe, and temperate desert. In the low latitudes
lie the humid tropical domain, differentiated on
the basis of rainfall seasonality into savanna and
rainforest divisions.
We have identified two principles in the
global pattern of ecosystem regions. One is the
principle of regularity which relates to those
features of the Earth’s surface that are associated
with climate; the other is the principle of
38
4 Continental Types and Their Controls
low latitudes.
Trewartha (1968) describes them briefly.
The low latitudes contain a winterless, frostless
belt with adequate rainfall. This is the tropical
humid climate, or the A group. It is subdivided
into two types, tropical wet (Ar) and tropical
wet-and-dry (Aw). On the low-latitude margins
of the middle latitudes, where winters are mild
and killing frosts only occasional, is the subtropical belt, or C group. Here two subdivisions
are recognized: subtropical dry summer (Cs)
and subtropical humid (Cf). Poleward from the
subtropics is the temperate belt, or D group. It
contains two types, temperate continental (Dc)
and temperate oceanic (Do). Two subtypes of
temperate continental are recognized: a more
moderate one with hot summers and cold
winters (Dca), and a more severe subtype
(Dcb), located poleward, which has warm summers and rigorous winters. Still farther poleward is the boreal of subarctic belt, the E
group. It has not been subdivided. In the very
high latitudes are the summerless, polar
climates (F group), subdivided into the tundra
climate (Ft) and ice-cap climate (Fi). The dry
climates, group B, are subdivided into semiarid
or steppe type (BS) and an arid or desert type
(BW). A further subdivision separates the hot
tropical–subtropical deserts and steppes (BWh,
BSh) from the cold temperate–boreal deserts
and steppes (BWk, BSk) of middle latitudes.
Highland climates, which are lowtemperature variants of climates at low
elevations in similar latitudes, are designated by
the letter H.
4.3
Distribution of the Continental
Regions
Although we can define ecoregions climatically,
they are most effectively treated by combining
and rearranging the 15 climatic types to maximize correspondence with major plant
formations. Through this process I have mapped
the Earth into zones called ecoregion provinces,
each of which has characteristic ecosystems.
This map is based on a world map of natural
climate–vegetation landscape types in the
Fiziko-geograficheskii atlas mira (Gerasimov
1964). Eight-six such subdivisions are
recognized (Bailey 1989), but for simplification
I have grouped them into 15 divisions. They
range from the tundra at high latitudes to the
rainforest at low latitudes. Mountains exhibiting
elevational zonation and having the climatic
regime of the adjacent lowlands are distinguished
according to the character of the zonation.
We can further simplify this classification of
ecosystems by grouping the divisions into four
large regions called domains. Four such subdivision are recognized—three are humid zones,
thermally differentiated: polar, with no warm
season; humid temperate, rainy with mild to
severe winters; humid tropical, rainy with no
winters. The fourth, dry, is defined on the basis
of moisture alone, and transects the otherwise
humid domains.
These domains can be described briefly. In the
very high latitudes lie the polar domain,
differentiated on the basis of ice formation and
plant development into icecap, tundra, and subarctic tayga divisions. In the mid latitudes is the
humid temperate domain of mid-latitude forests,
differentiated according to the importance of
winter frost into warm continental, hot continental, subtropical, marine, prairie, and mediterranean divisions. In low and middle latitudes is the
dry domain, differentiated on the basis of rainfall
(steppe versus desert), and winter temperature
(cold versus warm), into tropical/subtropical
steppe, tropical/subtropical desert, temperate
steppe, and temperate desert. In the low latitudes
lie the humid tropical domain, differentiated on
the basis of rainfall seasonality into savanna and
rainforest divisions.
We have identified two principles in the
global pattern of ecosystem regions. One is the
principle of regularity which relates to those
features of the Earth’s surface that are associated
with climate; the other is the principle of
38
4 Continental Types and Their Controls