clustering algorithm to factors derived from
climate and soils data. Although the variables
were chosen because of their hypothesized relationship to vegetation patterns, this relationship
was not formally defined.
A similar approach to ecoregionalization is
to overlay thematic maps either manually
(Omernik 1987; Gallant et al. 1995; Harding
et al. 1997; Olson et al. 2001) or within a GIS
(Host et al. 1996; Bernert et al. 1997; Zhou et al.
2003). Typically, ecoregion boundaries are
placed where boundaries of several input layers
are located in close proximity to one another.
Boundaries defined in this manner represent
areas of spatially abrupt changes in ecological
characteristics. The overlay method has been
referred to as the weight of evidence approach
(McMahon et al. 2001) and the gestalt method
(Bailey 2009; Jepson and Whittaker 2002)
because homogeneous-appearing regions are
recognized and boundaries are drawn through a
process of intuitive and holistic reasoning based
largely on visual appearance. Ambiguity arises
from the fact that boundaries of input layers
Table 4.3 General environmental conditions for ecoregion divisions
Name of division
Equivalent
Ko ¨ppen–Trewartha
climates
Zonal vegetation
Zonal soil type
a
110 Icecap
120 Tundra
Ft
Ice and stony deserts: tundras
Tundra humus soils with
soilifluction (Entisols,
Inceptisols, and associated
Histosols)
130 Subarctic
E
Forest-tundras and open
woodlands; tayga
Podzolic (Spodosols and
Histosols)
210 Warm
continental
Dcb
Mixed deciduous–coniferous
forests
Gray-brown podzolic (Alfisols)
220 Hot continental
Dca
Broadleaved forests
Gray-brown podzolic (Alfisols)
230 Subtropical
Cf
Broadleaved–coniferous
evergreen forests;
coniferous–broadleaved semievergreen forests
Red-yellow podzolic (Ultisols)
240 Marine
Do
Mixed forests
Brown forest and gray-brown
podzolic (Alfisols)
250 Prairie
Cf, Dca, Dcb
Forest-steppes and prairies;
savannas
Prairie soils, Chernozems
(Molisols)
260 Mediterranean
Cs
Dry steppe; hardleaved
evergreen forests, open
woodlands and shrub
Soils typical of semiarid climates
associated with grasslands
310 Tropical/
subtropical steppe
BSh
Open woodland and
semideserts; steppes
Chestnut, brown soils, and
sierozems (Mollisols, Aridisols)
320 Tropical/
subtropical desert
BWh
Semideserts; deserts
Desert (Aridisols)
330 Temperate
steppe
BSk
Steppes; dry steppes
(same as BSh)
340 Temperate desert BWk
Semideserts and deserts
(same as BWh)
410 Savanna
Aw, Am
Open woodlands, shrubs and
savannas; semievergreen forest
Latisols (Oxisols)
420 Rainforest
Ar
Evergreen tropical rain forest
(selva)
Latisols (Oxisols)
a
Great soil group. Names in parenthesis are Soil Taxonomy soil orders (U.S. Department of Agriculture, Soil Survey
Staff 1975). Described in the Glossary, p. 153
4.4 Relationship to Other Ecoregional Zoning Systems
41
climate and soils data. Although the variables
were chosen because of their hypothesized relationship to vegetation patterns, this relationship
was not formally defined.
A similar approach to ecoregionalization is
to overlay thematic maps either manually
(Omernik 1987; Gallant et al. 1995; Harding
et al. 1997; Olson et al. 2001) or within a GIS
(Host et al. 1996; Bernert et al. 1997; Zhou et al.
2003). Typically, ecoregion boundaries are
placed where boundaries of several input layers
are located in close proximity to one another.
Boundaries defined in this manner represent
areas of spatially abrupt changes in ecological
characteristics. The overlay method has been
referred to as the weight of evidence approach
(McMahon et al. 2001) and the gestalt method
(Bailey 2009; Jepson and Whittaker 2002)
because homogeneous-appearing regions are
recognized and boundaries are drawn through a
process of intuitive and holistic reasoning based
largely on visual appearance. Ambiguity arises
from the fact that boundaries of input layers
Table 4.3 General environmental conditions for ecoregion divisions
Name of division
Equivalent
Ko ¨ppen–Trewartha
climates
Zonal vegetation
Zonal soil type
a
110 Icecap
120 Tundra
Ft
Ice and stony deserts: tundras
Tundra humus soils with
soilifluction (Entisols,
Inceptisols, and associated
Histosols)
130 Subarctic
E
Forest-tundras and open
woodlands; tayga
Podzolic (Spodosols and
Histosols)
210 Warm
continental
Dcb
Mixed deciduous–coniferous
forests
Gray-brown podzolic (Alfisols)
220 Hot continental
Dca
Broadleaved forests
Gray-brown podzolic (Alfisols)
230 Subtropical
Cf
Broadleaved–coniferous
evergreen forests;
coniferous–broadleaved semievergreen forests
Red-yellow podzolic (Ultisols)
240 Marine
Do
Mixed forests
Brown forest and gray-brown
podzolic (Alfisols)
250 Prairie
Cf, Dca, Dcb
Forest-steppes and prairies;
savannas
Prairie soils, Chernozems
(Molisols)
260 Mediterranean
Cs
Dry steppe; hardleaved
evergreen forests, open
woodlands and shrub
Soils typical of semiarid climates
associated with grasslands
310 Tropical/
subtropical steppe
BSh
Open woodland and
semideserts; steppes
Chestnut, brown soils, and
sierozems (Mollisols, Aridisols)
320 Tropical/
subtropical desert
BWh
Semideserts; deserts
Desert (Aridisols)
330 Temperate
steppe
BSk
Steppes; dry steppes
(same as BSh)
340 Temperate desert BWk
Semideserts and deserts
(same as BWh)
410 Savanna
Aw, Am
Open woodlands, shrubs and
savannas; semievergreen forest
Latisols (Oxisols)
420 Rainforest
Ar
Evergreen tropical rain forest
(selva)
Latisols (Oxisols)
a
Great soil group. Names in parenthesis are Soil Taxonomy soil orders (U.S. Department of Agriculture, Soil Survey
Staff 1975). Described in the Glossary, p. 153
4.4 Relationship to Other Ecoregional Zoning Systems
41