rarely conform to one another (the “GIS trap”;
see Bailey 1988). The general procedure is consistent in concept with the empirical approach
because it emphasizes pattern over process
(Omernik 2004).
The empirical approach seeks to discern
patterns in the data. The resultant maps frequently show highly fragmented map units,
with small, noncontiguous units of the same
region distributed over wide areas. In the
approach presented in this book, the boundaries
of terrestrial ecoregions are determined to a considerable extent by the changing nature of the
climate over large areas. This approach takes
into account compensating factors (see Chap.
11) that override the climatic effect. For example, in the High Plains of the semiarid southwestern United States, forests extend along streams
because of the extra water supply. Ponderosa
pine and shrub islands within the grasslands of
Table 4.4 Approximate area and proportionate extent of ecoregions
km
2
Percent
100 Polar domain
38,038,000
26.00
110 Icecap division
12,823,000
8.77
M110 Icecap regime mts
1,346,000
0.92
120 Tundra division
4,123,000
2.82
M120 Tundra regime mts
1,675,000
1.14
130 Subarctic division
12,259,000
8.38
M130 Subarctic regime mts
5,812,000
3.97
200 Humid temperate domain
22,455,000
15.35
210 Warm continental division
2,187,000
1.49
M210 Warm continental regime mts
1,135,000
0.78
220 Hot continental division
1,670,000
1.14
M220 Hot continental regime mts
485,000
0.33
230 Subtropical division
3,568,000
2.44
M230 Subtropical regime mts
1,543,000
1.05
240 Marine division
1,347,000
0.92
M240 Marine regime mts
2,194,000
1.50
250 Prairie division
4,419,000
3.02
M250 Prairie regime mts
1,256,000
0.88
260 Mediterranean division
1,090,000
0.75
M260 Mediterranean regime mts
1,561,000
1.07
300 Dry domain
46,806,000
32.00
310 Trop/sub steppe division
9,838,000
6.73
M310 Trop/sub steppe regime mts
4,555,000
3.11
320 Trop/sub desert division
17,267,000
11.80
M320 Trop/sub desert regime mts
3,199,000
2.19
330 Temperate steppe division
1,790,000
1.22
M330 Temperate steppe regime mts
1,066,000
0.73
340 Temperate desert division
5,488,000
3.75
M349 Temperate desert regime mts
613,000
0.42
400 Humid tropical domain
38,973,000
26.64
410 Savanna division
20,641,000
14.11
M410 Savanna regime mts
4,488,000
3.07
420 Rainforest division
10,403,000
7.11
M420 Rainforest regime mts
3,440,000
2.35
Source: World Conservation Monitoring Centre
42
4 Continental Types and Their Controls
see Bailey 1988). The general procedure is consistent in concept with the empirical approach
because it emphasizes pattern over process
(Omernik 2004).
The empirical approach seeks to discern
patterns in the data. The resultant maps frequently show highly fragmented map units,
with small, noncontiguous units of the same
region distributed over wide areas. In the
approach presented in this book, the boundaries
of terrestrial ecoregions are determined to a considerable extent by the changing nature of the
climate over large areas. This approach takes
into account compensating factors (see Chap.
11) that override the climatic effect. For example, in the High Plains of the semiarid southwestern United States, forests extend along streams
because of the extra water supply. Ponderosa
pine and shrub islands within the grasslands of
Table 4.4 Approximate area and proportionate extent of ecoregions
km
2
Percent
100 Polar domain
38,038,000
26.00
110 Icecap division
12,823,000
8.77
M110 Icecap regime mts
1,346,000
0.92
120 Tundra division
4,123,000
2.82
M120 Tundra regime mts
1,675,000
1.14
130 Subarctic division
12,259,000
8.38
M130 Subarctic regime mts
5,812,000
3.97
200 Humid temperate domain
22,455,000
15.35
210 Warm continental division
2,187,000
1.49
M210 Warm continental regime mts
1,135,000
0.78
220 Hot continental division
1,670,000
1.14
M220 Hot continental regime mts
485,000
0.33
230 Subtropical division
3,568,000
2.44
M230 Subtropical regime mts
1,543,000
1.05
240 Marine division
1,347,000
0.92
M240 Marine regime mts
2,194,000
1.50
250 Prairie division
4,419,000
3.02
M250 Prairie regime mts
1,256,000
0.88
260 Mediterranean division
1,090,000
0.75
M260 Mediterranean regime mts
1,561,000
1.07
300 Dry domain
46,806,000
32.00
310 Trop/sub steppe division
9,838,000
6.73
M310 Trop/sub steppe regime mts
4,555,000
3.11
320 Trop/sub desert division
17,267,000
11.80
M320 Trop/sub desert regime mts
3,199,000
2.19
330 Temperate steppe division
1,790,000
1.22
M330 Temperate steppe regime mts
1,066,000
0.73
340 Temperate desert division
5,488,000
3.75
M349 Temperate desert regime mts
613,000
0.42
400 Humid tropical domain
38,973,000
26.64
410 Savanna division
20,641,000
14.11
M410 Savanna regime mts
4,488,000
3.07
420 Rainforest division
10,403,000
7.11
M420 Rainforest regime mts
3,440,000
2.35
Source: World Conservation Monitoring Centre
42
4 Continental Types and Their Controls