The biodiversity characteristic of each biome, especially the diversity of fauna and sub-
dominant plant forms, is a function of abiotic factors and the biomass productivity of the
dominant vegetation. Species diversity tends to be higher in terrestrial biomes with higher
net primary productivity, moisture availability, and temperature. Biodiversity also generally
increases most rapidly near the equator and less rapidly toward the poles, and increases with
humidity.
The most widely used systems of classifying biomes correspond to latitude (or temperature
zoning)andhumidity. Onescheme, developedbytheWorldWildlifeFund(WWF),identified
fourteen biomes, called major habitat types, and further divided the world’s land area into
825terrestrialecoregions. ThisclassificationisusedtodefinetheGlobal200listofecoregions
identified by the WWF as priorities for conservation. Some of these habitat types are
similar to others already discussed, while others include mangroves, flooded grasslands, and
savannas.
Biomes are often given local names. For example, a temperate grassland or shrubland biome
is known as steppe in central Asia, prairie in North America, and pampas in South America.
Tropical grasslands are known as savanna or veldt in southern Africa and outback or scrub
in Australia.
Terrestrial Biomes
Terrestrial biomesare defined based on factors such as plant structures (such as trees,
shrubs, and grasses), leaf types (such as broadleaf and needleleaf), and plant spacing (forest,
woodland, savanna). Climate is also a major factor determining the distribution of terrestrial
biomes. Among the important climatic factors are latitude, from the poles towards the
equator (Arctic, boreal, temperate, subtropical, tropical); humidity (humid, semi-humid,
semi-arid, and arid), with seasonal variation in rainfall; and elevation (increasing elevation
causes a distribution of habitat types similar to that of increasing latitude) (Table(23.6)).
Terrestrial biomes (Figure23.22) lying within the Arctic and Antarctic Circles are relatively
barren of plant and animal life, while most of the more populous biomes lie near the equator
(Figure23.23).
Table 23.6:Characteristics of Terrestrial Biome Description of Characteristics
Plant structures Trees, shrubs, grasses
Leaf types Broadleaf, needleleaf
Plant spacing Forest, woodland, savanna
Latitude from poles towards the equator Arctic, boreal, temperate, subtropical, trop-
ical
Humidity Humid, semi-humid, semi-arid, arid