temperate deserts. Humid grasslands have taller and more diverse grass species
than their drier counterparts. Major temperate world grasslands include prairie,
veldt, pampas, and steppe.
The Mediterranean biome is sometimes classified as a woodland and sometimes as
a grassland. In reality, it is area dominated by shrubs and grasses with some trees
interspersed. Coincident with the Mediterranean climate, this biome is found in
selected coastal areas of the middle latitudes. The largest extent of this biome is
around the Mediterranean Sea, but it is also found along the California coast,
southwestern Africa, southwestern-most Australia, and in southwestern South
America. Unlike the other biomes, the Mediterranean biome receives most of its
precipitation (rainfall) during the winter and has persistent drought in the summer.
Indeed, the biome is brownest in the summer and this leads to a pervasive risk of fire.
Although the native plants are drought- and fire-tolerant, the fire regime does not meld
nicely with human activities. Animals tend to be nocturnal and small so as to avoid
the high heat of the summer. This thermally mild climate has been heavily inhabited
for thousands of years and has undergone substantial alterations by humans. In the
case of the Mediterranean basin there are few areas that can be called natural.
Desertbiomes are regions with sparse vegetation and animal life but life does
exist. There are subtropical and temperate deserts and, so, great aridity can occur
over a wide range of latitudes. There is no yearly precipitation amount defining
the borders of deserts. Rather, deserts are the results of great moisture stress occur-
ring in climates ranging from hot to cool. The key to moisture stress is the balance
betweenprecipitationand potential evapotranspiration. Generally, deserts are
places where the annual precipitation is less than half of the potential evapotran-
spiration. Plants are xerophytic, meaning that they are adapted to perennial
drought through mechanisms such as deep root systems and thick, leathery leaves.
Desert plants are usually spaced far apart to lessen the competition for the scarce
water resource. Animals are few and nocturnal. Thus, the nature biomass is low
compared to most other biomes. Ironically, the nutrient desert soils can be very
productive for agriculture if properly irrigated.
The tropical savanna is a biome consisting of open grassland with scattered
trees. This biome occupies intermediate regions between tropical rainforest and
subtropical deserts. Temperatures are always tropically warm. The tropical sav-
anna has a wet season near the time of the high sun and a long dry season the rest
of the year. The landscape browns out and is subject to fires during the dry season.
Biodiversity and biomass are both greater than in the desert. This is the region of
herding big game animals. Indeed, over half of Africa is covered by savanna.
Tropical rainforest is a warm, wet biome usually found close to the Equator. Not
as hot as the desert, the year-round warm temperatures encourage plentiful plant
growth because of unlimited water availability. Precipitation comes from36 Biomes