plateaus (in much of the American West, for instance) producedry conifer forests
with relatively low average annual precipitation.Mediterranean forestshave peak-
ing of precipitation during mild winters and droughty summers. Broadleaf trees
such as small oaks and some evergreen, thick-leaved, water-conserving species
are common with winter being the “green” season. Many of the trees are virtually
dormant in parts of the summer. In selected areas on upper middle latitude coasts
(for example, Washington state’s Olympic peninsula) aretemperate rainforests
that have in excess of 2,000 mm of precipitation per year (much less than tropical
rainforest but much more than any other temperate forest). Infrequent freezes and
a year-round excess of precipitation over evapotranspiration make this type fairly
diverse and high in biomass.Deciduous forestshave rainy summers and cold,
snowy winters for which the trees prepare by losing their leaves. This kind of for-
est, topped with tall trees, is ecologically diverse and covers the greatest area of all
the temperate forest subtypes.
The boreal forest (taiga) represents the largest forest on Earth. Dominating the
northern continental surfaces from 50°to 60°latitude (there is little land at
Forests 133In places where there are long growing seasons and adequate water, forests are the most common
vegetated landscape. There are many varieties of forest; this one is a temperate rainforest near
Ketchikan, Alaska. (Photo courtesy of Steve Stadler)