Geography Reference
In-Depth Information
careless planting, have resulted in urban ecosystems. These ecosys-
tems include highly managed parks and gardens with deliberate
introductions of species as well as abandoned land with habitats
containing native and alien species. This means that habitat diver-
sity in urban areas can be high. The various structures produce
large and small habitats that are quite different and changes in
buildings and land use means there is often change in habitats across
different parts of the urban zone.
The warmer temperatures, resulting from the urban heat island
effect (see Chapter 1), modified air flows and poorer air quality,
compared to nearby rural areas, are components of urban ecosys-
tems. Typically, urban areas produce more organic waste through
sewage and foodstuffs than can be biologically decomposed and
cycled back into the ecosystem. Some species have found the com-
bination of resources in urban zones to be to their advantage. The
rich nutrition provided by waste dumps attracts many birds and
other species. House mice and house spiders, together with the
brown rat are all part of the urban nutrient cycle. Released pets
have sometimes colonised urban areas (e.g. parakeets) that are not
native. Predators at higher trophic levels have also come into urban
areas to take advantage of new prey available in the urban ecosys-
tems. Indeed, agricultural change in rural areas has removed places
of shelter, such as shrubs and woodland, and may have pushed
some species into urban areas where the shelter is better.
Climate change
Research has shown that vegetation zones on mountains have been
moving upwards and trees expanding from the taiga further north.
Spring flowering has been occurring earlier and growing seasons
have been lengthening. These changes have been taking place but
it is not certain how the biosphere will respond to rapid climate
change forecast to take place over the next 100 years (see Chapter
2). There are simply too many plant species to examine how each
one individually might respond given its characteristics. So instead
a number of models have been designed that predict how systems
might respond using
plant functional types
(plants that share
similar traits and similar in their association with environmental
variables). These models seem to suggest that some tropical forests
