Geography Reference
In-Depth Information
Early applications of the systems approach within physical
geography consolidated the shift of emphasis from Earth-surface
forms to processes and from long-term development of
the landscape to how it is maintained in a state of balance
(steady-state equilibrium) over the short term. It was soon
realized, however, that landscape systems are more complex
than this and are rarely stable for long. Instability may be
caused by the internal dynamics of the system or by natural
or human-induced disturbance. In the case of soils, for
example, the natural leaching process may gradually exhaust
the nutrients and lead to a decline in the vegetation cover and
hence soil erosion. Poor agricultural practices have similar
disruptive effects, while extreme natural events such as fl oods
and hurricanes may erode the soil more abruptly. Landscape
systems differ in their sensitivity and resilience to disturbance
and in the thresholds that have to be overcome before a system
is tipped from one relatively stable state to another. These
concepts are important at the frontiers of physical geography
today. All aspects of the natural landscape - whether reference
is being made to the surface landforms, the vegetation and soil
cover, or the climatic envelope - are subjected to disturbance and
change.
Long-term environmental change
Physical geographers now regard the study of past, present,
and future environmental change as very important. The
environmental change theme rose to prominence towards the
end of the 20th century but the seeds were sown earlier. It may
be traced back to members of the Helvetic Society in Switzerland
in the fi rst half of the 19th century. The president of that society,
Louis Agassiz, who published the topic
Études sur les Glaciers
in 1840, was both an early convert and a particularly infl uential
advocate of their ideas. They recognized that many of the
erosional and depositional features apparent on the forelands
