Figure 4.18. Percentage of non-domesticated
land area projected to be under different degrees of pressure from
human population and associated activities.
- RIVM/UNEP (1997).
- Non-domesticated land under
pressure is expressed as a percentage of total regional area. Pressure
is calculated for areas that are non-domesticated during the whole
Pressure categories; The following linear functions were used:
i) Population density: 0 to 100 persons per square kilometre.
The maximum pressure values for population density are derived from Hannah
et al. (1994). Harrison (1992) and Terborch (1989) mentioned
ii) Consumption and production rate: US$0 to US$6,000,000 gross national product (GNP)
per square kilometre per year.
The GNP per square kilometre value is an approximation of the production
and consumption rate and the related use of, and pressure on, non-domesticated
areas such as emissions, extraction, physical disturbances, and fragmentation.
The maximum GNP per square kilometre is similar to values found in
highly populated and highly industrialized countries such as Germany
and the Netherlands.
iii) Forest clearance for timber: not logged since 100 to 0 years ago.
The maximum pressure value for forest clearance for timber is set at 0
years ago, assuming total ecosystem destruction; the minimum value
at 100 years, assuming no pressure and total regeneration of the forest
ecosystem. Generally a longer period for forest regeneration is assumed.
For example, "old growth forest" is generally defined as
more than 200 years (Dudley, 1992).
iv) Climate change: a change in mean temperature of 0 degrees to 2.0 degrees Celsius
within a 20-year period. For example, an increase in mean temperature
of 0.2 degrees Celsius in 20 years results in a pressure rating of
1, while an increase of 2.0 degrees Celsius in 20 years results in
a pressure rating of 10).
This rate is based on the still
rudimentary understanding of the vulnerability of ecosystems to historical
temperature changes. The maximum value of 2.0 degrees Celsius over
two decades is high in comparison with the maximum temperature increase
of 2.0 degrees Celsius, which is suggested as the "absolute limit
beyond which the risks of grave damage to ecosystems, and of non-linear
responses, are expected to increase rapidly" (Jåger, 1987 and 1990).