Environmental Engineering Reference
In-Depth Information
forest. In particular, forests have been shown to provide soil protection for
downstream agricultural land (Anderson, 1987), protect downstream water
courses from increased levels of sedimentation caused by surface run-of
and increased erosion and leading to high costs of de-siltation (Panayotou,
1990; Lal, 1997), to impact on water yield and groundwater recharge, and
to control watershed hydrology and provide protection against erosion
(Rawat and Rawat, 1994; Atarof and Rada, 2000; Putuhena and Cordery,
2000). For dry savanna ecosystems, the invisible benei ts may be as signii -
cant as those of forest ecosystems. Hydrological functions of dry savannas
have been shown to have a direct impact on the productivity of surrounding
areas. The vegetation cover of woodlands is thought to stabilize the local
climate and maintain rainfall patterns (Myers, 1995) as well as prevent soil
erosion and l ooding, and control the recharging of groundwater reservoirs
(Huntoon, 1992). These positive external ef ects, although they may occur
outwith the boundary of the ecosystem, are nonetheless specii c in their area
of impact. As such, there is a limit to the number of individuals upon which
they will have an ef ect.
A second type of externality, however, is also provided by forest and
savanna ecosystems, and has a greater range of impact. It is now known
that areas of vegetation cover, in particular forested areas, act as import
sinks for atmospheric carbon (Harmon, 2001; Pautsch et al., 2001; Uri,
2001). This function is globally important in terms of regulating atmos-
pheric composition and controlling global temperature. Many savanna
ecosystems also form the watershed zones of major international rivers,
for example, the Zambezi (Kundhlande et al., 2000), which are interna-
tionally important for domestic water consumption and power supply.
This type of ecosystem service dif ers from all others in that its use is
'public' in nature, that is, it is used by society as a whole, and individuals
do not have a choice over whether or not they wish to use it.
Both of these invisible benei ts are termed indirect-use values, since
although not consumed directly they are essential for the production of
direct-use values. However, their very nature implies that they will have
no direct market value and thus are dii cult to quantify in a cost-benei t
analysis.
Past valuation studies
A number of research studies have focused on attempting to value forest
and savanna resources (Hanemann, 1988). In all of these studies, valua-
tion of various aspects of the complete ecosystem has been undertaken.
The relative ease of valuing direct-use resources rather than indirect-use
resources is immediately obvious and for this reason, although some
studies have attempted to value indirect-use resources, the majority of
Search WWH ::




Custom Search