Page 12 - Module_5

This is a SEO version of Module_5. Click here to view full version

« Previous Page Table of Contents Next Page »
12
FAO/UNEP/UN-Energy Bioenergy Decision Support Tool -
MODULE 5: Land Resources
defnitions are applied. The land may be marginal for particular
uses or for commercial production of particular crops, but the
land itself is not marginal for those farmers and/or the crops they
have chosen to grow. From a suitability assessment perspective,
marginal land is that where the suitability is zero (Salvatore, 2010).
Consequently, understanding the signifcance of marginal land
requires consideration of the appropriate local socio-economic
context.
WHAT IS DEGRADED LAND?
Land degradation relates to bio-physical processes that reduce
the productivity of land in some way; it can be understood from
a variety of perspectives, and more recently there has been an
emphasis on the linkage between land degradation and ecosys-
tem goods and services. A simple and systemic defnition of land
degradation is given by the Millennium Ecosystem Assessment
(MA), which uses the ecosystem functions/services framework
and defnes land degradation as any land related phenomenon
that causes:
“… any decline in ecosystem function and services
over an extended period....(MA, 2005).”
Unsustainable land use practices are some of the most common
and widespread drivers of land degradation, often involving loss of
topsoil, loss of biodiversity, increased carbon emission and loss of
carbon sequestration potential (Gustafson 2005).
Further complications arise once additional aspects are consid-
ered such as the sources of degradation (human, natural, or
both), recovery processes and the time horizon over which
degradation is observed, measured and assessed. However, all
forms of land degradation will ultimately lead to a reduction of soil
fertility and productivity, resulting in reduced plant growth, which in
turn causes loss of protective soil cover and increased vulnerabil-
ity of soil and vegetation to further degradation (El-Beltagy 2000).
This leads directly to a possible indicator for land degradation,
such as applied in the LADA defnition (see Box 2) on degraded
land:
“Land degradation is a long-term decline in ecosystem
function and productivity and measured in terms of net primary
productivity (Bai/Dent 2006).”
In operational terms, it is important to distinguish degraded land
(bio-physical defnitions) from marginal land (socio-economic)
as well as other categories that are related, such as abandoned
(agricultural) lands, idle land, and wastelands (Wiegmann et al,
2008).
LAND DEGRADATION PROCESSES
Land degradation is appropriately viewed as a process rather
than a state; three types of land degradation are often identi-
fed—physical, chemical or biological—as shown in Figure 2. The
state of degraded lands can show the effects of one or all of the
types of degrading processes, with different degrees of intensity
and varying spatial extents, and as a result differing properties in
relation to bioenergy feedstock options. The assessment of land
degradation therefore must address dynamic factors related to
land use, soils and management practices as well as the overall
socio-economic context for land use and the provision of ecologi-
cal services.
A decline in primary productivity and ecosystem functions and
services is the focus when evaluating land degradation processes.
Moderately degraded land that has lost its natural cover and is
not suitable for food production can alternatively (or in addition)
be regarded as marginal—or in the case of more severe degrada-
tion—infertile. Planting perennial, drought resistant, or salinity/
food tolerant crops with good soil binding properties in combina-
tion with good management practices can help to regenerate
soils.
Soil
Compaction Laterization
Soil
Erosion
Soil Fertility
Depletion
Soil
Elemental
Imbalance
Decline in Soil
Organic
Matter
Reduction in
Micro and
Macro Biota
Soil
Erosion
by Water
Soil
Erosion
by Wind
Physical Land Degradation
Chemical Land Degradation
Biological Land Degradation
Soil
Acidification
Soil
Sodication
Toxic
compounds
in the soil
Land Degradation
Figure 2: The various types of land degradation processes