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| Spain Desertification characteristics. |
SPAIN
All of the arid regions of Spain have been moderately to severely desertified for
decades, if not for centuries. Most of the damage has been done by heavy grazing
and woodcutting, but wind and water erosion on cultivated land has also been
extensive. Salinization and waterlogging of irrigated land is a major problem in
parts of the Ebro River watershed in northeastern Spain. Destruction of the native
vegetation and the subsequent water erosion of thin soils on slopes has had a
devastating effect on the plant environment and on the potential productivity of the
land. Mobile sand dunes are found along the Mediterranean coast.
Desertification Characteristics
During the past several centuries, heavy grazing by sheep and goats has led to
the destruction of much of the herbaceous and woody vegetation on the
noncultivated land (Albareda, 1955). Water erosion has been severe on the
overgrazed slopes as a result of the loss of vegetative cover and the torrential
character of the rains. Cutting of wood for fuel and construction and the extension
of dryland farming into the pasture lands has accompanied overgrazing. Plant
cover has changed to a more xeric type and surface runoff has increased.
A monoculture of grain in the cultivated regions has depleted the native fertility of
the soil and has been responsible for increasing the susceptibility of the land to
wind and water erosion. Extended droughts from time to time have served to
accelerate desertification. Water erosion is severe nearly everywhere on sloping
land.
Salinization and waterlogging do not affect a high percentage of the total
cultivated land in Spain but important and large areas of affected soils do occur in
irrigated valleys. The major salt-affected areas in the northeast are in the Ebro
River watershed in the vicinity of Zaragosa and Herida. Seepage water from
irrigation on the higher land has caused waterlogging and salinization of
lower-lying areas (Martinez, 1978). Gypsum is a common constituent of the soils.
The other major salt-affected areas are in southwest Spain near the coast. The
soils are composed of fine-textured sediments that were subjected regularly to
flooding by seawater in the past. Surface and internal drainage of the irrigated
land is poor and water tables generally are close to the surface. Pumping is
required to lower the water tables (Ayers et al., 1960).
Magnitude of Desertification
Approximately 50 percent of Spain is arid. In the arid regions about 70 percent is
moderately desertified and 30 percent is severely desertified .
Virtually all of the rangeland has suffered severe land degradation. Range
productivity is probably stabilized at a low level now, with little improvement
anywhere. Erosion continues on the extensive dryfarm lands except in a few
places where soil and water conservation measures have been instituted. Soil
fertility remains low.
Salinization and waterlogging affect about 240,000 hectares of irrigated land to
various degrees (Ayers et al., 1960). Reclamation has been undertaken in several
areas. Because of the need for more agricultural production and the gradual
worsening of the salt problem, irrigation has received special attention in recent
decades. Much remains to be done.
Soil and water conservation techniques for dryland farming are known but their
application to the field is limited. Range management is not a well-supported
science in Spain. Considerable progress has been made in the reclamation of
saline soils and procedures for doing so are quite well-known (Martinez, 1978).