The outsiders who brought modern winemaking to the region may
have put Priorat on the map, but when they planted new vineyards, they built
wide terraces that could support tractors, not realizing until later how
terraces could cause erosion and disrupt the land's natural water retention.
The steep relief of the Priorat region and the typical
Mediterranean climate with torrential downpours often reaching 100 mm in a few
hours makes the area very vulnerable to soil erosion. Traditionally, wine
growers have overcome these adverse conditions by constructing small dry stone
walled terraces to reduce the natural slope of the land. This technique, based
on plentiful and cheap labour, has created a characteristic and highly valued
landscape, attracting wine tourism.
Functions of Terracing
Keep the soil and retain water. The primary purpose of the
terraces is controlled evacuation of rainwater, so as to avoid soil erosion as
much as possible.
Control of water runoff increases the chances of infiltration of water into
the root zone of the plant.
Allow for safe mechanisation without the occupational hazard of machinery
overturning. The terraces act as service corridors for maintenance tasks such as
pruning, disease control and harvesting. Mechanization requires that the width
of terraces is the minimum necessary for the passage of agricultural machinery.
However, traditional hand-built dry stone terracing is no
longer economically viable. One of the main techniques for increasing
productivity in Priorat is industrial terracing that allows for the
mechanization of farming. The characteristics of Priorat viticulture and the
environmental problems created by industrial terracing are summarised below.
Priorat mountain viticulture
The average gradient is 46%.
Vineyards are located between 200m and 600m above sea level.
Between 1986 and 2003, 60% of the traditional vineyards were abandoned.
In the same period, mechanised vineyard terraces increased by 1,450%
the number of vineyards have increased by 44% between 1986 and 2003, and 93%
between 1998 and 2003.
Environmental problems caused by modern terracing
Impact on the landscape. The wider terraces tend to break
the harmony of the landscape producing an industrial 'quarry' effect.
Soil Erosion. Loss of soil can be intense, because of the excessive length
of the slopes, and a lack of well designed drains.
The wider terraces allow for
mechanisation and are more economically viable. However, they tend to break the
harmony of the landscape producing an industrial 'quarry' effect. They are often
poorly drained and vulnerable to landslides.
Process of water erosion
Erosion by water operates through two basic mechanisms:
Impact of raindrops. If the rain is very intense, the force
of raindrops destroys components of the soil structure. This process is
accompanied by a decrease in porosity. The erosive power of water is heightened
by long periods of drought which leaves the soil dry, cracked and devoid of
vegetation cover that helps mitigate the impact of downpours.
Runoff. This is the main mechanism of water erosion. The rainwater that
cannot infiltrate into the ground runs across the surface, dragging particles of
soils in its wake. Runoff erosion depends on many factors, including the
intensity of rainfall, the density of vegetation cover, the topography of the
land, the infiltration rate and water storage capacity.
Negative impacts of soil erosion
Among the many negative impacts of erosion include:
Reducing the thickness of the layer of soil on the plots
affected.
Declining soil fertility, associated with the loss of mineral and organic
nutrients.
Destabilisation of slopes and increased risk of landslides.
Sediment and the chemicals from fertilizers and pesticides can pollute
waterways.
Water will accumulate in terrace depressions or where the build up of
sediment acts as a small weir. The impasse of water can suddenly break, leading
to a runoff of water and mud with a remarkable destructive power.
New Environmental Regulations
Recently, as the people in the region have witnessed the
environmental challenges created by the rush to build terraced vineyards on
ever-steeper hillsides, new regulations have been passed. Terraces are forbidden
on the steeper slopes, and at least 40% of the natural vegetation must be
preserved. Guidelines for sustainable terracing including terrace design
criteria, are summarised below.
Sustainable terracing in Priorat
Environmental problems of industrial terracing can be overcome
if adequate design criteria are implemented. The risk of erosion is not a
function of the natural slope of the terrain, but the design of the terraces: a
poorly designed vineyard on a slope of 25% will have more erosion that some
well-designed terraces on a slope of 50%.
Harmonious integration of the terraces in the landscape,
with the height of embankments limited to 1.5 m to reduce visibility and a
'quarry' effect.
The width of the terraces should only allow for the planting of one row of
vines.
All terraces should have side drainage channels. The drainage channels
should be located in the 'ribs' of the mountain, where the rock is resistant to
erosion.
Poor terrace design: terraces
and drainage channels should avoid concave areas where sediments accumulate and
there is a high risk of erosion. Terraces should not be constructed on the
summit line.
The length of the terraces is limited to 200 m, in order to
avoid erosion. Half of the terrace (100 m) drains into a canal and the other
half, toward the opposite channel.
The plant layout in the terraces should follow the contour lines.
Terraces should not be constructed on the mountain summit line.
Trees and rock outcrops should be preserved to maintain the traditional
landscape value, to break the continuity of the vineyard and at the same time,
provide a rest area with shade for workers.
Preservation of riverbank vegetation of gullies or streams.
Preservation of buildings of heritage value.
Farm roads should be open for public use and integrated into the
infrastructure network to support wine tourism.
Access roads to the terraces should be zigzagged, so that the slope does not
exceed 10-15%. With steeper slopes, the risk of roll-over of machinery is
considered unacceptable.
Wine Farms or Wind Farms?
The revival of the region has shown the value of maintaining
mountain viticulture and social and political mobilisation backed by the
vinicultural sector managed to halt a government plan to convert Priorat into a
major wind-power producing centre. Priorat alleged that the plan was
incompatible with the project designed to foster the quality of the wine and
landscape. The Priorat has begun to debate its development model while, in the
meantime, the region's main mountain range, the Serra del Montsant, has been
declared a Natural Park. The debate has begun and time will tell.
Wind farm overlooking the village of
Pradell de la Teixeta in Priorat
The importance of maintaining mountain viticulture
Maintains economic activity and prevents rural
depopulation.
Preserves a unique landscape formed over centuries of balanced human
intervention.
Develops a land use mosaic as one of the most appropriate measures to
prevent forest fires. It has been proven that the vineyard creates a good
firewall.
Keeps the indigenous grape varieties that are especially adapted to the
terrain and climate.
Supports the development of unique, high quality wines.
Makes an important contribution to the cultural and biological diversity of
the planet.
Provides a tourist attraction.
Helps to create a strong local identity.
