The Douro Region, NE Portugal, where the grapes for Port Wine are
produced, faces a high potential erosion risk due to its natural setting, for
long tackled with heavy labour inputs. These allowed the stabilization of
steep vineyard covered hill-slopes by means of traditional terracing,
manually built and following models that changed through time.
Alternative vineyard installation and cultivation techniques were tested and
progressively adopted, namely row plantation perpendicular to the contour,
nowadays an integral yet small part of the plantation schemes accepted
under the rules of the World Heritage status, granted by UNESCO in 2001.
This paper investigates the effects of vine plantation schemes on longterm
(I 0 years) runoff and soil loss data recorded in the Douro Region
using a set of meso-scale erosion plots installed in vineyards planted in
rows perpendicular to the contour. It also aims at identifying, and
quantitatively deriving the significance of erosion factors helping to
interpret the results obtained, namely rainfall characteristics and vine plant
density.
Runoff and soil loss were measured in five plots, 32.1 m long and 5.2
m wide, on a 45% slope, over a silt loam soil containing 60% rock
fragments by mass, under Mediterranean climatic regime with less than
600 mm mean annual rainfalL Vine plantation schemes tested correspond
to three different plant densities (3571, 4808, 5917 plants ha·1) on paired
plots (except for the intermediate plant density, tested in a single plot),
which provided a mean vegetation cover of 50, 60 and 75%, respectively.
The 10 year data analyzed correspond to 167 runoff events.
Mean annual runoff and soil loss were 22 mm and 361 kg ha·1,
respectively. These relatively low soil loss rates are explained by the very
high rock fragment cover, protecting the topsoil from wash by runoff. Soil
loss was very much concentrated in a few erosive events, 3 of them being
responsible for ca.75% of the total soil loss recorded in 10 years. These
events occurred in spring and summer, whereas most erosive events in
Mediterranean conditions occur in autumn and winter. Results also show
that increasing the vine plant density by 66% resulted in a reduction of
mean annual runoff by 19% and of mean annual soil loss by 57%,
demonstrating the significant effect on erosion control of platation scheme
decisions taken prior to the installation of permanent crops such as
vineyards.
