Soil loss rates currently recorded in forests are
very low. Nevertheless, that may not be the case during stand
installation and early tree growth stage, when soil is disturbed
and scarcely covered. Site preparation techniques,
performed to improve soil conditions for plant growth,
should help reducing this erosion potential. In this study,
several site preparation techniques were applied prior
to installing a mixed stand (Pseudotsuga mensiezii and
Castanea sativa) and a subsequent monitoring scheme of
run-off and soil loss ran for 2 years in order to compare
their effectiveness for erosion control. The experimental
area, near Macedo de Cavaleiros, NE Portugal, at 700 m
elevation, with annual means of 656 mm rainfall and
12 C temperature, has Mediterranean climatic conditions.
Experimental design comprised three blocks, corresponding
to different topographical positions (near flat plateau, moderate
slope shoulder and steep mid-slope), where eight
treatments were randomly distributed in plots with 375 m2
area: (1) Original soil control (no intervention on the original
abandoned field); (2) No subsoiling, no ploughing, plantation
with hole digger; (3) Subsoiling over the whole area,
with covering shovel; (4) No subsoiling, contour bunds
shaped by two plough passes; (5) Subsoiling in future plantation
rows, contour bunds shaped by two plough passes;
(6) Subsoiling over the whole area, contour bunds shaped by
two plough passes; (7) Subsoiling over the whole area,
contour ploughing over the whole area; and (8) Potential
erosion (subsoiling over the whole area, ploughing downhill).
Sediment and water exported from small plots (2.5 m2
average area), two replicates per treatment and block, were
collected after each rainfall erosion event, in a total of 21,
summing 1,876-mm precipitation in 2 years. Mean annual
run-off and soil loss in the original soil were 3.4 mm and
11.6 g m-2, respectively. In treatments 2–7, values were
higher 3–7 times, for run-off, and 5–12 times, for soil loss.
Potential erosion averages 2.3 t ha-1 year-1. Soil loss and
run-off tend to increase with tillage intensity associated with
site preparation technique, even though average two-year
losses, in all cases, are below tolerable rates. Soil loss and
run-off rates decreased with time, becoming globally negligible
after 2 years. Slight and moderate soil disturbance
intensity site preparation techniques reduce erosion rates to
30% of potential erosion, halving the critical period when
above tolerance rates may occur.
