Land degradation due to agricultural land abandonment in Southeast Spain

Land degradation due to agricultural land abandonment in Southeast Spain

J.P. Lesschen and L.H. Cammeraat

Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, The
Netherlands (lesschen@science.uva.nl)

Land abandonment is nowadays widely spread in Mediterranean countries and is
expected to increase, due to changing European policies, urbanisation and climate change. Several studies showed that land degradation will increase after abandonment, especially under semi-arid conditions. The main cause of increased erosion is the absence of ploughing and a slow vegetation recovery, which results in the formation
of soil crusts and bare spots with low infiltration rates, leading to more concentrated
runoff and gully erosion.
To assess the extent and impact of agricultural land abandonment in relation to land
degradation we analysed land use, soil properties and erosional processes within a
semi-arid catchment in Southeast Spain. Our results showed that soil properties can
recover after abandonment to the level of semi-natural shrublands, but this improvement
is slow, e.g. only after 40 years of abandonment the soil organic carbon content
was comparable to soils under semi-natural vegetation. This means that these fields
are especially vulnerable to erosion during the first years after abandonment. Within
the study area 17% of the agricultural land was abandoned and more than half of these
fields experienced moderate to severe erosion.
Gully erosion and piping through terrace walls appeared to be the main erosional processes.
From a data set of almost 300 terraces we analysed which factors determined
terrace failure. Variables that significantly increased the risk of terrace failure were
land abandonment, steeper terrace slope, loam texture, valley bottom position and
shrubs on the terrace wall. To mitigate land degradation after abandonment the soil
and water conservation practices should focus on reducing the risk of concentrated
flow, and revegetation of critical spots in the landscape with indigenous grass species
to prevent terrace failure.