Slow and unsteady? Soil carbon accumulation rates in Mediterranean and
semi-arid post-agricultural landscapes
Abstract
Increases in soil organic carbon (SOC) during secondary succession in
Mediterranean and semi-arid climates, global hot-spots for agricultural
land abandonment, have been notoriously difficult to predict and are
subject to multiple environmental and land management factors. Field
studies have reported positive, negative and no change varying over
extended periods of time. To better evaluate the potential carbon sink
capacity of regenerating semi-natural landscapes in these climates
requires an improved understanding of the rates of SOC gains and losses.
We compiled Mediterranean and semi-arid chronosequences and paired plots
to investigate the effects of past land use, restoration intensity, and
various environmental factors on SOC stocks during post-agricultural
succession. Based on a preliminary synthesis of the western
Mediterranean basin, we expect significant long-term accumulation rates
globally although with high variability and the potential for net losses
(compared to cropland control sites) even after several decades. Losses
or minimal change are likely due to high initial SOC stock at the time
of abandonment (e.g. from anthropogenic organic matter inputs) and too
high or too low mean annual precipitation (e.g. < 450 or
> 1000 mm), among other factors. A consolidated SOC
accumulation rate for both Mediterranean and semi-arid soils undergoing
post-agricultural succession is provided to better inform
decision-makers on the benefits and challenges of agricultural land
abandonment.