Environmental Engineering Reference
In-Depth Information
as a reaction to the progressive land abandonment caused by rural depopulation.
The objective of this chapter is to present the results of a case study which quanti-
fies the impact of agricultural abandonment and afforestation on soil organic car-
bon stock. The study has been carried out in Sicily, the southernmost region of
Italy, which is characterized by a multitude of environmental sub-regions due to a
high variability of local environmental factors such as altitude, outcropping rock
types, etc.. For example, in Sicily there is a wide bioclimatic gradient, ranging
from the infra-mediterranean to the cryo-oromediterranean thermotype. Therefore,
the case study of Sicily may be considered as representative also for other regions
of S Italy and of the Mediterranean Basin.
In this chapter, the term “natural afforestation” indicates the spontaneous pro-
cess of secondary succession that follows agricultural abandonment, and “artificial
afforestation” indicates (FAO) the
≪
“Man-made Forest”: A forest crop raised arti-
ficially, either by sowing or planting
≫
.
12.1.1 Natural Afforestation
Land-use change (LUC) is considered the second greatest cause of carbon (C)
emissions after fuel consumption (Watson et al.
2000
). During the past 250 years,
about 200 Pg of C were released to the atmosphere as a consequence of LUC
(Scholes and Noble
2001
). Crop cultivation in areas previously covered by native
woody vegetation induces huge C losses from biomass and soil and it is today
considered, along with the deforestation of tropical areas, one of the main causes
of CO
2
concentration increase in the atmosphere.
On the other hand, in some regions of the world, such as the mid-latitudes of
the Northern Hemisphere, one of the most important types of LUC is the aban-
donment of agricultural land. In Italy, between 1961 and 2009, almost 39.2 % of
the “Arable Land and Permanent Crops”, corresponding to an area of 61,230 km
2
,
have been abandoned (FAO database).
In general, the abandonment of cultivated or grazed lands is the starting
point for secondary succession processes, i.e. the spontaneous colonization of
the areas by herbaceous and woody plants. The species composition of the suc-
cessional plant communities and their turnover rates depend on a variety of abi-
otic and biotic factors, such as macro- and mesoclimate. In most cases and in
the absence of strong disturbance factors such as grazing or wildfires, secondary
succession leads within few decades to the creation of forest communities. In the
Mediterranean area, the recent abandonment of marginal agricultural areas (pas-
ture and/or arable lands) has caused an increase in the area occupied by pre-forest
and forest communities (Bonet
2004
). In Italy, total forest area has increased by
17.5 % during the period 1950-1990 (Italian National Statistical Bureau).
Changes in soil organic carbon (SOC) content after agricultural abandonment
have been quantified by various authors, and some of them reported an increase in
SOC during woody plant encroachment within old ields or grasslands (Pr￩vosto
