Afforestation and Reforestation: The Sicilian Case Study - The Greenhouse Gas Balance of Italy - page 165

et al. 2006 ; La Mantia et al. 2007 ; Montan￩ et al. 2007 ; Alberti et al. 2011 ), while
others found a decrease in SOC during secondary succession (Paul et al. 2002 ;
Guo and Gifford 2002 ; Jackson et al. 2002 ; Goodale and Davidson 2002 ; Alberti
et al. 2008 ). So, there is a need of further studies on the factors that determine
if the soils of the areas subject to secondary succession are either C sinks or C
sources. On a regional scale, such kind of information could be particularly impor-
tant for identifying land-use classes that act as C sinks.
One of the factors that influence SOC dynamics after land abandonment is cli-
mate (Jackson et al. 2002 ). In Italy, a negative relationship between changes in
SOC after agricultural abandonment and total annual rainfall has been found, pos-
sibly related to soil N stock dynamics (Alberti et al. 2011 ). This relationship has
recently been confirmed for Sicily (La Mantia et al. 2013 ).
12.1.2 Artificial Afforestation
In Mediterranean countries, the surface of tree plantations has strongly increased
during the 20th century. Under semi-arid climatic conditions, afforestation
activities have been carried out mostly by using various species of Pinus and
Eucalyptus , and they were often planted in abandoned agricultural or degraded
lands. After the Second World War, the surface of afforestations and reforestations
increased of 435,906 ha in Italy and of 73,228 ha in Sicily, and areas dedicated
to “arboriculture for timber” increased of 122,252 ha in Italy and of 1,137 ha in
Sicily (INFC 2007 ).
Within the last decade, an increasing amount of research has focused on the
impact of afforestations on soil parameters, and some studies analysed SOC stocks
in afforested sites (see Paul et al. 2002 ). Some authors found a decrease and oth-
ers an increase of SOC after afforestation with respect to sites characterized by
spontaneous pre-forest plant communities (Jackson et al. 2002 ; Farley et al. 2004 ;
Kelty 2006 ; Goberna et al. 2007 ; Vil￠ et al. 2007 ; Fern￡ndez-Ondo￱o et al. 2010 ;
Novara et al. 2013 ). The C increase or decrease after afforestation is, in fact, deter-
mined by many factors, including previous land use, climate, soil type and site
preparation (Turner and Lambert 2000 ; Guo and Gifford 2002 ; Paul et al. 2002 ).
Considering the high extent of afforested areas in the Mediterranean countries,
understanding the ability of afforested soil to sequester C is therefore relevant.
12.2 Study Sites and Data Analysis
In order to quantify the effects of (1) agricultural abandonment and (2) artificial
afforestation on SOC, a joined dataset of original data sampled in various sites in
Sicily (34 sites) as well as existing data from literature (14 sites), has been ana-
lysed. Since previous studies showed that SOC dynamics in secondary succession