Environmental Engineering Reference
In-Depth Information
Furthermore, in order to confront SOC among succession stages within each
bioclimate, an average index of SOC content change has been used:
Succession Carbon Change Index
(
SCCI
)
=
(
C
older
−
C
younger
)/
C
younger
,
where C
older
=
SOC content in the older successional stage, and C
younger
=
SOC
content in the younger successional stage. A positive value indicates a gain in
carbon stock from a younger succession stage to an older stage, while a negative
value indicates a loss in carbon stock.
In order to evaluate for each bioclimate the effect of artificial afforestation in
comparison with a considered stage of succession, another average carbon change
index has been used as follows:
Afforestation Carbon Change Index
(
ACCI
)
=
(
C
afforestation
−
C
succession stage
)/
C
succession stage
,
where C
afforestation
=
SOC content in the afforestation, and C
succession stage
=
SOC
content in the succession stage. A positive value indicates a gain in carbon stock
by afforestation activities in confront with the respective succession stage, while a
negative value indicates a loss.
Lastly, the C stock data have been used to calculate the total C gain in areas
subject to secondary succession in the region of Sicily between the years 1990 and
2006. Surface data of agricultural abandonment and areas subject to secondary
succession processes were elaborated from CORINE land cover classification data.
12.3 Results
12.3.1 SOC Variation in Natural Afforestation
In all bioclimates, SOC stock increased more than twice from cultivation to
the last stage of succession (Fig.
12.2
). A noteworthy difference in SOC stock
between the bioclimates has been observed: from cultivated soils to forest soils,
SOC stock increased from 28.31 to 78.60 Mg ha
−
1
in the thermo-mediterranean
bioclimate, from 45.51 to 106.29 Mg ha
−
1
in the meso-mediterranean bioclimate
and from 31.25 to 73.70 Mg ha
−
1
in the supra-mediterranean bioclimate.
Furthermore, in all bioclimates SOC stock increased from one succession stage
to the next one (Fig.
12.3
). In the thermo-mediterranean belt, there was a high
increase in SOC from the cultivated soils to the soils under herb-dominated plant
communities. So, the cessation of soil tillage or chemical weed control after culti-
vation abandonment seems to be an important factor for SOC accumulation.
On the contrary, we observed only a low SOC stock increase from herb-domi-
nated plant communities to perennial grasslands, and SOC gain during the woody-
dominated stages of succession assumed intermediate values.
