Environmental Engineering Reference
In-Depth Information
aboveground, roots and soil) and (ii) to quantify annual carbon sequestration
among these different pools both in mixed broadleaf and poplar plantations in the
Friuli Venezia Giulia Region. To achieve these two objectives, a chronosequence
approach was adopted.
13.2 Study Area and Data Analysis
The study area is the Friuli Venezia Giulia plain where climatic conditions are
quite uniform (average annual temperature: 13.5 °C; average annual precipitation:
1,100-1,500 mm). However, depending on the substrate characteristics, this area
can be divided into two sub-areas: the Northern part is characterized by a very per-
meable substrate made up of pebbles and gravel whose diameter decreases moving
towards the valley; the Southern part is characterized by clay soils with an high
water retention potential. In particular, this last area is quite suitable especially for
poplar cultivation because of the high water requirements of this species.
The basic unit considered in this work coincided with individual land parcels
or sets of contiguous parcels uniform in terms of stand characteristics (i.e. species
composition, structure, age). This study considered mixed broadleaf plantations
planted after 1992 with a rotation period of at least 20 years. Moreover, poplar
plantations realized after 2002 with a rotation period of 8-10 years were also con-
sidered. On the basis of the data given by the Regional Forest Administration, a set
of 36 mixed broadleaf plantations and 9 poplar plantations distributed across the
plain and across different age classes was selected.
Within each stand, 5 points within a 50 50 m grid were randomly selected
avoiding plantation's edge. At each point, a 10 m radius plot (314 m
2
) was set up
for dendrometric measurements. In each plot, all standing trees were recognized,
numbered, diameters at breast height (DBH, 1.30 m) and total height were meas-
ured. Total aboveground carbon stock was determined according to specific allo-
metric equations for broadleaf plantations (Alberti et al.
2006
).
Instead, specific allometric equations elaborated by the Regional Forest
Administration for poplar were used. Root biomass was derived using a root/shoot
ratio of 0.26 (IPCC
2003
).
Aboveground NPP (Mg ha
−
1
y
−
1
) was modeled assuming a logistic growth
model. In particular, it was considered equal to the first derivative of Richard's
logistic model (Cooper
1983
; Hooker and Compton
2003
):
B
B
=
B
MAX
·
1
−
EXP
(
A
·
T
)
where B
max
is the maximum aboveground carbon stock (Mg C ha
−
1
), t is stand
age (years), a and b are fitting parameters.
For the mixed broadleaf plantations, a subsample of six stands distributed in
two age classes (10 and 20 years) were considered for soil carbon stock assess-
ment. Instead, in the case of poplar plantation, all previously nine selected stands
