52
J. Canadell, A. Djema, B. L6pez, F. 1., S. Sabate, D. Siscart and C.A. Gracia
few studies have provided direct experimental data (e.g. Canadell and L6pezSoria 1998; Sabate et al. 1998). These studies indicate that nutrients and carbohydrates stored in the lignotuber play an important role in providing resources for rapid regrowth during the first years after a disturbance.
4.5 Allometric Relationships Between Aboveand Belowground Biomass
Root excavation studies enable us to develop allometric equations that can be
used to investigate the relationships between the aboveground and belowground parts of trees. They are also used to estimate large-root biomass of
individual trees by measuring their aboveground dimensions. Table 4.1
shows these equations for Montseny and Prades. Several regressors were used
depending on the tree structure. Diameter at breast height (dbh) and stem
diameter at 50 cm (Dso) were good regressors to estimate the root biomass of
single-stemmed trees, which is the dominant tree structure in the Montseny
mesic site (Canadell et al. 1988). On the other hand, multi-stemmed trees are
dominant in Prades and the root biomass of a stool is best estimated using
the total cross-sectional area (CSA), at 50 cm from the ground, of all the
stems it bears (Djema 1995).
It is worth noting that trees with dbh < 20 cm at Montseny had more root
biomass in the xeric site than in the mesic site, as it would be predicted according to our current understanding of carbon allocation and soil water
Table 4.1. Allometric equations for total large-root biomass (kg dry weight, including lignotuber) for single-stemmed holm oaks at Montseny and multi-stemmed holm oaks at Prades
t
x
a
b
~
n
Montseny - mesic and xeric sites (single-stemmed trees)
Total large roots
Dbh
- 1.047
2.191
0.73
32
Total large roots
Dso
- 1.687
2.623
0.79
32
Total large roots
TAB
- 0.212
0.894
0.83
30
Montseny - mesic site (single-stemmed trees)
Total large roots
Dbh
- 1.393
2.451
0.81
20
Montseny - xeric site (single-stemmed trees)
Total large roots
Dbh
- 0.448
1.734
0.71
12
Prades (multi-stemmed trees)
Total large roots
CSA
- 55.210
0.605
0.91
6
dbh, Stem diameter at 1.3 m from the ground (cm); Dso, stem diameter at 50 cm from the
ground (em); TAB, total aboveground biomass (kg dry weight); CSA, cross-sectional area at Dso
(cm 2 ) of all the stool stems.
a The model is log y = a + b log x for Montseny and y = a + b log x for Prades. Log indicates
logarithm to base 10.
J. Canadell, A. Djema, B. L6pez, F. 1., S. Sabate, D. Siscart and C.A. Gracia
few studies have provided direct experimental data (e.g. Canadell and L6pezSoria 1998; Sabate et al. 1998). These studies indicate that nutrients and carbohydrates stored in the lignotuber play an important role in providing resources for rapid regrowth during the first years after a disturbance.
4.5 Allometric Relationships Between Aboveand Belowground Biomass
Root excavation studies enable us to develop allometric equations that can be
used to investigate the relationships between the aboveground and belowground parts of trees. They are also used to estimate large-root biomass of
individual trees by measuring their aboveground dimensions. Table 4.1
shows these equations for Montseny and Prades. Several regressors were used
depending on the tree structure. Diameter at breast height (dbh) and stem
diameter at 50 cm (Dso) were good regressors to estimate the root biomass of
single-stemmed trees, which is the dominant tree structure in the Montseny
mesic site (Canadell et al. 1988). On the other hand, multi-stemmed trees are
dominant in Prades and the root biomass of a stool is best estimated using
the total cross-sectional area (CSA), at 50 cm from the ground, of all the
stems it bears (Djema 1995).
It is worth noting that trees with dbh < 20 cm at Montseny had more root
biomass in the xeric site than in the mesic site, as it would be predicted according to our current understanding of carbon allocation and soil water
Table 4.1. Allometric equations for total large-root biomass (kg dry weight, including lignotuber) for single-stemmed holm oaks at Montseny and multi-stemmed holm oaks at Prades
t
x
a
b
~
n
Montseny - mesic and xeric sites (single-stemmed trees)
Total large roots
Dbh
- 1.047
2.191
0.73
32
Total large roots
Dso
- 1.687
2.623
0.79
32
Total large roots
TAB
- 0.212
0.894
0.83
30
Montseny - mesic site (single-stemmed trees)
Total large roots
Dbh
- 1.393
2.451
0.81
20
Montseny - xeric site (single-stemmed trees)
Total large roots
Dbh
- 0.448
1.734
0.71
12
Prades (multi-stemmed trees)
Total large roots
CSA
- 55.210
0.605
0.91
6
dbh, Stem diameter at 1.3 m from the ground (cm); Dso, stem diameter at 50 cm from the
ground (em); TAB, total aboveground biomass (kg dry weight); CSA, cross-sectional area at Dso
(cm 2 ) of all the stool stems.
a The model is log y = a + b log x for Montseny and y = a + b log x for Prades. Log indicates
logarithm to base 10.