Structure and Dynamics of the Root System
53
availability. Santantonio et al. (1977) compiled alometric regressions (log-log)
of large-root biomass (kg) on dbh (cm) for a number of tree species. In the
dbh range 10-20 cm, which contains most of our sample trees, values of
large-root biomass (0) 5 cm) predicted by our equation for single-stemmed
holm oak are very close to those derived from their mean regression for coniferous trees, and about 2.5 times higher than those from their mean regression for deciduous trees.
4.6 Root Biomass
The proportion of biomass allocated to belowground tissues by perennial
plants usually increases as the environment becomes more severe (Rundel
1980). Thus, root systems may account for up to 90% of total plant biomass in
many arctic plants and some desert shrubs (Rodin and Bazilevich 1967;
Caldwell and FernandeZ 1975).
In the Montseny mesic site, a holm oak stand dominated by singlestemmed trees had 28% of its total tree biomass belowground (Table 4.2). Of
the 63 Mg dry wt. ha- 1 of root biomass, 48% was in lignotubers and roots
larger than 5 cm in diameter, 27% in roots of 01-5 cm, and 24% in roots of
o < 1 cm. The allocation of 28% of the total biomass into the belowground
compartment is quite high, but it still falls within the range of 15-35% commonly found in temperate forest ecosystems (Rodin and Bazilevich 1967),
Table 4.2. Basal area (m 2 ha- I ), aboveground biomass (Mg drywt. ha- I ) and various fractions of
root biomass (Mg drywt. ha- I ) for the Montseny mesic and xeric sites, and Prades
Site
Basal
AboveRoots
Roots
Roots
Total
Root
area
ground
Q) > 5cm a Q) 1-5 cm Q) < 1 cm
roots
biomass
biomass
(% of total)b
Montseny
mesic c
26.6
160
30
17
16
63
28
Montseny
108
58
xeric d
16.3
79
--91.0-16"
Prades f
37.1
103
66
37
128 8
ssg
Data compiled from Canadell and Rodll (1991), Gracia et al. (1994), Djema (1995), and Sabate
et al. (1998).
a Biomass of roots of Q) >5 cm and lignotuber.
b Percentage of total root biomass respect to total aboveground and belowground biomass.
C Data for the permanent plot at La Castanya, using the tree sizes of 1978.
d Data for a 0.03-ha plot, tallied in 1990.
" Roots of Q) <1 cm were not measured at the xeric site, but their biomass was assumed equal to
the mesic site.
f Data for three control plots on the north-facing slope of Tomers, tallied in 1992.
g Does not include roots of Q) < 1 em.
53
availability. Santantonio et al. (1977) compiled alometric regressions (log-log)
of large-root biomass (kg) on dbh (cm) for a number of tree species. In the
dbh range 10-20 cm, which contains most of our sample trees, values of
large-root biomass (0) 5 cm) predicted by our equation for single-stemmed
holm oak are very close to those derived from their mean regression for coniferous trees, and about 2.5 times higher than those from their mean regression for deciduous trees.
4.6 Root Biomass
The proportion of biomass allocated to belowground tissues by perennial
plants usually increases as the environment becomes more severe (Rundel
1980). Thus, root systems may account for up to 90% of total plant biomass in
many arctic plants and some desert shrubs (Rodin and Bazilevich 1967;
Caldwell and FernandeZ 1975).
In the Montseny mesic site, a holm oak stand dominated by singlestemmed trees had 28% of its total tree biomass belowground (Table 4.2). Of
the 63 Mg dry wt. ha- 1 of root biomass, 48% was in lignotubers and roots
larger than 5 cm in diameter, 27% in roots of 01-5 cm, and 24% in roots of
o < 1 cm. The allocation of 28% of the total biomass into the belowground
compartment is quite high, but it still falls within the range of 15-35% commonly found in temperate forest ecosystems (Rodin and Bazilevich 1967),
Table 4.2. Basal area (m 2 ha- I ), aboveground biomass (Mg drywt. ha- I ) and various fractions of
root biomass (Mg drywt. ha- I ) for the Montseny mesic and xeric sites, and Prades
Site
Basal
AboveRoots
Roots
Roots
Total
Root
area
ground
Q) > 5cm a Q) 1-5 cm Q) < 1 cm
roots
biomass
biomass
(% of total)b
Montseny
mesic c
26.6
160
30
17
16
63
28
Montseny
108
58
xeric d
16.3
79
--91.0-16"
Prades f
37.1
103
66
37
128 8
ssg
Data compiled from Canadell and Rodll (1991), Gracia et al. (1994), Djema (1995), and Sabate
et al. (1998).
a Biomass of roots of Q) >5 cm and lignotuber.
b Percentage of total root biomass respect to total aboveground and belowground biomass.
C Data for the permanent plot at La Castanya, using the tree sizes of 1978.
d Data for a 0.03-ha plot, tallied in 1990.
" Roots of Q) <1 cm were not measured at the xeric site, but their biomass was assumed equal to
the mesic site.
f Data for three control plots on the north-facing slope of Tomers, tallied in 1992.
g Does not include roots of Q) < 1 em.