4 Structure and Dynamics of the Root System
Josep Can adell, Arezki Djema, Bernat L6pez, Francisco Lloret,
Santiago Sabate, Daniel Siscart and Carlos A. Gracia
4.1 Introduction
The belowground component of terrestrial ecosystems is much less understood than any of the aboveground components, yet important ecosystem
processes such as nutrient recycling, water storage, and long-term carbon accumulation occur largely in this compartment. For instance, belowground
structures accounted for ,up to 83% of the total biomass in 13 Mediterranean
woody communities (Hilbert and CanadellI995), and belowground primary
production was 60-80% of the total net primary production in a variety of
woody systems (Coleman 1976; Agren et al. 1980; Fogel 1985). Yet both root
biomass and production are infrequently studied and technical difficulties
make the measurements often inaccurate. Furthermore, plant root distribution
and maximum rooting depths play important roles in overall ecosystem function, but it was not until recently that ecosystem-level and global comprehensive studies have been undertaken (Canadell et al. 1996; Jackson et al. 1996).
In water-limited systems, as in the case of Mediterranean ecosystems, root
growth is among the deepest of all biome-types (Canadell et al' 1996), and
carbon allocation patterns strongly favour accumulation belowground (Oechel
and Lawrence 1981). This pattern occurs because of the development both of
deep root systems and of large subterranean structures such as lignotubers
(James 1984; Canadell and Zedler 1995; Canadell and L6pez-Soria 1998).
Ultimately, the gaps in our understanding of root system attributes and
function are manifested in the poor implementation of root properties in
whole-ecosystem and biospheric/atmospheric models. These models often
represent the belowground compartment using a simple bucket model or
two or three arbitrary layers (Prentice et al. 1992; Melillo et al. 1993; Potter
et al. 1993). Furthermore, these models use maximum rooting depths between 1 and 2 m, yet we know that deep roots (> 3 m) are very common in
most biomes (Stone and Kalisz 1991; Canadell et al. 1996) and have important consequences for ecosystem processes (Silva et al. 1989; Nepstad et al.
1994; Richter and Markewitz 1995; Schulze et al.1996).
Ecological Studies, Vol. 137
Ferran Roda et al. (eds) Ecology of Mediterranean
Evergreen Oak Forests
© Springer-Verlag, Berlin Heidelberg 1999
Josep Can adell, Arezki Djema, Bernat L6pez, Francisco Lloret,
Santiago Sabate, Daniel Siscart and Carlos A. Gracia
4.1 Introduction
The belowground component of terrestrial ecosystems is much less understood than any of the aboveground components, yet important ecosystem
processes such as nutrient recycling, water storage, and long-term carbon accumulation occur largely in this compartment. For instance, belowground
structures accounted for ,up to 83% of the total biomass in 13 Mediterranean
woody communities (Hilbert and CanadellI995), and belowground primary
production was 60-80% of the total net primary production in a variety of
woody systems (Coleman 1976; Agren et al. 1980; Fogel 1985). Yet both root
biomass and production are infrequently studied and technical difficulties
make the measurements often inaccurate. Furthermore, plant root distribution
and maximum rooting depths play important roles in overall ecosystem function, but it was not until recently that ecosystem-level and global comprehensive studies have been undertaken (Canadell et al. 1996; Jackson et al. 1996).
In water-limited systems, as in the case of Mediterranean ecosystems, root
growth is among the deepest of all biome-types (Canadell et al' 1996), and
carbon allocation patterns strongly favour accumulation belowground (Oechel
and Lawrence 1981). This pattern occurs because of the development both of
deep root systems and of large subterranean structures such as lignotubers
(James 1984; Canadell and Zedler 1995; Canadell and L6pez-Soria 1998).
Ultimately, the gaps in our understanding of root system attributes and
function are manifested in the poor implementation of root properties in
whole-ecosystem and biospheric/atmospheric models. These models often
represent the belowground compartment using a simple bucket model or
two or three arbitrary layers (Prentice et al. 1992; Melillo et al. 1993; Potter
et al. 1993). Furthermore, these models use maximum rooting depths between 1 and 2 m, yet we know that deep roots (> 3 m) are very common in
most biomes (Stone and Kalisz 1991; Canadell et al. 1996) and have important consequences for ecosystem processes (Silva et al. 1989; Nepstad et al.
1994; Richter and Markewitz 1995; Schulze et al.1996).
Ecological Studies, Vol. 137
Ferran Roda et al. (eds) Ecology of Mediterranean
Evergreen Oak Forests
© Springer-Verlag, Berlin Heidelberg 1999