Nutrient Distribution and Cycling
267
18.8 Nutrient Cycling and Stand Structure
The relationships between nutrient cycling and stand structure were given
scant attention in the pioneer works on forest nutrient dynamics (Ovington
1959; Rodin and Bazilevich 1967; Duvigneaud and Denaeyer-De Smet 1970),
and even in most of the International Biological Programme studies (Cole
and Rapp 1981). Our own earlier work on nutrient cycling in holm oak forests at Montseny was concentrated on a single, 0.23-ha permanent plot (Roda
1983; Ferrt~s 1984; Verdu 1984); a summary of its nutrient pools and fluxes
was given by Escam~ et al. (1987). Since this plot was a high-quality site, with
an aboveground tree biomass of 160 Mg ha- 1 (compared to an average of 104
Mg ha- 1 for the closed-canopy Torrent de la Mina plots), its nutrient cycle
differed in some aspects from those reported here for these plots. For instance, N contents in the aboveground tree biomass were 411 kg ha- 1 in the
permanent plot compared with an average of 275 kg ha- 1 in closed-canopy
plots within the Torrent de la Mina catchment. Within a given tree species,
nutrient pools in the vegetation are closely related to biomass amounts, while
nutrient fluxes linked to production of new tissues are related to the rate of
primary production of the stand. Other nutrient fluxes, such as those in litterfall, are usually less dependent on stand structure, at least for closedcanopy stands. For example, litterfall in the high-biomass permanent plot
was very close to the average of the 18 closed-canopy plots during 1 year of
simultaneous sampling (Mayor 1990).
18.9 Spatial Variation in Nutrient Cycling
Within a given ecosystem type, spatial variations in nutrient pools and fluxes
are expected, mainly as a result of spatial differences in either site conditions
or stage of stand development. Spatial patterns in nutrient cycling can reveal
the underlying controlling factors at the landscape scale. Also, knowledge of
such patterns is important for predicting the functioning of forest ecosystems above the plot scale, since given the non-linear nature of many ecological phenomena, the behaviour of a set of cells (or patches) may differ from
the average of individual behaviour.
As an example of the kind and degree of spatial variation in nutrient cycling observed in holm oak forests, we will consider here nutrient fluxes in
litterfall because they integrate the intensity of nutrient cycling within a forest ecosystem. Litterfall nutrient fluxes were measured for 1 year in the 18
closed-canopy plots at Montseny systematically distributed over the 100-ha
holm oak stand of the Torrent de la Mina catchment.
Nand P fluxes in litterfall varied over the 18 plots by a factor of 2, while
those of K and Mg varied by a factor of 3. The relative variabilities of Nand P
267
18.8 Nutrient Cycling and Stand Structure
The relationships between nutrient cycling and stand structure were given
scant attention in the pioneer works on forest nutrient dynamics (Ovington
1959; Rodin and Bazilevich 1967; Duvigneaud and Denaeyer-De Smet 1970),
and even in most of the International Biological Programme studies (Cole
and Rapp 1981). Our own earlier work on nutrient cycling in holm oak forests at Montseny was concentrated on a single, 0.23-ha permanent plot (Roda
1983; Ferrt~s 1984; Verdu 1984); a summary of its nutrient pools and fluxes
was given by Escam~ et al. (1987). Since this plot was a high-quality site, with
an aboveground tree biomass of 160 Mg ha- 1 (compared to an average of 104
Mg ha- 1 for the closed-canopy Torrent de la Mina plots), its nutrient cycle
differed in some aspects from those reported here for these plots. For instance, N contents in the aboveground tree biomass were 411 kg ha- 1 in the
permanent plot compared with an average of 275 kg ha- 1 in closed-canopy
plots within the Torrent de la Mina catchment. Within a given tree species,
nutrient pools in the vegetation are closely related to biomass amounts, while
nutrient fluxes linked to production of new tissues are related to the rate of
primary production of the stand. Other nutrient fluxes, such as those in litterfall, are usually less dependent on stand structure, at least for closedcanopy stands. For example, litterfall in the high-biomass permanent plot
was very close to the average of the 18 closed-canopy plots during 1 year of
simultaneous sampling (Mayor 1990).
18.9 Spatial Variation in Nutrient Cycling
Within a given ecosystem type, spatial variations in nutrient pools and fluxes
are expected, mainly as a result of spatial differences in either site conditions
or stage of stand development. Spatial patterns in nutrient cycling can reveal
the underlying controlling factors at the landscape scale. Also, knowledge of
such patterns is important for predicting the functioning of forest ecosystems above the plot scale, since given the non-linear nature of many ecological phenomena, the behaviour of a set of cells (or patches) may differ from
the average of individual behaviour.
As an example of the kind and degree of spatial variation in nutrient cycling observed in holm oak forests, we will consider here nutrient fluxes in
litterfall because they integrate the intensity of nutrient cycling within a forest ecosystem. Litterfall nutrient fluxes were measured for 1 year in the 18
closed-canopy plots at Montseny systematically distributed over the 100-ha
holm oak stand of the Torrent de la Mina catchment.
Nand P fluxes in litterfall varied over the 18 plots by a factor of 2, while
those of K and Mg varied by a factor of 3. The relative variabilities of Nand P