Leaf Traits and Canopy Organization
131
At Avic, leaf-area-based Nand P contents tend to be lower in summer than
in autumn or winter (Fig. 9.4) This is a common temporal trend that has
been documented in other holm oak forests (see De Lillis and Fontanella
1992). The lower leaf Nand P contents during summer suggest that during
the active growth period in late spring, Nand Pare retranslocated from
leaves to new growth and that during the autumn, when growth activity is
low and there is no water stress, leaves exhibit Nand P replenishment (see
also Chap. 18; Chabot and Hicks 1982; Nambiar and Fife 1987; Chapin 1988).
Temporal trends suggesting withdrawal and resorption are more apparent in
the uppermost canopy layer than at lower canopy layers, where growth activity is limited by light. Escudero et al. (1992) did not find temporal changes
of N content in holm oak as resorption processes. However, their results were
expressed on a dry weight basis, which makes it difficult to distinguish
whether changes in leaf nutrient concentrations are simply due to dilutionconcentration effects (i.e. relative increases or decreases of nutrient-poor
carbon compounds) or to resorption of mineral nutrients. In particular, resorption of mineral nutrients may not affect foliar nutrient concentrations
on a dry weight basis if non-structural carbohydrates are also being resorbed
at a similar rate.
In conclusion, holm oak canopies exhibit a typically unimodal leaf area
distribution, with most of the leaf area accumulated in the upper canopy. As
a consequence of this skewed leaf area distribution and the radiation extinction patterns associated with it, strong gradients in leaf morphological and
functional traits are found from the top to the bottom of the canopy. Leaves
at the top of the canopy are smaller, have higher stomatal and hair densities,
higher LSM and higher area-based nutrient content than leaves at the bottom
of the canopy. Holm oak leaves appear to be very plastic depending on the
environmental conditions (mainly radiation and water availability) in which
they develop. Overall, holm oak exhibits many characteristics of a stress tolerant, slow-growing species with parsimonious carbon and nutrient cycling
(Chaps. 13 and 18).
References
Anderson JM (1986) Photoregulation of the composition, function and structure of thylakoid
membranes. Annu Rev Plant PhysioI37:93-136
Bellot J (1989) Amilisis de los flujos de deposici6n global, trascolaci6n, escorrentia cortical y
deposici6n seca en el encinar mediternineo de l'Avic (Sierra de Prades, Tarragona). PhD
Thesis, University of Alicante, Alicante
Bellot J, Sanchez JR, Lled6 MJ, Martinez P, Escarre A (1992) Litterfall as a measure of primary
production in Mediterranean holm-oak forest. Vegetatio 991100:69-76
Chabot BF, Hicks DJ (1982) The ecology ofleaflife spans. Annu Rev Ecol Syst 13:229-259
Chapin III FS (1988) Ecological aspects of plant mineral nutrition. Adv Mineral Nutr 3:161-191
Cole DW, Rapp M (1981) Elemental cycling in forest ecosystems. In: Reichle D (ed) Dynamic
properties of forest ecosystems. Cambridge University Press, Cambridge, pp 341-409
131
At Avic, leaf-area-based Nand P contents tend to be lower in summer than
in autumn or winter (Fig. 9.4) This is a common temporal trend that has
been documented in other holm oak forests (see De Lillis and Fontanella
1992). The lower leaf Nand P contents during summer suggest that during
the active growth period in late spring, Nand Pare retranslocated from
leaves to new growth and that during the autumn, when growth activity is
low and there is no water stress, leaves exhibit Nand P replenishment (see
also Chap. 18; Chabot and Hicks 1982; Nambiar and Fife 1987; Chapin 1988).
Temporal trends suggesting withdrawal and resorption are more apparent in
the uppermost canopy layer than at lower canopy layers, where growth activity is limited by light. Escudero et al. (1992) did not find temporal changes
of N content in holm oak as resorption processes. However, their results were
expressed on a dry weight basis, which makes it difficult to distinguish
whether changes in leaf nutrient concentrations are simply due to dilutionconcentration effects (i.e. relative increases or decreases of nutrient-poor
carbon compounds) or to resorption of mineral nutrients. In particular, resorption of mineral nutrients may not affect foliar nutrient concentrations
on a dry weight basis if non-structural carbohydrates are also being resorbed
at a similar rate.
In conclusion, holm oak canopies exhibit a typically unimodal leaf area
distribution, with most of the leaf area accumulated in the upper canopy. As
a consequence of this skewed leaf area distribution and the radiation extinction patterns associated with it, strong gradients in leaf morphological and
functional traits are found from the top to the bottom of the canopy. Leaves
at the top of the canopy are smaller, have higher stomatal and hair densities,
higher LSM and higher area-based nutrient content than leaves at the bottom
of the canopy. Holm oak leaves appear to be very plastic depending on the
environmental conditions (mainly radiation and water availability) in which
they develop. Overall, holm oak exhibits many characteristics of a stress tolerant, slow-growing species with parsimonious carbon and nutrient cycling
(Chaps. 13 and 18).
References
Anderson JM (1986) Photoregulation of the composition, function and structure of thylakoid
membranes. Annu Rev Plant PhysioI37:93-136
Bellot J (1989) Amilisis de los flujos de deposici6n global, trascolaci6n, escorrentia cortical y
deposici6n seca en el encinar mediternineo de l'Avic (Sierra de Prades, Tarragona). PhD
Thesis, University of Alicante, Alicante
Bellot J, Sanchez JR, Lled6 MJ, Martinez P, Escarre A (1992) Litterfall as a measure of primary
production in Mediterranean holm-oak forest. Vegetatio 991100:69-76
Chabot BF, Hicks DJ (1982) The ecology ofleaflife spans. Annu Rev Ecol Syst 13:229-259
Chapin III FS (1988) Ecological aspects of plant mineral nutrition. Adv Mineral Nutr 3:161-191
Cole DW, Rapp M (1981) Elemental cycling in forest ecosystems. In: Reichle D (ed) Dynamic
properties of forest ecosystems. Cambridge University Press, Cambridge, pp 341-409