13 Water and Nutrient Limitations
to Primary Production
Ferran Roda, Xavier Mayor, Santiago Sabate and Victoria Diego
13.1 Introduction
Primary production is typically low in holm oak (Quercus ilex L.) forests
(Chap. 3). Water availability is likely to limit primary production in most
Mediterranean terrestrial ecosystems given that summer drought is a characteristic trait of Mediterranean-type climates (di Castri 1981). Despite its
deep roots (Chap. 4) and its relative tolerance to foliar water deficits, such
water limitation also applies to holm oak (Chaps. 10 and 11).
Nutrient availability can be also involved in the low production of Mediterranean forests, either through the inherently low fertility of some soils or
through recurrent nutrient export resulting from a centuries-long history of
harvesting and fire. Nutrient limitations to plant growth are widespread in
Mediterranean-type shrublands in Australia, South Africa, and California
(Hellmers et al. 1955; Oechel et al. 1981; Specht 1981; McMaster et al. 1982;
Witkowski et al. 1990). From these and other studies, and from the general
close link between sclerophylly and oligotrophic soils (Loveless 1961), the
view emerged that low nutrient availability shaped the evolution and functioning of Mediterranean-type ecosystems (e.g. Kruger et al. 1983). However,
the soils of the Mediterranean Basin are usually more eutrophic than those of
Mediterranean-type shrublands in Australia, South Africa, and California.
Despite substantial information on nutrient distribution and cycling in
holm oak forests (Chap. 18), we did not know whether, or to what extent,
these forests were nutrient limited. We therefore conducted a fertilization
and irrigation experiment to assess (1) the relative importance of water, nitrogen, and phosphorus as limiting factors for tree growth and primary production in holm oak forests, and (2) the responses to increased resource
availability at the tree, stand, and ecosystem levels.
In this chapter, we first summarize the experiment layout, and then explore how the aboveground net primary production and its components
were affected during the first 3 years of the experiment. We go on to discuss
the mechanisms of the observed responses and, finally, incorporate what we
Ecological Studies, Vol. 137
Ferran Rodil et al. (eds) Ecology of Mediterranean
Evergreen Oak Forests
© Springer-Verlag, Berlin Heidelberg 1999
to Primary Production
Ferran Roda, Xavier Mayor, Santiago Sabate and Victoria Diego
13.1 Introduction
Primary production is typically low in holm oak (Quercus ilex L.) forests
(Chap. 3). Water availability is likely to limit primary production in most
Mediterranean terrestrial ecosystems given that summer drought is a characteristic trait of Mediterranean-type climates (di Castri 1981). Despite its
deep roots (Chap. 4) and its relative tolerance to foliar water deficits, such
water limitation also applies to holm oak (Chaps. 10 and 11).
Nutrient availability can be also involved in the low production of Mediterranean forests, either through the inherently low fertility of some soils or
through recurrent nutrient export resulting from a centuries-long history of
harvesting and fire. Nutrient limitations to plant growth are widespread in
Mediterranean-type shrublands in Australia, South Africa, and California
(Hellmers et al. 1955; Oechel et al. 1981; Specht 1981; McMaster et al. 1982;
Witkowski et al. 1990). From these and other studies, and from the general
close link between sclerophylly and oligotrophic soils (Loveless 1961), the
view emerged that low nutrient availability shaped the evolution and functioning of Mediterranean-type ecosystems (e.g. Kruger et al. 1983). However,
the soils of the Mediterranean Basin are usually more eutrophic than those of
Mediterranean-type shrublands in Australia, South Africa, and California.
Despite substantial information on nutrient distribution and cycling in
holm oak forests (Chap. 18), we did not know whether, or to what extent,
these forests were nutrient limited. We therefore conducted a fertilization
and irrigation experiment to assess (1) the relative importance of water, nitrogen, and phosphorus as limiting factors for tree growth and primary production in holm oak forests, and (2) the responses to increased resource
availability at the tree, stand, and ecosystem levels.
In this chapter, we first summarize the experiment layout, and then explore how the aboveground net primary production and its components
were affected during the first 3 years of the experiment. We go on to discuss
the mechanisms of the observed responses and, finally, incorporate what we
Ecological Studies, Vol. 137
Ferran Rodil et al. (eds) Ecology of Mediterranean
Evergreen Oak Forests
© Springer-Verlag, Berlin Heidelberg 1999