76
Daniel Siscart, Victoria Diego and Francisco Lloret
On the other hand, some studies have addressed the reverse relation, that
is, the effect of predation on the establishment of new cohorts of trees
(Matsuda 1985; Jensen and Nielsen 1986; Crawley and Long 1995). Some of
these studies suggest that tritrophic interactions, such as mammals consuming acorns infested by weevils, may also be relevant to the dynamics of
oak forests (Crawley and Long 1995). These interactions will occur over a
relatively short period of time, because the life span of acorns is short before
they decay.
At the ecosystem level, fruit production may achieve a sizeable proportion
of the annual production in temperate forests (Pregitzer and Burton 1991).
Therefore, studies on the functional performance of these ecosystems must
consider acorn production as an important component of both energy and
nutrient balances.
In this chapter, we analyze the main abiotic and biotic factors contributing
to the observed pattern of acorn production and acorn fate before germination in Catalonian holm oak ecosystems, and particularly in the Montseny
and Prades forests. Abiotic factors mainly include climatic conditions and
soil resource availabil'ity. Biotic factors include both seed infestation by insects, which can affect the development and abscission of acorns (Crawley
and Long 1995), and predation-dispersal of acorns by vertebrates, which potentially may control the recruitment of new genets both inside forests and in
adjacent open areas (Crawley 1992).
6.2 Acorn Production
6.2.1 Reproductive Biology of Holm Oak
Quercus ilex is a monoecious specit;s with unisexual inflorescences. Staminate flowers are borne in catkins. Female inflorescences have 1-8 flowers and
are borne at the top of a stalk growing from leafaxils. Pistillate flowers have
an ovary, from which only one ovule develops after fertilization (Ruperez
1957). The development of both male and female inflorescences is asynchronous in each tree. From April to June, depending on altitude, catkins develop
before pistillate inflorescences do. After fertilization by wind, acorns begin to
grow. Acorn development is very slow during summer and fruits are very
small (less than 0.5 cm width) in early September, when a fast growth period
begins. From late November to early December, acorns begin to dry and turn
brown. Mean weight of mature acorns ranges from 2 to 4 g. They drop normally from December to January, although this varies depending on altitude,
continentality of the locality, and weather conditions.
Daniel Siscart, Victoria Diego and Francisco Lloret
On the other hand, some studies have addressed the reverse relation, that
is, the effect of predation on the establishment of new cohorts of trees
(Matsuda 1985; Jensen and Nielsen 1986; Crawley and Long 1995). Some of
these studies suggest that tritrophic interactions, such as mammals consuming acorns infested by weevils, may also be relevant to the dynamics of
oak forests (Crawley and Long 1995). These interactions will occur over a
relatively short period of time, because the life span of acorns is short before
they decay.
At the ecosystem level, fruit production may achieve a sizeable proportion
of the annual production in temperate forests (Pregitzer and Burton 1991).
Therefore, studies on the functional performance of these ecosystems must
consider acorn production as an important component of both energy and
nutrient balances.
In this chapter, we analyze the main abiotic and biotic factors contributing
to the observed pattern of acorn production and acorn fate before germination in Catalonian holm oak ecosystems, and particularly in the Montseny
and Prades forests. Abiotic factors mainly include climatic conditions and
soil resource availabil'ity. Biotic factors include both seed infestation by insects, which can affect the development and abscission of acorns (Crawley
and Long 1995), and predation-dispersal of acorns by vertebrates, which potentially may control the recruitment of new genets both inside forests and in
adjacent open areas (Crawley 1992).
6.2 Acorn Production
6.2.1 Reproductive Biology of Holm Oak
Quercus ilex is a monoecious specit;s with unisexual inflorescences. Staminate flowers are borne in catkins. Female inflorescences have 1-8 flowers and
are borne at the top of a stalk growing from leafaxils. Pistillate flowers have
an ovary, from which only one ovule develops after fertilization (Ruperez
1957). The development of both male and female inflorescences is asynchronous in each tree. From April to June, depending on altitude, catkins develop
before pistillate inflorescences do. After fertilization by wind, acorns begin to
grow. Acorn development is very slow during summer and fruits are very
small (less than 0.5 cm width) in early September, when a fast growth period
begins. From late November to early December, acorns begin to dry and turn
brown. Mean weight of mature acorns ranges from 2 to 4 g. They drop normally from December to January, although this varies depending on altitude,
continentality of the locality, and weather conditions.