7 Seedling Recruitment
Javier Retana, Josep Maria Espelta, Marc Gracia and Miquel Riba
7.1 Introduction
Processes operating during the seed, seedling and juvenile phases are crucial
for understanding patterns, dynamics and succession in plant communities
(Schupp 1990; Grime and Hillier 1992). Many recent studies in temperate forests have emphasized the difficulties seedlings encounter in establishing
themselves and the problems hardwood tree species face for survival, in particular the species of the genus Quercus (Lorimer 1984; Ross et al.1986; Crow
1988, 1992; Johnson 1992; Keeley 1992; Ward 1992). This apparent paradox
presented by late-successional species which, while dominant in the landscape, do not regenerate easily has long been noticed (Crow 1988), but the
reasons for this are still poorly understood. The reasons for failure to recruit
may include many factors, such as adequacy of seed dispersal (McClanahan
1986; Willson 1992), seed predation by animals (Crawley 1992), abiotic
stresses such as drought or light limitation (Pons 1992; Espelta et al. 1995),
and availability of suitable microsites for seed germination and seedling establishment (Crawley 1990). Furthermore, the regeneration failure of recent
oak forests has also been attributed to the fact that the distribution of oaks
overlaps to a large extent zones of intense human activity and thus oak forests have suffered from human impact (Matsuda et al. 1989).
Anthropogenic factors have played a major role in shaping the vegetation
structure in the Mediterranean Basin (Naveh and Lieberman 1984; Fox and
Fox 1986). There is no other region in the world where the development of
ecosystems has been so closely associated with human social systems and for
so long (Blondel and Aronson 1995). Thus, it is difficult to analyze dynamics
of Mediterranean forests, in particular holm oak (Quercus ilex L.) forests,
without taking into account disturbances produced or favoured by man.
Holm oak forests have long been severely and continuously modified by
wood cutting (coppicing for firewood or charcoal production), repeated fires,
and grazing by sheep and goats (Barberoet al. 1992). A large proportion of
these forests have been maintained as coppices, where cuttings at regular inEcological Studies, Vol. 137
Ferran Roda et al. (eds) Ecology of Mediterranean
Evergreen Oak Forests
© Springer-Verlag, Berlin Heidelberg 1999
Javier Retana, Josep Maria Espelta, Marc Gracia and Miquel Riba
7.1 Introduction
Processes operating during the seed, seedling and juvenile phases are crucial
for understanding patterns, dynamics and succession in plant communities
(Schupp 1990; Grime and Hillier 1992). Many recent studies in temperate forests have emphasized the difficulties seedlings encounter in establishing
themselves and the problems hardwood tree species face for survival, in particular the species of the genus Quercus (Lorimer 1984; Ross et al.1986; Crow
1988, 1992; Johnson 1992; Keeley 1992; Ward 1992). This apparent paradox
presented by late-successional species which, while dominant in the landscape, do not regenerate easily has long been noticed (Crow 1988), but the
reasons for this are still poorly understood. The reasons for failure to recruit
may include many factors, such as adequacy of seed dispersal (McClanahan
1986; Willson 1992), seed predation by animals (Crawley 1992), abiotic
stresses such as drought or light limitation (Pons 1992; Espelta et al. 1995),
and availability of suitable microsites for seed germination and seedling establishment (Crawley 1990). Furthermore, the regeneration failure of recent
oak forests has also been attributed to the fact that the distribution of oaks
overlaps to a large extent zones of intense human activity and thus oak forests have suffered from human impact (Matsuda et al. 1989).
Anthropogenic factors have played a major role in shaping the vegetation
structure in the Mediterranean Basin (Naveh and Lieberman 1984; Fox and
Fox 1986). There is no other region in the world where the development of
ecosystems has been so closely associated with human social systems and for
so long (Blondel and Aronson 1995). Thus, it is difficult to analyze dynamics
of Mediterranean forests, in particular holm oak (Quercus ilex L.) forests,
without taking into account disturbances produced or favoured by man.
Holm oak forests have long been severely and continuously modified by
wood cutting (coppicing for firewood or charcoal production), repeated fires,
and grazing by sheep and goats (Barberoet al. 1992). A large proportion of
these forests have been maintained as coppices, where cuttings at regular inEcological Studies, Vol. 137
Ferran Roda et al. (eds) Ecology of Mediterranean
Evergreen Oak Forests
© Springer-Verlag, Berlin Heidelberg 1999