Establecimiento de cuatro especies de Quercus en el sur de la ...

Reforestation with Quercus ilex L. and Q. suber L. by direct seeding and planting in southern Spain
INTRODUCTION
Holm oak [Quercus ilex L. ssp ballota (Desf.)] and cork oak (Q. suber L.) are two
evergreen woody species widely represented in wild and managed forests of the
Iberian Peninsula. Also, they constitute two essential elements of the agrosylvopastoral
system known as “dehesa”. Ensuring sustainable use of natural resources
in savanna‐like ecosystems (dehesas) is of a high economic importance for rural areas.
Establishment success in Quercus species is strongly limited and their
regeneration quite difficult. The low natural regeneration ability of oaks has been
ascribed to a number of factors including acorn predation, unsuitable germination
conditions, soil impoverishment and the presence of herbivores (Watt, 1919; Leiva and
Fernandez Ales, 2005; Pulido and Díaz, 2005; Pérez‐Ramos and Marañón, 2008;). Oak
tree mortality has increased considerably over the past 20 years by effect of the
combined action of pathogens, xylophagous insects and adverse climatic conditions
(Brasier, 1996; Sanchez et al., 2002). Poor regeneration and a high adult mortality in
many areas have led to the implementation of reforestation programmes, mainly in
areas where the tree population has declined or disappeared, or the land has been
converted to agriculture, and transformation into forested areas is desirable (Costa,
2006).
Afforestation with Quercus trees is limited by their difficult natural regeneration,
and low growth and survival rates (Villar et al., 2004; Quero et al., 2008b), especially
when the first summer drought they are confronted with is very strong (Navarro‐
Cerrillo et al., 2005). In addition, Quercus seeds are recalcitrant, so they can only be
stored for a few months (Roberts, 1973; Finch‐Savage, 1992).
No consensus exists as to which is the best available reforestation method for
Quercus. Oaks have heavy seeds, so they initially have large amounts of available
resources (Quero et al., 2007; González‐Rodríguez et al., 2008b) which can be used at
an early growth stage until they can rely on photosynthesis. As a result, directly sown
Quercus seeds have high emergence likelihood (Stanturf et al., 1998).
The greatest advantage of seeding is probably its low cost relative to planting; in
fact, the latter requires nursery care and planting has higher associated costs than
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