Biodiversity of woody species in oak woodlands of southern Spain and northern Morocco T. Maran Äo Ân a,* , R. Ajbilou a , F. Ojeda b , J. Arroyo b a IRNA, CSIC, PO Box 1052, 41080 Seville, Spain b Departamento de Biologõ Âa Vegetal y Ecologõ Âa, Universidad de Sevilla, Apartado 1095, 41080 Sevilla, Spain Abstract Three biodiversity parameters ± species richness, endemic species richness and taxonomic singularity ± have been evaluated for the woody understorey of oak woodlands on sandstone-derived substrates, on both sides of the Strait of Gibraltar. There is a similarity in ¯oristic composition and ecological distribution of woody plant communities across the Strait. Nevertheless, we have detected signi®cant differences. These include a general reduction in species richness, number of endemic species and taxonomic singularity (at the community level), and a greater abundance of widespread, generalist species, on the southern side (Moroccan) communities, as compared to the north (Spanish ones). We interpret these differences as partly caused by the contrasting management of woodlands, with higher slashing and browsing pressure in Morocco. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Cork oak; Diversity; Mediterranean woodlands; Quercus; Strait of Gibraltar; Species richness 1. Introduction Woodland areas in the Mediterranean Basin have been much reduced during historical times. Thirgood (1981) points out six major agents of deforestation: climatic change; agricultural clearance; exploitation for timber and fuel; wars and invasions; ®re; and grazing. Present-day woodlands thus tend to occupy rough, little-fertile mountains (Maran Äo Ân and Ojeda, 1998); although their area size is relatively stable or even expanding, their biodiversity may be currently diminishing by exploitation of their resources. There is a lack of knowledge about the evaluation of Med- iterranean woodland biodiversity and how it is affected by management practices. The Strait of Gibraltar, 14 km wide at its narrowest point, separates two sub-areas of the same, Betico- Rifean ¯oristic region (Valde Âs, 1991). This region is characterised by a high plant diversity at various levels (Arroyo, 1997), and is considered as one of the ten `hot-spots' of plant biodiversity within the Mediter- ranean Basin (Me Âdail and Que Âzel, 1997). The use of the woodland resources is different on each side of the Strait, because of the contrasting socio-economical conditions (Deil, 1990). This situation offers a good opportunity to study the effects of management on woodland biodiversity. In this paper, we compile a data set of woody community samples in the understorey of oak wood- lands in southern Spain and northern Morocco. We Forest Ecology and Management 115 (1999) 147±156 *Corresponding author. Tel.: +345 462 4711; fax: +345 462 4002; e-mail: teodoro@irnase.csic.es 0378-1127/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S0378-1127(98)00395-8