Experimental management of Mediterranean temporary pools for conservation of the rare quillwort Isoetes setacea M. Rhazi a,b , P. Grillas a, * , A. Charpentier a , F. M edail b a Station biologique de la Tour du Valat 13200, le Sambuc, Arles, France b Institut M editerran een dÕEcologie et de Pal eo ecologie (IMEP, CNRS UMR 6116), Universit e dÕAix Marseille III, Facult e des Sciences et Techniques Saint J er^ ome, 13397 Marseille Cedex 20, France Received 10 February 2003; accepted 21 October 2003 Abstract Mediterranean temporary pools represent unique species-rich habitats with many rare and endangered species. The Roque-Haute Natural Reserve is one of the few sites in France with Isoetes setacea Lam., a very rare Mediterranean quillwort, considered as a keystone species determining a priority habitat for the European Union. Land uses changes have favoured the invasion of the pools by several shrub and tree species (e.g., Ulmus minor, Fraxinus angustifolia subsp. oxycarpa). Clearing shrubs in an experimental area of one pool resulted in the increase of I. setacea as compared to control, combining a higher cover in previously occupied quadrats and more quadrats occupied. Litter accumulation had a negative effect on the population of Isoetes but this effect was detectable only in the cleared area. Light attenuation was shown experimentally to be detrimental to the vegetative and regenerative production of I. setacea. Clearing of the shrubs and removal of the litter led to an increase in the I. setacea populations and therefore appears to be an effective technique for restoring these plant communities invaded by shrubs. Long-term shrub control should be ensured by reintroducing sheep grazing in order to enhance the sustainable conservation of this oligotrophic habitat. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Mediterranean seasonal pools; Isoetes setacea; Grazing; Litter effect; Light reduction; Endangered species; Spore-bank; Artificial shading; Vegetative growth; Sexual reproduction 1. Introduction Temporary oligotrophic pools are particularly spe- cies-rich habitats, found in most Mediterranean and dry regions of the world (e.g., Braun Blanquet, 1936; Bliss et al., 1998). In these habitats, species of plants, inver- tebrates and amphibians have adapted to the harsh conditions imposed by their drying up in summer, inter- annual fluctuations in hydrology and the paucity of nutritive elements (e.g., plants: Qu ezel, 1998; amphibi- ans: Jacob et al., 1998; and invertebrates: Williams, 1987). There are convergences between the floras of these temporary oligotrophic habitats in all five conti- nents, with vascular cryptogams playing a major role, in particular the genera Isoetes, Marsilea, and Pilularia (Qu ezel, 1998). These Mediterranean temporary pools are of major conservation importance, being considered as priority habitat in the European Union Habitats Directive 92/43/EEC (e.g., Gaudillat et al., 2002), be- cause they shelter many rare and endangered species. In the Mediterranean region the temporary pools have been considerably degraded by diverse disturbances. Apart from direct destruction, which is common all over the region, there are noticeable differences in the causes of this degradation between the southern and northern parts of the Mediterranean. With increasing human pressure, the principal causes of degradation in north African countries are hydrological alterations, extraction of ma- terials, crop cultivation and overgrazing (Rhazi et al., 2001). In southern Europe, the abandoning of extensive agricultural practices leads to a degradation of temporary Mediterranean pools through the establishment of eco- logical succession processes and other consequences such Biological Conservation 118 (2004) 675–684 www.elsevier.com/locate/biocon BIOLOGICAL CONSERVATION * Corresponding author. Fax: +33-4909-72019. E-mail address: grillas@tourduvalat.org (P. Grillas). 0006-3207/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.biocon.2003.10.016