Plant Biosystems, Vol. 143, Supplement, 2009, pp. S113–125 ISSN 1126-3504 print/ISSN 1724-5575 online © 2009 Società Botanica Italiana DOI: 10.1080/11263500903220224 BRYOPHYTE DIVERSITY & CONSERVATION Epiphytic bryophyte flora in dry environments from the Western Mediterranean: The special case of Sierra Alhamilla (Almería, South- eastern Spain) V. MAZIMPAKA 1 , N. G. MEDINA 1 , I. DRAPER 2 , & F. LARA 1 1 Departamento de Biología (Botánica), Universidad Autónoma de Madrid, Spain and 2 Departamento de Biología Vegetal, Universidad de Murcia, Spain Taylor and Francis Abstract In dry Mediterranean environments, the epiphytic habitats are generally poor in bryophytes. However, Sierra Alhamilla, a mountain embedded in one of the driest areas in Europe, is an exception. It shelters an evergreen oak wood, whose richness in epiphyte bryophytes is similar to or higher than that of humid mountain ranges from the Iberian Peninsula and North Africa. The genus Orthotrichum, besides dominating the epiphyte communities on tree trunks and bases, is the most diverse group (45% of the catalogue), and comprises a bulk of species (e.g., Orthotrichum scanicum, Orthotrichum ibericum, Orthotrichum speciosum var. brevisetum) that makes this site especially original. The profiles of the recorded bryoflora (dominance of Orthotrichaceae and Pottiaceae, prevalence of cushions and short turfs and high similarity of tree base and trunk bryophyte communities) indicate an epiphytic bryoflora mainly conditioned by the dry climate. However, the species richness and the biogeographical profile (e.g., dominance of temperate element and occurrence of species that have mesic affinities), together with the altitude influence on structure and composition of bryophyte communities, suggest the existence of microclimatic factors that soften the environmental aridity. This softening effect could be more important at higher altitudes, which are floristically richer than the lower ones. Keywords: Mosses, liverworts, epiphytes, arid environments, life forms, Iberian Peninsula Introduction Several abiotic and biotic factors direct or indirectly affect the epiphytic habitat, and influence its coloni- zation by epiphyte cryptogams (Barkman 1958). Some of these factors are related to the physical envi- ronment, whereas others are linked to biological inter- actions among the epiphytes themselves. Although these factors act simultaneously in a complex net of reciprocal interactions, climate exerts a dominant influence (Barkman 1958). On one side, it determines the phorophyte type and its development. On the other side, it directly or indirectly influences the water balance, which is a critical factor for epiphyte cryp- togams. Due to their poikilohydric character, these organisms are sensitive to environmental moisture or dryness conditions, especially when living on a hard and vertical substratum like the tree bark. In Mediterranean environments, available data suggest that climate greatly influences species richness and diversity of epiphytic communities, as well as the distribution of epiphyte taxa (Lara 1995; Lara & Mazimpaka 2001; Mazimpaka et al. 2004; Draper et al. 2006). In areas subject to humid or sub-humid climate (with precipitation above 600 mm), the epiphytic cover of trunks is dense and the taxonomical diversity is high. This has been observed in the north-western Iberian Peninsula (Albertos et al. 2005), in the Moroccan Rif (Draper et al. 2003, 2005), and in northern Tunisia (Draper et al. 2008). When mean annual precipitation falls below 600 mm and the summer drought turns heavier, the epiphytic cover also falls and is reduced to a small number of xerophytic species (Draper et al. 2006, 2007). In arid or semi-arid environments (below 400 mm of precipitation), there are usually no epiphytes, or those present correspond to sparse small cushions of the xerophyte Orthotrichum diapha- num on tree bases or lower part of tree trunks. Correspondence: V. Mazimpaka, Facultad de Ciencias, Departamento de Biología (Botánica), Universidad Autónoma de Madrid, C/Darwin 2, Campus de Cantoblanco, Madrid E-28049, Spain. Tel: +34914978104. Fax: +34914978344. Email: vicente.mazimpaka@uam.es