Plant Biosystems, Vol. 143, Supplement, 2009, pp. S113–125
BRYOPHYTE DIVERSITY & CONSERVATION
Epiphytic bryophyte flora in dry environments from the Western Mediterranean: The special case of Sierra Alhamilla (Almería, Southeastern Spain)
V. MAZIMPAKA1, N. G. MEDINA1, I. DRAPER2, & F. LARA1 1
Departamento de Biología (Botánica), Universidad Autónoma de Madrid, Spain and 2Departamento 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 colonization by epiphyte cryptogams (Barkman 1958). Some of these factors are related to the physical environment, whereas others are linked to biological interactions 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 cryptogams. 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 diaphanum 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:
[email protected] ISSN 1126-3504 print/ISSN 1724-5575 online © 2009 Società Botanica Italiana DOI: 10.1080/11263500903220224
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However, this general trend is sometimes broken. In some situations, microclimatic factors linked to topographic conditions allow the establishment of a rich epiphytic stratum. This is the case of Sierra Alhamilla, a mountain located in south-eastern Spain, whose epiphytic bryophyte flora and communities are here studied in order to approach the understanding of this phenomenon. For this purpose, epiphytic bryophyte diversity, ecological and chorological characteristics, as well as the influence of the altitude on the composition of the epiphytic bryophyte stratum are analysed. Study area Sierra Alhamilla is located in the extreme southeastern Iberian Peninsula (Figure 1), between the coordinates 36°59′/37°01′ N and 2°13′/2°23′ W, within the group of mountains that constitute the eastern border of the Betic Cordillera. It is a compact, south-western–north-eastern oriented massif that arises from the soft terrains of Tabernas Desert on the northern side and Campos de Níjar on the south, near the Mediterranean coast of Cabo de Gata. Whereas the southern faces and spurs of this mountain are softly inclined, those of the northern side are sharp and sometimes inaccessible, ranging from 700 m to almost 1300 m a.s.l. Figure 1. Localization of the study area.
Figure 1. Localization of the study area.
As for the climate, Sierra Alhamilla is embedded in one of the most arid areas in Europe: annual precipitation averages below 200 mm at lower altitudes, and ca. 430 mm at the top of Sierra Alhamilla (Colativí Meteorological Station), whereas mean annual temperature ranges from 16°C at lower altitudes to 12°C in upper mountain areas. Rainfall is very irregular and, in most years, there are no records of precipitations during 7–10 months. The ombrothermic diagram (Figure 2) shows a deep summer drought combined with high temperatures. According to Rivas-Martínez (1987), three bioclimatic belts can be recognized in the area: the thermo-Mediterranean (lower altitudes up to 700 m), the meso-Mediterranean (median altitudes from 700 to 1000 m), and the supra-Mediterranean (altitudes above 1100 m). In thermo-Mediterranean areas, the potential vegetation is a mosaic of xerophytic shrubby formations dominated by Quercus coccifera L. These areas have been subject to a strong human pressure and only few remains of natural vegetation nowadays subsist. At higher altitudes (meso- and supra-Mediterranean belts), the potential vegetation corresponds to an evergreen oak wood of Quercus ilex subsp. ballota (Desf.) Samp. Human activities (cattle, coaling, conifers reforestation, etc.) have drastically reduced the extension of the oak wood which, however, keeps a
Epiphytic bryophyte flora in Sierra Alhamilla
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Figure 2. Ombrothermic diagram of Iniesta summit in Sierra Alhamilla. P: annual average precipitation and T: annual average temperature.
valuable representation in some areas on the northern face of Sierra Alhamilla. Figure 2. Ombrothermic diagram of Iniesta summit in Sierra Alhamilla. P: annual average precipitation and T: annual average temperature.
Materials and methods Field work was carried out in the course of three prospecting visits to the best preserved areas of Sierra Alhamilla oak wood, on the northern face of the Sierra, between 800 and 1300 m a.s.l. Samples of 400 cm2 in flexible quadrates were taken from tree trunks (between 1 and 3 m above ground) and bases (below 1 m) in six localities at different altitudes (Table I). All tree types were prospected, but only oak trees had bryophytes. A total of 231 bryophyte samples were collected. Tree diameter was measured, and bryophyte cover on each quadrate was estimated before taking off the samples. Relative abundance of taxa was expressed by the Index of Ecological Significance (IES; Lara & Mazimpaka 1998; Albertos et al. 2001), whose mathematical expression is as follows: IES = F (1 + C) or IES = ( x + ∑ ci )
100 n
where F (relative frequency of the taxon considered) = 100x/n and C (mean cover of the taxon) = Σ ci/x. In all cases, n is the total number of considered samples, x is the number of the samples containing the species considered, and ci the cover class of the taxon, established in accordance with the following cover percentages of the species in the corresponding sample: 0.5(
