Abstract
Plant and soil landscapes across bioclimatic belts and drainage basins were studied using
georeferenced databases in arid lands of SE Spain, the driest area of Europe. The syntaxonomic
system was used to analyze phytocenoses and bioclimatic belts, as well as the concept of potential
natural vegetation (PNV), a common approach in many countries of continental Europe. Soil types
included in pedological databases were classified using the World Reference Base for Soil Resources
international system (FAO 1998). Both bioclimatic belts and drainage basins effectively discriminate
soil and plant assemblages in the study area of the Almeria province. The syntaxonomic perspective
permits distinguishing between PNV dependent on (i) climate (climatophylous), (ii) climate and
lithology, and (iii) soils (edaphophylous). Richness-area relationships of plant and soil assemblages fit
well to power law distributions, showing few idiosyncratic differences. PNV, lithological associations,
and soil richness are clearly correlated with the area of each climatic belt and watershed. PNV and
pedotaxa richness (understood as a number of taxa at a given hierarchical level) increases from the
mountain tops to the coastal lands. Around 59% of the PNV units are edaphophylous and 87% of
these are edaphohygrophylous that require water supply or tolerate water excess in riverbed ramblas
(dry watercourses). Edaphohygrophylous PNV are distributed in small patches within a very arid
matrix. They can be considered as plant “biodiversity islands”, a concept different from that of “fertility
islands” used by ecologists in arid land studies. The spatial dispersion of these phytocenoses prevents
adequate preservation in the frame of conservation biology policies. At landscape level, the extent of
plant communities is as follows: PNV climate dependent > PNV climate-lithology dependent > PNV
soil dependent. The diversity of plant communities follows an opposite trend: PNV soil dependent > PNV climate-lithology dependent > PNV climate dependent. The PNV most conditioned by soil
properties are located along the streambeds of ramblas. These fluvial sediments are not reported as
soil materials in soil maps. PNV, soils and lithological associations by drainage basins conform to the
predictions of the statistical tool termed nested subsets theory. However, lithological associations by
climatic belts depart from this spatial pattern.
