An approach to quantitative plant–soil relationships of saltcedar woodlands throughout central and southeastern Iberian Peninsula (Spain)

Abstract

Saltcedar woodlands are plant formations dominated by several species of the genus Tamarix (Tamaricaceae), representing the potential vegetation in saline, subsaline and wet environments under dry and semi-arid conditions. The broad ecological range of Tamarix communities leads to a heterogeneous floristic composition, with significant differences among habitats in terms of soil and vegetation. Some classification systems for Tamarix communities are only based on vegetation features and do not take any quantitative soil characteristics into account. Twelve Tamarix populations were selected under different ecological environments throughout central and southeastern Iberian Peninsula (Spain). Soil samples and vegetation inventories were collected over the course of 1 year to establish the plant–soil relationships based on constrained ordination analyses. The results showed that three different edaphic gradients were relevant to define the floristic composition of the Spanish saltcedar woodlands: a sodium–moisture gradient, a sulphate–magnesium gradient and a texture gradient. On the basis of these findings, we suggest a new classification system for Tamarix woodlands for the Mediterranean area based on plant–soil relationships. Three vegetation types have been proposed: hyperhalophilous, mesohalophilous and freshwater plant communities. Hyperhalophilous plant communities were characterised by soils with high E.C., high Na+ concentration, low soil moisture and high percentage of clay, being usually dominated by T. boveana and halophytes. Mesohalophilous plant communities had soils with high E.C., high Mg2+ and SO42− concentrations and high percentage of sand, being dominated by T. gallica with mesohalophilous and nitrophilous species. Finally, freshwater plant communities typically showed low E.C., low Na+ concentration and high soil moisture, being characterised by T. gallica with riparian and nitrophilous plants. Since the studied saltcedar woodland communities are notably dependent on soil salinity and moisture, the control of the human activities and hydrological alteration should be considered as a priority to contribute to the global preservation of the Tamarix woodlands.