Diversity of maritime juniper woodlands

Abstract

Plant composition and diversity of Juniperus oxycedrus subsp. macrocarpa woodlands were studied along the southwestern coast of Spain, including juniper communities on sand dunes, cliffs, and as understorey of pine plantations. Cliffs showed significantly higher richness and diversity values than dunes and pine plantations, while those in dunes and pine plantations were the same. Juniper woodlands on dune systems have a lower diversity of woody species due to the harsher environmental factors such as salt spray and sand mobility, showing their dominance–diversity curves geometric patterns. On the cliffs, the environmental stress promoted by the salt spray is reduced by the elevation of the coast, and plant species composition is mainly controlled by lithology and climate. Juniper communities on cliffs had higher diversity values, and dominance–diversity curves followed log normal patterns. Coastal Pinus pinea plantations tend to attenuate the effect of the harsh maritime physical environmental factors, causing the disappearance of endemic juniper woodland vegetation and by promoting the establishment of landward species, which change the structure and composition of these plant communities. Diversity values correlated with the management of both, the pine trees and the understorey. Where pine trees are managed and maritime juniper is favoured over other woody species as understorey, the diversity was high and the dominance–diversity curve showed a log normal distribution. However, removal of the understorey by management for wood production and a later abandonment of the exploitation has resulted in higher densities of small pine trees which produce low diversity and geometric distributions in dominance–diversity curves. Given that J. oxycedrus subsp. macrocarpa woodlands is an endangered community, its conservation in southwest Spain is a priority. For the conservation of this community to be successful it would be necessary to restore this locally endemic community from abandoned coastal pine plantations. Results of this study show that juniper woodlands on the coastal dunes represent natural reference communities for planning the restoration of the original vegetation found in abandoned coastal pine plantations.