Biotopes with extreme environmental conditions, such as beaches and coastal dunes, suffer a high environmental stress, and biological adaptations of plants are dictated by environmental factors. The proximity to the sea, the influence of salted marine spray, the psophile susbtrato (from mobile to semi-fixed sands), and climatic factors such as temperature and geomorphology, determine a high specialization and fidelity of plants. When the balance between erosion and accretion in the sandy coasts is balanced, the plant communities are distributed in well-defined bands and with clear transitions, which are succeeded according to the sea clearance. Thus, there are plants characteristic of the high beach, embryonic dunes, primary dunes, interdunares corridors, secondary dunes and finally, tertiary dunes, which usually exist only in this type of habitats (likewise, only these plants occur in these places, usually being the presence of more conspicuous species, caused by a disturbance, usually of anthropic origin).
In geomorphological terms, the closer to the sea, the more mobile the sands will be, gradually decreasing inland. However, in situations of erosion of the beaches and advance of the sea, the sands of the beach and the primary dune tend to recede, and with them, some of the plants characteristic of these sectors, whose biological specificities allow it, since they are colonizing plants, adapted to the mobility and instability of the substrate and with tolerance to burial. Since the reaction capacity of plants in the less mobile interior sectors is lower due to their biological types, the species from the sectors near the sea end up overlapping and mixing with them. Thus, plants characteristic of the high beach and primary dunes, when found in more indented sectors of the coastal dunes and mixed with the typical vegetation of these sectors, constitute very reliable bioindicators of coastal erosion.
This is the case of polygonum maritimum L., which we present this week, photographed at São Torpes Beach (Sines), whose sand has been gradually decreasing for some years, causing in some places, the vegetation of various sectors, is currently constrained and mixed in a small area!