Vegetation classification and conservation aspects of Atlantic dune pine forests in the southwest of the Iberian Peninsula

This study refines the classification framework for Portuguese dune pine forests included in the alliance Coremato albi-Pinion pinastri at the association level after the syntaxonomic revision of Mediterranean pine forests of the class Pinetea halepensis. We collected 61 original vegetation plots between 2017 and 2022 in the southwestern Iberian Peninsula, analysing them through Principal Coordinate Analysis (PCoA) and UPGMA clustering. Numerical analysis identified four associations within the alliance Coremato albi-Pinion pinastri, specific to the sandy Atlantic coast of the Iberian Peninsula. Of these, three associations are newly described (Cytiso grandiflori-Pinetum pinastri, Aristolochio baeticae-Pinetum pineae, and Ulici australis-Pinetum pineae). Our study classified pine forests on sand in southwestern Iberia and identifies conservation-significant species in their understory. The floristic diversity in these psammophilous pine forests is enhanced by numerous endemics and relic species from the Tertiary period, shaped by past climatic refugia and multiple floristic migration routes, including Atlantic, Mediterranean, and North African pathways. This has resulted in a unique blend of thermophilic, oceanic, and xeric species with high conservation value. Our study contributes to the understanding of Atlantic dune pine forest ecology and inform habitat conservation efforts.