Grass silica short cell phytoliths in Pyrenean subalpine grasslands: taxonomy and palaeoecological relevance.

Background and aims: Subalpine grasslands of the Central Pyrenees (1600-2300 m a.s.l.) are semi-natural ecosystems shaped by millennia of pastoral land use. Reconstructing their long-term dynamics requires proxies with higher taxonomic resolution than Poaceae pollen. Grass silica short cell phytoliths (GSSCPs) offer this potential. We aim to build a taxonomically broad, ecologically grounded reference collection and assess the diagnostic value of GSSCP assemblages across grass lineages and habitats.

Methods: We inventoried 251 grass species and selected 66 native taxa to maximize phylogenetic breadth (five subfamilies, 14 tribes, 49 genera) and capture pastoral relevance. Leaf phytoliths were extracted from multiple individuals per species, classified under ICPN 2.0, and counted to ≥300 GSSCPs per sample, yielding 29 sub-morphotypes. Multivariate ordinations explored taxonomic and ecological structure.

Key results: Phytolith assemblages revealed strong taxonomic signals and clear ecological patterns. In Pooideae, specific sub-morphotypes were identified in mesic subalpine pastures dominated by Avenula pratensis and Bromus spp., in open, stress-prone grasslands characterized by Stipa spp. and Achnatherum calamagrostis, and on xerophilous calcareous slopes characterized by Koeleria vallesiana. PACMAD grasses also showed strong diagnostic value: Setaria viridis in low-elevation, warm, nutrient-rich, disturbed habitats; Danthonia decumbens in acidophilous uplands; Eragrostis minor in disturbed dry soils; and Molinia caerulea in hydromorphic meadows. These taxa occur mainly in habitats warmer, drier or more disturbed than the core humid subalpine grasslands, which show more conservative profiles. Ordination analyses confirmed that morphotype-habitat associations structure assemblages along elevational gradients.

Conclusions: This first GSSC phytolithotheque for the Central Pyrenees provides an ICPN-compliant framework that enhances the taxonomic and ecological resolution of phytolith-based palaeoecology, improving reconstructions of past vegetation and pastoral dynamics in mountain landscapes.