Euro-limpacs Deliverables

ABSTRACT - DELIVERABLE 83

Report on plant functional groups and plant assemblages in response to change in environmental drivers (hydrology, nutrient, land use)

This report aims to analyse habitat dynamics due to land abandonment in the Atlantic European Wet grasslands as a result of predicted of global change. Changes were analysed as a nearly in natura experiment in relation with hydrology, nutrient (oligo− vs meso−trophic conditions) and land use. Climate change probably will accentuate land abandonment as agricultural phenomenon especially in wet meadows. The targeted study area in west of Brittany were ground water discharge ones and river marginal wetlands both characterised by oligo−mesotrophic wet meadows dominated by sharp−flowered rush (Juncus acutiflorus). 118 sites (relevés) were sampled during 1974−1977 and 2003−2004 periods using paired−site sampling approach. Methods used were phytosociological table analysis and multidimensional analysis (DCA, CCA and PCA). Environmental variables retained for direct gradient analyses are Ellenberg Community (relevé) Indicator Values (E−CIVs) derived from species values (E−SIVs) for moisture (F), Nitrogen (N) and Reaction (or pH R), species traits to identify plant functional types (PFTs) and functional vegetation types (FVTs) and diversity indices. Identified plant assemblages (or syntaxa) from DCA, phytosociological analyses and direct gradient analyses allow detection of multi−species responses along environmental gradients in synthetic ways and operational context for describing vegetation. Various dynamics trajectories were identified, all different from wooded plants re−growth or afforestation that is generally the expected change following land abandonment. In areas with poor nutrient content and ground water recharge and/or fluctuation Molinia caerulea grassland is a medium term change followed later by a Myrica scrub. The 2nd trend is a development of Filipendula stand which occurs in hydro−morphic units defined by spring overland flow and spring ground water discharge from adjacent areas. In permanent or high ground water discharge areas (gentle slope or depression) Carex paniculata tussocks establishment as a 3rd trajectory, occurs in mesotrophic conditions. A 4th trajectory is represented by Potentilla palustris raft as pioneer communities that are built in flood plains or slight depressions, with long duration of surface water retention. Land use change affects both hydrological processes (increasing overland flows and nearly standing water) and nutrients processes (meso−oligotrophy). A decrease of global species richness at habitat scale (a diversity) might be compensated by a slight increase at site (e.g; head catchment) scale (ß diversity). A particular attention should be paid to oligotrophic species that, in some cases, are rare or threatened in most areas in Europe.

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