Identifying drivers of species compositional change in a semi-natural upland grassland over a 40-year period

Abstract

Question: Few long-term studies exist with integrated vegetation and soil omposition data, coupled with detailed environmental driver records. Can hanges in community composition in an upland grassland be identified by evisitation after a 40-year period and allow the main environmental drivers of hange to be identified? Location: Snowdon, Wales, UK. Methods: Changes in plant community and soil composition were assessed by esurveying an upland Agrostis–Festuca grassland in 2008, 40 years after the oiginal survey. PCA and ecological indicators were used to determine changes i plant community composition. Redundancy analysis (RDA) allowed the mpact of soil chemical composition on the vegetation community to be assessed. Results: A significant shift in community composition was found between ears. A 35% reduction in species richness and an increase in the grass:forb ratio, suggest significant ecosystem degradation. Indicator values suggest acidification of the community with an increased acidity preference of species recorded in 2008. However, soil pH measurements showed that soil pH had increased. RDA suggested that the main shifts in species composition were correlated with an increase in pH and a reduction in soil exchangeable base cation concentration. Clear ecosystem responses to climate, land-use change or nitrogen enrichment were not observed. Conclusions: Shifts in vegetation and soil composition are clearly identifiable after 40 years. The shifts in community composition are consistent with ecosystem degradation due to acidification during the period between surveys. Ecological indicator values and soil chemical composition displayed differing degrees of change. Whilst soils appear to be recovering from historic effects of sulphur deposition, vegetation community composition changes appear to lag behind those in soil chemistry