Richard L. Hewison

Explaining the variation in the soil microbial community: do vegetation composition and soil chemistry explain the same or different parts of the microbial variation?

AimTo assess whether vegetation composition and soil chemistry explain the same or different parts of the variation in the soil microbial community (SMC).MethodThe above and below-ground communities and soil chemical properties were studied along a successional gradient from moorland to deciduous woodland. The SMC was assessed using PLFAs and M-TRFLPs. Using variance partitioning, Co-Correspondence Analysis (CoCA) and Canonical Correspondence Analysis (CCA), the variation (total inertia) in the SMC was partitioned into variation which was uniquely explained by either plant composition or soil chemistry, variation explained by both soil chemistry and plant composition, and unexplained variation.ResultsPlant community composition uniquely explained 30, 13, 16 and 20% of the inertia and soil chemistry uniquely explained 5, 18, 9 and 9% of the inertia in the archaeal TRFLPs, bacterial TRFLPs, fungal TRFLPs and all PLFAs, respectively.ConclusionFor the first time, variance partitioning was used to include data from a CoCA; although the current limits of such an approach are shown, this study illustrates the potential of such analyses and shows that soil chemistry and plant composition are, in substantial amounts, explaining different parts of the variation within the SMC. This marks an important step in furthering our understanding of the relative importance of different drivers of change in the SMC.

Drivers of species richness and compositional change in Scottish coastal vegetation

Question What are the main drivers of vegetation change within coastal dune and machair habitats and are these amenable to action to protect biodiversity at a local and national scale? Location Coastal areas of Scotland. Methods A national-scale, quadrat-based re-visitation survey was used to assess where changes were occurring in terms of species richness and composition. Regression trees and linear mixed modelling were used to identify the main drivers of change between 1976 and 2010. Results There were losses of habitat to erosion (4.7% of previously visited quadrats) and development (2.3%). Species richness changes were largely positive where sand dune and machair habitats remain part of an agricultural management system in the Inner and southern part of the Outer Hebrides. Richness losses were driven by acidic deposition and reduced grazing. Compositional changes were less related to agricultural changes, climate change and pollutant deposition than species richness changes. Conclusions Reintroduction of grazing to coastal areas appears to be a policy that would have positive effects on biodiversity, as would continued efforts to reduce atmospheric deposition and coastal planning that allowed for realignment as sediment supply decreases and sea level rise continues.

Potential impacts of the loss of Fraxinus excelsior (Oleaceae) due to ash dieback on woodland vegetation in Great Britain

The non-native fungus Hymenoscyphus fraxineus which causes ash dieback is now established across much of Europe including the UK. The disease may potentially kill large numbers of Fraxinus excelsior (ash) trees in infected areas. Ash woods tend to be relatively rich in vascular plants and the composition of the flora might be expected to change if F. excelsior is lost and the environmental conditions (levels of shading, nutrient addition/recycling) change. We explore this possible scenario for the UK, using the floristic tables from the UK National Vegetation Classification (NVC) to identify for analysis eight ash-constant woodland types (where F. excelsior is a constant species) and four woodland types where F. excelsior is a frequent species. From these 12 communities, we identify 58 ground flora species that may be described as being ash woodland-associated species, including five species with some level of conservation protection. Changes in the ground flora are likely to be driven initially by increased light due to the opening up of the canopy as F. excelsior is lost, followed by increases in the shrub layer and eventually a closing of the canopy by other tree species. Using existing knowledge of plant species traits and habitat preferences (regeneration strategies, Ellenberg light values and Grime CSR scores) and community composition from NVC tables, we predict how the vascular plant community of ash-woodlands may change over time if F. excelsior is lost. We show that ash dieback could drive substantial changes in the ground flora community composition of currently ash-dominated woodlands.

Decline in atmospheric sulphur deposition and changes in climate are the major drivers of long-term change in grassland plant communities in Scotland

The predicted long lag time between a decrease in atmospheric deposition and a measured response in vegetation has generally excluded the investigation of vegetation recovery from the impacts of atmospheric deposition. However, policy-makers require such evidence to assess whether policy decisions to reduce emissions will have a positive impact on habitats. Here we have shown that 40 years after the peak of SOx emissions, decreases in SOx are related to significant changes in species richness and cover in Scottish Calcareous, Mestrophic, Nardus and Wet grasslands. Using a survey of vegetation plots across Scotland, first carried out between 1958 and 1987 and resurveyed between 2012 and 2014, we test whether temporal changes in species richness and cover of bryophytes, Cyperaceae, forbs, Poaceae, and Juncaceae can be explained by changes in sulphur and nitrogen deposition, climate and/or grazing intensity, and whether these patterns differ between six grassland habitats: Acid, Calcareous, Lolium, Nardus, Mesotrophic and Wet grasslands. The results indicate that Calcareous, Mesotrophic, Nardus and Wet grasslands in Scotland are starting to recover from the UK peak of SOx deposition in the 1970s. A decline in the cover of grasses, an increase in cover of bryophytes and forbs and the development of a more diverse sward (a reversal of the impacts of increased SOx) was related to decreased SOx deposition. However there was no evidence of a recovery from SOx deposition in the Acid or Lolium grasslands. Despite a decline in NOx deposition between the two surveys we found no evidence of a reversal of the impacts of increased N deposition. The climate also changed significantly between the two surveys, becoming warmer and wetter. This change in climate was related to significant changes in both the cover and species richness of bryophytes, Cyperaceae, forbs, Poaceae and Juncaceae but the changes differed between habitats.