Multivariate identification of plant functional response and effect traits in an agricultural landscape

Plant functional traits have been proposed as a linkage between the environmental control of vegetation and ecosystem function. Identification of traits that mediate the response of plant species to the environment is well established, but the identification of effect traits and the linkage between the two sets is less developed. This was attempted for a study of eight contrasting land uses in a marginal agricultural landscape where data on vegetation, management controls of the disturbance regime, and soil characteristics, including nitrogen release, were measured simultaneously with measures of ecosystem function such as litter decomposition rates and primary productivity on 30 sites. Trait data were assembled from databases, and an iterative multivariate approach using the three table (species, trait, environment) method RLQ was employed to identify a parsimonious set of traits that predict plant species responses to the environment and a parsimonious set of traits that link vegetation to ecosystem function. The lists of response and effect traits were similar, and where differences were observed, traits were usually highly correlated with at least one trait in the other list. This approach identified a small number of traits (canopy height, leaf dry matter content, leaf size, and specific leaf area) that provide a means of linking vegetation responses to environmental change with changes in ecosystem function. Other response traits included vegetative spread strategy, start of flowering, and seed terminal velocity, but within the system studied these traits were all significantly correlated to the traits shared between the response and effect lists.     

The effects of tropospheric ozone on the species dynamics of calcareous grassland

Although ozone has been shown to reduce the growth of individual species and to alter the composition of simple species mixtures, there is little understanding of its long-term effects on species dynamics and composition in real communities. Intact turfs of calcareous grassland were exposed to four different ozone regimes in open-top chambers over three consecutive summers. Treatments provided a mean seasonal AOT40 ranging from approximately zero to 15 ppm h. Cumulative ozone exposure was a significant factor in compositional change, but only explained 4.6% of the variation. The dominant grass species (Festuca rubra) showed a consistent decline in cover in the high ozone treatment over time and the forb Campanula rotundifolia was lost from all three ozone treatments. The frequency of some species (Galium verum and Plantago lanceolata) increased with ozone exposure. Long-term effects of ozone on species composition in chalk grassland may be a function of both the sensitivity of individual species and the response of the dominant species.     

Competing conservation goals, biodiversity or ecosystem services: element losses and species recruitment in a managed moorland-bracken model system

Conservation management in Europe is often geared towards restoring semi-natural ecosystems, where the objective is to reverse succession and re-establish early-successional communities, to comply with national and international conservation targets. At the same time, it is increasingly recognised that ecosystems provide services that contribute to other, possibly conflicting policy requirements. Few attempts have been made to define these conflicts. Here, we assess some potential conflicts using a Calluna vulgaris-dominated moorland invaded by bracken (Pteridium aquilinum) as a model system, where the current policy is to reverse this process and restore moorland. We examined impacts of bracken control treatments on services (stocks and losses of C and mineral nutrients), litter turnover and biodiversity within a designed experiment over 7 years. Bracken litter was >2000 g m(-2) in untreated plots, and treatments reduced this quantity, and its element content, to varying degrees. Cutting twice per year was the most successful treatment in reducing bracken litter and its element content, increasing litter turnover, and increasing both mass and diversity of non-bracken vegetation. Diversity was greatest where bracken litter had been reduced, but species composition was also influenced by light sheep grazing. There was a significant loss of some chemical elements from bracken that could not be accounted for in other pools, and hence potentially lost from the system. In absolute terms large amounts of C and N were lost, but when expressed as a percentage of the total amount in the system, Mg was potentially more important with losses of almost a third of the Mg in the surface soil-vegetation system. There is, therefore, a potential dilemma between controlling a mid-successional invasive species for conservation policy objectives, especially when that species has evolved to sequester nutrients, and the negative effect of increasing environmental costs in terms of carbon accounting required, the potential input of nutrients to aquatic systems, and long-term nutrient loss. There is, therefore, a need to balance conservation goals against potential damage to biogeochemical structure and function.     

Assessing the relation between the distribution of salt-marsh communities and the sediment budget of the North Norfolk coast

Very high resolution imagery from an airborne multi-spectrål scanner has been used to estimate the distribution of different salt-marsh communities along a 30-km stretch of the North Norfolk coast. Field observations have been used to develop a mathematical relationship between the vegetation, physical environment and sediment accumulation. This relationship has been used to produce provisional sediment accretion maps for the north Norfolk coast.     

Heathland Seedbanks under BrackenPteridium aquilinum(L.) Kuhn and their Importance for Re-vegetation after Bracken Control

In Great Britain, the regeneration of heathland and moorland plant communities after bracken control is slow and variable. Successful restoration depends on the availability of seed and the provision of suitable regeneration niches, as well as on the expansion of the plants previously present underneath the bracken canopy. This study investigates the availability of the seed resource of heathland species and its distribution, both in relation to increasing time since bracken invasion and with respect to its presence in litter or mineral soil.Calluna vulgariswas found to be the predominant species that germinated from the soil and litter beneath bracken at the sites studied. It appeared in greatest numbers from samples taken outside and at the edge of the bracken patch; numbers decreased deeper into the patch. Land which has been under bracken for a considerable period (>50 years) is likely to have a very reduced seedbank so that some form of propagule introduction, as well as litter disturbance, may be needed to speed up regeneration. On sites which have been invaded by bracken more recently, it is likely that litter incorporation into the soil would conserve the seed resource, whereas burning or litter removal would remove a significant proportion of that seed resource.