Ruth J. Mitchell

Species richness of lichen functional groups in relation to land use intensity

Changing land use has a major impact on lichen diversity. This study attempts to identify patterns or trends of lichen functional groups along a land use gradient, ranging from natural forests to open agricultural landscape. In eight countries, covering six main European biogeographic regions, lichen vegetation was assessed according to a standardized scheme. Data on reproductive, vegetative and ecological traits was compiled and relative species richness for all classes of all traits calculated. Relationships between the land use gradient and relative species richness of trait classes were analysed. Open and intensively managed landscapes harbour more fertile species while sterile species are relatively more important in forests. This finding is also supported by analyses of different classes of dispersal propagules. The importance of species with the principal photobiont Trebouxia s.l. increases linearly with intensification of land use. A converse pattern is revealed by species with Trentepohlia. Concerning substratum specialization only generalists show an effect along the land use intensity gradient. Their relative species richness decreases from landscapes dominated by forests to open agricultural landscape. A considerable decline in the rare lichen species richness as a result of land intensification is predicted.

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.

Variation of lichen communities with landuse in Aberdeenshire, UK

The distribution of lichen species in upland regions of Aberdeenshire, Scotland, is investigated along a landuse gradient from natural forest to intensive agriculture. Quantitative data on lichen communities on saxicolous, epiphytic and terricolous substrata were collected from 16 hectares in one km 2 in each landuse type. Multivariate analyses, NMDS and Cluster analysis were used to identify lichen communities associated with environmental factors including landuse, substratum type and age. The epiphytic community of native pinewoods was distinguished from all others by the highest species richness, the presence of indicators of ecological continuity and the absence of nitrophytes, while the epiphytic communities of farmland were distinguished by absence of acidophytes and a high contribution of nitrophytes. Plantations of conifers were distinguished by low species richness and an increase in tolerant species. Saxicolous communities were frequent on walls in all sites except native pinewood, where saxicolous substrata were rare. Intensively farmed sites were distinguished by an increase in percentage contribution of nitrophytes. The high acidophyte contribution in all sites suggests that crustose species of acid rocks may not respond rapidly to an increase in applied nitrogen. In landscapes where tree cover is sparse or non-existent combined assessment of habitat diversity and nitrophyte indicator species can be used to assess changes associated with agricultural intensification.

Much beyond Mantel: Bringing Procrustes Association Metric to the Plant and Soil Ecologist’s Toolbox

The correlation of multivariate data is a common task in investigations of soil biology and in ecology in general. Procrustes analysis and the Mantel test are two approaches that often meet this objective and are considered analogous in many situations especially when used as a statistical test to assess the statistical significance between multivariate data tables. Here we call the attention of ecologists to the advantages of a less familiar application of the Procrustean framework, namely the Procrustean association metric (a vector of Procrustean residuals). These residuals represent differences in fit between multivariate data tables regarding homologous observations (e.g., sampling sites) that can be used to estimate local levels of association (e.g., some groups of sites are more similar in their association between biotic and environmental features than other groups of sites). Given that in the Mantel framework, multivariate information is translated into a pairwise distance matrix, we lose the ability to contrast homologous data points across dimensions and data matrices after their fit. In this paper, we attempt to familiarize ecologists with the benefits of using these Procrustean residual differences to further gain insights about the processes underlying the association among multivariate data tables using real and hypothetical examples.

Evaluating the process of ecological restoration

We developed a conceptual framework for evaluating the process of ecological restoration and applied it to 10 examples of restoration projects in the northern hemisphere. We identified three major ...

The influence of nitrogen in stemflow and precipitation on epiphytic bryophytes, Isothecium myosuroides Brid., Dicranum scoparium Hewd. and Thuidium tamariscinum (Hewd.) Schimp of Atlantic oakwoods

The spatial relationship between the concentration and deposition of the major ions in precipitation and stemflow and their influence on the tissue nitrogen concentration of three epiphytic bryophytes on Quercus petraea (Matt) Liebl. and Q. robur L. was investigated at seven UK Atlantic oak woodland sites with a range of total N deposition of 55-250 mmol m(-2). The main driver of change in tissue N concentrations of three epiphytic bryophytes (Isothecium myosuroides Brid. (Eurhynchium myosuroides (Brid.) Schp.), Dicranum scoparium Hewd. and Thuidium tamariscinum (Hewd.) Schimp.) was total N deposition in stemflow, dominated by ammonium deposition. The three epiphytic species also showed strong relationships between tissue N concentration and total N deposition in rainfall but a poor correlation with total N ion concentration in rainfall. This study shows that epiphytic bryophytes utilise stemflow N and thus increase their risk from inputs of total N deposition compared to terricolous species at the same site.

How to Replicate the Functions and Biodiversity of a Threatened Tree Species? The Case of Fraxinus excelsior in Britain

The suitability of alternative tree species to replace species that are either threatened by pests/disease or at risk from climate change is commonly assessed by their ability to grow in a predicted future climate, their resistance to disease and their production potential. The ecological implications of a change in tree species are seldom considered. Here, we develop and test 3 methods to assess the ecological suitability of alternative trees. We use as our case study the systematic search for an alternative tree species to Fraxinus excelsior (currently declining throughout Europe due to Hymenoscyphus fraxineus). Those trees assessed as most similar to F. excelsior in selected ecosystem functions (decomposition, leaf litter and soil chemistry) (Method A) were least similar when assessed by the number of ash-associated species that also use them (Method B) and vice versa. Method C simultaneously assessed ecosystem functions and species use, allowing trade-offs between supporting ecosystem function and species use to be identified. Using Method C to develop hypothetical scenarios of different tree species mixtures showed that prioritising ecosystem function and then increasing the mixture of tree species to support the greatest number of ash-associated species possible, results in a mixture of trees more ecologically similar to F. excelsior than by simply mixing tree species together to support the greatest number of ash-associated species. We conclude that establishing alternative tree species results in changes in both ecosystem function and species supported and have developed a general method to assess suitability that simultaneously integrates both ecosystem function and the ‘number of species supported’.

Developing monitoring protocols for cost-effective surveillance of lichens

The criteria set out by the International Union for Conservation of Nature to identify threatened species requires information on population trends which, for priority lichen species within Scotland, is lacking. Collecting such data is problematic as there is a lack of empirical information on the performance of different sampling designs and survey methodologies. Using Pseudocyphellaria norvegica as an example species, we tested differences in the efficiency of 3 transect patterns and a 20 minute search for surveying 100×100 m cells of potentially suitable habitat. The methods were not intended to census the total population of the cells but, rather, to provide a standardized, repeatable estimate of the population density to allow detection of trends through time. We also tested the repeatability of the methods between surveyors. The results provided no evidence to suggest that controlled survey methodologies using fixed transect patterns were any better in terms of consistency between surveyors or numbers of occupied trees found than 20 minute searches of the areas within each 100×100 m cell deemed suitable for the target species by an experienced surveyor. Given that following the fixed transect patterns took approximately twice as long as a 20 minute search, the search method would clearly be more cost-effective when there are large numbers of cells to survey. For all survey methods variability between surveyors was high, meaning that it would be extremely difficult to detect temporal changes in populations, and hence identify population trends. We also examined the extent to which recording presence/absence at the 1 ha scale might improve consistency between surveyors and found that it reduced, but did not eliminate, the surveyor variability. Recording only presence/absence would allow greater numbers of cells to be surveyed using the same level of resources, but would reduce the amount of information available per cell for use in analysis of population trends. We conclude that controlling inter-surveyor variability while collecting adequate data for population trend analysis is a major issue when planning and implementing any large-scale survey of lichen species.

Slow recovery of heather (Calluna vulgaris L. (Hull)) in Scottish moorland after easing of heavy grazing pressure from red deer (Cervus elaphus L.)

Summary The study aimed to determine how quickly heather responds in Scottish moorland once deer grazing pressure is reduced. We monitored heather attributes and deer distribution over ten years in Glen Lui and Glen Derry, two contrasting nearby areas of it 200 ha at Mar Lodge in the eastern Cairngorms. In one area the deer received winter food, affecting the zonation of their impact. In both areas the deer were initially lightly culled, then culling was increased. Mean heather shoot utilisation was 35 % and 48 % less in the last five years of the study than initially in the two areas, and was very closely correlated with deer pellet-group counts. In Glen Lui heather cover increased significantly but height increases were small. In Glen Derry heather increased significantly in height but little in cover. We attributed the different response to the presence of a secondary grazer (rabbits, Oryctolagus cuniculus) in Glen Lui and also better conditions for heather growth on the drier soils there; rabbits grazemore delicately than deer, taking mainly the shoottips of heather and thus encourage lateral shootgrowth. In Glen Lui heather response also varied between four radial zones based on distance from the feeding grounds. At best, there was appreciable recovery four years after the easing of deer grazing pressure, but average amounts of recovery were modest.

Relative importance of local- and large-scale drivers of alpine soil microarthropod communities

Nitrogen (N) deposition and climate are acknowledged drivers of change in biodiversity and ecosystem function at large scales. However, at a local scale, their impact on functions and community structure of organisms is filtered by drivers like habitat quality and food quality/availability. This study assesses the relative impact of large-scale factors, N deposition and climate (rainfall and temperature), versus local-scale factors of habitat quality and food quality/availability on soil fauna communities at 15 alpine moss–sedge heaths along an N deposition gradient in the UK. Habitat quality and food quality/availability were the primary drivers of microarthropod communities. No direct impacts of N deposition on the microarthropod community were observed, but induced changes in habitat quality (decline in moss cover and depth) and food quality (decreased vegetation C:N) associated with increased N deposition strongly suggest an indirect impact of N. Habitat quality and climate explained variation in the composition of the Oribatida, Mesostigmata, and Collembola communities, while only habitat quality significantly impacted the Prostigmata. Food quality and prey availability were important in explaining the composition of the oribatid and mesostigmatid mite communities, respectively. This study shows that, in alpine habitats, soil microarthropod community structure responds most strongly to local-scale variation in habitat quality and food availability rather than large-scale variation in climate and pollution. However, given the strong links between N deposition and the key habitat quality parameters, we conclude that N deposition indirectly drives changes in the soil microarthropod community, suggesting a mechanism by which large-scale drivers indirectly impacts these functionally important groups.