KEVIN J GASTON

Edmondson, J.L., O’Sullivan, O.S., Inger, R., Potter, J., McHugh, N., Gaston, K.J. & Leake, J.R. 2014. Urban tree effects on soil organic carbon. PLoS One 9, e101872.

Urban trees sequester carbon into biomass and provide many ecosystem service benefits aboveground leading to worldwide tree planting schemes. Since soils hold ~75% of ecosystem organic carbon, understanding the effect of urban trees on soil organic carbon (SOC) and soil properties that underpin belowground ecosystem services is vital. We use an observational study to investigate effects of three important tree genera and mixed-species woodlands on soil properties (to 1 m depth) compared to adjacent urban grasslands. Aboveground biomass and belowground ecosystem service provision by urban trees are found not to be directly coupled. Indeed, SOC enhancement relative to urban grasslands is genus-specific being highest under Fraxinus excelsior and Acer spp., but similar to grasslands under Quercus robur and mixed woodland. Tree cover type does not influence soil bulk density or C:N ratio, properties which indicate the ability of soils to provide regulating ecosystem services such as nutrient cycling and flood mitigation. The trends observed in this study suggest that genus selection is important to maximise long-term SOC storage under urban trees, but emerging threats from genus-specific pathogens must also be considered.

Soga, M., Yamaura, Y., Koike, S. & Gaston, K.J. 2014. Woodland remnants as an urban wildlife refuge: a cross-taxonomic assessment. Biodiversity and Conservation 23, 649-659.

Urban nature is crucial for the quality of human life both within cities and beyond. In many developed cities, the numbers of restoration-through-revegetation projects have rapidly increased over the decades. However, the extent to which revegetated habitats perform compensatory roles for remnant habitats is poorly understood. We compared butterfly and ground beetle assemblages among three park types (five remnant parks, four newly established parks and five old established parks) and seven built-up sites in Tokyo, central Japan. Butterflies were classified into woodland or open-land and into patch-dependent or matrix-dwelling species. For both taxa, remnant parks and built-up sites had the highest and lowest species richness and abundance, respectively. Although the richness and abundance of open-land and matrix-dwelling butterflies did not differ among the three park types, those of woodland and patch-dependent species were significantly highest in remnant parks. In short, after 50 years, established parks did not attain the same insect assemblages as those in remnant parks. These results illustrate that whist revegetation is an effective and fast-acting conservation measure for generalist species (i.e., widely distributed species), this value is limited for specialists. In highly urbanised landscapes, therefore, even small remnant woodlands provide important refuges for urban wildlife. Remnant protection programs at the early stage of city development would decide the fate of urban biodiversity.

Lin^, B.B, Fuller, R.A., Bush, R., Gaston, K.J. & Shanahan, D.F. 2014. Opportunity or orientation?: Who uses urban parks and why. PLoS One 9, e87422.

There is growing recognition that interactions with nature provide many desirable human well-being outcomes, yet increasing urbanization is degrading the quality and quantity of nature experiences. Thus, it has become increasingly important to understand how and why urban dwellers interact with nature. Studies of urban green space use have largely focused on the availability and ease of access to green space, suggesting that greater opportunities to experience such space will lead to increased use. However, a growing literature emphasizes the potential for an individual’s nature orientation to affect their interaction with green space. Here we measure the importance of both opportunity and orientation factors in explaining urban park use. An urban lifestyle survey was deployed across Brisbane, Australia in November 2012 to assess patterns of green space use. Participants were asked to provide information on demographics, private yard use, park visitations in the past week, and their orientation toward nature. About 60% of those surveyed had visited a park in the past week, and while this park user population had significantly greater nearby park coverage (within a 250 m radius), a much stronger determinant of visitation was their higher nature orientation, suggesting that while both opportunity and orientation are important drivers for park visitation, nature orientation is the primary effect. Park users also spent significantly more time in their yards than non-park users, suggesting that yard use does not necessarily compensate for lower park use. Park users with stronger nature orientation (i) spent more time in their yard, (ii) traveled further to green spaces, and (iii) made longer visits than park visitors with weaker nature orientation. Overall, our results suggest that measures to increase people’s connection to nature could be more important than measures to increase urban green space availability if we want to encourage park visitation.

Edmondson, J.L., Davies, Z.G., McCormack, S.A., Gaston, K.J. & Leake, J.R. 2014. Land-cover effects on soil organic carbon stocks in a European city. Science of the Total Environment 472, 444-453.

Soil is the vital foundation of terrestrial ecosystems storing water, nutrients, and almost three-quarters of the organic carbon stocks of the Earth’s biomes. Soil organic carbon (SOC) stocks vary with land-cover and land-use change, with significant losses occurring through disturbance and cultivation. Although urbanisation is a growing contributor to land-use change globally, the effects of urban land-cover types on SOC stocks have not been studied for densely built cities. Additionally, there is a need to resolve the direction and extent to which greenspace management such as tree planting impacts on SOC concentrations. Here, we analyse the effect of land-cover (herbaceous, shrub or tree cover), on SOC stocks in domestic gardens and non-domestic greenspaces across a typical mid-sized U.K. city (Leicester, 73 km2, 56% greenspace), and map citywide distribution of this ecosystem service. SOCwas measured in topsoil and compared to surrounding extra-urban agricultural land. Average SOC storage in the city’s greenspace was 9.9 kg m−2, to 21 cm depth. SOC concentrations under trees and shrubs in domestic gardens were greater than all other land-covers, with total median storage of 13.5 kg m−2 to 21 cm depth, more than 3 kg m−2 greater than any other land-cover class in domestic and non-domestic greenspace and 5 kg m−2 greater than in arable land. Land-cover did not significantly affect SOC concentrations in non-domestic greenspace, but values beneath trees were higher than under both pasture and arable land, whereas concentrations under shrub and herbaceous land-covers were only higher than arable fields. We conclude that although differences in greenspace management affect SOC stocks, trees only marginally increase these stocks in non-domestic greenspaces, but may enhance them in domestic gardens, and greenspace topsoils hold substantial SOC stores that require protection from further expansion of artificial surfaces e.g. patios and driveways.

Dallimer, M., Tinch, D., Hanley, N., Irvine, K.N., Rouquette, J.R., Warren, P.H., Maltby, L., Gaston, K.J. & Armsworth, P.R. 2014. Quantifying preferences for the natural world using monetary and non-monetary assessments of value. Conservation Biology 28, 404-413.

Given that funds for biodiversity conservation are limited, there is a need to understand people’s preferences for its different components. To date, such preferences have largely been measured in monetary terms. However, how people value biodiversity may differ from economic theory, and there is little consensus over whether monetary metrics are always appropriate or the degree to which other methods offer alternative and complementary perspectives on value. We used a choice experiment to compare monetary amounts recreational visitors to urban green spaces were willing to pay for biodiversity enhancement (increases in species richness for birds, plants, and aquatic macroinvertebrates) with self-reported psychological gains in well-being derived from visiting the same sites. Willingness-to-pay (WTP) estimates were significant and positive, and respondents reported high gains in well-being across three axes derived from environmental psychology theories (reflection, attachment, continuity with past). The two metrics were broadly congruent. Participants with abovemedian self-reported well-being scores were willing to pay significantly higher amounts for enhancing species richness than those with below-median scores, regardless of taxon. The socio-economic and demographic background of participants played little role in determining either their well-being or the probability of choosing a paying option within the choice experiment. Site-level environmental characteristics were only somewhat related to WTP, but showed strong associations with self-reported well-being. Both approaches are likely to reflect a combination of the environmental properties of a site and unobserved individual preference heterogeneity for the natural world. Our results suggest that either metric will deliver mutually consistent results in an assessment of environmental preferences, although which approach is preferable depends on why one wishes to measure values for the natural world.

Bonnington, C., Gaston, K.J. & Evans, K.L. 2014. Squirrels in suburbia: influence of urbanisation on occurrence and distribution of a common exotic mammal. Urban Ecosystems 17, 533-546.

Urbanisation is widely considered to promote the establishment of non-native species, but there is limited empirical evidence of the ecological factors driving their responses. The grey squirrel Sciurus carolinensis (Gmelin 1788) is native to North America, but is widespread in the UK and is starting to spread across Europe. It is regarded as one of the world’s worst invasive animals due to its adverse impacts on native biodiversity. We use the non-native grey squirrel population in Sheffield (UK) as a case study to assess which factors limit its distribution and abundance in urban environments. In 2010 the city-wide population of adult squirrels peaked at an estimated 6539 in autumn (0.46 squirrels/ha), with maximum local densities of 8.29/ha. These densities appear to be slightly lower than those recorded in urban environments in the species’ native range. Grey squirrels occurred more frequently at urban sites with larger amounts of green-space in the surrounding region. Local habitat characteristics were, however, more powerful predictors of urban grey squirrel occurrence and abundance than regional availability of green space. Canopy cover, seed bearing trees and supplementary feeders, provided for garden birds, positively influenced grey squirrels. The potential for grey squirrels to connect city dwellers with nature thus appears to be highest in urban locations that have considerable capacity to support native biodiversity. The beneficial impacts of supplementary feeding on grey squirrel populations is notable given concerns that squirrels can adversely influence bird populations. These habitat associations also imply that grey squirrels typically respond negatively to urbanisation, which challenges arguments that urbanisation favours exotic species.

Bonnington, C., Gaston, K.J. & Evans, K.L. 2014. Assessing the potential for Grey squirrels Sciurus carolinensis to compete with birds at supplementary feeding stations. Ibis 156, 220-226.

Supplementary feeding of birds, particularly in urban areas, is often associated with increased population size and fecundity. In the UK, the non-native Grey Squirrel Sciurus carolinensis is common in rural and urban habitats. It exploits supplementary feeders and may induce interference competition by excluding birds, but empirical evidence of this is unavailable. Using controlled model presentation experiments, we demonstrate that Grey Squirrels could reduce bird use of supplementary feeders and induce interference competition. Total bird resource use was reduced by 98% and most species exhibited similar sensitivities. The likelihood and magnitude of interference competition will depend on how rapidly displaced birds find alternative food sources; it will be greatest where there are high Grey Squirrel densities and few supplementary feeders. Other studies suggest that supplementary feeding increases Grey Squirrel numbers, and the species is also predicted to expand its non-native range across most of Europe. Our data indicate that Grey Squirrels may eventually alter the net effect of supplementary feeding on bird populations across the European continent; increased use of squirrelproof feeders may help to minimize such effects.