Streetlighting impacts on vegetation

Bennie, J., Davies, T.W., Cruse, D., Bell, F. & Gaston, K.J. 2018. Artificial light at night alters grassland vegetation species composition and phenology. Journal of Applied Ecology 15, 442-450.

1. Human settlements and transport networks are growing rapidly worldwide. Since the early 20th century their expansion has been accompanied by increasing illumination of the environment at night, a trend that is likely to continue over the decades to come. Consequently, a growing proportion of the world’s ecosystems are exposed to artificial light at night, profoundly altering natural cycles of light and darkness. While in recent years there have been advances in our understanding of the effects of artificial light at night on the behaviour and physiology of animals in the wild, much less is known about the impacts on wild plants and natural or semi-natural vegetation composition. This is surprising, as effects of low-intensity light at night on flowering, phenology and growth form are well known in laboratory and greenhouse studies.
2. In a long-term experimental field study we exposed a semi-natural grassland to artificial light at intensities and wavelengths typical of those experienced by roadside vegetation under street lighting.
3. We found that lighting affected the trajectory of vegetation change, leading to significant differences in biomass and plant cover in the dominant species.
4. Changes in flowering phenology were variable between years, with grass species flowering between 4 days earlier and 12 days later under artificial light.
5. Policy implications. Our results demonstrate that artificial light, at levels equivalent to those in street-lit environments, can affect species composition in semi-natural vegetation. This highlights the importance of considering artificial light as a driver of vegetation change in urban, suburban and semi-natural ecosystems, and where possible, of minimising or excluding artificial light from habitats of conservation importance.

Quantifying the green

Casalegno, S., Anderson, K., Hancock, S. & Gaston, K.J. 2017. Improving models of urban greenspace: from vegetation surface cover to volumetric survey using waveform laser scanning. Methods in Ecology and Evolution, in press.

1. Urban greenspace has a major impact on human health and quality of life, and thus the way in which such green infrastructure is constructed, managed and maintained is of critical importance. A range of studies have demonstrated the relationship between the areal coverage and distribution of vegetation and the provision of multiple urban ecosystem services. It is not known how sensitive findings are to the spatial resolution of the underlying data relative to the grain size of urban land cover heterogeneity. Moreover, little is known about the three-dimensional (3D) structure of urban vegetation and delivery of services, and addressing such questions is limited by the availability of data describing canopy structure from the tree tops to the ground.
2. Waveform airborne laser scanning (lidar) offers a new way of capturing 3D data describing vegetation structure. We generated voxels (volumetric pixels) from waveform lidar (1.5 m resolution), differentiated vegetation layers using height as a determinant, and computed statistics on surface cover, volume and volume density per stratum. We then used a range of widely available remote sensing products with varying spatial resolution (1 to 100 m) to map the same greenspace, and compared results to those from the waveform lidar survey.
3. We focused on data from three urban zones in the UK with distinct patterns of vegetation cover. We found 3%, +7.5% and +26.1% differences in green surface cover compared with, respectively, town planning maps (<10 m resolution), national land cover maps (25 m) and European land cover maps (100 m). There were differences of 59.1%, +12.4% and 2.4% in tree cover compared with global (30 m resolution), European (25 m) and national (1 m) estimates. Waveform lidar captured sub-canopy structure and detected empty spaces in the understorey which contributed a 16% bias in the total green volume derived from non-waveform lidar observations. 4. We conclude that waveform lidar has a key role to play in estimating important quantitative metrics of urban green infrastructure, which is important because urban greenspace is highly fragmented and shows high levels of spatial and volumetric heterogeneity.

Green connections in 3D

Casalegno, S., Anderson, K., Cox, D.T.C., Hancock, S. & Gaston, K.J. 2017. Ecological connectivity in the three-dimensional urban green volume using waveform airborne lidar. Scientific Reports 7, 45571. shutterstock_95030080

The movements of organisms and the resultant flows of ecosystem services are strongly shaped by landscape connectivity. Studies of urban ecosystems have relied on two dimensional (2D) measures of greenspace structure to calculate connectivity. It is now possible to explore three-dimensional (3D) connectivity in urban vegetation using waveform lidar technology that measures the full 3D structure of the canopy. Making use of this technology, here we evaluate urban greenspace 3D connectivity, taking into account the full vertical stratification of the vegetation. Using three towns in southern England, UK, all with varying greenspace structures, we describe and compare the structural and functional connectivity using both traditional 2D greenspace models and waveform lidar-generated vegetation strata (namely, grass, shrubs and trees). Measures of connectivity derived from 3D greenspace are lower than those derived from 2D models, as the latter assumes that all vertical vegetation strata are connected, which is rarely true. Fragmented landscapes that have more complex 3D vegetation showed greater functional connectivity and we found highest 2D to 3D functional connectivity biases for short dispersal capacities of organisms (6 m to 16 m). These findings are particularly pertinent in urban systems where the distribution of greenspace is critical for delivery of ecosystem services. [Image from Shutterstock]

Biodiversity prospects for Antarctica

Chown, S.L. Brooks, C.M., Terauds, A., Le Bohec, C., van Klaveren-Impagliazzo, C., Whittington, J.D., Butchart, S.H.M., Coetzee, B.W.T., Collen, B., Convey, P., Gaston, K.J., Gilbert, N., Gill, M., Höft, R., Johnston, S., Kennicutt II, M.C., Kriesell, H.J., Le Maho, Y., Lynch, H.J., Palomares, M., Puig-Marco, R., Stoett, P. & McGeoch, M.A. 2017. Antarctica and the Strategic Plan for Biodiversity. PLoS Biology 15, e2001656. Weddell seals

The Strategic Plan for Biodiversity, adopted under the auspices of the Convention on Biological Diversity, provides the basis for taking effective action to curb biodiversity loss across the planet by 2020 an urgent imperative. Yet, Antarctica and the Southern Ocean, which encompass 10% of the planet’s surface, are excluded from assessments of progress against the Strategic Plan. The situation is a lost opportunity for biodiversity conservation globally. We provide such an assessment. Our evidence suggests, surprisingly, that for a region so remote and apparently pristine as the Antarctic, the biodiversity outlook is similar to that for the rest of the planet. Promisingly, however, much scope for remedial action exists. [Image from S.L. Chown]

Lighting up the tropics

de Freitas, J.R., Bennie, J., Mantovani, W. & Gaston, K.J. 2017. Exposure of tropical ecosystems to artificial light at night: Brazil as a case study. PLoS One 12, e0171655. Screen Shot 2017-02-18 at 14.52.57

Artificial nighttime lighting from streetlights and other sources has a broad range of biological effects. Understanding the spatial and temporal levels and patterns of this lighting is a key step in determining the severity of adverse effects on different ecosystems, vegetation, and habitat types. Few such analyses have been conducted, particularly for regions with high biodiversity, including the tropics. We used an intercalibrated version of the Defense Meteorological Satellite Program’s Operational Linescan System (DMSP/OLS) images of stable nighttime lights to determine what proportion of original and current Brazilian vegetation types are experiencing measurable levels of artificial light and how this has changed in recent years. The percentage area affected by both detectable light and increases in brightness ranged between 0 and 35% for native vegetation types, and between 0 and 25% for current vegetation (i.e. including agriculture). The most heavily affected areas encompassed terrestrial coastal vegetation types (restingas and mangroves), Semideciduous Seasonal Forest, and Mixed Ombrophilous Forest. The existing small remnants of Lowland Deciduous and Semideciduous Seasonal Forests and of Campinarana had the lowest exposure levels to artificial light. Light pollution has not often been investigated in developing countries but our data show that it is an environmental concern.

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Nearby nature brings multiple health benefits

Cox, D.T.C., Shanahan, D.F., Hudson, H.L., Fuller, R.A., Anderson, K., Hancock, S. & Gaston, K.J. 2017. Doses of nearby nature simultaneously associated with multiple health benefits. International Journal of Environmental Research and Public Health 14, 172. shutterstock_402920080

Exposure to nature provides a wide range of health benefits. A significant proportion of these are delivered close to home, because this offers an immediate and easily accessible opportunity for people to experience nature. However, there is limited information to guide recommendations on its management and appropriate use. We apply a nature dose-response framework to quantify the simultaneous association between exposure to nearby nature and multiple health benefits. We surveyed ca. 1000 respondents in Southern England, UK, to determine relationships between (a) nature dose type, that is the frequency and duration (time spent in private green space) and intensity (quantity of neighbourhood vegetation cover) of nature exposure and (b) health outcomes, including mental, physical and social health, physical behaviour and nature orientation. We then modelled dose-response relationships between dose type and self-reported depression. We demonstrate positive relationships between nature dose and mental and social health, increased physical activity and nature orientation. Dose-response analysis showed that lower levels of depression were associated with minimum thresholds of weekly nature dose. Nearby nature is associated with quantifiable health benefits, with potential for lowering the human and financial costs of ill health. Dose-response analysis has the potential to guide minimum and optimum recommendations on the management and use of nearby nature for preventative healthcare. [Image from Shutterstock]

Lighting impacts on invertebrates

Davies, T.W., Bennie, J., Cruse, D., Blumgart, D., Inger, R. & Gaston, K.J. 2017. Multiple night-time light-emitting diode lighting strategies impact grassland invertebrate assemblages. Global Change Biology, in press. Rigs1

White light-emitting diodes (LEDs) are rapidly replacing conventional outdoor lighting technologies around the world. Despite rising concerns over their impact on the environment and human health, the flexibility of LEDs has been advocated as a means of mitigating the ecological impacts of globally widespread outdoor night-time lighting through spectral manipulation, dimming and switching lights off during periods of low demand. We conducted a three-year field experiment in which each of these lighting strategies was simulated in a previously artificial light naive grassland ecosystem. White LEDs both increased the total abundance and changed the assemblage composition of adult spiders and beetles. Dimming LEDs by 50% or manipulating their spectra to reduce ecologically damaging wavelengths partially reduced the number of commoner species affected from seven to four. A combination of dimming by 50% and switching lights off between midnight and 04:00 am showed the most promise for reducing the ecological costs of LEDs, but the abundances of two otherwise common species were still affected. The environmental consequences of using alternative lighting technologies are increasingly well established. These results suggest that while management strategies using LEDs can be an effective means of reducing the number of taxa affected, averting the ecological impacts of night-time lighting may ultimately require avoiding its use altogether.

Benefits of doses of neighbourhood nature

Cox, D.T.C., Plummer, K.E., Shanahan, D.F., Siriwardena, G.M., Fuller, R.A., Anderson, K., Hancock, S. & Gaston, K.J. 2017. Doses of neighborhood nature: the benefits for mental health of living with nature. BioScience, in press. shutterstock_305124968

Experiences of nature provide many mental-health benefits, particularly for people living in urban areas. The natural characteristics of city residents’ neighborhoods are likely to be crucial determinants of the daily nature dose that they receive; however, which characteristics are important remains unclear. One possibility is that the greatest benefits are provided by characteristics that are most visible during the day and so most likely to be experienced by people. We demonstrate that of five neighborhood nature characteristics tested, vegetation cover and afternoon bird abundances were positively associated with a lower prevalence of depression, anxiety, and stress. Furthermore, dose–response modeling shows a threshold response at which the population prevalence of mental-health issues is significantly lower beyond minimum limits of neighborhood vegetation cover (depression more than 20% cover, anxiety more than 30% cover, stress more than 20% cover). Our findings demonstrate quantifiable associations of mental health with the characteristics of nearby nature that people actually experience. [Image from Shutterstock]

Where to find aliens

Dyer, E.E., Cassey, P., Redding, D.W., Collen, B., Franks, V., Gaston, K.J., Jones, K.E., Kark, S., Orme, C.D.L. & Blackburn, T.M. 2017. The global distribution and drivers of alien bird species richness. PLoS Biology 15, e2000942. shutterstock_289070456

Alien species are a major component of human-induced environmental change. Variation in the numbers of alien species found in different areas is likely to depend on a combination of anthropogenic and environmental factors, with anthropogenic factors affecting the number of species introduced to new locations, and when, and environmental factors influencing how many species are able to persist there. However, global spatial and temporal variation in the drivers of alien introduction and species richness remain poorly understood. Here, we analyse an extensive new database of alien birds to explore what determines the global distribution of alien species richness for an entire taxonomic class. We demonstrate that the locations of origin and introduction of alien birds, and their identities, were initially driven largely by European (mainly British) colonialism. However, recent introductions are a wider phenomenon, involving more species and countries, and driven in part by increasing economic activity. We find that, globally, alien bird species richness is currently highest at midlatitudes and is strongly determined by anthropogenic effects, most notably the number of species introduced (i.e., colonisation pressure). Nevertheless, environmental drivers are also important, with native and alien species richness being strongly and consistently positively associated. Our results demonstrate that colonisation pressure is key to understanding alien species richness, show that areas of high native species richness are not resistant to colonisation by alien species at the global scale, and emphasise the likely ongoing threats to global environments from introductions of species. [Image from Shutterstock]