Global comparisons of urban ecosystems: Two case studies
Knowledge on the effects of urbanization on ecosystems across regional, continental and global scales is scarce. To address this issue, ecological networks are useful tools to foster international collaboration among scientist towards common goals. Yet, these networks require intensive measurements and experiments, are cost prohibitive, thus hindering broad participation. Coordinated distributed experiments, however, aim to be extensive, cost-effective, garner participation by scientists and citizens and at the same time address big questions at various spatial scales. Here we evaluate two international networks that investigate the effects of urbanization on beetle communities (GLOBENET) and soil ecosystems (GLUSEEN). GLOBENET had a relatively simple design; sample carabid beetles in urban, suburban and rural fragments of similar (forest) type, using the same methodology for one year. The main aim was to investigate whether urbanization is homogenizing beetle communities, and whether this is a recurring pattern across eight cities. GLUSEEN, or the Global Urban Soil Ecological Education Network, is a distributed network that aims at establishing a worldwide multi-city comparison investigating the effects of urban environments on the soil biota. Unlike GLOBENET, GLUSEEN builds upon decomposition experiments of varying levels of complexity, making it possible for citizens to participate. Various measurements are made in four soil habitat types differentiated by levels of management and disturbance, including decomposition using nylon teabags, earthworm abundance, soil analyses and soil microbial community structure.
The most striking result of GLOBENET was the loss of forest-associated beetles towards city centres, suggesting the homogenisation of urban communities. The project lasted for 10 years and produced close to 20 papers, also including taxa other than carabid beetles. Due to the simple design, GLOBENET was a popular topic for master’s level students, yet required time and taxonomic expertise, which prevented citizen participation. Preliminary results from GLUSEEN show that soil pH and organic matter concentrations varied less among highly disturbed and managed soils (ruderal, turfgrass) than remnant and reference soils across the cities investigated (Baltimore, Budapest, Helsinki, Lahti, Potchefstroom), thus supporting the ecosystem convergence hypothesis. Furthermore, after 1 year in the soil, teabags lost between 20-40% of their mass, with teabags in turfgrass soils showing the greatest loss. The simplicity of experiments (especially teabag decomposition) in GLUSEEN is conducive for use in citizen science programs. We aim to expand on the network by producing more simplified protocols, forming a global virtual community through a web interface, and measuring additional abiotic factors and soil invertebrate biodiversity.