Year: 2012
Type: dissertation
Abstract: Man is now an urban species, because most of the mankind lives in cities.In cities, the only thing permanent is change. There are several agents of change in operation in cities, producing environmental disturbances at various temporal and spatial scales and regimes. This affects the living conditions of both man and other urban species. This study was an ecological stress tests how different urban habitats and species survived the actions of the agents of change. The disturbances can be divided into pulse disturbances and press disturbances.In this study, air and water pollution were typical pulse disturbances.The ecosystems may have enough adaptive capacity to renew and remain in a stable state, but they may also shift to a new state. The ecosystems that maintain their stable state have high resilience, but others shift into a new,possibly undesirable domain (from the perspective of biodiversity conservation and ecosystem services). The pulse of air pollution caused a temporary disappearance of urban epiphytic lichens in the city of Tampere (Finland). After ameliorating the air quality, the lichens returned, albeit in a reorganised combination of species.Thus, the ecosystem showed resilience as it was able to recover after the disturbance ended. Enough of external ecological memory was available and most of the lichens returned after the pollution episode was over. Within a period of 100 years, water pollution and other disturbances of the urban lake of Iidesjärvi (in Tampere) caused a shift from one stability domain (a clear-water state) to a new domain (turbid-water state). This domain shift presents a challenge for urban environmental management. A deadlock situation was created because the shift back to the desirable state would require excessive technical and economic resources. The upstream, nonpolluted lake of Kaukajärvi in the samem catchment area remained in a clear water state with rich flora of elodeids and isoetids. The dynamic macrophyte species pool (1902 2008) of Iidesjärvi consisted of 48 species, some of which disappeared temporarily and later returned.The shallow species-rich lakes in the region may occasionally experience species turnover; a species that disappears may recolonise later from other lakes. The gradient paradigm provides a useful basis for studies in cities to quantify the intensity of urbanisation. In the present study, a 21 km long string of grid cells was established through the city of Tampere. The aim of the gradient study was to examine the distribution of native and alien plants along the gradient line and to find the most important variables, which determine the location and abundance of species along it. The urban forest fragment under study (1.27 ha in the city of Tampere) had enough adaptive capacity to remain in the same stability domain since it has been isolated 120 years ago. The urban pressure affected the forest in several cumulative ways and domain shift will occur in the foreseeable future. A special feature of boreal cities is the presence of remnants of seminatural habitats,mostly forests, close to central business districts. As a result, Nordic cities are resilient and show remarkably low extinction rates of plants. The urban traffic corridors were compared with a river corridor on the municipal level. Despite their small area, the corridors are very rich in species.The corridor plants in the City of Vantaa represented 61 percent of the total number of species of the biogeographical province of Uusimaa. Disturbance regimes were the common denominator of the ecological profiles of traffic corridors and river corridors. In spite of the richness in species, urban corridors are not included in the networks of protected areas. The Finnish cities showed a high degree of resilience in spite of the concomitant actions of several agents of change. This was a result of the urban structure of the Finnish cities. In Finland,fragments of original nature of different types are embedded in the urban structure. Keywords: urban ecology, monitoring, disturbance, resilience, ecological memory
Source: Työväentutkimus Vuosikirja
Author: Pertti Ranta
Language: English
Subfield: Global and Planetary Change
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2164558962