Spatiotemporal patterns of urbanization in three Swiss urban agglomerations: insights from landscape metrics, growth modes and fractal analysis

Martí Bosch Padros, Jérôme Chenal, Rémi Jaligot
SPRINGER, 2020
Journal paper

Abstract

Context Urbanization is the most important form of landscape change and is increasingly affecting biodiversity and ecosystem functions. Understanding how landscape patterns change in space and time is central to the evaluation of the environmental impacts of urbanization. Objectives This research explores the spatiotemporal patterns of land use change in the Swiss urban agglomerations of Bern, Lausanne and Zurich at two characteristic spatial extents, and compares them to prominent hypotheses of urbanization patterns. Methods For each urban agglomeration, four temporal snapshots from 1980 to 2016 have been derived from the land use inventory of the Swiss Federal Statistical Office. Fractal analysis of the area-radius relationship of urban land is used to separate each agglomeration into two characteristic spatial extents according to the distance of the city center, namely the inner and outer zones. The landscape metrics and growth modes are then computed at such extents. Results The time series of landscape metrics and growth modes reveal fairly different patterns when computed in the inner and outer zones respectively. Bern and Lausanne exhibit mostly traits of coalescence stages at the inner zone while displaying many characteristics of diffusion in the outer zone. In contrast, the trends of observed in the inner and outer zones of Zurich are both reminiscent of a coalescence stages. Conclusions Fractal analysis can be a useful approach to detect characteristic extents of urban agglomerations at which distinct spatiotemporal patterns might be observed. Current models of urbanization patterns should incorporate the notion of characteristic extents more explicitly.

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Martí Bosch Padros, Jérôme Chenal, Rémi Jaligot
SPRINGER, 2020
Journal paper

Abstract

Official source

https://infoscience.epfl.ch/record/277178?ln=en

About this result

Related concepts (18)

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Spatiotemporal patterns of urbanization during the last four decades in Switzerland and their impacts on urban heat islands

Martí Bosch Padros

Urbanization is nowadays a global phenomenon which is increasingly concentrating the world's population in cities. In Switzerland, recent decades have seen an unprecedented loss of arable land due to urbanization, which has triggered amendments in the spatial planning laws with the aim of promoting urban densification. Nevertheless, despite remarkable efforts, the environmental impacts of distinctive urban patterns such as compact cities and urban sprawl remain poorly understood. One of the most remarkable environmental impacts of urbanization is the urban heat island effect, a phenomenon by which urban temperatures are warmer than in its rural surroundings. Central Europe, and therefore Switzerland, is among the regions in the world where temperatures are rising faster and the urban heat island effect is most prominent, which represents a central challenge for spatial planning. Most studies suggest that the urban heat island effect can be aggravated in compact cities, especially when considering the larger share of urban dwellers that are exposed to the highest temperatures. At the same time, the literature on the subject has seen a growing development of mitigation strategies, which suggest that the urban heat island effect can be significantly alleviated by an adequate planning of the building materials and urban green spaces. This doctoral dissertation intends to address the issues expressed above by performing a quantitative evaluation of the spatiotemporal patterns of urbanization in Switzerland and their impact on the urban heat island effect. To that end, the thesis adopts a landscape ecology perspective to quantify urban patterns and to spatially simulate the biophysical processes that underpin the urban heat island effect. The first article presents PyLandStats, an open- source library to compute landscape metrics in a repeatable and reproducible manner. In the second article, such a library is used to evaluate the spatiotemporal patterns of urbanization observed in the urban agglomerations of Bern, Lausanne and Zurich from 1980 to 2016. The results reveal that the outer zones of Bern and Lausanne are still undergoing diffusive urban expansion, whereas infill development is the dominant growth mode in both the inner and outer zones of Zurich. The thesis follows with the development of a spatially-explicit method to simulate urban heat mitigation using a recent model of urban cooling based on three biophysical mechanisms, namely tree shade, evapotranspiration and albedo. The study introduces an automated procedure to calibrate the parameters of the model, and shows that the proposed approach can outperform regression models based on remote sensing features. Then, in the fourth article, such an approach is applied to Lausanne in order to evaluate heat mitigation in a variety of urban greening scenarios which modify both the abundance and spatial configuration of the tree canopy cover. The simulations suggest a potential alleviation of the maximum nighttime temperatures of 2°C, which represents a major reduction of the human exposure to the urban heat island effect. Finally, a concluding chapter summarizes the main contributions of the dissertation and reviews key implications for urban planning in Switzerland. Overall, rather than prescribing urban densification as the customary strategy for spatial development, land use regulations and local plans should incorporate spatially-explicit evaluations of the ecosystem services.

EPFL2021

Subalpine Pasture-Woodlands in a Changing Climate

Konstantin Svetlozarov Gavazov

Climate change in temperate mountain systems and associated increase in temperature and decrease in precipitation are expected to have strong implications for vegetation productivity, species diversity and carbon turnover in subalpine grasslands. Little is known, however, about the interaction between the effects of climate change and those of local land use management and possible changes in landscape structure. Pasture woodlands in the Swiss Jura Mountains are a traditional landscape, resulting from a long-lived sustainable use of grasslands and woodlands, and as such provide a suite of important ecosystem services to human society. These range from carbon sequestration and biodiversity preservation, to provision of timber and forage for livestock, and last but not least an aesthetic value, much appreciated by tourism. In this thesis various aspects of ecosystem functioning have been studied, investigating the combined effects of experimental climate change and land use on structurally different wooded pastures. An altitudinal gradient method has been used to simulate future climate change conditions, by imposing warmer and drier climate on subalpine turfs transplanted at lower elevation. The resulting gradient in mean annual temperature and precipitation – ranging from cold and wet in the subalpine zone, to warm and dry in the colline zone – has allowed for the detection of tipping points and altered states of ecosystem functioning in response to the treatments. The method employed provided also the possibility for a direct comparison of three land use types: unwooded pastures, sparsely wooded pastures, and densely wooded pastures (the result of pasture management intensity), in their response to climate perturbation. During the four years of experimental work, a series of observations have been made at the plot scale (square metre) in terms of plant performance and biogeochemical cycles, as well as at the landscape scale (hectare) in terms of forage production. A general threshold level for ecosystem resistance to experimental climate change was detected between the moderate IPCC scenario (+2 K mean annual temperature; -20 % annual precipitation) and the intensive IPCC scenario (+4 K mean annual temperature; -40 % annual precipitation). A concomitant gradient in ecosystem response to climate change was observed across the three land use types. The intensively managed unwooded pasture type was consistently more affected by the experimental treatment and rarely exhibited signs of resistance, especially under the intense climate change scenario. A drastic loss of plant species diversity, reduction of herbaceous biomass, impaired litter decomposition and soil microbial metabolic activity have all contributed to the altered state of ecosystem functioning. In contrast, the two extensively managed wooded pasture types showed considerable resistance to climate perturbation in terms of both above and belowground ecosystem processes. The reported inter-annual variation in herbaceous diversity and biomass production within these land use types demonstrated their resilience (recovery) potential too. Using a modelling approach for upscaling these results to the heterogeneous landscape of pasture woodlands in the Swiss Jura Mountains, has proven that extensively used wooded pastures could grant sustainable ecosystem services in terms of forage provision for cattle under climate change. Considering that the two experimental climate change intensities implemented this study are the projected ‘best’ and ‘worst’ case scenarios for the coming decades, the reported resistance of wooded pastures to climate change has to be embraced, and sustainable land use set as a goal in high altitude mountain pastures.

EPFL2013

The present thesis deals with the understanding of the origins and the mechanisms of maintenance of biodiversity in natural landscapes, in particular by identifying key processes that define large-scale patterns of abundance and diversity. Biological communities often occur in spatially structured habitats where connectivity directly affects dispersal and metacommunity processes. Recent theoretical work suggests that dispersal constrained by the connectivity of specific habitat structures affects diversity patterns and species interactions. This is particularly relevant in dendritic networks epitomized by fluvial ecological corridors. This thesis addresses whether connectivity alone can explain observed features of biodiversity and selectively promote different components of community composition in river-like landscapes, such as local species richness or the among-community similarity. The relevance of this thesis lies in the major ecological challenges posed by the topic, and its fundamental importance to conservation biology. The studies pursued herein are also deemed relevant because of the influence of the spatial connectivity and dispersal on population dynamics and of the relevance of biodiversity to ecosystem functioning. Mechanisms of species coexistence were investigated with a blend of theoretical tools (broadly related to statistical mechanics and the theory of stochastic processes) and experimental work using laboratory microbial communities. The research tools ranged from aspects of modern coexistence theory in a local perspective to the recent concept of the metacommunity in spatial ecology, within a unified framework. The study of biodiversity in riverine ecosystems guided by observational data has been addressed by combining theoretical metacommunity models with laboratory experiments. The results are diverse. First, they show experimentally that connectivity per se shapes key components of biodiversity in metacommunities. Local dispersal in isotropic lattice landscapes homogenizes local species richness and leads to pronounced spatial persistence. By contrast, dispersal along dendritic landscapes leads to higher variability in local diversity and among-community composition. Although headwaters exhibit relatively lower species richness, they are crucial for the maintenance of regional biodiversity. By suitably arranging patch sizes within river-like networks the effect of local habitat capacity (i.e., the patch size) and dendritic connectivity on biodiversity can be experimentally disentangled in aquatic microcosm metacommunities. It is shown in this thesis that species coexistence and community assembly depend on intricate, non-trivial interactions of local community capacity and network positioning. Furthermore, an interaction of spatial arrangement of habitat capacity and dispersal along river-like networks also affects a key ecosystem descriptor, namely regional evenness. High regional evenness in community composition is found only in landscapes preserving geomorphological scaling properties of patch sizes. In riverine environments some of the rarer species sustained regionally more abundant populations and were better able to track their own niche requirements compared to landscapes with homogeneous patch size or landscapes with spatially uncorrelated patch size. All the experimental results were supported and extended by a theoretical analysis where the above mechanisms have been generalized. This thesis provides the first direct experimental evidence that spatially constrained dendritic connectivity is a key factor for community composition and population persistence in riverine landscapes. As such, this thesis assesses a longstanding issue in spatial community ecology. It offers unique insights into the ecological forces structuring natural communities in a key ecosytem, and demonstrates principles that can be further tested in theoretical metacommunity models possibly to be extended to real riverine ecosystems. Taken together, the analyses show how the structure of ecological networks interacts with the spatial environmental matrix in determining biodiversity patterns and the functioning of biological communities. The analyses also suggest that altering the natural linkage between dendritic connectivity and patch size strongly affects community properties at multiple scales. The first part of this thesis (chapters 2 and 3) addresses key aspects of biodiversity-ecosystem functioning research where the combination of theory-guided experiments and theoretical investigations shows how a stochastic implementation of population dynamics proves fundamental for key community properties such as species persistence and community stability. The diversity-productivity and diversity-stability relationships are explored. Both experimental findings and the results of a stochastic model fitted to the experimental interaction matrix, suggest the emergence of strong stabilizing forces when species from different functional groups interact in the same environment, increasing species coexistence and community biomass production. The last part (chapter 6) provides a synthesis of this thesis work, in that it aims at unifying aspects from niche-theory, usually adopted in spatially implicit models, with those characteristic of a spatially explicit context from a typical real-life mountainous regions. It is dedicated to the possible explanation for a macroecological pattern routinely observed from organisms in different domains of life, that is, the mid-elevational peak in local species richness. Guided by empirical observations on diversity of macroinvertebrates in Swiss river basins, a theoretical ansatz is provided which is deemed to capture the essential geomorphological drivers and controls relating species-fitness to altitude. A set of overarching conclusions and perspectives for future research are discussed in the concluding chapter.

EPFL2013

Subalpine Pasture-Woodlands in a Changing Climate

Konstantin Svetlozarov Gavazov

EPFL2013

Spatiotemporal patterns of urbanization during the last four decades in Switzerland and their impacts on urban heat islands

Martí Bosch Padros

EPFL2021

EPFL2013