Predicting Ecological Connectivity in Urbanizing Landscapes

Abstract

Nearly half the world's population lives in urban centers, and these areas are increasingly important components of regional and global land cover. However, their ecological attributes are often overlooked, despite the presence of species, ecosystem services, and risks associated with the spread of pests or threatening processes such as fire. Movement and dispersal of organisms contribute to species persistence in urban landscapes; however, landscape patterns that promote ecological connectivity may also facilitate the spread of undesirable organisms or processes. I investigate how urban form can be used to predict ecological connectivity and assist in prioritizing urban landscapes for conservation activities and risk management. I examine the value of qualitative and quantitative descriptions of urban morphology as predictors of ecological connectivity by comparing sixty-six cities in the USA. Results show that qualitative categories are not adequate for describing ecological connectivity; multivariate descriptions are much better predictors, with urban area, number of urban patches, urban patch extent, level of aggregation, and perimeter area fractal dimension composing the significant synthetic variables. The dominance of area as a differentiating variable led to the development of a new urban connectivity index using a combination of urban area and state population size. This metric, based on readily available aspatial data, explains 78% of variation in ecological connectivity. These results provide a simple but novel tool for beginning to understand the role of urban morphology in promoting desirable environmental outcomes and managing environmental risks in urbanizing landscapes.

Assessing the capacity of different urban forms to preserve the connectivity of ecological habitats

“…Their study yields no conclusive results and shows that similar urban forms may induce a varying environmental quality. Conversely, Bierwagen (2005) shows that urban areas that differ visually may nonetheless have similar ecological connectivity scores. Her study also shows that ecological connectivity declines with the increasing size of the urban area.…”

“…While numerous studies have analyzed responses of animals to anthropogenic habitat fragmentation, little research has addressed the relationship between habitat fragmentation and form of urban patterns (Bierwagen, 2005(Bierwagen, , 2007. The limited transfer of knowledge between the eco-physical and spatial planning domains, underlined by Termorshuizen, Opdam, and van den Brink (2007), may partly explain the lack of knowledge about the relationship between urban forms and ecological systems.…”

Spatial assessment of landscape ecological connectivity in different urban gradient

“…There are some statistical procedures proposed to select potential indicator species, including ordination and clustering methods (Dufrêne and Legendre 1997) and quantitative criteria such as the frequency of occurrence and habitat specialization (Carignan and Villard 2002). Third, this study utilized a circular shape for zonal classification, but using different geometric shapes or any other arbitrary shapes to describe urban forms would be possible (Snellen et al 2002;Bierwagen 2005Bierwagen , 2007. If asymmetric or irregular shapes can technically be applied to this type of analysis, it may capture more realistic urbanization density structure even though little difference would likely to be found for connectivity patterns.…”

Invasive alien plant species, fragmentation and scale effects on urban forest community composition in Durban, South Africa

“…Forest edges have lower canopy cover and are closer to transportation corridors and thus they may have weaker physical and environmental barriers to invasion (Hansen and Clevenger 2005). Forest edges create a favourable micro-climate for establishment of invasive alien plants (IAPs) (Vidra 2004;Bierwagen 2005;Bergsten et al 2013). This implies that forest patches that are highly fragmented can have altered successional processes, whereby early successional exotic species alter and increase the risk of decline in native species (Singer et al 2016).…”

“…This means that connectivity is a vital element to maintain gene flow and to facilitate species movement, distribution, dispersal and recolonisation (LaPoint et al 2015;Naicker et al 2016;Nor et al 2017). Consequently, it may also influence the success of establishment and spread of IAPs (Vidra 2004;Bierwagen 2005;Procheş et al 2005).…”