Image caption Current urban expansion differs greatly from historical patterns of growth, say researchers

The way researchers assess urban ecology needs to change in order to take into account the way modern cities are developing, a study suggests.

Scientists in Australia said urban areas were expanding rapidly in a complex "non-linear" way that existing models failed to capture effectively.

Assessments needed to be modified if ecologists were to get an accurate picture of the environment, they added.

The findings appear in the Trends in Ecology and Evolution journal.

"Our paper aims to raise the awareness that the ingrained perception in ecology that urbanisation intensity and age - and associated environmental changes - vary in a [uniform manner] from the core to the city fringes, does not apply easily to contemporary patterns of urbanisation," said co-author Cristina Ramalho, a researcher from the University of Western Australia's School of Plant Biology.

"It is necessary, therefore, that ecologists adjust the way they think and conduct research to the reality of contemporary cities."

'Dramatic impacts'

She explained that, historically, cities grew slowly in a relatively compact manner, through progressive rings of urban development.

However, Ms Ramalho added, contemporary patterns of expansion were "markedly different".

"Cities are growing very rapidly, they are increasingly expansive and dispersed, sprawling in... spider-like configurations across large distances, and embedding fragments of other land uses in the rapidly changing landscape," she said.

Image caption Existing assessment models are based on historical but outdated urbanisation patterns, they explained

Ecologically, this type of expansion was having "dramatic impacts".

"It is driving the large-scale loss and fragmentation of natural and semi-natural habitats in several countries and cities worldwide," she told BBC News.

"In countries such as the US and Australia, urbanisation is one of the main drivers of biodiversity loss."

The researchers said current models used by ecologists to assess urbanisation looked at this issue in a "rather simplified" way - such as using broad categories, including urban, suburban and rural.

Ms Ramalho explained why this needed to be updated: "If contemporary cities expand in a complex, non-linear manner, then the assumption that urbanisation intensity and age can be assessed based on a site's position along a linear urban-to-rural gradient can be misleading."

She added that the measures also failed to adequately capture the effects of important drivers, such as landscape fragmentation and disturbances. She also said that the changing nature of urbanising landscapes were not reflected in systems that did not have a temporal dimension.

Sharper focus

The researchers suggested, as an alternative, that the impacts of an urbanising landscape should be assessed by looking at the changing attributes of a particular area, or the characteristics of a neighbouring landscape.

"Ecologists should move beyond the use of aggregated urbanisation measures and consider a comprehensive set of driving factors selected based on the characteristics of the study area and ecological question of interest," Ms Ramalho said.

"Ecologists should also consider the temporal dynamics of landscape change, and the effects of land-use history and time lags on biodiversity responses to on-going environmental change."

By adopting such an approach would provide information that would help policymakers and planners, she added.

"A temporal perspective considering the fragmentation and land-use history can provide insight into the remnants environmental conditions and conservation value and, therefore, be used in prioritising conservation.

"Priorities could be, for instance, those remnants without significant land-use legacies and those that were recently fragmented."