Swayambhunath "monkey temple' overlooking the rooftops of Kathmandu, Nepal

Swayambhunath "monkey temple' overlooking the rooftops of Kathmandu, Nepal

Cities Can Be Part of the Solution in Sustaining Species

Urban land expansion of up to 1.53 million square kilometers of new land will threaten the survival of more than 800 species but a focus on urban planning that protects habitats can mitigate the impact.

Within the next 30 years, the global urban population is projected to increase by 2.5 billion people, which will greatly increase urban spread. Much of this urban expansion is predicted to occur in biodiversity hotspots, imperiling a wide variety of species, many of which are already threatened by extinction.

Expansion is projected to result in up to 1.53 million square kilometers of new urban land, directly threatening 855 species, according to the findings of a new PNAS study co-authored by Karen Seto, Yale School of the Environment Frederick C. Hixon Professor of Geography and Urbanization Science, YSE PhD student Rohan Simkin, Walter Jetz, director of the Yale Center for Biodiversity and Global Change and professor of ecology and evolutionary biology, and Robert McDonald, lead scientist for nature-based solutions at The Nature Conservancy.

The study identified hotspot cities that are predicted to have particularly large impacts on species habitats. Many of the hotspot cities are in equatorial regions where urban growth coincides with biodiverse habitats. The cities that pose the greatest threat to species due to expansion are predominately located in the developing tropical regions of sub-Saharan Africa, South America, Mesoamerica, and Southeast Asia.

We can build cities differently than we have in the past. They can be good for the planet; they can save species; they can be biodiversity hubs and save land for nature.’’

Karen SetoFrederick C. Hixon Professor of Geography and Urbanization Science, Yale School of the Environment

Threatened species on the International Union for Conservation of Nature’s Red List are disproportionately represented among the heavily impacted species.

But focusing global efforts on minimizing impacts on habitats in these growth regions can help conserve and protect species, the authors say.


Threatened Species

New urban land expansion is directly threatening 855 species. Explore the projected patterns of urban expansion and biodiversity impact.

The study relied on data from Yale’s Map of Life — a collection of species distribution data used to monitor, research, and create policies that protect species worldwide. It also used a recently developed suite of land-use projections to assess future habitat loss from urban land expansion for more than 30,000 terrestrial species globally. It found that urban land expansion is a significant driver of habitat loss for about one-third of these.

The report comes as the 15th Conference of Parties convenes in April to decide the new post 2020 biodiversity conservation framework. The study demonstrates the need for global conservation efforts to include policies to preserve species in urban lands.

“Cities are actually part of the solution,’’ says Seto. “We can build cities differently than we have in the past. They can be good for the planet; they can save species; they can be biodiversity hubs and save land for nature.’’

The study found that the largest impacts on species were not from the largest cities in the world, but from urban areas with a myriad of endemic species where expansion can destroy habitats. And these areas are rapidly becoming more urbanized.

“One of the aims of the study was to identify those species, not that just are threatened, but that are specifically threatened by urban land development,’’ says Simkin, the lead author of the study. “I think that the average person on the streets is very aware of the climate crisis now, but I’m not sure they are aware of the biodiversity crisis.”

But obstacles to containing sprawl include economic pressures, governance structures and awareness of the importance of habitats and preserving biodiversity. It’s easier to build out, not up, Seto notes.

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Species under the most expansion pressure are concentrated in areas from central Mexico through Central America, the Caribbean, Haiti, Nigeria, Cameroon, Sri Lanka, Indonesia, Malaysia, Thailand, Brazil, and Ecuador.

“We are at a critical moment when the world’s governments are renegotiating their commitments to the Convention on Biological Diversity. This study is important since it lets us quantify, for the first time, which specific species are most threatened by urban growth and where urban protected areas are needed to safeguard them,’’ McDonald says.

Global agreements on biodiversity and conservation that focus on protecting the habitat of species that are predicted to be the most vulnerable, investments from the Global Environment Facility and targeted action at local scales can help mitigate impact on species.

“The study offers vital decision-support in regions across the world to plan for urban growth that minimizes the loss of biodiversity,’’ says Jetz. “It leverages the Species Habitat Index, a central biodiversity change indicator of the draft post-2020 Global Biodiversity Framework of the Convention on Biological Diversity, to assess future scenarios.”

Seto says despite the potential for loss of species from land expansion, the study highlights how cities can proactively protect biodiversity.

“The majority of these places have yet to be built,’’ she notes. “Science-driven policies that guide how the cities of tomorrow get built will have a tremendous effect.”

Seto is the coordinating lead author of the urban mitigation chapter of the upcoming Intergovernmental Panel on Climate Change (IPCC) report, which will address the most up-to-date physical understanding of the global climate system and climate change.

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