The evolution of naturescapes, over time and space

I love maps. Since I was a child, I loved looking at maps and navigating. When I started getting into ecology, I ended up specializing in what is called “landscape ecology”, the study of the reciprocal relationships between the patterns and processes that shape landscapes, in large part so I had an excuse to look at lots of maps. My graduate work was focused in the urban area where I am from (the Raleigh-Durham area in the United States), trying to understand why the remnant forest patches, mostly second-growth regrowth from abandoned agricultural fields, are located where they are located. Again, lots of maps, moving my gaze over time and space.

That background prepared me for my role in the Naturescapes collaboration, studying how the naturescapes in our 30 research landscapes are structured spatially, and how they changed over time. Each landscape (a Functional Urban Area, centered on a city but including rural and agricultural surrounding areas that are within a commuting distance of the city) has its own story.

In some places like Lima, there has been quite rapid urban growth, expanding into surrounding natural land cover (in the case of Lima, this is mostly desert). This is true to a lesser extent in Gothenburg, where the urban area has slowly expanded into surrounding forests. Conversely, the story in Lisbon and Iasi is the expansion into agricultural landscapes, which means urban growth has implications for food production and security.

History matters!

So what have we found in our study of all these landscapes over time? One of the biggest research questions we wanted to answer was, what is the role of history in determining the amount and kinds of urban nature? We knew from past research that often older cities (at least European cities) have denser cores that newer cities (at least in North America and Australia), which were settled at lower density. And other research has showed that denser cities often have less nature, especially less large patches of natural habitat, simply because more of the landscape is buildings and pavement [1].

The pattern we found was a little more complicated. We reconstructed the history of urban development for each urban area, calculating the median settlement date (the average date in which a neighbourhood within the urban area was built). If we simply compare older cities (those whose average neighbourhood was built before 1970) to newer cities, we find that older cities have generally more cropland but less natural habitat than newer cities. Basically, most of our older cities were in Europe, and have expanded into historically agricultural landscapes (like Lisbon and Iasi), while our newer cities were in the Americas, and were expanding into landscapes dominated by natural habitat.

Figure 1. Changes in land cover across four metropolitan areas, utilizing data from the ESA-CCI 300m land cover datasets for the years 1992 and 2019, and the ESA-CCI 10m data for 2023.

Figure 2. The effect of mediant settlement period on land cover.

Climate matters!

Another research question we wanted to answer was, how much does climate influence the amount of urban nature available for residents? We were particularly interested in urban tree canopy cover, which past research has shown was related to climate, especially to how arid the landscape is. It takes a certain amount of water to support trees. In humid climates, this is supplied by rainfall, while in semi-arid and (especially) arid climates, trees have to be supported by supplemental watering. We hypothesized that we would also see this trend in our sample of urban areas studied in Naturescapes.

This hypothesis was supported. Generally, more humid climates have more tree cover and more arid climates have less. However, there are interesting exceptions. Dublin for instance is a very moist climate, but has relatively low tree cover. This is consistent with its history, as an older city and one located in an agricultural landscape. Conversely, Phoenix is an arid environment, but has a relatively high tree cover considering that. This may have to do with the American obsession with having a landscaped garden with lots of green, and a willingness to spend a lot of irrigation water to maintain trees.

Figure 3. The effect of aridity on tree cover in our 12 functional urban areas.

Context matters when setting targets

Context is important for evaluating trends over time and space for nature in urban areas. We can’t set meaningful targets without taking this into account. One of the overarching goals of Naturescapes is to understand what transformative change means, and how we measure progress toward it over time. Our research shows that different functional urban areas start in really different situations, with different amounts and kinds of urban nature, so any attempt to measure progress toward transformative change must take these different starting points into account.

Footnotes

[1] McDonald, R.I., Aronson, M.F., Beatley, T., Beller, E., Bazo, M., Grossinger, R., Jessup, K., Mansur, A.V., Puppim de Oliveira, J.A., Panlasigui, S. and Burg, J., 2023. Denser and greener cities: Green interventions to achieve both urban density and nature. People and Nature, 5(1), pp.84–102.

Author: Robert McDonald

Robert is Lead Scientist for Nature-Based Solutions and Lead Scientist for Europe at The Nature Conservancy. He researches the impact and dependencies of communities on the natural world, studying how nature can increase resilience in the face of climate change and improve human health and well-being. In his free time, he loves exploring the Alps with his family, in summer or in winter.