Public Domain
Audio of People, Cities, and the Suburbitat
There are more and more people filling in the corners and hidden spaces of the Earth. I remember when I was in grade school (sometime in the early 1960’s) our teacher told the class that there were 3 billion people in the world. We then did some exercises to try to visualize that immense number. I don’t remember exactly what those exercises were, but I remember the number we were trying to understand staying quite abstract and difficult to grasp. Now, the Earth’s population is almost 8 billion people, and I don’t need to do any exercises to clearly appreciate that it is a staggeringly huge number! There are still parts of the world that are only sparsely populated. It is quite easy from where I am living now in Northern Colorado to drive off into a “Big Empty!” But, there are also many more parts of the planet that have gotten incredibly crowded!
New Jersey forest. Photo by N. Tonelli, Flickr
A good friend of mine grew up in New Jersey in a town across the Hudson River from New York City. He talked about rambling through the woods and wetlands near his home in the 1950’s collecting frogs, turtles and, to his father’s great horror, snakes. He listened to scarlet tanagers singing high up in the trees and saw their nests. He fished for eels in the local ponds and streams. I had a similar experience in Houston in the 1960’s with wild bayous and streams and open scrublands within a short walk of my suburban home. Both of these idyllic places, though, quickly filled up with houses and people! Overnight, wetlands were drained and filled, trees were cut and lawns installed. My rural-edged Houston house is now in the middle of a vast city. The turtles never had a chance! Cities always win.
In 1900 only 3% of the world’s population lived in cities. By the close of the Twentieth Century, that number had risen to 47%. In 1950 there were 83 cities in the world that had populations of over one million people, by 2007 that number had risen to 468.
In 1950, two cities (New York and Tokyo) had populations of over ten million people. In 2020, thirty-three cities had populations over ten million people. These very large urban areas are now referred to as “mega-cities.” The largest of these megacities are either Tokyo (37.9 million people) or Jakarta (34.5 million people) although some demographers combine the cities of Guargzhou (“Canton”) and Schezhen in China to form a megacity of over 40 million people. The largest city in the United States is New York City (with 20.9 million people) followed by Los Angeles (with 15.4 million people) (Population data from Demographia World Urban Atlas, 15th Edition (2020)). A good friend who lives in LA commented the other week that more people live in his county than live in the entire state of Ohio (or in 43 other American states, for that matter).
A United Nations report forecasts that by 2030 (only nine years away!) 60% of the world’s population will live in cities! The growth of the megacities and the growth of the slums in which people are crowded and sequestered are rapidly increasing.
New York City street. Public Domain
These urban and suburban ecosystems seem the antitheses of biodiversity. The great structural, energetic and goal-directional similarities of a city anywhere in the world would logically seem to drive their biotic systems to their lowest common denominators of plant and animal species diversity. One hypothesis concerning urban ecosystems infers that they must favor a limited set of species that are hardy and extremely generalized in their food and habitat preferences. Cities, according to this hypothesis, should all have very similar biotic communities. This idea, though, was not supported by some data published a few years ago (see Signs of Winter 6, January 7, 2016).
Looking at the plant and bird species of 110 cities around the world a study published in the Proceedings of the Royal Society B in February of 2014 emphasized that each urban area retained a unique set of endemic (“native”) plant and bird species. These species combined with a number of shared, “urban-tolerant” species generated unique biodiversity profiles for each urban area. Cities, of course, had fewer plant and animal species than surrounding “natural” areas, but cities were shown to support nearly 20% of the world’s bird species and 5% of the world’s plant species. Urban areas were far from the “biological deserts” that they have often been hypothesized to be.
Milan. Photo by Pikist
Trees in urban and suburban environments are often planted as a solution to the environmental problems of a city, and trees can be extremely important in these ecosystems. Trees not only can serve as habitats and food sources for a variety of animal species, but they are also extremely beneficial to human beings (see Signs of Spring 2, March 3, 2016). For example, trees help to reduce air temperatures by both blocking sunlight and also by transpiring water from their leaves (an evaporative cooling system similar to your body’s use of perspiration to cool your skin’s surface). A single tree can cool air to a comparable degree as ten, room-sized air conditioners running twenty hours a day! These cooling impacts can reduce energy consumption in the summer and also mitigate dangerous summertime “urban heat island” (UHI) effects.
Researchers have documented direct connections between UHI’s event peaks and human related debilities, illnesses and even fatalities. Heat stroke, heat exhaustion, heat cramps, and aggravation of heart diseases are just a small list of these UHI impacts on people. Further, the elevated temperature of the lower atmosphere over a city can lead to the accelerated production of ozone and smog with concomitant increases in respiratory disorders and diseases including asthma.
What else do trees do? Trees block the wind and reduce noise and glare. They trap dust and pollen and help to both reduce the high velocity impact of raindrops on soil (a major erosive force!) and absorb surface runoff of rainstorms. One tree can make enough oxygen to supply the daily needs of four people. One tree can also store 13 tons of carbon (from carbon dioxide) per year.
Trees are extremely important, but, trees are not really the answer to all of our urban and suburban ecological questions.
Doug Tallamy of the University of Delaware has looked deeply into the human-created habitats in our cities and suburbs and has some important insights about the quality of these ecosystems. He has compiled his observations and ideas into a concept that he calls the “suburbitat.”
It is not enough, Tallamy states, to just make green, leafy spaces around our homes. Those spaces have to be conducive to the growth and survival of native insects in order to be considered a fully functional component of the biosphere. We need to think about trees and also about all of the plants growing next to and under and on top of those trees in order to really develop functioning ecosystems!
Photo by L. Kalbers
Tallamy proposes that we “re-wild” the America landscape by shrinking our lawns (a very unproductive and lifeless expanse of alien plant species), by removing invasive plants (so many of these species are not palatable to vertebrate or invertebrate consumers), by creating no-mow zones (to stop from grinding up billions and billions of grass-dwelling organisms), by reducing outdoor lighting (which disrupts local invertebrate and vertebrate activity patterns and also long distance migration pathways), by planting keystone species (those plants that are shown to be , region by region, critical to the life cycles of our pollinating and decomposing insects), by welcoming pollinators and by avoiding chemical herbicides and pesticides. The resulting, complex suburban and urban vegetative habitats would be full of munching caterpillars, hunting spiders and a glorious diversity of beetles and other insects than would, in turn, support and sustain a myriad of birds and other vertebrates that feed on them.
This new ecosystem would be a “Homegrown National Park” where each of us could actually interact with Nature and not just look out at a lifeless, static, sanitized version of it. We wouldn’t have to fly or drive off to some distant place to experience Nature, but, instead, we could become part of it by just stepping out of our front or back doors.
A really excellent article about Doug Tallamy and his ideas about the suburbitat was in the Smithsonian Magazine in April 2020. Check it out!