A Different Perspective on a Familiar Place

 Sep 21, 2015    by Adam Dale

Do you live in a city or its suburbs? Probably. If not, you’re one of the few. I have either lived in the suburbs or near the heart of a city for my entire life.

Do you ever think about how plants and animals are enjoying the city life? I certainly didn’t until the past few years.

Over 80% of people in the United States and 60% of people (3.4 billion) in the world live in urban areas, and this number is increasing faster than ever (~5 billion by 2030). Cities are expanding and becoming less dense, which means it’s taking fewer people to affect our environment more, and people are multiplying like aphids (insect metaphor, anyone?). However, few notice the actual aphids and other closely related insects that are thriving around them.

Towards the end of my time in college I started to think more about cities. That led me to graduate school where I have been studying the plants and insects that live in cities. Specifically, I research how things like roads, plants, and temperature affect insect pests of trees. Once you start to critically think about what is around you as you walk through town, it can be a real eye-opener.

The next time you are driving through town; take a look around at what the town is made of. Look at the cement sidewalk with a tree planted in the middle of it and ask yourself if that tree looks happy, if there are any insects visiting it, and if there is a better alternative to where it is planted. Think about how hot it is when you walk across the asphalt parking lot on your way into the grocery store. Look at how many trees or shrubs are planted (and living) along the road, sidewalk, or parking lot. Look at the flowers and see if there are any bees or butterflies visiting them. Look at the chunk of hot dog someone dropped on the ground and see if anything is eating it, or think about what happened to it if it’s gone when you walk by tomorrow. As you step over a pile of fresh dog poo, think about where that poo may end up. It’s got to go somewhere, and hopefully not on the bottom of your shoe.

My point is there are living organisms everywhere in cities that do the dirty work, suffer, or take advantage of what we’ve turned their environment into. And most of the time they go unnoticed.

When people build cities they generally use roads, buildings, parking lots, and sidewalks, which soak up the sun and release it as heat. This makes cities really hot, unless you live in a desert. If you want the nitty gritty, NASA recently came out with a nice review on the impact that cities are having on the surface climate of the U.S. But in essence, people replace plants with pavement and make it painfully hot.

Many people talk about the doom and gloom of global climate change and how it will affect us by the end of this century. However, if you live in or near a city you don’t have to wait 85 years. Cities have a different climate than their surrounding natural areas. No, the ocean isn’t in your living room yet (without a storm to help). But places like newly developed neighborhoods, shopping centers, and downtown city centers are much warmer than the older neighborhoods and parks within city limits.

The pavement backbone of cities also breaks up woods and meadows into smaller spaces for plants and animals to live. In cities, these small patches equal hot (pavement) and cold (vegetation) areas that when looked at as surface temperatures from above create something like a mosaic from a cathedral window. As you may imagine, these temperature and vegetation differences affect the plants and animals trying to live there. However, we have a lot to learn about what these effects are and how to manage them. This is where my work comes in.

It has long been known that many plant-eating insects thrive in urban landscapes but not in natural forests. There are multiple reasons for this, but we don’t fully understand them. This is bad because those plants filter the air we breath, create cooler temperatures, and make everything prettier. But not when they have bad pest problems.

If you live in the southeastern U.S., there is a native insect, disguised as a bark-colored wart, that is probably feeding on the maple tree in front of your house or business. And on the one down the street. This insect is called the gloomy scale, and it loves soaking up the sun and basking in the heat coming off the road next to it. That heat means it can pump out more babies that will also feed on the tree, which means several years from now that tree may be near death. It turns out that if you had planted that maple tree in a place with less pavement nearby, it may not have this problem.

That insect’s cousin on the oak tree down the road is also ecstatic because the heat is helping it escape from being stabbed in the gut with a harpoon and injected with an egg that will eat it from the inside out. A less gruesome effect of this temperature difference may have implications for pollinators. If flowers in warmer urban areas bloom earlier than normal, how will bees find and pollinate them?

As issues like these come to light, it is becoming more apparent that addressing them requires the work of people with several expertise. The days of laboring away and solving problems alone are over if you want to make real progress. An ecologist isn’t going to come up with the best planting method and tree species to plant along city streets that will maximize biodiversity and tree health while serving a purpose in a functional and safe landscape. But an ecologist, entomologist, sociologist, horticulturalist, landscape architect, and the public working together might.

As we understand cities better, it will not only tell us more about where we live, but it can help us understand where we’re going. It turns out that the sneaky gloomy scale feeding on the maple on your street corner also loves when natural forests get hot. Over the past century, numbers of this insect have gone up and down as temperature went up and down in natural forests. Climatic temperature fluctuation is normal, but now forests are warming more than ever because of us. Therefore, learning about these things in cities could really help us prepare for the future.

Now, the next time you’re driving down the road, think about how you might do things differently if you were the one making the decisions. Like selecting which trees to plant along the sidewalk or how to make the parking lot cooler so you can walk across it without breaking into a sweat. These are very difficult decisions to make. However, they are decisions that we should question so that we can ensure that we’re doing the best thing for now and the future.

I was recently near Asheville, NC at a new brewery, which had solar panels shading the parking spaces in their huge parking lot. Renewable energy, shade, and cold beers. That’s great! Figure out a way to get some lush trees and shrubs into the mix that don’t have any pest problems, and you’ll really be doing something.

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Photo: Adam Dale

Photo: Environmental Systems Research Institute(ESRI); Modified graphic from Dale, A.G. and Frank, S.D. 2014. PLoS One. doi:10.1371/journal.pone.0102996