In wrapping up the functions of landscapes series, it is fitting to end with ecosystem service functions. Ecosystem services function in order to sustain life through the use of natural systems. As Landscape Architects it is our responsibility to design landscapes that utilize natural systems for human benefit. In Part I of the ecosystem services discussion, we discussed the value of Stormwater Management. For this blog post, we’re going to discuss how ecosystem services function to control air and soil temperatures and create habitat for animals and insects.
Wait A Second. Plants Providing Heating and Cooling?
It might sound strange to say that plants – trees and shrubs – can help to control the temperature of the air and ground. After all, we pay big money to heat our homes and offices in the winter and air condition them in the summer. But it’s really not as strange as it sounds.
Think about the last sunny day that you went to the grocery store. It was your lucky day! You found a parking spot with a tree casting shade right between the yellow lines.
Those spaces are always the first to be taken! Why? Because everyone knows that on a hot day, parking in the shady spot will keep your car much cooler than parking in a sunny spot. This tree is controlling the air temperature in and around your car.
Urban Heat Islands
A little heat from the sun isn’t a big deal, but once you get it in greater quantities it quickly becomes a problem. The term for this problem is the Urban Heat Island Effect. Merriam-Webster defines a heat island as “an urban area in which significantly more heat is absorbed and retained than in surrounding areas”.
Think about the example of keeping your car cool in a parking lot. The tree adjacent to your parking space kept your car (and the pavement surrounding it) at a manageable temperature. However, the rest of the parking lot heated right up.
When I was a kid, I loved going to the beach. When it was time to leave, I would often walk barefoot to the car so that I wouldn’t have to put shoes on my sandy feet. I can remember “walking the tightrope” on the yellow parking stripes through the parking lot. They were cooler than the surrounding asphalt. I could walk on them comfortably in bare feet.
This is because dark colors absorb more heat than light colors. And this concept plays out in the urban heat island problem. Most of the pavement in our cities is asphalt (as are most of the shingles on our roofs). Dark, black asphalt absorbs the heat from the sun all day, everyday – summer and winter.
Why Urban Heat Islands Are A Problem
Urban heat islands are a problem because of what happens after all that solar heat is absorbed during the day. It is released at night. This keeps urban areas overall warmer than their rural neighbors. Urban heat islands increase temperatures of stormwater runoff, which in turn raise the temperatures of local lakes and streams, like we discussed in the stormwater management blog. Additionally, urban heat islands create conditions that promote heat waves in cities. High temperatures can be detrimental to human and animal health, not to mention spikes in your utility bills.
How Do Ecosystem Services Mitigate The Effects of Urban Heat Islands?
As we discussed with the example of parking under a shade tree, we know that trees can help to reduce the effects of urban heat islands. Trees intercept solar radiation with their canopies and use that energy to produce food for the tree. They also perform a function called evapotranspiration, which means that trees release water vapor into the air that can have a cooling effect.
These natural functions that trees provide can decrease the effect of the urban heat island when tree canopy increases and unshaded surfaces decrease. These dense pockets of trees are called urban forests.
I have the pleasure of experiencing an urban forest on a daily basis. The street where our office is located is lined with mature shade trees. The canopies often overlap and hide the sun from the road and sidewalk. There is a noticeable increase in temperature (and need for sunglasses) when I drive from our office onto Martin Luther King Blvd. This concept is easy to see from the google aerial image of the neighborhood!
When Trees Are Strategically Planted
Unfortunately, urban forests aren’t created automatically. It takes thoughtful design professionals to develop a site plan that creates a place where trees can perform the function of mitigating the urban heat island. Planting areas that are adjacent to pavement are often harsh growing conditions for trees and shrubs. It is imperative that the designer know the cultural preferences and limitations of the selected trees. As my favorite MSU Horticulture prof always says, “You need to put the right plant in the right place!” When you place a plant in a location where the site conditions will allow it to thrive you begin to create an ecosystem, which leads us to our next function of ecosystem services.
The Goal of Ecosystem Services
Merriam-Webster defines an ecosystem as “a community of organisms and its environment functioning as an ecological unit.” This definition means that an ecosystem is more than just landscape. And it is more than weather. And ecosystem needs to sustain life – insects, animals, and humans. In order for an ecosystem to fully function, all these aspects need to work together.
When Ecosystems Lack Biodiversity
A bio-diverse habitat is an area that sustains many different types of trees, shrubs, grasses, forbs (flowering plants) as well as a broad range of insects and animal life. It is often tempting for a designer to limit the biodiversity of a site for the sake of creating a unified design. A designer may, for example, want to create a bold statement with Flowering Pear trees lining a walkway. These trees will standout with their impressive bright white spring blooms.
While there is a time and a place for this type of unity, it needs to be used carefully. There is a cost to planting with only one species.
Planting with one species can lead to a decimated landscape if a pest or disease is introduced, which attacks that particular plant. This happened during the mid-20th century with the introduction of Dutch Elm Disease. More recently in the late 20th and early 21st century the same occurred with the Emerald Ash Borer. In both cases, communities across the US lost millions of trees in urban and rural forests alike. While the losses were devastating, areas with greater plant diversity suffered fewer losses because they had other types of trees growing in their communities.
When Ecosystems Promote Biodiversity
On the other hand, there are great benefits to creating a biodiverse ecosystem. First, a biodiverse ecosystem can be very beautiful. When plants are mixed together to establish a diverse ecosystem, they display their aesthetic characteristics at various times. Some flower in the spring and/or summer. Some display fiery leaf color in the fall. There are often unexpected surprises throughout the year.
But biodiversity is more than beauty. A diverse landscape creates habitat for insects, birds and animals. I previously discussed our home landscape and why we designed it the way that we did. In order to achieve our goal of testing out different plants, we created a very diverse landscape. Even in our small city lot, we planted over 70 different cultivars of plants. We also built a bubbling water feature.
In the short time since we’ve planted these plants, we’ve seen countless different species of birds sitting in our dogwood tree, visiting our fountain to preen, and eating seeds from our coneflowers. We have observed squirrels playing tag through our shrubs, rolling in some open soil under our arborvitae, and chowing down on our neighbor’s spruce tree cones.
We’ve had rabbits and chipmunks, though they have acted more like nuisances than thoughtful garden visitors. Our resident hawk doesn’t mind their presence though!
Of late, we’ve observed a bevy of pollinator activity on two different plants in our garden. We’ve noticed bees – the big fuzzy ones all the way down to the little fast ones – collecting nectar and pollen from Allium ‘Millennium’. We’ve also seen bees and other pollinator insects (including flies) on our Hydrangea paniculata ‘Pinky Winky’.
Bees have been featured in the news a lot lately. The varroa mite is attacking the hives in the winter. There is a link between neonicotinoid pesticides and bee death when the pesticide is sprayed on flowering plants. We need bees (and other pollinators) to do the hard work of pollinating the fruits and vegetables that we like to eat! So, it is important to create environments where they can find constant sources of food, water and protection from predators. This is what an ecosystem is all about.
Growing the Design Toolbox
All in all, it is amazing to think of the ways that our environment has the potential to make our lives comfortable. Trees and other plants mitigate extreme temperatures. Bees and other pollinators go about their daily lives, and as a byproduct, they create food for us to eat. When designers develop landscapes that utilize these ecosystem services, our lives are profoundly enhanced.
Read about the other functions of landscapes: architectural functions, engineering functions, aesthetic functions and part I of the Ecosystem Services functions of landscape, which discusses the role of stormwater.