The City Tree

Most days, a city tree is just a tree. It stands there, out of the way, but close enough if you need a shaded parking or walk. Other days, a tree will make one pause and wonder.

Cities all over the world remember to add trees to their streets and build parks from scratch to bring some nature closer to citizens. Parks and city gardens will have collections of beautiful trees which, much like a city’s inhabitants, are brought together from near and far.

Tall, elegant palm trees along the side of roads, or trees with spreading crowns so people can walk beneath; flowering trees that add hints of color, and trees with round crowns to soften the city landscape.

How do we choose which trees move to the city with us?

Tree choices can tell us something of the history and importance of a place, and the nature of the tree.

Cities built in the colonial era have plenty of introduced trees, sometimes because more was known about them than native trees. Newer parts of an urban area might have trees that mature faster so they are ready to adorn the city.

Trees that make it to the city are usually tougher, so to speak, chosen for their ability to withstand disturbances like road vibrations and strong winds, and their tolerance for fumes. There are also practical considerations. Trees that bear heavy, falling fruits or have large roots near the ground surface are not good choices where they pose hazards to people, property or infrastructure.

Urban trees are also chosen for their aesthetic or distinguishing qualities, especially those we find in public parks, open spaces or around prestigious public buildings. They are chosen depending on the context to produce a certain effect: comfort, grandeur, delight.

How trees benefit cities

Just like in their natural habitats, the roles that trees play in urban ecosystems are much more than meets the eye. Like all plants, they help keep excess carbon out of the air within their trunks and roots; their leaves and textured wood filter particulate matter and gases that are released by engines.

Our building materials and activities in cities make urban temperatures higher than they would be otherwise. Trees can cool cities as they release water vapor through their leaves and also by creating shade cover. The right tree selection and arrangement can also help block some of the noise we create as we travel, build and work in cities.

Trees and urban biodiversity

Urban trees also cater to the city wildlife. Tree flowers offer nectar to many kinds of bees, butterflies and moths, and fruits and seeds feed birds, squirrels and shrews. Tree branches and canopies provide spaces for nests and shelters and oftentimes, convenient transit throughout the city.

juvenile monitor lizard on tree trunk with building in background

Trees also make it possible for more plants to flourish in cities as they offer shade for young shoots growing beneath their canopies and support for ferns and climbing plants.

City view

Perhaps cities can offer trees something in return too.

City residents can experience and appreciate trees in a slightly different way than they would in the wild.

A bird’s-eye view of massive trees from atop the LRT, or high rise windows that offer a view of tree tops laden with tiny flowers and hidden nests.

And the luxury of time to watch and follow a sapling’s growth into a grand tree that flowers and fruits, nurtures and shelters, in a suburban backyard.

Oikos: An introduction to ecology

Sometime in the 19th century, Ernest Haeckel, a naturalist, came up with the word ‘ecology’ to draw attention to something that he thought was important: the ‘entire relations’ of an organism. By this, he meant that it was not enough to study one plant or animal species at a time. He believed it was important to study not only the organism but also its relationships with other living organisms and how it interacts with non-living things like climate, water, soil and light.

This came from the idea that an organism’s home (habitat or surroundings) has a great influence on its form (what a plant or animal looks like) and its behaviour (how it grows, moves, communicates and so on).

Tropical rainforest trees have shallow roots access nutrients found closer to the surface, unlike temperate trees that have deeps roots for nutrients found deeper in the soil.

Ecology is derived from the Greek ‘oikos’ which means home or household. It is the study of the relationships that exist among living things and between living things and their environment. This includes both non-living things like water, soil, climate and minerals, and other organisms that are of the same or different species.

All plants, animals, fungi and microorganisms form a complex web of relationships—an ecosystem—that supports their survival. Interactions occur at many levels and there are different types of relationships.

A group of the same species living in an area make up a population. Think, for example, of the myna birds you see anywhere near your home: together they make up your neigbourhood’s myna population.

Photo by Bishnu Sarangi from Pixabay

Ecologists can study populations of organisms, examining their behaviours, their adaptations to their habitats, and how their numbers change over time and geographic regions. Some ecologists will spend years studying individuals in a population. They will record their births and deaths, diets, movements, and the impact they have on their surroundings.

Plants or animals also interact with other species in their habitats. A community is a set of several, different species that occupy a given area.

Take a simple house garden. Its trees, flowering shrubs, grass, worms, birds, bees, butterflies, snails, moss and mushrooms form a small community. As a community, they interact with each directly (bees feeding on flower nectar) and indirectly (worms dig through soil and this makes it better for plants to grow later).

Communities can be as small as that of a thinly-populated backyard garden or be found within huge national forests.

Interactions within communities involve processes like pollination, decomposition, and feeding. These benefit the organisms and also provide many services for us. Ecosystem services include:

  • food and fuel provision
  • fresh water supply
  • pest and pathogen control
  • soil improvement
  • climate regulation

Ecologists study such relationships and their outcomes, exploring how ecosystems are formed and how they are sustained. Thus, ecology studies contribute to a wide range of fields and practices including agriculture, conservation, natural resource management and sustainable development.

Here are some of the questions that ecologists try to answer:

  • How do behaviour and physiology change in response to the physical environment?
  • How do organisms use the resources in their habitats?
  • How will ecosystems respond to human activities?
  • How can we restore degraded ecosystems?

As the world deals with changing environmental conditions, pollution, food security and species loss, ecology helps us understand ecosystems and how to protect them—for our own well-being and that of the planet.


References

Egerton, F.N. (2013), History of Ecological Sciences, Part 47: Ernst Haeckel’s Ecology. The Bulletin of the Ecological Society of America, 94: 222-244. doi:10.1890/0012-9623-94.3.222

https://www.britannica.com/science/ecology


You can learn more about ecology and ecosystems closer to home here:

Biodiversity in Cities

plant shoot road

In recent years, ecologists have begun to take a second look at plants and animals appearing in cities. There seems to be more ‘nature’ in urban areas than one would expect. Cities are supposed to be human territories—steel, brick and concrete—not exactly welcoming to wildlife. But urban places display a variety of species and habitats – biodiversity—in places we did not plan for them.

This makes us ask some questions:

Why are these plants and animals surviving in human settlements while others disappear? How and when did they move in? How many of them can survive in our cities?

Urbanized areas often share characteristics like:

  • hard surfaces (roads, pavement)
  • roads and buildings that break up natural, vegetated spaces
  • bright light at night, loud sounds, water and soil pollution

All of these are known to make it difficult for ‘natural’ habitats to survive near cities.

But there are also ‘built’ green spaces like public parks and private gardens that cultivate a wide range of native and exotic plants. These can form the bases of food chains that attract consumers (like ants, grasshoppers, bees, beetle, squirrels) and their predators (lizards, birds, and monkeys), without our approval. If left uninterrupted, patches of wild ecosystems can be established within these built spaces.

But exactly which species of birds, bees and trees settle in cities? Where in a city are you more likely to come across wildlife? And, how come I can see kingfishers in one district but not another?

Another attribute of cities is the diversity of the habitats (or shelters) they can, unintentionally, form. Within one city, you can find

  • abandoned lots-turned-grasslands
  • waterways
  • old buildings that create dark and cool shelters
  • long stretches of roadside vegetation
  • food gardens
  • golf courses
  • remnant forests

Each of these will have unique structural features, creating different kinds of habitats.

gliding lizard

For instance, reptiles that inhabit open spaces within their original forest habitats will probably adapt well to places in cities that have widely spaced trees and vegetation.

Wildflowers too benefit from the abundant sunlight and absence of competition (bigger plants) in urban patches. These are conditions not found beneath dense, natural forest canopies.

A more familiar example is the ubiquitous city pigeon. Have you ever wondered why this bird in particular flocks in cities worldwide? One reason might be the similarity between its original habitat – rocky cliffs – and the hard, ledged surfaces of city buildings that offer it space for nesting.

There is also another feature of cities that might be important for supporting biodiversity – the greater amount of food available. For species that are not very particular about their diet, gardens, cafeterias, litter, bird feeders, ornamental trees and nutrient-rich waterways offer abundant food resources.

So what does this mean for us?

One reason that ecologists are interested in urban wildlife is the benefits associated with biodiversity.

In natural ecosystems, there is abundant tree and vegetation cover, and processes like pollination, seed dispersal and decomposition that are carried out by large and small animals. All of these contribute services like food production, climate and water supply regulation.

These benefits (also known as ecosystem services) are important for us. If cities can support biodiversity, then they can help in species conservation and contribute these services that keep our environment healthy.

Urban biodiversity still poses many questions for ecologists to explore.

  • How much green space is enough for biodiversity conservation?
  • What ecosystem services can we expect from urban biodiversity?
  • How are urban plants and animals different from those in natural habitats?
  • How and why do biodiversity patterns vary among cities and geographical regions?

Answering these questions will take time and require that we pay closer attention to the other lives unfolding parallel to ours. 


Resources for further reading:

Müller, N., Ignatieva, M., Nilon, C. H., Werner, P., & Zipperer, W. C. (2013). Patterns and trends in urban biodiversity and landscape design. In Urbanization, biodiversity and ecosystem services: Challenges and opportunities (pp. 123-174). Springer, Dordrecht.

Schilthuizen, M. (2019). Darwin comes to town: How the urban jungle drives evolution. Picador.

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Visit @ubi_my and @Urban Biodiversity Malaysia for more on Malaysia’s urban biodiversity