We put forest trees back into our urban landscapes, not the way they were before, not the way they have evolved to exist, but according to our needs and our designs. Find out more in this blog by Naomi Zürcher.
The topic Resilient Cities has prompted me to sit back and get analytical. Most of us know what a City is – the attributes as well as the downside. I have lived in a City for most of my entire life – 70 years mostly in New York but also Mexico City and now Luzern Switzerland. The 3 represent a good sampling of cities and diverse city life.
But, what about resilience? If one looks at the Oxford definition of resilience, one finds the following:
- the capacity to recover quickly from difficulties; toughness;
- the ability of a substance or object to spring back into shape; elasticity.
While I would never equate a city itself with resilience given all the layers of Governance, what a city does do is demand resilience from everything that resides within it. Envisioning a city’s residents, I can think of none that better represents the definition than the urban trees that reside in a city’s Urban Forest.
Historically, almost all of our urban trees originate in a Forest somewhere in the world. In order to understand the underpinnings of our urban trees and the extent of their resilience, we first have to understand the where and what they came from:
- Forests are a Process of Succession, of Evolution.
- Forests don’t happen in a day, a week, a year. They occur over millennia, beginning with the specific soils they populate.
- Forests are a sophisticated, highly-developed community of trees and all their associates – other flora, fauna and, most importantly, soil containing a healthy soil microbial community, providing the nutrients, macro and micro, all associates in the Forest community depend on.
- Forests evolve in direct relationship to their environment – temperature range, the soil’s pH and the availability of light and water will all dictate what is growing and where – edge or interior.
- Although a Forest may consist of many different species of trees, space above ground is shared in competition while space below ground is shared in community.
- Forest soil is always covered by plants, leaf litter or other organic Forest debris – a constant renewing and recycling of organic nutrient resources.
- Trees grow with their root crown – their buttress roots – above the soil line; all parts of the tree that are covered with bark are always above the soil.
So, here are all these trees, growing in a Forest community somewhere and along we come!!!
First, we built roads inside the Forest creating new edges, introducing sunlight to the Forest floor, where it never was before. Then we cleared the land and evolved through cultivating it into urbanizing it. Now that most of us are living in cities, we’ve decided we want to put these Forest trees back into our urban landscapes, not the way they were before, not the way they have evolved to exist, but according to our needs and our designs:
- When we plant inner Forest trees out in the landscape, the above ground competition is now gone and with it the space restriction on the spread of the tree’s branches, resulting in a much larger crown which, when not thought about before buying the tree, usually results in the wrong tree being planted in the wrong place – requiring either constant, excess pruning or the unnecessary and premature removal of the tree.
- We plant trees out in the lawn ignoring the competition turf inflicts on trees, both above and below ground; as a heavy feeder, grass deprives trees’ roots of essential moisture and nutrients, thus impacting and reducing tree root development.
- If we don’t plant our trees in lawn, then we plant them where the soil is bare and we leave it that way, diminishing the soil food web and leaving trees without the renewable nutrient resources they must have.
- We use construction equipment to build a project within a treed landscape, not realizing what we are doing to the soil and those important absorbing roots found within the top 30cm of soil; construction activities on unprotected soil usually compacts the entire underground landscape, making it inhospitable for trees’ roots. Healthy soil contains pores for air and water. Compaction crushes the pores that hold air and water. Roots cannot live in soil that has no air or water so existing roots begin to die and new ones will not grow.
- We plant our public trees into hardscape coffins in an inaccessible, inadequate soil volume and we expect those large canopy trees to thrive and provide all those wonderfully beneficial Ecosystem Services.
- Because the landscape underground is out of sight, it’s usually out of mind, leading to trees being planted in impossible growing conditions – too deep, in the wrong type of soil, in compacted soil or in an inadequate amount of soil to support the tree’s rooting needs – and then we blame the tree or the nursery we bought the tree because it didn’t survive or do what we had expected.
The fact that our urban trees, given their genetics and evolution, have found ways to deal with everything our cities and the new, very dynamic associate – us – inflict on them, one could, without any hesitation, give them the resilience award of the century. They not only embody the very spirit of the word “resilience”, they endure.
It behooves us – scientists, researches, academics and practitioners – to afford the powers that be an enhanced understanding of what City life could be if we, in the midst of all our urban UN-naturalness, recognized that when you plant a tree, you begin an entire universe so why not begin it tree -positive and really create a Forest in a then resilient city.
Naomi Zürcher is an independent Consulting Arborist and Urban Forester as Arbor Aegis and is involved with the current COST Action GreenInUrbs project.
Photo courtesy of the New Yorker Magazine.