Architectural design proposals often depict high-rise buildings with trees flourishing on rooftops in an attempt to look more ‘green.’
Despite this, trees and skyscrapers are a lethal mix – for the trees.
Regrettably, trees rarely survive on the top of skyscrapers, undercutting ideas of including them as a nod to sustainability and environmental friendliness in the renderings. Such designs are not realistic as the trees will be stripped of their foliage and perish at such heights.
Rooftop gardens on residential homes and apartment blocks, on the other hand, are a viable way of adding a ‘green’ element to homes as plants and trees are able to survive much more easily there than atop a skyscraper.
Altitude poses many obstacles, making it virtually impossible for trees to thrive. Every form of weather becomes magnified on top of a skyscraper, meaning trees planted there can be exposed to extreme cold, heat, wind and precipitation.
Atop a skyscraper, wind is typically the most destructive force and can affect the form, growth, and survival of the tree. Wind affects the boundary layer of leaves, which functions to control the loss of gas and water through the leaf’s pores. The thickness of the boundary layer reduces and removes moisture-laden air replacing it with dry air, which increases the rate of transpiration.
Heavy winds cause pulling and stretching of the trees’ roots when they sway, disrupting root-soil contact and decreasing water absorption. Overall, wind increases the severity of water stress in trees, especially at high altitudes.
Extremely cold conditions can kill plants and trees by turning the water in their cells to deadly crystalline knives. Extremely hot conditions cause plants to sweat and release much needed water, breaking down their photosynthetic machinery.
There are also plenty of logistical concerns with putting trees on top of skyscrapers including maintenance and replacement. If the tree dies, it may disturb the daily functioning of the building occupants when it is removed.
Trees have a hard enough time growing on the ground in dense city landscapes, let alone on the top of a skyscraper in variable conditions. Skyscraper renderings should focus on adding trees to more practical areas such as streetscapes and low, flat roofs or balconies.
Trying to squeeze the growing population into urban areas is a challenge, and conserving the nature that still exists in these areas should be a priority.
The city of Brussels requires that flat roofs of a certain size must plant rooftop gardens. Designers should let go of the pipe dream of trees growing on top of skyscrapers and focus on areas where plants and trees are more likely to thrive.