We live in a warming world, where growing threats from climate change require climate adaptation.
As the world seeks solutions to the crisis, urban forestry is a key component of any civic strategy that’s looking at ways to maximise the benefits that trees provide.
Clean The Air
Trees are our survival tool.
They are often referred to as the “lungs of the planet” because they alter our environment by using their leaves to filter the air we breathe, by absorbing carbon dioxide from the air while releasing oxygen.
Did you know that just one tree can produce enough oxygen for four people?
Trees also filter pollutant gases by intercepting airborne particulates such as nitrogen oxides, ozone, ammonia, and sulphur dioxide in their leaves – which help reduce smog.
Researchers have found that urban trees and forests are saving an average of one life every year per city because of the particulates that they remove from the air.
And that old-growth trees hold much larger amounts of carbon and harmful pollutants than their younger counterparts.
Each year, one tree cleans and purifies around 100,000 square metres of polluted air, creates 700 kg of oxygen, and absorbs 20 tons of carbon dioxide.
Annually, a hectare of trees absorbs the amount of carbon dioxide equal to driving your car 100,000 km. A mature hectare of trees can yearly provide oxygen for 40 people.
Cool Down The Streets
Global warming is on the rise.
Temperatures are increasing while tree coverage is declining.
With over half of the world’s population living in cities — notoriously hotter because of concrete buildings, poorer air quality, limited shade and reduced green space — we must try all we can to beat the heat.
Removing trees and replacing them with heat-absorbing tar roads, large impervious surfaces such as parking lots, industrial complexes and concrete buildings, makes cities much warmer.
Studies suggest we need at least 40 percent canopy coverage to combat the heating effects of concrete in cities.
Trees can cool cities more than 5 °C by providing shade and releasing water.
Shaded surfaces can be 11–25°C cooler than unshaded surfaces.
Just three trees around your house can reduce air conditioning costs up to 30 percent, and by providing windbreaks, save 10–50 percent of energy needed for heating.
A tree is a natural air conditioner.
The evaporation from a single tree can produce the cooling effect of ten room-size, residential air conditioners operating 20-hours a day.
Acting as a natural air-conditioner, leafy green neighbourhoods with a lush canopy ensure that summer temperatures are at least 3 to 4 °C lower than in comparable suburbs without trees.
Trees reduce storm water runoff, which reduces flooding, decreases the flow of polluted water into the sea, and protects the banks of rivers.
This makes them a very important part of storm water management for a city, because they hold vast amounts of water that would otherwise stream down hills, surge away, and be wasted – to say nothing of reducing water management costs.
Filter Storm water Pollution
Without trees, storm water flows into waterways without being filtered.
By breaking the rainfall and allowing water to seep into the soil, trees prevent storm water from polluting oceans and rivers, since storm water can be full of phosphorus pollutants and nitrogen.
Rain and wind are two primary erosion forces that damage bare soil.
As they fall, drops of rain gain power and momentum strong enough to penetrate soil once they hit the ground. But if the land is dried out, then wind can do significant damage.
Trees break droplets of rain and weaken their strength, while roots hold the soil together and protect it from effects of wind. Trees help soil obtain moisture.
Did you know that the loss of topsoil is SA’s greatest export?
Trees increase fertility and help soil retain moisture.
Fallen tree leaves lower soil temperature and prevent soil from losing too much moisture.
Decaying leaves that fall onto the ground turn into nutrients for tree growth, boost biomass, and promote micro-organism development.
Trees bring natural elements and wildlife habitats into urban surroundings, all of which increase the quality of life for residents in the community.
These habitats support an incredible variety of living things, known as biodiversity.
By protecting trees, we also boost the other plants, birds and animals that they shelter.
Studies show that high levels of biodiversity have a “dilution effect” on disease within hosts, making diseases less likely to jump to humans (zoonotic). Already, three out of every four new infectious diseases in people come from animals.
By protecting forest habitats and the species that live within them we could prevent future pandemics.
Burning fossil fuels puts heat-trapping carbon dioxide into our atmosphere, changing our climate in dangerous ways.
Deforestation accounts for roughly one-fifth of greenhouse gas transmissions – greater than the entire global transport sector.
Growing trees can slow down this process. A tree can absorb as much as 22 kg of carbon dioxide per year, so can sequester 1 000 kg of carbon dioxide by the time it reaches 50 years old.
Bump Up Climate Resilience
Urban forests include street trees, parks, and other elements of green infrastructure.
They provide benefits for both carbon mitigation (removing carbon dioxide from the atmosphere via photosynthesis and reducing greenhouse gas emissions) and climate adaptation (helping human and natural communities adapt to changing conditions, such as more frequent extreme heat or longer periods of drought).
Fuel Energy Source
If harvested and treated sustainably, woody biomass from trees can provide a low (not zero) carbon fuel and a great renewable source of energy.
Trees are simple to use, have been around since the beginning of time, and with smart management, can become an excellent eco-friendly fuel – to say nothing of braai wood.