Stifling Cape Town drought puts the heat on urban trees
Everything is parched or wilting in the drought, but for trees in urban environments it means they can't perform their valuable ecosystem services
Thousands of kilometres away, researchers studying thirsty trees have come up with information that could save trees wilting in Cape Town’s worst drought.
The study, in North Carolina, US, found that urban trees “can survive heat and insect pests fairly well – unless they are thirsty”.
This means that when there isn’t enough rain, trees in urban environments don’t just become stressed through thirst, they become unable to handle problems such as insect invasions.
“This is important because trees need to grow in order to perform valuable ecosystem services, such as removing pollutants from the air and storing carbon,” said Steve Frank, an associate professor of entomology at North Carolina State University and co-author of the paper.In Cape Town, dead lawns and withered flowers have become the norm, but what is happening in the secret lives of city trees? And what is happening to small urban animals such as squirrels and rats, whose ecosystems are part of the urban environment?
According to mayoral committee member JP Smith, some plant and tree species have been “more susceptible to the drought than others”.
Landscaped areas had taken a “definite knock” owing to the lack of irrigation, because even though most of them were planted with indigenous species they still required limited watering.
Plants with shallow root systems had “died as a result of the drought”, but “more established trees with deeper root systems” had survived.
These were mainly in the affluent suburbs along Table Mountain, but “older trees in more sandy areas are not as lucky since the soil does not retain water well”.
For many saplings the drought had been a disaster, and the city council had done “very little replacement of dead materials” since the sustainability of new plants could not be guaranteed.Smith said “work on existing landscaping projects has been altered to focus on hard landscaping and mulching”. Trees and landscape plants along roads were “particularly in need of protection, as road surfaces are hot and they create wind tunnels which dry out the soil very quickly”.
For many of the wild urban creatures of Cape Town it has also been a stressful time: the hunt for water has often resulted in extermination by human beings.
“The drought has had a huge effect on their natural environments, which usually carry some groundwater but which are now all dried up,” said Shaun MacLeod, director of Reptile Education Awareness Consultants.
Residential areas bordering natural areas were attracting rats, mice and geckos on the hunt for water “from a dripping tap, a swimming pool even if it is covered, a water feature, whatever”.Even water and food left out for dogs was “an invitation for rats, mice, squirrels and others. It is like a five-star hotel for them.”
Sources of water and food became “congregation points” for animals, which in turn attracted snakes looking for prey. Any bit of water “attracts an ecosystem”, said MacLeod, and snakes were part of that.
He said it was disturbing that people chose to live on the borders of natural reserves but then “complain about bees, snakes and spiders”.Many of these animals coming to look for water were being “destroyed” by property owners.
Said MacLeod: “Human interaction is the problem – we are the ones exterminating the animals, but we have built our homes on wild land.”
One contentious animal in Cape Town’s urban environment was the grey squirrel, an alien brought in by colonialists like Cecil John Rhodes, which eats the eggs of indigenous birds.
“Yes, they are fluffy and cute and people like to rescue them,” he said, but they were not the ones we should be worrying about most in the drought.