Climate change is being brought home to ordinary Joburgers, who have noticed trees shedding their leaves early and plants flowering out of season, or not flowering at all. In response, planting trees is a small step each resident can take.
 
Climate change causes trees to shed their leaves early IT'S only the end of February and the leaves are already changing colour. Earlier in the month the morning air surprised everyone with its crisp autumn pinch. And around the country people have reported the early blooming of certain species of plants.

Cosmos, an early autumn bloomer, started flowering as early as December. Some people reported mass displays of the annual. Clivias and azaleas, both early spring bloomers, were also found blooming in certain gardens this month.

These are just some of the changes in nature that have concerned people. We have come to know it as climate change - and its long term effect bodes ill for mankind.

Alan Buff, the general manager for technical support and horticultural training of Johannesburg City Parks, says that over the past five years the effects of climate change have started to become more pronounced in the natural environment.

Buff points out that global warming is a natural event - some scientists believe climate change is much more likely to be part of a cycle of warming and cooling that has happened regularly every 1 500 years for the last million years. "It would have happened anyway, but we are accelerating the process."

Normal carbon dioxide levels in the air are 300 parts per million; this figure has increased to 370 parts per million. The balance in the stratosphere, our life-giving barrier, has been disturbed, leading to ozone depletion. "The chemical soup has been thickened," Buff explains.

Increased light intensity
He says a noticeable effect of seasonal change on the Highveld is the higher light intensity we are experiencing, causing stress to trees. "Leaf drop is earlier and can be throughout the season."

Another effect is an increase in humidity, leading to more fungal infections. Rain patterns have also changed, with higher water volumes experienced at any given time. Because of excessive urban development, this water runs away instead of seeping into the ground to feed the groundwater system, which in turn replenishes our rivers.

And climate change has a profound effect on the fine balance of the five known plant hormones. Just a slight deviation can lead to quicker flowering or plants not producing fruit and going into seed straight away.

The young plants literally "bolt".

"Plants grow quicker but are weaker because they are not taking in enough nutrients." This leads to a knock-on effect on insects and bird species, which rely on the exact seasonal flowering or fruiting of plants to survive. Farmers are especially at risk, with crops needing a specific seasonal period and circumstances in which to grow.

"Johannesburg lies high above sea level. What we have been noticing is lots of plants are becoming stressed."

City Parks started looking into seasonal change on a more intensive scale about two years ago. It aims to plant 200 000 trees over the next two years. "We are trying to correct the [environmental] balance with tree planting."

Tree collateral
It follows a strict regimen in which 80 percent of trees planted must be indigenous. But indigenous trees have very specific needs and are often unsuited for high density city streets. For one, indigenous trees do not like to be pruned and trimmed excessively, a given for street trees as they have to be shaped to make way for telephone lines, large vehicles and pedestrians.

Indigenous trees also do not deal as well with pollution as the hardier exotics. That is why City Parks often opts for birches, oaks and plane trees for high density streets. Good local varieties are Celtis Africana (white stinkwoods), Rhus lancea (karee) and the various hardy acacias (thorn trees).

Buff often has to answer queries relating to tree planting and the effect of this on the country's water shortage. Planting more trees is definitely the answer, he confirms. Almost all the new trees the City is planting are watered with grey water, and just a small percentage is watered with fresh water. Grey water is obtained from the final purification stage of the City's sewage works.

By utilising grey water, which otherwise would have been put back into the river systems, the new trees are, in effect, contributing to purifying the water system in an indirect way. "People don't realise the value of trees - they are an asset for humanity."

Each new tree planted by City Parks costs R1 000.

And trees can assist the environment's recovery in profound ways. They are not just natural converters of carbon dioxide to oxygen; neither are they just pretty to look at. Research done in the United States has found that they can reduce household energy consumption by up to 30 percent by providing insulation in various weather conditions - cooling homes in summer and decreasing the effects of cold weather in winter.

Trees contribute in other, less well-known ways. By keeping tarmacs cool during the boiling summer months, trees triple the lifespan of tar roads. And by absorbing excess water through their extensive root systems, road erosion is reduced substantially. They are also natural air purifiers, their leaves acting as natural traps of particulate matter.

Armageddon
Buff maintains that climate change is bound to have far reaching effects on the world in the near future. Wars may be started over scarce water resources. The demographics of societies will be changed - some for the better, some for the worse. A place like Sabie in Mpumalanga, for example, may become too hot and dry to sustain the forestry industry that drives the economy there.

The odds are stacked against farmers, too. Sandra Bell, a horticulturist at Kew Botanical Gardens in the United Kingdom, recently spoke to 702 Talk Radio on the subject; she agrees with Buff.

"The long term effects we see are very significant, for example, in crop pollination, the propagation of species, and pest behaviour." Kew Gardens has tracked plant propagation over the last 50 years and is concerned with the findings. "The mid-season for planting has become dryer and hotter. Phenologists also note earlier frog spawning."

Britain seems to be much more vocal about global warming, Buff maintains. A lot of emphasis is placed on individuals' carbon footprints by way of advertising. "Yet, nothing is happening here in South Africa."

Seeing wood and trees
In April this year the City will plant another 20 000 trees in Soweto and on Arbour Day in September, 60 000 fruit trees will be planted in one hour. "We are planting trees but we would like to see the community more involved."

Buff suggests residents should get in the habit of planting trees as living memorials to loved ones by planting a tree for a new birth, on a birthday or when someone has passed away. City Parks is also planning to create another park in 24 hours in Diepkloof this year.

With 70 percent of Joburg's trees growing on private property, Buff hopes to build up a City Parks database for each and every tree in the city. "We are looking at legislation to protect all trees, even those growing in private gardens."

And he hopes to have a section on the City Parks website in the near future where people can register any new trees they are planting in their gardens. Buff says hopes to see Johannesburg communities become more involved, cleaning their own pavements and recycling their own green garden waste.

If you want to get involved in the massive tree planting operation on Arbour Day, contact City Parks on 011 712 6600 or visit the City Parks website.

Buff says that if everyone in the city planted one tree on Arbour Day, Johannesburg would be almost three million trees richer in just one day. "We want the whole community behind this project."

http://www.joburg.org.za/content/view/2217/168/