Scientists from Indiana have demonstrated the effect of forests on air temperature, giving World Land Trust another reason to continue their vital replanting work.

It’s well known that replanting trees in areas affected by deforestation not only improves biodiversity but sequesters carbon to help stop the effects of climate change. Whether that reforestation is by natural means or through human intervention, increasing the number of trees provides a vast number of benefits for local communities and the planet as a whole.

But scientists in the US have recently discovered another advantage to replanting trees: it has the effect of directly cooling the air temperature around the reforestation area. For environmental charities such as World Land Trust (WLT), this is further evidence of the value of their replanting projects.

Transpirational thinking

For a long time, scientists in the US have been trying to work out why, when the vast majority of the country has been warming over the past century, the temperature of much of the eastern US has either remained the same or even cooled. The new study has found that the reason for this temperature stability is the huge amounts of reforestation that’s happened in the area, following the loss of millions of trees in America’s early colonial history in the 19th century.

As people moved back into cities and the country began an ambitious replanting programme in the 1920s, the trees returned and land returned to forestry. This led to a total of 15 million hectares of reforested land, which cools the air around it because of transpiration, which is similar to human sweating. Today, the forests cool the surrounding air by between 1-2ºC, rising to 2-5ºC on hot days.

“The reforestation has been remarkable and we have shown this has translated into the surrounding air temperature,” said Mallory Barnes, an environmental scientist at Indiana University. “Trees have a really beneficial impact upon surface temperatures through transpiration, and they have really cooled things off.”

Putting theory into practice

As well as buying vast areas of threatened land and forestry to protect it from being destroyed by agriculture, logging or mining, WLT works with local partners all over the world in a number of replating projects. In those projects, seeds are collected from native tree species and carefully grown in tree nurseries. Once they are ready to be planted, the saplings are nurtured and protected, with any saplings that don’t survive replaced.

The Carbon Balanced Paper scheme helps to fund a number of WLT replanting projects. These  include the reforestation of the Khe Nuoc Trong forest in Central Vietnam, which will result in the annual sequestration of 41,686 tCO2e, and the Nangaritza Valley in the south-east of Ecuador, which aims to purchase 1,235 acres of land to restore degraded habitats.

Reforestation is now being seen by scientists all over the world as a mechanism of directly cooling air temperatures, and WLT are leading the way in putting that theory into practice.


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