Out of breath

Our forests, crucial for the planet’s climate, are at a crisis point (8 minute read)

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In 1897, a group of Wellington residents, subsidised by the government, purchased 31 acres of land on the south-eastern slopes of Tarikākā and created the Khandallah Domain. They were motivated to protect the land because it contained one of the few remaining fragments of forest in the area. Once, Tarikākā and the surrounding hills had supported dense forest, but the whole area had been logged, and much of what had survived the logging was burned and turned into pasture. Because it grew on steep, inaccessible land, the forest that became the Khandallah Domain lasted long enough for the settlers to begin to appreciate it, and the forest was protected.

Today, the forest protected in 1897 is part of the Western Wellington Forests Key Native Ecosystem. The forest supports native birds, including the endangered but recovering kākā, a population of a rare carnivorous snail and healthy regrowth of native trees. When I walk through this forest, as I do several times a week, I can hear constant birdsong. But I’ve spent enough time in the forest to know that it’s a shadow of what was once there. None of the trees are particularly large and the forest lacks the diversity found in areas that are less modified. It’s a reminder to me of just how much has been lost.

Since the arrival of humans, three quarters of New Zealand’s original forest cover has gone. Much of what remains, especially in the North Island, is degraded – logged, fragmented and invaded by browsing mammals like possum and deer. Despite this, New Zealand isn’t doing too badly. We haven’t stopped the destruction of native forest completely, but the rate has slowed dramatically. Estimates vary, but losses appear to be in the range of hundreds of hectares per year.

On a local and a national scale, that deforestation still matters, because most of the losses are in areas where little forest remains. On a global scale, however, the losses in New Zealand are tiny. The current rate of deforestation around the world is about 10 million hectares per year (nearly twice the total forest area of New Zealand). That’s an almost incomprehensible loss, but it’s actually an improvement since the 1990s, when the rate of deforestation was 16 million hectares per year.

Losing forests is a problem for many reasons. For a start, one third of all known tree species are endangered, and deforestation is pushing them ever closer to extinction. Forest is an important habitat for many other species as well – 75% of the world’s bird species and 68% of mammals are found in forests, for example. But the reason that deforestion is on my mind right now is because of the crucial role that forests play in regulating our climate.

Forests regulate our climate in a number of different ways, on both a local and a global scale. Locally, forests affect the water cycle. Water that falls as rain lands on leaves or on ground covered with a layer of leaf litter. Some of that water filters through into the soil, is absorbed by tree roots and is then released from leaves. In this way, forests increase humidity and rainfall (there’s a nice video explaining the process here). The evaporation process also cools the air, so areas with forests are cooler than those without.

As well as the water cycle, forests are part of the carbon cycle. A living tree is made up of 15-18% carbon, which it absorbs from the air in the form of carbon dioxide. Animals also contain carbon, although the overall volume of carbon in animals is trivial in comparison to plants. When plants and animals decay, they release carbon dioxide back into the atmosphere (here’s another nice video, showing the carbon cycle). The balance between the carbon absorbed by forests and the carbon released is important for the global climate.

When plants are alive, much of the carbon they absorb from the atmosphere stays in their tissues. In the case of small, short-lived plants, that doesn’t make much difference to atmospheric carbon levels. But trees store large amounts of carbon in their trunks and branches. They release a small amount of carbon when leaves fall, but overall, trees act as “carbon sinks”. Globally, there is a huge amount of carbon locked up in forests – around 400 gigatons in forest biomass alone, not counting soil. To put that in perspective, the total volume of carbon in the atmosphere was just under 600 gigatons before humans started burning fossil fuels, and is now around 760 gigatons. A healthy forest is, overall, absorbing more carbon from the atmosphere than it’s releasing – something that’s very important when we are flooding the atmosphere with carbon dioxide from the burning of fossil fuels.

But when forests are cut down or burned the stored carbon is released. If forests are logged for timber, then some of the stored carbon remains locked up in the wood. However, that’s only a small proportion, and the rest of the carbon goes back into the atmosphere. Maybe that doesn’t sound so bad, since the carbon in the forest came from the atmosphere in the first place. But some of these forests are ancient and have been storing carbon for thousands of years, since the retreat of the last ice age.

If tropical deforestation was a country, it would be the third largest emitter of carbon dioxide, after China and the USA, and ahead of the whole European Union. That’s a frightening statistic, but tropical forests are also absorbing carbon. It’s more important to look at the emissions in relation to what’s absorbed. Those figures aren’t comforting either. The three most important areas of tropical rainforest are the Amazon, the Congo and south-east Asia. Of these, only the Congo is absorbing more carbon than it emits. The Amazon is now releasing as much carbon as a result of deforestation as it is absorbing. The south-east Asian rainforest, however, is in the most dire situation. Annually, it absorbs about 1.1 gigatons of carbon, roughly the same as the Congo and Amazon. But it’s releasing much more – 1.6 gigatons – back into the atmosphere as the result of deforestation.

Oil palm plantation (left) next to swamp rainforest in Malaysia (Image credit: Getty Images)

There’s a lot of attention on the tropics, but there are other important forests as well, especially boreal forests, which include the vast forests of Russia and Canada just south of the Arctic Circle. These forests aren’t so important for their biomass, or living plant tissue. In boreal forests, much of the carbon is stored in the soil, because decomposition is slow in cooler climates. With the slow rate of decomposition, dead plant material builds up and holds a massive quantity of carbon.

We don’t automatically think about soil when we think about climate change, but soil actually contains much more stored carbon than living plant tissue – globally about 2500 gigatons. The boreal forests alone store about 1100 gigatons of carbon, and almost all of that is in the soil. Destruction of boreal forest, such as by forest fires, can release carbon stored in the soil. And forest fires are getting worse in these areas, as they become warmer and drier because of climate change – which in turn contributes to more climate change. Siberia has had some particularly bad fire seasons recently, resulting in smoke being detected in the atmosphere over the North Pole (for more information, check out this article in The Green Dispatch).

The recent COP26 climate summit did give some small cause for hope. The leaders of 141 countries promised to stop deforestation by 2030. Among those signing the pledge were Brazil, the African nations that make up the Congo Basin, and south-east Asian nations including Indonesia and Malaysia. Russia, China, the United States and Canada also signed. There are some absences from the list – Thailand, Cambodia and Laos, which all have large areas of rainforest, did not sign. Myanmar also did not sign, as the military junta was barred from attending. Despite these absences, those who endorsed the pledge collectively cover 90% of the world’s forests.

Unfortunately, this isn’t the first time world leaders have made such a pledge. Prior to COP26, world leaders had already promised to halt deforestion by 2015, 2020 and 2030. They’ve missed the first two targets already, and so another promise to end deforestation by 2030 isn’t reassuring. There are some differences this time, though. The previous promise to end deforestion by 2030 included only 40 countries, and Brazil wasn’t one of them. And deforestation has slowed, as I mentioned earlier, even if it hasn’t slowed enough.

But if we really want to stop deforestation, it’s going to take more than the promises of world leaders. It wasn’t New Zealand’s political leaders who stopped deforestion here. Much of the impetus for change came from ordinary people like the Wellington residents who protected the remnant forest on Tarikākā, or the protesters who prevented logging at Pureora forest in the 1970s. And it’s ordinary people who have finally brought us some good news about the rainforests of south-east Asia.

Back in May, senior members of the Selangor state government in Malaysia quietly removed the legal protection from more than 500 hectares of protected swamp rainforest. They had already promised most of the area to a development company. There was widespread outrage from the public and even from within their own political party when the news was publicly announced at the end of August. Within two weeks of the announcement, the government had reversed its decision, and reinstated legal protection for the forest.

Rainforest in peninsular Malaysia (Image credit: Getty Images)

Stories like this, not the promises of politicians, give me hope that the balance is shifting. Deforestation can end by 2030. For that happen, people everywhere must care enough to demand that their forests and soils are protected.

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