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New estimates of tree and forest cover: should we be cheerful or glum?

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Issue date: 
11 September 2015
Publisher Name: 
Will Ashley-Cantello
Author e-Mail: 
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Three reports. One counts trees. Another counts hectares of tree cover. The third counts hectares of forest cover. All three reached the headlines in the last week but with different figures. What should we make of them?

The first report is by Tom Crowther et al (formerly Yale University) and is the first comprehensive estimate of the number of trees on our planet. The second report is the latest version of the Global Forest Watch reports that use satellite monitoring to estimate annual tree cover loss. The third is the official five yearly Forest Resource Assessment from the UN Food and Agriculture Organisation (FAO) that draws together national statistics on areas defined as forest. They each are measuring different things of course (follow the link for the Global Forest Watch explanation of the difference between ‘tree cover loss’ and ‘deforestation’) but we can identify useful trends in bringing the three together. There is both good news and less good news, as I discuss below.

Reasons to be glum…

  1. We may have lost half the number of trees that once lived on our planet. Crowther et al. estimated there was likely to once have been nearly six trillion trees on our planet (at the end of the Pleistocene, roughly 11,000 years ago). Now there are just over three trillion. Using the same data source on tree cover loss as WRI, it is estimated that just over 15 billion trees are currently lost each year in gross terms, which provides some insight into the ecological impact of the vaguer measure of hectares of tree or forest cover.
  2. The FAO report that in the more recent period of 1990 to 2015 the total global forest area has reduced by 129 million ha, or by roughly the size of Peru.
  3. Again according to the FAO, an average of 8.8 million ha of natural forest (as opposed to planted) was lost each year between 2010 and 2015. That’s a football (soccer) field about every three seconds.
  4. Looking at an even more recent period, the Global Forest Watch found that 18 million ha of tree cover was lost globally in 2014. This global figure for tree cover loss is significantly higher than the FAO average annual loss estimate. It could be said that the relative weaknesses of both measurement approaches mean that tree cover loss estimates may exaggerate measures of forest loss, while forest area changes as measured by the FAO may underestimate deforestation. In other words, the true rate of deforestation may be somewhere between the two.
  5. Although that figure for global tree cover loss continued a year-on-year reduction since the peak in 2012, it did also include a rise in tree cover loss in the tropics. Tree cover loss in Brazil and Indonesia has yo-yoed since 2009 and continued to do as the rate of loss bounced back with an increase in 2014.
  6. Both reports highlighted an increasing risk of forest loss in Africa. WRI highlighted West Africa in particular as a hotspot of tree cover loss, while Nigeria, Tanzania, DRC and Zimbabwe all rank in the FAO’s top 8 countries by forest area loss


Reasons to be cheerful…

  1. A gross loss of 8.8 million ha of natural forest is huge, but it is still a decrease from the average rate of deforestation in the previous five year period which was 13 million ha per year.
  2. The FAO mostly promoted their new figure of net forest area loss of 3.3 million ha, representing a 50% decrease on the same figure in 1990 (as opposed to gross loss, this factors in new forest growth or planting).
  3. Policy developments show a positive trend. The FAO report that 99% of forests are now covered by a national or sub-national policy that promotes sustainable forest management. An increasing proportion of forest now lies in protected areas – globally it’s 17% but in Brazil it’s as much as 42%. The area of forest under a sustainability certification scheme has dramatically risen. The contradiction between these positive developments and continued forest loss highlights the real challenge: implementation of those policies.
  4. The three year average annual loss of tree cover for WRI shows a rising trend, but taken year by year there has been a global decline in 2013 and 2014, since the peak in 2012.
  5. There may have been six trillion trees in the past. But, hey, we still have three trillion and each one is valuable. Let’s make sure we take that value into consideration more readily.

What can history tell us about the future?

In a recent interview I was asked by Unilever whether zero deforestation is possible. I said it was possible, but certainly not easy. I think these reports support that.

I do think there is enough evidence in this to suggest the brakes are being applied to deforestation despite economic and demographic pressure for the opposite. Progress is being made, but it’s slow, stuttering and varies from place to place. Of course, there remains a long way to go, but it’s worth recognising this progress because otherwise there is a temptation – particularly among the public – to assume the decades of discussion, campaigns, finance etc around deforestation has not led to change.

At the same time the risk that this trend reverses remains strong and the pace of change matters a great deal. As WWF highlighted in its recent analysis, without further intervention we could lose an area of forest equivalent to the size of Germany, France, Spain and Portugal combined by 2030. But that same report highlighted that we have a suite of known solutions at our disposal.

Crowther et al highlight that temperature and moisture generally determine where tree densities are the highest, with some exceptions. Where there are exceptions, this is often where humans have changed land use to agriculture. Indeed, they found that the “direct effect of human development… on tree density represented the only common mechanism across all biomes.” Our indirect impacts could have an even greater say as – according to “On the Edge” by Claude Martin – climate change threatens to conspire with deforestation and forest degradation by drying areas of rainforest, increasing fire risk and accelerating tree mortality.

Since the Pleistocene we have lost three trillion trees. It’s now up to us to make sure the Anthropocene is known for halting and reversing that trend. And clearly – in these three reports alone – we have the means to measure our progress in achieving that.

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Extpub | by Dr. Radut