A very commonly held opinion is that the number of trees in the world are decreasing over time. Indeed, that’s the opinion I held until recently.
On the FAO’s website, it states:
“Since 1990, it is estimated that 420 million hectares of forest have been lost through conversion to other land uses, although the rate of deforestation has decreased over the past three decades.”
Technically this statement is true. A lot of forests have reduced in size. However, a letter published in Nature (ungated link here), “Global land change from 1982 to 2016” by Song et al. (2018), shows that the number of trees have increased since 1982. Song and coauthors use global satellite imaging data to investigate this question alongside others.
The authors explain:
“A global net gain in tree canopy contradicts current understanding of long-term forest area change; the Food and Agriculture Organization of the United Nations (FAO) reported a net forest loss between 1990 and 2015. However, our gross tree canopy loss estimate (−1.33 million square kilometres, −4.2%) agrees in magnitude with the FAO’s estimate of net forest area change (−1.29 million square kilometres, −3%), despite differences in the time period covered and definition of forest.”
Therefore, there was an overall net gain. There was a net loss in the tropics, but there was a larger net gain in the subtropical, temperate, and boreal climate zones.
Observant readers will notice that I have only used the word trees so far, I haven’t mentioned the word forests. This is because tree coverage does not necessarily correspond to forest coverage. For example:
‘Cutting down a 100-hectare tract of primary forest and replacing it with a 100-hectare palm plantation will show up in the data as no net change in forest cover: the 100-hectare loss is perfectly offset by the 100-hectare gain in tree cover. Yet, that activity would be counted as “deforestation” by FAO. Therefore tree cover loss does not directly translate to “deforestation” in all cases.’
I should stress here, in the example above, despite the effects ‘cancelling each other out’, it doesn’t take into consideration the effects on biodiversity or other negative ramifications.
Nevertheless, I found this paper interesting. My original prior when confronted with this question was massively wrong. I thought that the number of trees in the world was decreasing overall. It seems likely that following the media coverage of deforestation shaped my opinion on this particular fact. Thus, it was refreshing to have a positive picture painted in this (very specific!) domain. We’re making some progress on this front, an area often thought to be plagued by a complete lack of progress. Overall, the paper paints a negative picture (I didn’t cover all of the findings), however, sometimes it’s good to dwell on the positives, even if in the grand scheme of things, it’s pretty small.
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