When we think of the Holocene-Anthropocene Mass Extinction we may think of coral reefs, birds, amphibians and iconic mammal species – essentially following the IUCN Red List.

But it really is time we started to take a closer look at trees. Their total biodiversity is far larger – and if we can make a blunt statement: it’s also more important.

Tree biodiversity per biome (or rather per ‘biogeographical realm’ or ecozone). The highest number of tree species can be found in the Neotropics (South and Central America), with the Indomalayan or Oriental realm (South and Southeast Asia) coming second.

Tree diversity is crucially important for the stability of our climate system – and crucially important for the protection of terrestrial biodiversity as a whole. But until very recently no one had even made up to full count of the world’s known tree species, and we’re just beginning to realise how threatened tree biodiversity may actually be.

It took until 2017 for science to make up the count. And although the presented number is of course not definitive, there is now an official database – presenting information about all the tree species (angiosperms and gymnosperms) that have been documented in scientific literature and are still alive today.

This global tree database, called GlobalTreeSearch, was published in March of this year in the Journal of Sustainable Forestry by a team of researchers led by Emily Beech [Fagus for friends] of Botanic Gardens Conservation International.

The publication states that the number of tree species currently known to science is 60,065, representing 20 percent of all angiosperm and gymnosperm plant species [although that’s still a wide range of estimates: just flowering plants (angiosperm) biodiversity lies between 223,000 and 420,000 species – this group would include most of the world’s tree species].

Our own extrapolation: almost half of all the tree species threatened with extinction – but that’s probably an underestimation

Of only about a third (roughly 20,000) of this total of 60,065 tree species the conservation status has been assessed. In this group 9,600 tree species are considered to be threatened with extinction.

Based on extrapolation we conclude a staggering 48 percent of the world’s tree species should be listed as threatened – and possibly more:

That’s because even this simple extrapolation could be an underestimation of the actual global tree biodiversity extinction status, if at least we assume that the two-thirds of global tree species of which the status has not been specifically assessed is likely to have a larger representation of ‘rare tree species’ – trees that are not only more difficult to study, but also more vulnerable to extinction.

The new tree database emphasizes the vulnerability of a large number of tree biodiversity as it shows that actually 58 percent of all tree species are single-country endemics, which means they occur only in one country on Earth – and nowhere else.

58 percent of all tree species in the world are single-country endemics. Image above shows the global top-10 of countries ranked by highest number of endemic tree species.

Many links with climate change – and overall biodiversity

The relevance to climate change is of course large. Not just because climate change is one of the direct drivers of tree extinctions (for instance through climate-driven rainforest droughts and forest fires, boreal forest plagues and forest-steppe biome tipping points) but also as a direct cause of climate change (anthropogenic deforestation) and a possible positive feedback to climate change (carbon release from ecological forest degradation).

The authors state the following about the climate relevance:

“In the climate change negotiations in Paris in 2015, the conservation of trees, the cessation of deforestation, and the sustainable management of forests were all recognized as activities that address climate change. Diversity enhances carbon storage in tropical forests.”

“However, effective forest conservation requires species-specific action, as individual tree species face threats that are unique to that species.”

That’s noted. Now please help spread the word.

© Rolf Schuttenhelm | www.bitsofscience.org