THE GLOBAL FOREST

The GlobalTHE MIND-BLOWING DIVERSITY OF TREE

SPECIES IS BEING REVEALED WRITES

BILLY FLYNN

Some years ago, I was taken to visit a wildlife rescue facility near Melbourne, Australia. This was during the first week of my one and only visit to that country and my cousin rightly believed that I’d like the chance to see some iconic Aussie animals in real life. It didn’t disappoint. Within minutes we were up close and personal with some extremely laid-back koalas and possums. During the few days I’d been Down Under, I’d heard people mention different kinds of eucalyptus trees, often with lovely descriptive names like strippy bark, ironwood and red gum. And now, one of the volunteer guides was talking about which types of eucalypt are preferred by koalas. In my ignorance, I had never thought about there being lots of different eucalypts. Until now, outside of the occasional arboretum, I’d only ever seen them as a curious addition to a suburban Irish garden. So, when the guide wasn’t busy, I confessed as much and asked him how many species of eucalyptus there were. “Oh God” he said. “Probably three hundred or so”. I clearly remember how instantly dubious of that figure I was but of course I said nothing at the time to betray that and just filed it away to be checked later.

A few weeks later I was on a rather thrilling boat trip in Queensland. This time to see crocodiles, although not at such close quarters. The pilot was also our guide and during the times when we weren’t seeing any sinister reptiles sliding into the water or lolling menacingly on its surface, he kept up a steady chatter on what trees and plants were overhanging the river and growing along the valley slopes. In conversation later, when he informed me that he was a botanist by training, I knew I had my fact-checker. I told him of the figure I’d been quoted in Victoria and he shook his head. “No, no. More like eight hundred and something. Still counting”. I was gobsmacked.

We’re just not that used to many different types of trees here in Ireland, I suppose. One of my favourite tree books listed 42 species we could count as native. In Ireland’s Woodland Heritage (2012)1, John Cross includes 36 species in the native list (with one as a possible introduction – purple willow, if you were wondering). Maybe this is the reason why I’d never bothered myself to wonder how many tree species there are worldwide. This February we found out, or at least, got the best guess that has ever been made. Ready?

There are an estimated 73,300 species of tree on planet Earth. That’s not the best bit. The really big news is that around 9,000 of these have yet to be discovered. The study2 by a massive team of ecologists and other scientists worldwide combined tree abundance and occurrence data from two global datasets – TREECHANGE and the Global Forest Biodiversity initiative – to form the biggest database of tree knowledge yet assembled. The study used the information we have on the roughly 64,000 known and documented tree species and used a novel statistical method to estimate the total number of unique tree species at biome, continental and global scales. To be exact, the researchers’ modelling arrived at a total of 73,274 tree species, meaning that there are a likely 9,200 species of tree yet to be discovered.

About 40% of the trees still ‘out there’ are considered likely to be in South America where there are 27,000 species known. This makes this continent the greatest ‘hot-spot’ in terms of diversity of undiscovered species. It also underlines the importance of conservation in this part of the world where existing manmade pressures from logging and climate change are already making their effects felt. The model also showed that around one third of the undiscovered species are likely to be rare, meaning that these are more vulnerable to extinction than those rare species we have already documented. While the data suggest that South America harbours the most new species, tropical and subtropical forests on all the other continents have far more unique species than previously thought.

While we have no news of new tree species in Ireland, we can still play our part in protecting them elsewhere. This includes sourcing our timber and other forest-derived products from sustainable activities, supporting international agencies that offer communities alternatives to agriculture which may necessitate deforestation and by sticking to our own climate commitments. As humble as these seem in the greater scheme of things, the onus is on us as a ‘developed’ nation to play our part. As this article is being written, inflation is driving up pressure on our household budgets and there are calls for a moratorium on the carbon tax. These must be resisted. Inflations come and go. Extinctions only need to occur once.

1. Cross, J.r. (2012). Ireland’s Woodland Heritage. Department of Arts, Heritage and the Gaeltacht. 2. Gatti et al. (2022) The number of tree species on Earth. Proceedings of the National Academy of Sciences of the United States of America (PNAS) February 8, 2022 119 (6) e2115329119; https://doi.org/10.1073/pnas.2115329119