In 1987, German botanist Eberhard Fischer was exploring East Africa’s Great Rift Valley when he encountered something he had never seen before. The Great Rift Valley, it must be noted, is a vast system of ancient geologic rifts that remains a hotspot of tectonic activity. It has active volcanoes, earthquakes and – more pleasantly – geothermal hot springs. One day, Fischer found himself crouching by the edge of the Mashyuza hot spring in Rwanda’s Bugarama Valley, regarding the smallest waterlily he had ever laid eyes on. Fischer knew that waterlilies come in a variety of sizes. The largest, Victoria amazonica, produces flowers some 40 centimetres across and lily pads up to 3 metres in diameter that will support the weight of an adult human or a few small children willing to sit still. Most waterlilies are more modestly sized. Yet, here was this impossibly small thing, with tiny floating leaves and a flower scarcely bigger than Fischer’s fingertip. If that weren’t remarkable enough, it was growing in hot water. The colour was curious, too. At its centre, the flower contained a cluster of bright lemon-hued stamen surrounded by a crown of brilliant white petals. The petals of African waterlilies, Fischer knew, are only rarely bright white. Blues, purples and pinks are more common. Intrigued, he collected specimens. Not long after, he formally confirmed the discovery of an entirely new species of waterlily, although arguably the locals who frequented the hot springs had known about it for ages. Fischer called it Nymphaea thermarum, the smallest waterlily in the world and the only one known to grow in a hot spring environment.
In the years that followed, Fischer and others searched for N. thermarum in hot springs up and down the Great Rift Valley, from Uganda to Tanzania, but they found none. The species seemed to exist only in Rwanda, and there only in the heated shallows of the Mashyuza spring, where it endured until a severe drought arrived in 1998. Rwanda has a population roughly one-third the size of Canada’s, all living on a land area smaller than that of Hawaii, and after two years of this drought, most of the nation’s crops were failing. It was in this context that the water from the Mashyuza spring was diverted into nearby fields for irrigation, and the original population of N. thermarum died off. Some seeds must have floated into the nearby fields of rice and sweet potato, and for a time a few tenacious waterlilies grew there, but eventually the water was diverted yet again and N. thermarum disappeared altogether. Just thirty years after its scientific debut, this extraordinary little waterlily was declared extinct in the wild.
High in the Ko‘olau Mountains on the Hawaiian island of O‘ahu grows a flowering plant called Hāhā mili‘ohu whose fate has not yet been decided, but whose existence is nonetheless precarious. Its long, curved flowers are a vibrant shade of aubergine and covered in fine, hair-like structures called trichomes, which lend it a velvety texture. In Hawaiian, mili‘ohu means ‘caressed by the mist’, a name given because the plant in question only grows in a high-altitude cloud forest near the summit of Kōnāhuanui. Just twenty individual specimens can be found there, and conservationists worry the entire population could be wiped out by a single fierce storm or even a landslide. After all, it has happened before. On Pitcairn Island in the South Pacific, the last remaining member of a species of flowering mallow, the yellow fatu, was destroyed in a mudslide in 2005.
Islands are often treasure troves of the exotic and the unique, but they are also perilous places where the last members of many species live out their final days. Such is the case on the island of St Helena, the very same place where the exiled Napoleon Bonaparte spent his final days. On this island there grows a single tree descended from some long-lost species of sunflower. This is the Commidendrum rotundifolium, colloquially known as bastard gumwood. It juts out from a cliffside fissure, defiant and lonely – it is the last of its kind in the wild. Meanwhile, on Lord Howe Island, 600 kilometres off Australia’s east coast, a tiny flowering vine grows in the basalt soil on the eastern slope of a place called Dawson’s Ridge. This is the critically endangered twiner Calystegia affinis which, when conditions are right, sprouts pinkish, funnel-shaped blooms. There are very few left in the world: some on that ridge, some in another place high in the island’s southern mountains, and a few on Norfolk Island, about 900 kilometres away as the kestrel flies. There is some debate as to whether the vines on these two islands are truly one species or two closely related subspecies. It is a matter of splitting hairs, or trichomes, because both populations are threatened. Weed spores carried by human and avian travellers, and sometimes just by the wind itself, have arrived from the mainland and compete with C. affinis for nutrients. The weeds always win. At last count, there were forty-five individuals of C. affinis left in the wild.
The problem of endangered plant species is limited neither to islands nor hot springs, of course. In the wide expanse of California’s Mojave Desert, a tiny perennial herb grows in the salt flats of the Amargosa River Basin. The river here flows mostly underground, only occasionally rising to the surface. For the most part, whatever grows on the surface is left to endure extremes of temperature, salinity and drought. Remarkably, a great deal of biodiversity has managed to survive for eons in the vast stretches of land between those occasional glimpses of water. Even so, there are limits to survival – there always are. That tiny herb is called Amargosa niterwort, and though it once thrived, its numbers have declined in recent years and the individuals that remain are having trouble producing seeds.
Elsewhere in the Mojave, another population is in trouble. The Joshua tree, Yucca brevifolia, is not so much a tree as an enormous member of the asparagus family, with thick, spiny branches and tufts of spiked leaves. It has been called ugly, unpleasant, nightmarish, grotesque, and also strangely beautiful. There are rumours that it provided the original inspiration for the trees in Dr Seuss’s books. Joshua trees are a keystone species, meaning numerous other species rely on them for survival, but the population has been decimated by wildfires, invasive weeds and habitat loss, and those that survive aren’t reproducing as well as they once did. As temperatures rise further, many Joshua tree seedlings are beginning to struggle and die.
The stories go on. In Tanzania’s miombo woodlands grow some of the world’s last Karomia gigas trees. These are 24-metre-tall, shade-giving members of the mint family and there are fewer than two dozen remaining in the wild. In a forest north of Beirut, you can find some of the last cedars of Lebanon. Once prized as sturdy building material in the ancient Middle East, from Egypt to Mesopotamia, they, too, are now on the verge of disappearing from the wild. They have been logged far too much and, in addition, those that remain require cool conditions, yet temperatures are rising beyond what the cedars can handle. Meanwhile, sitting in the Kew Gardens is an old cycad tree, Encephalartos woodii. Like palms, cycads are dioecious – each plant is either male or female – and this one is male. It arrived in 1899 and in all the time since, a female counterpart has never been found, so it cannot reproduce. E. woodii is now entirely extinct in the wild, so there it is in London, all by itself. It has been called ‘the loneliest plant in the world’.
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About a decade ago, the late Lord Robert May, an eminent mathematical ecologist and once president of the Royal Society of London, suggested that if aliens were to land on Earth and ask how many living species there are on our planet, our answer – or more precisely, our lack of one – would be embarrassing. We did not know the answer then, and we still don’t. It’s not for lack of trying. ‘Current estimates for the number of species on Earth range between 5.3 million and 1 trillion,’ write environmental scientists Tanya Latty and Timothy Lee in The Conversation. Still, they add, ‘that’s a massive degree of uncertainty. It’s like getting a bank statement that says you have between $5.30 and $1 million in your account.’
It might seem careless to be unsure of the existence of nearly 1000 billion species, but to be fair, most of them are really small. When you attempt to include every known and possible species of bacteria on the planet, you quickly end up with a potentially astronomical number of living species. That’s before you decide whether to include all known and possible viruses, which may or may not count as it’s debatable whether they are technically ‘alive’. So, while this vast swathe of the microbial world is absolutely critical to the entire ecosphere, for simplicity’s sake, let’s focus on counting only the eukaryotes.
Eukaryotes are organisms with cells that contain a nucleus. They’re a notch up in complexity on the evolutionary ladder. They include single-celled organisms such as protists – think algae and amoebae – as well as some species of fungi. Eukaryotes also include all complex, multicellular organisms. Many fungi make this list, too, as do all plants and animals, so that’s still a lot to work with. A 2011 study put the global number of eukaryote species at 8.7 million, give or take 1.3 million. Most of these, around 88 per cent, are animals, many of which are insects. The remaining 12 per cent comprise plants, fungi and a suite of single-celled eukaryotes. However, that 8.7 million figure is still a huge guesstimate, because many of the species have not yet been identified.
We are only certain of the existence of around 2.1 million species of animals, plants and fungi on Earth. Of these, it is estimated that up to one million species are under threat of extinction. Simply put, mounting evidence suggests the world is in the midst of the biggest decline in biodiversity since the mass extinction at the end of the Cretaceous. We are losing a lot of animals, both in terms of individual species becoming endangered and extinct, as well as a reduction in population sizes across the board. According to the WWF’s Living Planet Index, animal populations have thinned to such an extent that we have lost around 68 per cent of the world’s vertebrate animals since 1970.
And what of plants? In 2020, an international consortium of researchers led by scientists at Kew Gardens reported that around 40 per cent of the world’s approximately 435,000 species of plants are threatened with extinction. Yet, this picture remains incomplete. The International Union for Conservation of Nature (IUCN) has been steadily assessing the status of our planet’s species since 1964, determining population numbers, threats and habitat loss. Where data is sufficient to do so, they have categorised species as ‘least concern’, ‘near threatened’, ‘vulnerable’, ‘endangered’, ‘critically endangered’, ‘extinct in the wild’ or, with grim finality, ‘extinct’. Despite steady progress, the sheer volume of the work involved means we are only aware of the status of a small fraction of the world’s known species – for plants in particular, the status of only 10 per cent of species is known. As more data is becoming available, however, it appears that the number of threatened plant species is growing.
Certainly, we have already lost far more plant species than we should have. For example, around 600 species of seed-bearing plants have gone extinct in the last 250 years, with disappearances occurring more frequently since the year 1900. This extinction rate is about 500 times greater than that observed during pre-industrial times. The outlook for trees is particularly fraught. A recent report published by Botanic Gardens Conservation International revealed that nearly one-third of the world’s 60,000 tree species are at risk of extinction. Of these, 440 tree species have fewer than fifty individuals left in the wild. Some, like the bastard gumwood on St Helena, have just one wild member remaining. As with animals, overall abundance is in decline and even populations of ‘least concern’ trees are thinning.
Trees are vital to many different ecosystems, from savannahs and deserts to coastal wetlands and rocky shrublands, but they are perhaps best known for the central role they play in forests. Forests cover 31 per cent of land on Earth and are believed to be the primary habitat of around 80 per cent of the world’s species of plants, animals and fungi. Moreover, by acting as enormous filters of rainfall and source water, forests provide around 75 per cent of the world’s fresh water. Clearly, forests are critical to water security, and as global agriculture uses the overwhelming majority of accessible fresh water, it stands to reason that forests are critical to global food security, too. Then there’s all that lovely oxygen forests produce, as well as the carbon they draw down. Alongside oceans and soils, global forests are the most massive carbon sinks we have on this planet. Each year they capture and store around 2 gigatonnes of atmospheric carbon.
A few years ago, scientists at Yale used a combination of satellite data and on-the-ground field data to assess the global tree population and estimated that there are around three trillion trees on Earth. That sounds like a lot, but it’s paltry compared to what it used to be. In that same study, the researchers also found that the current number of trees is just 46 per cent of what was here prior to the rise of human civilisation. Most of that decline in tree cover has occurred since industrial times began, and of this, the last several decades have been the worst. Humans are now causing the net loss of more than ten billion trees each year. Since 1990 we have lost 420 million hectares of forest, and 20 per cent of this was ancient ‘primary’ forest.
Why is this happening? Well, some of it is due to climate change. Longer-lived species, as many rainforest tree species are, tend to reproduce more slowly. They have longer regeneration times, which makes it difficult to adapt quickly to rapidly changing environments. Even fire-adapted species begin to struggle as fire frequency changes with rising temperatures. Plants in the tropics are particularly at risk. Although they tend to prefer warmer temperatures, many are already close to their upper thermal limits. Even so, climate change is not the primary cause of global biodiversity loss, at least not yet. Instead, the leading culprit is habitat loss. Deforestation through land clearing is the biggest contributor to habitat destruction, and much of it is done in the pursuit of more land for farming and grazing. This highlights just how inexorably entwined food security and biodiversity are. It doesn’t have to be a zero-sum game – a biodiverse, food-secure world is possible – but right now that’s how it’s mostly being played.
Habitat loss also manifests via fragmentation and degradation. The former occurs when larger ecosystems are broken up bit by bit. A highway here or a housing development there, and just like that, migration paths are cut, waterways are diverted, keystone species are isolated, or a vast root network – by which trees communicate and share resources – is severed. It is a slow, sundering death by inches. Meanwhile, in habitat degradation no such overt fractionation takes place, and yet pollution seeps in, invasive species arrive and outcompete native species, pollinators are lost, an underground water table is siphoned, a tree species thins out and is no longer abundant precisely where it is needed most, a seed disperser slips quietly into the footnotes of evolutionary history. Or, the climate shifts just enough that the forest’s exquisitely timed ecological dance falters. Something blooms too early, but the pollinators are still larval and unready. Something else fruits late or drops seeds too soon. A seed germinates too quickly, another no longer germinates at all. Things fall out of step, then things fall apart.
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Afforestation and reforestation initiatives, in which new trees are planted, have attempted to mitigate the loss of trees. For example, 110 million hectares of new ‘forest’ was planted in the quarter-century between 1990 and 2015. Unfortunately, this didn’t come close to compensating for the deforestation that took place during that same period, which wiped out a cumulative area of native forest nearly three times that size.
The issue, particularly relating to afforestation, is this: the replacement of an area of native forest with the same area of new trees elsewhere is not an equivalent countermeasure. As entomologist and ecologist David Wagner and his colleagues recently wrote in the journal PNAS:
Insect biomass is not interchangeable across food webs or among major taxa any more than hummingbirds and jaguars can be summed.
This statement refers to insects, but the same can be said of plants. A conifer is not interchangeable with a cactus, no more than a cycad can be swapped for an oak. A 2017 study led by scientists in Brazil and the UK confirmed the presence of over 14,000 plant species in the Amazon rainforest, including 6727 tree species. That’s just known species from lowland areas that had been surveyed, enormous areas of the Amazon remain to be studied. Nevertheless, it is clear that even just a square kilometre of Amazon rainforest contains an astonishing amount of plant biodiversity. There is no ecological equivalence with square kilometre of oil palm trees.
Yet numerous afforestation initiatives are tied with commercial endeavours wherein trees are planted but are later harvested for food or timber. As such, despite what the term implies, this kind of afforestation does not produce new forests or even expand existing ones. Instead, much of it takes the form of monoculture plantations – nearly half of the world’s newly planted ‘forests’ contain only one or two tree species. Such plantations can help draw down carbon, and proposed large-scale tree planting initiatives project that just under 1 billion hectares of newly planted trees could ultimately draw down as much as 205 gigatonnes of carbon. This sounds really good, in theory. But as ecologist Bonnie Waring at Imperial College London and her colleagues have since pointed out in their 2020 paper in Frontiers in Forests and Global Change, it would take more than 100 years for all those trees to draw down that much carbon. Such an endeavour could still draw down an ‘impressive quantity’ of carbon in the nearer term, say the authors, but the trees would need time to reach maturity and even then are likely to only store about a decade’s worth of emissions. But many large-scale tree planting efforts have very little to do with saving biodiversity. And when tree plantations are misleadingly presented as new ‘forests’, it can enable some of most egregious offenders, from corporations to governments, to continue eroding biodiversity while presenting an environmentally friendly public image.
There are numerous important initiatives that genuinely aim to restore natural forests. There are also initiatives that work to establish the much-needed growth of new biodiverse forests, but even these don’t belong everywhere. As Waring has pointed out, there are many places, such as peatlands or arctic tundras, where new trees should not be planted as they disrupt the existing environment. Planting trees in the wrong habitats can inadvertently increase carbon emissions. Then there is the matter of time. As home to most of the world’s terrestrial plant and animal biodiversity, existing forests contain intricate ecological networks that took decades, centuries, millennia or sometimes millions of years to establish. When an old forest is cleared away, it’s not just trees that are felled. So, too, go these networks. As Sarah Kaplan, a climate and science reporter at The Washington Post, once wrote, ‘It appears that ecosystems are a lot like trust: they take a moment to break and forever to rebuild.’
Where protections of existing forests fail, then reconstruction is necessary. Rebuilding, reforesting, rewilding, regenerating: for this, you need resolve, and you need time. You also need seeds.