Stephen Humphrey | Issue 31
The good news is while plants have the potential to go extinct, they also have the capacity to bounce back.
Excerpt from Paths of Pollen
Pollen’s Progress: Where’s It All Going (and Where Has It Been)?
Pollen’s job is to go places. It is an organism with no limbs, physical senses, or consciousness, yet it’s nonetheless tasked with a do-or-die mission to accomplish one of nature’s great errands: plant reproduction. Plants don’t move, and mostly they don’t need to. They are nourished by their own alchemy of water, CO2, and sunlight, so they don’t need to roam around searching for food. Sex is another matter. Since plants are immobile, they can’t go out and search for mates. Instead, they release pollen grains, tiny portable vessels, which deliver their sex cells to other plants. This act of remote conception is called pollination. When pollen consummates this vegetative union, a fertilized plant makes seeds.
Plants exchange pollen, frequently but not always assisted by animal agents (sometimes wind is their only ally). A range of different animals pollinate plants, including birds, reptiles, a few mammals, and scores of insects. This diverse cast of creatures all bear the title “pollinator.” Pollen is small and transportable, but it doesn’t know where it’s going and can’t move under its own power. Since animals are built for mobility and inclined to move around, they’re natural helpers. Not that they know they’re helping. Pollinators go to flowers for reasons relevant to themselves, not plants. They arrive seeking food, shelter, spots to lay eggs, or places to mate. Their plant-bound journeys just happen to coincide with a plant’s need to spread pollen. Pollen is spread through networks of self-interested, mutually dependent stakeholders. However, when pollination succeeds, these unwitting partners help far more than themselves. They benefit much wider webs of life. Plants could not perform their ecological roles if they did not reproduce, so pollination is necessary to ecosystems. Crops require pollination, so it’s essential for agriculture. The world would be less green, and hungrier, if pollen could not get where it needs to go.
However, like other systems in nature, pollination networks are vulnerable to stress. Nature is currently beset by many kinds of ecological stress, and signs point to overstress across living communities. Notably, there are upticks in species extinctions. Die-offs have gotten so extreme, some ecologists suggest Earth is facing its sixth mass extinction. Mass extinctions involve rapid drops in biodiversity. When key species disappear, webs of interdependence collapse, dragging more species to oblivion. Given time (millions of years), life recovers and repopulates, but things don’t come back just like before, and numerous things are gone forever. No-one has seen a T. rex since the previous mass extinction, except in movies and museums.
No living thing is guaranteed permanence. Nor has any form of life always been here. If we look back one billion years, we’ll see nothing alive on land – no animals or plants, not even soil, just bare virgin rock. Half a billion years later, when plants started greening the world, there was no such thing as pollen. For millions of years plants propagated with spores, but when pollen arrived, it brought certain innovations, such as the creation of seeds. Like pollen, seeds were tough, portable, and more resistant to moisture loss than spores. Millions more years passed before flowers and their by-products, fruits, came along. Up until 140 million years ago, land vegetation had nothing to show but greenness. Yet by the time plants finally revealed their colourful, “flowery” side, scores of species had vanished in four mass extinctions and several minor extinction “pulses.” Flowers, themselves, are not safe from going extinct. Fossil evidence from the fifth mass extinction hints that the largest lineage of flowers, along with their pollinators, came close to disappearing (see chapter 6). Had history followed a different path, flowers might not even exist today. For all we know, the next mass extinction, or the one after, will finish off flowering plants, once and for all.
How the next round of extinctions proceeds might well be in humanity’s hands. The human race’s impact on nature has intensified since Homo sapiens first began to exploit nature’s bounty. Some experts even propose calling our current geologic epoch the Anthropocene. Environmentalists fret over the prospect that human actions (and inactions) may drive nature to inexorable “tipping points.” A tipping point is where an event, once set in motion, become unstoppable, like a roller coaster hurtling over a rise. Past a certain point, gravity takes over, and the rest is downhill.
If anything is going up these days, it’s the planet’s temperature. As we burn through fossil fuels, greenhouse gases released into the atmosphere push global temperatures ever higher. According to America’s climate-monitoring agency, the National Oceanic and Atmospheric Administration (NOAA), the ten warmest years on record have occurred since 2005, the last seven since 2014. Even if greenhouse gas emissions hold steady or decline, computer models predict the Earth’s average temperature will rise between 2.4 and 5.9 degrees Celsius by the end of this century. Those numbers may not sound large, but the last time world temperatures approached this level was 56 million years ago. That dramatic warming event, called the Paleocene-Eocene Thermal Maximum (PETM), was especially hard on marine species, killing more than 90 per cent of ocean life. Greenhouse gases, from volcanoes most likely, saturated the air over 20,000 years, a geologic eyeblink. That period of “rapid” heating was slow compared to now. By recent estimates, human activity pumps CO2 and other compounds into the atmosphere nine to ten times faster. If emissions keep to their current rate, Earth could match the PETM’s levels in 140 to 259 years (five to ten human generations), a hundred times faster than the PETM.
Pollen plays a fascinating part in researching past climate events such as the PETM. Among its climate-monitoring tools, NOAA maintains a global pollen database. There, pollen extracted from sediments all over the world helps scientists infer past climate conditions without “direct observational data.” Pollen particles are useful for this sort of analysis because they age well as fossils. Pollen grains are strong as well as small. The sex cells inside them stay viable for just a short time, but their outer shells remain intact for millions of years. “Pollen” derives from two Greek words: “paluno,” which means “to sprinkle,” and “pale,” meaning “dust.” Leftovers of this once-living dust hint at how long pollen has played its role in nature’s story.
Pollen can also teach us about climate history – if we look very closely, more closely than the naked eye can manage. It takes powerful lenses to examine these durable little grains. In 1682, when microscopes were relatively new, English botanist Nehemiah Grew first discovered that clumps of “bee bread” from honeybee hives were made up of individual grains. He called these “globulets.” Grew conjectured, correctly, that pollen’s purpose was sexual in nature. Their hardy shells harbour gametes, or reproductive cells, within them.
Grains of pollen may have simple-looking designs, or might be geometrically complex, even sculptural. From species to species, they present a range of forms. Grew was the first scholar to notice that grains of pollen are different-looking, depending which plant they come from. Pollen grains are like fingerprints for plant species. Their distinctiveness makes them useful to NOAA’s climate researchers. By extracting pollen fossils from sediments, scientists can deduce which plants used to live in a place and how plentiful they were. To researchers, pollen grains are like tiny time capsules, in situ records of which plants perished and which ones persisted through ice ages, droughts, and global heat waves. This knowledge helps to model future climate trends.
Which plants will flourish as the world warms up? In the near term, probably lots of plants will. At first, longer growing seasons and more carbon dioxide (which plants consume) could make the world leafier. But there can be too much of a good thing. Plant leaves vacuum up CO2, turning carbon into sugars, which plant metabolisms use, while releasing oxygen, which animal metabolisms need. However, plants can only suck in so much carbon. Research shows some rainforests, the so-called “lungs of the planet,” have begun emitting, rather than absorbing, CO2. With so much carbon floating around, will the world keep getting leafier, or will plants wither and wilt, overwhelmed by their new global hothouse?
Plants have plenty of problems already. In 2019, scientists announced 571 plant species had gone extinct over the past three centuries. Climate change was not even the top cause. Other human-led factors did more to trigger declines in plant diversity, such as plants losing habitat to industry and cities, invasive species out-competing local plants, and pollution – climate-warming and otherwise. Meanwhile, humanity’s need for plant products keeps growing. Demand is trending up for plant-sourced goods such as food, medicines, fibres, wood and other construction materials, and biofuels. In 1960, the world had 3 billion human beings. In 2022 Earth’s population officially reached 8 billion, according to the United Nations’ World Population Prospects report. That number is up from 7 billion in 2010. We could reach a projected 9.7 billion people by 2050. One survey predicts that global food demand will rise by 35–56 per cent between 2010 and 2050; complications from climate change could bump up this figure to 62 per cent. The United Nations Food and Agriculture Organization (FAO) says food production will need to increase by 70 per cent within that timespan to keep up with consumption.
Pollinator populations also look to be trending downward. In 2016, a panel of experts filed a report for the United Nations commission on biodiversity, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES). The document, titled “Assessment Report on Pollinators, Pollination and Food Production,” concluded that 75 per cent of food crops and nearly 90 per cent of wild flowering plants depend to some extent on animal pollination. It also found that pollinators were increasingly under threat, as “Nature across most of the globe has now been significantly altered by multiple human drivers.” While pollinators exist across the animal kingdom, the majority are insects. Bees get most of the press, but flies, beetles, butterflies, and wasps pollinate as well. Unfortunately, population data for insects points to steep declines in their numbers. A New York Times article in 2018 announced, “The Insect Apocalypse Is Here.” The piece referenced a European study published in 2017 that warned the world has 75 per cent less insect biomass since 1989.
Still, pollination is not merely a numbers game that measures so many pollinators versus so many plants. It is webs of different species mutually adapting to changes in their environments. Pollination networks, being complex, are vulnerable to change; but they also have some flex. They might lose plants or pollinators might go away, but the networks themselves stay intact – up to a point. Attrition happens in nature, it’s nothing new, but living communities can crash if too many species vanish. At some point, too much is too much.
In 2020, scientists at the Georgia Institute of Technology looked at fossil pollen from over the past 20,000 years. They were testing for “landscape resiliency” of plant communities in North America. They found that North America currently has the lowest landscape resilience since the so-called “end-Pleistocene megafaunal extinctions,” when the continent’s biggest mammals died out, 40,000 to 50,000 years ago. What worried the researchers was the present-day ratio between “residence times” and “recovery times.” The longer plants reside in places, the more diverse they become and the faster they recover from disturbance. Sadly, say the scientists, right now too many habitats are too young. We have forests, but not as many old forests. We have grasslands, but those grasslands are less biodiverse. It is harder for younger, less diverse ecosystems to build back up when they’re knocked down. The scientists warn of “foreboding potential extinctions to come.”
The good news is while plants have the potential to go extinct, they also have the capacity to bounce back. Plants spring from seeds in just weeks. A grain of pollen forms over a day or so. People know how to plant seeds. They’ve done it for thousands of years. We can declare plants or pollinators endangered and make plans to protect them. But how do we protect pollination, which is not a species but an ephemeral network of organisms? Preserving networks requires stewardship, which is not just action but habit. After you plant a garden, you need to keep tending it. Stewarding takes time, and also learning. Like a garden, knowledge too needs tending. Pollination is complex ecologically, and difficult scientifically. As a topic, it’s a moving target, in no small part because plants, pollinators, and the natural world keep changing. But before we race further into pollination’s (potentially daunting) future, let’s pause for a moment to peek into the past, where innumerable adaptations led to life as we now know it, and somehow resulted in the little vessel of life called pollen.
© 2023 Humphrey, Stephen, Paths of Pollen, MQUP, 2023. Print and Digital, pages 3-9. Used with permission of McGill-Queen’s University Press.
Stephen Humphrey is a writer, radio contributor, and citizen naturalist originally from Western Canada, now based in Toronto. Follow The Paths of Pollen Podcast on YouTube.
Paths of Pollen by Stephen Humphrey McGill-Queen's University Press, 2023
Order from MGUP or your favourite local bookstore.
A tiny organism called pollen pulls off one of nature’s key tasks: plant reproduction. Pollination involves a complex network of different species interacting with one another and mutually adapting to their ecosystems, which are constantly changing.
Some pollen grains require just a puff of wind to set them in motion, but most plants depend on creatures gifted with mobility. These might be birds, bats, reptiles, or insects including butterflies, beetles, flies, wasps, and over twenty thousand species of bee. In Paths of Pollen Stephen Humphrey asks readers to imagine a tipping point where plants and pollinators can no longer adapt to stressors such as urbanization, modern agriculture, and global climate change. Illuminating the science of pollination ecology through evocative encounters with biologists, conservationists, and beekeepers, Humphrey illustrates the significance of pollination to such diverse concerns as food supply, biodiversity, rising global temperatures, and the resilience of landscapes.
As human actions erase habitats and raise the planet’s temperature, plant diversity is dropping and a growing list of pollinators faces decline or even extinction. Paths of Pollen chronicles pollen’s vital mission to spread plant genes, from the prehistoric past to the present, while looking towards an ecologically uncertain future.
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