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Carbon dioxide is a fertiliser for plants, so if its concentration increases in the atmosphere then plants will grow better. So what is the problem? – a question from Doug in Lower Hutt
Rising atmospheric carbon dioxide (CO₂) is warming our climate, but it also affects plants directly.
A tree planted in the 1850s will have seen its diet (in terms of atmospheric carbon dioxide) double from its early days to the middle of our century. More CO₂ generally leads to higher rates of photosynthesis and less water consumption in plants. So, at first sight, it seems that CO₂ can only be beneficial for our plants.
But things are a lot more complex than that. Higher levels of photosynthesis don’t necessarily lead to more biomass production, let alone to more carbon dioxide sequestration. At night, plants release CO₂ just like animals or humans, and if those respiration rates increase simultaneously, the turnover of carbon increases, but the carbon stock doesn’t. You can think of this like a bank account – if you earn more but also spend more, you’re not becoming any richer.
Even if plants grow more and faster, some studies show there is a risk for them to have shorter lifespans. This again can have negative effects on the carbon locked away in biomass and soils. In fact, fast-growing trees (e.g. plantation forests) store a lot less carbon per surface area than old, undisturbed forests that show very little growth. Another example shows that plants in the deep shade may profit from higher levels of CO₂, leading to more vigorous growth of vines, faster turnover, and, again, less carbon stored per surface area.
The effect of CO₂ on the amount of water plants use may be more important than the primary effect on photosynthesis. Plants tend to close their leaf pores slightly under elevated levels of CO₂, leading to water savings. In certain (dry) areas, this may indeed lead to more plant growth.
But again, things are much more complex and we don’t always see positive responses. Research we published in Nature Plants this year on grasslands around the globe showed that while dry sites can profit from more CO₂, there are complex interactions with rainfall. Depending on when the rain falls, some sites show zero or even negative effects in terms of biomass production.
Currently, a net amount of three gigatons of carbon are thought to be removed from the atmosphere by plants every year. This stands against over 11 gigatons of human-induced release of CO₂. It is also unclear what fraction of the three gigatons plants are taking up due to rising levels of CO₂.
A recent survey on the world’s plants found a shocking number have gone extinct – 571 since 1750. And this is likely to be a stark underestimate. Not all plants have been discovered, so it’s likely other plants have gone extinct before researchers know they’re at risk, or even know they exist.
In Australia, the situation is just as dire. The Threatened Species Recovery Hub recently conducted two evaluations that aren’t yet published of extinct plants in Australia. They found 38 have been lost over the last 170 years, such as the Daintree River banana (Musa fitzalanii) and the fringed spider-orchid (Caladenia thysanochila).
But uncertainty about the number of plant extinctions, in addition to the 38 confirmed, is an ongoing concern.
Both studies pointed out the actual number of extinctions is likely to be far more than those recognised in formal lists produced by the Commonwealth and state and territory agencies.
For example, there is still a high rate of discovery of new plant species in Australia. More than 1,600 plants were discovered between 2009 and 2015, and an estimated 10% are still yet to be discovered.
The extinction of Australian plants is considered most likely to have occurred in areas where there has been major loss and degradation of native bushland. This includes significant areas in southern Australia that have been cleared for agriculture and intensive urbanisation around major cities.
Many of these extinct plants would have had very restricted geographic ranges. And botanical collections were limited across many parts of Australia before broad scale land clearing and habitat change.
Why extinction goes undocumented
There is already one well recognised Australian plant extinction, a shrub in Phillip Island (Streblorrhiza speciosa), which was never formally recognised on any Australian threatened species list.
Researchers also note there are Australian plants that are not listed as extinct, but have not been collected for 50 years or more.
While undocumented extinction is an increasing concern, the recent re-assessment of current lists of extinct plants has provided a more positive outcome.
The re-assessment found a number of plants previously considered to be extinct are not actually extinct. This includes plants that have been re-discovered since 1980, and where there has been confusion over plant names. Diel’s wattle (Acacia prismifolia), for instance, was recently rediscovered in Western Australia.
A significant challenge for accurately assessing plant extinction relates to the difficulties in surveying and detecting them in the Australian landscapes.
Many have histories associated with fire or some other disturbance. For example, a number of plants spend a significant part of their time as long-lived seeds – sometimes for decades – in the soil with nothing visible above ground, and with plants only appearing for a few years after a fire.
But by far, the greatest reason for the lack of information is the shortage of field surveys of the rare plants, and the availability of botanists and qualified biologists to survey suitable habitat and accurately identify the plants.
What we’ve learnt
The continuing decline of Australia’s threatened plants suggests more extinctions are likely. But there have been important achievements and lessons learnt in dealing with the main causes of loss of native vegetation.
Our understanding of plant extinction processes – such as habitat loss, habitat degradation, invasive weeds, urbanisation, disease and climate change – is improving. But there is still a significant way to go.
One challenge in dealing with the causes of Australian plant extinction is how to manage introduced diseases.
Two plant diseases in particular are of major concern: Phytophthora dieback, a soil-borne water mould pathogen, and Myrtle rust, which is spread naturally by wind and water.
Both diseases are increasingly recognised as threats, not only because of the impact they are already having on diverse native plant communities and many rare species, but also because of the difficulties in effective control.
Two Australian rainforest tree species Rhodomyrtus psidioides and Rhodamnia rubescens were recently listed as threatened under the NSW legislation because of myrtle rust.
While extinction associated with disease is often rapid, some individual plants may survive for decades in highly degraded landscapes, such as long-lived woody shrubs and trees. These plants will ultimately go extinct, and this is often difficult to communicate to the public.
While individual species will continue to persist for many years in highly disturbed and fragmented landscapes, there is little or no reproduction. And with their populations restricted to extremely small patches of bush, they’re vulnerable to ongoing degradation.
Thanksgiving may be uniquely American, but its core spirit was exported from harvest festivals stretching back for millennia. Its essence is being grateful for what one has, while noting a duty to share one’s good fortune.
For centuries, people in agrarian societies shared seeds to help each other subsist from year to year. Today, thanks to intellectual property rights and often well-intentioned laws, our ability to share seeds is restricted. Realizing this, food activists, garden enthusiasts and community leaders are trying to make it easier by making seeds available through libraries. Surely there’s nothing controversial about that, right? Actually, there is.
Free seeds by mail
Until the early 1800s, U.S. farmers either saved seed from their own crops or obtained it through personal networks. Then in 1819, Treasury Secretary William Crawford called upon all ambassadors and military officers stationed overseas to collect seeds and bring them home, where they would be shared freely.
Initially this program was informal, but in 1839 Commissioner of Patents Henry Ellsworth persuaded Congress to appropriate funds for it. Ellsworth owned large tracts of land in the Midwest, so his motives may not have been strictly public-minded. Soon his office was distributing 60,000 seed packages annually through the U.S. mail. By the turn of the 20th century, the Department of Agriculture was shipping a billion free packages of seed each year.
This was relatively uncontroversial until 1883, when a group of representatives from mostly vegetable seed trade firms formed the American Seed Trade Association. No business model can work if the government gives away for free what private merchants want to sell.
After decades of lobbying, the group convinced Congress to end the free seed program in 1924. Without granting ownership rights to plant breeders, members argued, there would be no incentive to “improve” seed for qualities such as yield, tolerance, germination length, root depth or aesthetics. As two plant breeders put it in 1919:
“The man who originates a new plant which may be of incalculable benefit to the whole country gets nothing – not even fame – for his pains, as the plants can be propagated by anyone.”
The 1930 Plant Patent Act was a watershed. It initially applied only to nursery plants propagated through cuttings, such as roses and apple trees. Soon, however, breeders of agricultural commodities pressed to expand the law in recognition of their labor. As a result, the majority of commercial crops and garden plants in use today were developed by agricultural companies, to the point that three companies – Bayer Monsanto, DuPont and Syngenta – account for roughly 50 percent of all global seed sales.
Today the seed industry is highly controlled. Every state has laws that require suppliers to obtain licenses, test seeds to ensure they are the variety advertised and properly label them. And the federal government regulates seed sales across state lines.
These laws exist for good reason. If farmers buy seed that turns out to be the wrong variety, or doesn’t germinate, their livelihood is at risk. Seed laws hold providers accountable and protect buyers. Some laws apply even to those who offer seeds for barter, exchange or trade.
Seed sharing redux: Seed libraries
But another community pillar is distributing seeds without charge: Libraries. The process works much the same as with books. Patrons receive seeds and plant them, then allow some of their plants to go to seed and return those seeds to the library for others’ use.
One of the nation’s first seed libraries is the Bay Area Seed Interchange Library, or BASIL, which opened in 2000 at the Berkeley Ecology Center in Berkeley, California and is run by volunteers. Sascha DuBrul, its founder, is said to have came up with the idea after wanting to find a home for seeds that were left when the University of California, Berkeley closed its campus farm.
People who I interviewed for my research say the seed library movement has grown exponentially, starting with a few pioneers but expanding rapidly in the past five years. The movement includes food and community activists, gardeners, lawyers and citizens who support the idea that everyone has a right to seed.
Libraries don’t test seeds or place expiration dates on packaged seed, so some states have moved to regulate seed libraries. For example, in 2014 the Pennsylvania Department of Agriculture informed the Joseph T. Simpson Public Library in Mechanicsburg that it was violating the state’s Seed Act of 2004 and needed to follow the same stringent requirements as agricultural supply companies.
Labels had to be in English and clearly state the plant’s species name or commonly accepted name, and the library had to conduct germination and purity analyses. Failure to do so, one county commissioner asserted, could threaten local food supplies through what she called “agri-terrorism.”
The seed library eventually reopened after officials
agreed that patrons would not be required to bring seed back to the
library, and that seeds it provided would be commercially packaged. It now hosts seed swap events to encourage person-to-person sharing.
Defending the right to share
Seed sharing advocates believe, as one who I will call Barry told me, that “people ought to be able share seeds without being treated like they’re Monsanto.” Many are alarmed by government crackdowns on seed libraries.
I met Barry in Lincoln, Nebraska, where he was advising state officials on adding an exemption to the state’s seed law for seed libraries. “I’ve made the rounds”, he confessed when asked how many states’ revised seed laws have his fingerprints on them.
Since 2015, states ranging from Minnesota to Nebraska, Illinois and, more recently, Alaska have adopted such exemptions. In North Carolina, seed libraries are legal thanks to a blanket seed sharing exemption that applies to all nonprofit oganizations. Alabama exempts any providers who sell up to US$3,000 worth of seed.
In September 2016, California Governor Jerry Brown signed Assembly Bill 1810, known among activists as the Seed Exchange Democracy Act, into law. The measure amended state law to exempt seed libraries from burdensome testing and labeling requirements.
Despite these successes, a number of activists I spoke with fear that agribusinesses seeking to protect their intellectual property rights will push back if the seed library movement keeps expanding. The hard reality is that sharing is not a right, even in this age of the so-called sharing economy, if the thing people want to share is a valuable commodity.
Sign up to the special Beating Around the Bush newsletter here.
Australia is classified as “megadiverse” meaning it’s a global hotspot for plant and animal diversity, and has vast numbers of unique species found nowhere else on Earth. With this newsletter we want you to be able to wander down the garden path, off the beaten track, and smell the gum leaves. Specifically, what kind of gum leaf? What is it from? Where does it grow?
We’ll let you know every time a new edition in our Beating Around the Bush series comes out, putting the spotlight on a different native plant every time. We’re on a roughly fortnightly schedule, but like any garden there might be a few surprises along the way. I’ll also be rounding up some of the greatest hits from our archives, and talking about what’s new in the plant world.
If someone else in your life might enjoy this mix in their inbox, please let them know about it. And if you have any feedback, feel free to let us know in the comments.