Plants are not animals. This may seem obvious but too often the techniques used to protect plants from extinction are based on methods developed for animals. Ask an eight-year-old what a plant is and you will be told that they are green, rooted to the spot and boring.
The fact that they are green is fundamental to the animals, including humans, and most of the other species on Earth. If plants were not able to take the energy from the sun and use it to mix together air, water and soil, we would not be here. The silent hum of photosynthesis is seen as a green hue from space but rarely appreciated here.
The fact that plants are rooted to the spot is of profound importance to the plants themselves. If you are unable to run away from danger then you have to develop strategies that enable you to tolerate whatever life and nature might throw at you. The technical term for this is phenotypic plasticity and it is very much more developed in plants than in animals.
The divergence of plant and animal evolution began 1,200m years ago when plants went down the route of self-sufficiency while animals were content to continue exploiting those organisms that harvested or extracted energy from the natural world. However, the plants are much more than just self-sufficient individuals because they give far more than they receive. These individuals have evolved into some of the greatest chemists ever.
Indeed, in 1947 Sir Robert Robinson was awarded the Nobel Prize in chemistry as a result of his investigation of plant-synthesised molecules in plants grown in the University of Oxford Botanic Garden. I feel sure Sir Robert would have acknowledged his vegetable co-workers in his acceptance speech.
Among the plant-derived products for which we should be eternally grateful are artemisinin, used in the treatment of malaria, and digoxin, which has kept my old mother alive for nearly a decade. A common, and reasonable, suggestion is that plants have evolved these extraordinary chemicals as defences against the wretched animals that eat them.
The plants are more than Nobel-worthy chemists, synthesising our every need. Plants provide us with our habitat and all the other terrestrial ecosystems that supply habitats (with the possible exception of the ice-dominated landscapes at the Poles). In addition, they are at the bottom of some food chains in the oceans and fresh water habitats. In these circumstances the plants as a community provide what are collectively known as ecosystem services.
Thanks to the UN Millennium Ecosystem Assessment classification, ecosystem services can be grouped together under four headings: provisioning, supporting (or habitat), regulating and cultural. Provisioning includes food and medicines, supporting includes the primary photosynthetic products of plants and nutrient cycling, regulating includes carbon sequestration and purification of water, and cultural includes recreational use and spiritual enrichment.
It has been calculated that the annual value of these services is $17tn. Given that no one else can supply these services, this price does not represent their true value which is priceless and irreplaceable.
The acronym Hippo, accredited to the great Professor EO Wilson, reminds my undergraduates that Habitat destruction, Invasive species, Population growth, Pollution and Over-exploitation alone and together are the reasons why, at current estimates, 28 per cent (or more than 100,000) of all plant species will be extinct by the time that I am 100 years old in 2058.
When choosing the places on Earth to protect first as a matter of urgency the number of species native and endemic to an area is taken into account along with the current level of Hippo in the area. Using this method a top 25 “biological diversity hotspots” has been drawn up. These include Mediterranean-type regions of Europe as well as areas of tropical woodland, the most stunning of which is southwest Western Australia, home to the tallest hardwood trees in the world – the jarrah. The jewel in this botanical crown is the Stirling Range where in an area the size of London there are more plant species than in the whole of Canada.
Within the Stirling Range there are hundreds of species, some of whose future is threatened by Phytophthora cinnamomi, commonly known as bush dieback and closely related to Phytophthora infestans which caused the Irish potato famines of the 1840s and 1850s. Among the species threatened by the bush dieback is Banksia gardneri. This beautiful little plant was already struggling due to the demise of its pollinators, the possums who are being wiped out by feral cats and rats and foxes. The likelihood of being able to eliminate all of the fungal spores and all of the cats and rats and foxes is so low that an alternative way to save the banksia has to be found. Seed banks are the obvious candidate because they work.
While Banksia gardneri might sound like a minor player in life’s rich tapestry of species, respected research by Professor Forest Isbell at Montreal’s McGill University shows indisputably that the resilience of an ecosystem to the normal stochastic fluctuations in weather and climate is proportional to the number of species in the community. Or to put it another way, the more species you lose, the greater the likelihood of complete breakdown of the natural interactions that hold together the community and most importantly its soil.
There are clear parallels with human society here. You would not want a community of just lawyers, just farmers, or just engineers because we need them all.
The inspirational Professor Gren Lucas describes plants as the green glue that holds life on Earth. This a particularly appropriate phrase because should the plants fail to glue the soil in place then erosion will remove that soil quickly and we shall be back to the situation 470m years ago when the first land plants began their migration out of the watery habitat they had occupied for more than 700m years.
Trying to save Banksia gardneri by controlling the dieback and the European mammals is doomed to failure; the task is just too big for the resources available. This means that the only way to protect individual plant species is to take advantage of one of evolution’s greatest innovations, namely seeds. We now know that the embryos in seeds can survive for 30,000 years in frozen soil and still grow into mature flowering plants. The exploitation of this remarkable survival strategy in artificial seed banks, such as the Millennium Seed Bank project in the UK, is the best way to protect individual species.
This is where the conservation of plants diverges very strikingly from that of animals. Animals are much less obliging and must be conserved in their habitats because they are simply far more needy than plants. This is apparent from the fact that to protect bitterns in the UK requires hundreds of hectares of artificial reed beds that are not only perfect for the iconic bittern but are also home to many other species as well as providing ecosystem services.
The conservation of plants for their aesthetic properties is in the safe hands of the world’s gardeners. Among the 70,000 different plants found in UK gardens are many plants such as Kolkwitzia amabilis that are struggling in the wild but are widely grown in cultivation. Strangely, gardens are more often lauded as the refuges of birds than they are identified as safe homes of many beautiful plants, both endangered and common in their habitats. The world’s gardeners need to be less modest and they need to stand up and proclaim the great contribution that they are making to the Global Strategy for Plant Conservation that will result in us handing over this planet to our children and grandchildren in a better state than the one we inherited.
Finally, I have one word for any eight-year-old who describes plants as boring – chocolate. QED.
Timothy Walker is Horti Praefectus of Oxford Botanic Garden. He will be talking about plant conservation at Hay on Earth, part of the Hay Festival, on May 22. For more details, visit hayfestival.com