The hidden battle behind formal gardens

With a third of the world’s plants facing extinction, the leading botanic gardens have shifted focus to make restoring degraded ecosystems their primary goal in the 21st century

WHAT USE ARE botanic gardens? Most people might respond, reasonably enough, that they are delightful places to walk at weekends, and oases of colour and calm in stressed urban contexts. Gardeners will, of course, be aware that they provide information and inspiration for their hobby (sorry, for their passion).

On reflection, many people would probably add that their national or local gardens play a role in horticultural research and education in general. So it may come as a surprise to learn that many leading botanic gardens today, from Kew to Guangzhou, see their great mission in the 21st century as conserving biodiversity, though they still embrace their more traditional roles. And they are talking not only about preserving rare plants within their collections but about restoring degraded ecosystems across the planet, so that the plants in their collections will survive in the wild.

That’s a tall order in a world where, as one botanist put it recently, “even common is becoming rare”. But that is precisely what has prompted this shift in botanic gardens’ policy: an increasing awareness that a third of plants face extinction in the near future and that a few specimens in gardens, with a very limited genetic stock, will not guarantee a species’ survival.

That policy shift has itself been ratcheted up several gears by recent predictions from climate-change scientists, and this is leading into uncharted territories. “Climate change suggests that many plants are not going to survive at all where they are now,” says Peter Raven, outgoing director of Missouri Botanical Garden, and widely regarded as one of the greatest living botanists (and a tireless advocate of combining conservation with poverty relief). “The model of building up plant populations in botanic gardens and then putting them out in nature to help the species survive is threatened at both ends,” he says.

“You don’t know what conditions are going to be like where you put the plants out – but you also don’t know what conditions you are going be able to maintain in your garden in the future,” he continues, outlining a scenario that threatens to turn his own lifetime’s experience upside down. Raven sees the recent development of highly sophisticated seed banks at a number of gardens as a positive response to this dilemma. We can stockpile the seeds from most species until the climate stabilises again and we have some idea where they might prosper.

Science fiction on our doorstep, you might say. But it is depressing rather than exhilarating to think that many of the plants that now delight us – and provide us with invaluable services – may exist only in a sealed drawer for the next few generations. In the meantime, Raven insists, we must continue with restoration initiatives, but he concedes that the outcomes will be increasingly unpredictable.

Botanists from around the world gathered in Dublin last month for the fourth Global Botanic Gardens Congress. The event was hosted by Peter Wyse-Jackson, currently director of the National Botanic Gardens of Ireland, in Glasnevin, but soon to replace Raven – a great, but no doubt daunting, honour – at Missouri. Wyse-Jackson co-wrote the ground-breaking International Agenda for Botanic Gardens in Conservation,published in 2000, which the congress reassessed in the light of subsequent developments.

Perhaps the most radical update on the table now is the concept of “assisted migration”, a benign phrase that just might be the key to keeping many trees, shrubs and flowers in the landscape – and out of the chilled filing cabinets. But it is a concept that also raises as many problems as it proposes to lay to rest. As with animals, plants migrate to find the best living conditions, but plants do it slowly, over generations. Trees, with their very long life spans, are especially slow. Earthworms are sprinters by comparison.

Ten thousand years ago, as the ice sheets retreated from the North American Midwest, trees migrated up the continent at the rate of about 100km per century, until the global climate settled into relative stability – the condition we thought of as normal until very recently. Global change models suggest that climate “envelopes” will soon be moving north at speeds of 1,000km per century. So, if the models are right, this is a race that trees are certain to lose.

Morton Arboretum, in Chicago, with its majestic woodlands and quiet lakes, feels like a place where time has stood still for many years, though its exquisitely restored prairie tells an eloquent story of great changes over the past two centuries. In any case, its chief executive, Gerard T Donnelly, knows that things are on the move even there, so he proposes that we must consider moving trees north of their current ranges at a rate that corresponds to changes in climate. Otherwise we will lose entire forests, he says, and probably many species.

Donnelly knows all too well that this leaves him open to the charge of hubris – of “gardening the wild”. He knows that conservationists, himself among them, have spent the past 40 years combating any wild (and many domestic) introductions of non-native plants, because they can become invasive and wipe out unique local species and plant communities. Now he is proposing that introductions may often be the lesser evil.

He knows that the best outcome of assisted migration will involve the disintegration of cherished and valuable communities of plants and animals. Whatever novel communities will emerge may be poorer, or even richer, in biodiversity than what we know today, but they will certainly be different. However, he argues soberly that assisted migration must be among our options for “managing long-lived trees for an uncertain future”.

Restoration used to be about attempting to return ecosystems to a past (and more biodiverse) state, but the wild card of climate-change is pushing restoration science towards the creation of new systems, with the proviso that maintaining biodiversity is still the target.

Restoration at this level requires a knowledge of the workings of ecosystems that is often beyond current science. But, the theory goes, science will learn more through the large-scale real-time experiments involved in restoration. Let’s hope so.

To see restoration in practice in this country you can’t do much better right now than visit Kilmacurragh, the Co Wicklow arboretum that has just been granted National Botanic Garden status. Wild-flower meadows have been restored there after decades of close lawn-mowing, and have revealed a wealth of biodiversity simply by being allowed to grow back with minimal management, and no new planting at all. Dozens of native species have emerged from long dormancy in the seed bank, or simply blown in. The meadows are currently studded with hundreds of orchids (of four species) that you might be hard put to find elsewhere in such profusion.

Strolling among them is a good, if alas temporary, cure for climate-change headaches, as well as a time-honoured use for a botanical garden.

An international agenda

Botanic Gardens Conservation International

bgci.org.

Global Strategy for Plant Conservation

bgci.org/worldwide/gspc.

UBC Botanical Garden and Centre for Plant Research

ubcbotanicalgarden.org.

National Botanic Gardens at Kilmacurragh

botanicgardens.ie/kilmac/kilmhome.htm.

Paddy Woodworth’s book on ecological restoration,

Restoring the Future

, is due from University of Chicago Press next year