Winnie-the-Pooh famously scoured Hundred Acre Wood in search of honey. In Ashdown Forest in Sussex, the wood鈥檚 real-life inspiration, Alice Hudson and Ian Willey are hunting the gorse and bracken for something less sweet, but equally vital.
The researchers from the Royal Botanic Gardens, Kew are seeking willow seeds to collect and deposit in an underground vault a few kilometres away. The plan is to preserve them as聽an insurance policy against future invaders or evolving threats. 鈥淲e don鈥檛 know what鈥檚 going to happen in the future,鈥� says Willey.
The willow family is not yet at risk from an imported pest or pathogen like the UK鈥檚 ash trees, which a deadly fungus has been killing for the last six years, at great economic cost, but disease outbreaks have
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More than 12.5 million seeds have been collected and banked by Kew鈥檚 since 2013, to preserve their genetic diversity in the long term. Most willow today is backed up in clone banks, which preserve less diversity and are exposed to threats.
Willow is a uniquely tricky customer when it comes to seed-banking, which is why Hudson and Willey鈥檚 field trip is one of the first of its kind. As cattle graze freely nearby, Willey spots the yellow catkins of creeping willow (Salix repens), a shrubby tree that spreads across the ground.
There鈥檚 just one problem 鈥� the seeds have already gone. This is one of three reasons banking willow can be challenging. There is a brief window of opportunity, usually just a few days in April or May, to grab them before they are borne off by the wind. 鈥淭he difficulty is you blink and you miss it,鈥� says Willey.
Fortunately, nearby willow clumps hold the tell-tale white fluff which will soon disperse their seeds on the wind.
The second issue is that even for experts like Willey and Hudson, identifying willow correctly can be a taxonomic challenge. That鈥檚 because the family is well known for hybridisation, for example between goat willow (Salix caprea) and grey willow (Salix cinerea). The UKNTSP is reliant on partners, such as local Wildlife Trust groups, for collecting seed from true species, not hybrids.
Salix repens is relatively easy, because it is the only one with such a creeping growth form and height. Paper bags are soon filled with seeds, marking the firing gun on the race to get them to the seed bank.
This is the third difficulty 鈥� if the seeds are not safely stowed in the seed bank within a fortnight from collection, they will no longer be viable. Most arrive at the nearby 聽(MSB) by post, while today鈥檚 are driven over by Willey and Hudson.
Inside the bank, the seeds are dried to 15 per cent relative humidity and cleaned, with fluff removed by vacuuming. Half then enter the bank to be stored at -20掳C and the rest are cryopreserved in liquid nitrogen 鈥� the former allows easy access to seeds, while the latter is better for long term storage.
Willey says it鈥檚 鈥渓iterally, stop everything鈥� when willow seeds arrive because, unlike other trees, they need to be banked quickly or lose their viability. This need for speed, combined with the short window when the seeds can be collected off the maternal plant, posed a big demand on the centre during a trial run last year, with staff diverted from other work to cope with the deluge.
Resourcing is one challenge facing seed banks. Another is whether a species is suitable for banking: conventional storage only works for seeds that can tolerate drying, known as orthodox seeds. Not all UK native tree species have orthodox seeds. Oak is one of those, though Dani Ballesterous of the MSB is exploring cryopreservation as an alternative for the species.
Then there is the vital issue of trying to replicate the genetic diversity of the wild. The UKNTSP seems to be managing that 鈥� found the bank had 86 per cent of the alleles present in wild yew populations, for example.
And what about bringing the seeds out of storage and back to life? 鈥淲e are confident in our ability to germinate them once they come out of cryo or the bank,鈥� says Hudson. Should disaster befall the UK鈥檚 creeping willow, it could be a seed collected today that ensures the forest that inspired AA Milne鈥檚 fiction lives on.
