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Michael Eason hiking in Anza-Borrego Desert State Park to observe Washingtonia filifera in situ
Currently at San Antonio Botanic Garden, Michael's work has...
Amy Byrne | Feb 15, 2023
An exhibition that beautifully depicts and locates oaks
Roderick Cameron | Feb 09, 2023
Burke Oak Collection at New York Botanical Garden
The Coleman and Susan Burke Oak Collection at The New York...
Todd Forrest | Feb 08, 2023

Plant Focus

Quercus xjackiana acorns
The hybrid of Q. alba and Q. bicolor

A Forum for Garden-Sourced Oak Seed?

Quercus monimotricha acorn (and next year’s developing acorns) at Chevithorne Barton, on a tree descended form the specimen growing at Hillier Gardens © James MacEwen

It was a mast year in 2017 here in southwest France, spreading acorns so thickly under some trees they formed a solid carpet. So Quercus pubescens is evidently not in danger for now, but what of less plentiful species elsewhere? The Nagoya Protocol, however well meant, will have the effect of putting obstacles in the way of obtaining wild-collected seed outside of the country of origin. As most of us are aware, oaks are something of a special case when it comes to their conservation: although research is ongoing into the cryopreservation of oak embryos, it cannot as yet be guaranteed. Thus, for species severely threatened in the wild, trees already in collections are a vital resource which we undervalue at our peril (in this respect I think the importance of private collections is often overlooked by the “big players”, but then I would say that, wouldn’t I?).

So what can we do to widen the footprint of at-risk species? We can of course use vegetative propagation to multiply rare oaks; cuttings in the case of some species or, more reliably as long as the rootstocks are chosen carefully, by grafting. The latter may even be used to confer additional benefits such as enabling a calcifuge oak grafted onto a lime-tolerant stock to tolerate high pH soils.

But back to those acorns… Seeds are wonderful things, they are easily posted or otherwise transported, and can provide enough natural intraspecific variation to aid resistance to environmental challenges, which reduces the risk one takes with vegetative cloning that all will simultaneously fall prey to the same pest or malady.

The conventional wisdom is that arboretum-produced acorns should be rejected out of hand due to the risk of hybridization. But in fact the risk of hybridization does not apply in all cases — yes, one should be cautious, but

Quercus baloot in Arboretum de la Bergerette - © Shaun Haddock

there are several, perhaps many, species which reproduce true from seed (the statistical probability of this will vary both according to species and to the proximity of potential suitors, and may change from year to year as flowering timing varies). Perhaps the best known of these is Quercus monimotricha at the Sir Harold Hillier Gardens, a seemingly unfailing pure source of this species. Amongst those of which I have experience, Q. baloot, Q. dolicholepis, Q. hypoleucoides, Q. miquihuaensis, and of commoner species, Q. ilex, Q. phillyreoides, and Q. variabilis provide a useful percentage of true offspring. Oak pollen can travel a long way, so a spatial barrier to hybridization is not always effective, but there are other barriers, both biological (for instance a Red Oak cannot fertilize a White Oak, and vice versa) and temporal (not all species flower at the same time as each other).

So where are these thoughts leading me? I feel it would be useful to have an internet forum relating to oak seed: a forum which can be approached in two directions — by those who are searching for a particular species, and by those who have seed from wild-collected parents, particularly if they are known to produce a reasonable percentage of true offspring. If such a forum would interest you, and/or if you have data relating to the production of true offspring from seed of particular species, please contact me at shaun.haddock@orange.fr

Because of the problems of importing seed into some countries (notably the USA), and the short life of certain acorns, the traditional exchange with a central "bank" would not work. I would envisage instead that those who wish to exchange or donate seed would do so directly (via a "wants" list and a "haves" list). This would also avoid the expense of posting seed which is not actually required.