Is irreplaceable the same as valuable?

What would be the one possession you would grab if you had to leave the house in a rush because it was on fire? Some 50 years ago I was given some pressed flowers on a card for my 21st birthday by a young woman I had just started to go out with. A few years later I received a lovely print from her, called ‘The Botanist’ by the Kent artist, Graham Clarke. I still have both, but which present should I choose as the flames crackle at my heels?

The first is irreplaceable: even if Trudy decided to make another for me it would not have the same meaning. However, it has no intrinsic value and is somewhat discoloured by past damp. My ‘artist’s proof’ of The Botanist is one of fifteen and there are the wider limited-edition prints available online for about £60. So, it is not irreplaceable but it does have a value as a piece of art.

When George Peterken made the case for protecting ancient woodland in the mid-1970s (Peterken, 1977) he stressed that they would be difficult to recreate in a meaningful way – likely to take at least 400 years; they were effectively irreplaceable. However, irreplaceability and value are not interchangeable measures for woods any more than they are for my pictures. They are different axes by which a site, feature, assemblage might be judged.  Sites may be irreplaceable, but not intrinsically very valuable, for example an ancient woodland that is small and much degraded by past management; and some new sites may be very valuable – the Knepp Estate – but are theoretically replaceable within a 25 year time-frame.

Hangman’s Wood is ancient (irreplaceable) but with limited biodiversity interest; the fields at Knepp are recent woodland (replaceable) with high biodiversity value.

It does though also depend on how precise a degree of replaceability is required. Chaos theory suggests that even if we started with a second Knepp, now, in the Weald, on similar soils, with similar grazing, it would not turn out in 25-years’ time, exactly the same. So Knepp is moving along the irreplaceability axis, and the same applies to woodland that is 200, 300 years old, even if not ancient. The recent studies of Norfolk woodland by Barnes and Williamson suggest that sites may often show ecological signs of ancientness where the documents say no: should the decision on their irreplaceability rest on ecology or paper.

Which brings me on to a saying from Oliver Rackham, that a thousand 100 year-old oaks are no substitute for one five-hundred-year-old tree, or some variants of these figures. A five-hundred-year-old tree is likely to have lichens, deadwood beetles, historical associations that the hundred-year-old trees do not and cannot have. Those features are an irreplaceable aspect of the ancient one. However, it is still only one tree occupying perhaps 0.1 ha. A thousand 100-year-old oaks would be likely to occupy a minimum of 10 hectares, considerably more if the trees are open-grown. That area would – whatever its starting point – have acquired considerable biodiversity interest over the course of a century, even if mainly common species (and not the old tree specialists); the stand would be storing more carbon than the single (retrenched canopy) ancient; the area might have become important for recreation by the local community. It is also probably a more sustainable asset for the future in carbon, biodiversity and cultural terms than the single ancient tree.

This old tree is magnificent, but would it always be right to priorise keeping this, over keeping >10 ha of younger (100-200 yr) growth?

Ancient trees and woods are important and worth conserving; they have unique features and associated species for which there are no substitutes; but new sites and assemblages have their own different characteristics which collectively may sometimes be of greater value. Part of the recent woodland at Wytham for example has developed over First World War practice trenches; scrappy field-corner woods at Rothamsted Research Station provide a unique documented record of woodland change from a late 19th century field; the colonisation of old plotlands at Dunton in Essex captures a particular phenomenon of early twentieth-century land-use development and abandonment. Those histories cannot be re-created any more than can that of the 500-yr tree.

Recent woodland with unique and unrepeatable histories.

The future of conservation will involve hard choices; we will not always be able to conserve everything that we want. We need to think what we really value and be prepared for such decisions, not just rely on slogans to decide what we can save from the fire.

PETERKEN, G. F. 1977. Habitat conservation priorities in British and European woodlands. Biological Conservation, 11, 223-236.

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