Almost All Male

The native black poplar is the rarest timber tree in England, and it is in trouble for two reasons that have nothing to do with anyone cutting it down.

Nowhere to germinate

The tree is a floodplain species and it is fussy in a very specific way. Its seed is tiny, short-lived, and will only take on bare, wet, freshly deposited silt — the sort of surface a river makes when it bursts out sideways and dumps a new bank of mud, and then leaves it alone.

England used to be full of that. It is not now. Rivers have been straightened, embanked, dredged and confined; floodplains are drained and farmed or built on; and the bare silt the seed needs appears, if at all, briefly and in the wrong places.

So natural regeneration has effectively stopped. Almost every black poplar standing in England was put there by a person, from a cutting, which the tree does very readily — a lopped branch shoved into wet ground will root.

Nobody planted the females

The second problem is stranger and is entirely our fault.

Black poplars have separate sexes: male trees and female trees, and you need both.

The female produces her seed in a mass of white cottony fluff, which comes off in early summer in quantity, drifts about, blocks gutters, sticks to washing, gets into houses and looks like an infestation. It is harmless and it is extremely annoying.

So for generations, when people planted black poplars — along lanes, on village greens, at field corners, as boundary markers — they planted males. And when a female came down, they replaced it with a male. Nobody made a decision about this; everybody made the same small decision separately, for a hundred and fifty years.

The result is a surviving national population overwhelmingly skewed towards one sex, scattered in ones and twos across the country, in which a male may be nowhere near a female, and in which the females that do exist are frequently clones of each other.

A species can be numerous and functionally sterile at the same time.

The Hay Wain

Constable painted them. The big, leaning, deeply fissured trees in the Stour valley pictures are black poplars, and they are there because that was the ordinary tree of an English river meadow — the thing you would see, not a thing you would seek out.

It is now down to a few thousand individuals, maintained largely by enthusiasts with secateurs.