Hampstead Heath's 'invasive' species: Parakeets oaks, and swimmer-nibbling crayfish
PUBLISHED: 11:30 06 July 2019
Hampstead Heath is a 790-acre oasis in which to de-stress and reconnect with nature.
But every time I take a stroll on the Heath, I'm struck by just how much around me isn't "natural" in the sense of representing native British fauna and flora.
Take the resident ring-necked parakeets. With eyes closed, you could be roaming a Darjeeling tea estate. The birds originate from sub-Saharan Africa and South Asia, and the stories of their introduction to London are every bit as colourful as their plumage.
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The most enduring legend is that they flew off the set of The African Queen during filming in 1951. More probable is that they established themselves after successive escapes from pet shops. Elsewhere, parakeets are accused of beating woodpeckers and nuthatches to the choicest nesting sites, but the Heath's contingent seems to coexist with the locals.
There's not much natural about the landscape either. Cattle, sheep and goats - all first domesticated in the Middle East - have been raised on the Heath since the Neolithic period, suppressing forest regrowth and creating pasture. These days, grazing duties fall to rabbits introduced from the Iberian Peninsula by the Normans. Or was it the Romans?
From the 18th century, the native oak, beech and birch woodland began to be "enhanced" with exotic Turkey oaks, horse-chestnuts and rhododendrons. Meanwhile, mineral-rich springs, dribbling out where porous Bagshot Sands meet impermeable London Clay, were corralled into a series of ponds, today a playground for bathers and anglers. Here, too, the roll-call of introductions is impressive, from mandarin ducks and alpine newts, to catfish and red-eared terrapins.
Human agency is suspected for the arrival of two types of crayfish, too. The Turkish crayfish reached Britain in the 1930s, being joined in the 1990s by the red swamp crayfish from North America. Culinary motives are thought to have driven both introductions, with persons unknown correctly considering Hampstead Heath the ideal place to rear them. Both varieties are today well-entrenched - as became painfully evident when swimmers in the men's pond complained of being nipped on the toes and "in altogether more sensitive places".
Dan's new book Invasive Aliens: Plants and Animals From Over There That Are Over Here (William Collins, RRP £16.99) expands on this topic.