ES Views: Wild London: the popular horse chestnut has an uncertain future

Big and bold, the horse chestnut arrived in London in 1616, imported from northern Greece and Albania as an ornamental tree that was soon widely planted in gardens and parks. These handsome trees sport impressive, white and pink spikes of flowers in the spring, much loved by bees and other insects. Over summer the pollinated flowers develop into glossy, red-brown conkers, protected inside leathery, spiked green husks, which fall in early autumn. Once eagerly collected by schoolboys, these beautiful, shiny nuts now lie mostly unclaimed, swept up only by street cleaners.

Conkers are eaten by deer and wild boar, and may be stored by grey squirrels as an emergency food cache, but they are mildly poisonous to most British mammals. Their use as a cough-prevention remedy for horses most likely led to the tree’s name.

This non-native but familiar tree is now coping with a threat posed by a non-native insect - the horse chestnut leaf miner moth. In July, their caterpillars tunnel through the tree’s leaves, causing them to wilt and die. Trees usually survive, but if sufficiently weakened, a fungal infection known as bleeding canker can take hold, which is sometimes deadly.

Horse chestnuts provide welcome food for blue tits and great tits in the form of all those leaf-munching caterpillars, and in the heat of the summer city, the tree’s wide spreading branches provide welcome shade.

A horse chestnut tree can grow to an impressive 40 metres high and live for up to 300 years. Fine examples can be seen at Morden Hall Park, Bushey Park and along the threatened Chestnut Avenue on Tooting Common, and in many other parks and gardens. Horse chestnut is rarely planted these days, so today’s giants may be the last examples of a popular tree with an uncertain future.

The London Wildlife Trust campaigns to protect the capital’s wildlife and wild spaces. Backed by Sir David Attenborough, President Emeritus of The Wildlife Trusts.