George Monbiot’s recent Guardian blog – Native trees help wildlife – so why do councils plant so many exotic ones? – echoes many of the feelings of the Woodland Trust. While there are many great exotic trees out there, our wonderful native trees are essential for providing homes and food for wildlife and we need more planting throughout the UK.
“The differences can be stark and remarkable: native trees tend to harbour far more wildlife than exotic species. Indigenous oak species, for example – according to the table extracted from scientific papers by the Offwell Woodland and Wildlife Trust – harbour 284 insect species in the UK. Birch supports 266. But horse chestnut, introduced from the Balkans, hosts only four.
Scots pine is associated with 91 species, larch, from elsewhere in Europe (or Japan), just 17. Sycamore, which comes from southern Europe, carries 15 species; the London plane tree, which is a hybrid between two exotic species, supports just one.
The highly invasive rhododendron species (Rhododendron ponticum), which, introduced from southern Europe or the near east, has colonised many of our woods, gives life to a grand total of zero insect species. Interestingly, this plant lived on the land which later became the British Isles during the last interglacial period. Something must have eaten it, or it would have overwhelmed the rest of the flora and dominated the ecosystem. Could it have been browsed by the straight-tusked elephant, or by one of our two woodland rhino species?
The reason is straightforward: our insects have co-evolved with the trees on which they feed, acquiring adaptations which allow them to cope with the chemicals and other defences with which those trees equip themselves. They have not evolved to feed on trees they have never encountered before. Acquiring this ability can take hundreds of thousands of years or more.”
“To help wildlife, we should plant more native trees. So why are nine out of every 10 trees planted by local authorities exotic?”
Kay Haw, Conservation Team