People bring Holly into their homes for Christmas and the tradition goes back into pre-Christian times with Holly seen as a symbol of eternal life defeating winter. There are many myths and legends about Holly, but it is also an important part of our natural world.
Holly trees are one of the few evergreen trees native to Britain, but they grow right across temperate Europe and Asia. They are slow growing but will grow in a wide range of habitats including under the shade of beechwoods, they do not thrive in wet ground. They were one of the hardiest tree species in the 1976 drought and there is a chance they will still thrive as our climate changes.
Holly leaves are shiny because of a rich wax coating. This cuts down water loss and allows the tree to keep its leaves in winter, but the wax also makes the leaves highly nutritious and a potential favourite with browsing animals such as deer.
Famously, Holly leaves are prickly and this deters browsers. It also makes Holly a wonderful hedge if you want to keep out intruders. That is true for those that grow close to ground level, however, if you look at a mature Holly tree you will see that the leaves above your head height tend not to have spines. They are out of reach of the browsing animals and the tree does not have to waste resources making the unproductive spines.
Holly is shade tolerant and, in the past, it was grown as an under-storey in woodland to be used as a winter fodder with the upper branches harvested and brought down to the animals. It is still a common under-storey in woodlands such as Combe Wood in Salcombe Regis.
As well as the spines, Holly leaves have a thickened margin that makes it difficult for caterpillars to get their mandibles into them. The Holly Blue butterfly gets round this by synchronising its egg laying with the Holly flower buds fattening and opening, a rich feast for the caterpillars and no prickly spines.
Holly has separate male and female trees and only the females carry berries. Blackbirds, Thrushes, Redwings and Fieldfares enjoy the Holly berries as a winter food source but it is the tree that is in control. The Holly needs the birds to spread its seeds when they are ripe, if they are eaten too early then they will be wasted. Before the seeds are ripe, the green berries have high levels of various chemicals called saponins making them bitter and toxic and the birds will not eat them.
As the seeds ripen the berries change colour and the toxin levels drop. The birds recognise the signal and they begin to tuck in, but the berries still contain some saponin and the birds will not eat many in one visit. This means the crop of berries is eaten gradually over more visits giving more birds to have a share. This means there are still berries available to the birds throughout most of the winter, and the seeds are spread more widely because they are taken in so many separate portions by more birds. Nature is amazing.
Image attribution: Ed Dolphin
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