Wild Service Trees & Redwings
For the past 30 years I have been collecting berries of the wild service tree, Sorbus torminalis. I extract the seeds and grow the young plants in my tree nursery. I have only ever been able to collect a small proportion of the available berries due to the particular habits of the tree.
The best wild service trees generally grow as isolated specimens within ancient semi natural woodland. The berries are born high in the crown making it impossible to use a mechanical cherry picker or similar for collecting the berries. Poorly shaped specimens may be found on the woodland edge. There berries can sometimes be collected by reaching up or from a ladder.
Although poorly shaped, these edge trees are probably genetically very similar to the better trees inside the woodland. Their poor shape is simply due to the unfavourable environmental conditions on the woodland edge. For this reason I collect berries from these edge trees when they are available. Whenever there is a good crop of berries on a wild service tree within woodland, I lay nets under the tree in October and wait for the berries to fall.
In early October the berries are very hard and clay coloured, but in late October the berries suddenly turn squidgy and at the same time change to a wine red colour. Unfortunately, most of these ripe berries cling resolutely to the tree, any berries that do fall to the ground immediately get eaten by mice which eat the seeds and discard the pulp. Meanwhile my nets fill with autumn leaves.
By early November there is still a good crop of berries on the trees, but also a quiet flock of 20 or so redwings gorging themselves before flying off to another bit of woodland to roost. Within a week the trees have been stripped and I have a net full of wet leaves.
Seed dispersal of the wild service tree is very closely matched to the autumn migration of redwings.
- The berries are hard and inedible until late October when the redwings arrive.
- The change in edibility is advertised by the change in colour.
- Berries seldom fall to the ground. If they do the seeds are immediately eaten by rodents and have no chance of germinating.
- Redwings travel in small flocks. During migration they often roost in woodland several miles from their feeding sites. Here they defecate on the woodland floor, ideal for the germination of tree seeds.
Wild service trees are found singly or in small clonal groups in ancient semi natural woodlands throughout western and southern Europe. Their distribution is closely matched to the winter distribution of redwings. This is an example of a relationship between a species of tree and a species of bird which is of mutual benefit. But the relationship is in no way an equal one.
Redwings have a wide range of possible foods as they migrate through Britain. The loss of wild service berries would have no significant impact on their population. But for the wild service trees seed dispersal is a critical part of their life cycle and migrating redwings play an important role in this. In the original forested cover of western Europe there would be a strong selection pressure on wild service trees to produce berries which attract redwings. This is done by producing berries which are hard and inedible until late October when the redwings arrive. In late October the berries suddenly become soft and juicy, advertised by the change in colour. The berries stay on the tree for another month even after the leaves have fallen to give the redwings every chance of eating them.
Rowan, Sorbus aucuparia, similarly has seeds within an edible berry. The red berries ripen and become edible in September, then stay on the trees into the Winter, or until they are eaten by birds. Berries are eaten by several thrush species and nomadic bands of waxwings in response to cold weather. Rowan has a much wider distribution throughout Europe.
Hawthorn, Crataegus monogyna, has berries enclosing a very hard seed which is difficult for animals to eat. Rodents often store the seed in a cache which may be some distance away from the parent tree. Some berries are eaten from the bush by thrushes, the remainder generally fall naturally from the bush by late November, although some stay on the bush into the new year. On the ground they are eaten by pheasants and other birds, which disperses the seed more widely.