DESCRIPTION AND USE OF SERVICE TREE
Department of Crop Production - University of Tuscia, Viterbo - Italy
BOTANICAL SPECIES: Sorbus domestica L.
HABITAT. The area of origin of service tree is believed to be southern and eastern Europe. The species is generally considered naturalised in central Europe, northern Africa and in the Black Sea area. As a fruit plant service tree has been probably diffused in some European countries by the Romans; these events complicate the identification of native or naturalised state and this doubt is presently analysed and discussed in some countries (Austria, Switzerland, UK). Service tree should be indigenous in Switzerland, where it represents the rarest native tree. In Italy service tree is present in all the regions from sea level to 900 m altitude, but it is particularly widespread in low mountains and hills. Once planted for its fruit, service tree is still present near farmhouses and at the edge of fields and country roads, in marginal areas and abandoned farmlands, as a memory of better days for this species. The plant is quite resistant to cold during winter, tolerant of dry conditions in summer and adaptable to a wide range of soil types, except those that are very clayey and subject to waterlogging. It prefers sunny positions. Fruiting occurs quite regularly in the South of the area of distribution, but can be sporadic in the northern part.
GENETIC VARIABILITY. Service tree has been propagated by seed for centuries. As a result, a wide, underexploited variability exists for different aspects of plant, fruit and wood. As a fruit tree, service tree has undergone only minimal selection activity by man, who has fixed the most interesting traits of the plant or the fruit by means of grafting. Two botanical varieties, pyrifera (Hayne) Rehd (or pyriformis Lodd) and pomifera (Hayne) Rehd. (or maliformis Lodd), are generally distinguished. In Italian nurseries service tree is not generally available in different varieties. Plants for selling are mostly obtained by seed; in the case of grafted plants, two races are available: with apple-shaped fruit and with pear-shaped fruit. Several cultivars, which cannot be found anymore, are remembered by the farmers or were described by pomologists and naturalists in past centuries when service tree had a minor, but well-recognised, function as fruit tree. Among them, ‘russet sorb’, ‘ashen grey sorb’, ‘autumnal’, October sorb’, etc. Presently this classification has been almost completely lost. Several types, differing mainly in the shape, size and colour of the fruits or in the time of ripening and plant shape and habit can be observed.
PLANT. Deciduous tree 12-20 m high, with open round crown and scaly bark; big, green winter buds, which, in contrast to S. aucuparia, are glabrous and glutinous. Service tree is a long-living plant, which can live from over 200 years to 400-600 years, according to some statements.
LEAVES. Alternate, pinnate, with 11-21 obovate leaflets, ovate to oblong , entire near the base, with acuminate teeth at the apex, green and glabrous in the upper surface, tomentose in the lower surface, particularly when young.
FLOWERS. Small flowers in corymbs, at the apex of the new growth. The flower has a pubescent stalk when young, five white petals, 5 styles and 20 stamens. Flowering time occurs from late April to mid-May.
FRUIT. Pomes, in group of 4-10; 2-3 cm in diameter, with generally 2-5 seeds (maximum potential number 10); yellow or greenish skin, often shaded pink or red and sometimes russeted. The shape is variable from apple-shaped to pear-shaped, with quite a wide range of types. The fruits ripen in September-November depending on the environment and genotype and can be eaten only after bletting.
USES. Service tree can be used for ornamental purposes, wood and fruit production. Presently, the most important destination is in forestry. The plant is slowly growing, but the wood is highly estimated and it is sold at high prices. The heavy, hard and compact wood was much appreciated for many products: screws, gear teeth, bearings and other objects subject to attrition; rifle butts. It was also used for carvings: many statues of saints were made with sorb in Italian villages. The service tree pomes have a high content of sugars, vitamin C, malic acid and sorbitol. The pomes of service tree have been well known since ancient times, when they were traditionally consumed raw, after bletting, or transformed in cider, a popular tradition among Gauls and Celts. Similarly to medlar, at the time of ripening the flesh is not edible due to the high content of tannins which give it its characteristic astringent taste. The storage on straw until over-ripening gives to the fruit a sweet, slightly acid and somewhat fermented taste. Not many years ago, in Italian villages the fruits were split, strung to form a sort of necklace and dried, to satisfy the need of fruit consumption during winter. The consumption of the fruit has been almost forgotten in the last decades, but recently in Italy a revival of the ‘forgotten fruits’ has stimulated the rediscovery of old recipes with service tree (jams, sauces, liqueurs). The fruits, often in bunches, are at present sold in Autumn until Christmas only in the most specialised fruit shops. In some countries a cider is still produced from sorb, to correct the apple or pear cider (Germany, France) and appreciated schnapps are obtained (Austria, Germany, France, Luxembourg).The fruits can also be made into vinegar. Malic acid can be extracted from the flesh. The medicinal properties of the fruit (astringent, tonic, diuretic, cholagogic) have also been recognised since ancient times and are related to the content of tannins, sorbitol and pectic substances.