Choosing Suitable Planting StockWhen considering quality in planting stock the nurseryman, forester and arboriculturalist has two distinct ideas in mind. The first is genetic or inherent quality and the second is the ability of the plant to survive and grow after planting. Inherent quality is expressed for the forester by rapid rate of growth, straightness of stem, persistence of the leading shoot, resistance to frost and drought, freedom from disease or insect attack, and good characteristics of the timber. The arboriculturalist who is creating amenity will look for stature, form of crown, size and colour of leaves, colour and form of flowers and fruits, and features of the bark. Those responsible for planting in housing estates, along motorways and trunk roads, or on restored industrial sites look for resistance to wind or fumes and tolerance of difficult soil conditions. All these are inherited characters which can be ensured by careful selection of the sources of seeds or cuttings; they can also be improved by selection and breeding. The second aspect of quality in plants derives from the way they are grown in the nursery; these characters are phenotypic or induced and together ensure that the plants will have a high capacity to survive and grow after planting on the chosen site. The nurseryman seeks to produce plants which are healthy and are well furnished with buds and branches and have stems which are thick at the base and sturdy in relation to their height. He raises plants from seed, or propagates them vegetatively under carefully defined conditions of soil, temperature, moisture, nutrition and day length. A feature of modern nurseries is the control that can be exercised over these and other factors. Polythene tunnels and cloches, supplementary lighting, mist irrigation, additional carbon dioxide and applications of nutrients are all available for use. Of course, the nurseryman cannot prescribe for a severe frost or drought after planting, or strong competition from weeds, or neglect of the plant but he can prescribe for good survival if normal care is taken before and after planting. The precise specifications for the two aspects of quality mentioned above appear in British Standard 3936 Part 1 and Part 4. A suitable size of planting stock is important for good survival, as also is season of' planting. On forest sites mechanically prepared by ploughing so that weed growth is suppressed, small plants are preferable. On all other sites it is the height and strength of the weeds that determines sizes of' plants; they must be sufficiently tall to have buds and branches above the weeds. The aftercare of' most broadleaved species must include control of weeds by mechanical, chemical or hand methods. Selecting Suitable SpeciesIn the pages which follow we describe the silvicultural, arboricultural and timber characters of more than 30 broadleaved species native or long-cultivated in Britain. They can be classified into four main groups: Those that grow quickly when young but soon culminate in height and diameter increment. They produce useful timber on short rotations but can also be grown on rotations of medium length (say 40 years). The poplars and tree willows produce light timber and reach their best development in southern England on moist, fertile soils. The alders and birches produce medium to heavy timbers and can be grown throughout Britain. Those that are fast growing when young and can be grown on rotations of medium length ranging from 45 to 60 years. Sweet chestnut and Red oak produce ring porous timbers of medium to heavy density; the Small leaved and Large leaved limes, Norway maple and London plane are diffuse porous woods of medium density. All five species grow best in the south of Britain. Ash, various species of elm, Wild cherry or gean and sycamore are grown throughout Britain and the last named is especially well suited to northern Britain. All produce useful timbers, the elms and ash being ring porous and heavy to medium in density, while Wild cherry and sycamore are diffuse porous and medium in weight. The Scuthern beeches Nothofagus obliqua and N. procera appear to belong to this group and show promise in the western and central parts of Britain. They produce diffuse porous timbers of medium density. Those that are normally grown on long rotations of 80 to 120 years and have in the past been planted throughout Britain. Beech, Pedunculate oak and Sessile oak reach their best development on lowland sites in the southern half of Britain but good stands are also found on fertile sheltered sites throughout Wales, northern England and lowland Scotland. The timbers are classed as heavy; beech is diffuse porous and the oaks are ring porous. Walnut can also be placed in this group of long rotation species but it requires fertile soils in the south of England. There is also a fourth group of species which play important roles in the silviculture of the main species and contribute to amenity and conservation. Horse chestnut, holly, hornbeam, Field maple and Robinia produce medium to heavy woods often with specialised uses. Hazel, hawthorn and dogwood, the Osier and Basket willows and Goat willow are rarely allowed to reach timber size and the Sorbus species -rowan, whitebeam and Wild service - have silvicultural, conservation and amenity values. |
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