White Poplar

Populus alba

The poplar trees, of the genus Populus, comprise a very large number of species, nanve to Europe, Asia, and North America, and an even larger number of hybrids between them. Many of these are represented in the populetum, or collection of living poplars, maintained at the Forestry Commission's Research Station at Alice Holt, south-west of Farnham in Surrey.

Though no single simple feature marks out the Populus genus, poplars are in practice easily known by a group of characters. Their twigs are ribbed or angular in outline, their buds many-scaled and alternately set their leaves show a random pattern of veins (see Figure 66}, and their branches are likewise random and irregular. Poplar leaves arenearly always simplein outline, but the White and Grey poplars bear lobed leaves on their less vigorous twigs. Poplar leaves are always long-stalked, and in some the leafstalk, or petiole, is flattened from side to side (see Figure 66). This leads to a perpetual fluttering motion, which is very marked in the aspen (Plate 29),

figure 52

Winter twig and bud of White poplar, "typical poplar features are the angular twigs, with many-scaled buds, set alternately. White poplar beats characteristic white down along twigs and on bud-scales. (Twig, life size; bud xio).

figure 52

Winter twig and bud of White poplar, "typical poplar features are the angular twigs, with many-scaled buds, set alternately. White poplar beats characteristic white down along twigs and on bud-scales. (Twig, life size; bud xio).

Most poplars are easily increased by cuttings, and this feature enables timber growers and gardeners to propagate new kinds rapidly, cheaply, and certainly. Strains of trees or plants that are increased by vegetative means in this way are called 'clones', and their cultivar names are printed in Roman type with a capital letter and single quotation marks, e.g. Populus 'Regenerata.' A few kinds, such as the aspen, will not grow readily from cuttings and must be increased by seed or sucker shoots. Suckers are shoots that arise naturally from underground roots; they are common and indeed troublesome with some poplars, though absent from most

Shoots Suckers

During the brief flowering season in March, before the leaves open, the poplar genus is easily known by its remarkable catkins. Male and female catkins always appear on separate trees. Male catkins (see Figure 55} are long slender structures that look dark red at first, but are later tinged with golden pollen. Each catkin carries about 50 separate flowers, and each flower consists of a basal bract and a green cup holding numerous stamens. Pollination is by wind and the male catkins fall in April.

Female catkins (Figure 55) are looser, more open structures, that have been likened to necklaces or strings of beads. Each carries about 50 flowers, and every flower consists of a single green bract a basal cup, and a pear-shaped green ovary tipped by

FIGURE 53

Female catkins and single flower of White poplar. Male and female catkins appear before leaves on separate trees. Slender female catkins consist of many flowers, each having one green bract a basal cup and a pear-shaped ovary topped by four styles. (Catkins x 1!; flower X 20).

Strings Flowers

FIGURE 53

Female catkins and single flower of White poplar. Male and female catkins appear before leaves on separate trees. Slender female catkins consist of many flowers, each having one green bract a basal cup and a pear-shaped ovary topped by four styles. (Catkins x 1!; flower X 20).

four styles. These flowers ripen rapidly to small green fruit-pods (see Figure 59). and about midsummer the pods split to release masses of tiny seeds. Each seed bears a tuft of fine white hairs. These hairs carry the seed on the wind but are considered a nuisance by gardeners, since the mass of fluff makes paths and lawns untidy, and it also sticks to fresh paint. For this reason, most nurserymen prefer to sell male poplars, raised as cuttings from male trees, because these never produce seed.

Poplar seed has a very short life and cannot be stored or sold commercially. It must be sown within a few days of ripening, and on a moist seedbed. In the wild therefore, poplars only spring up in marshy places, or along streamsides, where bare, damp soil or mud is available for colonisation in midsummer. Seedlings have two blunt seed-leaves, followed by normal foliage, and grow rapidly.

Poplar wood has remarkable, distinct characters that ensure peculiar uses. It is pale cream to white in colour, and has large water-conducting vessels. When freshly felled and full of sap it is very heavy, but after it has been seasoned, and the vessels only hold air, it is remarkably light These features make it worthless for most constructional jobs, but it has another character, a supple toughness and resistance to splitting or splintering, that makes it thebest of all timbers for matches, match-boxes, and chip baskets for holding fruit or vegetables. The matches, matchboxes, and basket slats are all cut from veneers. Veneers are thin sheets of wood cut from a round log by turning it, on a special lathe, against a long sharp knife. Knots would cause holes in the veneer and poplars are therefore grown so as to avoid this fault.

Commercial strains of poplar are increased by striking cuttings, using branches from a named rootstock. After each cutting has taken root it is lifted, the thin first branches are cut back, and it is replanted as a 'stumped cutting.' One good bud is always left and this fornis a straight, upright fast-growing set The set is planted out on fertile, well-watered land of agricultural quality, trees being spaced at least 6m apart So treated, poplars grow rapidly and are often 2m round and fit for felling after only years. Their lower side branches are pruned off at an early stage, and all the wood formed on the outside of the central core is then clear, and will yield knot-free veneer. A few small knots or 'buried branches' remain In the centre, but that cannot, in any event be cut into veneer sheets.

Poplar wood was once used for the bottoms of carts and wheelbarrows because it is light and does not split when stones are thrown on it Poplar wood fetches the best prices for matchmaking veneer, but can also serve the same purposes as a softwood - for example in joinery and packing-case making. It is not durable out of doors, unless treated with a preservative. Occasional uses include wood-wool and paper pulp. As a firewood, it is almost useless, for even when seasoned it will only smoulder.

Poplars occasionally cause damage to buildings because their great crowns of foliage, aided by their open large-pored wood, remove water rapidly from the soil during hot dry summer days. Serious harm only occurs on clay soils in regions of low rainfall -notably London and Essex. There the rapid drying and shrinkage of the day may be given a directional trend that upsets the foundations of walls and houses. In such places, poplars should never be planted within 20m of any structure.

Exact recognition of all the many kinds of poplars is very difficult even for the specialist, but a few wild and cultivated strains that are not too hard to spot are shown and described here.

White poplar, Populus alba, is best known by the white downy underside of its leaves (see Plates 23 and 31). the white down that clothes twigs and buds, and the creamy white bark on its larger branches and trunks. On the shorter, less vigorous twigs its leaves are five-iobed, but on vigorous shoots, even on thesame tree, you will find partially-lobed leaves {see Figure 66) or simple ones having a wavy edge.

An introduced tree. White poplar is naturalised only in the south-east of England, though often grown elsewhere, it often produces sucker shoots, and may form thickets on coastal cliffs, or in dunes where it resists saltwinds. On a clay cliff, it helps to bind soil and so check erosion. Otherwise it is only planted for ornament. as a very effective pale-barked, white foliaged tree.

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Responses

  • ariosto
    Do poplars throw up suckers?
    7 years ago

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