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Acer pseudoplatanus L., Sycamore

Account Summary

Introduction, neophyte, commonly naturalised. European temperate.

1934; Praeger, R.Ll.; Co Fermanagh.

Throughout the year.

Growth form and preferred habitats

Sycamore can form a large, or very large deciduous tree when it is then at its most handsome, although it is very much more frequently of modest proportion or as saplings. Irrespective of size, Sycamore trunks always stand erect even in windswept situations, perhaps because its young shoots are surprisingly stout (Hadfield 1957). The buds are green and their time of opening varies greatly from tree to tree; the earliest trees break buds around mid-March in NI. In other places, in B & I, buds can break as early as January. The familiar palmate 5-7-lobed leaves, 10-18 × 11-25 cm, are very often blotched with black spots by the fungus Rhytisma acerinia (Pers.) Fr. Autumn leaf colour is a disappointing drab, rather dingy yellow, turning brown (Sell & Murrell 2009).

Despite the disfiguring leaf-spot fungal attacks, Sycamore suffers little harm from pests and diseases, although Grey Squirrels and other rodents may cause extensive damage by peeling the bark (Edlin 1964).

A. pseudoplatanus will grow on all types of soil chemistry, although it performs best on moist, fertile, base-rich substrates. Young plants are extremely hardy and tolerant of most environmental factors, except the most acidic and waterlogged soils. However, they prefer woodland conditions, or at least some shade. It avoids, or does poorly in badly drained sites where there is a degree of waterlogging or inundation that could lead to root-rot. This includes wet podsols and heavy clay soils where gleying comes close to the surface. Having said this, it occasionally strays onto peat bog surfaces where there is a little drainage, although it is unlikely to grow to tree dimensions. Sycamore is also generally absent in overly hot, dry situations where soils are subject to drought. It is commonly abundant on limestone, although where this is very pure and gives rise to very shallow light soils, the tree does poorly, even when planted. Sycamore naturalises itself best where humus decay is rapid and nitrification is active (free). Jones (1945) regards it as, "to some extent a nitrophilous species", and "its presence usually indicates a fertile soil".

Sycamore trees withstand exposure to wind and to salt spray better than almost any other large deciduous species and hence it has been commonly planted around exposed farms in hilly areas and on or near sea coasts either as copses or shelter-belts, which despite wind-pruning, provide excellent weather cover (Jones 1945).

A. pseudoplatanus is often associated with Ash (Fraxinus excelsior), the habitat ranges of the two species largely overlapping, although Ash is usually on somewhat heavier, wetter soils than Sycamore, and pure stands of the latter are rare. In Ash or Beech woodlands, Sycamore generally occurs as scattered individual trees, rather than in pure stands. It often seeds into gaps in conifer plantations, anywhere there is bare ground and along the margins of such stands (Jones 1945).

In many older woodland stands, A. pseudoplatanus represents an undesirable woody weed as it can germinate and establish in moderately deep deciduous woodland shade where there is at most a thin discontinuous carpet of herbaceous species and little litter, with plenty of mineral soil exposed. A. pseudoplatanus can form an under-storey under the canopy of Oak, Ash, Birch or Larch woods, but Sycamore's own leaf litter is plentiful, very slow to decompose, and where it accumulates it suppresses woodland ground and herb flora layers, limiting local species diversity. Again, it is noticed that Sycamore seedlings appear to be somewhat nitrophilous, their distribution often coinciding with Mercurialis annua (Annual Mercury), M. perennis (Dog's Mercury), Sambucus nigra (Elder), Silene dioicum (Red Campion) and Urtica dioica (Stinging Nettle) (Jones 1945).

A. pseudoplatanus now occurs in B & I from sea-level to at least the upper limits of cultivation and habitation. The potential upper limit of the tree is determined more by the presence of suitable soil and regeneration conditions rather than by levels of exposure or temperature (Jones 1945).

Flowering reproduction

Flowers open from late April and they continue being produced for at least a month. Yellowish-green, they are borne in narrow pendulous racemes up to 20 cm long containing 6-100 flowers in stalked clusters 4-6 mm in diameter. It has been noted that often up to 60% of flowers in a raceme are male and that male flowers open first. The proportion of male to hermaphrodite (perfect, bisexual) flowers varies greatly from tree to tree and it is possible that some trees are entirely male, although if this is the case, they are very rare. Trees with few hermaphrodite flowers are not uncommon (Jones 1945).

The flowers are scented and produce nectar, attracting bees (including honey-bees) and flies as pollinators. The samara fruit are formed very quickly, the earliest being of appreciable size before flowering on the tree has finished. Trees in open situations can produce fertile seed when only 20 years old and good seed crops are produced practically every year (Hadfield 1957). Samara are released from the tree gradually, beginning about the last week in October and continuing through into the first few months of the following year. Wind dispersal usually carries the fruit only a short distance (ie up to around 80 m), but high winds can occasionally disperse it for up to 4 km. Seed does not germinate, even under favourable temperature conditions, before the mid-January after production. No hybrids have been reported (Jones 1945; Stace et al. 2015).

Sycamore readily seeds itself in pre-existing woodlands and in hedgerows. Well-established trees are extremely difficult to extirpate, the root and stump very stubbornly regenerating the plant. Since wind transport of the winged samara fruit is very effective, small seedlings often appear in the spring as lawn weeds, in gravel paths and as pioneer colonists of neglected ground in parks, gardens and roadside verges. The lawnmower, however, quickly dispatches them. In wilder situations, A. pseudoplatanus is generally kept in check by competition from more vigorous, taller herbaceous species and also by the browsing of grazing animals (Jones 1945).

Status and introduction to Britain

This is such a common and often a well-grown, large tree in B & I that many people assume it is native, while in reality it is certainly a neophyte, ie a post-1500 AD deliberate human introduction. A. pseudoplatanus is a native tree of upland parts of C & S Europe and the oldest trees in these islands are in Scotland, possibly planted around 1550 AD or a little earlier (Mitchell 1996, p. 183; see also Jones 1945, p. 236). Subsequently, the tree became very widely planted all across B & I for its excellent timber and it quickly naturalised itself from the 18th century onwards in older, native or semi-native woods and other more open habitats, especially hedges (Rackham 1980, p. 58). In Ireland, there is reliable evidence that Sycamore was being planted near Derry (Londonderry) around 1610, during the plantation of Ireland by Scottish settlers in the reign of James I (Nelson & Walsh1993).

The same level of plantation occurring on the continental mainland means it is difficult or near impossible to determine its original centre of origin and natural distribution (Hadfield 1957).

Variation

A. pseudoplatanus is sufficiently variable that as many as 34 distinct cultivars are listed in the Royal Horticultural Society Index of Garden Plants (Griffiths 1994). In the critical Flora of B & I, two varieties are recognised. Var. pseudoplatanus, with samara wings 20-40 mm, contains four formae : forma pseudoplatanus; forma variegatum (Weston) Rehder; forma purpureum (Loudon) Rehder; and forma erythrocarpum (Carrière) Pax, the latter three corresponding to cultivars. The other variety is var. macrocarpum Spach, which has samara with larger wings (50-60 mm) (Sell & Murrell 2009).

Fermanagh occurrence

Sycamore is now an extremely common and widespread self-sown tree in woods and hedges throughout Fermanagh, as is the case almost everywhere in B & I. In Fermanagh, it has been recorded in 403 tetrads, 76.3% of those in the VC, making it the 9th most widespread woody plant in the post-1975 survey by RHN & the current author (RSF), although it still lies well behind Fraxinus excelsior (Ash), Alnus glutinosa (Alder), Ilex aquifolium (Holly) and Corylus avellana (Hazel) in terms of tetrad frequency.

Seedlings or saplings are frequent just about everywhere in Fermanagh, except in the wettest, most acidic, most exposed or very heavily disturbed situations.

European and world occurrence

Some authorities claim that A. pseudoplatanus reaches SE Denmark and SW Sweden in the north, but others believe it spreads southwards only from NW France, S Germany and Poland to N Spain, Corsica, Sicily and C Greece and thence into Asia Minor and the Caucasus (Jones 1945). It grows mixed with other trees, particularly Beech and Ash and is seldom found growing in pure stands (Jones 1945; Hadfield 1957).

Uses

Sycamore wood is very pale-brown to yellowish-white in colour, darkening with age. It is fairly hard, moderately heavy and strong, but it is not durable outdoors, being unsuited to prolonged exposure to weather (Edlin 1964). When polished it is one of the most beautiful timbers available to the cabinet maker and wood turner. Some forms have colour flecks or wavy patterned grain, when it is called 'fiddle-back' sycamore. It is also suitable for steam bending and can be used for making musical instruments including violins and harps. Sycamore wood has also been used for veneers, carving, furniture making (including for tables). It is smooth enough for making good dance floors and, as it can withstand wear and scrubbing without the grain picking up, staining or tainting food, it is perfect for the manufacture of smaller everyday kitchen items such as bowls, plates, ladles, spoons and for rollers for printing machines and clothes' mangles. It also makes excellent firewood, but its greatest use so far has been as a shelter tree for buildings (Edlin 1964; Nelson & Walsh 1993; Mitchell 1996; Sell & Murrell 2009).

Names: 'Sycamore' properly is the common name of a species of Fig, Ficus sycomorus L. (Mulberry-leaved Fig), native in W Asia and tropical Africa, but the name 'Sycamore' was more loosely applied in 14th century England, and somehow here became attached to Acer pseudoplatanus. Gerard (1597) wrongly called it 'Sycomore', but he preferred to refer to it as 'Great Maple' or 'Giant Maple'. To add to the confusion, in N America the name 'American Sycamore' is applied to Platanus occidentalis L., their species of Eastern Plane and, in Scotland, the tree is often called the 'Plane' (Elias 1980; Mitchell 1996). Grigson (1955, 1987) lists twelve additional English common names, several of them linked with children using the twigs to make whistles.

Threats

The presence of Sycamore might well downgrade the conservation status of old woodland. The recently arrived, rapidly spreading fungal pathogen, Phytophthora ramosum, reportedly attacks A. pseudoplatanus in southern England.