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Introduction and planting

Jones (1944) found that the first definite record of sycamore in England is that of Lyte in 1578, but suggests that it is probable that it was introduced to Scotland at a slightly earlier date. Some workers have argued that the Romans could have introduced it, but no conclusive evidence can be found (Bleay 1987). Sycamore remained rare around houses and in hedges though by the 17th and 18th centuries nursery records show stocking and sale of young sycamores (Bleay 1987). However, it was not extensively planted until the late 18th century (Jones 1944). At that time sycamore was especially popular in amenity planting of some ancient parks and was planted with many other exotics for a classical effect (Mabey 1980) and it is said that this practice encouraged its spread (Pennington 1969). In Scotland the first Gaelic name for sycamore - the Plinntriinn - was first referred to in 1772 suggesting that the tree was not common enough prior to that date to warrant a name (Fergusson 1878).

Evidence from pollen diagrams support the view that sycamore is introduced and has only become common in recent times. For instance Peglar et al. (1989) found that sycamore pollen first appeared in lake sediments in the zone dated about 0 to 150 B.P. and was a result of tree planting around the lake and in the nearby town over the previous two centuries. Continental pollen diagrams from natural forests (beech dominated with a some sycamore) contain a steady quantity of sycamore pollen (<1%) throughout the investigated profiles (e.g. Kral & Mayer 1968) indicating that the lack of sycamore pollen in the pollen diagrams from the British Isles is due to the absence of sycamore rather than to the decay of its pollen.

Present distribution and abundance

Sycamore is widely distributed and occurs in 2267 10km squares of the Atlas of the British Flora, and of all tree and shrub species only ash (2344 squares) and Crataegus monogyna are more widely distributed (Perring & Walters 1962). Apart from Sorbus aucuparia, sycamore ascends higher than any other broadleaved species and has been recorded up to an altitude of 480m in Shropshire (Jones 1944). On exposed and often tree-less islands of both the far north (Orkney and Shetlands) and the south-west (Scilly Isles) sycamore is the commonest tree (Low 1987, Davey 1909).

In the Lothian Region of Scotland sycamore constitutes 18.4% of the total number of trees in residential areas, 15.3% in lowland rural and 5.5% in upland rural areas. It is the commonest species except in upland areas where soils are poorly drained (Good et al. 1978). In terms of habitats Good et al. (1978) found a large variation in the occurrence of sycamore, it represented only 1% of all the trees found in hedgerows, 2% pastures, 0% in marsh and fens, 1% of industrial spoils, 2% in coniferous woodland, 21% in mixed woodland, 20% in broadleaved woodland, 13% arable fields, 19% in park (commonest tree), 10% in shelterbelts, 8% in scrubs and 7% in gardens. Large geographical variations do occur; for instance in the Galloway region, some parts of Lancashire and near Aviemore sycamore is the commonest hedgerow timber species (Moore et al. 1967). 

In North Wales sycamore was the 3rd most common roadside tree (14% of the total) (Good & Steele 1981) while in Derbyshire it occurred in small numbers: 2% in brookside and field hedges and 8% in garden hedges (Willmot 1980). Work by Allison & Peterken (1985) suggests that in Avon and Norfolk sycamore is six times more common in built up areas and along highways than in woodlands. Sycamore has often been reported as an important part of the flora of walls (e.g. Payne 1978, Risbeth 1948, Woodell & Rossiter 1959).

Sycamore is a common feature of human habitations. In Wales sycamore was commonly planted about farmhouses (Woods 1990), while in the city of Manchester sycamore and other maples represented 11% of the total number of trees surveyed (Wong et al. 1988).

In broadleaved high forest of Great Britain sycamore represents 8.8% of the total (Evans 1987) and a similar figure is given for Cumbria where it is the third commonest broadleaved species after oak and birch (Bunce 1989). According to Rackham (1976) the expansion of sycamore has occurred chiefly into highland woods.

Rodwell et al. (1991) have recently classified the woodlands of Great Britain and found that sycamore was present in 14 of their 25 recognized woodland types. They assert that sycamore is increasing in importance towards the west and the north with a marked association with Ulmus glabra and areas with rainfall in excess of either 762mm/yr or 1000mm/yr (Rodwell et al. 1991, pp. 138 and 255 respectively). They suggest that sycamore is not so much an indicator of human interference but rather of areas of higher rainfall. It is worth noting that sycamore is not recorded in the Quercus petraea and Betula spp. community type (W11) characteristic of western Great Britain, where rainfall is high and soils are free-draining.

In a Cumbrian valley Kirby (1986), in a survey, recognized four types of semi-natural woodlands. Quercus petraea woodland (old coppice) was the commonest type, while stands dominated by Betula pubescens, ash and Corylus avellana or Alnus glutinosa were also found. However, sycamore was only present where ash is dominant, mostly on scree slopes.

In eastern England sycamore invasion of ancient woods is recent, covers only 0.5% of the woodland area and is more common in ash and elm woods (Rackham 1980). In his investigation of west Suffolk woodlands Bleay (1987) found that sycamore was very common in secondary woodlands and forestry plantations and occurred in half of primary woodlands and deciduous plantations. In woodlands the frequency of sycamore was very variable but at the majority of the sites no tree regeneration was observed. Bleay (1987) found that in some ancient woodlands sycamore regenerated prolifically and sycamore invasion was more commonly found close to the largest anthropogenic centres. He also suggests that sycamore may be more invasive following the decline in woodland management.

Table 1. Percentage occurrence of sycamore in four woodland types in west Suffolk (data adapted from Bleay 1987).

Planting and change in abundance

Recent changes in amenity tree planting in rural landscapes of England and Wales have been documented by Wright (1983) which show that County Councils appear to have dramatically increased their rate of planting of sycamore from 3.2% to 12% of the total number of trees planted within a few years prior to 1981 (Table 2). In contrast, other agencies stopped planting sycamore altogether. 72% of 25 authorities planted sycamore regularly, and planting was common in most of England except in the East and in Wales. Sycamore has also been widely used for land reclamation, particularly spoil heaps (e.g. Jobling 1987).

Table 2. Recent changes in tree planting by County Councils and other agencies in England and Wales (data from Wright 1983).

In Great Britain in terms of volume there has been an increase in sycamore from 2.11 to 2.47 million m³ from 1951 to 1980 according to Forestry Commission surveys and it is the fourth commonest species by volume. All main species except oak and of course elm showed increases (Allison & Peterken 1985).

Forestry

Sycamore has had some importance in British forestry, although it has never received the attention given to it by continental foresters. This of course may not be totally surprising given the present neglect of broadleaved forests in England when compared to those of Central Europe. The silviculture, growth, yield and economics of sycamore in Wessex has been documented by Stern (1989).

Pure sycamore coppice (about 2500ha or about 7% of the total coppiced area) occur on a wide range of soils in the south of England, whereas coppice with standards is rare. The rotations are typically of 10 to 20 years and the wood is used in turnery (Evans 1984).

Due to its "prolific seeding" sycamore, as well as ash, is potentially good for selection and shelterwood management systems of high forest (Pryor & Savill 1986). The shelterwood management of sycamore was first applied in England by Garfitt (1953, 1963) to hazel coppice, which was thinned out in groups to release ash and sycamore saplings which regenerated underneath it. However, in areas where the hazel coppice was subsequently not completely removed it has remained dominant (Pryor & Savill 1986).

Although little use of the shelterwood system appears to have been made Pryor & Savill (1986) suggest that with ash, sycamore is the most promising species for shelterwoods because no gap planting is necessary because of vigour of regeneration and it requires less weeding than oak.

In areas where the selection system is practised sycamore and ash are the most abundant seedlings and are used as nurse trees for the final crop species, usually beech, oak and cherry (Pryor & Savill 1986).

The timber price of rippled (wavy-grain) sycamore in Ireland is high and this wood has obviously a good market prospect (Gallagher 1987). Although sycamore has been under-used in modern forestry (Stern 1982), large plantations of rippled sycamore is potentially feasible, but the conditions determining the expression of the character have yet to be ascertained (e.g. Stevenson 1985). 

At present sycamore is investigated for its use in agrenforestry systems (mixture of agricultural, energy and forestry crops) in Scottish hill farms (Newman et al. 1989). This system is designed to provide shelter for sheep and cattle, and sycamore is interplanted with Alnus incana which is coppiced.

Invasive potential

The first accounts of sycamore's potential for natural regeneration were published in 1847. Watson (1847) noted that "It propagates itself by seed, along the course of streams in several of the western counties, as those of Lancashire, Cumberland and Invernessshire; and Winch asserts it to be `certainly indigenous on the high moors' of Tyne province. As it rises freely from seeds falling in our shrubberies, and will flourish from the north to the south coast of Britain, there can be little doubt that it would establish itself perfectly, if allowed to do so" while Johns (1847) observed "the extreme fecundity of this tree" and added that "many young plants may be discovered in the spring at a considerable distance from the parent tree." Both authors noted that if the tree was indigenous it would have "filled the whole country, instead of being a simple occupant of plantations and hedges." According to Rackham (1976, 1980) sycamore apparently did not invade woodlands before the 19th century.

By the turn of the century Simpson (1903, 1905) provided further descriptions of its invasive power when he wrote "I have known large self-sown areas that came up so thickly as to overcome everything and yield a nice crop of poles in a short time" adding that "the overhead canopy is maintained ... so densely as to kill all undergrowth including elder, which will endure a great deal of bad usage." He also noted that sycamore propagated itself more freely than any of our forest trees except birch and that it could quickly invade the undergrowth of conifer plantations. 

Bean (1914) was the first author to fear that sycamore might replace native vegetation; he stated "judging by the way the seedlings spring up in the wilder parts of Kew Gardens, it would seem that, in the course of time, the place if left undisturbed, would become a forest of young sycamores."

Although Tansley noted that sycamore "is springing up freely from seed" in a semi-natural beech wood in Gloucetershire (Tansley & Adamson 1913), he does not dwell on the matter in his books on British vegetation (Tansley 1911, 1939). In his British Islands and their Vegetation, Tansley (1939) states that "locally it springs abundantly from self-sown seed, and owing to its free growth and deep shade it may become locally dominant in various kinds of woodland. In some of the South Down beechwoods on deep loams sycamore may even become co-dominant with beech." This statement is based on the work by Watt (Watt 1924, 1925, 1934) and details will be given in Section 5.5.3. Although it could be suggested that, apart from the South Down beechwoods, few sites of semi-natural vegetation were invaded at the time to warrant only a small discussion on sycamore, it is more likely that Tansley did not show much interest in plant invasions. Tansley once remarked to Elton "that it fills a natural position in the woodland structure occupied by various species of maples in North America, though ordinarily only to a rather limited extent by our native common maple, Acer campestre." (Elton 1966, p 54). 

During this latter part of the 20th century all authors agree that sycamore is regenerating and spreading, but it is said that it regenerates profusely from seed only on suitable sites but can be difficult to establish on grassy sites (Low 1986). In the absence of heavy grazing it regenerates very readily in most parts of Britain (Pennington 1969). In Guernsey it is a frequent tree, self-sowing itself readily (McClintock 1975), and in Radnorshire (Wales) the tree is "now so well naturalized in hedgerows and woodlands it behaves like a native species" (Woods 1990). The size distribution classes of sycamore in Scotland suggest that it is regenerating well (Good et al. 1978). Sycamore becomes readily established in southern English chalk quarries where it is described as a pioneer species (Davis 1983), and on Welsh slate waste tips (Sheldon 1975). At Monks Wood (Huntingdon), in recently planted hedgerows (mainly Crataegus monogyna) along a road, sycamore with ash is the most frequent colonizing tree, but was absent from the old hedges and the field hedges (Pollard 1973) indicating that the sycamore invasion is recent. Tobin et al. (1987) believe that the frequency of sycamore in Telford woods is indicative of past woodland disturbance and that it is a highly competitive, if not aggressive, species. 

Elton never appeared to promote or favour the control of sycamore. Rather he thought that if "left to itself the sycamore would probably settle down eventually to a normal ecological balance in our deciduous woods" (Elton 1966, p 54) and added that "although Britain is slightly north-west of its natural limits in Europe, the sycamore can reasonably be regarded as filling a more normal niche in our woods than some other invaders" (Elton 1966, p 193). Gilbert (1989) has suggested that in fertile valley woodland sycamore, with ash, "are likely to occupy the niche recently left vacant by elm".

In recent years, because of its high regeneration potential sycamore has been seen as presenting one of the major problems in conservation management plans for the Telford woods (Tobin et al. 1987) and it's profuse regeneration has often been controlled in urban woodlands (Nicholson & Hare 1986) and National Nature Reserves (Gibbons 1990a,b, 1991).