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Establishment of sycamore has been recorded in both South and North Islands and in the north as far as Auckland (Esler 1989). Natural regeneration was first recorded by Cockayne (1921, p 287). At one site he found young plants arising in thousands, but noted that it had not, as yet, "spread spontaneously beyond the original plantation, except into neighbouring hedges". Thomson (1922, p 562) reported that sycamore was spreading in many localities in the neighbourhood of plantations, though Allan (1940) recorded sycamore but described it as a non-persistent escape. By 1958, the New Zealand Forestry Commission became concerned with the potential weediness of sycamore. It was noticed that a 30 year old Pinus radiata plantation situated two chains (37m) south of a sycamore - Lombardy poplar (Populus nigra cv. Italica) firebreak was being invaded by sycamore. Saplings, ranging in height from 15cm to 2.2m, were found up to 65m into the stand. At the time some fears were expressed as to its potential invasiveness: "the heavy regeneration could easily become a menace when clear felling operations commence in such stands, though the increased light and its effect on the young sycamores is perhaps a matter of conjecture" (Anon 1958). However, since this note no further publications on the invasion of sycamore into conifer plantations has been traced in the New Zealand literature.

Webb et al. (1988) state that sycamore is very common in many modified and partially modified habitats such as abandoned gardens (seedlings can be a nuisance), waste land, scrub bordering roadsides, river gullies, and in and around stands of secondary and regenerating forest. Sometimes dense copses develop from the freely-produced seed, and some forest communities are composed almost solely of sycamore. 

In New Zealand most secondary vegetation is dominated by exotic species. On South Island, Ulex europaeus dominates large areas and Lee et al. (1986) found that sycamore occurs in 5.6% of the 125 10x10m quadrats surveyed in gorse stands around Dunedin. Sycamore appears to be regenerating following gorse establishment. A similar pattern of sycamore regeneration appears to take place on hill slopes (altitude 300m) with scrub-grasslands dominated by a spiny shrub (Discaria toumatou) and which also includes Coprosma propinqua and the exotic currant, Ribes sanguineum, which suppresses D. toumatou. Saplings of sycamore and larch protrude above the currant in places. Williams (1984) concludes that "any taller vegetation that may succeed the currant will probably be composed of these and other wind-dispersed trees."

Many exotic tree species have been found to invade high country tussock grassland, and at present only represent a problem in a small portion of the ecosystem (Ledgard 1988). Tussock grassland is a semi-natural type of community grazed by sheep and heavily invaded by many exotic grasses. Among exotic broadleaves, sycamore is the commonest species and is frequently accompanied by self-sown seedlings, but its distribution appears to be limited to sheltered moist sites. Ledgard & Belton (1985) suggest that, as for other broadleaves, its absence from exposed sites and its low total area may have reflected its unsuitability for much of the high country environment rather than limited plantings in the past.

The impact of sycamore in New Zealand is best given by Timmins & Williams (1987, p 243), who conclude that sycamore and other long-lived trees "are likely to have a severe impact on forest remnants in which they become established. Once established, not only do the original individuals persist but they continue to contribute seed." It is apparent that sycamore will remain a permanent feature of the New Zealand vegetation. Though it does not appear to threaten undisturbed forest it is described as a problem weed in forest and scrub (Timmins & Williams 1991) and is able to colonize semi-natural tussock grassland.

Little information is available on the species itself. First seed production appears to take place at a very early age and Ledgard (1988) quotes seven years. A large amount of phenotypic variation has been observed, and, apart from that observed in several cultivars, wild plants differ in the hairiness of leaves and inflorescences, the colour of the leaf underside and in samara colour (Webb et al. 1988). 

Bussell (1968a,b) carried out a study comparing the growth of sycamore with that of six native species, both deciduous and conifer. He also investigated the impact of light and temperature on growth in seedlings. He found clear differences between the invader and the natives at the seedling, sapling and adult stages. The following differences were observed:

1. Adult sycamore was the latest of all species to come into bud.
2. Leaf production continued relatively longer in natives than in sycamore.
3. Shoot extension was lowest in sycamore seedlings and mature trees but higher in young trees than in natives.
4. Bud scales of sycamore are reduced leaves, whereas in native spp. they are mostly stipules.
5. Leaf fall in sycamore occurs in the autumn and is under photoperiodic control, but native trees lost leaves at certain times during the growing season and this appears to be temperature controlled. Some natives are leafless in winter while others retain up to 50% of their leaves. 
6. Almost no sycamore seedling came into leaf after wintering in a greenhouse with the temperature kept at 10°C, while natives grew in Spring as early as outdoors.

The impact of these differences on the invasive potential are not discussed by Bussell and are difficult to interpret. One major difficulty is that the study did not include aspects of the reproductive biology.