Ulmus'Sapporo Autumn Gold' is one of the most commercially successful hybridelm cultivars ever marketed, widely planted across North America and western Europe, although it has now been largely supplanted by more recent introductions. Arising from a chance crossing of the Japanese elm and Siberian elm, seed was sent in 1958 by Prof. Nobuku Takahashi and his colleagues at the Sapporo Botanical Garden of Hokkaido University, Sapporo, to Eugene Smalley at the University of Wisconsin–Madison. The patent issued in 1975 has expired, and there are now no propagation restrictions.
Description
The tree usually forks at 1.5-2 m from the ground to produce a broad, rounded, densely foliated crown, though immature plants produce vigorous side shoots requiring assiduous pruning to maintain shape. The bark is pale grey, and longitudinally fissured to form a random lattice pattern. The leaves are narrowly elliptical, < 9 cm long by < 4.5 cm wide, with 8 mmpetioles. As the name implies, the leaves turn pale yellow in autumn. The perfect, apetalous wind-pollinated flowers appear in early March, followed by the seeds in April; flowering usually begins when the tree is aged six years.
Pests and diseases
'Sapporo Autumn Gold' possesses a very high resistance to Dutch elm disease; in trials in Italy, it sustained only 2.8% defoliation and 1.2% dieback when inoculated with unnaturally high concentrations of the fungal pathogen. The cultivar also has a tolerance of Verticillium wilt. The tree's foliage was adjudged 'resistant' to black spot by the Plant Diagnostic Clinic of the University of Missouri , however it can be severely damaged by the elm leaf beetle in the United States Several mature specimens near the Hampshire coast in England have become afflicted by Dryad's saddle fungus.
Cultivation
In favorable conditions; notably a moist, well-drained soil, the tree can grow at a rate of almost one meter per year. Trials by the Northern Arizona University found that it is not very tolerant of a hot, arid climate although its leaves sustained comparatively little scorch damage. In trials in southern England conducted by Butterfly Conservation, the tree was found to be intolerant of ponding overwinter. 'Sapporo Autumn Gold' was first introduced to the UK by technology company Pitney Bowes as part of its 'Elms Across Europe' campaign. The company supplied the cultivar to schools, parks and gardens throughout the UK and Europe. The tree remains popular in continental Europe but does not assimilate well in the countryside. In trials in France by Cemagref at Nogent-sur-Vernisson, Loiret, it was found to grow too vigorously in hedgerow conditions, eclipsing neighbouring shrubs and consequently creating gaps. In rich soils in the Netherlands the tree grows too fast and has poor wind resistance, whereas in poor, dry conditions growth is slower and more robust. The hybrid was included in trials in Canberra, Australia started in 1988, but has not performed well there. In the UK, 'Sapporo Autumn Gold' has been found to host the endangered white-letter hairstreak butterfly, whose larvae feed exclusively on elm.
Notable trees
The very first tree planted in the UK in 1979 at Pitney Bowes by Denis Thatcher survives in perfect health . Of five trees planted in 1980 on the green in Clifton, one survives, the others having suffered "catastrophic branch collapse" in storms. Other notable plantings were as street trees across Bexhill-on-Sea, East Sussex in late 1980s, and as riverside trees along the Ouse in York. The largest specimen in Europe known to Dutch elm expert Hans M. Heybroek grows at the Istituto per la Protezione delle Piante's Monna Giovanella nursery at Antella, near Florence.
Synonymy
Shapiro Autumn Gold: Whitcomb, C. E. Know it and grow it, p. 171, 1976, missprint for 'Sapporo'.
Accessions
North America
Bartlett Tree Experts, US. Acc. nos. 88-1153, 88-1154
