Betula papyrifera Marsh.

With a range stretching from the Atlantic to the Pacific, Betula papyrifera is a familiar tree throughout the northern parts of North America, planted for its rapid growth and attractive bark, which varies from white to pink or dark orange-brown. In the eastern part of the range, from Ontario eastward to the coast, the species is best known as a large stately tree with very white bark, commonly planted in botanic gardens and residential settings, and frequently seen as a slender, drawn-up tree growing in sporadic gaps in climax deciduous and (at higher latitudes) coniferous forest. In populations west of the Rockies – for example in the huge old trees found on the coastal plain between the mountains and Vancouver – the bark can be orange-brown or brown – this form, thought by Bean (1976) ‘one of the very finest of birches’, was named Betula commutata by Regel (= B. papyrifera var. commutata (Regel) Fernald) and is also found more sporadically in Atlantic Canada (Nova Scotia and Newfoundland); Bean cited two particularly fine specimens in the Victory Glade at ‘Westonbirt (catalogued as B. lyalliana). There are also pink-barked trees at the east end of Lake Superior (see ‘Vancouver’ and ‘Saint George’).

Betula papyrifera was described by Humphrey Marshall in Arbustrum Americanum (Marshall 1785), an alphabetical catalogue of trees and shrubs native to North America, and one of the earliest botanical books published in America. Marshall was a cousin of the Bartrams, and had his own botanic garden in Chester Co., Pennsylvania. It is primarily a lowland tree, its ecology comparable with that of Eurasian Betula pendula, though it differs in not forming extensive stands. By contrast the tree-line birches in North America are B. pendula subsp. mandshurica in the northwest of the continent (Brittain & Grant 1967) and B. cordifolia in the east. As a hexploid, the species is exceptionally variable: the shoots and twigs vary from densely pubescent and eglandular to quite glabrous and roughly verrucose, and the leaves can vary considerably in size.

Bean (1976) reports the wood being used for fuel, and the bark for a variety of purposes, notably canoes, but also for roofing and drinking utensils. A single tree of Betula papyrifera high on a volcano in the island of Flores in the Azores in the middle of the Atlantic is probably Betula papyrifera – a species otherwise confined to North America – suggesting natural long distance dispersal.

In cultivation Betula papyrifera is grown for its bark, most often very white, but sometimes brown or pink and quite dark — perhaps with a ‘bloom’ of betulin in some populations. It makes splendid specimens in the arboretum or the larger garden, and is often planted as a street tree in Ontario, Quebec and the northeastern United States (also occasionally in the United Kingdom). The species is probably the quickest growing of any of the birches. The root system extends quickly, and in nursery conditions first-year seedlings can reach in excess of 2 m and be well furnished with side branches. The autumn colours are always very fine and of a deep orange-yellow. Darker-barked trees from west of the Rockies (though apparently not the white-barked eastern form) possess the ability to regenerate powerfully from even the most closely-levelled stump – at Stone Farm, Devon, seedlings originating from the Vancouver area, originally planted in 1981, all sprouted vigorously from stumps when felled in subsequent years. In North America a major deterrent to growing this species in a park or arboretum or in neighbourhoods is its susceptibility to the bronze birch borer (Santamour 1999), although the insect appears to present no problems in wild stands and is not (yet) known to occur in Eurasia.

Selected and named clones are treated below. Also worthy of propagation would be named varieties such as var. pensilis Fernald – ‘very striking, not only as a weeping birch but on account of the mostly acute-based leaves and the very abundant fruiting aments […] often clustered on the spurs in fascicles of 2–4’ (Fernald 1945).

The hybrid with Betula occidentalis (Betula × utahensis Britton) can form stable tetraploid populations, behaving as a species in the absence of both parents. Betula papyrifera also hybridises with B. glandulosa to produce hybrids which would probably be referrred to ‘B. × minor’, though that name properly refers to the cross B. cordifolia × B. glandulosa. The Alaskan Betula kenaica, with the fruiting catkin scales hairy on the margin and smaller leaves, recorded from around the Kenai peninsula, is recognised in Flora of North America (Furlow 1997) as a distinct species on the basis of the pentaploid chromosome number (2n=70) reported in a cultivated tree from the Arnold Arboretum. McAllister and Ashburner (2013) considered pentaploidy to be implausible in a true species, and noted that Dugle (1966) interpreted herbarium collections under this name as B. papyrifera, B. pendula subsp. mandshurica, and hybrids.They proposed that B. kenaica be viewed as a westward extension of B. papyrifera into southern Alaska, perhaps affected by introgression from B. pendula subsp. mandshurica. It is here placed in synonymy with B. papyrifera.