Editing Elm (section)

== Ecology ==

=== Propagation ===
[[File:White Elm rooted cutting.jpg|thumb|left|80px|A rooted cutting of European white elm (July)]]
Elm propagation methods vary according to elm type and location, and the plantsman's needs. Native species may be propagated by seed. In their natural setting, native species, such as [[wych elm]] and [[Ulmus laevis|European white elm]] in central and northern Europe and [[Ulmus minor|field elm]] in southern Europe, set viable seed in "favourable" seasons. Optimal conditions occur after a late warm spring.<ref name="Richens">Richens, R. H. (1983). ''Elm''. Cambridge University Press.</ref> After pollination, seeds of spring-flowering elms ripen and fall at the start of summer (June); they remain viable for only a few days. They are planted in sandy potting soil at a depth of 1&nbsp;cm, and germinate in three weeks. Slow-germinating [[American elm]] will remain dormant until the second season.<ref name="ReferenceA">forestry.about.com/od/treeplanting/qt/seed_elm.htm</ref> Seeds from autumn-flowering elms ripen in the fall and germinate in the spring.<ref name="ReferenceA" /> Since elms may hybridize within and between species, seed propagation entails a hybridisation risk. In unfavourable seasons, elm seeds are usually sterile. Elms outside their natural range, such as English elm [[Ulmus minor 'Atinia'|''U. minor'' 'Atinia']], and elms unable to pollinate because pollen sources are genetically identical, are sterile and are propagated by [[vegetative reproduction]]. Vegetative reproduction is also used to produce genetically identical elms (clones). Methods include the winter transplanting of [[Basal shoot|root suckers]]; taking hardwood cuttings from vigorous one-year-old shoots in late winter,<ref>{{cite web |title=Propagation: Root an Elm Tree Cutting &#124; DoItYourself.com |url=http://www.doityourself.com/stry/propagation-root-an-elm-tree-cutting |url-status=live |archive-url=https://web.archive.org/web/20131203103220/http://www.doityourself.com/stry/propagation-root-an-elm-tree-cutting |archive-date=3 December 2013 |access-date=2013-11-30 |df=dmy-all}}</ref> taking root cuttings in early spring; taking softwood cuttings in early summer;<ref>cru.cahe.wsu.edu/CEPublications/pnw0152/pnw0152.html</ref> [[grafting]]; [[layering|ground and air layering]]; and [[micropropagation]]. A bottom heat of 18&nbsp;°C<ref>resistantelms.co.uk/elms/ulmus-morfeo/</ref> and humid conditions are maintained for hard- and softwood cuttings. The transplanting of root suckers remains the easiest and most common propagation method for European field elm and its hybrids. For specimen urban elms, grafting to wych-elm rootstock may be used to eliminate suckering or to ensure stronger root growth. The mutant-elm cultivars are usually grafted, the "weeping" elms [[Camperdown Elm|'Camperdown']] and [[Ulmus glabra 'Horizontalis'|'Horizontalis']] at {{convert|2|–|3|m|ft|0|abbr=on}}, the dwarf cultivars [[Ulmus 'Nana'|'Nana']] and [[Ulmus × hollandica 'Jacqueline Hillier'|'Jacqueline Hillier']] at ground level. Since the [[Siberian elm]] is drought tolerant, in dry countries, new varieties of elm are often root-grafted onto this species.<ref name="Clouston">Clouston, B., Stansfield, K., eds., ''After the Elm'' (London, 1979)</ref> 
<gallery>
Image:Ulmus minor MHNT.BOT.2010.12.3.jpg|Ripe samarae of field elm 
Image:Rock Elm seedling.JPG|[[Rock elm]] ''Ulmus thomasii'' germinating
Image:Klijavac ulmus glabra goc 0427.jpg|Seedling of wych elm ''U. glabra'' 
Image:Ulmus minor 14.jpg|Root-suckers spreading from [[Ulmus minor|field elm]] ''U. minor''
Image:Root cuttings of Ulmus 'Dodoens'.jpg|Root cuttings of [[Ulmus 'Dodoens'|''U.'' 'Dodoens']] 
Image:Elm clone rooted hardwood cutting Faculty of Forestry Belgrade 1983.09.01.jpg|Rooted hardwood elm cutting 
Image:Rooting of softwood cuttings of elm under the mist propagation system.jpg|Rooting of softwood cuttings under mist
Image:Ulmus campestris 'ARGENTEOVARIEGATA'.jpg|Mutant [[Ulmus 'Variegata' (Smooth-leafed Elm cultivar)|variegated smooth-leafed elm]] graft 
Image:Air layering of Ulmus pumila Faculty of Forestry Belgrade 7.6.1986.jpg|Air [[layering]] of [[Ulmus pumila|''U. pumila'']] 
File:Ulmus chenmoui in vitro.jpg|In vitro propagation of [[Ulmus chenmoui|''U. chenmoui'']] by bud [[meristem]] 
File:Ulmus (unknown cultivar). Royal Terrace, Edinburgh (5).jpg|[[Aerial root]]s, hybrid elm cultivar
</gallery>

=== Associated organisms ===
<gallery>
File:20130702Ulmus glabra1.jpg|Pouch [[Gall|leaf gall]]s on a wych elm ([[aphid]] ''Tetraneura ulmi''), Germany
File:Tetraneura ulmi (Aphididae sp.) gall, Elst (Gld), the Netherlands.jpg|Pouch leaf gall on elm leaf (aphid ''T. ulmi''), the Netherlands
File:Colopha compressa 1 beentree.jpg|Cockscomb leaf galls (aphid ''Colopha compressa''), Poland 
File:Eriosoma lanuginosum 1.JPG|Bladder leaf galls on elm leaves (aphid ''Eriosoma lanuginosum''), Italy
File:Eriosoma lanuginosum 2.JPG|Bladder leaf galls on a narrow-leaved elm (aphid '' E. lanuginosum''), Italy
File:Colopha compressa 4 beentree.jpg|Aphids in leaf gall, Poland 
File:Ulmus-minor---Eriophyes-ulmicola-agallas.jpg|Pimple leaf galls on a field elm ([[mite]] ''Eriophyes ulmi''), Spain
File:WLH Julita.JPG|White-letter hairstreak ''[[Satyrium w-album]]'', on {{tdes|Lutece|caps}}, Sweden: The larvae feed only on elm. 
File:Satyrium w-album egg1.jpg|Egg of ''Satyrium w-album'' near flower-bud of an elm
File:01a Scolytus multistriatus Imago 20fach rechte Seite.jpg|Elm-bark beetle ''Scolytus multistriatus'' (size: 2–3&nbsp;mm), a vector for Dutch elm disease
File:04 Scolytus multistriatus Fraßbild.jpg|''Scolytus multistriatus'' galleries under elm bark
File:Xanthogaleruca luteola 1.JPG|Elm-leaf beetle ''[[Xanthogaleruca luteola]]'', which causes serious damage to elm foliage 
File:Xanthogaleruca luteola 20060905 525 part.jpg|''Xanthogaleruca luteola'' caterpillar on elm leaf, Germany
File:Xanthogaleruca luteola 20060905 530.jpg|Elm-leaf damage caused by ''X. luteola'', Germany
File:Slime flux on Camperdown elm.png|Bacterial infection ''Erwinia carotovora'' of elm sap, which causes [[slime flux]] (wetwood) and staining of the trunk (here on a 'Camperdown' elm) 
</gallery>

=== Pests and diseases ===
{{Main|List of elm diseases}}

==== Dutch elm disease ====
{{main|Dutch elm disease}}
[[File:Iepziekte op goudiep (Ophiostoma ulmi on Ulmus hollandica 'Wredei' 4 May 2009).jpg|thumb|[[Ulmus × hollandica 'Wredei'|Golden elm]] tree with [[Dutch elm disease]]]]
Dutch elm disease (DED) devastated elms throughout Europe and much of North America in the second half of the 20th century. It derives its name "Dutch" from the first description of the disease and its cause in the 1920s by Dutch botanists [[Marie Beatrice Schol-Schwarz|Bea Schwarz]] and [[Christine Buisman|Christina Johanna Buisman]]. Owing to its geographical isolation and effective quarantine enforcement, Australia has so far remained unaffected by DED, as have the provinces of [[Alberta]] and [[British Columbia]] in [[western Canada]].

DED is caused by a micro[[fungus]] transmitted by two species of ''[[Scolytinae|Scolytus]]'' elm-bark [[beetle]]s, which act as [[Vector (epidemiology)|vectors]]. The disease affects all species of elms native to North America and Europe, but many Asiatic species have evolved antifungal genes and are resistant. Fungal spores, introduced into wounds in the tree caused by the beetles, invade the [[xylem]] or vascular system. The tree responds by producing [[tylose]]s, effectively blocking the flow from roots to leaves. Woodland trees in North America are not quite as susceptible to the disease because they usually lack the root grafting of the urban elms and are somewhat more isolated from each other. In France, inoculation with the fungus of over 300 clones of the European species failed to find a single variety that possessed of any significant resistance.

The first, less aggressive strain of the disease fungus, ''[[Ophiostoma ulmi]]'', arrived in Europe from Asia in 1910, and was accidentally introduced to North America in 1928. It was steadily weakened by viruses in Europe and had all but disappeared by the 1940s. However, the disease had a much greater and longer-lasting impact in North America, owing to the greater susceptibility of the American elm, ''Ulmus americana'', which masked the emergence of the second, far more virulent strain of the disease ''[[Ophiostoma novo-ulmi]]''. It appeared in the United States sometime in the 1940s, and was originally believed to be a mutation of ''O. ulmi''. Limited gene flow from ''O. ulmi'' to ''O. novo-ulmi'' was probably responsible for the creation of the North American subspecies ''O. novo-ulmi'' subsp. ''americana''. It was first recognized in Britain in the early 1970s, believed to have been introduced via a cargo of Canadian rock elm destined for the boatbuilding industry, and rapidly eradicated most of the mature elms from western Europe. A second subspecies, ''O. novo-ulmi'' subsp. ''novo-ulmi'', caused similar devastation in Eastern Europe and Central This subspecies, which was introduced to North America, and like ''O. ulmi'', is thought to have originated in Asia. The two subspecies have now hybridized in Europe where their ranges have overlapped.<ref name = Webber>Webber, J. (2019). What have we learned from 100 years of Dutch Elm Disease? ''Quarterly Journal of Forestry''. October 2019, Vol. 113, No.4,&nbsp;p.264-268. Royal Forestry Society, UK.</ref>  The hypothesis that ''O. novo-ulmi'' arose from a hybrid of the original ''O. ulmi'' and another strain endemic to the [[Himalayas]], ''[[Ophiostoma himal-ulmi]]'', is now discredited.<ref name=Brasier,1>Brasier, C. M. & Mehotra, M. D. (1995). Ophiostoma himal-ulmi sp. nov., a new species of Dutch elm disease fungus endemic to the Himalayas. ''Mycological Research'' 1995, vol. 99 (2), 205&ndash;215 (44 ref.) {{ISSN|0953-7562}}. Elsevier, Oxford, UK.</ref>

No sign indicates the current pandemic is waning, and no evidence has been found of a susceptibility of the fungus to a disease of its own caused by [[d-factors]]: naturally occurring virus-like agents that severely debilitated the original ''O. ulmi'' and reduced its sporulation.<ref name=Brasier,2>Brasier, C. M. (1996). New horizons in Dutch elm disease control. Pages 20-28 in: ''[http://www.forestry.gov.uk/pdf/New_horizons_DED.pdf/$FILE/New_horizons_DED.pdf Report on Forest Research] {{webarchive|url=https://web.archive.org/web/20070628155810/http://www.forestry.gov.uk/pdf/New_horizons_DED.pdf/$FILE/New_horizons_DED.pdf |date=28 June 2007 }}'', 1996. Forestry Commission. HMSO, London, UK.</ref>

==== Elm phloem necrosis ====
[[Elm Yellows|Elm phloem necrosis (elm yellows)]] is a [[phytopathology|disease]] of elm trees that is spread by [[leafhoppers]] or by root grafts.<ref name="Elm Yellows">"[http://www.elmcare.com/disease/elm_yellows.htm Elm Yellows] {{webarchive|url=https://web.archive.org/web/20111004214753/http://elmcare.com/disease/elm_yellows.htm |date=4 October 2011 }}". Elmcare.Com. 19 March 2008.</ref> This very aggressive disease, with no known cure, occurs in the [[Eastern United States]], southern [[Ontario]] in Canada, and Europe. It is caused by [[phytoplasmas]] that infect the phloem (inner bark) of the tree.<ref name=Price>Price, Terry. "[http://www.forestpests.org/gfcbook/wiltdiseases.html Wilt Diseases] {{webarchive|url=https://web.archive.org/web/20110928145148/http://www.forestpests.org/gfcbook/wiltdiseases.html |date=28 September 2011 }}". Forestpests.Org. 23 March 2005. 19 March 2008.</ref> Infection and death of the [[phloem]] effectively girdles the tree and stops the flow of water and nutrients. The disease affects both wild-growing and cultivated trees.
Occasionally, cutting the infected tree before the disease completely establishes itself and cleanup and prompt disposal of infected matter has resulted in the plant's survival via stump sprouts.

==== Insects ====
[[File:Xanthogaleruca luteola MHNT Dos.jpg|thumb|The [[Xanthogaleruca luteola|elm leaf beetle]]]]
Most serious of the elm pests is the [[Xanthogaleruca luteola|elm leaf beetle]] ''Xanthogaleruca luteola'', which can decimate foliage, although rarely with fatal results. The beetle was accidentally introduced to North America from Europe. Another unwelcome immigrant to North America is the [[Japanese beetle]] ''Popillia japonica''. In both instances, the beetles cause far more damage in North America owing to the absence of the predators in their native lands. In Australia, introduced elm trees are sometimes used as food plants by the larvae of [[Hepialidae|hepialid]] [[moth]]s of the genus ''[[Aenetus]]''. These burrow horizontally into the trunk then vertically down.<ref>{{Cite Americana|wstitle=Elm-Insects}}</ref><ref>{{Cite NIE|year=1905|wstitle=Elm-Insects}}</ref> Circa 2000, the Asian Zig-zag sawfly ''[[Aproceros leucopoda]]'' appeared in Europe and North America, although in England, its impact has been minimal and it is no longer monitored.<ref name = Forest>[https://www.forestresearch.gov.uk/.../elm-zigzag-sawfly-aproceros-leucopoda Elm zigzag sawfly (Aproceros leucopoda)]</ref>

==== Birds ====
[[Sapsucker]] woodpeckers have a great love of young elm trees.<ref>{{Cite web|url=https://www.forestwildlife.org/sapsucker-vs-woodpecker/|title=Sapsucker Vs Woodpecker: How To Tell The Difference|website=Forest Wildlife|date=10 May 2022 |language=en-US|access-date=2022-07-01}}</ref> [[File:RN Ulmus minor Umbraculifera.JPG|thumb|left|upright=0.9|The ball-headed graft [[Ulmus minor 'Umbraculifera'|narvan elm]], ''Ulmus minor'' 'Umbraculifera', cultivated in Persia and widely planted in central Asia]]
[[File:Lafayette Street, Salem, MA.jpg|thumb|left|upright=0.9|Lafayette Street in [[Salem, Massachusetts]] - an example of the high-tunneled effects of ''[[Ulmus americana]]'' avenues once common in New England (colorized postcard, 1910)]]