Mark Rowe investigates attempts to reintroduce elms to Britain

马克·罗（Mark Rowe）对英国重新引种榆树的计划进行了调研。

AAround 25 million elms, accounting for 90% of all elm trees in the UK, died during the 1960s and '70s of Dutch elm disease. In the aftermath, the elm, once so dominant in the British landscape, was largely forgotten. However, there's now hope the elm may be reintroduced to the countryside of central and southern England. Any reintroduction will start from a very low base. 'The impact of the disease is difficult to picture if you hadn't seen what was there before,' says Matt Elliot of the Woodland Trust. 'You look at old photographs from the 1960s and it's only then that you realise the impact [elms had] … They were significant, large trees… then they were gone.'

A 20世纪60年代至70年代，英国约2500万棵榆树(占英国所有榆树的90%)死于荷兰榆树病。此后，曾经在英国景观中占主导地位的榆树，很大程度上被遗忘了。然而，现在有希望将榆树重新引入英格兰中部和南部的乡村地区。所有重新引入的工作都将从一个非常低的起点开始。“如果你没有见过那里以前的景象，就很难想象这种疾病带来的影响，“林地信托基金的马特·埃利奥特说。“你得看看20世纪60年代的老照片，才会意识到榆树曾经的影响(有多大)它们(那时)是重要的巨大树木..接着就消失了。

BThe disease is caused by a fungus that blocks the elms' vascular (water, nutrient and food transport) system, causing branches to wilt and die. A first epidemic, which occurred in the 1920s, gradually died down, but in the '70s a second epidemic was triggered by shipments of elm from Canada. The wood came in the form of logs destined for boat building and its intact bark was perfect for the elm bark beetles that spread the deadly fungus. This time, the beetles carried a much more virulent strain that destroyed the vast majority of British elms.

B 这种疾病是由一种真菌引起的，这种真菌会阻塞榆树的维管系统(水分、营养和食物运输系统)，导致树枝枯萎死亡。该病20世纪20年代发生的第一次疫情/传播逐渐平息，但在70年代，从加拿大运来的榆树引发了第二次传播。这些木材是原木形式运来的，用于造船，其完好的树皮为传播这种致命真菌的榆树皮甲虫提供了理想的生存环境。这一次，甲虫携带了一种毒性更强的菌株，摧毁了英国绝大多数的榆树。

CToday, elms still exist in the southern English countryside but mostly only in low hedgerows between fields. 'We have millions of small elms in hedgerows but they get targeted by the beetle as soon as they reach a certain size,' says Karen Russell, co-author of the report 'Where we are with elm'. Once the trunk of the elm reaches 10-15 centimetres or so in diameter, it becomes a perfect size for beetles to lay eggs and for the fungus to take hold. Yet mature specimens have been identified, in counties such as Cambridgeshire, that are hundreds of years old, and have mysteriously escaped the epidemic.

C如今，英格兰南部的乡村仍有榆树，但大多只存在于田野间低矮的树篱中。“在树篱中有数百万棵小榆树，但它们一长到特定大小就会成为甲虫的目标，“《榆树现状报告》的合著者卡伦·拉塞尔说。“一旦榆树的树干直径达到10-15厘米左右就达到了甲虫产卵和真菌滋生的理想大小。然而，在剑桥郡等郡，人们发现了一些有数百年树龄的成熟榆树，它们不可思议地躲过了这场疫病。

The key, Russell says, is to identify and study those trees that have survived and work out why they stood tall when millions of others succumbed. Nevertheless, opportunities are limited as the number of these mature survivors is relatively small. 'What are the reasons for their survival?' asks Russell. 'Avoidance, tolerance, resistance? We don't know where the balance lies between the three. I don't see how it can be entirely down to luck.'

拉塞尔说，关键是要找出并研究那些存活下来的树木，弄清楚为什么在数百万棵榆树病死的情况下，它们还能存活下来。然而，由于这些存活到成熟的榆树相对较少，研究机会有限。“它们存活下来的原因是什么?“拉塞尔问道。“是它们避开疫病，还是对这种病有耐受力或者抵抗力?(但是)我们不知道这三者之间的平衡在哪里。我不认为这完全是运气。“[注释:"Where we arewith elm'是一份关于榆树现状的报告。

DFor centuries, elm ran a close second to oak as the hardwood tree of choice in Britain and was in many instances the most prominent tree in the landscape. Not only was elm common in European forests, it became a key component of birch, ash and hazel woodlands. The use of elm is thought to go back to the Bronze Age, when it was widely used for tools. Elm was also the preferred material for shields and early swords. In the 18th century, it was planted more widely and its wood was used for items such as storage crates and flooring. It was also suitable for items that experienced high levels of impact and was used to build the keel of the 19th-century sailing ship Cutty Sark as well as mining equipment.

D 几个世纪以来，在英国，榆树作为硬木树种在受欢迎程度方面仅次于橡树，而且在许多情况下，它是景观中最显眼的树。榆树不仅在欧洲森林中常见，还是桦树、白蜡树和榛树林的重要组成部分。榆树的使用可以追溯到青铜时代，当时它被广泛用于(制作)工具。榆树也是制盾和早期制剑的首选材料。18世纪，榆树被更广泛地种植，其木材被用于制作储物箱和地板等物品。它也适用于(制作)承受高强度撞击的物品，19世纪的帆船“卡蒂萨克号“的龙骨以及采矿设备就都是用榆树制作的。

[p:e}Given how ingrained elm is in British culture, it's unsurprising the tree has many advocates. Amongst them is Peter Bourne of the National Elm Collection in Brighton. 'I saw Dutch elm disease unfold as a small boy,' he says. 'The elm seemed to be part of rural England, but I remember watching trees just lose their leaves and that really stayed with me.' Today, the city of Brighton's elms total about 17,000. Local factors appear to have contributed to their survival. Strong winds from the sea make it difficult for the determined elm bark beetle to attack this coastal city's elm population. However, the situation is precarious. 'The beetles can just march in if we're not careful, as the threat is right on our doorstep,' says Bourne.

E 鉴于榆树在英国文化中根深蒂固，它有很多拥护者也就不足为奇了，比如布莱顿国家榆树收藏馆的彼得·伯恩。他说:“我小时候目睹了荷兰榆树病的蔓延。那时候榆树似乎是英格兰乡村的一部分，但我记得我眼睁睁地看着树叶凋零，那种景象真的挥之不去。“如今，布莱顿市的榆树总数约17000棵。似乎当地有些因素能够帮助它们存活下来。来自海上的强风使顽固的榆树皮甲虫难以攻击这座沿海城市的榆树群。然而，情况仍然岌岌可危。“威胁近在咫尺，要是我们不小心，甲虫就会入侵。“伯恩说。

FAny prospect of the elm returning relies heavily on trees being either resistant to, or tolerant of, the disease. This means a widespread reintroduction would involve existing or new hybrid strains derived from resistant, generally non-native elm species. A new generation of seedlings have been bred and tested to see if they can withstand the fungus by cutting a small slit on the bark and injecting a tiny amount of the pathogen. 'The effects are very quick,' says Russell. 'You return in four to six weeks and trees that are resistant show no symptoms, whereas those that are susceptible show leaf loss and may even have died completely.'

F 榆树未来是否能够回归，很大程度上取决于树木对这种疾病是否具有抵抗力或耐受力。这意味着大规模重新引入将涉及(使用)现有的或新的杂交品种，这些品种源自有抵抗力的、通常是非本地的榆树物种。新一代的幼苗已经培育出来并进行了测试:通过在树皮上切一个小切口并注入少量病原体，来观察它们是否能抵抗这种真菌。“效果很快就会显现，“拉塞尔说。“四到六周后你再去看这些树，有抵抗力的树木没有任何症状，而易受感染的树则会落叶，甚至可能完全死亡。

GAll of this raises questions of social acceptance, acknowledges Russell. 'If we're putting elm back into the landscape, a small element of it is not native – are we bothered about that?' For her, the environmental case for reintroducing elm is strong. 'They will host wildlife, which is a good thing. Others are more wary. 'On the face of it, it seems like a good idea,' says Elliot. The problem, he suggests, is that, 'You're replacing a native species with a horticultural analogue*. You're effectively cloning.' There's also the risk of introducing new diseases. Rather than plant new elms, the Woodland Trust emphasises providing space to those elms that have survived independently. 'Sometimes the best thing you can do is just give nature time to recover over time, you might get resistance,' says Elliot.

G 拉塞尔承认，所有这些(做法)会引发社会接受度的问题。“如果我们把榆树重新引入当地/景观中，且其中有一小部分是非本地的树--我们会担心吗?“对她来说，重新引入榆树，从环境角度出发，理由是很充分的。“它们会为野生动物提供栖息地，这是一件好事。“其他人则更为谨慎。"表面上看，这似乎是个好主意，“埃利奥特说。他认为问题在于，“你在用一种园艺类似物取代本地物种。实际上你是在克隆。“这还会有引入新疾病的风险。林地信托基金强调的是要为那些独立存活下来的榆树提供生长空间，而不是主张种植新的榆树。“有时候，你能做到最好的事情，就是(这些给大自然时间去恢复.…随着时间的推移，榆树)可能会产生抵抗力。“埃利奥特说。

* horticultural analogue: a cultivated plant species that is genetically similar to an existing species

*园艺类似物:一种与现有物种基因相似的栽培物物种*[注释:“园艺类似物“就是人工培育的、与天然物种相似的“替代品”。