Butterfly Conservation says it "opposes Sheffield City Council and Amey’s plans for large-scale felling as a means of managing street trees and specifically opposes the felling and excessive pruning of the Chelsea Road Elm".
The tree, in the city's Nether Edge area, came runner-up in last year's Tree of the Year poll for England. As a Huntingdon elm (Ulmus × hollandica 'Vegeta'), an old English hybrid cultivar, it is thought to have some resistance to Dutch elm disease (DED).
It is also home to a colony of white-letter hairstreak (Satyrium w-album), one of the UK’s most threatened butterflies and is a Priority Species in the UK Biodiversity Action Plan.
"Having undergone a 96% decline in numbers between 1976 and 2014, the loss of any colony is of concern," the conservation charity said.
The species breeds specifically on elms, and its decline is attributed to the loss of trees to DED, which claimed at least 30 million elms in the UK.
"Any elms which are disease-resistant are therefore particularly important in helping maintain the long-term presence of the butterfly in an area," Butterfly Conservation said.
Butterfly Conservation along with Sheffield and Rotherham Wildlife Trust have worked with Sheffield City Council to develop a "mitigation plan" for the tree, involving moving the eggs from the colony to other elm trees in the city.
The council says the tree is causing "severe damage" to the adjacent pavement and road, and says it cannot afford the £50,000 required to rectify this given the tree "is already suffering from severe decay".
It added: "The tree will undergo essential safety works to mitigate the risk of the tree branches failing due to decay, but will be retained for a number of months in order to allow time for the mitigation plan for the butterfly to take its course."
It has also committed to planting 100 new resistant elm trees across Sheffield before the end of March, and plans to clone the Chelsea Road elm.
But Butterfly Conservation has said: "A number of mitigation measures have been proposed by Sheffield City Council to which we have responded. This should not be interpreted as BC supporting that mitigation strategy as none would be needed were the tree to be retained."
It added: "Given the fact that it may take two decades for planted elms to grow to a size acceptable to the butterfly, a minimum 20-year monitoring period will be required to assess the effectiveness of this mitigation measure."
Royal Botanic Garden Edinburgh science communicator Dr Max Coleman warned: "Severe pruning would have a serious impact on the butterfly population as eggs remain attached to twigs during winter. It would be quite possible to exterminate the butterfly through such action even if the tree remained alive."
He added: "This tree should really be viewed as one of the jewels in the crown of Sheffield’s biodiversity rather than a problem that needs to be removed. Some planning for the future survival of the butterfly is really what is needed. Planting disease resistant elms (of which there are many to choose from) nearby will ensure a succession of habitat for this rare butterfly."
(C) 2018 Horticulture Week reproduced for personal use only to show poor relationship with contractors, if you would like to read much more every working day then please subscribe to this excellent publication by visiting www.hortweek.com/subscriptions