Their numbers swelled recently thanks to the arrival of 2,500 further trees, all grown to order in the US.
Ulmus americana ‘Princeton', an American elm with proven tolerance to Dutch elm disease, is being imported by Neil Lucas, the owner of Dorset's Knoll Gardens.
"Despite our best efforts we have yet to find a native elm tree with proven tolerance to Dutch elm disease. Planting the fast-growing Princeton elm ensures that the elm remains within our botanical matrix, and opens new possibilities to the wide variety of flora and fauna once dependent on our native trees.
While scientific trials are still underway, my own experience tells me that, at least here in Dorset, the wildlife is enjoying all the trees have to offer."
Of the recent arrivals, 100 large trees are now en route to Dublin's Phoenix Park.
"The park lost 2,000 trees to Dutch elm disease in the 1980s," said Dr John McCullen, head of historic parks and gardens, at the office of public works.
"This was particularly devastating as the elm has been a major feature at Phoenix Park since it opened to the public in 1747.
"Elms formed an historic central avenue, planted by Lord Chesterfield, the Lord Lieutenant in a unique fashion, offsetting regular groups of nine trees on hilly mounds along its whole length.
"We are now using the Knoll elms to recreate part of this distinct feature within the 1,752 acre (709ha) park - the largest enclosed park in any European capital city."
Knoll is selling 1,500 bare-rooted elm whips at £39 each.