An environmental organisation has apologised after deliberately killing hundreds of trees on an island in Loch Lomond.

Scottish Natural Heritage (SNH) said it should have informed the landowner before poisoning all the beech trees on Inchtavannach island with an injection of chemical herbicide glyphosate.

SNH had agreed a tree management plan for “selective felling” of non-native trees on the island in 2013 but did not tell landowner Luss Estates of the change to the plan for the widespread killing of more than 300 trees.

Previously, Luss Estates, owned by ninth baronet of Luss Sir Malcolm Colquhoun, said the island was left looking like a “wasteland” and accused SNH of creating a “major eyesore in one of the Scotland’s foremost beauty spots”.

The two parties have now reached an agreement in the long-running dispute, with SNH agreeing to pay to remove fallen trees.

David Maclennan, SNH area manager for Argyll and the Outer Hebrides, said: “Although Luss Estates was party to the original management agreement in 2013, which posited the removal of rhododendron and, by selective felling, of ‘non-native species’ over a five year period, Scottish Natural Heritage accepts that the subsequent amendment, which proposed to kill all the beech trees on Inchtavannach in a single operation by chemical injection of glyphosate was not shared with Luss Estates Company.

“SNH apologise for what was, with hindsight, an error on our part.

“We should have ensured that Luss Estates Company was informed of and consented to the proposed operations.”

He added: “The speed, scale, and visual impact of the operation was much greater than anticipated and we recognise that this has caused considerable detriment and upset to Luss Estates Company and to Sir Malcolm Colquhoun personally. For this we unreservedly apologise.

“There remains a need to undertake works to remove fallen timber from agreed areas – and we have offered to do this through a new agreement.”

He said the organisation remains committed to working with the estate “to protect and enhance the island for future generations”.

Simon Miller, of Luss Estates, said “After nearly six years, we are pleased that SNH has apologised for the killing of the beech trees at Inchtavannach and accept this gesture.

“SNH has now agreed, at its expense, to remove as much of the fallen timber as possible this year.

“Luss Estates are proud to be the custodians of these islands and look forward to working with SNH to protect them.”

He added: “Inchtavannach and other nearby islands deserve to be treated as some of the most protected countryside in Scotland, as national treasures and designated Nature Reserves.

“We hope to work with SNH in future towards this end.”