The tallest tree at the National Botanic Gardens (NBG) in Dublin has died after it began showing signs of poor health in 2020.
The Giant Redwood tree, which is native to California, stood at a height of 33 metres. Tests carried out by the Department of Agriculture, Food and Fisheries (DAFF) discovered two fungal pathogens that could be the cause of the tree's death.
A spokesperson said that "within a period of 12 months all of the branches had decayed and were beginning to become brittle, with some snapping off in strong winds".
In 2021 it was decided by the NBG to remove all of the branches from the Giant Redwood, Sequoiadendron giganteum, because the weakened branches posed a potential safety hazard to the Gardens’ staff and visitors.
"The main trunk has remained in place since, sitting as a splendid monolith above the gardens," a spokesperson said.
They added it was difficult to be sure of the precise cause of the tree’s death, but the DAFF lab results identified a couple of fungal pathogens that may be responsible.
"The plant health section of the Department of Agriculture, Food and Fisheries have kindly examined bark and roots from the dead tree, including samples from the living trees opposite the director’s residence - sadly also showing signs of poor health," they said.
"Neofusicoccum luteum and Neofusicoccum australe were isolated and identified from the samples taken. Species of Neofusicoccum have been identified as causing cankers and dieback in woody species around the world, including Sequoiadendron giganteum.
"Neofusicoccum is one of the main suspects for the disease based on symptoms displayed on the Giant Redwood at the National Botanic Gardens," a spokesperson said.
The lab results also detected an additional fungal pathogen, Cytospora also a known Sequoiadendron pathogen (Cytospora canker of redwood), in the tree.
"Other fungal pathogens were isolated and identified, however, the DAFF team are satisfied that these are likely to be secondary pathogens affecting the diseased tree.
"We are continuing to monitor the Giant Redwood trees opposite the director’s residence and have commenced a programme of soil enhancement in an effort to bolster the tree’s defences," they said.
The National Botanic Gardens said they conduct regular health inspections in order to identify damaged or potentially diseased trees.
No action is usually taken after inspections except in some cases when work is required to make a tree safe after a damaged limb is identified.
"In these instances, we consider the actions required to make the tree and site safe. Actions vary from lightly pruning damaged branches to the unpleasant task of removing the tree entirely – a normal part of managing old tree collections," a spokesperson said.
