Welsh woodland charity Coed Cadw says the Pontfadog was the oldest oak tree in Wales, and probably one of the oldest in Northern Europe, said to have grown since 802.
The charity, part of the Woodland Trust, says "we must learn lessons" from the tree collapsing, because it was not adequately protected.
Just last December, Coed Cadw presented a petition, bearing over 5,300 names, to the Welsh Assembly, calling for better protection for our ancient, veteran and heritage trees and in particular, support for the owners of trees in caring for them, just as the owners of listed buildings can receive support in caring for them.
Also last year, a group of experts from the Ancient Tree Forum visited the Pontfadog Oak and put together a list of actions that they believed could help conserve it.
Although the total cost was only £5,700, these actions were never taken as no funding source was available.
– Angharad Evans, Coed Cadw
Moray Simpson, Tree Officer for Wrexham, said "it would be good to try and save the fallen parts of the tree for posterity and to show future generations what we had and what was lost due to the nation not doing enough to save these trees."
An oak tree in the Ceiriog Valley near Llangollen, which is thought to be the oldest in the UK, has collapsed.
Coed Cadw - the Welsh arm of the woodland conservation charity The Woodland Trust - says the Pontfadog Oak, the fattest in Wales, was covered in very heavy snow over the last month, and has now blown over in high winds.
A Facebook page on the tree says it is thought to be between 1,200 and 1,600 years old.
The charity says legend has it that Owain Gwynedd rallied his welsh troops under this tree in the 12th century and then went on to defeat Henry II in a great battle.
It says: "What a loss to history, biodiversity and landscape interests."
Organisers of the Llangollen International Musical Eisteddfod say it has staged a dramatic reversal of fortune by making a profit for the first time in five years and ploughing £1.5 million into the local economy.
They say the event defied the recession and bad weather to record a profit of £22,668.
Advance sales for this year's International Eisteddfod are said to be breaking previous records.