Swansea Council brought the prosecution after 70 protected trees, including the giant redwood, were cut down in November 2018 on land close to Swansea's Penllergare Valley Woods, next to the site of a housing development.
According to press reports, Enzo's Homes director Fiorenzo Sauro, 49, had denied the charges, telling Swansea Magistrates’ Court that he had nothing to gain from cutting down the tree and it was an accident caused by people not following his instructions.
But district judge Neale Thomas found both Sauro and the firm guilty of contravening a tree preservation order.
"I am conscious there is considerable public interest in this case," the judge is reported to have said. "Having listened to all of the evidence today I am satisfied each of these defendants are guilty of the offences of which they are charged."
Earlier this week, self-employed tree contractor Arwyn Morgan pleaded guilty to contravening a tree preservation order after initially denying the charge.
In a statement, Swansea Council cabinet member for environment and infrastructure, Mark Thomas, said: "Swansea Council was determined from the outset to take the strongest possible action to ensure those responsible for felling the tree were held accountable for their actions.
"There were calls from some quarters for a rush to prosecution but by conducting a thorough investigation that took a number of months to complete we have secured the result we have seen today.
"In our view this was never a victimless crime. The felled tree was part of the heritage of this area of Swansea and one of the first of its kind to be planted in the city. The decision to prosecute was not taken lightly and the convictions should serve as a warning to others."
The sentencing date has been set for 24 September.
Source: ENDS Report