He died from his injuries while being taken to a hospital, Dyfed-Powys Police said.
The incident occurred when he was felling trees in the Cascob area of Presteigne. All three emergency services were called to the scene along with an air ambulance.
A Mid and West Wales Fire and Rescue Service spokeswoman said they responded to reports that a man was trapped underneath a tree at the rear of a timber lorry on an unclassified road.
In a bid to free him, firefighters used an airbag, saws and hydraulic cutting equipment and later placed him on a spinal board before he was flown from the area.
A spokeswoman for Dyfed-Powys Police said: "Police received a call advising that a man had been injured whilst cutting trees in the Cascob area of Presteigne.
"Police, Fire Brigade and the Ambulance Service attended the scene. Tragically the man died on his way to hospital. Health and Safety have been advised."
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