Yes, it's illegal but if anyone cared, it wouldn't be laying there a week later. Anyone that gathers firewood with a bow saw and axe, gets a special dispensation directly from God. It's the equivalent of those guys on the news beating themselves with chains and poking pipes through their cheeks.
Firewood warms you at least twice, cutting it and burning it....sometimes moving, splitting, and stacking will warm you more times.
The trunk is the part with value. You were harvesting "slash" that loggers normally burn, chip or leave in the woods. If someone took your license plate number and you get a complaint later, present them with a bill for services rendered...... $100 per hour for clearing slash.
Uh.....wait...bow saw? $200 per hour!