to cultivate land by first setting fire to it
畲 centers on a specific agricultural method: clearing land by burning off vegetation before cultivation. The meaning is narrow and technical, referring to slash-and-burn farming.
畲 combines 佘 (possibly a phonetic component) with 田 (field), suggesting a field prepared by burning. The exact historical development is uncertain, but the character likely reflects early agricultural practices.
The top part 佘 looks like a person with a tool, and the bottom 田 is a field. Imagine someone setting fire to a field to clear it for planting.
For ヨ, picture a farmer saying 'Yo!' as they light the fire to clear the field: Yo -> ヨ.