The mangrove roots can be burned and destroyed directly, but cannot be used as a fuel source. This is also not parity with Java, which allows the mangrove roots to be used as fuel sources.

How to Reproduce
1. Get furnace/blast furnace/smoker.
2. Smelt or cook anything with mangrove roots as the fuel source.

Observed Result
Mangrove Roots cannot be put into the fuel slot.

Expected Result
Mangrove Roots can be put into the fuel slot.