Native timber species (that just might be offered to you) as fuel (all 5% moisture):
- Beech 17Mj/kg
- Oak 16MJ/kg
- Pine 17MJ/kg
(BTU/cord would be little understood in these islands)
Remember that pine is substantially less dense than the hardwoods
A source for the info: UN FOOD AND AGRICULTURE ORG WOOD FUELS HANDBOOK
Most important: CLEAN YOUR CHIMNEY!
As pointed out in other posts, soot buildup is a serious fire hazard.
btw, "flue" is the same as "chimney". I suspect that when you state that your "flue doesn't go all the way to the top...", you actually mean that the stove pipe (the pipe that connects your stove to the flue) feeds into a chimney.
Ensure that the seal around the stovepipe is good and that the flue has only one outlet (at the roof level). This should improve the "draw" in the flue