It can beat a bioreactor since the effiency of the bioreactor is very low when you produce power with only 1 type.
The charcoal... Well it is possible. You need just a large supply at the start to heat up. And it also depends which trees you use. I would go with jungle or brich wood...
Apple trees is not a good way because handling them would give something which you can use to rais the effency but the supply of that from each tree is so low that it would make your system only slower.
Also i would not go with Plums, at the orchard. Nuts/chestnuts are way more powerfull...
Also as i said the exses oil/fruityouce you can use to create more power. (Biogas engine)