It isn't because of the trees. It is because of the fuel nerf. You need alot more charcoal to keep the boiler going. You need twice as much infrastructure of half as many boilers.
If you have rotarycraft, use it's fertilizer instead. It can cover a huge area depending on how much power you give it. It uses bonemeal or fertilizer. It makes things grow as fast as the extra utilities watering can. It will cover any automated farms too. It make Forestry multi farms ridiculously fast.You can have it in a central area covering all of your farms.