Yes! Biomass is the general term for organic materials that can be burned as fuel—trees, yes; but also grasses like rice straw or cornstalks (which make great bonfires); even your kitchen waste (like vegetable trimmings). But since they’re more difficult to harvest than wood, it takes longer to dry them out before burning. And if you have a lot of trees on your property just go ahead and cut down some branches for free!