Moisture, not wood species, governs heat output
Per kilogram, dry wood of any species yields roughly the same energy, because all wood is made of cellulose and lignin in similar proportions; denser species just pack more kilograms into each stacked cubic meter. What really cuts usable heat is water, since the fire spends energy boiling off moisture before the wood burns cleanly. Getting fresh wood from around 40–50% moisture down to about 20% or lower matters more than choosing birch over spruce or oak over pine.