Below you'll find some common types of African wood used in drum making,
ordered from most dense to least dense.  

Density may affect the tonal qualities of the drum  (warmth vs. crispness for instance), and the amount of sound 'absorbed' by the wood vs. bounced out to the ears.  Common assumption is that the LESS dense woods are warmer in sound, and the MORE dense woods will be slightly more crisp-sounding, but that is not always the case...  Density can also affect the cost of shell/drum if carving is intricate, since it takes more time to hand-carve a design on woods with higher density.

MANY other factors contribute to the final sound of the drum  (skin type/thickness/tightness, playing technique, inner-carved dimensions of shell top/bottom, ring size/placement, etc.), so type of wood & density is best-used as a gauge of the weight of the drum, hardness of the shell, and the natural color of the wood.