Majority of the MR shafts were aspen (Populus tremula - not "poplar" as most people mistake it for, as the commonly named poplar today is actually tulipwood (Liriodendron tulipifera)) followed in frequency by birch, alder, willow and rarely ash. There were no hazel shafts identified from the MR selection.
It does make superb arrows though - straight growing, very light and easily strong enough to stand in bows up to and probably over 160lb. As it was an indigenous species during the Medieval era it stands to reason that it was likely used, but I certainly don't know if any documented cases I'm afraid.
Aspen was most common as it has extremely good resistance to rot, which means you don't need any sealant or waxing of the shaft at all.
Hazel on the other hand is pretty much the opposite, and would need careful and constant application of fat and wax coats to keep the wood dry.
