See "The Yews of Alice Holt" by Toby Hindson, Ancient Yew Group 1998 (rev. 2008), available online as a pdf.
Edited quotation from Hindson: "There are reasons for supposing that the Hourglass is the oldest tree in the forest. The girth is 16'6'' at 3 feet, at the base 19'10'' and at the narrowest point of the “waist” in between these measure points it is 14'10'' (1997). There is a layer still attached to a branch which reaches the ground, and the canopy is fuller and more vigorous than one would expect for such a contorted and decrepit looking bole. The bole seems to consist of columns of growth about the thickness of a man’s arm that have a base in the basal bulge of the tree, and run up the trunk hugging the hourglass form all the way to the base of the branches at about head height. If one looks between these columns it can be seen that there are chunks of dead burr wood that was clearly outer bole imprisoned within. The inside of the tree appears to be packed out with internal stems. This suggests a tall but dead or dying stump that has regenerated, or perhaps a pollard."
See "The Yews of Alice Holt" by Toby Hindson, Ancient Yew Group 1998 (rev. 2008), available online as a pdf.
Edited quotation from Hindson: "There are reasons for supposing that the Hourglass is the oldest tree in the forest. The girth is 16'6'' at 3 feet, at the base 19'10'' and at the narrowest point of the “waist” in between these measure points it is 14'10'' (1997). There is a layer still attached to a branch which reaches the ground, and the canopy is fuller and more vigorous than one would expect for such a contorted and decrepit looking bole. The bole seems to consist of columns of growth about the thickness of a man’s arm that have a base in the basal bulge of the tree, and run up the trunk hugging the hourglass form all the way to the base of the branches at about head height. If one looks between these columns it can be seen that there are chunks of dead burr wood that was clearly outer bole imprisoned within. The inside of the tree appears to be packed out with internal stems. This suggests a tall but dead or dying stump that has regenerated, or perhaps a pollard."