The exact type of「tree that dies hard」referred to is unclear. Likely, a species in a family of trees that includes oak, beech, and chestnut. HORSE CHESTNUTS are excellent animal fodder (as in, not the sweetest variety, so use these highly nutritious nuts to feed horses, as fodder), and the spikes on hulls of chestnuts might be the「ten thousand scorpions.」The grain of OAK-CHESTNUT wood is extremely straight「straight up repeatedly」making the wood very easy to split and fashion into lumber with a minimum of tool use and effort (perhaps「ten thousand straight wood grains」). The hard wood is highly resistant to decay and rot (「dies hard」…chestnut trees fallen in the United States due to blight in Tennessee were still on the forest floor after 110 years, albeit not in pristine condition) and was therefore apparently favored for building HORSE STABLES, per the scholars (both the wood and any building constructed with that wood remains「in a stable condition for a long time」as the origin of the word meaning「horse barn, stable」).
　A「stable」is also the name given to groups of sumō wrestlers who practice together under the tutelage of a stablemaster, and this glyph appears often in wrestler names (perhaps because the wrestlers die hard or eat like horses?).
　This glyph was often substituted with another meaning「hemp, cannabis」due to many similarities in meanings, although the two glyphs refer to different plant species entirely.
　Horse chestnuts:「Aesculus seeds were traditionally eaten, after leaching, by the Jōmon people of Japan over about 4 millennia, until 300AD. Aesculus species are woody plants from 4 to 36m tall (depending on species), and have stout shoots with resinous, often sticky, buds…」
　　[　https://en.wikipedia.org/wiki/Aesculus 2012-08-03　]　

Modern definitions (that generally disregard history) …excluding politically incorrect concepts and other meanings deemed offensive today; may list only pigeonholed definitions, euphemisms, or meaningless mnemonics)
Chinese: archaic variant of 櫪|枥, oak; type of tree in ancient books; stable (for horses)
Japanese: Japanese horse chestnut
Unihan extended: type of oak; stable
EDRDG: horse chestnut; (kokuji)