Riven wood means split wood. It is commonly applied to carefully split wood being prepared for making furniture. But it could apply to logs split with an axe for kindling wood.
The etymology from
http://www.etymonline.com/ is:
riven (adj.) "split, cloven, rent," c.1300, past participle adjective from rive "to tear, rend."
rive (v.) "tear in pieces, strike asunder," c.1200, from a Scandinavian source akin to Old Norse rifa "to tear apart" (cf. Swedish rifva, Danish rive "scratch, tear"), from PIE root *rei- "to scratch, tear, cut"
There are many words from the PIE root of riven, including one of Hyacinth Bucket’s favorite words “riparian” adj. - the bank of a stream.