door jamb question

Refer to these pics in the URL below and in particular where the tape
is near the bottom of the door jamb. Can I just splice out say 6" of
the wood where taped and just splice in another or do I need to
replace the entire jamb? Meanwhile I did a work in progress spackle
job where the wood rotted (taped areas) to make it somewhat
presentable till I decide how to really fix it.

What size wood(s) is used for the jamb here?