WHy not, but right now there is a way around this problem.
The game will never let a skill go under 30 if the next skill has at least 0.001 (something like that) skillpoints allocated.
So, for logging, you just raise it to 30. something, you do one carpentry action, then you set the logging skill down and skill up something else so it goes down to 30. Then, lock the logging skill and set carpentry skill down. You should end up with exactly 30 logging and 0 carpentry when you try to skill something else up.
This trick works for any skills.
Nope, it doesn't work no more... Now the "thirty's skill" raise only to 29.99 if you don't have the previous skill up to 60. Surprise!
So this system it's always very usefull because you can adapt it with skills, character skill (like strongh, agility etc) and all the other skills.
The actually system is too many various because the "food multiplier" is different with every player.. you can rise it or low when you eat but the result is the same. You don't have a good control on the "skill rising".