Ideally? Have public transport that runs to these national parks. Japan has train stations that bring you right up to the foot of a mountain – I’m almost very certain that one train station requires less space than a carpark (thinking in terms of capacity here). Of course this requires a massive revamp in infrastructure, but one can wish. There are also some buses that feed into these parks, which is fantastic, give me more! As a tourist, I’ll gladly give these buses more money than whatever car rental company I have to use.

P. S. I think the immediate short-circuiting to “guess we won’t have forests” is kinda worrying.