There are no dangerous animals or unusual health risks around Alishan. Be prepared for rain at any time and bear in mind that, especially outside summer, it can be quite cold. It is about 10C colder in Alishan than Chiayi.
At the risk of stating the obvious, while the trails are exceptionally well guided during the daytime, there is next to no lighting — so head back when the night starts to fall.
fees/permits
Entry to Alishan costs NT$150 per person if arriving on public transport, NT$200 if arriving by car, charged on arrival.
If you show a student ID the cost is NT$100.