Kashyyyk isn't Earth.
I think they did a crappy job with Kashyyyk. The person in charge of mapping is an idiot.
Kashyyyk is a planet of forests. Wookiees are even fearful of going to ground level. There are dangerous plants and predators that hunt Wookiees among others.
Plus, the ground level of Kashyyyk is pitch black because the trees block all sunlight.