Yakushima: Japan's damp, green eco-capsule

They say it rains 35 days a month on Yakushima, arguably Japan's most singular island. There are almost 7000 others to choose from, but nowhere quite like this damp, green eco-capsule off the southern coast of Kyushu.

I'm about to start trekking to the interior and the sign prohibiting smoking at the trailhead could hardly seem more redundant. Situated on the edge of the palaearctic and oriental biogeographic zones, Yakushima has a unique climate that fuels a huge range of flora. It's often humid, and almost always wet, but despite being just 24km in diameter with a predominantly rainforest climate, its 1800m-high peaks regularly receive snow in winter, too.

I'm travelling in autumn before that weather arrives, but as promised the island is very wet. The plan is to follow guide Junichi Aida to Tachu Dake, an enormous granite monolith that looks out across the dense jungle below. From the photos, it looks like the sort of thing early homo sapiens would have worshipped.

The same is true of Jomon Sugi, Yakushima's most popular attraction. This 25m-tall cedar is said to be one of the oldest trees of the world. Legend has it that it's been on the island for 7200 years, which would have it breaking the record by over two millennia.

Whatever its true age, these days the tree receives 500 visitors a day in peak season, despite the exhausting 10-hour trek required to go up and back. Some argue that the paths should be widened and improved to cope with the 90,000 people who visit each year to see the "grim titan"; others say this would simply increase the number of people scrambling up the slopes. For his part, Junichi is glad that Yakushima's greatest treasure is not easily won.

We set off on the mulchy path, mosses and ferns carpeting the forest floor all around. Perhaps it's the humidity, perhaps it's a semi-dream state left over from our 5am start, but Yakushima does feel strangely different, uncanny.

Master animator Hayao Miyazaki, the Studio Ghibli founder, felt this supernatural pull on this island. It was after a visit here that he felt inspired to write his 1997 classic Princess Mononoke. It's a sort of ultra-violent Avatar, without the rubbish effects and with rounded characters: a battle of nature vs mankind, where the forest itself seems to be a living entity, filled with strange creatures and spirits.

The most beloved are the iconic kodama – kooky, spooky sprites which live in the trees. I didn't expect to actually see them on Yakushima, but when I accidentally took a photo with the flash on, the light caught dozens of rain drops that looked like the haunted little faces from Miyazaki's film.