I love being near coastlines with lots of greenery, so for me many of the Greek islands that I've seen photos of don't look to interesting. But then I saw some photos of Corfu and was intrigued as it looked closer to my ideal. I'm wondering what Greek islands are the greenest, most forested and have the easiest access for nature walks.

Robin, may I suggest something radical? A guide book! Look at "Eyewitness: the Greek Islands" -- a splendid VISUAL overview of all islands ... shows u at a glance and ALSO, where they are located ...because if you have 6 days only, you'll have to take the transportation into account. I also love Green islands -- and SAMOS is one of MY favorites,. It's way over in the N.E. Aegean, but if you take a domestic flight as soon as u get to ATH airport, it's just 50 minutes away. Here are a few videos of "Greek & Green Samos" by a Samos enthusiast -- http://vimeo.com/channels/samos1/videos Western Crete is heavily forested, mountainous scenery. Heaven for hikers. http://www.west-crete.com/walking_hi...rete-walks.htm If you want the Cycladic Islands (the ones with the whitewashed houses, blue shutters) -- Naxos is about the Greenest in my experience. The Pelion Peninsula on the eastern side of the mainland is also very forested. Finally if you want maximlum Greenery, go in May-June, just after rainy season has ended. In Autumn, Greece will have been rainless for 4 or 5 months so even the greener islands will be more brownish. Corfu is one of the northern-most islands, that's why it's greener, also is colder longer in Spring, and rainier off-season (Maybe that's why the British feel so at home there).

The interior of Rhodes has plenty of trees at elevation. I once asked a bartender in Athens which island to visit and he said 'the green island, Rhodos.'

But it seems opinions vary.
https://www.google.ca/?gfe_rd=cr&ei=...e+green+island

Traveljan, thanks for ideas and insights. So much to see and explore out there.

The Pelion peninsula is very green even during the summer. The cliffs that drop down straight into the sea and the forests are very beautiful. It's a contrast to the rest of Greece and more spectacular even than any island.
I would expect Thassos to be green, considering the meaning of the name.

Check Thassos, Skopelos, Alonissos and may be Chios.
All North Aegean islands are green in spring, Samos, Lesbos, Lemnos, Imros, Samothraki too.

I agree, the Pelion peninsula is lovely and green.

Cephalonia is very green, there is even a specific fir tree called after the island "Abies cephalonica' . And of course neighborhood Ithaki too. There are many options but I feel you need to explain a bit "the easiest access for nature walks" part of your question.
How do you envision your trip exactly? Is hiking your main focus or what? Are you planning to do a couple of hours walking here and there every day using a specific spot asd a base or what? Do you plan to hire a car or rely on public transport? How long you plan to stay? And as other people mentioned, very crucial, WHEN you plan to visit?