I understand Lewis and Orkney, which are now completely without trees except for plantations (e.g. woodland near Stornoway) was due to excessive farming from the neolithic onwards.
"Excessive" farming! Brilliant!
There are extant native trees in these islands.
There are many factors which severely limit tree growth in these island groups.
Yes, my wording could have been more precise inasmuch I meant without significant areas of ancient woodland.