While I've seen yellow-cedar, cedar, redwood, spruce, western hemlock, among other deciduous and coniferous trees in various ecos & habits of Alaska, the image presented likely is what the author says it is. 


Some rough trees on the edge area that may be on their own way out. Around a city, they'd be looking to fall across a power line out of boredom or frustration; to get attention for unspoken cause, or a last stand.


A bit of additional yet limited reading, but not a map as title suggested, can be found here:
http://onlinelibrary.wiley.com/doi/10.1111/gcb.13555/full
http://onlinelibrary.wiley.com/doi/10.1890/ES14-00225.1/full


Speaking of 'stand-ins' there are said to be increasingly more western hemlock where yellow-cedars once grew; so they would be more common side-by-side in some instances. 


Maybe they've a 'buddy system' against the elements? ;)