Sometimes a blogger should be aware that other people have covered ground so well, there’s nothing to add. Here are links to some commentary over the summer on the planned Washington Boulevard Trail, including a discussion of the tree removal and some alternatives:
Arlington County DES, Arlington Boulevard Trail.
Donaldson Run, Build it and they will bicycle: Wash Blvd Bike Path.
Along the Pike, Bike Trail Benefits. Be sure to take a look at the comments to that post.
Transform to Sustainability, Tree Hugger Meets the Bike Hugger.
Clarendon Patch, Build The Washington Boulevard Trail.
Removing trees is a basic part of living in an urban environment, so it seems that planting new, native species trees should be enough to compensate for the tree removal.