I think this must be the tree I was sent to look at, at the Park Board Office at the edge of Stanley Park. I remembered in Gerald Straley's Trees of Vancouver (UBC Press, 1992) that English Walnut has around five leaflets, possibly up to nine, with the terminal one the largest. These photos show three to seven leaflets. But Straley says "[t]he smooth bark is pale grey". For this age tree, does English walnut bark become rough as shown here, or is this something else? A little old lady passing by said these trees are walnuts planted by the Park Board to feed the grey squirrels, which are not native and are not primarily seed and cone eaters like the natives. This worked very well, and now all the grey squirrels are fat and healthy and have muscled out the native squirrels. (Those aren't exactly the words she used). However, BC SPCA web page says the grey squirrels are not to blame for the decline of the native squirrels, which are suffering more from loss of habitat.
Looks like J. regia. Leaflets range in number from 5 to 13, with an intermediate leaflet count being usual rather than the extremes (5, 13). Smoothness of nuts seen in photo characterstic of this one, smoothness of stems seen when these are young only.
Ditto to Persian Walnut for the tree's identity. Yes, the bark does stay smooth and grey for a good while, but becomes fissured later; your tree is typical in that - if you look at the ridge tops between the fissures, they are still smooth grey. A similar-sized Black Walnut would have much rougher bark.
