Some of my undergraduate urban ecologists and I spent the afternoon yesterday talking photographs of the tree canopy in Lincoln Park (in that section west of the Alfred Caldwell Lily pond and north of the Conservatory). In all we processed 14 hemispherical canopy images (they overlapped to some extent) and calculated that in this section of the park the canopy is about 62% open (standard error of about 1.8%). The canopy will provide even more shade as leaf-out continues. There are 2 fairly sizable sycamores there that have yet to emerge and they will shade the area quite nicely.
(The analysis was done with Gap Light Analyzer).