Green Infrastructure and Scale

Lately I've been thinking about how some landscape projects are restricted by available space. For instance, its fairly difficult to establish new conservation areas or stream buffers in many dense urban cores because there just isn't enough room amongst the hardscape and buildings. Conversely, for rural properties where there are plenty of farms, fields and forests, it looks odd to see a tiny green roof or green wall. Other than demonstration, what are these small scale projects in a large greenspace really accomplishing? So it occurred to me that some of these best management projects are scale dependent upon the available space. And while there may be real opportunities for a downtown urban farm or a a rural vertical farm, it may be practical to think about appropriate sized projects according to available space. If we use New Urbanist terminology along the urban to rural transects (Newurbanism.org), we might prioritize our best management practices according to the following graphic. Does it make a better environment to have many small greenspaces in a large area like the Portland park system or just one large one like Central Park? What are your thoughts?