add4fe5e_thsonian_Migratory_Bird_Center_Friendly__Criteria_at_a_Glance_Criterion
[Concept] Structural diversity [Criterion] 
The "architecture," or profile, of the shade should reveal obvious layers or strata of foliage-preferably 3. The layers are: the stratum formed by the "backbone" species and others of similar height; the "emergent" stratum, normally composed of native forest species of the region; and a layer beneath that formed by the backbone species made up of shrubs, small trees, and fruit plants like Musa spp. (bananas) and citrus. The emergent layer and the lower stratum should each account for about 20% of the foliage volume, with the remaining 60% of foliage volume consisting of principal canopy made up of the backbone species and species of similar height.
Coffee Criteria - Smithsonian Migratory Bird Center
Criterion