Water Efficient Landscaping

That is a very good question, and one that seems to have a slightly vague compliance path. The LEED Reference Guide itself says that the species factor is somewhat subjective (see pg 184 of the Reference Guide). So first, yes, you should include the area of the trees. The best strategy I have seen so far is to include trees in the "mixed" category which includes a mix of trees, shrubs, and groundcover (see page 185 of the Reference Guide.) The mixed strategy is probably the most straightforward because you do not need to calculate a separate area for the trees but instead include the trees in a mixed vegetation area. (I have also heard that the mature tree canopy is sometimes calculated to figure out the total area of the trees. If pursuing this strategy, make sure the total of all the vegetation type square footages equals the total landscaped area - i.e. do not count the tree canopy and also the groundcover below that same canopy.) I would also consult with your landscape architect if there is one on the project.