New Orleans' Southern Magnolia Trees

A friend of mine who suffered about two and half feet of floodwater in his home in Mid City observed early on that Southern Magnolia (Magnolia grandiflora) trees located in the heavily flooded (two-week plus) areas of New Orleans were all dead or dying. Broadway is an Uptown street lined with these trees and today I noticed exactly what he had pointed out back in late-September. Looking at the condition of the Southern Magnolias on Broadway, there is a clear line of demarcation between Birch and Green Streets where the floodwaters reached. Towards South Claiborne from the 1600 block of Broadway on all of them are fried--deader than Elvis. The Southern Magnolias towards the River from this point are at their pre-KTMB leaf dropping, sap producing, overall messy normalcy. Throughout the flooded portions of the City of New Orleans any plant materials near the ground that were completely or near-completely submerged are dead--including shrubs, bushes, ground covers, and grasses--and are brown. From what I have seen, it seems most tree species (minus the Southern Magnolias) seem to have survived the long-standing water--at least for now. On Broadway, many Oaks and Crepe Myrtles and other trees planted in the same streetside areas as the fried Magnolias survived the floodwaters with no obviously noticeable negative effect. It seems as if the Southern Magnolia tree can be used as a sort of litmus test to if an area severely flooded or not.