We have two river birch trees over 20 years old. One lost one of the three stems in derecho. This spring a second stem had a large number of dead branches. I assumed because of the extended drought and/or weather extremes this spring. I had a certified arborist come out for estimate to remove dead branches. He wants to remove the tree. He said cause could be combination of latents derecho stress, loss of one of the stems, drought, and says suffers from magnesium deficiency. The other tree shows no damage and no indication of magnesium problem, but he suggests an injection at cost of $360. This tree is 10 to 15 feet from damaged tree so i am not sure of the need or benefit of this. Also, ground in this area is heavy clay. Every summer during dry spell they turn yellow and drop leaves.