Many Alder trees were planted in the San Fernando Valley by developers in the 50's. The trees do well in poor soil which may have been a reason for their selection. They provide shade in the summer then drop their leaves and allow sun to get in the windows of houses in the winter providing some warmth. But they need a lot of water. The developers were putting in lush lawns and sprinkler sysetms. They must have thought water would not be a problem for the trees except...water is a problem in the San Fernando Valley.