Why are my 3 river birch trees dying? These river birches are something like 10 years old and were healthy till last year. The largest is slightly taller than our 2-story house. Last summer, their leaves started to turn a little more yellow than normal. This spring, the leaves came out but began to yellow by June and by the end of July almost all of them had fallen off one tree, most of a 2nd tree and the 3rd tree is loosing its lowest leaves. All the leaves are yellowish. I don't see any insects on them, though we had some aphids in past years. These trees grow in mostly full sun. The soil is sandy loam, fairly well drained and alkaline due to oyster shell middens left by Native Americans in centuries past. We don't use pesticides or fertilizers other than compost and Hollytone.