Aluminum-induced calcium deficiency syndrome in declining red spruce.

Prolonged suppression of cambial growth has apparently caused a decline in radial growth in many mature red spruce, Picea rubens. Surveys indicate that this decline occurs in trees throughout the natural range of red spruce and is independent of elevation, tree size, and age class. In addition, crowns of mature red spruce at high elevations across the northeastern United States have been dying back. Understanding the physiological basis for the growth decline is essential for the judicious management of the red spruce resource. A sequence of events is inferred through which an imbalance of aluminum and calcium in the fine root environment reduces the rate of wood formation, decreases the amount of functional sapwood and live crown, and leaves large trees more vulnerable to extant secondary diseases and insect pests.