Abstract
Calcium resources for forest growth are limited by acid rain and repeated logging harvests. The exchangeable calcium budget is considered inadequate for forest regeneration; however, most young stands show that they have mobilized sufficient calcium from the soil. Studies of the granitoid parent soils in the forests of New Hampshire, upstate New York, and Maine show that apatite in the soil is a source of plant-available calcium. Where sedimentary parent materials are more dominant on sites in Pennsylvania, apatite is not as important.