Root Development and Height Increment of Ponderosa Pines in Pumice Soils of Central Oregon

Sixty trees were excavated from three different pumice soils in central Oregon. Stems and roots were sectioned and the annual rings of each section were counted and plotted so that the height at a given age could be related to the depth the roots reached at that age. A significant increase in rate of stem elongation occurred when roots grew from surface soil into subsoil. Acceleration of growth was attributed to improvement of moisture relations and, possibly, nutrition in the subsoil.