Varieties of ponderosa pine adapted to the eastern side of the Cascade Crest have developed specific physiological adaptations that enable them to persist in much drier conditions than Douglas-fir. The Willamette Valley Ponderosa Pine (WVPP) has shown similar drought resistance in addition to tolerance of saturated (water) soil conditions, making it an ideal timber species for sites in which Douglas-fir will not grow. As water is transpired from the leaves of trees, tension builds up in the water column, as soil moisture decreases this tension can reach a point at which air bubbles are sucked into the transport cells (embolism), rendering them incapable of transporting water. Trees have developed a variety of strategies to counteract this phenomenon. In this study we have compared several sapwood specific characteristics of drought tolerance, such as water storage, vulnerability to drought induced embolism, and water transport efficiency (axial and radial specific conductivity), between east side and WVPP varieties. The results indicate that sapwood of WVPP is almost twice as resistant to drought induced embolism at the expense of a halving of water storage capacity and a 30% reduction in water transport efficiency. This change in water transport properties is correlated with a decreased sapwood depth and an increased sapwood density in the WVPP of 0.45 g/cm3 compared to 0.39 g/cm3 in eastern varieties. Furthermore, radial conductivity results indicate that the sapwood of WVPP is over 50% more conductive of water in the radial direction. This information may prove of particular interest in studying radial pathways of preservative movement as well as presenting applications for wood drying studies. Samples of eastern ponderosa pine were collected at various sites through out Central Oregon; WVPP samples were collected at two sites near Sweet Home, managed by Cascade Timber Consulting, with the assistance of Bill Marshal, and at one site in the OSU MacDonald Forest in Corvallis.
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