Factors influencing height-age relationships and recruitment of ponderosa pine regeneration in Northern Arizona

In the southwestern United States, there are currently no regeneration models for the growth and recruitment of ponderosa pine (Pinus ponderosa C. Lawson var. scopulorum Engelm.) from seedlings to the sapling size class. The objectives of this study were to (1) develop a height-age relationship for ponderosa pine seedlings on soils derived from sedimentary parent material following a shelterwood establishment cut and (2) use the model and existing regeneration inventory data to estimate seedling and sapling recruitment rates. Ages of 80 cross sections from 19 seedlings collected on the Mollogon Rim Ranger District in northern Arizona were used to construct the model. The model generally fit well and indicated that it takes ponderosa pine seedlings approximately 20 years to reach breast height. Using regeneration inventory data from four stands used to construct the model, estimated seedling recruitment was nearly continuous during the 1st decade following an establishment cut and, in most stands, recruitment declined exponentially. Based on these findings, we recommend that management activities, such as the use of prescribed fire, be conducted within at least 20 years after tree cutting to maintain a forest structure that is not vulnerable to high-intensity crown fire.