Plantation site index comparisons for shortleaf pine and loblolly pine in Oklahoma, USA

Abstract

Quantitative relationships between the site indices of shortleaf and loblolly pine are needed by foresters who want to compare the productivity and the financial performance of shortleaf and loblolly pine plantations on the same site. A randomized complete block planting of loblolly and shortleaf pine at four sites near the western boundary of the southern pine commercial range in Oklahoma makes it possible to develop these quantitative relationships for the first time. Although several quantitative relationships between shortleaf and loblolly site indices exist for naturally occurring shortleaf and loblolly pine, these are all base age 50 years, whereas the customary base age for the plantation site index in southern pines is 25 years. The relationships developed here indicate that the site index of shortleaf pine will be smaller than that of loblolly pine for plantations in the region near our study sites. Tests for significant differences between five definitions of dominant stand height in a repeated-measurements context failed to show significant differences between these definitions for these data. Regression relationships that can be used to predict the shortleaf pine site index from the loblolly pine site index are presented for plantations having a base age of 25 years.