Long-term evaluation of intra- and inter-provenance hybrids of loblolly pine in the Piedmont region of the southeastern United States

Long-term response of two intra- and two inter-provenance populations of loblolly pine (Pinus taeda L.) were evaluated in the Piedmont region of the southeastern United States. In total, 82 polycross families of the Atlantic Coastal (C) and Piedmont (P) provenances (CxC, PxP) and their hybrids (CxP, PxC) were field tested for growth, sawtimber potential, and survival through age 19 years. The Coastal pure (CxC) families were the tallest, and the hybrid populations (CxP, PxC) were intermediate for height. The four populations did not differ for diameter at breast height. The hybrid CxP population, followed by the CxC population, showed significantly higher stand volumes per hectare. These two populations maintained higher survival and stand density compared to the Piedmont pure populations. Sawtimber potential was significantly higher in the Piedmont pure families at the coldest study sites, presumably due to defect in the CxC and CxP from cold damage. No significant genotype -by-environment interactions were detected for any traits. The genetic gain for height, stand volume, and survival was considerable in the CxC and CxP over the Piedmont source, suggesting potential for benefiting from the faster growth of the Coastal material in the Piedmont region. The performance of the Coastal intra-and inter -provenance populations was marginally affected by the minimum winter temperatures (MWT). These results indicate that the Coastal and the hybrid families can be planted in the Piedmont region with MWT's of-13 degrees C or greater and where the difference in MWT between the origin of the Coastal parents and the test sites was not extreme (e.g., the difference did not exceed 2.8 degrees C). These MWT limits encompass the southern Piedmont of North Carolina (< 35.615 degrees N) and the Piedmont of South Carolina, Georgia, and Alabama.