Stability and seed movement for loblolly pine in the Western Gulf Region

Fifteen test plantings of loblolly pine (Pinus.taeda L.) were established throughout the Western Gulf Region to assess genotype by environment (G X E) interactions and to establish seed movement guidelines. Open-pollinated families from five selected trees plus a checklot from each of four seed zones were planted at each location. Seed zones tested were southeastern Texas, southern Louisiana, northern Louisiana and southern Arkansas, all in the USA. Heterogeneity of regressions was significant for height and volume at age five and for volume at age 10. Data suggest that G X E interactions could be managed by stratifying environments. Significant concurrence was detected for volume at ages 5 and 10 indicating a significant portion of G X E interaction was due to changes in family rank. Family differences were significant at ages 5 through 15. Regression estimates of slope and standard deviation for volume through age 10, indicated northern Louisiana and southeastern Texas families were intermediate in stability while southern Arkansas and southern Louisiana families were equally unstable. Families from southern Arkansas were least responsive to changes in site quality while those from southern Louisiana were most responsive. At age 15, northern Louisiana and southeastern Texas families remained intermediate in stability but southern Arkansas families exhibited increased responsiveness and southern Louisiana families showed decreased responsiveness to site quality. All zones exhibited a linear trend with respect to site quality. Perhaps greater drought tolerance of southern Arkansas families enabled them to continue growing in dense stands where competition for water could be great. The rapid early growth and reduced subsequent growth of southern Louisiana families may highlight a consequence of seed movement without timely regulation of stand density. Ecovalences and directional responses were large and negative if seed movement exceeded 125 miles north or south of origin. Ecovalences and coefficients of genetic prediction suggested coastal families should not be planted on poor sites. Favorable performances were observed for families planted in regions requiring specific adaptability often along their latitude of origin or areas of higher moisture. Local material showed adaptiveness to local planting conditions.