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

Fifteen test plantings of loblolly pine (Pinus.taeda L.) were established t hroughout the Western Gulf Region to assess genotype by environment (G X E) interactions and to establish seed movement guidelines. Open-pollinated fa milies from five selected trees plus a checklot from each of four seed zone s were planted at each location. Seed zones tested were southeastern Texas, southern Louisiana, northern Louisiana and southern Arkansas, all in the U SA. Heterogeneity of regressions was significant for height and volume at age f ive 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 inter action was due to changes in family rank. Family differences were significa nt 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 inte rmediate in stability while southern Arkansas and southern Louisiana famili es were equally unstable. Families from southern Arkansas were least respon sive to changes in site quality while those from southern Louisiana were mo st responsive. At age 15, northern Louisiana and southeastern Texas familie s remained intermediate in stability but southern Arkansas families exhibit ed increased responsiveness and southern Louisiana families showed decrease d responsiveness to site quality. All zones exhibited a linear trend with r espect to site quality. Perhaps greater drought tolerance of southern Arkan sas families enabled them to continue growing in dense stands where competi tion for water could be great. The rapid early growth and reduced subsequen t 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 movem ent exceeded 125 miles north or south of origin. Ecovalences and coefficien ts of genetic prediction suggested coastal families should not be planted o n poor sites. Favorable performances were observed for families planted in regions requiring specific adaptability often along their latitude of origi n or areas of higher moisture. Local material showed adaptiveness to local planting conditions.