Abstract Loblolly pine ( Pinus taeda L.) progenies from controlled crosses showed genetic variation in the seasonal pattern of net assimilation and dry weight growth. The rank of progenies in net assimilation rate (NAR) changed during the first growing season. A progeny group characterized by a high NAR shortly after germination may subsequently have a low rate in comparison with other progeny groups; i.e. the curves of NAR over time intersect. Dry matter production at 21 weeks is related to the area under the seasonal curve of NAR with a linear correlation of 0.80. This correlation relates assimilation rate and growth and indicates that both intensity anti intensity-duration aspects of photosynthesis and respiration are important to dry matter production.