RELATION BETWEEN LIGHT INTENSITY AND RATE OF PHOTOSYNTHESIS OF LOBLOLLY PINE AND CERTAIN HARDWOODS

One of the most important forestry problems in the south concerns the tendency of pine stands to be succeeded by hardwoods. This occurs because pine seedlings usually fail to survive under forest canopies while the seedlings of many hardwood species survive and grow. It is often supposed that the failure of pine seedlings to grow under a forest canopy results from their high light requirements. Pine seedlings are assumed to be unable to carry on photosynthesis rapidly enough in the shade of a forest canopy to survive. Many hardwoods which presumably have lower light requirements and can therefore manufacture food more efficiently in the shade are able to grow" vigorously under these conditions. Experiments of Korstian and Coile (?) indicate, however, that pine seedlings will thrive in the shade of a pine or hardwood stand if protected from the root competition of the over-story trees by trenching. Evidently pine seedlings can carry on enough photosynthesis in the shade to provide food for growth, if supplied with sufficient water.