Effect of Grass Competition and Depth to Water Table on Height Growth of Coniferous Tree Seedlings

Pinus banksiana, P. resinosa, Picea glauca, and P. mariana seedlings were grown in combination with three grasses on a loamy sand and on a sand, each forming a small catena with a controlled water table. A much greater total vegetative production was achieved on the loamy sand than on the sand with equal water supply. The greater production on the loamy sand, however, did not result in greater tree—seedling heights. On the contrary, at optimum depth to water table (where maximum heights had occurred when grown without grasses in an earlier experiment) for seedlings on the loamy sand the grasses grew more vigorously and suppressed the tree seedlings. On the sand, seedling height trends were not significantly altered from those observed without competition in a previous experiment. Characteristics of competition are elucidated in relation to root— and shoot—growth patterns of seedlings.