Juvenile growth and crown morphological plasticity of eastern white pines (Pinus strobus L.) planted along a natural light gradient: Results after six years

Underplanting white pine (Pinus strobus L.) is a promising method to reduce competition and protect against white pine weevil (Pissodes strobi (Peck)) damage. However, shading caused by overstory trees can reduce growth, vigo r and survival of white pine. The objective of this study was to determine the effects of a Light gradient on the growth and overall crown morphology of white pine saplings planted in 3-meter strips within a hardwood forest s ome six years earlier. In 1994, we measured total height and diameter, lead er length (in 1994) and numerous crown morphological variables. We then est imated the Light environment above the crown of 63 young white pine sapling s representing six families of close provenance. White pine grew well (i.e. , >20 cm in height/year) for the first six years when planted at light leve ls between 10 and 66% of full sunlight. Total height and diameter after six years tended to decline more sharply below 30% full sunlight, confirming e arlier experiments made in controlled conditions. No significant changes in crown morphology were evident along the light gradient. This lack of crown morphological plasticity presumably contributes to limiting the ability of white pine to grow and compete in a very low light environment. Various si lvicultural options are discussed in light of the results obtained in this study.