Relationships between root form and growth, stability, and mortality in planted versus naturally regenerated lodgepole pine in north-central British Columbia

Abstract

The roots of container-grown and manually planted lodgepole pine, Pinus contorta Dougl. ex Loud. var. latifolia Engelm., are often deformed, potentially impacting their health relative to that of naturally regenerated trees. We evaluated 12 root characteristics to elucidate the type and severity of root deformities in planted pine aged 3–10 years, as well as to determine the impact of root form on their growth and stability. Results showed that root deformity is widespread: 95.0% of planted trees versus 50.9% of naturally regenerated trees had either moderate or severe root deformities. A logistic regression using the 12 root characteristics strongly distinguished between planted and naturally regenerated trees. Aboveground growth form was affected in that planted trees had a lower height-to-diameter ratio than naturally regenerated trees. In young planted trees with low or moderate root deformities, but not in trees with severely deformed roots (65.0% of all planted trees in our study), both height- and diameter-growth rates were higher than in naturally regenerated trees. Growth differences may be attributed to differential resource allocation resulting from translocation inhibition caused by root deformation. In spite of very different root systems, there was no difference in the horizontal stability of planted versus naturally regenerated trees. However, planted trees have a significantly lower root cross-sectional area and may therefore be at a higher risk of mortality, primarily from attack by the Warren root collar weevil, Hylobius warreni Wood.