Establishment success of seven hardwoods in a tree-based intercropping system in southern Quebec, Canada

Abstract

In temperate tree-based intercropping (TBI) systems, good survival and early growth of selected tree species without wood defects is critical, when taking into account both economic considerations and rapidly accruing environmental benefits that are provided by the trees. The establishment success of different tree species that have contrasting growth strategies in Northeastern American TBI systems have not been assessed in a well-documented manner, which is an important influential barrier limiting their adoption by farmers. We analyzed establishment success after five growing seasons of six hardwood species and four hybrid poplar clones in a 50 stems ha−1, tree-based intercropping system. The hardwood species being evaluated were Carya ovata, Juglans nigra, Quercus bicolor, Quercus macrocarpa, Quercus rubra, and Acer saccharum. The hybrid poplar clones being evaluated were four clones of Populus deltoides × P. nigra × P. maximowiczii. We also compared 3-year-old bareroot (165 cm in height) with tree shelter versus 6-year-old root-balled transplants (370 cm in height) without tree shelter for two hardwood species (Quercus rubra and Acer saccharum). Mean survival rate of the six hardwood species originating from 3-year-old transplants was 70% after 5 years. Acer saccharum (33%) and Carya ovata (57%) had the lowest survival rates. Tree height of Quercus bicolor and Quercus macrocarpa was taller than that of Carya ovata, Juglans nigra and Quercus rubra. Tree height of Acer saccharum was intermediate among species. Mean survival rate of hybrid poplar after five growing seasons was 82% and did not differ among the clones. Growth of DN 4813 was lower than that of DN×M 915508, DN 3570 and DN 3585. Tree external defects (forks, frost cracks, trunk inclinations, trunk wind bends, and physical injuries) were observed in 63% of the hardwoods and 55% of the hybrid poplars. Red oak and sugar maple originating from 6-year-old transplants had survival rates of 100%. Over 5 years, height increment of 6-year-old transplants was higher than that of 3-year-old transplants. The 6-year-old transplants of Quercus rubra and Acer saccharum were the most cost-effective stock type. We conclude that tree survival, tree growth and tree external defects in establishment phase of TBI systems may vary considerably across hardwood species, hybrid poplar clones and planting stock type.