Could alder plantation help promote conifer growth in boreal forests?
The boreal forest is a carbon sink and an important source of wood. Canopies created by boreal forests are opening at northern limits mainly because of tree regeneration failure after natural or anthropogenic disturbances. Regeneration failure threatens the sustainable provision of ecosystem services such as carbon sequestration.
One way to maintain stand productivity in boreal forests is with restoration planting — a recognized management practice of planting native conifer trees to regenerate forests.
Read this open access paper on the FACETS website.
Companion vegetation can promote the survival and growth of planted conifer trees by offering protection against stressful environmental conditions or by reducing competition from other species.
A known companion plant is the alder tree — it can fix atmospheric nitrogen for growth and increase soil nitrogen content. Its presence could have a facilitative effect on planted conifers by promoting their establishment and growth. Conversely, alder could also compete for light and water and therefore hinder conifer establishment and growth.
We tested the effect of alder on growth of jack pine and black spruce seedlings over six growing seasons at an experimental plantation in northern Québec, Canada.
Did alder promote or hinder growth of the planted conifer seedlings?
We showed that the presence of alder increased growth in jack pine but had no effect on black spruce. We found a significant competition for light between alder and planted conifers.
Although we did not detect a facilitative effect of alder on conifers through soil nitrogen enrichment, the positive and neutral effects of alder on jack pine and black spruce growth suggest facilitative interactions have indeed occurred.
Further studies are needed to investigate these interactions and to predict the net outcome of facilitation or competition between alder and planted conifers.
After six years, planted alder seems to have promoted conifer growth. But will this continue in the longer term?
Read the paper — Role of green alder in boreal conifer growth: competitor or facilitator? by Morgane Urli, Nelson Thiffault, Daniel Houle, Sylvie Gauthier and Yves Bergeron.
