Release of Naturally Established White Pine Seedlings from Competition: An Objective Field Index

Gap cutting has been recently prescribed in Quebec to favor the regeneration of midtolerant species such as white pine. However, this new practice may lead to increased competition, jeopardizing the survival of established seedlings. One important question, therefore, is how much care will be required to ensure that the seedlings will reach the sapling stage. More importantly, a practical field tool is needed to determine under which conditions a seedling must be released from competition. For the present study, three sets of 42 white pine (Pinus strobus L.) seedlings were selected from 4-year-old gaps in a mixed tolerant hardwood–white pine stand so as to cover the widest range of competition intensity, and so the main competitor species would be individuals of one of the following: pin cherry (Prunus pensylvanica L.f.), trembling aspen (Populus tremuloides Michx.), or wild raspberry (Rubus idaeus L.). A seedling vigor index was developed, and counts of and measurements on stems of competitor species were conducted. Several competition indices were computed, and regression analyses were performed to determine which indices explained the most of the observed variation in seedling vigor. A composite competition index to be used as a decision rule to release a white pine seedling was developed by combining selected competition indices, balancing precision of the models with ease-of-use in the field. Finally, the integration and the economic assessment of the field index into the planning of regeneration efforts are presented.