Draining an unproductive black spruce peatland stand: 18-year post-treatment tree growth and stand productivity estimation

In the eastern Canadian boreal forest, drainage of unproductive black spruce peatlands is an infrequently used silvicultural treatment. The sparse scientific literature concerning its influence on tree growth is, however, relatively positive about the possibility of using drainage to convert unproductive stands into productive ones. This study aimed to address this issue by assessing the individual tree growth and by estimating the future stand productivity on a drained black spruce peatland stand. Results showed larger mean annual post-drainage stump diameter increment with increasing ditch proximity but they also showed the lack of effect of the treatment at distances greater than 15 m from the ditch. Small-sized trees reacted more strongly to the treatment than larger ones. Estimated site productivity was also influenced by the ditch proximity. The presence of excavating mounds on only one side of the ditch greatly influenced tree growth and site productivity. Considering the obtained results, intensive drainage operations, utilizing narrow ditch spacing, would be necessary in order to transform the type of unproductive sites studied into productive ones. Key words: diameter growth, site index, forested peatland, forest drainage, Picea mariana