Tamarack and Black Spruce Growth on a Boreal Fen in Central Alberta 9 Years after Drainage

Abstract

Tree growth was measured before, and 9 years after draining a boreal fen that supported a 50- to 60-year-old stand of tamarack (Larix laricina (Du Roi) K. Koch) and black spruce (Picea mariana (Mill.) B.S.P.). Treatments consisted of a series of ditches spaced 30, 40 or 50 m apart, and an undrained control. Nine years after drainage, the diameter, height, basal area, and volume growth of tamarack had increased by 2-5 times that on the control site. Black spruce growth on the drained site was 1.6-5 times that on the control. Tamarack average volume growth (1.20 m 3 ha 1 year 1 ) on the drained site was superior to that of black spruce (0.21 m 3 ha 1 year 1 ). In general for both species, there were no significant differences in growth between trees on the different ditch spacings. This result was attributed to the water table being low enough that adequate aeration zones existed across the strips between ditches on all spacings. Regeneration after treatment was greater on the drained than on the control plots, particularly in the disturbed areas near the ditches where new tamarack seedlings reached densities between 9400 and 12,000 stems ha 1 . There was no relationship between increased tree growth and tree distance from the ditches for both species, probably because the water table had been lowered sufficiently so that inadequate substrate aeration was no longer a limiting factor.