Assessment of patterns of response of tree ring growth of black spruce following peatland drainage

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Abstract
A new procedure was developed for assessing the effects of drainage on tree ring growth. It uses both the predrainage growth of the drained site and the postdrainage growth on an adjacent undrained site as controls in estimating tree ring growth response following drainage. The procedure allows the calculation, on a yearly basis, of the net response of tree ring growth to peatland drainage. The new procedure was applied to black spruce on six peatlands in central Alberta; these sites were drained in 1966. The average age of trees on the sites ranged from 33 to 107 years at time of drainage. The response patterns were as follows: for the first 3 to 6 years following drainage, the tree ring growth did not increase in response to drainage. After that, the net increase in tree ring growth increased nearly linearly until reaching a maximum 13 to 19 years after drainage. The maximum net increases ranged from 76 to 766% of the projected growth of the trees if the sites had not been drained. The net increases fluctuated near the maximum value thereafter. The year to year fluctuations in tree ring index on the drained sites corresponded to the yearly fluctuations on the natural sites.