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UBC Theses and Dissertations

Vegetation responses to ecological restoration (rewetting) of abandoned block-cut peatlands in eastern Québec Henstra, Steven W.


Abandoned block-cut peatlands are typified by an alternating topography of mined trenches and raised baulks. Although these sites re-vegetate densely with native bog species, Sphagnum species characteristic of undisturbed bogs are conspicuously absent and peat accumulation has not recommenced. Ecological restoration of abandoned block-cut peatlands involves blocking remnant drainage ditches, “rewetting” the residual peat body to: 1) re-establish vegetation assemblages dominated by Sphagnum, and 2) re-establish the upper, hydrologically active layer (acrotelm) that characterizes intact peatlands. This study evaluates the progress towards achieving these goals in three rewetted block-cut sites in eastern Québec. Plant species composition, above-ground biomass, and accumulated organic matter data were collected from mined trenches within rewetted and non-rewetted sectors of the study sites and used for comparison with nearby undisturbed reference bogs. Comparisons of current patterns of community vegetation structure in rewetted and non-rewetted sectors of the study sites indicated that vegetation assemblages are strongly influenced by water table position. In areas where rewetting resulted in a water table position at or just above the peat surface, rapid community scale vegetation change occurred, with widespread mortality of vascular vegetation followed by recolonization by hydrophytic ericaceous and herbaceous species, and hollow/lawn Sphagnum species (<4 years following rewetting). Despite this positive change, vegetation assemblages within rewetted sectors still differ significantly from those found in natural reference sites up to 17 years following rewetting. Changes in above-ground biomass indicated a significant reduction in tree biomass, a significant portion of which is present as dead-standing tree biomass 4 years following rewetting. Shrub biomass initially decreased, but then increased 10 years following rewetting as species compositions shifted. Accumulated organic matter shifted from a predominance of ericaceous litter to fibric peat in rewetted sectors, the depth of which is increasing as a function of time. These findings provide initial evidence of re-establishment of the acrotelm; however, additional research is required to determine whether the newly accumulated peat will provide the hydrological functions perceived of the acrotelm in undisturbed bogs. Continued detailed observation of the biotic recovery of these ecosystems will provide valuable information for future restoration endeavors.

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