THE DYNAMICS OF A COTTON-GRASS (ERIOPHORUM VAGINATUM L.) COVER EXPANSION IN A VACUUM-MINED PEATLAND, SOUTHERN QUÉBEC, CANADA

We studied from 1998 to 2003 the fine-scale vegetation dynamics of an abandoned vacuummined bog located in southern Quebec in which cotton-grass (Eriophorum vaginatum) has become dominant. A water table no deeper than 30–40 cm below the soil surface combined with a volumetric peat water content>70% in the surface peat layer favored the increase in cotton-grass cover in abandoned peat fields. In one of the two peat fields that was monitored, the density of living tussocks was 30,750/ha in 1998. The density decreased constantly to reach 25,900/ha in 2002; a 16% decrease. The expansion of cotton-grass cover was mainly the result of the growth of established tussocks following a rise of the water table. The strong relationship between cotton-grass cover and water table suggests that the latter could be used as a predictor for cotton-grass cover change in mined bogs. The present study does not provide evidence that cotton-grass facilitates the establishment of moss species. At the study site, moss establishment was more highly associated with particular hydrologic characteristics (volumetric peat water content ≥85%) than with the presence of a dense cotton-grass cover. The use of cotton-grass to facilitate the establishment of Sphagnum colonies in mined peatlands is questionable, particularly where other efficient restoration techniques are available.