Peatland fragments of southern Quebec: recent evolution of their vegetation structure

One of the main problems associated with small natural reserves is their pr ogressive loss of ecological integrity owing to the influence of surroundin g human activities. In southern Quebec (Bas-Saint-Laurent, Canada), peatlan ds are extensively mined to extract peat for the production of horticultura l compost and are isolated within agricultural lands. Government environmen tal agencies have proposed that peat industries set aside 5-10% of a bog's area as a natural refuge for peatland plants and animals. Do these fragment s constitute reliable refuges? Do they maintain their ecological characteri stics over a long period? We studied the recent evolution of plant communit ies in peatland fragments using paleoecological techniques and a geographic al information system. In the study area, some treeless fragments dominated by Sphagnum species have recently (since 1940) converted to forest sites. Macrofossil and dendrochronological analyses suggest that peat-mining activ ities were not the main factors responsible for the afforestation of peatla nd fragments. On the other hand, the isolation of the Bas-Saint-Laurent pea tlands within an agricultural plain for more than 100 years may explain the afforestation process (drainage activities). Furthermore, fires may have a ccelerated afforestation by facilitating the spread of seeds of tree specie s with serotinous cones. Because most peatlands of the Bas-Saint-Laurent re gion are still affected by drainage and fires, it is probable that several open bog fragments will not maintain their treeless vegetation structure ov er a long period. Consequently, peatland fragments should not be considered as a solution to long-term conservation needs in southern Quebec, at least not for plant and animal species of open bogs. This study also shows that even ecosystems known to be resistant to invasions by exotic species (such as peatlands) can be strongly affected by fragmentation and by their surrou nding environment on a long-term basis.